Ultrahigh-Resolution Photon-Counting Detector CT of the Lungs: Association of Reconstruction Kernel and Slice Thickness With Image Quality.

Prior work has shown improved image quality for photon-counting detector (PCD) CT of the lungs compared with energy-integrating detector CT. A paucity of the literature has compared PCD CT of the lungs using different reconstruction parameters. The purpose of this study is to the compare the image quality of ultra-high-resolution (UHR) PCD CT image sets of the lungs that were reconstructed using different kernels and slice thicknesses. This retrospective study included 29 patients (17 women and 12 men; median age, 56 years) who underwent noncontrast chest CT from February 15, 2022, to March 15, 2022, by use of a commercially available PCD CT scanner. All acquisitions used UHR mode (1024 × 1024 matrix). Nine image sets were reconstructed for all combinations of three sharp kernels (BI56, BI60, and BI64) and three slice thicknesses (0.2, 0.4, and 1.0 mm). Three radiologists independently reviewed reconstructions for measures of visualization of pulmonary anatomic structures and pathologies; reader assessments were pooled. Reconstructions were compared with the clinical reference reconstruction (obtained using the BI64 kernel and a 1.0-mm slice thickness [BI64]). The median difference in the number of bronchial divisions identified versus the clinical reference reconstruction was higher for reconstructions with BI64 (0.5), BI60 (0.3), BI64 (0.5), and BI60 (0.2) (all < .05). The median bronchial wall sharpness versus the clinical reference reconstruction was higher for reconstructions with BI64 (0.3) and BI64 (0.3) and was lower for BI56 (-0.7) and BI56 (-0.3) (all < .05). Median pulmonary fissure sharpness versus the clinical reference reconstruction was higher for reconstructions with BI64 (0.3), BI60 (0.3), BI56 (0.5), BI64 (0.5), BI60 (0.5), and BI56 (0.3) (all < .05). Median pulmonary vessel sharpness versus the clinical reference reconstruction was lower for reconstructions with BI56 (-0.3), BI60 (-0.3), BI56 (-0.7), BI64 (-0.7), BI60 (-0.7), and BI56 (-0.7). Median lung nodule conspicuity versus the clinical reference reconstruction was lower for reconstructions with BI56 (-0.3) and BI56 (-0.3) (both < .05). Median conspicuity of all other pathologies versus the clinical reference reconstruction was lower for reconstructions with BI561.0 mm (-0.3), BI56 (-0.3), BI64 (-0.3), BI60 (-0.3), and BI56 (-0.3). Other comparisons among reconstructions were not significant (all > .05). Only the reconstruction using BI64 yielded improved bronchial division identification and bronchial wall and pulmonary fissure sharpness without a loss in pulmonary vessel sharpness or conspicuity of nodules or other pathologies. The findings of this study may guide protocol optimization for UHR PCD CT of the lungs.