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

Abstract

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]

Linguistic Analysis of Laser Speckle Contrast Images Recorded at Rest and During Biological Zero: Comparison With Laser Doppler Flowmetry Data

“…Several data processing methods have recently been proposed to provide a better knowledge of laser speckle contrast images [47]- [51]. However, other studies in this field of interest are needed, among others to better understand the meaning of each pixel value, the differences found between pixel values, and the link with LDF signals [52].…”

Laser speckle contrast imaging: Multifractal analysis of data recorded in healthy subjects

“…Variations of skin perfusion are easily detected by LSCI and LDF techniques, but a robust interpretation of the information very often necessitates image and/or signal processing works (see, e.g., Refs. [24][25][26]. Moreover, LSCI and LDF skin data coming from the peripheral cardiovascular system, a comparison of the processing results with those obtained from signals of the central cardiovascular system (e.g., HRV signals) can bring interesting information to better understand the dynamics of the whole cardiovascular system.…”

Laser Method can Also be Used for Endothelial Function Assessment in Clinical Practice

“…In recent years, a new technology, called laser speckle contrast imaging (LSCI), has been developed, and has considerably improved reproducibility compared to LDF. This improvement of reproducibility was mainly due to the increased region of tissue studied 5, [9][10][11] . In brief, LSCI is a non-contact, real-time, non-invasive technology that relies on the speckle phenomenon to obtain a perfusion map of the tissues 12) .…”