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

Abstract

A compact imaging system with a novel front-end detector is under investigation and development. Unique aspects of this collimatorless system include the use of thin arrays of many thousands of microcolumnar (<10 /spl mu/m diameter) CsI front-end scintillators that are coupled through a four-times reducing fiber-optic (FO) bundle to a metal-channel multianode position sensitive photodetector. The tested arrays are 140 or 200 /spl mu/m tall on faceplates of plane glass, FO and FO with statistical extramural absorbers (EMAs). The highly discrete nature of the scintillator microcolumn arrays ensures very fine intrinsic spatial resolution, limited by the particle penetration and backscatter 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 light output was higher for the taller arrays, which indicates that these sizes are below the optimum for light output and energy absorption from the energetic beta particles; even taller scintillators, however, would suffer from increased backgrounds from annihilation radiation with positron detection. While MTF measurements with an X-ray source and microslit indicate the best response with the arrays on FO+EMA substrates, measurements with high and medium (1.7 MeV and 635 keV) energy beta line sources yield the best responses with the plane glass substrate, indicating that energy thresholding affects resolution in the classical way, even with these highly miniaturized 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.