Imaging the microcirculatory proton fraction of muscle with diffusion-weighted echo-planar imaging.

RATIONALE AND
OBJECTIVES: The diagnosis of exertional compartment syndrome is challenging. In this feasibility study, diffusion-weighted echo-planar magnetic resonance imaging was performed in human subjects to determine whether alterations in the circulating blood volume of muscle secondary to exercise or changes in compartment pressure could be visualized.
MATERIALS AND METHODS: The calf muscles of six subjects were studied before and after exercise and also during the application of external pressure to the calf. Gated, single-shot, diffusion-weighted echo-planar imaging (1.5 T) was implemented with signal averaging. Parametric images of the "perfusion" fraction (f) were generated, and regions of interest from anatomic compartments were analyzed. The precision of f was estimated by using propagation of error analysis.
RESULTS: Parametric images depicted visible increases in the microcirculatory proton fraction (f) of calf muscle after exercise (mean change, +0.016) and visible decreases in f on the application of 40 mm Hg to the calf after exercise (mean change, -0.023). Mean changes in f were only significantly different from zero for the group, however, under conditions of applied pressure to the calf after exercise. Changes in f were not significantly different across muscle compartments. The error variance in f was approximately 0.01.
CONCLUSION: Parametric images of f generated by diffusion-weighted echo-planar imaging may depict alterations in the circulating blood volume of muscle induced by exercise and changes in compartment pressure. The inherent imprecision of this technique, however, appears to limit its clinical utility.