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.