BACKGROUND. Head and neck CTA requires fine-detail evaluation, including characterization of potentially very small vessels and intrastent lumina. Blooming artifacts also hinder evaluation. OBJECTIVE. The purpose of this study was to evaluate image quality of ultrahigh-resolution (UHR) photon-counting detector (PCD) CTA of the head and neck and to explore variation of image quality across body vascular (Bv) reconstruction kernels. METHODS. This prospective study included patients who underwent clinically indicated head and neck CTA from September 2023 to December 2023. Participants underwent PCD CTA in the UHR mode. Reconstructions for each examination included a reference reconstruction (reflecting clinical protocols) using a 0.8-mm slice thickness and Bv40 kernel and six UHR reconstructions using a 0.2-mm slice thickness and kernels of varying sharpness (Bv48-Bv80). Quantitative measures were recorded. Two radiologists independently evaluated qualitative measures using a Likert scale ranging from 1 (lowest quality) to 5 (highest quality). RESULTS. The analysis included 103 participants (mean age, 61.3 ± 13.0 [SD] years; 56 men, 47 women). Median vessel sharpness (in Hounsfield units per millimeter) was 100.9 HU/mm for the reference reconstruction, and for the UHR reconstructions, it varied from 110.0 HU/mm for Bv48 to 121.6 HU/mm for Bv76 and 134.7 HU/mm for Bv80. Median right internal carotid artery C2 luminal diameter was 3.8 mm for the reference reconstruction, and for the UHR reconstructions, it increased from 4.1 mm for Bv48 to 4.9 mm for Bv80. For both readers, median overall image quality for the reference reconstruction was 3, and for the UHR reconstructions, it was highest for Bv64 (score of 5); calcified-plaque blooming artifact for the reference reconstruction was 1, and for the UHR reconstructions, it was highest for Bv72 (score of 5) and Bv76 (score of 5); stent blooming artifact for the reference reconstruction was 1, and for the UHR reconstructions, it was highest for Bv76 (score of 5) and Bv80 (score of 5); soft-plaque delineation for the reference reconstruction was 1, and for the UHR reconstructions, it was highest for Bv76 (score of 5) or Bv80 (score of 5); small-vessel visualization for the reference reconstruction was 1, and for the UHR reconstructions, it was highest for Bv76 (score of 5) or Bv80 (score of 5). CONCLUSION. UHR PCD CTA yielded reduced blooming artifact from calcified plaques or stents and improved visualization of soft plaque and small vessels. These advantages were more pronounced for strongest kernels, although subjective image quality was better for a weaker kernel. CLINICAL IMPACT. The findings indicate benefits from the use of UHR PCD CTA for head and neck evaluation and may help guide such examinations' kernel selection.

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