Polyacrylamide Gel Calibration Phantoms for Quantification in Sodium MRI

Area of Science:

• Medical Imaging
• Biophysics

Background:

• Quantitative sodium-23 MRI (²³Na MRI) relies on calibration phantoms for total sodium concentration (TSC) mapping.
• Traditional agarose phantoms present challenges due to inherent instabilities and inconsistencies.
• Standardization and harmonization of ²³Na MRI methods are crucial for reliable clinical applications.

Purpose of the Study:

• To develop and evaluate a novel, standardizable synthetic polymer calibration phantom for quantitative ²³Na MRI.
• To assess the stability and suitability of polyacrylamide gel (PAG) phantoms for in vivo sodium quantification.
• To contribute to the harmonization of quantitative ²³Na MRI techniques.

Main Methods:

• Seven crosslinked polyacrylamide gel (PAG) samples with varying sodium chloride (NaCl) concentrations (10-150 mM) were prepared.
• Sodium concentrations were determined via volumetrics and high-precision mass measurements.
• Relaxation time constants (T1, T2, T2*) and their stability over 14 months were measured at 3T.

Main Results:

• Measured sodium concentrations in PAG phantoms were on average 5% lower than nominal values, leading to apparent TSC (aTSC) quantification.
• Mean relaxation time constants for ²³Na in PAG were within ranges: T1=27-39 ms, T2=4.8-7.1 ms, T2*=16.8-18.8 ms, with a short fraction of 0.64-0.77.
• Relaxation times remained stable within 10% over 14 months for concentrations above 25 mM.
• In vivo aTSC measurements in human brain and calf muscle yielded expected results.

Conclusions:

• Polyacrylamide gel (PAG) phantoms are well-suited for quantitative ²³Na MRI.
• PAG phantoms offer tissue-matched relaxation properties and the advantages of a synthetic material for standardization.
• These synthetic phantoms can improve the reliability and reproducibility of in vivo sodium MRI quantification.