|
RSNA News - August 2005Multidetector CT Angiography Shows Promise in Detection of Coronary Artery DiseaseSixteen-slice CT really showed that cardiac CT is doable; 64 slice makes it a reality. Two European studies find multidetector computed tomography (MDCT) is highly accurate in the noninvasive detection of suspected obstructive coronary artery disease (CAD). 16-Slice CTIn the first study, published in the May 25 issue of the Journal of the American Medical Association (JAMA ), researchers evaluated MDCT with both subjective and quantitative measures derived from center-line placements and a true cross-sectional evaluation of a reference point of highest stenosis. “So what you see in this study for the first time is a receiver operating characteristic, or ROC, analysis,” according to lead author Martin H.K. Hoffmann, M.D., a cardiac radiologist in the Department of Diagnostic Radiology at the University Hospital in Ulm, Germany. “The discriminative power of this method is consistent over a wide range of stenosis gradings.” The Hoffmann study was conducted in a referral center setting from November 2003 to August 2004. Enrollment included 103 consecutive patients (mean age 61.5 years) who were undergoing both invasive coronary angiography and MDCT using a 16-slice scanner. Ninety-eight percent of patients had intermediate or high probability of disease. Invasive coronary angiography identified 1,384 vascular segments 1.5 mm in diameter or larger. MDCT was non-diagnostic due to image quality in 6.4 percent of these segments, mainly due to fast heart rates that could not be reduced sufficiently with β-blockers. Compared with invasive angiography for detection of significant lesions (defined as greater than 50 percent stenosis), the segment-based sensitivity of MDCT was 95 percent, specificity was 98 percent, the positive-predictive value was 87 and the negative-predictive value was 99 percent. “In this patient-based analysis, the area under the ROC curve was 0.97, indicating high discriminative power to identify patients who might be candidates for revascularization,” said Dr. Hoffmann. He added that his study had some disadvantages. “We still have 27 percent of our patients with incomplete coronary coverage,” he explained. “They have certain branches—even main branches—that show up with residual motion artifacts, and these artifacts impeded adequate reading of certain segments. Of course, to rule out coronary artery disease, you have to have excellent image quality in every segment.” Despite the study’s limitation, cardiac imaging experts in the United States are encouraged by this research. “These are about the best results I’ve seen anywhere with 16-slice technology,” said Elliot K. Fishman, M.D., professor of radiology and oncology at Johns Hopkins Hospital and director of diagnostic imaging and body CT at The Johns Hopkins University School of Medicine in Baltimore. CT Findings: Small eccentric calcification in the proximal left anterior descending artery (a (left)= maximum intensity projection, b (right)= volume rendering) , o therwise no significant coronary atherosclerosis or stenosis lesions. Proper coronary anatomy with right dominant circulation.
64-Slice CT“Sixteen-slice CT really showed that cardiac CT is doable; 64 slice makes it a reality,” Dr. Fishman added, pointing to a study in the August 2005 issue of the European Heart Journal. Sebastian Leschka, M.D., and colleagues in the Department of Medical Radiology at the University Hospital in Zurich, Switzerland, compared 64-slice CT with invasive angiography for assessing significant coronary stenoses in 67 patients (mean age 60.1 years). Overall sensitivity for classifying stenoses with 64-Slice MDCT was 94 percent, specificity was 97 percent, positive-predictive value was 87 percent and negative-predictive value was 99 percent. Dr. Leschka and his colleagues have now performed CT angiography using 64-slice technology on more than 200 patients with suspected coronary artery disease (CAD). “The most surprising finding of our study is that no coronary artery segment had to be excluded from analysis, even with higher heart rates and massive arterial wall calcification,” Dr. Leschka said. “For all of our patients, the exclusion rate for coronary segments is less than one percent, mostly affecting segments with diameters of little more than 1.5 mm and in patients with variations in heart rate during scan acquisition. Although our study investigated the accuracy for stenosis detection in a high prevalence for CAD group, the high negative-predictive value indicates additional potential for 64-slice CT coronary angiography to exclude coronary artery stenosis.” Dr. Fishman said that 64-slice is definitely the way to go. “If you want to do coronary angiography in your group, you have to have a 64-slice scanner,” he said. “Thirty percent of invasive coronary catheterizations are negative. That means that if you could do a CT and exclude disease, a patient may potentially not have to be catheterized. However, catheterization will always have a central role in cardiac treatment because it allows you to do therapeutic intervention. If a patient comes in with chest pain and classic EKG changes, you go right to angiography because you can perform a variety of therapeutic interventions, including inserting a stent.” Jill Jacobs, M.D., associate professor of radiology and chief of cardiac imaging at NYU Medical Center, agrees that the new 64-slice scanners add considerable accuracy to coronary CT. “We’re using a 64-slice scanner on all of our dedicated cardiac CT angiography patients. Most of the time we see patients because they have strong personal risk factors for CAD, because they have atypical chest pain or because they have had prior abnormal stress tests and don’t have clear-cut anginal syndromes. We also scan patients who are referred for evaluation of coronary artery anomalies,” she explained. “If the scans raise suspicion for significant cardiac disease, the patients have angiography.” Patients also tend to like CT angiography compared to traditional, invasive procedures. “Patients are unbelievably happy to have the option of having a test that’s non-invasive, that is fast and allows them to leave the hospital and go right to work,” said Dr. Jacobs. Radiation Risk with MDCT AngiographyWhile radiation exposure is always a concern with CT, Dr. Hoffmann said most patients are aware that the benefits outweigh the risks. He estimates that in non-obese patients, radiation exposure is approximately 1.5 to 2.0 times higher than with invasive angiography. “We are looking at dose limitation in terms of spatial resolution, and what we’ve got is even higher spatial resolution available from the scanner than we’re actually using in a daily routine,” he explained. “We’re restricting ourselves to a Z axis slice thickness of 0.8 to 0.9 mm because we want to use a lower radiation dose.” Advantages of 64-slice CT angiography as compared to invasive angiography
Disadvantages of MDCT
Source: Sebastian Leschka, M.D. Cardiac Radiology Refresher Courses at RSNA 2005
The following include information on Cardiac CT: Essentials of Cardiovascular Imaging A. CT Angiography of the Coronary Arteries: What You Need to Know RC103 RC303 RC432 RC708 |
|
||||
