GAMMA-INTRAOPERATIVE AND BETA-INTRAOPERATIVE IMAGING PROBES

Small area (similar to 1.5 cm(2)) scintillation cameras for imaging ga mmas and betas using inter-changeable detector front ends were built a nd characterized. Components common to both emission imaging cameras i nclude: (1) fiber optic bundles 2-3m long, comprised of multi-clad fib ers which connect the scintillation detector to (2) an MC-PMT; (3) par allel MC-PMT outputs feed a resistive positioning network and i-V conv erter/line driver network which produce balanced X+, X-, Y+, and Y- ou tputs; and (4) four ADCs and a Macintosh PC for system control and ima ge display. The beta and gamma devices used distinct scintillation det ectors which were characterized by both simulation and measurement. Th e beta camera utilized a 0.5 mm by 1.25 cm phi CaF2(Eu) scintillation crystal coupled, through a diffusing light guide, to 19 2-mm phi optic al fibers. These front-end fibers are in turn coupled by a more flexib le fiber bundle to the MC-PMT. CaF2(Eu) has high light output, high be ta sensitivity, and low gamma sensitivity. Image signals are histogram med and displayed after Anger logic computations are performed on digi tized signals. The beta camera has <0.6mm FWHM intrinsic resolution. T he gamma camera concept was tested with matrices of discrete 1 x 1 mm( 2) and 2 x 2 mm(2) CsI(Tl) and NaI(TI) crystals of various lengths, an d 3 mm thick continuous crystals. Configurations using 4 x 4 element m atrices with one-to-one coupling between crystals and fiber channels, and light diffusers between each crystal matrix and fibers were evalua ted. The continuous crystals were coupled directly to the fiber optics with signal and data processing analogous to the beta camera. Couplin g of discrete crystals to fiber optics by both methods gave essentiall y perfect identification of the crystal of interaction, allowing spati al resolution to be defined by the crystal size and collimator. The co ntinuous crystal gamma camera gave intrinsic resolution of similar to 1.4mm FWHM.