Deep Learning Reconstruction versus Hybrid Iterative Reconstruction for Spectral CT: A Multi-Institutional Image Quality Assessment

Purpose: To compare image quality between deep learning reconstruction and hybrid iterative reconstruction for conventional and virtual monoenergetic images derived from the same spectral CT examinations. Methods and Materials: This retrospective, post hoc secondary analysis of a multi-institutional, controlled, blinded reader study evaluated head, chest, cardiac, and abdomen/pelvis CT examinations acquired using dual-layer spectral CT. The parent study (clinicaltrials.gov identifier NCT07108205) included 147 examinations across a range of acquisition and reconstruction parameters. Raw data were reconstructed using hybrid iterative reconstruction (HIR; iDose, Philips Healthcare) and spectral deep learning reconstruction (DLR; Spectral Precise Image, Philips Healthcare). Conventional images and corresponding virtual monoenergetic images (VMI) were generated with both methods from identical raw data. Randomized image pairs were independently evaluated by two blinded board-certified radiologists or cardiologists, and image quality was scored on a 5-point Likert scale. A post hoc analysis was performed on previously collected scores from a subset of examinations acquired at standard resolution and reconstructed with thin sections and a soft tissue kernel to focus comparison on HIR versus DLR. Least squares means were estimated using a model accounting for multiple readers per examination. Noninferiority of DLR to HIR was tested; when established, superiority was tested using the same model. Results: 59 CT examinations from 56 patients met technical criteria for this analysis. DLR was noninferior and superior to HIR for head, abdomen, and cardiac examinations across conventional images and VMI, with p values ranging from <.0001 to .0058. DLR was noninferior but not superior for conventional chest images (p = .1430). Noninferiority was not established for chest VMI, although mean scores numerically favored DLR. This may reflect a ceiling effect from high HIR scores. Conclusion: Spectral DLR produced image quality that matched or exceeded HIR across most anatomic regions and image types, including conventional and virtual monoenergetic images.