Whole-Heart Coronary Magnetic Resonance Angiography Advance Shows Promise
BEIJING, CHINA, April 21, 2009 — A study comparing the diagnostic value of contrast-enhanced whole-heart coronary magnetic resonance angiography (MRA) with conventional X-ray angiography has shown that MRA can accurately detect coronary artery stenosis with high sensitivity and moderate specificity.
The findings, published online on April 15, 2009, in the Journal of the American College of Cardiology by Dr Qi Yang of Capital Medical University in Beijing, China, et al are from a single center using the 3T MRA, which has a higher signal-to-noise ratio (SNR) than existing 1.5T MRA machines. As the researchers pointed out, whole-heart coronary MRA using 1.5T has demonstrated promising results, particularly for high negative predictive value.
"However, long scan time and relatively low spatial resolution have prevented its wide acceptance as a routine test for coronary artery stenosis detection," wrote Yang et al. "The 3T systems have the potential to improve SNR by a factor of two as compared with 1.5T with the same imaging sequence."
In this study of coronary MRA at 3T, investigators included 96 patients with suspected coronary artery disease scheduled for conventional angiography, and of these, 62 patients underwent successful imaging with MRA. Among the excluded patients, 9 had previous stents or bypass surgery, whereas others were excluded because of claustrophobia, unstable angina, atrial fibrillation, or impaired renal function.
Overall, on a per-patient basis, the sensitivity of coronary MRA was 94.1%, with significant coronary artery disease, defined as stenosis greater than 50%, detected in 32 of 34 patients. Coronary disease was correctly ruled out in 23 of 28 patients, for a specificity of 82.1%. The imaging test also correctly identified the presence or absence of stenosis in 55 of 62 patients, which corresponded to 88.7% accuracy.
The acquisition time for the images was 9 minutes. Reduced imaging time is important for whole-heart coronary MRA, "as long scan times tend to cause lower image quality from increased motion artifacts and reduced coronary SNR," noted the researchers. The 3T MRA also allowed researchers to improve depictions of distal coronary artery segments and to assess segments with diameters greater than 1.5 mm, compared with 2 mm in previous 1.5T studies.
"A major challenge for coronary MRA remains respiration-induced motion artifacts," the researchers noted. "Patient training and practice before data acquisition for maintaining regular breathing should be useful to improve the gating efficiency and image quality of coronary MRA."
Commenting on the results of the study for Heartwire, Dr Raymond Kim, from Duke University in Durham, North Carolina, said 3T imaging with MR allows clinicians better image clarity, but "what this paper actually tells us is that we're not quite ready for prime time with 1.5T, because at 3T this is becoming more and more usable. The vast majority of MR sites don't have 3T available, at least for cardiac imaging."
Like the researchers, Kim noted that 3T does have some downsides regarding motion artifacts, although the promise is that these issues can be solved in the future. "As of right now, the study is intriguing, and it suggests that the way to go to improve coronary imaging is to go to higher fields and then to work on some of the limitations related to imaging quality," he told Heartwire.
Kim noted that the sensitivity, specificity, and accuracy reported by Yang et al is in line with existing coronary MRA data, but caution should be used when interpreting the findings, because 27 patients did not meet the criteria for MRA. Also, 7 patients were not scanned successfully. "Like all imaging studies, you have to be very careful where people drop off on the wayside before you get these final numbers," said Kim. "That's not just an issue with this study, but with all imaging studies."
Source: Heartwire
