Investigation of crystal geometries for fiber coupled gamma imaging intra-operative probes

CsI(Na), CsI(Tl) and NaI(Tl) scintillators coupled through optical fibers were investigated with simulations and measurements to evaluate their potential as gamma imaging intraoperative probes. Three coupling methods were employed: discrete crystals coupled one-to-one with the fibers; discrete crystals coupled through a light diffuser to an unmatched fiber array; and continuous crystals coupled directly to the fiber optic array. The discrete crystals were 4x4 element arrays ranging in size from 1x1x2.5 mm(3) to 2x2x6 mm(3). CsI(Na) produced the best pulse height and single crystal energy resolution (44% at 140 keV) when coupled through fibers to the photodetector. All elements of the arrays were completely resolved, indicating that the intrinsic spatial resolution will be determined by the crystal size. The spatial resolution for the 12.5 mm phi x 3.5 mm continuous crystals was similar to 1.33 mm FWHM. Preliminary imaging measurements faithfully reproduced the activity distributions and compared favorably with simulations.