Real-time contrast-enhanced ultrasound for the assessment of perfusion dynamics in skeletal muscle.

We developed a real-time low-MI contrast-enhanced ultrasound method (CEUS), compared it with venous occlusion plethysmography (VOP) and evaluated its robustness in the quantification of skeletal muscle perfusion during exercise. Contrast pulse sequencing (7 MHz) during continuous intravenous infusion of SonoVue (4.8 mL/300 s) was used repeatedly in eight healthy volunteers to monitor changes of the muscle perfusion before, during and after isometric exercises (10 to 50% of individual maximum strength for 20 to 30 s) of the gastrocnemius muscle in real time. CEUS was correlated with VOP at different time points, and the exactness of several CEUS parameters obtained from ultrasound-signal-intensity-time curves was evaluated. Real-time CEUS depicted a large variability of the skeletal muscle blood volume at rest (mean, 3.48; range, 0.60 to 9.92 [approximately mL]), with a significant reproducibility (r=0.72, p<0.05) and correlation with VOP (r=0.59, p<0.001). Mean blood volume during exercise was 1.58(approximately mL), increased to a mean maximum after exercise of 8.88 (approximately mL), the mean change of the local blood volume during and directly after the exercise was -0.10 and +1.57(approximately mL/s). The average CEUS signal during exercise decreased (mean area under the curve, -50.4 [approximately mL.s]) and subsequently increased post exercise (mean 118.6 [approximately mL.s]). CEUS parameters could be calculated with mean relative errors between 6 and 36%. Continuous assessment of local muscle microcirculation during exercise is possible with real-time CEUS with an acceptable robustness. Its application may be of particular interest in a better understanding of the role of perfusion during muscle training, and the monitoring of pathological vascular response, such as in diabetic microvessel diseases.