We examined the effects of a reduced exposure dose on the quality of images from an angiography device augmented with a noise reduction algorithm. Before its clinical application, we compared the diameter of the discrimination limit of the hole with that in the conventional method by a visual evaluation with a contrast-detail (C-D) phantom imaged using the target dose. Based on the results, a reducible dose was determined and applied clinically. The sample population consisted of patients being followed up after percutaneous coronary intervention (PCI) for coronary artery disease; we evaluated the effects of the exposure reduction on image quality. A significant dose reduction was observed by the noise-reduction method compared to the conventional method; the radiation dose to the flat panel detector (FPD) could be reduced to 70 nGy per frame. Clinically, a dose reduction of approx. 40% was obtained while maintaining image quality almost equal to that of the conventional method.