Optimization of a table-top Compton camera system by Monte Carlo simulation

Abstract

The Compton camera, a gamma-ray imaging device in which the physical laws of Compton scattering are employed to trace the gamma rays back to the emission point, is a promising candidate in nuclear medicine and molecular imaging. The Compton camera is characterized by 3-D gamma-ray imaging capability from a fixed position, no limitation to the energy of gamma rays (100 keV - 10 MeV), multiple radioisotope tracing capability, and high imaging sensitivity. The Compton camera, however, suffers from relatively low image resolution especially for a small-size (e.g., table-top) Compton camera. The objective of this study is to optimize a table-top Compton camera to maximize its performance for 18F which is one of the most popular radioisotopes in nuclear medicine these days. This study mainly investigates the effect of the geometrical configuration of the detectors on the image quality of the Compton camera. The variation of the image quality was also studied changing the segment size of the absorber. Our table-top Compton camera consists of two position-sensitive detectors, i.e., scatterer and absorber. The scatterer is a double-sided silicon strip detector (DSSD, 5 cm x 5 cm x 0.15 cm, 16 x 16 strips) and the absorber is a 25-segmented germanium detector (25-SEGD, 5 cm x 5 cm x 2 cm, 5 x 5 segments). Important detector parameters were considered in the detector simulation. The deposited energy in a detector was Gaussian-broadened to simulate the energy resolution of the detector. The discrimination level was simulated at 15 keV and 40 keV for the scatterer and absorber, respectively. Doppler energy broadening and detector segmentation were modeled by the Penelope physics model and the `G4PVReplica` class in the GEANT4 simulation toolkit. Our result shows that the image quality generally improves as we decrease the distance between the source and scatterer and as we increase the distance between the scatterer and absorber. The Compton camera provides the best image quality when the scatterer and absorber are parallel. It was also found that we can significantly improve the image resolution of the Compton camera, hardly affecting imaging sensitivity, by reducing the segment size of the absorber. If the segment size (currently, 1 cm x 1 cm x 2 cm) is reduced to 0.5 cm x 0.5 cm x 0.5 cm, the FWHM value of the point spread function (PSF) for a 18F source is reduced by about half.