|Year : 2007 | Volume
| Issue : 1 | Page : 17-23
Current status of CT coronary angiography
KM Das1, Marium Al Kuwari1, Ahmed J Omar1, Hussein Kamel1, Nidal Asaad2, Jassim Al Suwaidi2, H.A Hajar Al Binali2
1 Department of Radiology, Hamad Medical Corporation, Doha, Qatar
2 Cardiology & Cardiothoracic Surgery Department, Hamad Medical Corporation, Doha, Qatar
|Date of Web Publication||17-Jun-2010|
K M Das
Consultant Radiologist, Department of Radiology, Hamad Medical Corporation, P.O. Box 3050, Doha
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Das K M, Al Kuwari M, Omar AJ, Kamel H, Asaad N, Al Suwaidi J, Al Binali HH. Current status of CT coronary angiography. Heart Views 2007;8:17-23
|How to cite this URL:|
Das K M, Al Kuwari M, Omar AJ, Kamel H, Asaad N, Al Suwaidi J, Al Binali HH. Current status of CT coronary angiography. Heart Views [serial online] 2007 [cited 2020 Jul 4];8:17-23. Available from: http://www.heartviews.org/text.asp?2007/8/1/17/63693
| Introduction|| |
Noninvasive assessment of coronary artery anatomy has been possible with the latest generation of multidetector computed tomography (MDCT). With retrograde ECG gating, a sub millimeter scan with high spatial and temporal resolution enabled a reasonable prediction of coronary artery disease (CAD). With the current generation of 64-slices CT scanner with a spatial resolution of 0.5 to 0.6 mm, and temporal resolution of 100 to 164 milliseconds, are increasingly being used for the diagnosis of the coronary artery disease with the determination of the extent of coronary calcification, acquisition of CCTA, ventricular function and myocardial perfusion.
| Calcium scoring|| |
The detection of calcium in coronary arteries has been considered for the estimation of the plaque burden of the patient  . Soft plaques are more vulnerable to rupture compared to the calcified plaques. Hence, absence of calcified plaques does not rule the risk of CAD and warrant further testing to adequately rule out significant CAD  . In a recent randomized controlled trial, the calcium score data from EBCT (Electron beam CT), failed to demonstrate any improvement in cardiovascular risk among patients  . It is relatively a new investigation and looks promising. It may need further long-term prospective study to see the utility in the final patients' outcome. On the other hand, contrast-enhanced MDCT with high spatial and temporal resolution enables accurate, high-resolution noninvasive evaluation of coronary arteries with identification of vulnerable atherosclerotic plaques, which may have a higher likelihood of causing acute coronary syndromes. Few of the recent studies have suggested that unstable plaques had a less dense appearance in MDCT compared with nonculprit plaques in acute coronary syndrome , .
| Advantage of MDCT over conventional angiography|| |
One of the important advantages of MDCT is the cross-sectional imaging of the arteries. It has the inherent advantage of the visualization of the lumen as well as the status of the wall of the artery. With higher spatial resolution, MDCT enables detection of vulnerable soft or mixed plaques within the coronary artery wall that may or may not even cause luminal stenosis. On the other hand, although conventional catheter angiography has very good spatial resolution and widely accepted as the gold standard for the detection of CAD because of its unsurpassed spatial resolution, displays only the vessel, but fails to visualize the coronary artery wall.
MDCT with ECG-synchronized scanning and reconstruction techniques enables scanning of the continuously moving heart in the diastolic phase of the cardiac cycle in between the RR interval ,, . The faster image acquisition shortens breath hold and examination times for the patient and reduces the amount of contrast media needed for high and consistent vascular enhancement ,, .
| MDCT technique|| |
Generally, 10 evenly spaced phases throughout the cardiac cycle are obtained. The best phase with the least amount of coronary artery movement is selected for further analysis of the lumen of the artery. Maximum intensity projection (MIP), Multiplannar reformats (MPR) and 3D volume rendering (VRT) techniques are mainly used for the analysis of the vessels. The MIP technique can be used in 3D or 2D techniques. The arterial data sets can be arranged in the line of RCA, LAD and LCX [Figure 1] for multiple visualization of the arterial plane. This is one of the most reliable methods for the interpretation of the vessel lumen as well as the cross sectional imaging of the artery. With Multiplannar reformats, because of isotropic nature of the data, high resolution images can be rearranged either in original axial section or in plane reconstruction.
Intuitive visualization of the entire course of a coronary artery can be achieved by displaying a Multiplannar reformat along an automatically generated centerline of the vessel. The 3D volume rendering, can commonly be used to have the detail orientation of the artery in relation to the adjacent cardiac structures. This technique is useful in the mapping of grafts in bypass patients [Figure 2] A & B and in patients with anomalous course of the coronary artery [Figure 3] A & B  . Compared to the MIP, the 3D VRT has relatively poor resolution and hence cannot be used in the quantitative analysis of the stenosis [Figure 4] A & B.
| Hamad Hospital experience|| |
With these techniques, from November 2004 to May 2007, we have performed total of 407 CCTA in Hamad Medical Corporation. The main indications for the CCTA were coronary stent restensosis, coronary artery disease (CAD), congenital heart disease and other morphological abnormalities. This is an ongoing project and we have only the first phase of analysis available on 110 coronary stents compared with the angiographic results and preliminary result shows MDCT was highly sensitive (96.6%) in detecting stent restenosis
| Limitation of stress ECG|| |
Stress ECG is a widely accepted technique for the screening and definitive diagnosis of coronary artery disease. It has significant limitation because of a higher incidence of false-positive and false-negative results. Lesser et al, in a retrospective study of 1,053 patients who underwent CCTA after equivocal stress test result required invasive coronary angiography only in 17% of cases  .
| Present status of MDCT|| |
A recent review of the CCTA data on both 16 as well as 64-slice CT, in the spring of 2006 by the Duke Evidence-Based Practice Center noted that the analysis by coronary segment showed sensitivity varying between 30% and 99% and specificity between 91% and 98%  .
The patient level analysis reports sensitivities from 85% to 100% and specificities between 49% and 98% [Figure 5] A & B. The reason of these high numbers was attributed to exclusion of inevaluable coronary segments and cases with poor quality images. In another multicenter study after censoring all inevaluable segments as positive, the sensitivity for detecting more than 70% luminal stenoses was 94%, specificity 67%, positive predictive value 6%, and negative predictive value 99%  .
Dual-source computed tomography (DSCT) has a considerable impact in the noninvasive diagnosis of the coronary artery disease. It has a faster imaging technique with a temporal resolution of 83 milliseconds compared to 165 milliseconds of 64-slice single-source multidetector CT (MDCT). One of the recent reports suggests an overall sensitivity, specificity, positive and negative predictive value for evaluating CAD was 96.4, 97.5, 85.7, and 99.4%, respectively  . Moreover, compared to the 64-slice CT, controlling of the heart rate with beta blocker is not needed and the same result can be achieved even with high calcium Agatston score up to 821 ± 904 (range 0-3,110).
As far as the individual coronary segment is concerned, in Dual source, the incidence of inevaluable segments is around 1.4% compared to 12% in 64-Slice CT  . In the near future, with further development, the entire heart would be examined during one heartbeat or even 4D-CT scanning with simultaneous assessment of myocardial perfusion. Automatic or semiautomatic software tools will assume a central place in detecting and quantifying coronary artery stenoses and plaques as well as in the analysis of cardiac function.
| Coronary stent restenosis|| |
Until recently the diagnosis of coronary stent stenosis was not satisfactory due the stent strut artifact in the MDCT. Recently, Ehara et al has reported significant improvement in the diagnosis of coronary stent stenosis with 64-slice CT with a sensitivity, specificity, positive predictive value, and negative predictive value of 92%, 81%, 54%, and 98% for the overall population, and values of 91%, 93%, 77%, and 98% when excluding unassessable segments (15 segments, 12%)  . With the new generation MDCT the stent strut can be clearly visualized along with the noeintimal hyperplasia in the majority of the cases [Figure 6] A-C. A recent study in our department on 53 patients, had a sensitivity, specificity, positive predictive value, negative predictive value and accuracy of CCTA in the detection of in-stent restenosis was 96.9%, 88.0 %, 77.5%, 98.5% and 91% respectively  .
| General consensus|| |
The new Appropriateness Initiative currently is addressing the optimal use of imaging tests in cardiology. However, at the 2006 ACC Convocation, Dr. Steve Nissen advised: "New imaging modalities give us a clearer picture of the heart and vascular system than ever before but what may be useful and beneficial is still evolving. Our infatuation with technology can be wonderful, but it is costly and must be used appropriately."  . In another recent communication on a comparative evaluation of CCTA with angiography suggested good correlation (r=0.72) with considerable standard deviations which to some extent limits the accuracy ,, . Based on the clinical evidence and the high negative predictive value, it has been a conclusion that CCTA has a valid role in ruling out coronary artery disease  . It has the ability to identify calcified as well as non-calcified plaques and is itself a great contribution in the study of the progress of atherosclerosis. These views have been endorsed by various professional bodies including the American College of Cardiology Foundation  .
| Limitation|| |
CCTA may not provide adequate image in patients with fast or irregular heart rates, or respiratory motion and very high calcium score (>1,000 Agatston units)  . Motion and irregular beats may lead to step artifact and give a fallacious appearance of artery stenosis. A careful inspection of the raw data and the post processing images with different phases will help in a correct diagnosis of the stenosis [Figure 7] A & B.
One of the potential drawbacks of CCTA is the inherent radiation dose. On an average the radiation dose varies from 4 and 21.4 mSv in the recent generation MDCT compared to 5.6 mSv in the conventional coronary angiography , . With the introduction of the retrospective ECG gating and tube current modulation a considerable amount of reduction in radiation dose has been achieved in the newer generation MDCT.
| Conclusion|| |
In summary, over the last two decades CCTA has evolved as one of the promising new tool for the detection of coronary artery disease with high sensitivity and negative predictive value. It may be reserved for clinical situations in which the exclusion of coronary disease is of paramount concern. It should not be overrated nor should be taken as a final answer to the diagnosis of coronary artery disease. Despite being a powerful tool, is associated with a hazard of a considerable amount of radiation dose to the patients and it should be used judiciously.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]