Acute changes in extracellular volume fraction in skeletal muscle monitored by (23)Na NMR spectroscopy

In this article, we induced acute changes in extracellular volume fraction in skeletal muscle tissue and compared the sensitivity of a standard (1)H T(2) imaging method with different (23)Na‐NMR spectroscopy parameters within acquisition times compatible with clinical investigations. First, we analyzed the effect of a short ischemia on the sodium distribution in the skeletal muscle. Then, the lower leg of 21 healthy volunteers was scanned under different vascular filling conditions (vascular draining, filling, and normal condition) expected to modify exclusively the extracellular volume. The first experiment showed no change in the total sodium content during a 15 min ischemia, but the intracellular weighted (23)Na signal slowly decreased. For the second part, significant variations of total sodium content, sodium distribution, and T(1) and [Formula: see text] of (23)Na signal were observed between different vascular filling conditions. The measured sodium distribution correlates significantly with sodium T(1) and with the short and long [Formula: see text] fractions. In contrast, significant changes in the proton T(2)w signal were observed only in three muscles. Altogether, the mean T(2)w signal intensity of all muscles as well as their mean T(2) did not vary significantly with the extracellular volume changes. In conclusion, at the expense of giving up spatial resolution, the proposed (23)Na spectroscopic method proved to be more sensitive than standard (1)H T(2) approach to monitor acute extracellular compartment changes within muscle tissue.