Photon-Counting CT Versus Energy-Integrating CT Angiography for Craniocervical Fibromuscular Dysplasia: A Preliminary Retrospective Paired Analysis

BACKGROUND: Assessing craniocervical fibromuscular dysplasia (cc-FMD) can be challenging using cross-sectional imaging. We hypothesize that photon-counting detector CT (PCD-CT), owing to its superior spatial resolution over conventional energy-integrating detector CT (EID-CT), may better help appreciate changes in cc-FMD. MATERIALS AND METHODS: In this retrospective cohort, 24 patients with radiologically reported cc-FMD (mean age: 54 y; 75% women) underwent both PCD-CT and EID-CT within 180 days (median: 52 d). Bilateral internal carotid (ICA) and vertebral artery (VA) segments without dissection/occlusion were graded on a 3-point scale (absent/likely present/present). Intermodality agreement was evaluated with weighted Cohen κ, and radiation dose metrics (CTDIvol) were compared using the paired Wilcoxon signed-rank tests. RESULTS: Eighty-seven paired segments were analyzed. PCD-CT detected FMD in 48 segments (55.1%) versus 30 (34.5%) on EID-CT. The mean reader confidence scores were consistently higher with PCD-CT compared with EID-CT, for both ICAs (2.16±0.95 vs. 1.93±0.99) and VAs (1.86±0.95 vs. 1.36±0.75). Intermodality agreement was almost perfect for ICAs (κ=0.807) and substantial for VAs (κ=0.662). Under our institutional protocols, median CTDIvol was lower with PCD-CT (16.6 mGy) than EID-CT (21.5 mGy; P=0.0112). CONCLUSION: PCD-CT demonstrated more frequent reader categorization of cc-FMD features than EID-CT, particularly in the VAs, and had a lower median CTDIvol under our institutional protocols. These preliminary findings suggest improved cc-FMD detection with PCD-CT as compared with EID-CT and require prospective, reference-standard validation to establish accuracy and clinical impact.