Abstract
A miniaturized fiber-optic laser Doppler velocimetry sensor has been developed to measure the local blood velocity in vivo. The laser beam emitted from the sensor tip can be focused at any distance between 0.1 and 0.5 mm from the tip. Consequently, the sensor has a sufficiently high signal-to-noise ratio to measure the local velocity in almost any opaque fluid, including blood. The sensor head is inserted in an injection needle or a catheter tube. In the former case, it is inserted at an angle to the wall of a vessel and is scanned across the vessel to measure the velocity distribution. In the latter case, it is aligned parallel with the flow in a vessel. For all flows of whole human blood, whole caprine blood, and 69% hematocrit of bovine blood, the velocity distribution across the vessel could be measured very accurately. The insertion angle of the fiber into the flow significantly affects the measurement accuracy; an angle of about 50° is suitable when an injection needle is used. When a catheter is employed, an insertion direction opposite to the flow direction is better than parallel to the flow due to the generation of a wake behind the fiber.
Highlights
Tanaka and Benedek [1] first developed a fiber-optic laser Doppler velocimetry (LDV) sensor
To reduce the flow disturbance caused by the probe and to improve the quality of the Doppler signal obtained by heterodyne interferometry, we have been developing a minimized fiber-optic LDV probe with a convex lens at the fiber tip fabricated by microelectromechanical systems technology [6]
Bovine blood 0.4 L/min 0.6 L/min (c) Influence of hematocrit in which we measured the optical transmittance of whole bovine blood, we found that light with wavelengths of 830 and 632.8 nm from a normal-cut fiber tip decayed in intensity to 13.5 and 2.5%, respectively, at a distance of L = 220 nm from the fiber tip [8]
Summary
Tanaka and Benedek [1] first developed a fiber-optic laser Doppler velocimetry (LDV) sensor. It was difficult to observe the dominant frequency in the spectrum of the signal as a function of the Doppler frequency shift. This technique has yet to be applied in diagnosis devices. The flow field is disturbed when the sensor head is directly inserted into the working fluid and the signal-to-noise ratio of the Doppler signal is low due to strong reflection at the interface between the fiber tip and the distributed index lens. To reduce the flow disturbance caused by the probe and to improve the quality of the Doppler signal obtained by heterodyne interferometry, we have been developing a minimized fiber-optic LDV probe with a convex lens at the fiber tip fabricated by microelectromechanical systems technology [6]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
