Design of an In Vivo-Like Phantom for Quantitative Body CEST MRI.

PURPOSE: To design and validate a reproducible in vivo-like fat-containing CEST phantom that enables robust quantitative CEST MRI for body applications by providing physiologically realistic relaxation properties, relevant endogenous CEST contrasts (amide, guanidino, rNOE, and semi-solid MT), and a controlled fat component. METHODS: An agar-based water-fat CEST phantom was designed using agar, gelatin, and bovine serum albumin, with adjustable fat fraction (FF) achieved through stable water-fat emulsions. Phantom composition was tuned to reproduce tissue-relevant T1 and T2 relaxation times and physiological pH. The accuracy and temporal stability of FFs and CEST contrasts were assessed over a 3-month period. Low-power CEST MRI at 7T was performed to quantify amide, guanidino, and rNOE contrasts using the inverse metric MTRRex, and their concentration dependence and temporal stability were evaluated. RESULTS: The proposed phantom-generated Z-spectra closely resembled in vivo body CEST measurements and reproduced major endogenous CEST and semi-solid MT effects with controllable contrast levels. Stable and reproducible FF values were achieved for FFs up to 50% over the investigated 3-month period, covering the clinically relevant range for most body tissues. Quantitative CEST metrics demonstrated linear concentration dependence and good temporal stability. CONCLUSION: An in vivo-like, fat-containing CEST phantom was developed and validated as a reproducible and physiologically relevant reference standard for quantitative body CEST MRI. By enabling controlled investigation of fat-induced effects on CEST contrast quantification, this phantom supports the standardized validation of fat suppression and correction strategies and facilitates methodological development and cross-study comparability in body CEST imaging.