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

Abstract

Abstract-A novel, less invasive, miniaturized fiber-optic laser Doppler velocimetry (LDV) sensor, which can be directly inserted into a blood vessel was developed for clinical use in measurements of local blood velocity. A convex lens-like surface was formed by a chemical etching on the fiber's tip that had a core diameter of 50 μm. A laser beam that was emitted from the fiber's tip was focused and formed the measuring volume. This fiber sensor was inserted at an insertion angle of 60° through an injection needle, into the flow duct of an acrylic pipe in which highly concentrated fluid, such as whole blood, was flowing in a pulsatile manner. The flow was modeled after human middle cerebral arterial flow. In this study, the local flow velocity and velocity profile across the duct were measured in the pulsatile flow of a dense suspension of a white pigment. The results were compared both with the results obtained using a fringe-mode LDV and with the results that were calculated on the basis of Womersley's oscillatory flow theory. Consequently, it was found that the local velocity and its profile in the pulsatile flow can be successfully measured using the present fiber-optic LDV sensor, which proved the capability of the sensor as a diagnostic device.

Fibre optic intravascular measurements of blood flow: A review

“…Tajikawa et al [121] used a convex lens tip at the distal end to mitigate reflections in the fibre tip. Kohri et al [122] also used chemical etching to make a miniaturised fibre optic LDV system that they used for local velocity measurement of pulsatile human blood flow. Mito et al [120], Kajiya et al [116] and Ohba et al [123] developed a dual fibre catheterbased system that used one fibre to introduce laser light into the blood stream, and another fibre to detect the backscattered light [124], with the aim of making more accurate measurements in disturbed flows than was possible with a single fibre.…”

“…Several challenges with LDV have been identified. First, laser light is prominently absorbed by blood, particularly with visible wavelengths, which significantly limits the sample volume [122]. Second, the systems can be sensitive to the confounding factors such as temperature and pressure [125].…”