High resolution CsI(Tl)/Si-PIN detector development for breast imaging

High resolution multi-element (8×8) imaging arrays with collimators, size matched to discrete CsI(TI) scintillator arrays and Si-PIN photodetector arrays (PDA´s) were developed as prototypes for larger arrays for breast imaging. Photodetector pixels were each 1.5×1.5 mm² with 0.25 mm gaps. A 16-element quadrant of the detector was evaluated with a segmented CsI(TI) scintillator array (1.5×1.5×6 mm³ segments with 0.25 mm septa) coupled to the silicon array. The scintillator thickness of 6 mm corresponds to >85% total gamma efficiency at 140 keV. Pixel energy resolution of <8% FWHM was obtained for Tc-99m (140 keV). Electronic noise was 41 e^- RMS corresponding to a 3% FWHM contribution to the 140 keV photopeak. Detection efficiency uniformity (±σ%) measured with a Tc-99m flood source was 4.3% for a ~10% energy photopeak window. Spatial resolution was 1.53 mm FWHM and pitch was 1.75 mm as measured from the Co-57 (122 keV) line spread function. Signal to background was 34 and contrast ([max-min]/[max+min]) was 0.94. The energy resolution and spatial characteristics of the new imaging detector exceed those of other scintillator based imaging detectors. A camera based on this technology will allow: (1) Improved Compton scatter rejection; (2) Detector positioning in close proximity to the breast to increase signal to noise; (3) Improved spatial resolution; and (4) Improved efficiency compared to high resolution collimated gamma cameras for the anticipated compressed breast geometries