AJR: Imaging vessel wall identifies vulnerable plaque in CTA

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While calcium scoring adds prognostic value to standard risk factors and serum markers, imaging the vessel wall directly may be helpful to identify non-calcified plaque and guide therapy, according to a study published in the July issue of the American Journal of Roentgenology.

“Identification of small-volume soft plaque is the crux of coronary artery disease management. Investigators have repeatedly shown that acute coronary syndromes most frequently result from the rupture of these small plaques, which are generally not flow-limiting, do not cause stenosis, and may not be calcified,” wrote the authors of a study conducted by clinicians at Radiology Imaging Associates in Englewood, Colo., and Nighthawk Radiology Services in Coeur d’Alene, Idaho.

Interpreting physicians at the practices reviewed 729 consecutive CT calcium scoring examinations conducted immediately prior to CT angiography (CTA), which were performed over a two-year period. The mean age of the patient cohort was 56, and 32 percent of the study group were female.

All patients had scans conducted on 64-slice CT systems, (either a Siemens Medical Solutions’ Somatom Sensation 64 CT or the LightSpeed VCT from GE Healthcare.) The clinician strived to expose the study group to as little radiation as was reasonably achievable.

“In our patient population, using single-source 64-multidetector CT scanners, dose modulation and retrospective gating, the median patient dose was 12 mSv,” the authors reported. “This dose includes the topogram, unenhanced CT for calcium scoring, timing bolus and coronary CTA.”

According to the authors, 28 percent of the patients were referred for atypical symptoms; 14 percent presented with abnormal or indeterminate findings on a nuclear stress test with an additional 5 percent demonstrating abnormal or indeterminate findings on an exercise stress test; and the remaining 53 percent were asymptomatic patients with risk factors referred for coronary artery disease assessment. For each study, the calcium score, presence and type of plaque and study quality were recorded as was follow-up data, including invasive angiography, intravascular sonography and stress test results.

Images were interpreted by at least one of seven radiologists on a 3D workstation, (either the Vitrea from Vital Images or the CardIQ Pro by GE Healthcare), using the axial and multiplanar reformatted data from the scans. The authors noted that although most cases were double-read to promote consistency of interpretations, interobserver variability was not evaluated.

In the patient cohort, the clinicians reported that 404 of the patients with an abnormal calcium score had detectable plaque on coronary CTA. The remaining 325 patients (45 percent of the total) had normal calcium scores. Of this group, 167 presented soft plaque on their findings.

“Plaque was seen in 66 of 148 women (45 percent) with a normal calcium score, which is significantly less than the 101 of 177 men (57 percent) with a normal calcium score,” they noted.

The interpreting radiologists determined that in the patient group with soft plaque visualized by CTA, mild disease without hemodynamically significant stenosis was present in 88 percent  of the cases. In the remaining patients, 7.2 percent had moderate stenosis and 3 percent had severe stenosis.

“We found a high prevalence of non-calcified plaque in patients with a calcium score of zero, with fewer than half of the patients in our study group being disease-free,” the authors wrote. “Considering all 729 calcium score studies, this yields a false-negative rate of 29 percent for any plaque in our patient population and underscores the limitations of calcium scoring.”

Although calcium scoring can help risk stratify patients for coronary artery disease, the clinicians do not believe patients or their primary-care physicians should rely on a negative calcium score as a disease-free diagnosis.

“Coronary CTA provides significantly more diagnostic information than the calcium score,” the authors stated. “Essentially, coronary CTA adds certainty to the evaluation of the coronary arteries, whereas the calcium score generates probabilities.”

Given the high false-negative rate for calcium scoring in the study, the interpreting radiologists believe that a CTA exam will provide greater diagnostic information for the referring physician and their patient.

“Although the calcium score adds prognostic value to standard risk factors and serum markers,