Ultra-high-resolution Photon-Counting CT for Leaflet-Specific Evaluation of Fibrosis and Calcification in Aortic Stenosis

Objectives: Ultra-high-resolution photon-counting detector (PCD)-CT may enable leaflet-specific analysis of aortic valve fibrosis and calcification, providing insights into early aortic stenosis (AS) disease progression. This study aimed to investigate how PCD-CT leaflet-specific calcific and fibrotic volumes influence cardiovascular magnetic resonance (CMR) leaflet mobility. Materials and methods: Participants with moderate aortic AS prospectively underwent both PCD-CT (n=80) and CMR (n=58). Using PCD-CT, calcific and fibrotic volumes were segmented for right (RCC), left (LCC), and non-coronary cusps (NCC) and indexed to the aortic annulus area (ICV and IFV). CMR-derived leaflet mobility index (LMI) was assessed. Two raters compared image quality using a Likert scale (1=poor to 5=excellent) and distinguishability of individual leaflets in PCD-CT with EID-CT (n=82). Results: PCD-CT analysis showed that calcification was higher in males (e.g., ICVRCC: 15+/-16 vs. 4+/-7 uL/cm^2; p<0.001), while fibrosis was higher in females (e.g., IFVLCC: 47+/-18 vs. 34+/-15 uL/cm^2; p=0.004) across all leaflets. Fibrocalcific ratio was higher in LCC (53+/-276) compared to RCC (19+/-48; p<0.001) and NCC (13.5+/-34; p<0.001). LMI of RCC was higher in females compared to men (0.66+/-0.21 vs. 0.38+/-0.33; p=0.008). LMILCC and LMINCC showed no sex differences. LMIRCC negatively correlated with ICVRCC (ρ=-0.64 [-0.77, -0.46]; p<0.001) and LMINCC with ICVNCC (ρ=-0.69 [-0.80, -0.53]; p<0.001), whereas LMILCC negatively correlated with IFVLCC (ρ=-0.35 [-0.56, -0.10]; p=0.007), particularly in females (ρ=-0.70 [-0.89, -0.31]; p=0.003). PCD-CT yielded higher image quality (5 [IQR 4-5] vs. 3 [3-4]; p<0.001) and leaflet distinguishability (79/80 [99%] vs. 42/82 [51%]; p<0.001) than EID-CT. Conclusions: Ultra-high-resolution PCD-CT allows for leaflet-specific quantification of indexed fibrotic and calcific volume. These volumes demonstrate sex- and leaflet-specific differences that may distinctly contribute to AS pathophysiology.