<title>Development of fiber optic laser Doppler velocimeter for measurement of local blood velocity</title>

Abstract

In order to measure the local velocity field in opaque fluid flows like blood flow, a new laser Doppler velocimeter having a pickup consisting of a small distributed index lens attached at the tips of two fibers which are joined side by side in parallel has been newly developed. The distributed index lens is in the shape of a truncated cone. The flow field around this sensor has been measured very precisely by means of an ordinary LDV. The effect of turbidity of fluid on the quality of the laser Doppler signal from this sensor has been examined by experiments. As a result, it has been shown that this LDV sensor has a high signal-to-noise ratio, and that the disturbance against flow by the sensor is very small, and it is very promising as a velocity sensor for opaque or semi-opaque fluid flow like blood flow.

Development of Miniaturized Fiber-Optic Laser Doppler Velocimetry Sensor for Measurement of Local Blood Velocity (Fabrication Method for Convex or Concave Lens-Like Fiber Tip and the Characteristics of Sensor Optical System)

“…6. This result indicates that the dominant factor contributing to the chemical etching of the fiber is hydrogen fluoride as shown in the following equations, and that ammonium fluoride suppresses and controls the effect of hydrogen fluoride in GeO 2 where X is either Si or Ge.…”

“…The focal point of the light path approached to the fiber tip with increase in the etching duration time. From the results of the previous study [5], it was clarified that the measuring volume must be located within a distance of 300 µm from the tip of the probe because of absorption and multiple scattering by erythrocytes in blood. On the other hand, a too short focal length causes an inaccuracy of measuring velocity due to the effect of the stagnation region of the fiber-optic probe itself.…”

“…Hence, these results indicated that etching duration time during 3 to 4 hours seems to be most appropriate in blood velocity measurement. The measuring volume, which is formed in water by the convex lens-like tip etched for 3 hours, is estimated under the Gaussian beam assumption [5] by using the focal length obtained from Fig. 7, the wavelength of the light source (He-Ne laser : wavelength λ =632.8nm and LD : wavelength λ =830nm), and the beam diameter, assumed the same as the core of the optical fiber as shown in Table 1 and Fig.…”

“…In order to receive the scattered light of high intensity, a fiber-optic LDV probe having a truncated cone-shaped distributed index lens (DIL) of which the diameter was 1 mm was developed. The emitted light from a fiber tip with a DIL was converged at a focal point, where the measuring volume was formed and the scattered light intensity was increased [2][3]. Although this fiber-optic LDV sensor with a DIL could measure the flow velocity in semi-opaque and opaque fluids such suspension of white pigment, it was not able to be used as a sensor for local blood velocity measurement.…”

Development of a Miniaturized Fiber-optic LDV Sensor for Local Blood Velocity Measurement

“…Therefore, the fringe-mode LDV cannot be used as a diagnostic device for blood flow velocity measurements. A fiber-optic LDV sensor has been developed as an alternative laser sensor that uses the LDV method [1][2][3][4]. Although this sensing method requires the sensor head to be inserted directly into the blood vessel, the associated risk is very low, because the optical fiber, as a sensor head, owing to its small diameter of 125 μm, can be easily and safely inserted into vessels for clinical use by using a catheter or a needle.…”