Cardiovascular CT Poised to Take Imaging Center Stage
"What we’re finding is that CT perfusion or stress testing with CT can be as accurate, if not more accurate, than the conventional stress testing methods that we’ve used until this day," Dr. Min said.
"CT perfusion or stress testing with CT can be as accurate, if not more accurate, than the conventional stress testing method," said Dr. James K. Min.
In the Combined Non-invasive Coronary Angiography and Myocardial Perfusion Imaging Using 320 Detector Computed Tomography (Core320) trial, researchers compared the diagnostic accuracy of CTA plus CT-based myocardial perfusion against ICA plus SPECT myocardial perfusion imaging in 381 patients with suspected or diagnosed coronary artery disease with a clinical indication for coronary angiography.
"When we add perfusion [to CTA alone] we gain power to diagnose flow-limiting stenosis," lead author Dr. Joao A.C. Lima said at the ESC meeting. Together, "they have the same power as invasive angiography and SPECT MPI in defining who are the patients who end up going through revascularization," he said.
The area under the receiver operating characteristic curve (ROC) – an effective method of evaluating the performance of diagnostic tests – was 0.79 for CTA-CTP and 0.81 for ICA-SPECT.
"At this point, the [CT perfusion] technology could be used precisely to find the patients who have flow-limiting disease and, therefore, are going to need revascularization," said Dr. Lima, director of cardiovascular imaging at the Johns Hopkins University in Baltimore.
Dual-Energy CT
Dual-energy CT (also known as dual-source CT) "interleaves sets of high- and low-keV images. The energy alternates between two energies (80 keV to 140 keV) every 0.5 msec," said Dr. James P. Earls. The result is two competing sets that can be used simultaneously. The importance of this dual-energy approach is that with higher energies and a software algorithm, calcium blooming is decreased. This means a more accurate size of calcium in lesions and lumen size.
Back-end software produces a range of monochromatic images (images at a single energy). "In terms of calcium reduction, the monochromatic images are probably more important," said Dr. Earls, codirector of the cardiac CT program at Inova Heart and Vascular Institute in Falls Church, Va.
Monochromatic images range from 40 keV to 140 keV. "At 40 keV you’re very close to the k-edge of iodine, so you have significant attenuation of anything that is enhancing ... at about 75 keV you have something that looks akin to a 120-keV image that we would normally get." As the energy increases, "you get away from what we would do on a routine clinical basis."
