Simulation study of DOI measurement based on light-sharing-window method

The purposes of this study is to investigate the Light-sharing-window (LSW) method for DOI measurement by optic simulation. When a gamma interaction happens in a crystal, most of the scintillating photons will be detected by the photo sensors directly coupled with it. However, some scintillating photons will pass through light-sharing windows, enter the adjacent crystals and be detected by the photo sensors coupled to them. DOI can be derived from the percentages of the photons detected by the photo sensors. Different light-sharing window designs (single window vs. dual windows; rectangular vs. triangle window) were simulated and compared. The effects of surface finish were assessed. The simulation results show: (1) the relations between DOI and energy differences between photo sensors are monotonic. Thus, they can be used to calculate the DOI; (2) When using single window, the DOI vs. Diff. Energy curves have two segments which are not desired for DOI measurement; (3) Crystals with rough surfaces are more desired since the qualities of their DOI vs. Diff. Energy curves are better. (4) The dual-window method has the best DOI vs. Diff. Energy curves in term of linearity. We conclude that dual-window LSW method is a very promising method for accurate DOI measurements. The LSW method didn't catch enough attentions before for two practical reasons. Firstly, it is very challenging to accurately fabricate the designed light-sharing windows on discrete scintillators. Secondly, LSW method requires to read out the light output from every single crystals accurately. In our previous studies, we have developed an anti-reflection coating technology which can “print” any designed light-sharing windows on a crystal. We have also developed an advanced read out electronics (called Pico-PET electronics), which is able to read out energy signals from hundreds of individual photo sensors accurately. Our next step is to apply those two technologies to fabricate dual-window LSW detectors to validate this simulation study.