Single-fibre laser Doppler flowmetry

A laser Doppler flowmeter with one optical fibre guiding light to and from the tissue under study has been developed. The outer diameter of the probe equals the optical fibre diameter (0·5 mm). The small size makes it useful for studying the deep tissue perfusion in organs. Differential-channel operation was compared with the single-channel operation and the benefit of this technique was evaluated theoretically as well as in a fluid model resembling tissue perfusion. The signal-to-noise improvement ratio was calculated and found to be related to the number of coherence areas detected and to the broadband noise of the laser. In vivo experiments in the gastrocnemius muscle of the pig were performed to compare the results from the single-fibre technique with those of the electromagnetic flowmeter. Linear regression analysis of femoral blood flow data obtained with the electromagnetic flowmeter and local muscle blood flow measured with the single-fibre technique showed a correlation coefficient of 0·88 (n=36, p<0·001).