Heavy ion CT system based on measurement of residual range distribution.

The heavy ion CT system is proposed which is based on measurement of the residual range distribution by a fluoroscopy detector consisting of an intensifying screen and a CCD video camera. To investigate the fundamental performance of the proposed system, the spatial and density resolutions of the CT image were evaluated. The heavy ion beam 12C accelerated up to 400 MeV/u by HIMAC was used in this study. A series of projection images of two types of phantoms (PMMA pipes with several sizes and various kinds of rods with different electron densities) were experimentally taken for five values of range shifter thickness at each projection angle. From these images, the residual range distribution was obtained and used to reconstruct CT images of the relative stopping power which were obtained by the filtered back projection method with the Shepp-Logan filter after noise reduction processing by the median filter. As a result, the spatial resolution was found to be less than 2 mm and the relative density resolution around the density of water was less than 0.07.