Photon-counting CT Extracellular Volume Fraction for Liver Fibrosis Assessment: Validation against MR Elastography...

Background Photon-counting CT (PCCT) can theoretically be used to quantify extracellular volume fraction (ECV) for liver fibrosis assessment, but its performance remains unclear. Purpose To determine the feasibility of PCCT-derived ECV for staging liver fibrosis by assessing its correlation with MR elastography-derived liver stiffness measurement (LSM) and comparing their diagnostic performance, using histopathologic findings as the reference standard. Materials and Methods Between July 2024 and July 2025, 157 participants with suspected hepatic malignancies were prospectively enrolled and underwent PCCT and MRI at Ruijin Hospital. Intraparticipant comparisons of ECV and LSM were performed, and their diagnostic performance in staging liver fibrosis was evaluated using histopathologic findings as the reference standard. Subgroup analyses of fibrosis staging using ECV were performed among participants with coexisting steatosis or inflammation and participants with a body mass index of 25 or higher. Correlation, receiver operating characteristic, and equivalence analyses were performed. Results Ultimately, 139 participants (mean age, 62 years ± 8 [SD]; 114 male) were included. ECV was strongly correlated with LSM (Spearman ρ = 0.84; P < .001) in an intraparticipant-level comparison. When histopathologic examination was used as the reference standard, the area under the receiver operating characteristic curve (AUC) values for ECV were 0.99 (95% CI: 0.98, 1.00), 0.98 (95% CI: 0.96, 1.00), and 0.98 (95% CI: 0.96, 1.00) for participants with fibrosis stages F2 or higher, F3 or higher, and F4, respectively. Equivalence analysis revealed comparable diagnostic performance between ECV and LSM (95% CI differences in AUCs: 0.005, 0.055 for stage F2 or higher; -0.015, 0.027 for stage F3 or higher; and -0.021, 0.012 for stage F4). With use of the cutoffs derived from the whole-group analysis, ECV showed excellent agreement with histopathologic stage overall and across each subgroup (all weighted κ coefficients ≥0.86; P < .001 for all). Conclusion PCCT-derived ECV was strongly correlated with MR elastography-derived LSM and showed equivalent, clinically feasible performance for liver fibrosis staging. © RSNA, 2026 Supplemental material is available for this article. See also the editorial by Wu and Shi in this issue.