Gamma and beta intra-operative imaging probes

Abstract

Small area (∼1.5 cm 2) scintillation cameras for imaging gammas and betas using inter-changeable detector front ends were built and characterized. Components common to both emission imaging cameras include: (1) fiber optic bundles 2–3 m long, comprised of multi-clad fibers which connect the scintillation detector to (2) an MC-PMT; (3) parallel MC-PMT outputs feed a resistive positioning network and i- V converter/line driver network which produce balanced + X, − X, + Y, and − Y outputs; and (4) four ADCs and a Macintosh PC for system control and image display. The beta and gamma devices used distinct scintillation detectors which were characterized by both simulation and measurement. The beta camera utilized a 0.5 mm by 1.25 cm φ CaF 2(Eu) scintillation crystal coupled, through a diffusing light guide, to 19 2-mm φ optical fibers. These front-end fibers are in turn coupled by a more flexible fiber bundle to the MC-PMT. CaF 2(Eu) has high light output, high beta sensitivity, and low gamma sensitivity. Image signals are histogrammed and displayed after Anger logic computations are performed on digitized signals. The beta camera has <0.6 mm FWHM intrinsic resolution. The gamma camera concept was tested with matrices of discrete 1 × 1 mm 2 and 2 × 2 mm 2 CsI(Tl) and NaI(Tl) crystals of various lengths, and 3 mm thick continuous crystals. Configurations using 4 × 4 element matrices with one-to-one coupling between crystals and fiber channels, and light diffusers between each crystal matrix and fibers were evaluated. The continuous crystals were coupled directly to the fiber optics with signal and data processing analogous to the beta camera. Coupling of discrete crystals to fiber optics by both methods gave essentially perfect identification of the crystal of interaction, allowing spatial resolution to be defined by the crystal size and collimator. The continuous crystal gamma camera gave intrinsic resolution of ∼1.4 mm FWHM.