Development of a positron-imaging detector with background rejection capability

We developed and tested a positron-imaging detector with background rejection capability for FDG guided surgery. The detector consists of an array of phoswich scintillators, multi-channel position-sensitive photo-multiplier tube (PSPMT) and a electronics circuit. The scintillators and the PSPMT are encased in a tungsten shield and collimators are mounted on the top of the detector. Positrons are detected by the plastic scintillators while annihilation photons are detected by the BGOs. By using a pulse shape analysis, we can distinguish the true events (positrons) from background gamma events. The size of a plastic scintillator is 2mm × 2mm × 3mm and that of BGO is 2mm × 2mm × 15mm. These scintillators are optically coupled to each other and combined in 8×8 array. The array is optically coupled to the 1-inch square 8×8 multi-channel PSPMT through an optical fibers 2mm in diameter 3mm in thickness. The position determination of the positrons is performed by 64 channel threshold circuits while the pulse shape analysis is applied for the summing signal. The spatial resolution was measured by positioning an F-18 point source on the one pixel of the detector. The spillover to the neighbor pixel was less than 20%. The background count rate was less than 2cps for a 20cm diameter, 20cm height cylinder phantom contained 3.7MBq of F-18. Results indicated that developed positron-imaging detector will be useful for FDG-guided surgery.