Investigation of microcolumnar scintillators on an optical fiber coupled compact imaging system

A compact imaging system with a novel front-end detector is under investiga tion and development. Unique aspects of this collimatorless system include the use of thin arrays of many thousands of microcolumnar (< 10 mum diamete r) CsI front-end scintillators that are coupled through a four-times reduci ng fiber-optic (FO) bundle to a metal-channel multianode position sensitive photodetector. The tested arrays are 140 or 200 pm tall on faceplates of p lane glass, FO, and FO with statistical extramural absorbers (EMAs). The hi ghly discrete nature of the scintillator microcolumn arrays ensures very fi ne intrinsic spatial resolution, limited by the particle penetration and ba ckscatter in the detector assembly. Their retro-reflector-tipped front ends facilitate light propagation toward the photodetector, ensuring good light collection. Monte Carlo simulations confirmed the limiting nature of beta particle penetration on measurable resolution. With this system, absolute l ight output was higher for the taller arrays, which indicates that these si zes are below the optimum for light output and energy absorption from the e nergetic beta particles; even taller scintillators, however, would suffer f rom increased backgrounds from annihilation radiation with positron detecti on. While MTF measurements with an X-ray source and microslit indicate the best response with the arrays on FO + EMA substrates, measurements with hig h and medium (1.7 MeV and 635 keV) energy beta line sources yield the best responses with the plane glass substrate, indicating that energy thresholdi ng affects resolution in the classical way, even with these highly miniatur ized arrays. Experiments with complex positron emission distributions along with large gamma-ray backgrounds, as may be expected during surgery, yield images with small background contamination and no distortions.