A Depth-Encoding PET Detector Inserting Glass Plate Between Crystal Layers

This study introduces a depth-encoding PET detector inserting a glass plate between the pixilated scintillation crystal layers. The principle of the proposed design was that the relative amount of light received by each photosensor will be altered by using the glass plate. This change in the light distribution can generate a pattern diagram of the 2D flood histogram that identifies depth position as well as X-Y position of γ-ray interaction. A Monte Carlo simulation was conducted for the assessment of the DOI-PET detector of 4 ×4 array photosensor coupled with 2-layers of LSO arrays which consist of 4 ×4 arrays of 3 ×3 ×10 mm³ discrete crystals. The traced light distribution for each event was converted by the modified resistive charge division networks into the 2D flood histogram. Optical glass plates with 11 different thicknesses that range from 0 to 10 mm with a 1 mm step were modeled. This was done, to estimate the thickness which allows the extraction of the depth information from the 2D flood histogram. An experimental study was performed to acquire the flood histograms of the DOI-PET detectors with 3 and 5 mm thick glass plate. The effect of glass plate on light loss and count rate loss were assessed for two detector configurations with and without glass plate. The simulation results showed that the flood histogram without overlapping of each crystal position can be generated for the detectors by inserting the glass plates with thickness of 3 ~ 10 mm. They were also demonstrated in the acquired representative flood histograms which were obtained by the experimental study. The light and count rate losses measured from DOI-PET detector with 3 mm thick glass plate was ~ 5% and ~ 2%, respectively. This study demonstrated that the proposed DOI-PET detector can extract the 3D γ-ray interaction position without considerable performance degradations of PET detector from the 2D flood histogram.