Development of a positron-imaging detector with background rejection capability

Abstract

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 2mmtimes2mmtimes3mm and that of BGO is 2mmtimes2mmtimes15mm. These scintillators are optically coupled to each other and combined in 8times8 array. The array is optically coupled to the 1-inch square 8times8 multi-channel PSPMT through an optical fibers 2 mm in diameter 3 mm 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 20 cm diameter, 20 cm height cylinder phantom contained 3.7MBq of F-18. Results indicated that developed positron-imaging detector will be useful for FDG-guided surgery