SCCT Guidelines for the Performance and Acquisition of Coronary Computed Tomographic Angiography (2016)

Journal of Cardiovascular Computed Tomography 10 (2016) 435—449

Contents lists available at ScienceDirect

Journal of Cardiovascular Computed Tomography

journal homepage: www.JournalofCardiovascularCT.com

Guidelines

SCCT guidelines for the performance and acquisition of coronary

computed tomographic angiography: A report of the Society of

Cardiovascular Computed Tomography Guidelines Committee

Endorsed by the North American Society for Cardiovascular Imaging

(NASCI)

Suhny Abbara^a^,^*, Philipp Blanke^b, Christopher D. Maroules^a, Michael Cheezum^c,

Andrew D. Choi^d, B. Kelly Han^e, Mohamed Marwan^f, Chris Naoum^g,

Bjarne L. Norgaard^h, Ronen Rubinshteinⁱ, Paul Schoenhagen^k, Todd Villines^j,

Jonathon Leipsic^b

^a University of Texas Southwestern Medical Center, Dallas, TX, United States

^b Department of Radiology and Division of Cardiology, University of British Columbia, Vancouver, British Columbia, Canada

^c Cardiology Service Ft. Belvoir Community Hospital, Ft. Belvoir, VA, United States

^d Division of Cardiology and Department of Radiology, The George Washington University School of Medicine, Washington DC, United States

^e Minneapolis Heart Institute and Children's Heart Clinic, Minneapolis, MN, United States

^f Cardiology Department, University Hospital, Erlangen, Germany

^g Concord Hospital, The University of Sydney, Sydney, Australia

^h Department of Cardiology B, Aarhus University Hospital-Skejby, Aarhus N, Denmark

ⁱ Lady Davis Carmel Medical Center & Rappaport School of Medicine- Technion- IIT, Haifa, Israel

^j Walter Reed National Military Medical Center, Bethesda, MD, United States

^k Cardiovascular Imaging, Cleveland Clinic Lerner College of Medicine, Cleveland, OH, United States

ARTICLE INFO

ABSTRACT

Article history:

In response to recent technological advancements in acquisition techniques as well as a growing body of

Received 5 October 2016

evidence regarding the optimal performance of coronary computed tomography angiography (coronary

Accepted 9 October 2016

CTA), the Society of Cardiovascular Computed Tomography Guidelines Committee has produced this

Available online 12 October 2016

update to its previously established 2009 “Guidelines for the Performance of Coronary CTA” (1). The

purpose of this document is to provide standards meant to ensure reliable practice methods and quality

Keywords:

outcomes based on the best available data in order to improve the diagnostic care of patients. Society of

Performance and acquisition of Coronary

Cardiovascular Computed Tomography Guidelines for the Interpretation is published separately (2). The

Computed Tomographic Angiography

Society of Cardiovascular Computed Tomography Guidelines Committee ensures compliance with all

existing standards for the declaration of conflict of interest by all authors and reviewers for the purpose

ofclarity and transparency.

1. Preamble

optimal performance of coronary computed tomography angiog-

raphy (coronary CTA), the Society of Cardiovascular Computed To-

In response to recent technological advancements in acquisition

mography Guidelines Committee has produced this update to its

techniques as well as a growing body of evidence regarding the

previously established 2009 “Guidelines for the Performance of

Coronary CTA”.¹ The purpose of this document is to provide stan-

dards meant to ensure reliable practice methods and quality out-

comes based on the best available data in order to improve the

* Corresponding author. UT Southwestern Medical Center, 5323 Harry Hines

diagnostic care of patients. Society of Cardiovascular Computed

Blvd., E6.120A Mail Code 9316, Dallas, TX 75390-9316, USA.

Tomography Guidelines for the Interpretation is published

E-mail address: Suhny.Abbara@UTSouthwestern.edu (S. Abbara).

http://dx.doi.org/10.1016/j.jcct.2016.10.002

436

S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435—449

separately.²

3.2. Technologist and ancillary personnel standards

The Society of Cardiovascular Computed Tomography Guide-

lines Committee ensures compliance with all existing standards for

All examinations should be performed by technologists

the declaration of conflict of interest by all authors and reviewers

adequately trained in cardiac CT, including adequate knowledge of

for the purpose of clarity and transparency.

the ALARA principle. Moreover, technologists should receive addi-

tional training to perform coronary CTA on their respective

equipment, including scanner and injection devices. Demonstra-

2. Introduction

tion of advanced proficiency in cardiac computed tomography such

as through holding of the Society of Cardiovascular Computed To-

Since the first publication of recommendations for performance

mography Technologist Certificate of Competency in Cardiovascu-

of coronary CTA in 2009,¹ further technological developments of

lar CT, or equivalent is desirable, but not required.

multi-detector row computed tomography (MDCT) have signifi-

At least one person with appropriate training in inserting

cantly increased the ability to image the heart and coronary arteries

intravenous access (peripheral IV) is required for patient prepara-

noninvasively, supporting the clinical utility of coronary CTA to

tion, and at least one person certified in advanced cardiac life

identify coronary artery stenosis, if image quality is adequate.^4—6 An

support (ACLS) has to be readily available during the acquisition. If

expert consensus document has defined a number of clinically

additional medications are used, a person with adequate training in

“appropriate”,

“inappropriate”, and

“uncertain” indications for

administering medications such as beta-blockers and nitroglycerin

coronary CTA.³

must be available. The above functions can be performed by a

It is generally accepted that the diagnostic quality of coronary

physician or physician assistant. If pediatric imaging is performed,

CTA images is highly dependent on a number of technical factors,

at least one person certified in pediatric advanced life support

including hardware, software, and acquisition protocols. These

(PALS) should be available during the scan, and pediatric specific

factors still continue to evolve at a rapid pace, resulting in the “state

emergency resuscitation equipment should be readily available.

of the art” being in a continuous “state of flux”. Several MDCT

scanner geometries are currently utilized for coronary CTA, and

3.3. Institution and equipment standards

provide a wide array of options. Technological advancements over

the last decade include: a range of 64—320 detector row systems;

The imaging facility should meet lab accreditation standards as

dual source scanners; dual energy imaging; iterative reconstruction

set forth by the applicable body, e.g. the Intersocietal Commission

algorithms; and a variety of new 3D workstations and software

for the Accreditation of Computed Tomography Laboratories

programs for processing and reviewing scan data.

(ICACTL), or the American College of Radiology (ACR). CT systems

Therefore, this publication aims to establish an updated

with fast gantry rotation (equal or less than 350 ms) should be

consensus of the minimally required standards for appropriate

utilized. The minimum detector requirement is a 64-slice scanner

coronary CTA acquisition and data processing; and to provide rec-

(collimations of 32

2 or 64

1, or newer generation, which

ommendations for methods to achieve robust image data, optimize

typically have detector element widths of 0.625 mm or less). Dual

scan results, maximize image quality and avoid unnecessarily high

head injection pumps that allow biphasic or triphasic injection

radiation exposure within the limits of the currently available

protocols with high injection rates (4—7 cc/sec) are recommended,

technology.

although single head injection pumps can yield appropriate results.

For a detailed description of the different injection protocols, please

refer to Section 5. Image data storage should be in the Digital Im-

3. Physician and technologist competencies; institution and

aging and Communications in Medicine (DICOM) standard format.

scanner standards

A picture archiving and communication system (PACS) or equiva-

lent CT image data archiving system is required to allow storage

3.1. Physician standards

and retrieval of the entire diagnostic image data set.

All examinations should be performed and interpreted by phy-

3.4. Radiation monitoring standards

sicians adequately trained in coronary CTA including an ability to

assess coronary arteries, cardiac and pericardial structures, great

Independent of local policy and legislation, it is recommended

vessels, and extra-cardiac structures within the acquired field of

that the radiation dose estimates from each coronary CTA, as re-

view. The interpreting physician(s) should have adequate training

ported by the scanner after coronary CTA acquisition, should be

as described in competency statements issued by medical specialty

recorded for each patient. Volume CT dose index (CTDIvol) and

societies e.g. the ACC/AHA Clinical Competence Statement on Car-

dose-length product (in mGy • cm) should be used; effective dose

diac Imaging with Computed Tomography and Magnetic Reso-

(in mSv) may be recorded, however the conversion factor for

nance⁷ or the ACR Practice Guideline for the Performance and

calculating effective dose is not unique to coronary CTA and as a

Interpretation of Cardiac Computed Tomography.⁸ This competency

result may change over time, giving discrepant results. The radia-

includes adequate knowledge of the ALARA (“As Low As Reasonably

tion doses need to be stored in a format that allows for retrieval and

Achievable”) principle from the standpoint of radiation exposure,

periodic review of representative samples of the data. Examples of

among others. For pediatric coronary artery imaging, knowledge of

formats for recording include, but are not limited to, a DICOM im-

age and size based modifications for patient preparation and image

age/DICOM standard reporting template with radiation informa-

acquisition are required to decrease diagnostic risk.

tion in a PACS, a paper based logbook, hospital information system

An imaging center should accordingly have a supervising

(HIS) or radiology information system (RIS), or a dedicated database

physician with advanced knowledge in cardiovascular CT and ra-

or local registry. It is imperative that the lab director, or equivalent

diation issues. Certification of advanced expertise in cardiac CT is

physician ensures (a) the presence of, and adherence to a periodic

desirable, e.g. Diplomat of the Certification Board of Cardiovascular

(e.g. biannual) review of the range of radiation doses, and the

CT (CBCCT), holder of the ACR Certificate of Proficiency in Cardiac

median and average radiation dose at the site and (b) comparison of

CT, or American Board of Radiology ABR/ABMS Focused Practice

the local data with national standards and other published refer-

Recognition in Cardiac CT (FP-CCT).

ences. This review process should trigger the review and

S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435—449

437

optimization of scanning protocols, especially if the site radiation

failure, severe hypotension); and renal impairment as defined by

dose is higher than comparable national or international references

local protocols. Regarding pregnancy in particular, a chest CT results

utilizing the same acquisition equipment that still meets the na-

in low radiation exposure to the fetus, however, a negative long

tional standards. More details and recommendations regarding

term effect even from low level radiation cannot be excluded.¹⁰

radiation dose optimization and reporting can be found in the

Furthermore, small amounts of absorbed iodine from the contrast

dedicated Society of Cardiovascular Computed Tomography

material may affect fetal thyroid function.¹¹ While coronary CTA in

guideline document.⁹

pregnant women may not be absolutely contraindicated, the indi-

For pediatric patients, the DLP and phantom size (16 cm or 32

cation should be critically reviewed. As with every procedure,

cm) should be recorded. There is variation in the phantom size used

alternative imaging modalities should be considered and the study

to calculate DLP at different institutions, which results in variable

with the best benefit-risk ratio should be employed. Screening for

estimates of patient dose for similar scanner outputs. If dose is

potential pregnancy by history and/or pregnancy testing should be

reported in mSv for a pediatric patient, the conversion factor used

performed according to the local imaging facilities policies for

in the calculation should be documented.

undertaking radiological examinations that involve ionizing radi-

ation in women of child-bearing age. For breast feeding mothers it

3.5. Recommendations

is reassuring to note that iodine accumulation in the breast milk is

considered too low to warrant interruption of their breast feeding

The supervising physician

(lab director, etc.) should have

schedule.

advanced knowledge and expertise in cardiovascular CT and

In addition to the above contraindications, there are also a

medical radiation. Certification of advanced expertise in cardiac

number of patient related variables that affect the diagnostic ac-

CT is desirable.

curacy of coronary CTA. The presence of such factors (in conjunc-

The interpreting physician should have adequate training as

tion with scanner variables) should trigger reconsideration of the

described in competency statements.

risks and benefits of coronary CTA with the decreased accuracy in

Technologists should be adequately trained to perform Coronary

mind. These variables include obesity; difficulty following breath-

CTA on the respective equipment, including scanner and injec-

hold commands, maintaining body position, raising one or both

tion pumps. Certification of expertise is desirable.

arms, or lying supine for scanning; contraindication to beta-

The institution should meet or exceed current standards for

blockade in the presence of an elevated heart rate and no alterna-

medical imaging facilities.

tive medications available for achieving target heart rate; heart rate

CT scanner technology should meet or exceed current standards.

variability and arrhythmia; and contraindication to nitroglycerin.

Radiation dose estimates from coronary CTA should be recorded

Regarding obesity in particular, scan restrictions for upper weight

for all patients.

limits depend on scanner dimensions and characteristics. Many

Periodic review of the site's radiation levels and comparison

scanners are approved to accommodate patients of up to 450

with published references

(and internal protocol review &

pounds body weight or more. Certain scanner systems provide

optimization) is necessary and should be performed at least

acquisition modes specifically adapted to improve image quality in

twice per year.

these scenarios. However, image quality for coronary assessment in

Pediatric coronary artery imaging should be performed by

such patients may be inadequate even with maximum scanner

physicians with training in scan preparation and dose optimi-

output. It is the attending physician's responsibility to consider the

zation techniques for pediatric patients.

scanner's characteristics appropriately for the probability of imag-

ing success.

4. Patient screening and preparation

Anesthesia with suspended respiration may be required for

pediatric patients unable to cooperate with breath holding in-

4.1. Introduction

structions. Scanners capable of high pitch spiral acquisition mode

may allow image acquisition without breath hold for some in-

The decision to order a coronary CTA examination should be

dications. If anesthesia is required, both the imaging and anesthesia

made by a qualified physician or under supervision of a qualified

risk must be taken into consideration in determining the appro-

physician following current national guidelines. Coronary CTA

priateness of pediatric coronary CTA.

should only be performed if the results of the test have the po-

It is recommended to evaluate for the following items prior to

tential to impact patient management or prognosis and if sufficient

coronary CTA:

image quality can reasonably be expected.

Patient preparation should be performed by a qualified indi-

Pregnancy or potential pregnancy: According to ACR recom-

vidual. Patients should be screened for contraindications to

mendations¹² “All imaging facilities should have policies and

contrast-enhanced CT in general, or for factors that may interfere

procedures to identify pregnant patients prior to imaging, and to

with image quality in coronary CTA. Blood pressure and heart rate

consider any possible risks to the fetus of any planned admin-

prior to administration of heart rate-slowing medication and/or

istration of contrast material, taking into consideration the po-

nitroglycerin should be noted. The following is a description of

tential clinical benefits of the examination.”

standard procedures that are required prior to a coronary CTA.

Presence of contraindications to contrast media or other medi-

cations including heart-rate slowing medications

(e.g. beta

4.2. Initial screening

blockers) and nitroglycerin.

Renal impairment and risk of contrast induced nephrotoxicity

Coronary CTA is generally contraindicated in the following

(CIN)

clinical scenarios, however, on a case-by-case basis, coronary CTA

Prior allergic reactions to any allergens

may be pursued in some of these scenarios if clinically warranted.

Active bronchospastic disease, hypertrophic cardiomyopathy,

Contraindications include a known history of severe and/or

severe aortic valve stenosis, or other precautions or contrain-

anaphylactic contrast reaction; inability to cooperate with scan

dications to beta-blockers

acquisition and/or breath-hold instructions; pregnancy; clinical

Current medications (especially sildenafil, vardenafil, tadalafil,

instability (e.g. acute myocardial infarction, decompensated heart

or metformin)

438

S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435—449

Any other pertinent medical history

of power injector bolus intravenous administration of contrast and

Assessment of the ability to follow breath-hold commands and

in accordance with the individual facility policy. A short 20 gauge IV

perform sufficient inspiratory breath-hold. If pediatric patients

catheter may be sufficient in normal or small patients but an 18

are unable to cooperate with breath holding, anesthesia with

gauge catheter is often necessary in adults to achieve rapid infusion

suspended respiration may be required.

rates (4—7 cc/sec). For pediatric patients, a 22 gauge IV is often

Body weight and height.

sufficient for the contrast injection rate required. New high flow IV

Assessment of heart rate (preferably following inspiration) and

catheters are available that offer the potential to use a smaller bore

arrhythmia

while maintaining high flow rates. The right antecubital vein is

Assessment of blood pressure if beta blockers and/or nitro-

preferable (median, cubital, basilic and cephalic veins), followed by

glycerin will be administered

a left antecubital vein. Contrast injection via the left antecubital

vein can result in a larger amount of streak artifact from the

contrast bolus as it passes through the left brachiocephalic vein,

4.3. Pre-test instructions

potentially degrading image quality. Hand veins (metacarpal and

dorsal) should be avoided, unless no other suitable access can be

Pre-test patient instructions are best given at the time when the

established. This generally requires a 20 gauge or smaller catheter

procedure is scheduled. The following is a list of the typical set of

and slower flow rates. Unless specifically labeled for power injec-

instructions:

tion, central lines should not be utilized.

No food for 3—4 hours prior to exam.

4.6. Renal precautions

May drink water or clear fluids without caffeine up until time of

exam (patient should be well hydrated for renal protection, for

Pre-test determination of estimated glomerular filtration rate

ease of establishing venous access, and to avoid post-procedure

(GFR) is not required for all patients, but should be performed for

hypotension).

patients considered at increased likelihood of renal impairment on

No caffeine products for 12 hours prior to exam in the non-acute

the basis of age and history, because impaired renal function is a

setting, because they might hinder efforts to reduce the heart

relative contraindication to coronary CTA. Calculation of GFR, rather

rate before scanning. This includes coffee, tea, energy drinks,

than creatinine alone, is encouraged.^14—16 The incidence of contrast

energy pills, diet pills and most soda.

induced nephropathy (CIN) increases in patients with impaired

Take all regular medications the day of exam, especially blood

kidney function (estimated GFR < 60 cc/min/m²) and other co-

pressure medicine.

morbidities such as cardiomyopathy

(left ventricular ejection

Take pre-medications for contrast allergy as prescribed by the

fraction < 40%) and diabetes mellitus. The risk is higher in the

ordering physician. As an example, the standard Greenberger

elderly as well as in patients with a low BMI. Patients who are

regimen is prednisone, 50 mg by mouth, 13, 7, and 1 hour prior

dehydrated or volume depleted prior to contrast exposure have an

to contrast exposure, in addition to diphenhydramine 50 mg by

increased risk and any condition that decreases renal blood flow

mouth 1 hour prior to contrast exposure.¹³

(hypotension, non-steroidal anti-inflammatory use) is also likely to

It is reasonable to suspend metformin for at least 48 hours after

increase the risk of CIN.

contrast administration. Metformin itself is not nephrotoxic, but

While a causal relationship between contrast material and ne-

is exclusively cleared by the kidneys. If renal failure is precipi-

phropathy has been postulated on the basis of data extrapolated

tated by iodinated contrast, a toxic accumulation of metformin

from intra-arterial administration,^17—20

some studies have sug-

may result, which can induce lactic acidosis. There is no evi-

gested that this relationship is overstated in the setting of intra-

dence that withholding metformin before a contrast procedure

venous contrast administration.²⁹ Indeed, it has been shown that

is protective although this approach has been adopted by some

creatinine levels increase in patients who are not receiving contrast

in the past.

material at a similar frequency to patients that receive intravenous

If a pediatric patient requires anesthesia, institutional NPO

contrast.²¹ Moreover, in a recent retrospective analysis of 21,346

guidelines should be followed as directed by the anesthesia

patients undergoing CT at a single center over a 10 year period

staff.

stratified based on whether contrast was administered and

following propensity score based matching to account for differ-

Instructions should also include information of the potential

ences in baseline risk, patients undergoing CT with contrast ma-

administration of pre-procedure medications (i.e. beta-blockade

terial were not at increased risk of acute kidney injury, dialysis or

and nitroglycerine) in order to prevent patient irritation, as pa-

death compared to patients undergoing CT without contrast

tients may not associate the performance of a coronary CTA with

material.²²

the necessity of potential medication administration.

Nevertheless, the risks and benefits of contrast administration

in patients with impaired renal function must be carefully consid-

4.4. Informed consent

ered. Patients considered to be at increased risk of CIN due to

baseline renal insufficiency may benefit from preventative mea-

Whether or not informed consent prior to performance of cor-

sures. Intravenous fluid volume loading is the single most impor-

onary CTA should be required may be regulated by institutional,

tant measure.²³ It is recommended that local protocols for pre-scan

regional or state regulations. A consent form, if used, should explain

hydration are utilized (these may need to be modified to avoid

in simple terms the procedure and the reasonably expectable risk

volume overload in patients with reduced left ventricular func-

to the patient.

tion.²⁴ In addition, the following measures are recommended in

patients with baseline renal insufficiency²³:

4.5. Intravenous access

Considerations when performing coronary CTA in patients at

risk of CIN:

Intravascular access should be established using the facility's

protocol and adequate flow should be ascertained prior to injection.

Consideration of alternative imaging, such as stress testing, that

Cannula size and position should be adequate for the high flow rate

does not require intravenous contrast

S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435—449

439

Avoid dehydration

The administration of oral and intravenous beta-blockers requires

Minimize the volume and frequency of contrast administration

compliance with institutional policies. Most beta-blocker protocols

(avoid repeat injection within 72hrs)

prior to coronary CTA involve oral premedication followed by

Avoid high osmolar agents. Iso-osmolar or low osmolar agents

supplemental IV beta-blocker if the target heart rate is not achieved

are recommended depending on institutional preference and

in the monitoring area prior to image acquisition. For pre-

availability

medication, metoprolol is most commonly used due to its

Avoid nephrotoxic medications 48hrs before contrast adminis-

demonstrated safety and low costs.^28,29 Atenolol may be chosen in

tration, including nonsteroidal anti-inflammatory drugs

patients with significant hepatic dysfunction due to its renal route

(NSAIDs)

of clearance (the opposite is true for patients with renal impair-

Consider IV fluid administration in at-risk patients as per pub-

ment). The most common approach uses oral metoprolol with

lished guidelines focusing on the administration of IV contrast in

staggered dosage based on the presenting resting heart rate

at-risk patients

ranging from 50 to 100 mg given 1 hour prior to the scan followed

by supplemental intravenous doses immediately prior to the CT

scan if the target heart rate (<60bpm) is not achieved.³⁰ While

4.7. Recommendations

patients presenting with resting heart rates of <60 bpm do not

require beta blockade for heart rate reduction, many advocate that

The decision to order a coronary CTA should be made by a

a low dose of metoprolol is helpful to reduce heart rate variability

qualified physician or under supervision of a qualified physician

and improve image quality.³¹ While oral drug administration 1hr

following current national guidelines.

prior to the scan is the usual practice (50—100 mg metoprolol by

Coronary CTA should only be performed if the results of the test

mouth), pre-medication during the 24 hour period before may be

have the potential to impact patient management or prognosis

more effective at lowering heart rate at the time of scanning as well

In the absence of national guidelines for pediatric and adult

as the need for supplemental intravenous beta-blocker.^32,33 If pre-

congenital patients, coronary CTA should be performed when

medication is considered safe, then a possible regimen would be to

the risk is considered less than, or the potential information

give 50 mg metoprolol by mouth 12 hours before the scan and

gained superior to alternate modalities.

another 50—100 mg metoprolol by mouth 1 hour before imaging. It

If pediatric patients are unable to cooperate with breath holding,

is important to note that for premedication regimens, slow-release

but coronary CTA has been determined necessary for clinical

forms of beta-blockers should not be used. At the time of scanning,

care, anesthesia for suspended respiration should be considered.

if the heart rate remains above target, supplemental IV beta-

Initial screening should take place for contraindications to cor-

blockers can be administered.

onary CTA and for factors that may reduce its diagnostic

Protocols that use IV beta-blocker alone can be used to shorten

accuracy.

the overall preparation time required and have been shown to be

Coronary CTA should not be performed in the presence of con-

effective and safe, even at high doses.³⁴ After the patient is placed

traindications (eg. Renal impairment), unless careful delibera-

on a cardiac monitor, 5 mg of IV metoprolol is given as an initial

tion demonstrates that the risks from coronary CTA are

dose, followed by 5 minutes of monitoring to observe the heart rate

outweighed by the potential benefit and the risk from not per-

response. Further repeated intravenous doses of 5 mg each may be

forming the scan.

administered as indicated to achieve the desired heart rate, typi-

In situations that increase the likelihood of non-diagnostic im-

cally up to a maximum dose of 20—25 mg. Esmolol may also be

age quality, the relative merits of coronary CTA should be judged

used in this setting. One reported protocol involves an initial dose

against the risks of additional radiation and nephrotoxicity.

of IV esmolol at 0.8 mg/kg. If the HR does not reach target within 20

Intravenous access should be adequate for high flow and high

seconds, another dose of IV esmolol can be administered (0.8 mg/

pressure contrast injection.

kg)³⁵). The main advantages of this approach include the rapid

Glomerular filtration rate (GFR) should be determined for pa-

onset of esmolol compared to oral metoprolol and its short half-life,

tients at increased likelihood of renal impairment.

which results in avoidance of possible prolonged side effects

observed with oral beta-blockers. In patients that are on chronic

beta-blockade, supplemental oral or IV beta-blockers may be given.

4.8. Pre-procedure medications and instructions

Pediatric patients have higher resting heart rates but have been

shown to respond to medical regimens to decrease heart rate. If

4.8.1. Heart rate control

given, a weight based approach to beta blockade should be used.

In general, optimal image quality is reliably achieved when the

Even with beta blockade, pediatric patients may have relatively a

patient has a low heart rate and a regular cardiac rhythm during the

relatively high heart, and sinus arrhythmia with the breath hold.

scan.^25,26 The requirement for heart rate reduction varies depen-

Initiating the breath hold earlier (with opacification of the pul-

dent upon the scanner temporal resolution, the method of image

monary arteries) will decrease the sinus arrhythmia at the time of

acquisition, and the indication for imaging. However, even though

image acquisition and decrease radiation dose, but requires a

some CT scan platforms are enabled with improved temporal res-

slightly longer breath hold.

olution that may afford diagnostic image quality at higher heart

Ivabradine, a direct I(f) current inhibitor, has limited interna-

rates, there remains a tangible benefit with heart rate control which

tional approval for use in the treatment of congestive heart failure,

includes both image quality but also the ability to employ dose

but currently is in the investigational phase for use in coronary CTA

reduction scan acquisitions that are not possible at higher heart

(both in addition or as an alternative to beta blockers). Ivabradine is

rates.²⁷ A target heart rate for coronary CTA set at 60 bpm or less is

available in an oral or intravenous formulation. In contrast to beta-

usually appropriate. However, depending upon the scanner pa-

blockers, ivabradine lowers heart rate (especially high heart rates)

rameters listed above, scanning at a higher heart rate may be

without affecting myocardial contractility, impulse conduction, or

acceptable if a target heart rate of 60 bpm cannot be reached.

blood pressure.³⁶ Importantly, ivabradine is ineffective in patients

Beta-blockers are considered first-line for achieving short-term

that are not in sinus rhythm due to its direct inhibition of current in

heart rate reduction for the purpose of coronary CTA and protocols

sinoatrial node cells. The use of Ivabradine for heart rate control

may utilize oral, intravenous or both routes of drug administration.

prior to coronary CTA has been investigated. Oral ivabradine can be

440

S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435—449

given as a premedication 2hrs before the coronary CTA with similar

4.9. Recommendations

reduction in HR compared to metoprolol but less reduction in

systolic blood pressure.³⁷ In the same study, ivabradine was more

Beta-blocker use should be considered based upon its require-

effective than metoprolol in patients treated with chronic beta-

ment as indicated by scanner and patient factors and the indi-

blockers. Possible ivabradine regimens prior to coronary CTA

cation for imaging. A target heart rate for coronary CTA set at 60

include: 15 mg or 7.5 mg (in chronic beta blockade) by mouth 1 h

bpm or less is usually appropriate. However, depending upon

before scanning. It may also be used for oral pre-medication (5 days

scanner parameters, scanning at a higher heart rate may be

before) with supplemental IV metoprolol on the day of coronary

acceptable if a target heart rate of 60 bpm cannot be reached. A

CTA with good heart rate control in the majority of patients.³⁸

single low dose of oral beta blockade should be considered to

Further, in patients with contraindications to beta-blockers who

reduce heart rate variability for patients presenting with low

present for coronary CTA, a bolus of IV ivabradine (10 or 15 mg) can

resting heart rates.

be administered to rapidly and safely achieve target heart rate.³⁹

The use of nitroglycerin should be the default protocol but

Screening for absolute and relative contraindications to beta

should be withheld in the presence of circumstances of absolute

blockers and ivabradine should be performed prior to administra-

contraindications. Importantly, image acquisition for coronary

tion. Beta-blockers should not be used in patients with active

CTA should not begin until 5 minutes after the administration to

bronchospastic disease.

ensure maximal effect.

Explicit breath-holding instructions and breath-hold training

must be provided prior to scanning.

4.8.2. Nitrates

Nitrates are direct vasodilators and provoke their pharmaco-

logical vasodilator effects by vascular smooth muscle relaxation.⁴⁰

4.10. Patient positioning

Similar to invasive coronary catheterization, nitroglycerin (glyc-

eryl trinitrate) should be administered prior to coronary CTA to

Proper patient positioning and electrocardiographic (ECG) lead

achieve coronary vasodilatation and in order to enhance coronary

placement are important to ensure adequate image quality in a

evaluation.^41,42 A commonly used regimen is 400—800 mg of sub-

gated cardiovascular CT acquisition. The major objectives for posi-

lingual nitroglycerin administered as either sublingual tablets or a

tioning of the patients are: 1) to minimize the presence of extra-

metered lingual spray (commonly 1—2 tablets or 1—2 sprays) 5

neous high density material (e.g. ECG leads) within the scan field

minutes prior to coronary CTA with 800 mg dosing and metered

(i.e. lower 2/3 of the chest) that may produce streak artifacts, and 2)

lingual spray preferred. Due to the specific pharmacodynamics and

to position the heart within the center of the gantry by adjusting

time-dependency of the effect of nitroglycerine,^43,44 it should be

the table height and lateral position of the patient on the scan table.

administered approximately

5 minutes prior to the contrast-

If possible, patients should be imaged supine and with both

enhanced data acquisition with vasodilatory effect only lasting

arms above the head, thereby removing the humeri from the field-

only for 20—30 minutes. Importantly, administration of nitroglyc-

of-view (FOV) and ultimately reducing streak artifact and image

erine has been shown to improve the diagnostic accuracy of coro-

noise. The arms should be positioned comfortably to avoid pectoral

nary CTA through improved vessel visualization and stenosis

fatigue or trembling, which can lead to ECG irregularities and

assessment.⁴⁵

gating errors. Care should be taken to keep the arm with the

Nitrates may reduce blood pressure, but are considered safe in

intravenous access as straight as possible to avoid line or vein

the supine position providing there is no severe hypotension or

kinking and facilitate contrast agent injection. The contrast pump

concomitant preload-dependent condition including severe aortic

and intravenous line should approach the patient from the cranial

stenosis. While nitroglycerine may induce a temporary headache

side so that the line does not cross through the gantry, which would

through its vasodilatory effect, it is generally safe among patients

produce streak artifact. The table height should be adjusted for each

referred for coronary CTA and is essential for optimal image quality

patient to center the heart within the gantry to optimize spatial and

and thus accuracy. Use of nitroglycerin is contraindicated if the

temporal resolution.^46,47 The horizontal positioning laser lights can

patient has recently taken a phosphodiesterase inhibitor (e.g. sil-

be used for this purpose: when correctly positioned, the laser line

denafil, vardenafil, or tadalafil) for the treatment of erectile

lies at the junction of the anterior 1/3 and the middle 1/3 of the

dysfunction or pulmonary hypertension.

patient's thorax.⁴⁸ It is reasonable to offset patients laterally by a

The use of nitroglycerine should be documented by the tech-

few centimeters in order to center the heart within the gantry,

nologist and reported by the interpreting physician.

however, without resulting in contact between the patient and

gantry during the acquisition. It is recommended to move the pa-

4.8.3. Breath-hold training

tient through the gantry for the expected respective scan range (i.e.

It is essential to minimize respiratory motion during image

a “test run”) to ensure that no lines or leads are tethered and that

acquisition. Coronary CTA should be acquired during an inspiratory

the patient does not contact the gantry. Contact of the patient with

breath-hold. Prior to scan initiation, patients should be provided

the gantry may result in passive or active (protective) body motion,

specific instructions and offered practice in the form of a test

producing artifacts that may not be correctable through post pro-

breath-hold, ideally following ECG lead placement with the patient

cessing. The ECG leads should be straightened and care taken that

on the scanner table. The purpose of the test breath-hold is three-

the leads do not unnecessarily traverse the scan range to avoid

fold: 1) to ensure appropriate quality of the breath-hold (patient

streak artifact and image noise. Likewise any other leads, metal, or

should not perform a Valsalva maneuver), 2) to ensure adequate

radio-opaque material should be removed (inferiorly onto the

timing of the breath-hold, and 3) to observe fluctuations in heart

abdomen, or superiorly) from the scan field.

rate and rhythm during the breath-hold exercise. Coronary CTA

In order to obtain a reliable ECG tracing, proper placement of

should not be performed if a patient cannot adhere to breath-hold

ECG leads is critical. The number and preferred location of leads

commands. It is strongly advised that all steps of the scan protocol

depends on the scanner type and design. Care should be taken to

(scout topogram, calcium score and test bolus, if performed, as well

place leads outside the imaging FOV to the extent possible to avoid

as the coronary CTA acquisition) be performed using identical

streak artifact. Cleaning the skin with alcohol and shaving at the

breath-hold commands.

site of electrode placement may be necessary to ensure sufficient

S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435—449

441

electrode-to-skin contact. For best recognition of ECG trigger

the scan delay should equal the contrast travel time from the

points, it is important to obtain a steep upslope towards the R-peak

accessed vein to the ascending aorta plus 2—4 seconds to allow

and sufficient R-peak voltage with minimal baseline noise. Repo-

complete filling of the coronary arteries. In general, two strategies

sitioning of ECG leads is necessary if the baseline noise is relatively

are commonly available to determine the vein-to-aorta travel time:

high compared to the R-peak amplitude, or of the amplitude of the

bolus tracking, and the test bolus technique.

T-wave is in a similar range as that of the R-peak because this may

Bolus tracking implies semi-automated scan triggering by

result in false triggering (R-peak detection).

monitoring the arrival of contrast through a sequence of repetitive

single slice scans at a pre-specified anatomical level and automated

4.11. Recommendations

measurement of the contrast attenuation within a region of interest

(ROI). The scan is triggered when the attenuation in the ROI exceeds

The preferred patient position is supine with arms raised above

a predefined threshold. The ROI can be placed in the ascending

the head and the heart centered within the gantry.

aorta, descending aorta or a cardiac chamber, depending on scan-

Special attention should be paid to ensure proper positioning

ner geometry, acquisition mode and preferences. The delay time

and firm contact of ECG leads to ensure a high R-peak amplitude

between passing the threshold and start of data acquisition must

and low baseline noise.

account for potential table position adjustment and breath-hold

instructions. Commonly the threshold is below the target attenu-

ation of the data acquisition as contrast is still arriving during the

4.12. Contrast injection protocols

delay time, with exceptions in protocols employing volume scan-

ners where the ROI may be placed in the left ventricle, no table

4.12.1. Contrast type, delivery, volume and rate

position adjustment is required, and breath-hold instructions may

Image quality is dependent on the contrast-to-noise ratio.

be initiated prior to monitoring, so that data acquisition may

Optimal images require high intra-arterial opacification of more

instantly commence when reaching the attenuation threshold.

than 250 Hounsfield Units (HU). Hence, contrast agents with high

The test bolus technique consists of a small test bolus injection,

iodine concentrations are preferred (270—400 mg Iodine/cc). An

typically

10—20 cc of contrast followed by a saline bolus of

injection rate between 5 and 7 cc/sec should be used for coronary

approximately 50 cc, both injected at the anticipated injection rate

CTA in most adults, although lower injection rates can be appro-

for the subsequent data acquisition. The test bolus images are ac-

priate in low kVp acquisitions depending on body habitus or the IV

quired during an inspiratory breath-hold, with repetitive single

line size (20G). Warming of contrast agent improves viscosity and

slice acquisitions at a pre-specified anatomical level e.g. ascending

allows higher injection rates at lower injection pressures. The

aorta, every 1—2 seconds. An enhancement curve is then generated

overall contrast volume is a function of the injection rate and the

to determine the contrast transit time to peak enhancement.

injection duration. The injection duration should be as long as (or

Commonly, 2—4 seconds are then added for calculation of the total

slightly longer than) the estimated scan duration. For very short

delay time before data acquisition, to allow for peak enhancement

scans, the injection duration should be at least 10 seconds. In pa-

in the coronary arteries.

tients with higher cardiac output, the injection rate should be

Advantages and disadvantages as well as institutional prefer-

increased to allow the arterial opacification to remain high. Typical

ences may favor one technique over the other. Advantages of the

contrast volumes range from 50 to 120 cc. Dual head injectors have

test bolus technique include an opportunity to acquaint the patient

the advantage of allowing contrast injection to be followed by sa-

with the breathhold commands and the sensation of contrast in-

line injection, or in some cases to be followed by a mixture of

jection, identification of contrast dilution complications, and

contrast and saline.^49—52 A biphasic injection protocol consists of a

establishing adequacy of IV access. In contrast, the bolus tracking

first injection of contrast at a rate of 5—7 cc/sec (volume depends on

technique offers the potential to reduce the overall contrast dose by

scan duration) and subsequent injection of approximately 40—50 cc

eliminating the test bolus. However, it adds complexity to the scan

of saline, typically at the same injection rate. In these protocols, the

protocol and may itself be a source for error.

right heart cavities typically appear washed-out, which generally

reduces streak artifacts otherwise caused by dense contrast mate-

4.14. Contrast volume reduction protocols

rial in the right atrium. In certain settings it may be desirable to

have some opacification of the right heart (e.g. for evaluation of LV

Contrast volume should be adapted to the duration of scan

geometry requiring delineation of the intraventricular septum, or

acquisition. Recently, a number of contrast volume reduction stra-

evaluation of right ventricular structural abnormalities). In such

tegies have been proposed, although data examining their impact

cases, a triphasic injection protocol may be used, consisting of an

on clinical management are lacking. Monochromatic image

initial high flow rate contrast injection (5—7 cc/sec), followed by a

reconstruction using dual energy coronary CTA (see below) may

second injection of either a mixture of contrast and saline (5—7 cc/

permit a 50% or greater reduction in contrast volume with no sig-

sec), or a contrast injection at lower injection rate (e.g. 2 cc/sec),

nificant compromise on diagnostic interpretability and cer-

followed by a third injection of a smaller volume of saline.

tainty.^53,54 Iterative reconstruction techniques may permit imaging

Flow rates as low as 1 cc/sec may be used in small pediatric

at lower kVp, potentially allowing for a decrease in contrast flow

patients through a small gauge IV. Contrast volume of 1—2 cc/kg

rate and hence contrast volume by enabling scanning at lower

can be used in pediatric patients depending on the anatomy

energies closer to the k-edge of iodine.⁵⁵

requiring evaluation. For isolated coronary imaging 1 cc/kg is suf-

ficient, for additional evaluation of complex anatomy a higher

4.15. Contrast reaction protocols

contrast load may be used (2 cc/kg).

The CT laboratory has to be equipped and staffed appropriately

4.13. Test bolus vs. bolus tracking

for handling the rare event of anaphylaxis.⁵⁶ Immediate treatment

by appropriately trained personnel is necessary in case of

Accurate timing of the data acquisition to the arrival of the IV

anaphylaxis. ACR or ACC guidelines for management of contrast

contrast in the target structures is necessary to ensure optimal

reactions should be followed in the appropriate settings.⁵⁷

intraluminal enhancement within the coronary arteries. Normally,

Recommendations:

442

S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435—449

High iodine concentration contrast agents are preferred to

deliver the lowest possible radiation exposure, in keeping with the

achieve greater contrast to noise ratios.

principles of ALARA (As Low As Reasonably Achievable) and the

Higher injection rates of 5—7 cc/sec for coronary CTA are usually

“Image Gently” campaign for pediatric patients.^62,63 For example, a

optimal in adults, although lower injection rates can be appro-

coronary CTA to delineate the course of a coronary anomaly in a

priate in low kVp acquisitions, depending on body habitus

pediatric patient may be performed with less radiation exposure

Contrast injection rates in pediatric imaging should be adjusted

than a coronary CTA intended to evaluate for coronary artery ste-

to patient size and IV gauge.

nosis in an adult patient, as the former protocol can tolerate higher

Total contrast volume should be based on injection rate and scan

image noise. Likewise, if scanning only for left atrial and pulmonary

duration, and is typically 50—120 cc.

vein anatomy prior to an ablative procedure when knowledge of

It is reasonable to use a total contrast volume of 1—2 cc/kg for

coronary artery anatomy is not needed, diagnostic image quality

pediatric patients until the standard adult volume is reached.

can be achieved at lower contrast-to-noise and higher motion

Dual head power injectors are preferred over single head

tolerance than a coronary CTA for evaluation of coronary stenosis,

injectors.

and as such the CT scan can be performed at a lower radiation

Biphasic or triphasic injection protocols should be used.

exposure.

Either bolus tracking or a test bolus protocol is acceptable.

Timed scans (using empiric timing alone without either bolus

5.2. Techniques to reduce radiation - general principles

tracking or a test bolus) are not recommended.

The CT lab should be appropriately equipped and staffed to

Factors influencing the overall radiation exposure include the

manage contrast reactions, including anaphylaxis.

scanner type (single or dual source; scanner geometry; gantry

rotation, available filters), tube voltage, tube current, scan range,

5. Coronary CTA acquisition

scan acquisition time, gating

(retrospective gating, prospective

triggering, high-pitch helical acquisition), slice thickness, overlap

Technical advances over the past decade have optimized CT

and pitch

(for helical scanning), and reconstruction method

systems for cardiovascular imaging. An understanding of these

(filtered back projection, iterative reconstruction). All of these

technical advances is important as the choice of the CT acquisition

factors need to be optimized with the goal of minimizing radiation

protocol determines image quality and diagnostic value, but also

exposure as low as reasonably achievable without significantly

radiation exposure. It is imperative to balance these characteristics

compromising image quality.

for individual patients and clinical indications as described below.

Since the first edition of these guidelines, the ACR relative ra-

diation level designation for coronary CTA has been lowered to

5.1. Overview of ionizing radiation

1—10 mSv for adult effective dose estimating the median radiation

dose in the USA.⁶⁴ With the integration of recent technological

Ionizing radiation, which includes x-ray radiation, has the po-

advancements, including wide detector and high-pitch helical dual

tential to cause harm and it is critically important for any physician

source CT, some patients can undergo coronary CTA with a radia-

ordering or performing coronary CTA to have a fundamental un-

tion dose of less than 1 mSv.^{65,66,68—70}

derstanding of its risks and measures to minimize patient exposure.

The average annual radiation exposure arising from natural

5.3. Scan range

sources (radon, cosmic radiation, terrestrial, etc.) for an individual

living in the United States accounts for an effective radiation dose of

Radiation exposure is proportional to the scan range. Therefore,

approximately 3.6

mSv.⁵⁸ While there are limited direct data

the scan range should be limited to the extent that is necessary for

available for the estimated risk from low-level radiation at the

addressing the clinical question and will enable radiation dose

range of diagnostic CT studies, some controversies remain. The

savings.⁷¹ In the case of most coronary CTA scans of the native

‘linear no threshold’ theory assumes that there is a direct linear

coronary arteries, the range should only include the heart.

relationship between the radiation exposure and the risk of can-

Obtaining a low dose scan to determine the smallest required scan

cer.⁵⁹ Furthermore, it is assumed that any radiation exposure is

field in order to minimize radiation dose is not recommended,

potentially harmful.⁶⁰ The harmful effect is cumulative, i.e., the

because it does add radiation and utilization of anatomic landmarks

more radiation exposure one experiences in life, the greater the

is generally sufficient. The scan range for coronary CTA typically

risk. In addition, there is long latency (>10—30 years) before the

starts below the tracheal bifurcation or the mid-level of the left

manifestation of radiation-induced cancer with available data

pulmonary artery and extends to just below the lower cardiac

suggesting that children and young adults are particularly at risk

border. In limited clinical scenarios such as the assessment of cor-

from radiation exposure.⁶¹ Lastly, growing tissue and organs may

onary artery bypass grafts including the internal thoracic (internal

be more susceptible to genetic damage induced by radiation than

mammary) arteries or in patients with congenital heart disease, an

tissue with low turnover. Because of higher sensitivity of breast

extended scan range may be required.

tissue to radiation, radiation risks of coronary CTA are higher for

women than for men.

5.4. Tube potential

For all of the above reasons, it is imperative to assure that CT

scanning is indicated for the individual patient, that the most

Typically, 100—120 kV tube potential is sufficient for cardiac

appropriate protocol is chosen for the specific clinical indication,

imaging in most patients. Increasing the tube voltage to 140 kV

and that all possible precautions are applied to minimize radiation

leads to a higher energy X-ray beam with better tissue penetration

exposure. However, the potential increased risk from radiation has

and a reduction in image noise, which may be necessary in very

to be weighed against the requirement to acquire images that are of

large patients. However, increasing the tube voltage typically a

diagnostic quality. Diagnostic image quality is determined by

increases radiation exposure proportional to the square of the tube

multiple factors, including the absence of motion and other image

voltage change.⁷² In smaller patients and children, reducing the

artifacts, high contrast-to-noise, and high spatial resolution. For

tube potential to 100 or 80 kVp can substantially lower radiation

each patient, the acceptable limits for image quality should be

exposure by 30—50%, while maintaining adequate contrast-to-

determined a priori in order to tailor the CT scan technique and

noise and diagnostic image quality.^67,73—75 Recently released CT

S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435—449

443

platforms supported by improved detector technology and specific

(end-systole and diastole) and image reconstruction during other

tube designs that maintain the ability to use high tube currents at

cardiac phases frequently results in motion artifacts, thus gener-

low tube potential permit coronary CTA at 70 kVp, although there is

ating non-diagnostic images of the coronary arteries. Accordingly,

limited data on the diagnostic performance at this tube poten-

tube current is reduced during phases of the cardiac cycle when

tial.^76,77 While 120 kV is often considered the “standard” tube po-

coronary motion is likely greater (early- and mid-systole) while

tential for coronary CTA, tube potential should be reduced from 120

reserving full-dose tube current to limited phases of the cardiac

kV to 100 kV when the patient's weight is below 100 kg and the

cycle when coronary motion is minimal. Dose savings of up to 50%

body mass index (BMI) is below 30 kg/m², particularly considering

can be obtained using ECG-based tube current modulation,

recent advancements in iterative reconstruction techniques (dis-

although the reduction in radiation exposure depends on several

cussed below), which preserve image quality at lower tube po-

factors, including heart rate (greater dose savings in patients with

tentials.⁷⁸ In favorable situations (e.g. body weight below 60 kg), it

low heart rates) and CT scanner used.⁸¹The disadvantage of ECG-

should be considered to lower tube potential even further. In

based tube current modulation is greater noise in images recon-

addition to BMI-based tube voltage selection, the use of automated

structed during phases of the cardiac cycle utilizing a lower tube

methods for kVp selection based on attenuation values in the scout

current. However, the increase in image noise does not usually

images may facilitate low radiation exposure in patients undergo-

hinder cardiac function analysis since ventricular contours can still

ing coronary CTA, especially women.⁷⁹

be delineated.

5.5. Tube current

6. Modes of data acquisition

More commonly, the tube current (mA) is modified to adjust for

6.1. Prospectively ECG triggered axial acquisition

patient size/weight and desired image noise. Increase in tube cur-

rent results in more photons per exposure time leading to less

Prospectively ECG-triggered axial acquisition should be

image noise, but greater radiation exposure. In contrast to the tube

considered for coronary CTA as the default scan mode of choice in

voltage, the increase in radiation dose is approximately directly

patients with adequate heart rate control. With prospectively ECG-

proportional to the change in tube current. In general, larger pa-

triggered axial acquisition, the X-ray tube is activated only during a

tients need greater tube current to reduce image noise (generated

pre-specified phase of the cardiac cycle (R-R interval). There is no

by more tissue penetration) to an acceptable level. It has to be

table movement during this time interval. X-ray data are obtained

emphasized again, that tube current should only be increased to a

during the phase of the cardiac cycle with presumably the greatest

level necessary for acquiring images of adequate quality. Since the

likelihood of minimal coronary motion. The acquisition window

previous guidelines, the major advance in relation to lowering tube

can be as narrow as required to reconstruct one phase of the cardiac

current has come through the integration of iterative reconstruc-

cycle (approximately one-half of the gantry rotation time), but this

tion methods, which improve image quality such that lower tube

leaves no flexibility to select additional phases of the cardiac cycle

current scanning is feasible without a significant compromise in

for image reconstruction in the event that coronary segments are

diagnostic image quality. Tube current needs to be selected based

degraded by motion. However, it is possible to widen the acquisi-

on the iterative reconstruction capabilities of the relevant CT

tion window for a longer interval of the cardiac cycle (“padding”),

scanner platform being used. Similar to automatic kVp selection

which allows for reconstruction of images at different time instants

above, patient attenuation data from the scout images may also be

so as to reduce the risk of a non-diagnostic exam at the expense of

used to select tube current and reduce dose.⁷⁹

greater radiation exposure.⁸² Since no X-ray data are acquired

during the remainder of the cardiac cycle, the savings in radiation

5.6. Anatomy-based tube current modulation

exposure compared to retrospective ECG-gating can be substantial

(up to 90%). Prospectively ECG-triggered axial acquisition is rec-

While the tube current should be adjusted for each patient ac-

ommended in patients with a regular heart rhythm. In heart rates

cording to the patient's size and scan indication, many scanners

<60 bpm, prospectively ECG-triggered axial acquisition with a

have additional features that can lower the tube current during the

narrow acquisition window during mid-diastole should be applied,

image acquisition, called “tube current modulation”. One form of

whereas in higher heart rates, the acquisition window may be

tube modulation, also called “automatic exposure control”, lowers

widened so as to include end-systolic phases.

the tube current when the X-ray beam is penetrating less dense

Large detector scanners with broad Z-axis coverage have

tissue (i.e., lungs) and increases the current when more solid tissue

recently been introduced into clinical practice.⁸³ The detectors may

is penetrated.⁸⁰ The selection of tube current is typically deter-

be wide enough to cover the entire volume of the heart and hence

mined by the estimated patient attenuation from the acquired

offer the opportunity for single heartbeat acquisitions, eliminating

scout/localizer scans in conjunction with the technologist's indi-

the risk of misalignment artifact and allowing for homogeneous

cation of a target image noise level. During CT acquisition, tube

blood pool attenuation.⁸⁴

current automatically increases or decreases longitudinally in

accordance with the degree of attenuation. Lastly, the tube current

6.2. Retrospectively ECG-gated helical or spiral acquisition

can be modulated as a function of x-ray source angle (or “X,Y

modulation”). Tube current modulation can significantly lower

In retrospectively ECG-gated coronary CTA, x-ray data are ac-

radiation exposure and should be strongly considered when

quired throughout the entire cardiac cycle while the patient table is

available on the respective CT scanning platform.

subjected to constant, slow motion. This generates an x-ray data set

with substantial oversampling and for image reconstruction; only

5.7. ECG-based tube current modulation

data acquired during the cardiac phase with the least motion are

used. Retrospective ECG-gating in coronary CTA should be consid-

In general, ECG-based tube current modulation should be

ered in cases where a regular heart rhythm cannot be obtained or if

applied during retrospectively ECG-gated coronary CTA. The prin-

the heart rate is high. In addition, retrospective ECG-gating should

ciple of ECG-based tube current modulation considers the fact that

be considered when seeking evaluation of ventricular or valvular

coronary motion is low during limited phases of the cardiac cycle

function. ECG-based tube current modulation should always be

444

S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435—449

considered when retrospectively ECG-gated helical or spiral

and thus should not be taken as a surrogate for total delivered dose.

acquisition is used for coronary CTA.

The closest estimate to the actually delivered dose is the dose-

length-product, DLP, which takes into consideration a weighted

6.3. Prospectively ECG-Triggered high-pitch helical or spiral

CTDI (accounting for dose heterogeneity in the scan field), the scan

acquisition

length and pitch/scan overlap. From the DLP, an estimation of

effective radiation dose can be derived by multiplying the DLP by a

High-pitch spiral coronary CTA is a recent scan mode developed

conversion factor for thoracic imaging (currently 0.014 is being

specifically for low-dose imaging and is currently available on dual

used for adult patients).⁸⁸ These values can be obtained during the

source CT platforms.⁸⁵ Dual-source CT technology enables seamless

planning stage of the scan, i.e., after determining the scan range,

z-sampling at helical pitch values of 3.4 by interleaving data ac-

heart rate during breath-hold, and should be considered for

quired from the two detector systems. Scan acquisition with high-

applying the least radiation to address the test indication. It is

pitch spiral coronary CTA is most commonly triggered during early

important to note however, that the derived numbers are only

diastole (60% of the R-R interval) and completed within one cardiac

rough estimates because they are based on phantom studies and

cycle. At higher heart rates it may be more appropriate to trigger

the anatomic assumptions are frequently not met in clinical prac-

during end-systole. High-pitch spiral coronary CTA may be applied

tice. It is also important to note, that radiation dose estimates

in patients in whom excellent image quality is expected (regular

typically underestimate the true radiation dose, when actually

heart rate <60 bpm, BMI <30 kg/m²). The major advantage of this

measured.⁹ Thus, the DLP should serve as a rough guide of esti-

protocol is the generation of very low-dose coronary CTA images

mated radiation dose delivered and one should assume that the

with radiation exposures often less than 2 mSv. The disadvantage of

actual delivered doses exceed these estimates. The DLP is most

high-pitch spiral coronary CTA is that only one phase during the

useful to assess the relative dose reductions with alterations of the

cardiac cycle is available for image reconstruction. In addition, the

image acquisition, i.e., change in tube voltage and current, imple-

process of image acquisition is triggered several heartbeats before

menting dose modulation etc., for optimized scan planning. It is

data acquisition actually occurs, so that the protocol is not suitable

therefore recommended to document DLP for every coronary CT

for patients with any variability in heart rates, nor is it useful in

angiogram and to institute periodic review of radiation exposure.

cases seeking evaluation of ventricular function.

Pediatric DLP estimates are often based on a 16 cm phantom,

which will increase the estimated dose for the same exposure of a

7. Shielding

32 cm phantom by a factor of 2.2. Thus, it is suggested that DLP, scan

range and the phantom size used for DLP and CTDI estimates are

Intuitively, shielding of radiosensitive organs within (breast,

reported for pediatric patients undergoing coronary CTA.

lung) or outside (thyroid, intestine, gonads) the scan field by pro-

tective materials (lead, bismuth, tungsten-antimony) should help

8. Scan protocols

minimize radiation exposure to the patient. Yet, the potential

benefits of shielding must be weighed against evidence that

8.1. Overview image

shielding impairs CT image quality by increasing noise, reducing

image signal and by the introduction of streak artifacts.⁹ While

Imaging starts typically with obtaining an anterior-posterior

phantom models and dosimetry studies suggest that shielding

projection overview image (scout, topogram, topographic scout

yields modest reductions (30—60%) of radiation exposure during CT

image, etc.) that allows prescription of the scan range. Generally the

imaging, further evidence is needed to demonstrate if any biologic

coronary CTA scan range begins at the level of the tracheal bifur-

benefits may offset impaired image quality. While a White Paper of

cation or the mid-level of the left main pulmonary artery and ends

the American College of Radiology suggests that “technologists may

just below the diaphragm, usually 12—15 cm in length.

need to use individualized shielding”,⁸⁶ until more conclusive data

are available, shielding is not considered a routine tool to lower

8.2. Coronary calcium scan

radiation exposure for coronary CTA.

As an alternative to breast shielding in female patients,

A coronary calcium scan is a non-enhanced ECG-synchronized

displacement of mobile breast tissue outside the CT scan range may

scan for the detection and quantification of coronary calcium. In

be considered. Breast displacement may lower radiation exposure

general, prospectively ECG-triggered axial acquisition should be

to breast tissue and improve CT image quality by reducing photon

used. The optimal phase of the cardiac cycle depends upon the

attenuation, while minimizing the radiation dose required to ach-

heart rate observed during the test breath-hold and typically

ieve a diagnostic CTA.⁸⁷

ranges between 65 and 80% of the R-R interval. Whether to proceed

with a coronary CTA in the presence of extensive coronary calcifi-

7.1. Other considerations

cation on the coronary calcium scan remains controversial. Coro-

nary calcification leads to high X-ray attenuation that can result in

Scatter from patient clothing, jewelry, and ECG leads should be

partial volume averaging artifacts.⁹ Some studies have demon-

considered and avoided by having patients change into hospital

strated a higher incidence of non-diagnostic coronary segments in

gowns prior to CT scanning, and carefully reviewing scout/localizer

the presence of significant coronary calcification.⁸⁹ At the same

images for high attenuation objects within the scan volume.

time, more extensive coronary calcification increases the likelihood

that the patient has obstructive coronary artery disease.^90,91

7.2. Monitoring radiation exposure

Accordingly, some centers do not proceed with coronary CTA in

the presence of an Agatston score exceeding 600—1000. However,

Current scanners display the estimated radiation exposure for

such approaches have not been adequately studied nor validated.

each component of the scan as well as the total estimated dose for

For selected patients in whom good image quality is expected

each study. The standard radiation dose parameter is the CT dose

(regular heart rate <60 bpm, low to moderate body weight, and

index, CTDI, which represents the estimated dose delivered to a CT

optimal patient corporation), coronary CTA may yield useful in-

phantom for given scan parameters (tube voltage, current, rotation

formation despite extensive coronary calcification. The decision to

time, etc.). However, the CTDI does not account for the scan length

proceed with coronary CTA in the presence of a high coronary

S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435—449

445

calcium score should be left to the discretion of the referring and

image quality. When appropriate, use of 100 kVp is recom-

attending physician.

mended to reduce radiation dose when the patient's weight is

below 100 kg and BMI is below 30 kg/m². Automated scan

9. Coronary CT angiography

parameter selection tools should be considered when available

The scan range should be as short as reasonably possible.

9.1. Heart rate considerations

Prospectively ECG-triggered axial acquisition is recommended

as the first choice protocol for coronary CTA. Alternatives such as

The heart rate and its variability obtained during breath-hold

high-pitch spiral acquisition or retrospectively ECG-gated heli-

are critically important for planning the scan. In general, routine

cal or spiral acquisition with ECG-based tube current modula-

lowering the heart rate for coronary CTA substantially contributes

tion may be applied in selected cases.

to radiation dose saving. A regular heart rate (preferably <60 bpm)

High-pitch spiral acquisitions should be considered for stable

allows one to obtain diagnostic images using conventional pro-

heart rates

≤ 60 bpm

spectively ECG-triggered or high-pitch spiral coronary CTA in most

If the patient's heart rate and/or rhythm remain unfavorable

patients. Depending on the scanner type and software specifica-

(given the site's scanner hardware) despite all efforts of heart

tions, higher heart rates may require the acquisition of data from

rate control, alternative diagnostic imaging strategies should be

both late systole and diastole, which may be achievable using

considered, although coronary CTA may remain the appropriate

prospectively ECG-triggered axial acquisition with a wide acquisi-

test.

tion window or through retrospectively ECG-gated helical or spiral

The imaging physician has to be familiar with specific technical

acquisition, usually performed with ECG-correlated tube current

limitations and strengths of the site's CT scanner system and has

modulation. Irregular heart rhythms may also require retrospec-

to adjust patient selection according to determinants of image

tively ECG-gated acquisition. The development of dual-source CT

quality (heart rate, coronary calcification, weight, and patient

and wide-detector scanners may allow imaging of selected patients

cooperation) and acquisition protocols accordingly.

with higher and irregular heart rates such as atrial fibrillation with

diagnostic imaging quality.^92,93 It should be acknowledged, how-

ever that coronary CTA in high or irregular heart rates typically is

10. Image reconstruction and post-processing

associated with a higher radiation dose. Moreover, in the event of

irregular heart rates or atrial fibrillation it is essential that other

10.1. Introduction

determinants of image quality such as coronary calcification, body

weight and patient cooperation are taken into consideration before

The immediate result of CT data acquisition is a raw attenuation

deciding whether to proceed with the scan. The presence of

data set, commonly referred to as ‘raw data’, and not actual view-

frequent premature complexes prior to scanning therefore should

able images. Viewable images are computed from the raw data by

trigger consideration of aborting the examination.

means of ‘image reconstruction’, producing digital images in which

each pixel is assigned a digital numerical value

(CT value),

9.2. Weight considerations

expressed in Hounsfield units. The default orientation of image

reconstruction is commonly axial (transverse). However, images in

Scan settings should be adjusted to the patient's body weight.

any orientation can be reconstructed directly from the raw data. In

Both tube voltage and tube current should be optimized to deliver

the past, image reconstruction has predominantly been performed

the least necessary radiation for adequate image quality. In obese

by a method referred to filtered backprojection. With increasing

patients, higher tube current and tube voltage are required in order

computational power, most hardware systems allow for iterative

to preserve contrast to noise ratio. More importantly, tube current

image reconstruction.

should be adjusted to the total volume of soft tissues within the

Alterations in the reconstruction method can influence the final

scanned region. The specific adjustments are dependent on the

appearance of the reconstructed images, in regard to image quality,

scanner specifications.

image artifact, edge enhancement, and resolution. In most cases

axial image reconstruction is pre-programmed into the scan pro-

9.3. Dual energy CT

tocol and takes place with minimal input from a technologist.

However, it is advisable to be familiar with the image reconstruc-

In 2008, dual energy CT was introduced into clinical practice

tion process so that modifications to image reconstruction can be

with a dual source CT platform. Alternative approaches include

made when necessary. This section will address the factors that

rapid kVp switching (rapidly toggling between 80 and 140 kVp) as

influence the final resulting image data set, and will make recom-

well as the use of a dual layer detector.

mendations for certain actions in certain scenarios.

Dual energy CT strategies have the capacity to reduce image

artifacts for myocardial assessment with a particular focus on

reducing beam-hardening artifact.⁹⁴ However, the role of dual en-

ergy CT for evaluation of coronary stenosis is not well defined and

10.2. Temporal resolution

no specific recommendations can be made.

Recommendations:

Image reconstruction requires a minimum of 180°

plus the

width of the fan angle of raw-data projections necessitating only

Physicians operating MDCT must be intimately familiar with the

180°

of tube rotation. The rotation time of the gantry dictates how

concepts of risks from radiation exposure.

much time is needed to acquire 180°

of projections. The approxi-

Every effort must be undertaken to allow the lowest radiation

mate temporal resolution of the reconstructed images is thus

exposure as reasonably achievable while maintaining diagnostic

dependent on the rotation time employed and, for the center of

image quality.

rotation, is calculated as rotation time/2 for an image reconstruc-

Tube potential and current should be adjusted for each indi-

tion utilizing 180°

of projections. To compensate for cardiac motion,

vidual patient according to patient characteristics and test

the minimum rotation time should be employed for routine coro-

indication with the lowest settings necessary to achieve good

nary CTA.

446

S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435—449

10.3. Half-scan (180°) vs. full-scan (360°) reconstruction

Proper selection of these time intervals for motion-free image

reconstruction is crucial to obtaining high-quality diagnostic im-

180-degree reconstructions are commonly referred to as a half-

ages.²⁷ Identification of this time is based on cardiac cycle length

scan reconstruction. However, images can be reconstructed using a

and is expressed as a percentage of the cardiac cycle length (R-R

wider array of projections, e.g. 270°

or 360°, the latter referred to as

interval) or as an absolute time (in ms) after the R-peak. The use of

a full-scan reconstruction. Adding projections beyond 180°

to the

absolute times for selection of image reconstruction (e.g., 700 ms

image reconstruction improves the signal-to-noise ration but de-

after the R-peak) may produce higher quality images, but has not

creases the temporal resolution. Half-scan reconstruction is the

been shown to significantly impact to make a difference diagnostic

default mode for coronary CTA image reconstructions, as it opti-

accuracy.²⁷ The optimal time for image reconstruction depends on

mizes the temporal resolution and reduces temporal averaging.

the patient's heart rate during the acquisition, and this holds true

Full-scan reconstructions can be employed obese patients to

for dual-source as well as single-source scanners.^27,97 There is

decrease image noise, but image degradation due to motion arti-

general agreement that at lower heart rates (<65 bpm), the optimal

facts has to be considered.

timing is during late-diastole, while at higher heart rates (>65 to 70

bpm) the optimal timing is more frequently (but not always) during

10.4. Field of view and image matrix

end-systole.^27,97 If the original data set is not free of motion artifact,

additional datasets at different phases of the cardiac cycle (R-R

The field of view (FoV) refers to the portion of the scan field

interval) must be reconstructed. In these cases, it is not sufficient to

comprising the image reconstruction, with certain, individually

rely solely on phases automatically selected by the reconstruction

selected in-plane dimensions. The reconstructed FoV can be rect-

software or on a pre-determined, fixed range of phases applied to

angular or circular. The image matrix refers to the number of pixels

all cases. If motion artifact is present, tailored image reconstruction

along both in-plane dimensions. The default matrix in coronary

must be repeated in intervals that correspond to 5% of the cardiac

CTA is 512

× 512. A lower matrix resolution (e.g. 256

× 256) de-

cycle or less until a data set without motion artifact is obtained or

creases the images resolution if the same FoV is employed and is

the phase with least motion is identified. It may be necessary to use

not recommended for coronary artery evaluation. For image re-

different phases of the cardiac cycle for various segments of the

constructions dedicated to coronary artery evaluation the FoV

coronary arteries.

should be limited to the cardiac structures (usually 200—250mm)

using a 512

× 512 matrix. Holding matrix size constant, increasing

10.8. Multi-segment reconstruction

the FoV will reduce spatial resolution of the data set. A 256

× 256

matrix can be employed for adjunct reconstructions, e.g. multi-

Multi-segment reconstruction can be utilized during retro-

phasic reconstructions for cardiac function analysis, in order to

spectively ECG-gated spiral acquisition or if more than one rotation

limit the file size.

is performed in axial acquisition to improve the effective temporal

resolution. Because multiple detector rows are stacked in the z-

10.5. Slice width (slice thickness) and overlap

axis, any given location in the body will pass multiple detector rows

at the same point in the cardiac cycle but during different,

For coronary artery evaluation, axial image reconstructions

contiguous heart beats. Rather than using the half-scan data from

should be performed with the smallest possible slice width (or

one cardiac cycle to reconstruct an axial image, multi-segment

thickness), varying between 0.5mm and 6.25mm, depending on

reconstruction uses data from multiple (contiguous) cardiac cy-

vendor and CT system. A thicker slice width results in lower image

cles and pieces them together to recreate a half-scan of data and

noise, but also lower spatial resolution as compared to thinner slice

hence an axial image. This reduces the effective acquisition time

width, resulting in volume averaging and decreased anatomical

within each cardiac cycle, and improves temporal resolution and

detail. In obese patients, image reconstructions employing a larger

image quality. Especially at higher heart rates, the use of multi-

slice thickness may be employed to reduce image noise. However,

segment reconstruction can significantly improve image quality

the same effect may be obtained by generating ‘thick’ or ‘averaged’

and diagnostic accuracy.⁹⁸ Caveats regarding this technique include

multiplanar reformatted images based on thin sliced axial re-

the requirement of an absolutely regular cardiac rhythm, and the

constructions using contemporary post-processing work-stations.

assumption (not always true) that the cardiac position will not vary

between heart beats during acquisition. Multi-segment recon-

10.6. Reconstruction kernel

struction can only be applied when using retrospective ECG-gating.

The reconstruction kernel is the mathematical algorithm used to

10.9. ECG editing

compute the CT values of the pixels within the CT data set. “Soft”

kernels produce an image of lower noise and lower spatial reso-

In cardiac CT, acquisition of ECG data occurs simultaneously

lution, while “sharp” kernels increase resolution at the cost of

with the acquisition of attenuation data, and the axial reconstruc-

higher image noise. In addition, algorithms can be designed spe-

tion process uses both sets of data. Hence, the ECG data set must be

cifically for reducing metal artifact or calcium blooming or to

reviewed if artifacts occur in the reconstructed image data set. If the

enhance the appearance of contrast and the vascular struc-

capability exists, errors that are due to incorrect triggering should

tures.^95,96 Understanding these differences is essential to selecting

be corrected by “editing” the trigger instants in the ECG data and

and applying the correct kernel for a given set of patient factors (e.g.

“tagging” or “removal” of trigger instances attributable to ectopic

body habitus) and clinical scenarios (e.g. imaging heavily calcified

beats should be performed if they cause artifact. This can often

arteries). It is important to also note that attenuation values may

salvage what would otherwise be an uninterpretable scan.⁹⁹

vary from one scanner to the next.

10.10. Image review

10.7. Cardiac phase

It is recommended that axial images should be reviewed

The heart's continual cyclical movement provides brief periods

immediately after reconstruction, either by a technologist or

of minimal motion during end-systole and mid-to-late diastole.

physician trained in cardiac CT, while the patient is still on the

S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435—449

447

scanner table in order to confirm sufficient quality of data

society of Echocardiography, the American society of Nuclear cardiology, the

North American society for cardiovascular imaging, the society for cardiovas-

acquisition.

cular angiography and Interventions, and the society for cardiovascular mag-

netic resonance. J Am Coll Cardiol. 2010;56(22):1864e1894 .

10.11. Recommendations

Budoff MJ, Dowe D, Jollis JG, et al. Diagnostic performance of 64-multidetector

row coronary computed tomographic angiography for evaluation of coronary

artery stenosis in individuals without known coronary artery disease: results

Half-scan reconstruction should be used by default for all cor-

from the prospective multicenter ACCURACY

(Assessment by Coronary

onary CTA examinations.

Computed Tomographic Angiography of Individuals Undergoing Invasive

Coronary Angiography) trial. J Am Coll Cardiol. 2008;52(21):1724e1732 .

The reconstructed field of view should be reduced to maximize

Meijboom WB, Meijs MF, Schuijf JD, et al. Diagnostic accuracy of 64-slice

number of pixels devoted to depiction of the heart, usually a FOV

computed tomography coronary angiography: a prospective, multicenter,

of 200—250 mm for coronary CTA studies of native coronary

multivendor study. J Am Coll Cardiol. 2008;52(25):2135e2144 .

arteries.

Miller JM, Rochitte CE, Dewey M, et al. Diagnostic performance of coronary

angiography by 64-row CT. N. Engl J Med. 2008;359(22):2324e2336 .

If extra-cardiac structures are of interest then a second data set

Budoff MJ, Cohen MC, Garcia MJ, et al. ACCF/AHA clinical competence state-

with a larger FOV (x-y plane) should be reconstructed.

ment on cardiac imaging with computed tomography and magnetic Reso-

Axial images should be reconstructed with a slice width <1.0

nanceA report of the American College of cardiology foundation/American

heart association/American College of physicians task force on clinical

mm for most coronary CTA studies of native coronary arteries.

competence and training. J Am Coll Cardiol. 2005;46(2):383e402 .

Minimum slice thickness (0.5—0.6 mm) should be considered

Jacobs JE, Boxt LM, Desjardins B, et al. ACR practice guideline for the perfor-

for studies that require maximum spatial resolution, insofar as

mance and interpretation of cardiac computed tomography (CT). Journal of the

American College of Radiology. JACR. 2006;3(9):677e685 .

image noise permits. A thicker slice width (1.0—1.5 mm) should

Halliburton SS, Abbara S, Chen MY, et al. SCCT guidelines on radiation dose and

be considered in obese patients to reduce image noise due to

dose-optimization strategies in cardiovascular CT. J Cardiovasc Comput Tomogr.

body habitus.

2011;5(4):198e224 .

10.

Valentin J. Pregnancy and medical radiation: ICRP publication 84.. Ann ICRP

A slice increment of 50% of the slice width should be used.

2000(30

(1)):1e39.

A semi-sharp reconstruction kernel should be used for most

11.

Webb JA, Thomsen HS, Morcos SK. Members of contrast media safety com-

patients. For cases that require maximum spatial resolution, a

mittee of European society of Urogenital R. The use of iodinated and gadolin-

ium contrast media during pregnancy and lactation. Eur Radiol. 2005;15(6):

sharp kernel may be used to reduce blooming and increase edge

1234e1240 .

definition. For obese patients, a soft or smooth kernel may be

12.

Rubin G, Bluemke D, Duerinckx A, et al. ACR Committee on Cardiac Imaging.

used to reduce image noise.

Practice guideline for the performance and interpretation of cardiac computed

tomography (CT) (Res. 10, 16g, 17, 34, 35, 36 e 2006). In: Practice Guidelines

A sufficient number of phases should be reconstructed in order

and Technical Standards. Reston, VA: American College of Radiology; 2008:

to find the optimal phase of the cardiac cycle (R-R interval) with

421e430 .

the least amount of coronary motion.

13.

Greenberger P, Patterson R. Prednisone-diphenhydramine regimen prior to use

Multi-segment reconstruction should be considered, especially

of radiographic contrast media. J Allergy Clin Immunol. 1979;63(4):295 .

14.

Elicker BM, Cypel YS, Weinreb JC. IV contrast administration for CT: a survey of

at higher heart rates, to improve temporal resolution and

practices for the screening and prevention of contrast nephropathy. AJR Am J

improve image quality.

Roentgenol. 2006;186(6):1651e1658 .

ECG-editing, if available, should be used to correct errors or

15.

Lee JK, Warshauer DM, Bush Jr WH, McClennan BL, Choyke PL. Determination

of serum creatinine level before intravenous administration of iodinated

artifacts occurring during acquisition, and to designate ectopic

contrast medium. A Surv Investig Radiol. 1995;30(12):700e705 .

beats for exclusion or special handling during data

16.

Ellis J, Davenport M, Dillman J, et al. ACR Committee on Drugs and Contrast

reconstruction.

Media. American College of Radiology; 2016. Version 10.2 .

17.

Briguori C, Airoldi F, D'Andrea D, et al. Renal insufficiency following contrast

media administration trial (REMEDIAL): a randomized comparison of 3 pre-

11. Conclusion

ventive strategies. Circulation. 2007;115(10):1211e1217 .

18.

Briguori C, Colombo A, Violante A, et al. Standard vs double dose of N-ace-

tylcysteine to prevent contrast agent associated nephrotoxicity. Eur Heart J.

Recent advances in CT technology have greatly improved image

2004;25(3):206e211 .

quality, feasibility, and accuracy of coronary CTA. A clear under-

19.

Lee PT, Chou KJ, Liu CP, et al. Renal protection for coronary angiography in

standing of the technique's capabilities and limitations, and an

advanced renal failure patients by prophylactic hemodialysis. A randomized

controlled trial. J Am Coll Cardiol. 2007;50(11):1015e1020 .

appreciation of the details of patient selection, preparation, scan

20.

Marenzi G, Assanelli E, Marana I, et al. N-acetylcysteine and contrast-induced

acquisition, and image reconstruction are required to develop and

nephropathy in primary angioplasty. N. Engl J Med. 2006;354(26):2773e2782 .

sustain a successful coronary CTA program. Supervision and care

21.

Newhouse JH, Kho D, Rao QA, Starren J. Frequency of serum creatinine changes

in the absence of iodinated contrast material: implications for studies of

must be taken at every step in the process to ensure that high

contrast nephrotoxicity. AJR Am J Roentgenol. 2008;191(2):376e382 .

quality results are achieved in all patients. These guidelines provide

22.

McDonald RJ, McDonald JS, Carter RE, et al. Intravenous contrast material

general instruction for the performance and acquisition of coronary

exposure is not an independent risk factor for dialysis or mortality. Radiology.

CTA, but proper execution of the procedure for any patient requires

2014;273(3):714e725 .

23.

Owen RJ, Hiremath S, Myers A, Fraser-Hill M, Barrett BJ. Canadian Association

expertise of all involved practitioners and staff, and recognition of

of Radiologists consensus guidelines for the prevention of contrast-induced

patient factors and clinical scenarios which will require tailoring of

nephropathy: update 2012. Can Assoc Radiologists J. 2014;65(2):96e105. ¼ J

the coronary CTA protocol.

l'Association Can des radiologistes .

24.

Ahuja TS, Niaz N, Agraharkar M. Contrast-induced nephrotoxicity in renal

allograft recipients. Clin Nephrol. 2000;54(1):11e14 .

References

25.

Brodoefel H, Reimann A, Heuschmid M, et al. Non-invasive coronary angiog-

raphy with 16-slice spiral computed tomography: image quality in patients

1. Abbara S, Arbab-Zadeh A, Callister TQ, et al. SCCT guidelines for performance of

with high heart rates. Eur Radiol. 2006;16(7):1434e1441 .

coronary computed tomographic angiography: a report of the Society of Car-

26.

Cademartiri F, Mollet NR, Runza G, et al. Diagnostic accuracy of multislice

diovascular Computed Tomography Guidelines Committee. J Cardiovasc Com-

computed tomography coronary angiography is improved at low heart rates.

put Tomogr. 2009;3(3):190e204 .

Int J Cardiovasc Imaging. 2006;22(1):7e9, 101-5; discussion .

2. Leipsic J, Abbara S, Achenbach S, et al. SCCT guidelines for the interpretation

27.

Achenbach S, Manolopoulos M, Schuhback A, et al. Influence of heart rate and

and reporting of coronary CT angiography: a report of the Society of Cardio-

phase of the cardiac cycle on the occurrence of motion artifact in dual-source

vascular Computed Tomography Guidelines Committee. J Cardiovasc Comput

CT angiography of the coronary arteries. J Cardiovasc Comput Tomogr.

Tomogr. 2014;8(5):342e358 .

2012;6(2):91e98 .

3. Taylor AJ, Cerqueira M, Hodgson JM, et al. ACCF/SCCT/ACR/AHA/ASE/ASNC/

28.

Le Jemtel TH, Padeletti M, Jelic S. Diagnostic and therapeutic challenges in

NASCI/SCAI/SCMR 2010 appropriate use criteria for cardiac computed tomog-

patients with coexistent chronic obstructive pulmonary disease and chronic

raphy. A report of the American College of cardiology foundation appropriate

heart failure. J Am Coll Cardiol. 2007;49(2):171e180 .

use criteria task force, the society of cardiovascular computed tomography, the

29.

Maffei E, Palumbo AA, Martini C, et al. In-house” pharmacological management

American College of radiology, the American heart association, the American

for computed tomography coronary angiography: heart rate reduction, timing

448

S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435—449

and safety of different drugs used during patient preparation. Eur Radiol.

2007). In: Practice Guidelines and Technical Standards. Reston, VA: American

2009;19(12):2931e2940 .

College of Radiology; 2008:73e78 .

30.

Roberts WT, Wright AR, Timmis JB, Timmis AD. Safety and efficacy of a rate

57.

Segal A, Ellis J, Baumgartner B, et al. ACR committee on drugs and contrast media.

control protocol for cardiac CT. Br J Radiology. 2009;82(976):267e271 .

Manual on contrast media. Version 6. Reston, VA: American College of Radi-

31.

Earls JP. How to use a prospective gated technique for cardiac CT. J Cardiovasc

ology; 2008 .

Comput Tomogr. 2009;3(1):45e51 .

58.

Verdun FR, Bochud F, Gundinchet F, Aroua A, Schnyder P, Meuli R. Quality

32.

Sadamatsu K, Koide S, Nakano K, Yoshida K. Heart rate control with single

initiatives* radiation risk: what you should know to tell your patient. Radio-

administration of a long-acting beta-blocker at bedtime before coronary

graphics. 2008;28(7):1807e1816 .

computed tomography angiography. J Cardiol. 2015;65(4):293e297 .

59.

Brenner DJ, Doll R, Goodhead DT, et al. Cancer risks attributable to low doses of

33.

Clayton B, Raju V, Roobottom C, Morgan-Hughes G. Safety of intravenous beta-

ionizing radiation: assessing what we really know. Proc Natl Acad Sci U. S. A.

adrenoceptor blockers for computed tomographic coronary angiography. Br J

2003;100(24):13761e13766 .

Clin Pharmacol. 2015;79(3):533e536 .

60.

Committee to Assess Health Risks from Exposure to Low Levels of Ionizing

34.

Kassamali RH, Kim DH, Patel H, et al. Safety of an i.v. beta-adrenergic blockade

Radiation; Nuclear and Radiation Studies Board. Division on earth and life

protocol for heart rate optimization before coronary CT angiography. AJR Am J

studies, National research council of the National academies. health risks from

Roentgenol. 2014;203(4):759e762 .

exposure to low levels of ionizing radiation. BEIR VII Phase 2. Washington, DC:

35.

Wang JD, Zhang HW, Xin Q, et al. Safety and efficacy of intravenous esmolol

The National Academies Press; 2006 .

before prospective electrocardiogram-triggered high-pitch spiral acquisition

61.

Don S. Radiosensitivity of children: potential for overexposure in CR and DR

for computed tomography coronary angiography. J Geriatric Cardiol JGC.

and magnitude of doses in ordinary radiographic examinations. Pediatr Radiol.

2014;11(1):39e43 .

2004;34(Suppl 3):S167eS172. discussion 234 eS241.

36.

Dobre D, Borer JS, Fox K, et al. Heart rate: a prognostic factor and therapeutic

62.

Einstein AJ, Henzlova MJ, Rajagopalan S. Estimating risk of cancer associated

target in chronic heart failure. The distinct roles of drugs with heart rate-

with radiation exposure from 64-slice computed tomography coronary angi-

lowering properties. Eur J Heart Fail. 2014;16(1):76e85 .

ography. Jama. 2007;298(3):317e323 .

37.

Pichler P, Pichler-Cetin E, Vertesich M, et al. Ivabradine versus metoprolol for

63.

Cohen MD. ALARA, image gently and CT-induced cancer. Pediatr Radiol.

heart rate reduction before coronary computed tomography angiography. Am J

2015;45(4):465e470 .

Cardiol. 2012;109(2):169e173 .

64.

Cody DD, Brateman LF, Favinger J, et al. ACR appropriateness criteria radiation

38.

Celik O, Atasoy MM, Erturk M, et al. Comparison of different strategies of

dose assessment introduction. 2015 .

ivabradine premedication for heart rate reduction before coronary computed

65.

Deseive S, Chen MY, Korosoglou G, et al. Prospective randomized trial on ra-

tomography angiography. J Cardiovasc Comput Tomogr. 2014;8(1):77e82 .

diation dose estimates of CT angiography applying iterative image recon-

39.

Cademartiri F, Garot J, Tendera M, Zamorano JL. Intravenous ivabradine for

struction: the protection V study. JACC Cardiovasc Imaging. 2015;8(8):888e896 .

control of heart rate during coronary CT angiography: a randomized, double-

66.

Deseive S, Pugliese F, Meave A, et al. Image quality and radiation dose of a

blind, placebo-controlled trial. J Cardiovasc Comput Tomogr.

2015;9(4):

prospectively electrocardiography-triggered high-pitch data acquisition strat-

286e294 .

egy for coronary CT angiography: the multicenter, randomized PROTECTION IV

40.

Parker JD, Parker JO. Nitrate therapy for stable angina pectoris. N. Engl J Med.

study. J Cardiovasc Comput Tomogr. 2015;9(4):278e285 .

1998;338(8):520e531 .

67.

Hausleiter J, Martinoff S, Hadamitzky M, et al. Image quality and radiation

41.

Dewey M, Hoffmann H, Hamm B. Multislice CT coronary angiography: effect of

exposure with a low tube voltage protocol for coronary CT angiography results

sublingual nitroglycerine on the diameter of coronary arteries. RoFo. For-

of the PROTECTION II Trial. JACC Cardiovasc Imaging. 2010;3(11):1113e1123 .

tschritte dem Geb Rontgenstrahlen Nukl. 2006;178(6):600e604 .

68.

Hausleiter J, Meyer TS, Martuscelli E, et al. Image quality and radiation expo-

42.

Decramer I, Vanhoenacker PK, Sarno G, et al. Effects of sublingual nitroglycerin

sure with prospectively ECG-triggered axial scanning for coronary CT angiog-

on coronary lumen diameter and number of visualized septal branches on 64-

raphy: the multicenter, multivendor, randomized PROTECTION-III study. JACC

MDCT angiography. AJR Am J Roentgenol. 2008;190(1):219e225 .

Cardiovasc Imaging. 2012;5(5):484e493 .

43.

Laslett LJ, Baker L. Sublingual nitroglycerin administered by spray versus

69.

Chen MY, Shanbhag SM, Arai AE. Submillisievert median radiation dose for

tablet: comparative timing of hemodynamic effects. Cardiology. 1990;77(4):

coronary angiography with a second-generation 320-detector row CT scanner

303e310 .

in 107 consecutive patients. Radiology. 2013;267(1):76e85 .

44.

Bachmann KF, Gansser RE. Nitroglycerin oral spray: evaluation of its coronary

70.

Stehli J, Fuchs TA, Bull S, et al. Accuracy of coronary CT angiography using a

artery dilative action by quantitative angiography. Am J Cardiol. 1988;61(9):

submillisievert fraction of radiation exposure: comparison with invasive cor-

7Ee11E .

onary angiography. J Am Coll Cardiol. 2014;64(8):772e780 .

45.

Takx RA, Sucha D, Park J, Leiner T, Hoffmann U. Sublingual nitroglycerin

71.

Khan A, Nasir K, Khosa F, Saghir A, Sarwar S, Clouse ME. Prospective gating

administration in coronary computed tomography angiography: a systematic

with 320-MDCT angiography: effect of volume scan length on radiation dose.

review. Eur Radiol. 2015;25(12):3536e3542 .

AJR Am J Roentgenol. 2011;196(2):407e411 .

46.

Wang G, Vannier MW. Spatial variation of section sensitivity profile in spiral

72.

Task Group on Control of Radiation Dose in Computed T. Managing patient

computed tomography. Med Phys. 1994;21(9):1491e1497 .

dose in computed tomography. A report of the International Commission on

47.

Ohnesorge B, Flohr T, Becker C, et al. Cardiac imaging by means of electro-

Radiological Protection. Ann ICRP. 2000;30(4):7e45 .

cardiographically gated multisection spiral CT: initial experience. Radiology.

73.

Hausleiter J, Meyer T, Hadamitzky M, et al. Radiation dose estimates from

2000;217(2):564e571 .

cardiac multislice computed tomography in daily practice: impact of different

48.

Halliburton SS, Abbara S. Practical tips and tricks in cardiovascular computed

scanning protocols on effective dose estimates. Circulation.

2006;113(10):

tomography: patient preparation for optimization of cardiovascular CT data

1305e1310 .

acquisition. J Cardiovasc Comput Tomogr. 2007;1(1):62e65 .

74.

Siegel MJ, Schmidt B, Bradley D, Suess C, Hildebolt C. Radiation dose and image

49.

Bae KT, Tran HQ, Heiken JP. Multiphasic injection method for uniform pro-

quality in pediatric CT: effect of technical factors and phantom size and shape.

longed vascular enhancement at CT angiography: pharmacokinetic analysis

Radiology. 2004;233(2):515e522 .

and experimental porcine model. Radiology. 2000;216(3):872e880 .

75.

Leipsic J, LaBounty TM, Mancini GB, et al. A prospective randomized controlled

50.

Fleischmann D, Rubin GD, Bankier AA, Hittmair K. Improved uniformity of

trial to assess the diagnostic performance of reduced tube voltage for coronary

aortic enhancement with customized contrast medium injection protocols at

CT angiography. AJR Am J Roentgenol. 2011;196(4):801e806 .

CT angiography. Radiology. 2000;214(2):363e371 .

76.

Zhang LJ, Wang Y, Schoepf UJ, et al. Image quality, radiation dose, and diag-

51.

Haage P, Schmitz-Rode T, Hubner D, Piroth W, Gunther RW. Reduction of

nostic accuracy of prospectively ECG-triggered high-pitch coronary CT angi-

contrast material dose and artifacts by a saline flush using a double power

ography at 70 kVp in a clinical setting: comparison with invasive coronary

injector in helical CT of the thorax. AJR Am J Roentgenol.

2000;174(4):

angiography. Eur Radiol. 2016;26(3):797e806 .

1049e1053 .

77.

Hell MM, Bittner D, Schuhbaeck A, et al. Prospectively ECG-triggered high-pitch

52.

Hopper KD, Mosher TJ, Kasales CJ, TenHave TR, Tully DA, Weaver JS. Thoracic

coronary angiography with third-generation dual-source CT at 70 kVp tube

spiral CT: delivery of contrast material pushed with injectable saline solution in

voltage: feasibility, image quality, radiation dose, and effect of iterative

a power injector. Radiology. 1997;205(1):269e271 .

reconstruction. J Cardiovasc Comput Tomogr. 2014;8(6):418e425 .

53.

Raju R, Thompson AG, Lee K, et al. Reduced iodine load with CT coronary

78.

Oda S, Utsunomiya D, Funama Y, et al. A hybrid iterative reconstruction algo-

angiography using dual-energy imaging: a prospective randomized trial

rithm that improves the image quality of low-tube-voltage coronary CT angi-

compared with standard coronary CT angiography. J Cardiovasc Comput

ography. AJR Am J Roentgenol. 2012;198(5):1126e1131 .

Tomogr. 2014;8(4):282e288 .

79.

Williams MC, Weir NW, Mirsadraee S, et al. Iterative reconstruction and

54.

Carrascosa P, Leipsic JA, Capunay C, et al. Monochromatic image reconstruction

individualized automatic tube current selection reduce radiation dose while

by dual energy imaging allows half iodine load computed tomography coro-

maintaining image quality in 320-multidetector computed tomography coro-

nary angiography. Eur J Radiology.

2015

Oct;84(10):1915e1920. http://

nary angiography. Clin Radiol. 2013;68(11):e570ee5707 .

dx.doi.org/10.1016/j.ejrad.2015.06.019 .

80.

Funama Y, Utsunomiya D, Taguchi K, Oda S, Shimonobo T, Yamashita Y.

55.

Yin WH, Lu B, Gao JB, et al. Effect of reduced x-ray tube voltage, low iodine

Automatic exposure control at single- and dual-heartbeat CTCA on a 320-

concentration contrast medium, and sinogram-affirmed iterative reconstruc-

MDCT volume scanner: effect of heart rate, exposure phase window setting,

tion on image quality and radiation dose at coronary CT angiography: results of

and reconstruction algorithm. Phys Med. 2014;30(3):385e390 .

the prospective multicenter REALISE trial. J Cardiovasc Comput Tomogr.

81.

Mayo JR, Leipsic JA. Radiation dose in cardiac CT. Am J Roentgenol. 2009;192(3):

2015;9(3):215e224 .

646e653 .

56.

Segal A, Ellis J, Baumgartner B, et al. ACR Committee on Drugs and Contrast

82.

Leipsic J, LaBounty TM, Ajlan AM, et al. A prospective randomized trial

Media. Practice guideline for the use of intravascular contrast media. (Res. 38 e

comparing image quality, study interpretability, and radiation dose of narrow

S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435—449

449

acquisition window with widened acquisition window protocols in prospec-

angiography in patients with suspected coronary artery disease. J Cardiovasc

tively ECG-triggered coronary computed tomography angiography. J Cardiovasc

Comput Tomogr. 2016 Sep-Oct;10(5):343e350 .

Comput Tomogr. 2013;7(1):18e24 .

92. Kondo T, Kumamaru KK, Fujimoto S, et al. Prospective ECG-gated coronary

83. Rybicki FJ, Otero HJ, Steigner ML, et al. Initial evaluation of coronary images

320-MDCT angiography with absolute acquisition delay strategy for patients

from

320-detector row computed tomography. Int J Cardiovasc Imaging.

with persistent atrial fibrillation. AJR Am J Roentgenol. 2013;201(6):1197e1203 .

2008;24(5):535e546 .

93. Marwan M, Pflederer T, Schepis T, et al. Accuracy of dual-source CT to identify

84. Raju R, Cury RC, Precious B, et al. Comparison of image quality, and diagnostic

significant coronary artery disease in patients with uncontrolled hypertension

interpretability of a new volumetric high temporal resolution scanner versus

presenting with chest pain: comparison with coronary angiography. Int J

64-slice MDCT. Clin Imaging. 2016;40(2):205e211 .

Cardiovasc Imaging. 2012;28(5):1173e1180 .

85. Achenbach S, Marwan M, Schepis T, et al. High-pitch spiral acquisition: a new

94. Scheske JA, O'Brien JM, Earls JP, et al. Coronary artery imaging with single-

scan mode for coronary CT angiography. J Cardiovasc Comput Tomogr.

source rapid kilovolt peak-switching dual-energy CT. Radiology. 2013;268(3):

2009;3(2):117e121 .

702e709 .

86. Amis Jr ES, Butler PF. ACR white paper on radiation dose in medicine: three

95. Maintz D, Seifarth H, Raupach R, et al. 64-slice multidetector coronary CT

years later. J Am Col Radiol JACR. 2010;7(11):865e870 .

angiography: in vitro evaluation of 68 different stents. Eur Radiol. 2006;16(4):

87. Foley SJ, McEntee MF, Achenbach S, Brennan PC, Rainford LS, Dodd JD. Breast

818e826 .

surface radiation dose during coronary CT angiography: reduction by breast

96. Seifarth H, Raupach R, Schaller S, et al. Assessment of coronary artery stents

displacement and lead shielding. AJR Am J Roentgenol. 2011;197(2):367e373 .

using 16-slice MDCT angiography: evaluation of a dedicated reconstruction

88. Deak PD, Smal Y, Kalender WA. Multisection CT protocols: sex- and age-

kernel and a noise reduction filter. Eur Radiol. 2005;15(4):721e726 .

specific conversion factors used to determine effective dose from dose-

97. Matsumoto H, Kondo T, Watanabe S, et al. ECG-edited middiastolic phase

length product. Radiology. 2010;257(1):158e166 .

reconstruction improves image quality at 64-MDCT coronary angiography of

89. Hecht HS, Bhatti T. How much calcium is too much calcium for coronary

patients with atrial fibrillation. AJR Am J Roentgenol. 2008;191(6):1659e1666 .

computerized tomographic angiography? J Cardiovasc Comput Tomogr.

98. Schnapauff D, Teige F, Hamm B, Dewey M. Comparison between the image

2008;2(3):183e187 .

quality of multisegment and halfscan reconstructions of non-invasive CT cor-

90. Yan RT, Miller JM, Rochitte CE, et al. Predictors of inaccurate coronary arterial

onary angiography. Br J Radiology. 2009;82(984):969e975 .

stenosis assessment by CT angiography. JACC Cardiovasc Imaging. 2013;6(9):

99. Yoshioka K, Tanaka R, Muranaka K, et al. Subtraction coronary CT angiography

963e972 .

using second-generation

320-detector row CT. Int J Cardiovasc Imaging.

91. Schuhbaeck A, Schmid J, Zimmer T, et al. Influence of the coronary calcium

2015;31(Suppl 1):51e58 .

score on the ability to rule out coronary artery stenoses by coronary CT