Laser Doppler flowmetry: characteristics of a modified single-fibre technique

Cai, Hongming; Rohman, H.; Larsson, Sven‐Erik; Öberg, Peter

doi:10.1007/bf02637015

Cited by 6 publications

(1 citation statement)

References 14 publications

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“…The calculated relative areas in Figures 3 and 4 show that by increasing the wavelength we can increase the scattering area/volume, since longer wavelengths are less scattered in tissue. 20,21 In Figures 3(a), 3(b), and 3(c) the He-Ne wavelength shows a more spherical scattering image compared to the images produced when using the NIR wavelength.…”

Section: Monitoring Area/volume Versus Wavelengthmentioning

confidence: 93%

Single Fiber Laser-Doppler Flowmetry—Dependence on Wavelength and Tip Optics

1998

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Single fiber, laser-Doppler flowmetry can be used for blood flow measurement in deeply located tissue structures by the insertion of optical fibers into the tissue. The geometry of the monitored volume has been estimated at two different wavelengths and when using two types of fiber tips, one of which has been modified with a lens formed at the fiber end surface. Physical models as well as intramuscular measurements have been used in the experiments. The scattering image was studied in latex solutions of three different scatterer concentrations. The wavelengths 632.8 and 750 nm were used. At higher concentrations of scatterers, the near infrared (NIR) wavelength gave a larger scattering area. At the lower concentration, the difference between the areas was smaller or nonexistent. The NIR wavelength also showed an increased monitoring depth than that of the He-Ne laser in an experimental model study. The properties of the tip optics were evaluated in a flow-through model where the distance between the fiber tips and the flow channel was varied. The flat tip fiber has a sensitivity maximum close to its end surface, whereas the modified fiber ("pear" tip) showed a sensitivity maximum 1.5 mm from the end surface. This property may decrease the influence caused by the insertion trauma in intramuscular measurements. © 1998 Society of Photo-Optical Instrumentation Engineers.

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Section: Monitoring Area/volume Versus Wavelengthmentioning

confidence: 93%

Single Fiber Laser-Doppler Flowmetry—Dependence on Wavelength and Tip Optics

1998

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Laser speckle contrast imaging of the skin: interest in processing the perfusion data

Humeau-Heurtier

Buard²,

Mahé

et al. 2011

Med Biol Eng Comput

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Laser speckle contrast imaging (LSCI) is a recent clinical powerful tool to obtain full-field images of microvascular blood perfusion. The technique relies on laser speckle obtained by the interactions between coherent monochromatic radiations and the tissues under study. From these speckle images, contrast values are determined and instantaneous map of the perfusion are computed. LSCI has gained increased attention in the last years and is now additional to laser Doppler flowmetry (LDF). In spite of the growing interest for LSCI in skin clinical research, very few LSCI perfusion data processing have been published from now to extract physiologically-linked indices. By opposition, numerous signal processing works have been dedicated to the processing of LDF signals. The latter works proposed methodological processing procedures to extract information reflecting underlying microvascular mechanisms such as myogenic, neurogenic and endothelial activities. Our goal herein is to report on the potentialities of studies dedicated to the processing of LSCI perfusion data. Linear and nonlinear analyses could be of interest to improve the understanding of LSCI images.Keywords Laser speckle contrast imaging Á Microcirculation Á Signal processing Á Image processing Á Laser Doppler flowmetryIn clinical research, the real-time monitoring of skin microvascular blood perfusion can be performed, among others, with laser Doppler flowmetry (LDF) and laser speckle contrast imaging (LSCI) (see, e.g., [7, 13, 18, 26,43,46]). LDF has been proposed in the 1970's [45] to monitor the microvascular blood perfusion in a small volume of tissue (approximately 1 mm 3 in skin when a 780 nm laser wavelength is used). Since that time, many works have led to the improvements of the technique (see, e.g., [1-6, 10, 29, 38, 39, 47]). LSCI is a more recent technique developed in the mid 1990s. It relies on the speckle phenomenon generated by the interactions between coherent monochromatic radiations and a scattering medium [7]. The first speckle imagers were commercialized very recently and from this time LSCI has been the subject of an increasing number of papers (see, e.g., [7,30,31,40]). LSCI and LDF have found widespread skin vascular application among which we can cite the reperfusion monitoring of skin flaps, the quantification of peripheral vascular diseases, the perfusion monitoring of burns, wounds and foot ulcers. LSCI has the advantage, over LDF, of being a noncontact method and giving a twodimensional image of the perfusion, thus reducing the spatial variability of the measure [42].In the last years, several LDF models and simulations [9, 16, 22-24, 27, 35-37] and many LDF signal processing studies have been published. A number of these signal processing works use wavelets to extract data from the heart rate, respiration, myogenic, neurogenic and endothelial activities (see, e.g., [12, 17,44]

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Assessing spatial resolution versus sensitivity from laser speckle contrast imaging: application to frequency analysis

Bricq

Rousseau

Humeau-Heurtier

et al. 2012

Med Biol Eng Comput

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For blood perfusion monitoring, laser speckle contrast (LSC) imaging is a recent non-contact technique that has the characteristic of delivering noise-like speckled images. To exploit LSC images for quantitative physiological measurements, we developed an approach that implements controlled spatial averaging to reduce the detrimental impact of the noise and improve measurement sensitivity. By this approach, spatial resolution and measurement sensitivity can be traded-off in a flexible way depending on the quantitative prospect of the study. As an application, detectability of the cardiac activity from LSC images of forearm using power spectrum analysis is studied through the construction of spatial activity maps offering a window on the blood flow perfusion and its regional distribution. Comparisons with results obtained with signals of laser Doppler flowmetry probes are performed.

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Laser Doppler flowmetry: characteristics of a modified single-fibre technique

Cited by 6 publications

References 14 publications

Single Fiber Laser-Doppler Flowmetry—Dependence on Wavelength and Tip Optics

Single Fiber Laser-Doppler Flowmetry—Dependence on Wavelength and Tip Optics

Laser speckle contrast imaging of the skin: interest in processing the perfusion data

Assessing spatial resolution versus sensitivity from laser speckle contrast imaging: application to frequency analysis

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