Assessment of the interstitial fluid in the subcutaneous tissue of healthy adults using ultrasonography

Objective: Lymphoedema involves swelling, especially in the subcutaneous tissues. For lymphoedema management to be successful, it is necessary to remove the interstitial fluid. Subcutaneous echogenicity may be associated with interstitial fluid, but echogenicity is not an indicator for the evaluation of management because we do not directly compare echogenicity with the interstitial fluid. We aimed to identify an outcome indicator for the evaluation of interstitial fluid using ultrasonography. We assessed the correlation between echogenicity and transverse relaxation rate (R₂) on magnetic resonance imaging. Methods: This was an observational study. Healthy adults with leg swelling after activity for >8 h were recruited. The legs of 13 women were evaluated using ultrasonography, magnetic resonance imaging and measurements of the limb circumference before and after an intervention to reduce the swelling. Results: Echogenicity in the oedema group was greater than that of the controls. Echogenicity decreased with reductions in oedema. The range of the strongest correlations with the changes in R₂ occurred at echogenicity values of 48–144 (Pearson’s correlation coefficient: r = −0.63 and p < 0.01). Thus, it was possible to evaluate the interstitial fluid using echogenicity. Conclusion: The outcome indicators for the evaluation of interstitial fluid using ultrasonography were echogenicities in the range of 48–144, and these values were valid for assessing the interstitial fluid in the subcutaneous tissue.