Although conventional invasive angiography remains the gold standard for detecting coronary artery disease (CAD), it is insensitive for detecting calcified atherosclerotic plaques and small, non-calcified plaques in the vessel wall. As such, it is limited in its capabilities to detect early atherosclerotic disease in patients with low to intermediate risk of CAD, according to a team of researchers from the departments of radiology and cardiology at Thomas Jefferson University Hospital in Philadelphia.
They reported that the utilization of coronary CT angiography (CCTA) has provided diagnostic imaging clinicians with the capability to non-invasively image the coronary artery lumen and the coronary artery wall; as well as allowing the characterization of atherosclerotic plaque as calcified, non-calcified or mixed and determination of the degree of luminal stenosis.
However, evaluating calcified plaque has been a challenge with CCTA, according to the scientists.
“Because of beam-hardening and blooming artifacts, it is difficult to determine the degree of stenosis caused by calcified coronary artery plaques at CCTA,” they wrote in an article about the team’s research in this month’s American Journal of Roentgenology. “Our goal was to determine how accurate CCTA is in evaluating these lesions.”
The retrospective study comprised 31 patients (25 men and 6 women) who had one or more calcified coronary artery plaques at CCTA and who also underwent invasive coronary angiography within three weeks of the CT procedure. The CCTA exams were performed on either a Brilliance 40- or 64-slice system (Philips Healthcare) and post-processing of the image data was conducted on a Brilliance workstation.
“The size of the calcified coronary artery plaques was graded subjectively as small, moderate, or large,” the authors wrote. “Using post-processing techniques such as segmentation and tracking, we attempted to determine whether the calcified lesions were obstructive (≥ 50 percent diameter narrowing) or non-obstructive ( < 50 percent diameter narrowing). Concordance with invasive coronary angiography was then determined.”
The scientists reported that in detecting obstructive lesions caused by 43 large calcified coronary artery plaques, CCTA had a sensitivity of 100 percent, a specificity of 44 percent, a positive predictive value of 56 percent, a negative predictive value of 100 percent and an accuracy of 67 percent.
“Coronary CTA underestimated the degree of stenosis in one small calcified coronary artery plaque but overestimated the degree of stenosis in two small, two moderate and 14 large coronary artery plaques,” they noted.
The overestimation of degree of stenosis in large coronary artery plaques was of concern to the clinical researchers, so they returned to the cases where this occurred and arrived at some general guidelines for CCTA large artery plaque interpretation as a result of their efforts.
Vessel tracking should be used whenever possible to obtain curved MPR (multiplanar reformation) and straightened lumen views to evaluate the vessel in both the long and short axes,” they advised. “The long-axis views should always be rotated to view the lumen from numerous different angles. The interpreter should also review cross sections of the lumen in the short axis and scroll along the vessel course while observing these sections.”
However, based on the overall results of their investigation, they said they believe CCTA can be used to accurately predict the presence of obstructive disease in more than 90 percent of small- and moderate-size calcified coronary artery plaques.