Glenn J. Richards

Kingston University

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J. D. Briers

Kingston University

Xiao Wei He

Kingston University

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Kingston University

Kingston College

Hutt Hospital

University of Duisburg-Essen

GNS Science

Imperial College London

PerkinElmer (United States)

Pilkington (United Kingdom)

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Capillary Blood Flow Monitoring Using Laser Speckle Contrast Analysis (LASCA)

Journal of Biomedical Optics (1999)

J. D. Briers Glenn J. Richards Xiao Wei He

Coherent light scattered from an ensemble of moving scatterers produces a time-varying speckle pattern. The intensity fluctuations observed in a single speckle can be regarded either as a time-varying interference effect or as a Doppler beating effect. Techniques based on each of these approaches have been developed to analyze the fluctuations in an attempt to measure the velocities of the scatterers. Most of these methods measure the temporal statistics of the intensity fluctuations in a single speckle, i.e., at a single point. If a map of the velocity distribution is required, some form of scanning must be introduced. One way of avoiding the need to scan is to make use of the spatial statistics of time-integrated speckle. This is the basis of a technique, already described in the literature, called laser speckle contrast analysis (LASCA). In this article, we present a brief review of the theory linking the intensity fluctuations to the velocity and of the various techniques that have been proposed to measure them. We then describe the present configuration of our LASCA technique and describe some recent developments in our search for a real-time, noninvasive, full-field technique for visualizing capillary blood flow. © 1999 Society of Photo-Optical Instrumentation Engineers.

Instrumentation

10.1117/1.429903

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<title>Capillary-blood-flow monitoring using laser speckle contrast analysis (LASCA): improving the dynamic range</title>

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (1997)

Glenn J. Richards J. D. Briers

We have developed a technique, called laser speckle contrast analysis (LASCA), to monitor capillary blood flow. Like the earlier method 'single-exposure speckle photography' it uses the phenomenon of time-varying speckle, drawing on models that relate the statistics of the speckle pattern, especially the contrast, to the velocity of the scatterers. Temporal variations in the pattern blur the captured image, whether photographic or digital, reducing the contrast. LASCA is a fully-digitized, full-field, non-invasive technique and operates in quasi-real-time: it grabs an image and then produces a 2-dimensional map of contrast variations representing differing velocities. Previously the data had been stretched, as a full range of contrasts could not be achieved. This problem has been addressed and we believe solved, thus giving us a full range of contrasts. In this paper we look at the effects of changing the exposure time. If it is varied it should be possible, according to the models used, to look at different ranges of velocity. Also we hope to show that by using different wavelengths together it is possible to distinguish between flow at different depths in the skin. We illustrate the validity of our technique with some of our results and then compare these to other methods of measuring capillary blood flow.

10.1117/12.274304

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<title>Laser speckle contrast analysis (LASCA) for flow measurement</title>

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (1997)

J. D. Briers Glenn J. Richards

Laser light, when scattered from a moving object or fluid, fluctuates in intensity. These fluctuations can yield information about the velocity of the scatterers involved. Most techniques analyze the temporal fluctuations of a single speckle. For information on the spatial distribution of velocities, some form of scanning is necessary. Exceptions include speckle photography and particle image velocimetry, which are full-field, double-exposure methods for measuring lateral velocities and flow. Another full- field technique, laser speckle contrast analyses, has the additional advantages of being a relatively cheap, single- exposure technique operating in quasi-real time and sensitive to both lateral and line-of-sight motion. LASCA was originally developed to monitor blood flow, but these advantages should also be useful in industrial flow measurement.

Velocimetry

10.1117/12.281163

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Laser speckle contrast analysis (LASCA): a technique for measuring capillary blood flow using the first order statistics of laser speckle patterns

Glenn J. Richards J. D. Briers

Deals with LASCA or laser speckle contrast analysis. This is a non-invasive, non-scanning technique that produces 2-dimensional velocity maps of blood flow in capillaries. The method is based on the use of the first order statistics, specifically the contrast of time-varying laser speckle. A brief introduction to the theory and practicalities of the method is given. Along with some improvements to the initial system and preliminary results which were obtained. (6 pages)

10.1049/ic:19970687

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Citations (21)