Comparison of a Photon-Counting-Detector CT with an Energy-Integrating-Detector CT for Temporal Bone Imaging: A Cadaveric Study

Abstract

Background and purpose: Evaluating abnormalities of the temporal bone requires high-spatial-resolution CT imaging. Our aim was to assess the performance of photon-counting-detector ultra-high-resolution acquisitions for temporal bone imaging and compare the results with those of energy-integrating-detector ultra-high-resolution acquisitions.

Materials and methods: Phantom studies were conducted to quantify spatial resolution of the ultra-high-resolution mode on a prototype photon-counting-detector CT scanner and an energy-integrating-detector CT scanner that uses a comb filter. Ten cadaveric temporal bones were scanned on both systems with the radiation dose matched to that of the clinical examinations. Images were reconstructed using a sharp kernel, 0.6-mm (minimum) thickness for energy-integrating-detector CT, and 0.6- and 0.25-mm (minimum) thicknesses for photon-counting-detector CT. Image noise was measured and compared using adjusted 1-way ANOVA. Images were reviewed blindly by 3 neuroradiologists to assess the incudomallear joint, stapes footplate, modiolus, and overall image quality. The ranking results for each specimen and protocol were compared using the Friedman test. The Krippendorff α was used for interreader agreement.

Results: Photon-counting-detector CT showed an increase of in-plane resolution compared with energy-integrating-detector CT. At the same thickness (0.6 mm), images from photon-counting-detector CT had significantly lower (P < .001) image noise compared with energy-integrating-detector CT. Readers preferred the photon-counting-detector CT images to the energy-integrating-detector images for all 3 temporal bone structures. A moderate interreader agreement was observed with the Krippendorff α = 0.50. For overall image quality, photon-counting-detector CT image sets were ranked significantly higher than images from energy-integrating-detector CT (P < .001).

Conclusions: This study demonstrated substantially better delineation of fine anatomy for the temporal bones scanned with the ultra-high-resolution mode of photon-counting-detector CT compared with the ultra-high-resolution mode of a commercial energy-integrating-detector CT scanner.

Fig 1.

Comparison of MTF curves for UHR modes reconstructed with a sharp kernel (U70) on the PCD-CT and EID-CT systems.

Fig 2.

Representative axial images of the modiolus (arrow) from the same specimen scanned with UHR PCD-CT and reconstructed with 0.25- (A) and 0.6-mm (B) image thicknesses, and UHR EID-CT, with a 0.6-mm image thickness (C). The pyramid-shaped modiolus is better depicted with the PCD-CT.

Fig 3.

Representative axial images of the stapes footplate (arrow) from the same specimen scanned with UHR PCD-CT and reconstructed with 0.25- (A) and 0.6-mm (B) image thicknesses, and UHR EID-CT, with 0.6-mm image thickness (C). An improved illustration of the stapes footplate and the limbs of the stapes is observed for PCD-CT.

Fig 4.

Representative axial images of the incudomallear joint (arrow) from the same specimen scanned with UHR PCD-CT and reconstructed with 0.25- (A) and 0.6-mm (B) image thicknesses, and UHR EID-CT, with 0.6-mm image thickness (C). The incudomallear joint between the incus and malleus is better defined in PCD-CT images compared with EID-CT images.

Fig 5.

Image noise measured from 10 cadaveric specimens scanned with 3 UHR protocols. White indicates PCD with a 0.25-mm image; gray, PCD with a 0.6-mm image; black, EID with a 0.6-mm image.

Fig 6.

Rankings from 3 readers regarding overall image quality and delineation of 3 key anatomic structures. For all 3 structures and overall image quality, UHR PCD-CT images with 0.25-mm thickness have the highest rank (average, 1.2–1.4), while UHR EID-CT images with 0.6-mm thickness have the lowest rank (average, 2.5–2.8). White indicates the first rank; gray, the second rank; black, the third rank.