Spectral Shaping Via Tin Prefiltration in Ultra-High-Resolution Photon-Counting and Energy-Integrating Detector CT of the Temporal Bone

Abstract

Objectives: Hardening the x-ray beam, tin prefiltration is established for imaging of high-contrast subjects in energy-integrating detector computed tomography (EID-CT). With this work, we aimed to investigate the dose-saving potential of spectral shaping via tin prefiltration in photon-counting detector CT (PCD-CT) of the temporal bone. Methods: Deploying dose-matched scan protocols with and without tin prefiltration on a PCD-CT and EID-CT system (low-/intermediate-/full-dose: 4.8/7.6-7.7/ 27.0-27.1 mGy), 12 ultra-high-resolution examinations were performed on each of 5 cadaveric heads. While 120 kVp was applied for standard imaging, the protocols with spectral shaping used the highest potential available with tin prefiltration (EID-CT: Sn 150 kVp, PCD-CT: Sn 140 kVp). Contrast-to-noise ratios and dose-saving potential by spectral shaping were computed for each scanner. Three radiologists independently assessed the image quality of each examination with the intraclass correlation coefficient being computed to measure interrater agreement. Results: Regardless of tin prefiltration, PCD-CTwith low (171.2 ± 10.3 HU) and intermediate radiation dose (134.7 ± 4.5 HU) provided less image noise than full-dose EID-CT (177.0 ± 14.2 HU; P < 0.001). Targeting matched image noise to 120 kVp EID-CT, mean dose reduction of 79.3% ± 3.9% could be realized in 120 kVp PCD-CT. Subjective image quality of PCD-CT was better than of EID-CT on each dose level ( P < 0.050). While no distinction was found between dose-matched PCD-CT with and without tin prefiltration ( P ≥ 0.928), Sn 150 kVp EID-CT provided better image quality than 120 kVp EID-CT at high and intermediate dose levels ( P > 0.050). The majority of low-dose EID-CT examinations were considered not diagnostic, whereas PCD-CT scans of the same dose level received satisfactory or better ratings. Interrater reliability was excellent (intraclass correlation coefficient 0.903). Conclusions: PCD-CT provides superior image quality and significant dose savings compared with EID-CT for ultra-high-resolution examinations of the temporal bone. Aiming for matched image noise, high-voltage scan protocols with tin prefiltration facilitate additional dose saving in EID-CT, whereas superior inherent denoising decreases the dose reduction potential of spectral shaping in PCD-CT.

Technical Basics and Clinical Benefits of Photon-Counting CT

“…36,[38][39][40] More recently, in a study on 5 cadaveric heads, the authors could show that PCD-CT provides superior image quality and significant dose savings (mean dose reduction of 79.3%) compared with EID-CT for ultra-high-resolution (UHR) examinations of the temporal bone. 41 In temporal bone examinations of 13 patients, PCD-CTwas rated superior for the evaluation of all individual anatomic structures at an average 31% lower radiation dose compared with an EID-CT. 42 Figure 6 shows a clinical example illustrating the potential of PCD-CT in inner ear imaging. In a comparison of the visualization of the smallest bone details between PCD-CT and EID-CT using a mouse as a specimen, PCD-CT was found to provide significantly less image noise, higher signal-tonoise ratio, and higher edge sharpness than EID-CT in dose-matched scans.…”

“…More recently, in a study on 5 cadaveric heads, the authors could show that PCD-CT provides superior image quality and significant dose savings (mean dose reduction of 79.3%) compared with EID-CT for ultra-high-resolution (UHR) examinations of the temporal bone 41 . In temporal bone examinations of 13 patients, PCD-CT was rated superior for the evaluation of all individual anatomic structures at an average 31% lower radiation dose compared with an EID-CT 42 Figure 6.…”

Photon-counting detector CT: early clinical experience review

“…latest generation) DS EID-CT systems across a variety of widely matching protocol parameters, reconstruction settings and radiation dose levels in terms of objective and subjective image quality. 59,60 The improved performance of PCD-CT was also confirmed invivo in a variety of clinical studies. Exemplarily, Symons et al showed that a prototype PCD-CT exhibited between 15 and 17% lower noise than EID-CT for 120 kV and 100 kV dose-matched chest CT scans.…”

Advanced Neuroimaging With Photon-Counting Detector CT

“…Accordingly, a recent in vivo study of temporal bones acquired with a full field-of-view PCD-CT system has shown better delineation of temporal anatomy by using dedicated sharp kernels that are not applicable for EID-CT without penalties in noise and image quality degradation 46 . Similar, Grunz et al 7 have shown that using ultra-high-resolution PCD-CT with spectral shaping and tin prefiltration of the temporal bone allows for a superior image quality and a substantial noise reduction compared with EID-CT.…”

“…45 Accordingly, a recent in vivo study of temporal bones acquired with a full field-of-view PCD-CT system has shown better delineation of temporal anatomy by using dedicated sharp kernels that are not applicable for EID-CTwithout penalties in noise and image quality degradation. 46 Similar, Grunz et al 7 have shown that using ultra-high-resolution PCD-CTwith spectral shaping and tin prefiltration of the temporal bone allows for a superior image quality and a substantial noise reduction compared with EID-CT. These results suggest that patients may benefit not only from less radiation but also from the new capabilities of PCD-CT, including utilization of the ultra-high-resolution mode to effectively discern even the smallest anatomical structures, particularly in assessment of more challenging pathologies, such as imaging of cholesteatoma (Fig.…”