Setup of freehand three-dimensional ultrasound to measure semitendinosus (ST) muscle morphology.

<p>Subjects were positioned on an examination bed on their left side, with the hip of the measured (right) leg at 70° flexion. At knee angles corresponding to a knee moment of 0 and 4 Nm and at a knee angle of 65°, a 30–40 seconds video sequence of transverse US images was collected by a conventional 2D ultrasound apparatus, starting distally at the ST tendon to the ischial tuberosity (white arrow on the thigh indicates scan direction). The position of each ultrasound image in space was recorded by tracking the ultrasound probe (based on three markers that were rigidly attached to it—indicated by markers probe) using a motion capture system (tracking device). The images from the ultrasound video sequence were combined with the probe position data an reconstructed to a voxel array that was used for further analysis.