Quantifying Skin Sodium Concentration With Novel Very Rapid Biexponential T₂ Relaxometry and Signal Loss Compensation...

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biophysics
• Medical Imaging

Background:

• Accurate measurement of skin tissue sodium concentration (TSC) is crucial for understanding physiological processes and diagnosing conditions.
• Existing ²³Na MRI methods face challenges in accurately quantifying TSC due to factors like blood sodium and complex relaxation properties.
• Development of advanced relaxometry techniques is needed to overcome these limitations.

Purpose of the Study:

• To develop and validate a novel spin-3/2 relaxometry methodology for precise measurement of skin tissue sodium concentration (TSC).
• To simultaneously account for confounding factors such as blood sodium concentration and magnetic field inhomogeneity (B₁).
• To improve the accuracy and reliability of ²³Na MRI for skin sodium quantification.

Main Methods:

• A new spin-3/2 relaxometry method was employed, utilizing a multi-scan approach with varying radiofrequency (RF) pulse durations and flip angles.
• The methodology disentangles and simultaneously fits skin fast (T_2f) and slow (T_2s) T₂ relaxation times, relative B₁, and blood sodium fraction.
• Image compensation was performed using simulated M_xy data derived from fitted parameters to attain accurate skin sodium concentration.

Main Results:

• The developed methodology successfully measured skin T_2f (0.10 ± 0.03 ms), T_2s (13.7 ± 1.5 ms), and blood sodium fraction (0.08 ± 0.05).
• The study achieved a mean skin tissue sodium concentration (TSC) of 90 ± 8 mM, showing no correlation with age or sex.
• A positive correlation was observed between blood sodium fraction and participant age.

Conclusions:

• This study presents the first skin TSC measurements validated against atomic absorption spectroscopy, demonstrating high accuracy.
• The findings highlight the significant impact of blood sodium on ²³Na MRI of skin and other fluid spaces.
• The developed spin-3/2 relaxometry method offers a robust approach for accurate skin sodium quantification in MRI.