Multireader Comparison of Photon-Counting Detector CT Reconstructions for Evaluation of Temporal Bone Cochlear...

Photon-counting CT (PCCT) offers several advantages over conventional CT for cochlear implant (CI) imaging, including improved spatial resolution and both signal-to-noise and contrast-to-noise ratios. However, the optimal PCCT reconstruction parameters for CI imaging have not been established. This study compared 6 PCCT reconstruction approaches for temporal bone CI imaging in a multireader design.

Twenty patients with CIs (24 implants) underwent temporal bone PCCT on a NAEOTOM Alpha scanner. Raw data were reconstructed using 6 different algorithms, as follows: Hr84 0.2-mm polyenergetic reconstructions (T3D) (head-regular, sharpness level 84), Hr84 0.4-mm T3D, Qr56 0.4-mm iterative metal artifact reduction (iMAR) T3D (quantitative-regular, sharpness level 56, iMAR), Qr76 0.4-mm M_140 (virtual monoenergetic 140 keV), Qr76 0.4-mm M_70 (virtual monoenergetic 70 keV), and Qr76 0.4 mm T3D. Two fellowship-trained neuroradiologists independently rated electrode visibility and overall image quality for all implants and wire visibility for implants with visible wires, on 0-2 Likert scales. Interreader agreement was assessed with a quadratic-weighted Cohen κ. A mixed-effects model was used to evaluate reconstruction differences for each metric.

The mean patient age was 50.9 (SD, 26) years, and 8 patients were women. Interreader agreement was substantial for electrode visibility (κ = 0.66) and overall image quality (κ = 0.79), and moderate for wire visibility (κ = 0.52). Reconstruction type significantly affected all 3 metrics. The sharp kernel reconstructions (Hr84 0.2-mm T3D and Hr84 0.4-mm T3D) consistently ranked highest, with significantly greater scores than most other reconstructions. Qr56 0.4-mm iMAR T3D was the lowest rated in every category, significantly worse than all other reconstructions.

PCCT reconstruction parameters substantially influence postoperative CI image quality. Ultra-high-resolution reconstructions provided the best combination of artifact suppression and fine structural detail, while iMAR and high kiloelectron volt monoenergetic reconstructions performed the worst. These findings can guide reconstruction selection to optimize PCCT protocols for CI evaluation.