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

Abstract

Laser speckle contrast imaging (LSCI) is a newly commercialized imaging modality to monitor microvascular blood flow. Contrary to the well-known laser Doppler flowmetry (LDF), LSCI has the advantage of giving a full-field image of surface blood flow using simple instrumentation. However, laser speckle contrast images are not fully understood yet and their link with LDF signals still has to be studied. To quantify the similarity between LSCI and LDF symbolic sequences, we propose to use, for the first time, the index adapted from linguistic analysis and information theory proposed by Yang For this purpose, LSCI and LDF data were recorded simultaneously on the forearm of healthy subjects, at rest and during a vascular occlusion (biological zero). We show that there are different dynamical patterns for LSCI and LDF data, and the distances between these patterns differ through the space scales explored. Moreover, our results suggest that these different dynamical patterns could be linked to blood flow. The quantitative metric used herein therefore provides new information on LSCI and brings knowledge on links between LSCI and LDF.

Multiscale Compression Entropy of Microvascular Blood FlowSignals: Comparison of Results from Laser Speckle Contrastand Laser Doppler Flowmetry Data in Healthy Subjects

“…This means that, for scale factors larger than three, LDF signals complexity becomes closer to the ones of LSCI time series with the largest ROI size. These results are in accordance with previous works where it has been reported that: (i) there are different dynamical patterns for LSCI and LDF data [26]; (ii) when the ROI size increases in LSCI data and when LSCI pixel values are averaged in ROI and followed with time, the patterns of the resulting time series approach the patterns of LDF signals [26,31,32,38]. Several studies have been carried on compression entropy [34,37,[39][40][41][42][43][44][45][46].…”

“…This pixel was followed with time to obtain a time series of 1,600 samples. Moreover, around each pixel chosen above, square regions of interest (ROI) of a size of 3 × 3 pixels 2 (1.44 mm 2 ) and 15 × 15 pixels 2 (36 mm 2 ) were determined [26,31,32]. For each ROI, the mean of the pixel values (in APU LSCI ) inside the ROI was computed and followed on each image of the sequence to obtain a time-evolution signal (see Figure 3).…”

“…By opposition, and probably because laser speckle contrast imagers have been commercialized only recently, LSCI data have been the subject of very few analyses [23]. Moreover, as both LDF and LSCI give perfusion values in arbitrary units, works aiming at comparing the results given by the two techniques have become necessary [24][25][26][27]. Thus, it has been reported that LSCI and LDF do not probe the same volume of tissue [28]: the penetration depth of LSCI is lower than the one of LDF for similar wavelengths.…”

Laser Speckle Contrast Imaging for Monitoring Changes in Microvascular Blood Flow

“…The biological zero has been the subject of many studies using laser Doppler flow and has been suggested as consisting of Brownian motions of molecules as well as local redistribution of blood cells within vessels [22,23]. The interpretation and handling of the biological zero is still under debate, but it has been proposed that the underlying mechanism causing the biological zero may not be probed in the same way by the laser Doppler flow and LSCI techniques [24]. In a similar way, figure 1 illustrates the very same issue where the curves are parallel but with different y-axis intercepts.…”

Optical methods for blood perfusion measurement—theoretical comparison among four different modalities

“…There are already experimental studies comparing them [39][40][41][42]. However, not much theoretical comparison has been conducted according to the authors' knowledge.…”