Self-mixing feedback in a laser diode for intra-arterial optical blood velocimetry

Intra-arterial measurements of the velocity and the average flow of red-blo od cells were investigated by means of a fiber-coupled laser Doppler veloci meter based on the self-mixing effect. The velocity of the red cells was ca lculated from the frequency of the signal that occurs when light, scattered back from a moving object in front of a fiber into a laser-diode cavity, i nterferes with the laser cavity's proper mode. These fluctuations occur at the Doppler frequency. The signal was obtained from the photodiode that is present in the laser diode's housing. Temperature control and stabilization of the diode cavity were introduced to reduce the light-intensity fluctuat ion that is due to mode hopping of the diode. The velocimeter was calibrate d with a rotating disk covered with white paper (nonlinearity of 2.6% for v elocities up to 0.4 m/s) and tested in vitro as a fluid velocimeter. The ve locimeter was used in in vivo tests on the iliac artery of a 35-kg pig and on the arteria pulmonaris of a healthy calf. The optical fiber was placed i n the iliac artery by a basket catheter 4 cm proximal to the bifurcation of the femoral artery. The average arterial blood flow velocity of the red ce lls were measured upstream and downstream. A special cleaving procedure for the fiber tip in downstream measurement is reported. Blood-velocity measur ement is compared with values generated by an ultrasound flowmeter, and a d ifference of less than 9% is found. (C) 2001 Optical Society of America.