Investigation of scintillation light spread in a hemi-ellipsoid monolithic crystal for Cardiac SPECT using Geant4

Hanif R. Soysal, Louisiana State University
Joyoni Dey, Louisiana State University
William P. Donahue, Louisiana State University


Dey group proposed a high sensitivity Cardiac SPECT system using hemi-ellipsoid detectors with pinhole collimation. To investigate detector resolution in more detail, we simulate the scintillator light spread on a monolithic hemi-ellipsoidal CsI crystal. We assume small optical light detectors will be placed on the outer surface of the crystal. Methods: We used Geant4 Monte Carlo simulation to produce the expected distribution of scintillation light on the outer surface of the crystal. This Lookup Table (LUT) is generated for 12 points, 4 at each of the apex, central region, and base of one slice of the crystal. Each set of points was situated at the corners of a "square" of side length 2mm. The light distributions were visualized using a flattened, cut hemi-ellipsoid. To test the performance of the LUT, 5 points inside each of the these "squares" were chosen as test points, and a light distribution was obtained for each. A light distribution match algorithm was developed to localize the test points. Results: Our results showed that, visually, we were able to distinguish the light distributions of points in the central region and base. Furthermore, our algorithm was able to localize the test points to within 1mm in these regions. The localization was slightly worse in the apex with a maximum error of about 1.5mm. However, the high magnification in the apex region will minimize the error in the system resolution for this region. In the future, we will simulate the full LUT and improve the search algorithm.