Testing of local gamma-ray scatter fractions determined by spectral fitting

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Abstract
The spectral-fitting method of correction for gamma-ray Compton scattering within objects separates the unscattered and scattered components of locally measured energy spectra. Here, the authors employ a third-order polynomial for the scattering and an approximately constant fitting window. A scatter fraction, defined as total scattered over total unscattered counts within a 20% window, is calculated for each point in the Anger camera images. These scatter fractions are tested against those from Monte-Carlo simulation for 99mTc and against results from semiconductor detector measurements for 131I. A radioactive sphere at several locations within a non-radioactive cylinder and the inverse are imaged for the testing. For one case, reproducibility of the spectral-fitting scatter fraction as a function of the number of unscattered counts within the 20% acceptance window was also determined.