IN-VIVO DOPPLER-SHIFT MEASUREMENTS USING MULTIMODE FIBEROPTIC CATHETERS

A new fiber-optic catheter for in vivo blood-how measurements has been developed. The catheter is designed to measure blood flow in both the forward (toward the catheter tip) and reverse (away from the catheter tip) how directions, It consists of two multimode optical fibers with core diameter of 50 Irm and cladding diameter of 125 mu m. One fiber transmits the laser beam into blood and the other receives the backsca ttered light from the erythrocytes within the probe volume. In the how experiment, it was found that the flow within the boundary layer is i ndeed laminar and, hence, the relationship between the Doppler shift f requencies and the flow velocities is linear, thereby making the linea r calibration possible for predicting the free stream flow velocity. P lots of the maximum shift frequency (frequency at which the Doppler sp ectrum disappeared into the noise spectrum) against the flow velocitie s are found to be more linear in both the forward and reverse how dire ctions than that of the dominant shift frequency (frequency with the h ighest amplitude). These results were reaffirmed by the numerical how simulation along the catheter side wall.