Standardized CT Value: A Promising Diagnostic Parameter to Differentiate Lipid and Fibrous Coronary Plaques

Abstract Purpose To evaluate the accuracy of the standardized CT value in differentiating between lipid-rich and fibrous coronary plaques and to examine the stability of its cutoff preliminarily. Methods Patients who underwent both coronary computed tomographic angiography (CCTA) and intravascular ultrasound (IVUS) were included. The CT values of the plaque assessed from all, four, and two short-axis slices were acquired. We defined the standardized CT value as the Hounsfield unit (HU) ratio of the plaque to the ascending aorta. The nature of the plaques was determined by IVUS. The receiver operating characteristic curve was applied to determine the diagnostic performance of the standardized and traditional CT values. Results A total of 60 patients with 74 plaques were included. 35 lipid-rich plaques and 39 fibrous plaques were diagnosed by IVUS. The CT value of the aorta showed a strong correlation with plaques (r = 0.420, P < 0.01). The threshold CT values differentiating the plaque types on all-slice, four-slice, and two-slice were 55 HU, 48 HU, and 52 HU, and the threshold of the standardized CT value was consistently 0.149. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the four-slice CT values differentiating lipid and fibrous plaques were 69%, 87%, 83%, 76% and the corresponding standardized CT values were 91%, 82%, 82% and 91%. Conclusions Compared with traditional CT values, standardized CT values can significantly improve the sensitivity and NPV for differentiating between lipid-rich and fibrous coronary plaques while achieving moderate to high specificity and PPV. Furthermore, the cutoff is stable.