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Journal of Cardiovascular Computed Tomography
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
Suhny Abbaraa,*, Philipp Blankeb, Christopher D. Maroulesa, Michael Cheezumc,
Andrew D. Choid, B. Kelly Hane, Mohamed Marwanf, Chris Naoumg,
Bjarne L. Norgaardh, Ronen Rubinshteini, Paul Schoenhagenk, Todd Villinesj,
Jonathon Leipsicb
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 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 2009Guidelines for the Performance of Coronary CTA (1). The
purpose of this document is to provide standards meant to ensure reliable practice methods and quality
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.
© 2016 Society of Cardiovascular Computed Tomography. Published by Elsevier Inc. All rights reserved.
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 2009Guidelines 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).
1934-5925/© 2016 Society of Cardiovascular Computed Tomography. Published by Elsevier Inc. All rights reserved.
S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435449
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.46 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
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 thestate
emergency resuscitation equipment should be readily available.
of the art being in a continuousstate 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 64320 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 (47 cc/sec) are recommended,
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) 435449
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
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
mendations12All 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
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)
S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435449
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 (47 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
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-
tion, central lines should not be utilized.
No food for 34 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
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.1416 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,1720
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
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
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) 435449
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-
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
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 (50100 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 50100 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
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 2025 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
S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435449
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 400800 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 12 tablets or 12 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 2030 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
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
atest 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) 435449
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 24 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 (270400 mg Iodine/cc). An
1020 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 12 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, 24 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.4952 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 57 cc/sec (volume depends on
technique offers the potential to reduce the overall contrast dose by
scan duration) and subsequent injection of approximately 4050 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 (57 cc/sec), followed by a
reconstruction using dual energy coronary CTA (see below) may
second injection of either a mixture of contrast and saline (57 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 12 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,
S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435449
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 57 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 50120 cc.
vein anatomy prior to an ablative procedure when knowledge of
It is reasonable to use a total contrast volume of 12 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,
and as such the CT scan can be performed at a lower radiation
Biphasic or triphasic injection protocols should be used.
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
110 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.65,66,6870
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 (>1030 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, 100120 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 3050%, while maintaining adequate contrast-to-
determined a priori in order to tailor the CT scan technique and
noise and diagnostic image quality.67,7375 Recently released CT
S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435449
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 thestandard 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, calledtube current modulation. One form of
whereas in higher heart rates, the acquisition window may be
tube modulation, also calledautomatic 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 (orX,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
S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435449
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
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 (3060%) 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 thattechnologists may
just below the diaphragm, usually 1215 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 6001000. 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) 435449
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-
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 asraw 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 ofimage 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.
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
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.
S. Abbara et al. / Journal of Cardiovascular Computed Tomography 10 (2016) 435449
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 200250mm)
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 generatingthick oraveraged
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, whilesharp 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 byediting the trigger instants in the ECG data and
and applying the correct kernel for a given set of patient factors (e.g.
tagging orremoval 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) 435449
scanner table in order to confirm sufficient quality of data
10.11. Recommendations
Half-scan reconstruction should be used by default for all cor-
onary CTA examinations.
The reconstructed field of view should be reduced to maximize
number of pixels devoted to depiction of the heart, usually a FOV
of 200250 mm for coronary CTA studies of native coronary
If extra-cardiac structures are of interest then a second data set
with a larger FOV (x-y plane) should be reconstructed.
Axial images should be reconstructed with a slice width <1.0
mm for most coronary CTA studies of native coronary arteries.
Minimum slice thickness (0.50.6 mm) should be considered
for studies that require maximum spatial resolution, insofar as
image noise permits. A thicker slice width (1.01.5 mm) should
be considered in obese patients to reduce image noise due to
body habitus.
Valentin J. Pregnancy and medical radiation: ICRP publication 84.. Ann ICRP
A slice increment of 50% of the slice width should be used.
A semi-sharp reconstruction kernel should be used for most
patients. For cases that require maximum spatial resolution, a
sharp kernel may be used to reduce blooming and increase edge
definition. For obese patients, a soft or smooth kernel may be
used to reduce image noise.
A sufficient number of phases should be reconstructed in order
to find the optimal phase of the cardiac cycle (R-R interval) with
421e430 .
the least amount of coronary motion.
Multi-segment reconstruction should be considered, especially
at higher heart rates, to improve temporal resolution and
improve image quality.
ECG-editing, if available, should be used to correct errors or
artifacts occurring during acquisition, and to designate ectopic
beats for exclusion or special handling during data
Briguori C, Airoldi F, D'Andrea D, et al. Renal insufficiency following contrast
11. Conclusion
Recent advances in CT technology have greatly improved image
quality, feasibility, and accuracy of coronary CTA. A clear under-
standing of the technique's capabilities and limitations, and an
appreciation of the details of patient selection, preparation, scan
acquisition, and image reconstruction are required to develop and
sustain a successful coronary CTA program. Supervision and care
must be taken at every step in the process to ensure that high
quality results are achieved in all patients. These guidelines provide
general instruction for the performance and acquisition of coronary
CTA, but proper execution of the procedure for any patient requires
expertise of all involved practitioners and staff, and recognition of
patient factors and clinical scenarios which will require tailoring of
the coronary CTA protocol.
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