Pulsed laser Doppler flowmetry for increased signal to noise ratio and probed depth

In laser Doppler flowmetry (LDF) deep perfusion measurements can be realized by using a large separation between the fibers used for illumination and detection. In order to achieve a sufficient signal-to-noise ratio, the power of the laser light can be increased, but only to the limit indicated by the safety regulations. In this paper, pulsed laser Doppler flowmetry (pLDF) is presented as a manner to increase the SNR without exceeding the safety limits. The method is based on the principle that light is needed only when the signal is being sampled. The setup is presented, and we will show results that indicate that equivalent results are obtained for a pulsed and continuous wave setup (cwLDF), however with a much smaller tissue exposure. Furthermore, the limits encountered in realizing a pulsed system will be discussed.