Ultrasound has been used to research mechanical properties of human muscle-tendon units since the early 1990s, providing real-time dynamic images. It has been used extensively to measure changes in length and strain of human muscles and tendons.

Typically these studies involve measuring the length of muscle fascicles and tendons at a large number of joint angles and levels of muscle contraction. Commercially available systems now provide high resolution images, but typically have fields of view of less than 60 mm, yet it is desirable to have a field of view greater than 100 mm. Current methods of accumulating wide field of view images preclude real-time assessment.

We describe a system that overcomes these limitations. The system comprises two portable ultrasound systems whose transducers are held together in a mould. The video signals from the two systems are digitally sampled in real time with a dual-channel video capture card and saved in compressed format. Custom-written software (Matlab) is used to “stitch” the two video images together. Matlab video processing routines are used to automatically track regions of interest in muscle fascicles and tendons.

This simple and relatively inexpensive system can be used to obtain high frequency (up to 13 MHz), wide field of view (116 mm), dynamic images of human muscles in real-time. It is currently being used to investigate whether contractures in calf muscles of people with stroke, spinal cord injury and multiple sclerosis are due primarily to changes in the properties of muscle fascicles or tendons.