Appropriate dose reduction using photon-counting detector CT for temporal bone imaging: phantom and clinical studies with helical acquisition

Purpose: To determine the extent of possible dose reduction with photon-counting detector computed tomography (PCD-CT) while maintaining image quality equivalent to that of energy-integrating detector CT (EID-CT) images at standard dose in the temporal bone.
Materials and methods: PCD-CT and EID-CT imaging quality were compared by visual evaluation of clinical temporal bone images and visual scores with Welch’s t-test at standard dose. A head phantom was used to evaluate imaging quality under dose reduction. The detectability index (d’) of the PCD-CT images at various dose levels and the EID-CT images at standard dose was evaluated. Dose reduction limit with PCD-CT used in the subsequent clinical evaluation was determined as the lowest dose with image quality equal to or better than EID-CT. The clinical equivalence of PCD-CT image quality at the determined reduced dose to that with EID-CT at standard dose was evaluated using visual scores. Equivalence was determined if the 95% confidence intervals of differences did not exceed the equivalence margin of ±1.
Results: At standard doses, PCD-CT images demonstrated significantly higher visual scores than EID-CT images (3.73 vs. 2.56 for incudomalleolar joint, 3.75 vs. 2.63 for stapes, 3.54 vs. 2.52 for cochlea, and 3.58 vs. 2.46 for facial nerve canal; all P 0.001). In the phantom study, the d’ value was 0.15 with EID-CT at standard dose and was 0.12 and 0.17 with PCD-CT at 25% and 50% of the standard dose, respectively. Clinically, the mean visual scores of PCD-CT images at 50% of the standard dose were equivalent to EID-CT images at standard dose in all regions (3.58 vs. 3.12 for incudomalleolar joint, 3.46 vs. 3.19 for stapes, 3.50 vs. 3.08 for cochlea, 3.58 vs. 3.27 for facial nerve canal).
Conclusion: PCD-CT may preserve image quality even at 50% of the standard dose in the temporal bone.