Multipoint Laser Doppler Research Articles

Blood flow velocity imaging of malignant melanoma by micro multipoint laser Doppler velocimetry

We have developed a laser Doppler velocimeter to measure blood flow, the micromultipoint laser Doppler velocimeter (μ-MLDV). This equipment can measure absolute velocity and, based on this, can display the course of blood vessels. In this study, we attempted to perform blood flow velocity imaging of malignant melanoma transplanted to the mouse ear. We found that blood flow velocity of the formed blood vessels originating in the melanoma was much greater than that of the capillary vessels in normal skin. Furthermore, the form of the tumor was clearly visible from the blood flow velocity image. These experimental results suggest that μ-MLDV has potential as a diagnostic method for distinguishing benign nevi from malignant melanomas.

Research on multipoint layer-type laser Doppler self-velocimeter

An idea of using a multipoint layer-type laser Doppler self-velocimeter (LDV) to offer velocity for the vehicle navigation system was proposed because the accelerometer had the error term generated by overload. The principle of measuring its own velocity with laser Doppler was expounded while a multipoint layer-type LDV was designed, and the Doppler signal was processed by the technique of tracking filter and digital autocorrelation. The result of theory and experiment showed that the multipoint layer-type dual-beam LDV system was suitable for measuring on rough road surfaces when the individual dual-beam LDV was in the status of out of focus. Low-frequency disturbance and some noises were eliminated by the tracking filter, and the residual noise was removed by digital autocorrelator so that the signal-to-noise ratio and the detection sensibility of the system was greatly improved. Comparing to the global position system, the relative accuracy of LDV is ~1.95%.

Multi-point differential laser doppler velocimeter using arrayed waveguide gratings with small wavelength sensitivity

A multi-point laser Doppler velocimeter (LDV) using the arrayed waveguide gratings (AWGs) with small wavelength sensitivity (less than 1/10 of that for a conventional LDV without the AWGs) is proposed, in which velocities at different points in the depth direction can be simultaneously measured with compact optical systems. The design and characteristics of the proposed LDV are investigated with the model using the grating equation of the AWGs. From our simulation results, the wavelength sensitivity for multiple measured points can be reduced to less than 1/10 of that for a conventional LDV without an AWG.

Three-dimensional imaging techniques for microvessels using multipoint laser Doppler velocimeter

We have succeeded in measuring the blood flow velocity in microvessels noninvasively, using an advanced multipoint laser Doppler velocimeter (M-LDV). We developed the M-LDV using a semiconductor laser with a wavelength of 785 nm and were able to improve the measurement of opaque fluids, including blood. Initially, the calibration of our equipment was checked by measuring the flow velocity of water in the glass tube with an inner diameter of 0.55 mm. These values were equal to that calculated from the indicated values of a flowmeter and succeeded in imaging the flow velocity distribution in the glass tube as two-dimensional images. Finally, we enlarged the optical magnification, and measured microvessels of an experimental mouse’s ear, and succeeded in imaging the blood flow velocity in microvessels as three-dimensional images. Compared with our previous report [T. Andoh et al., Jpn. J. Appl. Phys., Part 1 48, 017002 (2009)], the spatial resolution was improved by more than a factor of 10.

High-Resolution In vivo Three-Dimensional Mapping of Blood Flow and Blood Vessels Using Advanced Multipoint Laser Doppler Velocimeter

An in vivo three-dimensional (3D) mapping of blood flow and blood vessels was carried out using an advanced multipoint laser Doppler velocimeter (LDV). We developed a multipoint LDV system for the simultaneous measurement of data in transparent fluids. The multipoint LDV was constructed in order to apply linear measurement techniques to a series of single points. We developed an advanced multipoint LDV using a semiconductor laser with a wavelength of 785 nm, and were able to improve the measurement of opaque fluids, such as blood. An advanced multipoint LDV can enable the high-resolution in vivo 3D mapping of blood flow, particularly in small arterioles and venules, by scanning. An experiment was carried out using a mouse owing to the relative ease in visually verifying arterial and veinous patterns on the ear of this animal. Then a 3D mapping of the microcirculation was achieved through a spatial scan of the measurement area. The in vivo 3D mapping results roughly correlate with the front and rear pictures of the mouse's ear.

Multi-point laser Doppler velocimeter

This paper describes a novel multi-point laser Doppler velocimeter. By employing two acousto-optic modulators (AOMs) for both beam splitting and frequency shifting, we have demonstrated that multiple measuring volumes can be formed by intersecting the multiple diffraction orders generated by the AOMs. Each measuring volume has its frequency shift, which acts as a carrier frequency to that channel. Since the signals from different channels are multiplexed in the frequency domain, only a single photo-detector and a single-channel signal processor are necessary for multi-point measurements. The system has been demonstrated by making multi-point velocity measurements on a rotating disk.

Two-point laser Doppler velocimetry measurements in a Mach 1.2 cold supersonic jet for statistical aeroacoustic source model

Single and multi-point laser Doppler velocimetry measurements performed in a cold Mach 1.2 jet flow are used to assess those properties of the aerodynamic field most relevant in the generation of turbulence mixing noise. Single point measurements yield mean velocity profiles, turbulence intensity profiles and power spectral densities of both the velocity and Reynolds stress fields at seven axial stations between the jet exit and the end of the potential core. The longitudinal components of the second-order and fourth-order two-point velocity correlation tensor are obtained from a series of multi-point LDV measurements, whence a cartography of integral space and time scales, convection velocities and acoustic compactness is effected. These results are used to examine differences between subsonic and supersonic jet aerodynamics in terms of their sound generating potential. Finally analytical expressions are proposed for the spatial and temporal parts of the longitudinal correlation coefficient function. These are scaled using the integral space and time scales of the velocity and Reynolds stress fields, and excellent agreement is found with experimentally determined functions.

Instability of diffusion flames

The constant frequency oscillation of buoyant jet diffusion flames is a phenomenon that has been studied extensively during the past three decades. In recent experimental and theoretical works, the coherent flow field and flame structures were analyzed successfully. However, the inception of the wave-like flow structures, which result in coherent vortices further downstream, remained not fully understood. In a methane jet diffusion flame, we studied the flow field instability with multipoint laser Doppler velocimetry (LDV) and a linear stability analysis. The LDV experiments yielded information on the frequency, phase velocity, and location of inception of the instability waves. The influence of exit velocities of both methane and the coflowing oxidizer (air or pure oxygen) was examined. A linear stability analysis was conducted to study the role of density variations across the flame front. It is evident that absolute instability of the flow field close to the burner rim causes the constant frequency oscillation of the buoyant diffusion flame. Selfexcited, axisymmetric wave-like structures propagate up-and downstream of this location

The feasibility of fast single-bit sampling for multi-point laser Doppler anemometry

Consideration is given to a number of aspects concerning the design and implementation of a simultaneous multi-point laser Doppler anemometry (LDA) system. The difficulties of data collection and processing for many channels is seen to be the principle limiting factor to system development, and a practical route making use of highspeed components for fast LDA signal sampling and storage, followed by fast Fourier transform (FFT) signal analysis in software is explored. A demonstration system is constructed consisting of ten optical channels arranged in a linear array, a single LDA sampling card and a controlling microcomputer, and the arrangement is applied to a closed water circuit. Received signals are compared with software-generated equivalents and the effect of various signal-to-noise ratios on the accuracy of a reconstructed velocity distribution is examined. The overall configuration is shown to provide a modular approach enabling a piecewise increase in the number of processing channels according to requirements.

Automatic Scanner for Multi-Point Laser Doppler Flux Recordings on Human Skin

A computer-driven device is described which moves the probes of a laser Doppler flowmeter linearly back and forth over the skin and stops precisely at preselected points to measure capillary perfusion. It offers extended possibilities to record the spatio-temporal flux changes in response to a local stimulus (e.g. injection of a vasoactive substance).