Recipe for Hydrogels With Tunable Relaxation and Diffusion Properties for Use as MRI Test Materials.

Purpose: To develop and evaluate a preparation protocol (recipe) for hydrogels with specific relaxation times and ADC values to be used as tissue-like test materials for MRI experiments at 3 Tesla.

Methods: Gd-DTPA, agarose, and soy lecithin were used as modulators for T1, T2, and ADC. First, systematic measurements were performed to determine the relaxation- and diffusion-modifying properties of the single substances and combinations of them. An algorithm was developed to determine the necessary concentrations of the ingredients to achieve predetermined sets of target values (T1, T2, and ADC). To validate this approach, hydrogels mimicking the relaxation and diffusion properties of different tissues (pancreas, white matter, fibroglandular tissue, liver, prostate) were prepared and evaluated. All measurements (relaxometry, diffusion-weighted imaging) were performed on a 3 Tesla clinical scanner at 20°C.

Results: The proposed method allowed the preparation of hydrogels with specific diffusion and relaxation properties by adjusting the concentrations of Gd-DTPA, agarose, and soy lecithin. Test phantoms containing hydrogels for simulation of various tissue types showed good agreement between targeted and measured properties, with deviations of less than 8% for T1, 7.5% for T2, and 11.5% for ADC. With the present approach, the properties (T1, T2, and ADC) of most known tissue classes could be well approximated; only the gray matter of the brain was slightly outside the selectable range. Temporal stability over 3 months was acceptable.

Conclusion: This work provides a relatively simple, inexpensive, and reproducible method for the preparation of hydrogels with independently adjustable T1, T2, and ADC values at 3 T.