Evaluation of Crystals’ Morphology on Detection Efficiency Using Modern Classification Criterion and Monte Carlo Method in Nuclear Medicine

Abstract

Crystals used in medical imaging systems play a key role in obtaining images for the improvement of diagnoses in medicine. We investigated crystal material characteristics in detection efficiency, and a reliable definition of efficiency proposed for improving spatial resolution. In this study, bismuth germanate (BGO), lutetium oxyortho silicate, gadolinium silicate, and lutetium yttrium oxyortho silicate crystals have been evaluated to compare their special characteristics using Monte Carlo simulation. Additionally, a new criterion is introduced as scattering frequency at which the ratio of the number of Compton interaction to the minimum traversed distance of photons in crystal is suggested. This frequency is based on random numbers, Compton scattering, energy of γ-ray, geometry and material of crystal. The sensitivity of crystals as a function of crystal width at various incident angles of the photon is investigated. The simulated results have demonstrated that at a distinct width of crystal, the detection efficiency of the BGO crystal was more than that of other crystals in which the amount of scatter and random coincidences decreased. Crystal width at various applications, however, must be optimized with respect to the trade off among the signal-to-noise ratio, spatial and temporal resolutions, efficiency, and the untrue coincidences. Determining crystal width and material may be useful in collimator design to improve spatial resolution and efficiency.