Optimization of acquisition energy windows in simultaneous /sup 99m/Tc//sup 123/I brain SPECT

Simultaneous acquisition SPECT brain imaging using a /sup 99m/Tc labeled perfusion agent and an /sup 123/I labeled neurotransmitter agent has potential applications in diagnosis of neurodegenerative diseases. However, the close proximity of the photopeaks of the two isotopes results in significant crosstalk. We have previously optimized the acquisition parameters for /sup 201/Tl//sup 99m/Tc dual isotope imaging based on an ideal observer signal-to-noise ratio (SNR). In this work, we determined the optimal energy window, i.e., the one providing the optimal tradeoff between minimizing the crosstalk and maximizing the detection efficiency for /sup 99m/Tc//sup 123/I simultaneous acquisition brain SPECT. High-count listmode projections of an anthropomorphic striatal brain phantom were acquired. Projection images with different sets of energy window centers and widths were derived from the listmode data. Those projections were then weighted and summed appropriately to represent various /sup 99m/Tc//sup 123/I activity concentration ratios. The values of a no-low-frequency ideal observer SNR were calculated for a lesion detection task using /sup 99m/Tc only, /sup 123/I only and the simultaneous projection data. The maximum ideal observer SNR values were used as the metric to select the optimal acquisition parameters. For a /sup 99m/Tc only acquisition, the optimal energy window was 30 keV wide centered at 144 keV, and for an /sup 123/I only acquisition the optimal window was 30 keV wide centered at 161 keV. For simultaneous acquisition, the /sup 123/I window tended to be higher and narrower and the /sup 99m/Tc window tended to be lower and narrower than for the separate-isotope acquisition. Use of the projection images acquired with optimal parameters will provide improved data from which to perform simultaneous SPECT reconstructions.