Fundamental study on heavy ion CT using pencil beam scanning method

The feasibility of heavy ion computed tomography was investigated. A cylindrical polyethylene sample of 50 mm in diameter was used to establish the pencil beam scanning method and estimate the performance of the system. The sample was irradiated with carbon ions of 290 MeV/u and 400 MeV/u, and helium ions of 150 MeV/u. The residual beam energy was measured by a BGO scintillator in coincidence with two small plastic scintillators placed in front of and behind the sample to restrict the beam path and improve the spatial resolution in the CT reconstruction. The projection data were obtained by moving the sample only in the transverse direction because of its symmetrical structure. A Lucite sample with many holes of different diameters was used to demonstrate the spatial resolution of this CT system. From the reconstructed images the spatial resolution was estimated to be less than 2 mm under the conditions in this work. The electron density ratios of ethyl alcohol, water, and Lucite to polyethylene were obtained, which are in good agreement with the calculated values. (author)