Imaging Evaluation of CsI(T1) Arrays for Scintimammography

Recently the application of small imagers in nuclear medicine is growing, particularly in scintimammography. In this paper we propose the use of the Hamamatsu R7600-C8 Position Sensitive Photomultiplier Tube (PSPMT) for detection image optimization in scintimammography through the evaluation of image performances of detector pixellation and its interaction with a collimator lattice . To this aim, a number of CsI(T1) scintillating arrays with different pixel size and thickness were coupled to the same PSPMT. Considering the very high intrinsic spatial resolution, a look up table was realized to correct accurately the gain non uniformities. The results show an overall energy resolution FWHM, from flood field irradiation source, in close agreement with the individual crystal response and an uniformity response within k 10%. Finally an analysis of tumor signal to noise ratio (SNR) as a function of detection pixellation was performed, utilizing a breast phantom. Tumor SNR values are highest for 5 mm thick CsI(T1) arrays but shown slight differences with pixel size. The best tumor SNR value for 6 cm breast thick was obtained with 1.5 x 1.5 mm2 crystal pixel size. The collimator used was a low energy all purpose, parallel hole collimator with 22 mm length, 1.5 mm hexagonal hole, 0.2 mm Pb septa, currently utilized in scintimammography.