Characteristics of 40,000 quadrant-sharing BGO detectors made by the slab-sandwich-slice technique

We produced 40,000 high-resolution position-sensitive BGO detectors with a new method (slab-sandwich-slice or SSS). The detectors will be used in a high-resolution human PET system. The detectors were 2.68×2.68 mm (18 mm deep) encapsulated in about 800 detector blocks. There were three types of blocks/arrays made, 7×7, 7×8, 8×8. We studied the optical and physical characteristics of the production to evaluate the SSS production method. We also analyzed the data relative to production experience and time. We found that for the 7×7 symmetric blocks: the average block-composite energy resolution was 35%; the average individual-crystal energy resolution was 23%. Mean intra-block light-collection variation of individual crystals was 23% FWHM. The average number of clearly-decoded crystals was 47 out of a possible 49 for the 7×7 block in the early production, which was improved to 49 in late production. For the 7×8 asymmetric blocks, the average blocks-composite energy resolution was 32%. Mean intra-block light-collection variation was 23% FHWM. The average number of clearly decoded crystals was 51 for the early production improving to 55 for the late production (out of a possible 56). For the 8×8 asymmetric blocks, the average blocks-composite energy resolution was 29%. Mean intra-block light-collection variation was 18% FHWM. The average number of clearly decoded crystals was 59 in early production improving to 62 for the late production (out of 64). We have also studied other production quality issues and found production variability and imperfection in the areas of size, shape and color. We observed a (a) "darkness effect" that for a block with poor crystal-position decoding map there was generally darker regions within the blocks and several size and shape errors were also found, as (b) "X-Y thickness-difference effect", which is the difference between the axial and transaxial block dimensions, (c) "pyramid-effect" with the PMT-end of the block (top) and the patient-end of the block (bottom) had different sizes, (d) besides the pyramid-effect, the 4 sidewalls might not orthogonal due to a systematic lateral shift between slices, or "laminar-shift dislocation effect" (e) the- "slice-serration effect" which is caused by the variation in slice-widths between different sandwich types, (f) "paint-edge effect", where there was paint material build-up at the edge of the painting mask.