Quasi-Steady-State Equilibrium CEST Reconstruction Improves T₁-Normalized Apparent Exchange-Dependent Relaxation...

This study evaluates quasi-steady-state (QUASS) equilibrium CEST reconstruction for improving T₁-normalized apparent exchange-dependent relaxation (AREX) analysis in quantitative CEST MRI, aiming to reduce confounding T₁ contributions in brain tumor imaging at a clinical 3T scanner. Two- and five-pool CEST effects were simulated using Bloch-McConnell modeling in MATLAB. Phantom and in vivo imaging were performed on a 3T MRI system. Phantom experiments used MnCl₂ doping to vary T₁ relaxation times, and in vivo data were acquired from three healthy volunteers and one brain tumor patient. CESTR and AREX metrics, with and without QUASS correction, were evaluated using linear regression models to assess T₁ dependence. In phantoms, conventional AREX showed a significant T₁ dependence (slope = -0.75, p = 0.014), whereas QUASS-corrected AREX showed no significant dependence on T₁ (slope = 0.18, p = 0.16). Analysis of covariance confirmed that T₁ dependence differed between the two approaches (p = 0.0018). In vivo, QUASS correction reduced acquisition-dependent variability and stabilized AREX contrast across regions with substantially different T₁ values. QUASS reconstruction effectively mitigates confounding T₁ effects in CEST measurements, improving the robustness of AREX-based quantitative CEST analysis and supporting its use in clinical CEST MRI applications.