In this study, we proposed a new method of measuring temporal resolution using an impulse signal in the time domain in computed tomography (CT). We employed a metal ball with a diameter of 11 mm as the source of the impulse signal, which was shot to a slice plane at a very fast speed during scanning, along the perpendicular direction to the plane. A 4-slice multi detector-row CT (MDCT) system was employed to evaluate the new method, and images for region of interest (ROI) measurement were reconstructed with a z-increment corresponding to a very short time (< or = 0.03 sec). Temporal sensitivity profiles (TSPs) for various helical beam-pitches were obtained by plotting averaged CT values within the ROIs against the temporal axis. The accuracy of the method was examined by comparing the measured TSPs with theoretical TSPs corresponding to respective helical beam-pitches. As a result, the theoretical TSPs and measured TSPs demonstrated high coincidence in all beam-pitches. Since the TSPs indicated the profiles with sharp shapes faithful to the theoretical TSPs, it was proved that the new method had sufficient inherent temporal resolution. It was indicated that the new method we proposed would be an effective method for evaluating temporal resolution in CT.