Evaluation of the mechanical properties of active skeletal muscle using acoustic radiation force impulse imaging

Acoustic Radiation Force Impulse (ARFI) imaging is a method for characterizing local variations in tissue mechanical response. In this method, a single ultrasonic transducer array is used to both apply temporally short localized radiation forces within tissue and to track the resulting displacements. Tissue displacement is inversely related to tissue stiffness, and the temporal response of tissue to radiation force varies with tissue type. Utilizing a modified Siemens Elegra scanner with a 75L40 transducer array, ARFI images of bicep muscle were generated in the three authors for four levels of activation (0, 2, 4, and 8 kg). Four ARFI datasets were acquired for each loading condition. Data was acquired in real-time, and processed off-line. Statistically significant differences between the unloaded and loaded cases were found in each of the parameters studied (displacement magnitude, recovery velocity magnitude, and time to peak displacement, p < 0.005). Significant differences were also found between subjects (p < 0.01). These results suggest that ARFI imaging has potential for quantifying variations in tissue stiffness in real-time measurements.