Single-photon spatial and energy resolution enhancement of a columnar CsI(Tl) / EMCCD gamma-camera using maximum-likelihood estimation

摘要

We examined the spatial resolution of a columnar CsI(Tl), single-photon imaging system using an approach that estimates the interaction position to better than the spread of the light distribution. A columnar scintillator was directly coupled to a 512x512 electron multiplying CCD (EMCCD) camera (16 urn pixels) binned at 2x2 to sample at 32 um pixels. Optical photons from gamma-ray/scintillator interactions are sampled over multiple pixels. Resultant images show clusters of signal at the original interaction site, clusters from Cs & I K x-rays up to several hundred microns away, and clusters from collimator K x-rays. Also evident are depth-of-interaction effects which result in a broadening of the light distribution. These effects result in a degradation of spatial and energy resolution. Cluster pixel data was processed to better estimate the interaction position within the initial interaction cluster. Anger (centroid) estimation of individual gamma-ray events yielded spatial resolutions better than 100 um; a result previously achievable only with pixellated semiconductor detector arrays. After proper calibration, depth-of-interaction (DOI) effects are corrected by performing maximum-likelihood 3D position and energy estimation of individual gamma-ray interactions.