A discrete scintillation camera module using silicon photodiode readout of CsI(TI) crystals for breast cancer imaging

Abstract

The authors characterize a 3/spl times/4 element imaging array consisting of 3/spl times/3/spl times/5 mm/sup 3/ CsI(TI) scintillator crystals individually read out by 3/spl times/3 mm/sup 2/ PIN silicon photodiodes. The array is a prototype for larger modules (16/spl times/16 element) for use in single photon breast cancer imaging. The photodiode output signals are amplified with a 16 channel custom IC (<3 mm on a side), after which a Winner Take All (WTA) custom IC (<3 mm on a side) identifies the crystal of interaction based on relative signal amplitudes. The compact nature of these readout electronics will simplify the construction of larger imaging arrays. The photodiodes were developed for low leakage current (/spl sim/50 pA) and yield a total electronic noise of 390 e- full width at half maximum (fwhm) at a shaping time of 8 /spl mu/s, with signal levels of 6600 e- for the 140 keV emissions of /sup 99m/Tc. Array pixels demonstrate an average room temperature energy resolution of 10.7/spl plusmn/0.6% fwhm for these 140 keV gamma rays. The authors observe an intrinsic spatial resolution of 3.3 mm fwhm for a 2.5 mm diameter /sup 57/Co beam on the face of the crystal array, and a system resolution of 5.9 mm fwhm for a 2 mm diameter uncollimated /sup 99m/Tc source viewed through a high resolution hexagonal hole collimator (1.5 mm hole diameter, 32 mm length, 4300 events/mCi/sec) at an imaging distance of 5 cm.