Extending the usable areas of modular NaI(Tl) detector using crystal treatment

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Abstract
NaI(Tl) detectors have unusable areas at the crystal edges (normally about half the PMT's width), which will produce missing data on the sinogram and reduce the system efficiency. However, for SPECT systems in a cylindrical geometry, the modular detectors may have advantages in count rate performance and manufacturing cost over the traditional large crystals and the multi-bar detectors. In this study, the authors want to reduce the unusable areas at the interface of two adjacent detector modules. In the proposed approach, the authors cut grooves parallel to the crystal edge and have the PMT shared by two adjacent modules at the edge. To determine the optimal position, depth and shape of the grooves, the authors have varied those parameters in experiments. The authors found that these parameters can significantly affect the shape of the light distribution function. The slope of the light distribution function increases significantly for the crystal with grooves at appropriate position and depth accompanied by a slightly higher variation. The intrinsic resolution calculated with the centroid algorithm is improved as compared to that of a reference that does not have grooves.

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