coronary computed tomography - present status and future directions

Coronary computed tomography – present status andfuture directions

P. Apfaltrer,1,2 U. J. Schoepf,1,3 R. Vliegenthart,1,4 G. W. Rowe,1 J. R. Spears,1 C. Fink,2

J. W. Nance Jr.1

Introduction

Coronary artery disease (CAD) remains one of the

most important causes of morbidity and mortality in

the Western world (1,2), with an estimated

16,800,000 individuals suffering from CAD in the

United States alone. In 2009, it was estimated that

785,000 and 470,000 Americans will have new and

recurrent attacks of acute coronary syndrome,

respectively, and according to data from 2006, CAD

is still responsible for one in five deaths in the Uni-

ted States. The medical costs of CAD reflect its bur-

den, at $165.4 billion in the United States in 2009

alone (3).

Optimisation of preventative and curative medi-

cine for CAD has the potential to greatly reduce a

significant societal burden and improvements have

been made in risk stratification, diagnosis and disease

monitoring in the past decades (3). Unfortunately,

current strategies are often time consuming (e.g. hos-

pital observation and serial serum cardiac enzyme

measurements), expensive (e.g. nuclear stress testing),

and ⁄ or invasive (e.g. invasive coronary angiography,

ICA). Coronary computed tomography angiography

(cCTA) has the potential to directly visualise the cor-

onary arteries, providing a fast, non-invasive assess-

ment of atherosclerotic burden. cCTA has been

shown to have a particularly high negative predictive

value to rule out significant coronary artery stenosis

in selected patients, and for this reason it is increas-

ingly utilised in the evaluation of acute chest pain

and chest pain syndrome (4) (Figures 1 and 2). Fur-

thermore, cCTA is continuing its rapid evolution,

with advances in hardware and techniques resulting

in improved diagnostic performance, decreased

patient radiation exposure and potential expansion

of the currently approved clinical applications.

Technical Evolution

The relatively recent rise in cCTA is a direct reflec-

tion of technical advances in CT scanner technology.

The heart is subjected to nearly constant intrinsic

motion from myocardial contractions, subjecting CT

studies to a variety of artefacts that degrade image

quality. The fundamental solution to the problem of

SUMMARYThe use of coronary computed tomography angiography (cCTA) is growing rapidly,

in large part because of fast-paced technical innovations that have increased diag-

nostic accuracy while providing new opportunities for radiation dose reduction.

cCTA using recent generation CT scanners has been repeatedly shown to have

excellent negative predictive value for ruling out significant coronary stenosis in

comparison with invasive coronary angiography (ICA) and is now accepted for this

use in selected populations. Current work is increasingly focused on evaluating

and optimising radiation dose reduction techniques, the cost-effectiveness of cCTA

implementation, and the impact of cCTA on patient management and outcomes.

In addition, the potential value of emerging applications, such as atherosclerotic

plaque characterisation and myocardial perfusion and viability assessment, are

undergoing intense investigation.

Review CriteriaPubMed was used to obtain references for this

non-systematic review of coronary CT angiography.

In addition, unpublished data and expert opinion

from the three academic medical centres

represented by the authors was incorporated to

form a current and future perspective of the

technique, its applications and its potential.

Message for the ClinicCoronary computed tomography angiography is

able to exclude coronary artery disease (CAD) with

a high negative predictive value and is therefore

recommended in the evaluation of patients with

low to intermediate probability of CAD. Ongoing

developments in cCTA techniques should refine and

expand its clinical role while attenuating worries

over patient radiation burden.

1Department of Radiology and

Radiological Science, Medical

University of South Carolina,

Charleston, SC, USA2Institute of Clinical Radiology

and Nuclear Medicine,

University Medical Center

Mannheim, Medical Faculty

Mannheim – Heidelberg

University, Mannheim, Germany3Department of Medicine,

Division of Cardiology, Medical

University of South Carolina,

Charleston, SC, USA4Department of Radiology,

University Hospital Groningen,

Groningen, The Netherlands

Correspondence to:

U. Joseph Schoepf, MD,

Department of Radiology and

Radiological Science,

Medical University of South

Carolina,

Ashley River Tower,

25 Courtenay Drive, MSC 226,

Charleston, SC 29401, USA

Tel.: (843) 876 7146

Fax: (843) 876 3157

Email: [email protected]

Disclosures:

UJS is medical consultant for

and receives research support

from Bayer, Bracco, General

Electric, Medrad, and Siemens.

.

REV IEW ART ICLE

ª 2011 Blackwell Publishing Ltd Int J Clin Pract, October 2011, 65 (Suppl. 173), 3–13doi: 10.1111/j.1742-1241.2011.02784.x 3

cardiac motion involves decreasing the scan acquisi-

tion time to a minimum, and recent advancements

in two characteristics of CT hardware have helped

provide this: gantry rotation time and detector

width. In addition, synchronising CT acquisitions

with an ECG allows data to be collected and recon-

structed at the same portion of consecutive cardiac

cycles, ensuring that the heart (and hence coronary

artery) positions are continuous across a complete

image acquisition, which until recently required data

collection over multiple cardiac cycles. The first scan-

ners capable of coronary angiography were the ECG-

synchronised electron-beam CT systems, introduced

in 1984, that decreased scan acquisition times via

extremely fast gantry rotation (5). In 1999, however,

the first multidetector row CT (MDCT) scanner,

with four parallel detectors rather than one, was

introduced; this was rapidly followed by 16-, 32-

and, in 2004, 64-slice MDCT introduction. Increases

in the number of detectors provide greater longitudi-

nal (z-axis) coverage in a single rotation of the CT

gantry, reducing the number of cardiac cycles neces-

sary for a complete acquisition and thus decreasing

the possibility of misalignment from one cross-sec-

tional image to the next (resulting in ‘stair-step’ or

‘banding’ artefacts on certain image reconstructions).

In addition to increased volume coverage, the gantry

rotation time of subsequent MDCT scanners has

improved, resulting in decreased time to acquire each

tomogram and hence directly improving the tempo-

ral resolution of the final reconstructions (6).

While electron-beam CT enjoyed popularity dur-

ing the time of its existence, especially with coronary

artery calcium scoring, it was the advent of the

MDCT systems that allowed cCTA to expand. Each

generation of MDCT provided a higher proportion

of successfully examined patients (7); however, it was

the 64-slice systems that allowed cCTA to be imple-

mented into routine clinical practice (8). With tem-

poral resolutions of approximately 165 ms, detailed

images of the heart became possible with 5–10 s scan

times (9). The 64-slice MDCT systems have a negli-

gible percentage of unevaluable vessel segments and

higher contrast medium attenuation with lower con-

trast medium volumes compared with prior genera-

tions, resulting in high diagnostic accuracies to

detect coronary stenosis in comparison with the gold

standard, ICA (see below) (8).

As cardiac motion artefacts and reliable ECG-syn-

chronisation are directly related to the rate and regu-

larity of the cardiac cycle, respectively, acquisitions

in patients with high (> 60–70 beats per minute)

and or irregular (e.g. atrial fibrillation) heart rates

are still a challenge for standard 64-slice systems.

While this can be partially alleviated with the use of

pharmacological modulation (generally, beta blocker

administration prior to the examination) (10,11), the

most recent technical developments have mitigated

the problem further. Introduced in 2006, dual-source

CT (DSCT) systems combine two arrays of X-ray

tubes with corresponding detectors arranged at a 90�angle (12), allowing complete tomographic data to

be acquired in one quarter of the gantry rotation,

rather than one-half, effectively improving temporal

resolution to 83 ms and allowing high quality imag-

ing of the coronary arteries even in patients with

high heart rates or arrhythmia (13–16).

The most recent developments promise even

higher quality scans, often in combination with addi-

tional evaluative capabilities and ⁄ or decreased radia-

tion dose. DSCT scanners, as they have two

independent tube and detector arrays, may be run in

‘dual-energy mode’, allowing material differentiation

based on characteristics other than density (see

below). Second generation DSCT scanners, with dou-

ble the detectors (and hence volume coverage) of

first generation scanners, offer high pitch single

heartbeat acquisition, or ‘FLASH scans’. Increasing

the pitch, which is calculated by dividing the table

feed per gantry rotation by the collimated z-width of

the detector, decreases the time necessary to cover

the entire heart volume. Coverage times as low as

0.28 s have been reported (with total scan times

A B C

Figure 1 A 39-year-old man with chest pain on exertion, strong family history of

coronary artery disease. Second generation dual-source coronary CT angiography

study acquired within a single diastolic phase (270 ms) and an effective radiation

dose equivalent of 0.8 mSv. Displays as curved multiplanar reformations rule out

coronary artery stenosis in the (A) right (RCA), (B) left anterior descending (LAD)

and (C) circumflex (Cx) coronary arteries. The high negative predictive value of a

normal or near-normal coronary CT angiogram can reliably exclude coronary artery

stenosis as a reason for chest pain and obviate further work-up for coronary artery

disease (CAD) and very low dose scans as above may be obtained via high-pitch

spiral coronary computed tomography angiography (cCTA) in patients with low and

stable heart rates

4 Coronary computed tomography

ª 2011 Blackwell Publishing Ltd Int J Clin Pract, October 2011, 65 (Suppl. 173), 3–13

< 1 s), which allows an entire acquisition to be per-

formed in a single cardiac cycle in patients with a

regular rhythm and heart rates < 70 beats per minute

(6,17,18). Other developments include MDCT sys-

tems with up to 320 detectors that provide sufficient

z-axis coverage to acquire a complete acquisition in

a single cardiac cycle (19) and advances in image

reconstruction techniques that have been shown to

improve performance characteristics and lower the

radiation dose required for diagnostic scan quality

(6,20,21).

Radiation Dose

Coronary computed tomography angiography has

prompted concerns about ionising radiation expo-

sure to the patient since its introduction (22,23). The

traditional retrospectively ECG-gated acquisitions

collect overlapping data across the entire cardiac

cycle using high tube voltages, techniques that guar-

antee volumetric continuity, allow flexibility in

choosing optimal reconstructions and help ensure

diagnostic image quality. Unfortunately, these tech-

niques are also associated with high effective radia-

tion dosages. One multicentre study from 2006

reported an average effective radiation dose equiva-

lent of 12 milliSieverts (mSv) for cardiac CT, with

values as high as 30 mSv at some locations (22). For-

tunately, innovations in cCTA hardware and tech-

niques have allowed great reductions in patient

radiation exposure over the past several years

(Table 1) (20).

The most effective single-dose reduction method is

achieved by modifying the applied radiation

throughout the cardiac cycle rather than applying the

same dose continuously. The latter method allows

retrospective reconstruction of images based on the

ECG. In contrast, prospectively ECG-triggered acqui-

sitions collect sequential transverse sections only

during a predetermined interval in the cardiac cycle.

With this approach, effective radiation dose values as

low as 1.2–4.2 mSv have been reported (24–28);

however, the technique is typically restricted to

patients with low and regular heart rates and the lack

of data across the entire cardiac cycle precludes left

ventricular (LV) functional evaluation (6). A similar

method, ECG-based tube current modulation, applies

full tube current (which is directly related to radia-

tion dose) only during a predetermined portion of

the cardiac cycle (e.g., at end diastole) and decreased

current during the remaining portion. This tech-

nique, while unable to reduce dose as much as true

prospective triggering, maintains LV functional

assessment capabilities by providing data across the

entire cardiac cycle (6,29).

The recent introduction of second generation

DSCT scanners capable of prospectively ECG-trig-

gered high pitch examinations (see above) has also

provided opportunities for significant dose reduction.

The high pitch, in addition to limiting dose to a sin-

gle cardiac cycle, eliminates overlapping volume cov-

erage of sequential transverse sections and studies

have shown this method to be capable of providing

complete cCTA examinations with < 1 mSv effective

radiation dose (29,30).

Another investigative technique involves decreasing

the applied tube current from the standard 120–

100 kV in patients with low body mass indices; this

has been shown to provide dose reductions of

> 50% without compromising diagnostic perfor-

mance (29–32). Finally, new reconstruction tech-

niques, such as iterative reconstruction, may allow

further tube current reductions in more patients

while maintaining high accuracy for stenosis detec-

tion (6,20,21).

Optimising image quality while minimising radia-

tion exposure will require individualised cCTA pro-

tocols that consider institution- and patient-specific

..........................................................................

Table 1 Techniques to reduce radiation dose associated with CT coronary angiography

Technique Mechanism of effect Dose reduction potential

Tube current modulation

mode

100% tube current in predefined phase of the cardiac

phase. Reduction by 80% for the remainder of the

cardiac cycle

13–46% (29)

Prospective ECG gating

(regular heart rates)

X-ray tube is turned on only at the selected cardiac phase

and turned off during the rest cardiac cycle

31–86% (29)

Tube voltage (kV) 100 kV

(patients with a low BMI)

Radiation dose changes in proportion to the square of

changes in tube voltage

42–55% (104)

High-pitch helical

coronary CTA

At this preselected z-position, data acquisition is started. As

a result of the fast table movement, the entire heart can

be scanned in a fraction of a heartbeat (6)

80% (29)

Coronary computed tomography 5


factors, such as the available scanner hardware and

reconstruction software and patient body weight,

age, heart rate and heart rhythm. Ongoing and

future advancements promise to further alleviate the

current fears about the possible maleficence of cCTA.

Current Status of cCTA

Currently approved applications for cCTA are lim-

ited, but the field is highly dynamic. Perhaps the

most important current indication is in the evalua-

tion of acute chest pain, a condition for which over

6 million individuals per year currently present to

the emergency department (33). The most recent

professional society guidelines accept cCTA evalua-

tion of patients with acute chest pain and a negative

initial evaluation (electrocardiogram, ECG and car-

diac enzymes) who have a low to intermediate pre-

test probability of CAD (largely a function of age,

gender and symptoms) (4) (Figure 1). The tradi-

tional diagnostic pathway in such patients involves

hospital observation with serial cardiac enzyme mea-

surements followed by functional imaging (exercise

testing, nuclear medicine stress testing, etc.) (34,35).

Representative studies evaluating the performance

of 64-row CT and dual-source CT for detecting hae-

modynamically significant coronary artery stenosis in

these patients report sensitivities between 86% and

99%, specificities between 92% and 98%, positive

predictive values (PPV) between 47% and 91% and,

most importantly, negative predictive values (NPV)

between 92% and 100% compared with ICA

(Table 2) (11,36–39), with DSCT displaying slightly

higher performance (40). The excellent negative pre-

dictive value of cCTA to rule out significant coronary

artery stenosis allows rapid triage and may be suffi-

cient to obviate the need for further testing (41–43),

with significant time and cost savings. Using the

same rationale, cCTA is also acceptable to rule out

CAD in certain patients with low to intermediate

probability of CAD who have chest pain syndrome

(i.e. chronic chest pain or angina equivalent) (4).

Other, less prevalent currently approved applications

for cCTA are (i) in the evaluation of suspected coro-

nary artery anomalies, (ii) in patients with new-onset

heart failure and low to intermediate probability of

CAD, (iii) to rule out coronary artery bypass graft or

coronary stent occlusion in select patients, (iv) to

provide additional investigation of acute chest pain

or suspected CAD in patients with prior equivocal

studies and (v) to provide clearance of CAD prior to

non-coronary cardiac surgery, all of which were pre-

viously evaluated with ICA (4,44,45). cCTA is not

currently accepted for CAD screening, i.e., the evalu-

ation of non-symptomatic patients; however, the

most recent guidelines provocatively stated that the

appropriateness of cCTA use in the evaluation of

asymptomatic patients with a high global risk for

CAD was ‘uncertain’, opening the door to investiga-

tion of this application (4).

While the general indications for cCTA are well

defined, institution- and patient-specific factors must

be considered before ordering or performing examin-

ations. The minimum technical requirements include

CT scanners with 64 or more slices that can provide

submillimetre spatial resolution and gantry rotation

...................................................................................... .. .

Table 2 Accuracy of 64-Section CT and dual-source CT for detection of coronary stenosis in comparison with conventional coronaryangiography (per-segment analysis)

Author Scanner type Number of patients Sensitivity (%) Specificity (%) PPV (%)

Meijboom et al. (90) 64-Section CT 360 99 64 86

Budoff et al. (91) 64-Section CT 230 95 83 64

Mollet et al. (92) 64-Section CT 51 100 92 97

Miller et al. (93) 64-Section CT 291 85 90 91

Oncel et al. (94) 64-Section CT 80 100 100 100

Raff et al. (95) 64-Section CT 70 95 90 93

Ehara et al. (96) 64-Section CT 69 98 86 98

Baumuller et al. (40) Dual-source CT 200 96.4 97.4 83.2

Sun et al. (97) Dual-source CT 103 84.3 98.6 96.1

Achenbach et al. (98) Dual-source CT 50 100 82 72

Leber et al. (37) Dual-source CT 88 95 90 74

Ropers et al. (99) Dual-source CT 100 98 81 79

Tsiflikas et al. (100) Dual-source CT 170 94 79 88

Johnson et al. (101) Dual-source CT 35 100 89 89

Weustink et al. (102) Dual-source CT 100 99 87 96

Brodoefel et al. (103) Dual-source CT 100 100 81.5 93.6



times £ 420 ms (4). The experience of the institu-

tion, radiology technicians and interpreting physi-

cians should be considered; clinical competence

statements are available (46). While newer scanner

technology has improved the robustness of examina-

tions in patients with high and arrhythmic heart

rates, these patients may still pose diagnostic dilem-

mas because of poor image quality, as do patients

with high body mass indices (> 40 kg ⁄ m2). Symp-

tomatic patients with inconclusive results on cCTA

may require further evaluation with non-invasive

physiological testing (e.g. nuclear myocardial perfu-

sion imaging, ergometric stress testing) to rule out

haemodynamically significant stenosis (47).

The diagnostic accuracy of cCTA stenosis detec-

tion is well established and implementation of cCTA

has become part of the standard clinical workup at

select centres; however, long-term outcomes data on

the technique are not well defined. A study by Pun-

dziute et al. found that the presence of disease mark-

ers in CT was closely related to the occurrence of

major cardiac events while negative test results con-

firmed low risk (43) and another study was able to

differentiate patients with increased all-cause mortal-

ity from patients with excellent prognoses based on

cCTA results (41). Bamberg et al. (48) recently con-

ducted a systematic review and meta-analysis of the

available literature on cCTA prognostic value and

identified 11 eligible articles with a total of 7335 par-

ticipants with suspected or known CAD. They found

that cCTA demonstration of significant coronary ste-

nosis was associated with a 10-fold higher risk for all

cardiovascular events. The presence of any CAD also

had prognostic value, showing a 4.5-fold risk of

events compared with patients with a negative study

(48). However, prospective, long-term studies com-

paring traditional diagnostic pathways to those

incorporating cCTA are lacking and the effects of

cCTA implementation on patient management and

outcomes are not well known.

Cost-Effectiveness of cCTA

Among the almost 6 million patients who present

annually to an emergency department for acute chest

pain, approximately 20% receive the diagnosis of

coronary heart disease, yet a large number of these

patients are admitted for observation or hospitalisa-

tion and many receive expensive diagnostic testing

(35,49). In addition to direct costs, downstream

resource utilisation has a major impact on the eco-

nomic burden of acute chest pain evaluations. cCTA

is fast and has a high negative predictive value to

rule out significant coronary artery stenoses, provok-

ing considerable interest in the potential cost savings

of this technique. While data are limited, initial

reports suggest that cCTA is the most cost-effective

approach for the initial evaluation of individuals

with low or intermediate (10–50%) pretest likelihood

of CAD, whereas conventional catheterisation

remains the most effective first line test for patients

with a pretest probability of CAD > 60% (50). In

addition, several studies have suggested that cCTA is

more cost-effective than nuclear myocardial perfu-

sion imaging (42,51). Min et al. compared pathways

utilising cCTA vs. myocardial perfusion single-pho-

ton emission computed tomography (SPECT) in

symptomatic individuals without known CAD and

found that the least costly strategy (for both near-

term cost per diagnosis and long-term incremental

cost-effectiveness ratio per quality adjusted life year)

was to use cCTA first, followed by SPECT (if positive

cCTA) followed by ICA (if positive SPECT), which

yielded an expected 982.1 correct diagnoses per 1000

patients at an average cost of $1770 per patient

(including incidental findings). In comparison,

SPECT followed by ICA (if positive SPECT) yielded

964 correct diagnoses per 1000 patients at an average

cost of $2158 per patient (52). Of note, currently

available studies have relied on administrative claims

data and analytic decision models and prospective,

real-world studies are needed before the potential

cost benefits of cCTA can be definitively established.

Emerging Applications

The inherent and emerging capabilities of cCTA have

the potential to greatly expand its clinical applicabil-

ity and impact. As mentioned above, the main role

of cCTA is to rule out significant coronary artery ste-

nosis; however, additional coronary and extracoro-

nary information is available and routinely reported,

such as coronary atherosclerotic plaque characterisa-

tion (beyond degree of stenosis), myocardial attenua-

tion deficits and LV wall motion and function.

Researchers are actively investigating the clinical ben-

efits provided by these routinely acquired data. In

addition, exciting new cCTA techniques that may

provide information on the functional significance of

coronary artery lesions have become available and

are under intense investigation, potentiating a dis-

ruptive change in the diagnostic workup of coronary

artery pathologies.

Coronary Atherosclerotic PlaqueCharacterisation

Patient management based on both ICA and cCTA

relies on the quantity, location and stenotic degree of

atherosclerotic lesions; however, acute coronary



syndrome and sudden cardiac death have been

shown to be more likely associated with the rupture

of previously non-stenotic, predominantly lipid-rich,

‘vulnerable’ plaques than highly stenotic and calcified

lesions (53–55). In contrast to traditional ICA, cCTA

can provide some degree of atherosclerotic charac-

terisation based on plaque attenuation and morphol-

ogy. Studies comparing cCTA to the gold standard

for vessel wall and plaque evaluation, intravascular

ultrasound (56), have displayed favourable results

(57–61); however, cCTA characterisation is still

rather crude secondary to limited spatial resolution,

partial voluming effects and motion artefacts; cur-

rently, lesions are specified simply as non-calcified,

calcified or mixed rather than following the Ameri-

can Heart Association atherosclerosis classification

scheme (62). Still, several studies have shown prog-

nostic value in cCTA plaque characterisation, with

mixed plaques, non-calcified plaques, low attenuation

lesions and positive vessel wall remodelling all dis-

playing independent value to predict adverse events

(43,63,64). Refinements in cCTA technique should

allow more detailed evaluations which, in combina-

tion with long-term outcome studies based on cCTA

plaque characterisation, may provide significant

improvements in individualised CAD risk stratifica-

tion and disease monitoring.

Functional and Myocardial AnalysesAs noted above, cCTA has shown great value in

identifying and characterising atherosclerotic disease.

However, in addition to describing anatomy and

morphology, the comprehensive evaluation of CAD

requires assessment of the functional significance of

coronary artery pathology; specifically, the perfusion

status and subsequent condition of the myocardium.

This is vital for accurate risk stratification and, more

importantly, therapeutic decision making, as non-

viable, hibernating, stunned and at-risk myocardium

warrant individualised management (65). The func-

tional significance of coronary artery pathology has

traditionally been limited to evaluation by stress test-

ing, nuclear perfusion imaging or magnetic reso-

nance imaging (MRI); however, technological

advancements have suggested a possible role of cCTA

as a non-invasive, comprehensive modality for both

anatomical and functional assessment of CAD

(Figures 3 and 4).

Functionally significant CAD is reflected in the

performance of the LV, with ventricular wall motion

and global functional parameters having independent

clinical value. MRI has become the preferred tech-

nique for the exact determination of myocardial

function parameters (66–68); however, cCTA with

retrospective ECG-synchronisation has been shown

A B

C

Figure 2 A 70-year-old woman with chief complaint of increasing chest discomfort. ECG-gated 3D-volume rendered

image (A) shows massive dilatation of the left anterior descending artery (arrow). Enlargement is caused by coronary

artery-cameral fistulae forming diffuse fistulous shunts (arrows in B, C) between the left coronary arteries and the left

ventricle



to be accurate in measuring ventricular function in

comparison with MRI, with excellent interobserver

agreement (69–71). Visual evaluation of wall motion

abnormalities with cCTA has also shown good agree-

ment with cardiac US and MRI (72–74). It is unclear

how best to implement cCTA LV assessments into

clinical practice; however, this information, when

available, should be reported and considered.

Perhaps more exciting is the possibility of imaging

the myocardial blood supply with cCTA. Initial

efforts started with electron-beam CT and 4-row

MDCT, which revealed acute myocardial infarctions

as hypoattenuated myocardium in animal models

(75,76). Hypoattenuated myocardium seen on rou-

tine cCTA examinations should always be reported;

however, the value of this information is unclear.

More specialised techniques attempting to characte-

rise perfusion abnormalities have been developed,

including delayed enhancement imaging, stress

first-pass enhancement imaging, dynamic perfusion

imaging and dual-energy CT (DECT).

Delayed enhancement with cCTA relies on the

same principles as delayed enhancement with MRI,

which has become the gold standard for myocardial

A B C

Figure 3 A 53-year-old man with atypical chest pain. Contrast-enhanced retrospective ECG-gated dual-source coronary

CT angiogram displayed as (A) curved multiplanar reformation shows significant stenosis (arrow) of the right coronary

artery because of non-calcified plaque subsequently confirmed on (B) conventional angiogram. (C) Volume rendering

from right anterior oblique perspective shows significant ostial stenosis (arrow) of the right coronary artery because of

non-calcified plaque

A

B

C

Figure 4 A 54-year-old man with prior left anterior descending (LAD) stent implantation with suspected antero-septum

infarct and current atypical chest pain. Contrast-enhanced, ECG-gated dual-source coronary CT angiography displayed as

(A) curved multiplanar reformation shows LAD stent with in-stent restenosis because of intimal hyperplasia (arrowheads).

(B) A 17-segment polar view map and (C) 3D functional model of the left ventricle show hypokinetic segments

(arrowheads) in the antero-septum and normal wall motion in the remainder of the myocardium



viability imaging (77). The technique has been shown

to have excellent agreement with MRI (78); however,

larger studies are necessary to validate early findings

and establish optimal scan parameters. First-pass

enhancement imaging uses an arterial-phase image of

the heart at rest and under pharmacological stress to

attempt to identify and characterise perfusion

defects. Several studies have shown favourable

performance characteristics in comparison with

SPECT and ICA (79–82), with per-patient sensitivity

and specificity up to 86% and 92%, respectively (83).

Quantitative dynamic perfusion imaging has only

recently become feasible with the advent of dual-

source and high detector-width CT systems capable

of imaging the entire heart in minimal acquisition

times. This technique obtains time-resolved images

of the myocardium during contrast wash through

and has been shown to be feasible for the detection

of perfusion deficits in several recent studies (84,85).

Finally, dual-energy imaging has utilised the unique

dual tube and detector array of DSCT systems to

attempt to identify deficits in blood supply (Fig-

ure 5). The acquisition of two datasets at different

X-ray energy levels allows material differentiation

based on X-ray absorption characteristics in addition

to density (86). The myocardium is imaged during

first-pass of iodinated contrast material, and an

‘iodine map’ may be calculated that identifies areas

of myocardium with decreased iodine content. This

technique has shown good correlation with SPECT

in detecting decreases in the myocardial blood supply

(65,87,88).

None of the above techniques is currently used in

routine practice. While all have shown promising

early results, there are no large, prospective studies

demonstrating clinical benefits. In addition, there are

questions about the practicality of these advanced

techniques and most necessitate some degree of

increased patient radiation exposure. Nevertheless,

the prospect of a comprehensive, fast and non-inva-

sive assessment of CAD is extremely appealing and

could reasonably provide significant cost and

resource utilisation benefits while improving patient

care. As an example, a recent study by Meyer et al.

compared DECT with SPECT in the assessment of

myocardial perfusion deficits and found that DECT

imaging lowered the costs per patient, increased the

cost-effectiveness ratio per correct diagnosis and pro-

longed life while having 90% sensitivity and 71%

specificity compared with SPECT (89).

Conclusion

Advancements in CT technology have established

cCTA as an accepted modality for coronary artery

assessment in selected patients. The technique is fast,

non-invasive and may provide cost benefits when

integrated into traditional diagnostic algorithms.

Evolutions in scan techniques have also lessened con-

cerns about ionising radiation exposure, which was

an important early criticism of the modality. Further

refinements in cCTA promise more individualised

risk stratification and therapy monitoring and excit-

ing new techniques in future may allow cCTA to

serve as a comprehensive test for the assessment of

coronary artery anatomy and function.

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A B C

Figure 5 A 66-year-old man with atypical chest pain and prior abnormal stress test. Contrast-enhanced retrospectively

ECG-gated dual-source coronary CT angiogram was obtained in dual-energy technique. Dual-energy reconstructions

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Paper received 9 June 2011, accepted 15 August 2011



coronary computed tomography - present status and future directions

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