Impact of Spatial Resolution on CT Imaging of Middle Ear Prostheses: Comparison of Photon-Counting and Energy-Integrating Detectors

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ABSTRACT BACKGROUND AND PURPOSE: CT imaging of sub-millimeter middle ear prostheses—vital for post-surgery treatment—requires highspatial-resolution. This study evaluated the impact of spatial resolution for the visualization of prostheses using photon-countingdetector (PCD) CT, energy-integrating-detector (EID) CT, and EID-CT with attenuating comb filters. MATERIALS AND METHODS: Twenty-one middle ear prostheses of different makes were placed within a head phantom and scanned on a PCD-CT (NAEOTOM Alpha, Siemens), two dual-source CTs with comb filters (Force and Flash, Siemens), and a dual-layer CT without comb filter (7500, Philips). Scanning and reconstruction followed clinical temporal bone protocols for each scanner, with a matched 120kV and 80mm field-of-view; sharp kernels/algorithms of Qr89, Ur77, Ur77, and YD; and minimal allowable slice thickness of 0.2, 0.4, 0.5, and 0.67mm, respectively. Qualitative assessments were performed, including visual inspection, volume rendering, a blind reader study, and quantitative assessments using line profiles, and full-width at half-maximum (FWHM). One prosthesis was implanted in human cadaver head and scanned on a PCD-CT (NAEOTOM Alpha, Siemens), a 3rd generation dual-source (Force, Siemens), and a dual-layer CT (7500, Philips) following the same phantom study protocols. Image quality was compared among the scanners. RESULTS: PCD-CT provided images with the highest spatial resolution, allowing clinically relevant assessment of prosthesis position. EID-CT scanners with comb filters provided good results, with noticeable loss of detail, while EID-CT without a comb filter showed substantial resolution loss. These findings were consistent across readers (Kendall’s W=0.89, p-value<0.001) and validated by the line profiles and FWHM measurements. PCD-CT showed a 49.5% improvement over EID-CT without comb filter. Among scanners with ultra-high-resolution (UHR) capabilities, PCD-CT had lower radiation dose (CTDIvol: 31.5 vs 46.7 and 51.4 mGy) and lower noise (81.3 vs 93.0 and 274.8 HU) compared to two EID-CTs with comb filters. In the cadaver study, PCD-CT provided higher resolution and lower noise than both EID-CT scanners with and without comb filters (67.6 vs 118.6 and 50.1 HU). CONCLUSIONS: PCD-CT provided dose-efficient, accurate evaluation of ossicular prostheses, without the degradation of sub-millimeter structures, while maintaining lower dose and noise. ABBREVIATIONS: PCD＝ Photon-counting-detector; EID＝ Energy-integrating-detector; UHR＝ Ultra-high-resolution; FWHM＝ Full-width at half-maximum; FOV＝ Field-of-view; VRT＝ Volume rendering technique; CTDIvol＝ Volume CT dose index; PROP＝ Partial ossicular replacement prosthesis; TROP＝ Total ossicular replacement prosthesis.

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