An evaluation of three-dimensional imaging by use of Si/CdTe Compton cameras

Imaging technique of RI tracer for physiological function analysis is substantially useful and popular as positron emission tomography (PET), positron-emitting tracer imaging system (PETIS) or single photon emission computed tomography (SPECT). Recently, Compton camera is thought to become a promising imaging apparatus in several field, for example, medical, biological application and security inspection, because of its simultaneous imaging ability against the wide energy range gamma-rays from a few hundred keV to a few MeV. In this work, three-dimensional imaging ability of our Compton camera system developed for human body imaging has been studied by use of Monte Carlo simulation. The imaging system consists of plural Compton-camera head-modules having the diameter of 20 cm and height of 20 cm. Each of head modules has a 32 mm wide Si double-side strip detector (DSD) and four CdTe-DSDs stacked at intervals of 4 mm. The head modules are settled on XYZ-stages and can be moved by XYZ-stage around the subject imaged during data acquisition. The simulation study was performed by use of a Geant4-based Compton-camera simulator developed by JAXA/ISAS. Three sphere-shaped gamma-sources, having diameters of 10, 13 and 17 mm, of the NEMA NU2-2007 standard body-phantom was assumed to be placed around the center of simulation space. The RI density is uniform and the energy of gamma ray 511 keV. Six camera-placements around the back and a side of the body phantom. Three-dimensional image was reconstructed by use of the List-Mode Expectation-Maximizing Maximum-Likelihood method. The positions of each sphere were clearly identified at the correct positions. The RI distributions of the imaging result are not asymmetrical between X- and Z-direction, which is found to be owing to the asymmetrical placement of the detector stacks. The RI intensities deduced from the image tend to reflect the real RI intensities although improvement is still required.