Development of Miniaturized Fiber-Optic Laser Doppler Velocimetry Sensor for Measuring Local Blood Velocity: Measurement of Whole Blood Velocity in Model Blood Vessel Using a Fiber-Optic Sensor with a Convex Lens-Like Tip

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.

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

“…White pigments of titanium dioxide (TURNER COLOUR WORKS LTD), of 2 μm in diameter, and of calcium oxide, of 3μm in diameter, were used as the scattering particles instead of erythrocytes. In the previous study [6], measurements of blood velocity yielded a higher signal to noise ratio as compared to the measurements for the suspension in which the concentration of white pigment was 20 g/L. Fig.…”

“…The composition rate and etching time were HF: NH 4 F: H 2 O= 0.2:1.0:0.5 and t etch = 5 hours, respectively. These values were determined using the methods described in previous studies [6,8]. Fig.…”

“…The insertion angle is defined as the angle between the incident laser and flow vectors. From previous studies [6,8], the insertion angle was determined to be θ=60°, for which a Doppler signal with the highest signal to noise ratio was obtained and the error of the insertion angle made a small contribution to the calculation error. …”

“…However, some serious problems remain because light is easily absorbed in the blood, and multiple scattering events can occur due to the high concentration of erythrocytes in blood (human standard hematocrit H ct = 45% which is the percentage of the total volume of blood occupied by blood cells of mainly erythrocytes, leukocytes and platelets). In order to overcome these shortcomings, we have developed herein, a novel and improved fiberoptic LDV sensor, using which we were able to measure the flow velocity of a highly concentrated suspension such as blood [5,6]. This sensor had a convex lens-like surface on its tip, which allowed the emitted light from the sensor to be focused and to form a very small sampling volume at the point where the intensity of the light was highest.…”

Compact system for in situ laser Doppler velocimetry of blood flow

“…Scalise, Steenbergen and Mul [7] reported intra-arterial blood flow velocimetry using self-mixing feedback in a laser diode. The use of a fiber with a convex lens-like tip has been investigated by Tajikawa, Ishihara, Kohri and Ohba [11], but only to measure red cell suspension flow velocity. Influence of the insertion angle was investigated in this work and it was shown that laser Doppler velocimetry was not effective for an angle of 0°corresponding to the fiber pointing in the same direction as the flow.…”