Joint Spectral Image Reconstruction for Y-90 SPECT with Multi-Window Acquisition

Image reconstruction for Y-90 SPECT is challenging due to wide continuous energy spectrum of the bremsstrahlung photons. Previously, forward projection models with narrow single-energy window or wide multi-energy windows were used for image reconstruction with a single acquisition window. We propose a new Y-90 SPECT image reconstruction method referred to as joint spectral reconstruction (JSR) using multienergy window forward model and multiple acquisition windows. Monte Carlo (MC) simulation using SIMIND coupled with XCAT phantom (two tumors with 80, 41 mL) generated two sets of 6 acquisition window measurements (narrow window: 105- 135, 135-165, 165-195, 195-225, 225-255, 255-285 keV, and wide window: 100-200, 200-300, 300-400, 400-500, 500-600, 600-700 keV). Each measurement was scaled to the count level of a typical patient bremsstrahlung SPECT scan following Y-90 microsphere radioembolization of the liver. 3D OSEM with 6 window data and a single image was implemented with 6 energy-dependent collimator detector response, attenuation, and known scatter and was run with 100 iterations, 6 subsets. The reconstructed image was evaluated using the recovery coefficient (RC), the standard deviation (SD), the bias over tumors and liver. Results were compared with those of the single spectral reconstruction (SSR) method that models the projector with a single-energy window with a single acquisition window (105-135 keV for narrow case, and 100-200 keV for wide case). JSR yielded significantly higher RC and lower SD than SSR in all cases. For narrow window case, JSR achieved up to 11.19% increase in RC and up to 46.9% decrease in SD compared to SSR at the 100th iteration. For wide window case, JSR achieved up to 19.23% increase in RC and up to 19.01% decrease in SD compared to SSR at the 100th iteration. Therefore, our JSR was able to considerably improve Y-90 SPECT image reconstruction quality over SSR. The improvement in noise while maintaining comparable RC is particularly significant because the sensitivity of Y-90 SPECT is low and count levels for applications in targeted radionuclide therapy are low