We had the chance of clinical studies by new proto-type Digital Subtraction Angiography (DSA) System with the Flat Panel Detector (FPD). That system has two types of detector, FPD and I.I.-CCD camera, and we can compare with image quality in clinical. We measured and discussed about the physical characteristic data of both detectors. Up to physical characteristic evaluation, FPD has good MTF and SNR performance, comparing with I.I.-CCD camera. In clinical evaluation, DSA image of FPD was superior to that of I.I.-CCD camera by visual comparison of medical doctors. Finally we discussed about the feasibility of replacement of detectors. We expect that DSA system will accept FPD in near future.