Restricted Spectrum Imaging for Diagnosis of High‐Risk Metabolic Dysfunction‐Associated Steatohepatitis

ABSTRACT Background Conventional diffusion MRI inadequately characterizes heterogeneous microstructural changes in metabolic dysfunction‐associated steatotic liver disease (MASLD). The optimal restricted spectrum imaging (RSI) model and value for high‐risk metabolic dysfunction‐associated steatohepatitis (MASH) remain unclear. Purpose To optimize RSI modeling and evaluate its performance for high‐risk MASH. Study Type Prospective cross‐sectional study. Population 96 biopsy‐proven MASLD participants (median age, 46 years [IQR: 36–58]; 51 women [53.1%]), including 64 with high‐risk MASH. Field Strength/Sequence 3T; fat‐suppressed single‐shot echo‐planar imaging with multi‐ b ‐value diffusion‐weighted imaging, EPI‐based MR elastography, and 3D chemical shift‐encoded proton density fat‐fraction imaging. Assessment Two‐ to five‐compartment RSI models were compared using Bayesian information criterion (BIC). RSI fractions, apparent diffusion coefficient, FIB‐4, and MRI‐based MASH score (MAST) were evaluated against histopathologic features and high‐risk MASH. Statistical Tests Spearman correlation, Mann–Whitney U test, logistic regression, receiver operating characteristic analysis, DeLong test, bootstrap internal validation, decision curve analysis (thresholds, 0.20–0.60), and intraclass correlation coefficient (ICC). p   Results The five‐compartment model showed the lowest BIC (1472.30; ΔBIC = 0). RSI measurements showed excellent inter‐observer agreement (ICC, 0.955–0.994). RSI‐C1 ( r  = 0.357) and RSI‐C2 ( r  = 0.283) significantly correlated with steatosis; RSI‐C2 ( r  = 0.273) and RSI‐C5 ( r  = 0.282) with inflammation; and RSI‐C2 ( r  = 0.326), RSI‐C4 ( r  = 0.400), and RSI‐C5 ( r  = 0.386) with fibrosis (all p  p  = 0.219) or MAST (AUC = 0.899; p  = 0.146). Across thresholds of 0.20–0.60, RSI mean net benefit (0.504) exceeded FIB‐4 (0.438) but not MAST (0.559). Data Conclusion RSI provides compartment‐specific microstructural biomarkers associated with MASLD histology and may complement noninvasive tools for high‐risk MASH assessment. Evidence Level 2. Technical Efficacy Stage 2.