Ultra-High-Resolution Photon-Counting Detector CTA of the Head and Neck: Image Quality Assessment and Vascular Kernel Optimization.

Background: Head and neck CTA requires fine detail evaluation, including characterization of potentially very small vessels and intrastent lumens. Blooming artifacts also hinder evaluation. Objectives: To evaluate image quality of ultra-high-resolution (UHR) photon-counting detector (PCD) CTA of the head and neck and to explore variation of such quality across 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 UHR mode. Reconstructions for each examination included a reference reconstruction (reflecting clinical protocols) using 0.8-mm slice thickness and Bv40 kernel, and six UHR reconstructions using 0.2-mm slice thickness and kernels of varying sharpness (Bv48-Bv80). Quantitative measures were recorded. Two radiologists independently evaluated qualitative measures using Likert scales (1=lowest quality; 5=highest quality). Results: The analysis included 103 participants (mean age, 61.3±13.0 years; 56 male, 48 female). Median vessel sharpness (in HU/mm) was 100.9 for reference reconstruction, and for UHR varied from 110.0 for Bv46 to 121.6 for Bv76 and 134.7 for Bv80. Median right internal carotid artery C2 luminal diameter was 3.8 mm for reference reconstruction, and for UHR increased from 4.1 mm for Bv48 to 4.9 mm for Bv80. For both readers, median overall image quality for reference reconstruction was 3, and for UHR was highest for Bv64 (5); calcified plaque blooming artifact for reference reconstruction was 1, and for UHR was highest for Bv72 (5) and Bv76 (5); stent blooming artifact for reference reconstruction was 1, and for UHR was highest for Bv76 (5) and Bv80 (5); soft-plaque delineation for reference reconstruction was 1, and for UHR was highest for Bv76 (5) or Bv80 (5); small-vessel visualization for reference reconstruction was 1, and for UHR was highest for Bv76 (5) or Bv80 (5). Conclusion: UHR-PCD CTA yielded reduced blooming artifact from calcified plaques or stents, and improved softplaque and small-vessel visualization. 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 use of UHR-PCD CTA for head and neck evaluation and may help guide such examinations' kernel selection.