Development of Miniaturized Fiber-Optic Laser Doppler Velocimetry Sensor for Measurement of Local Blood Velocity (Measurement of Human Whole Blood Velocity in Modeled Blood Vessel Using Fiber-Optic Sensor Having Convex Lens-like Tip)

Abstract

In order to measure local blood velocity in artery and vein, a miniaturized fiber-optic LDV sensor has been newly developed. In the present fiber-optic sensor, laser beam emitted from the fiber tip can be focused at any position from about 0.1 to 0.5 mm distant from the fiber tip, and moreover a stray light or an unfavorable reflected light inside the light transmission system is remarkably decreased. Consequently the present sensor has a sufficiently high signal-to-noise ratio, and is capable of measuring the local velocity in almost all semi-opaque and opaque fluids including blood. The sensor head, i.e. the optical fiber is incorporated into either a injection needle or a catheter tube. In the former case, it is inserted inclinatorily from the wall into the vessel, and is made a tilted scan across the vessel to measure a velocity distribution. In the latter case, it is kept parallel to the flow in the vessel. In all the flows of whole human blood, whole caprine blood and a RC-MAP (red cell / Mannitol-Adenine-Phosphate) of bovine, of which hematocrit is 69%, the volocity distribution across the vessel can be very accurately measured. The insertion angle of the fiber to the flow has a significant effect on the measurement accuracy, and the appropriate angle is about 100 degree in the injection needle type. In the catheter type, the insertion direction adverse to the flow is better than that parallel to the flow because of an effect of wake behind the fiber tip. The influence of light source, i.e. a He-Ne gas laser and a He-Ne laser diode on the measurement accuracy is small.