Background : Previous MDCT has good ability to detect, differentiate, and quantify coronary atherosclerotic plaques. However, the reliable differentiation of the composition of individual non calcified plaques is still limited. The aim of this study was to compare the accuracy of 128-MDCT with that of virtual histology intravascular ultrasound (VH-IVUS) for the characterization analysis of non calcified coronary atherosclerotic plaques. Methods and results: 128 MDCT and VH-IVUS were performed in 7 patients (non calcified plaque, n=18), prospectively. The lumen cross-sectional area (CSA) and external elastic membrane (EEM) were measured via software program, automatically. The lumen and EEM CSA of MDCT were compared with VH-IVUS���s value. Among the four components (necrotic core, fatty-fibrous, fibrous and calcified ), fatty-fibrous and necrotic core components were summed up as fatty plaque. Non calcified plaque composition (two type: fatty and fibrous plaque) was analyzed according to VH-IVUS and CT coronary angiography criteria (Hounsfield units [HU]) The correlation coefficients for the measurements of the lumen CSA were 0.840 (p<0.0001) and the EEM CSA were 0.983 (p<0.0001), respectively. The fibrous (n=14,) group was significantly increased computed tomography density compared to the fatty (n=4) group (mean 100짹25 HU vs 43짹12 HU, p< 0.0001) (Figure). Conclusions: 128 MDCT provide an improved information to differentiate fatty from fibrous plaques.