Tendon displacement assessment by pulsed Doppler tissue imaging: validation with a reciprocating string test target

After hand trauma and surgery, assessment of tendon excursion is important in reconstructive surgery and rehabilitation. Aimed as a more reliable alternative to traditional noninvasive methods, a colour Doppler imaging scanner was adapted to measure longitudinal tendon displacement. Displacement was quantified by integrating the velocity estimated from the zero-crossing rate of the Doppler signal. The system was tested by measuring displaced distances of a rubber string that was moved back and forth. At a determined optimal receiver gain, 1.5-cm string displacements were measured with less than +/- 0.05-cm bias throughout an echo-signal dynamic range of 22 dB; standard deviations were around 0.05 cm. Regression analysis between measured and true displacements in the range 0.5-2.5 cm resulted in a best fit straight line with slope 0.927, intercept 0.041 cm and residual standard error of 0.06 cm. A transfer technique was conceived to ensure accuracy when measuring tendons in the body. This CDI-based pulsed Doppler system merits verification for measurement of tendon excursion in patients.