Direct Attenuation Correction Using Deep Learning for Cardiac SPECT: A Feasibility Study

Dedicated cardiac SPECT scanners with cadmium-zinc-telluride cameras have shown capabilities for shortened scan times or reduced radiation doses, as well as improved image quality. Since most dedicated scanners do not have integrated CT, image quantification with attenuation correction (AC) is challenging and artifacts are routinely encountered in daily clinical practice. In this work, we demonstrated a direct AC technique using deep learning (DL) for myocardial perfusion imaging (MPI). Methods: In an institutional review board-approved retrospective study, 100 cardiac SPECT/CT datasets with ^99mTc-tetrofosmin, obtained using a scanner specifically with a small field of view, were collected at the Yale New Haven Hospital. A convolutional neural network was used for generating DL-based attenuation-corrected SPECT (SPECT_DL) directly from noncorrected SPECT (SPECT_NC) without undergoing an additional image reconstruction step. The accuracy of SPECT_DL was evaluated by voxelwise and segmentwise analyses against the reference, CT-based AC (SPECT_CTAC), using the 17-segment myocardial model of the American Heart Association. Polar maps of representative (best, median, and worst) cases were visually compared to illustrate potential benefits and pitfalls of the DL approach. Results: The voxelwise correlations with SPECT_CTAC were 92.2% ± 3.7% (slope, 0.87; R² = 0.81) and 97.7% ± 1.8% (slope, 0.94; R² = 0.91) for SPECT_NC and SPECT_DL, respectively. The segmental errors of SPECT_NC scattered from -35% to 21% (P < 0.001), whereas the errors of SPECT_DL stayed mostly within ±10% (P < 0.001). The average segmental errors (mean ± SD) were -6.11% ± 8.06% and 0.49% ± 4.35% for SPECT_NC and SPECT_DL, respectively. The average absolute segmental errors were 7.96% ± 6.23% and 3.31% ± 2.87% for SPECT_NC and SPECT_DL, respectively. Review of polar maps revealed successful reduction of attenuation artifacts; however, the performance of SPECT_DL was not consistent for all subjects, likely because of different amounts of attenuation and different uptake patterns. Conclusion: We demonstrated the feasibility of direct AC using DL for SPECT MPI. Overall, our DL approach reduced attenuation artifacts substantially compared with SPECT_NC, justifying further studies to establish safety and consistency for clinical applications in stand-alone SPECT systems suffering from attenuation artifacts.