Study of Fast Acquisition Technique for Heavy Ion CT System Based on the Measurement of Residual Range Distribution

We proposed a new technique for the fast acquisition heavy ion CT (HICT) system based on the measurement of residual range distribution using an intensifying screen and charge coupled device cam-era. The previously used fast acquisition HICT system had poor electron density resolution. In the new technique, the range shifter thickness is varied over the required dynamic range in the spill of the heavy ion beam at each projection angle and the residual range distribution is determined by a series of acquisi-tion data. We examined the image quality using the contrast noise ratio and the noise power spectrum, and estimated the electron density resolution, using a low-contrast phantom for measurement of electron density resolution. The image quality of the new technique was superior to that of the previous fast ac-quisition HICT system. Furthermore, the relative electron density resolution was 0.011, which represent-ed an improvement of about 12-fold. Therefore we showed that the new technique was potentially useful in clinical use of HICT, including treatment and quality assurance of heavy ion therapy.