AbstractThe X‐ray computed tomography system has found widespread use worldwide in recent years. It is still requested that the system should provide further diagnostic information by providing CT images with higher quality. For this purpose, it is necessary to improve the high‐contrast spatial resolution and the low‐contrast density resolution. It is necessary also to establish a reduction method for various kinds of artifacts which are major causes of image deterioration. This paper examines quantitatively the spatial resolution and artifact, among various factors determining the CT image quality, and discusses their relation to the measured data sampling rate using computer simulation. As a result, it is shown that when other reconstruction parameters are kept constant in the fan‐beam CT system, the spatial resolution is determined largely by the projection data sampling interval rather than the angle sampling interval. The mechanism of artifact generation due to an insufficient angle sampling interval is examined. It is shown that to suppress this kind of artifact below a certain value, a certain condition must be satisfied by the measurement area, angle sampling interval, and projection data sampling interval. It is shown also that the artifact due to the projection sampling interval is proportional to the spatial frequency components of the object above the Nyquist frequency of the projecti