A Comparison of PET Detector Modules Employing Rectangular and Round Photomultiplier Tubes

We have compared the high resolution BGO detector blocks from the EXACT HR PET system which use two dual-cathode rectangular photomultiplier (PM) tubes with a new block design, the EXACT HR PLUS, which uses four round PM tubes. Despite the lower coupling area between photocathode and scintillator, the HR PLUS block compares favorably with the HR block. The energy resolution averages 20% for the HR PLUS block and 23% for the HR block, with efficiency In this study we compare a conventional high resolution BGO block detector which uses rectangular PM tubes (the EXACT HR block) with the new EXACT HR PLUS block which employs four circular PM tubes. We also look in further detail at the performance of the new block design and propose some changes which will be necessary if the resolution potential of the block design is to be fully realized. variations of 17% in both blocks. Additional measurements were carried out on the HR PLUS block to characterize depth 11* HR AND HR A CoMPAR1soN of interaction effects and cross-talk between elements. Coincidence line spread function measurements had a FWHM of 3.0 mm in the axial direction and 2.9 mm in the transaxial direction. In light of these results, limitations of the BGO block design are discussed and some solutions proposed. A* phYsicaz The principal characteristics of the EXACT HR and Table I: Physical construction of the two detector blocks EXACT HR PLUS blocks are summarized in Table I.