DESIGN CONSIDERATIONS AND INITIAL PERFORMANCE OF A 1.2 CM(2) BETA IMAGING INTRAOPERATIVE PROBE

A navel small area beta (beta(+/-)) detector is under development for nuclear emission imaging of surgically exposed, radiolabeled tumor bed s. The imaging device front-end consists of a 0.5 mm thick by 1.25 cm diameter CaF2(Eu) scintillator disk coupled to a rigid bundle of 2 mm diameter double clad optical fibers through a polystyrene light diffus er. The detector area (1.2 cm(2)) was determined by the requirement of introducing the probe into small cavities, e.g. during neuro-surgical lesion resection, but large enough to produce images of clinical sign ificance. Flexible back-end optical fibers (1.9 m long) were coupled t o the front-end components allowing similar to 75 photoelectrons to be detected for mean beta energies of 250 keV, indicating that sufficien t signal can be obtained with clinical beta emitters (e.g. F-18, I-131 ). The long flexible fibers guide the scintillation light to a Philips XP1700 series, fiber optic faceplate, Multi-Channel PMT. The parallel MC-PMT outputs are fed into a variable gain, charge divider network a nd an i-V pre-amplifier/line driver network, whose resulting four outp uts are digitized and histogrammed with standard Anger positioning log ic. The various components in the imaging chain were evaluated and opt imized by both simulations and measurements. Line spread functions mea sured in the 10.8 mm FOV were 0.50 mm +/- 0.038 mm and 0.55 mm +/- 0.0 65 mm FWHM in X and Y, respectively. A 20% variation in pulse height a nd minimal variation in spatial resolution was observed. The different ial image uniformity was measured to be +/-15.6% with similar to 150 c ts/pixel. Preliminary images show excellent reproduction of phantom ac tivity distributions.