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UBC Theses and Dissertations

Implementation of an analytically based scatter correction in SPECT reconstructions Vandervoort, Eric

Abstract

Photon scatter is one of the main effects that degrade the quality and quantitative accuracy of SPECT images. The objective of the work performed in this thesis was to develop and validate a scatter correction technique that uses an accurate physics-based model of photon scatter as part of an iterative image reconstruction algorithm. This work was performed in two distinct stages. The first stage was to develop a scatter calculation based on a simplified version of an existing technique, the analytic photon distribution (APD) method. The scatter distributions generated using the approximate technique were compared to those obtained using the original APD method. On average the differences between the two methods were small relative to the statistical uncertainty in SPECT projection data (between 6 to 30 times smaller depending on the activity distribution) for a typical perfusion study. The second stage was to implement this scatter correction in an image reconstruction algorithm, and test its performance using computer simulated projection data, experimental data obtained from physical phantoms, and patient data. Images corrected for scatter, attenuation and collimator blurring were compared to images corrected only for attenuation and collimator blurring. In the simulation studies results were compared to an ideal situation in which only the primary (unscattered) photon data is reconstructed. In all cases, the scatter corrected images demonstrate substantially improved image contrast relative to no scatter correction. In simulations the scatter corrected and primaryonly images had similar contrast (to within 3%) and noise properties. Images with no scatter correction had contrast values 29% poorer on average than the ideal correction. Currently this scatter correction takes 3 to 4 hours for a typical clinical myocardial study. In the future additional code optimization and some improvements in computer processor speed could allow this scatter correction to be implemented clinically.

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