Calcification has been well known to exist in atherosclerotic lesions from 19th century. The mechanisms of calcification are still unknown. Coronary stenoses can be treated by percutaneous coronary intervention using drug eluting stents at present. To the contrary, calcified coronary lesions are still difficult to be treated due to stent unexpansion despite of high pressure dilatation. Recent development of multi-slice CT (MDCT) has made it possible to diagnose coronary stenoses non-invasively. Coronary calcification is easily detected using MDCT, however, quantification of stenosis is difficult in calcified lesions.