Optimal Reconstruction Filter Parameters for Multi-Headed Brain SPECT: Dependence on Count Activity

Objective: Reconstruction parameters must be optimized to approach the improved spatial resolution that is theoretically possible from modern SPECT imaging devices. One important reconstruction consideration is proper selection of the back-projection filter parameters. The aim of this study was to determine which Butterworth filter optimized image resolution for brain SPECT scans. Methods: Ten normal subjects underwent brain SPECT following an intravenous injection of 15-20 mCi mTc-HMPAO (5 subjects) and 30-35 mCi mrc-HMPAO (5 subjects). Subjects were separated into two groups based on the counts per pixel in the anterior projection image: 5 subjects with low-count images (10.4-13.9 counts/pixel) and 5 subjects with high-count images (18.3-21.5 counts/pixel). All subject projection data were reconstructed at cutoff frequencies (Fe) ranging from 0.15-0.3 Nyquist, with orders ranging from 2-12 at each frequency cutoff. Optimal image selection was determined by blinded subjective assessment by three nuclear medicine faculty capable of evaluating brain SPECT image quality. Results: Results demonstrated that for low-count images, optimum Butterworth filter reconstruction parameters were: Fe = 0.20, order 6. For high-count images, optimum parameters were: Fe = 0.225, order 7. Conclusion: The proper selection of Fe is the most critical parameter for optimization of image reconstruction quality.