In-stent restenosis is a major reason of coronary heart disease recurrence .Even in drug eluting stent(DES), Restenosis rate could be up to 10% in diabetes and complex lesions though it was about 3-5% in general. It is particularly important that in-stent restenosis after implantation was early diagnosed and detected. The evaluation of OCT imaging is more accurate for narrow area calculation, more clear for narrow organization structure and more specific for detecting tissue types.It is currently the best way for restenosis histologic diagnosis.But it has many weakness such as the higher cost,an invasive test, expensive instrument, relatively complicated to operate,and etc.In this study, OCT image was regard as the "gold standard" of stent restenosis.

The improvement of spatial resolution of Gemstone CT can effectively improve the imaging quality and the measurement's accuracy of coronary artery stents.The diagnostic value of in-stent restenosis of Gemstone CT is higher than of the 320-detector row spiral CT. To a certain extent, the gemstone CT can replace OCT for examining the in-stent restenosis.

This study will examine the degree of in-stent restenosis by the gemstone CT and the 320-detector row spiral CT and compare the two ways on the basis of the result of OCT.

Inclusion Criteria:

1. Age 20-80， All genders
2. Unlimited time of implantation of coronary artery stents
3. Myocardial ischemia symptoms such as Chest tightness and/or chest pain in patients after stent implantation
4. No clinical symptoms, but myocardial ischemia suggested by other noninvasive tests
5. Routine re-testing 9-12 months after stent implantation.

Exclusion Criteria:

1. Renal insufficiency (serum creatinine > 120 umol/L)
2. Allergy of contrast
3. Severe heart failure
4. Uncontrollable heart rate or contraindication of taking metoprolol
5. Unstable condition
6. the ventricular rate beyond 70 beats / min and irregular rhythm after adjusting.