Background: Despite of recent advancement of technical aspects, the procedural success of chronic total occlusion (CTO) is still limited. Furthermore, the pathological nature of CTO is not well recognized. Methods: We prospectively enrolled 91 patients with CTO with TIMI 0 flow who undergone 64 multi-detector computed tomography (MDCT) before elective percutaneous coronary intervention (PCI). MDCT data was processed by dedicated software; Vitrea, Vital Images, and Sureplaque, Toshiba. We performed whole 3D volmetric Hounsfield Unit (HU) analysis for the coronary plaque within CTO segment. To compare proximal, mid, and distal segments, subsegment analysis per 5 mm axial length was also performed. Histological characteristics of plaque was estimated from HU values; lipid plaque, -100 ~ 49 HU; fibrous plaque, 50 ~ 249; calcification, > 250 HU. Results: Data obtained from 227 segments from 42 patients (age=61.9+-10.1, male sex=83%) are shown in this interim analysis. There was no difference of CTO segment length or vessel diameter between PCI success group (N=33) versus failed group (N=9) (p=NS). However, the mean volumetric HU was lower in success group (136.0 +- 70.1 vs 205.8 +- 120.5, p=0.03). The HU of proximal or distal 5 mm segment was not no significantly different between two groups, and the difference of HU was mainly derived from CTO mid segment (126.1 +- 74.1 +- 206.9 +- 138.8, p=0.02). Furthermore, subsegmental analysis revealed that mean volume percent of fibrous plaque is marginally lower in success group compared to failed group (49.9 +- 11.4 vs 37.3 +- 12.7%, p=0.067). Both mean volume percent of calcific plaque and mean volume of calcification were significantly lower in success group (26.9 +- 19.7 vs 45.0 +- 24.7%, p=0.03; 90.1 +- 127.2 vs 207.6 +- 198.8, p=0.04). Conclusion: Our study suggests that CTO PCI procedural success might be predicted from the preprocedural MDCT. Higher calcification volume in mid-CTO segment seems to be affect CTO procedural success. Further detailed full data would be shown at the meeting.