Semester of Graduation

Summer 2019


Master of Science (MS)


Department of Physics and Astronomy

Document Type



A high sensitivity Cardiac SPECT system using hemi-ellipsoid crystals with pinhole collimation was previously proposed by Dey et al. To investigate detector resolution for this design, the scintillation light spread on a monolithic hemi-ellipsoidal CsI crystal was simulated using Geant4 Monte Carlo. The expected distribution of scintillation light on the outer surface of the crystal from photoelectric absorption events was obtained from the simulations for selected points inside the crystal. Two sets of simulations were performed. For the first set, a look-up table (LUT) of 12 points was created and each point mapped to its expected light distribution—four points at each of the apex, the central region, and the base along one plane of the crystal, with each set of points situated at the corners of a “square” of side length 2mm. Algorithms were developed to localize test events by comparing the light distributions of the LUT points to that of the 5 test points in each region. The test points were also simulated as photoelectric absorption events. The results showed a visual differentiation between the light distributions of points in the central region and base, with the algorithms able to localize the test points in these regions to within a maximum of 1mm of where the events actually occurred. The apex exhibited worse performance with a maximum localization error of 1.5mm. In the second set of simulations, 1000 gamma ray interactions (“events”) were simulated in different regions of the crystal (apex, central region, base); the light distribution from each event was compared to a new set of LUT points that were chosen to encompass the line of sight of the gamma rays. More than 99.5% of the gamma rays had localization errors of less than 3mm. In future, an LUT that covers the entire hemi-ellipsoid surface needs to be generated, which will allow a localization assessment over the entire detector system.



Committee Chair

Dey, Joyoni