Laser speckle contrast imaging (LSCI) enables a noninvasive monitoring of microvascular perfusion. Some studies have proposed to extract information from LSCI data through their multiscale entropy (MSE). However, for reaching a large range of scales, the original MSE algorithm may require long recordings for reliability. Recently, a novel approach to compute MSE with shorter data sets has been proposed: the short-time MSE (sMSE). Our goal is to apply, for the first time, the sMSE algorithm in LSCI data and to compare results with those given by the original MSE. Moreover, we apply the original MSE algorithm on data of different lengths and compare results with those given by longer recordings. For this purpose, synthetic signals and 192 LSCI regions of interest (ROIs) of different sizes are processed. Our results show that the sMSE algorithm is valid to compute the MSE of LSCI data. Moreover, with time series shorter than those initially proposed, the sMSE and original MSE algorithms give results with no statistical difference from those of the original MSE algorithm with longer data sets. The minimal acceptable length depends on the ROI size. Comparisons of MSE from healthy and pathological subjects can be performed with shorter data sets than those proposed until now.
The present paper shows a method for pulse waveform extraction using laser speckle contrast analysis. An experimental apparatus was assembled, using a coherent light source and a digital video camera to record time varying speckle patterns emitted from the radial artery. The speckle data were analysed by computing the speckle pattern contrast on a sequence of video frames. The speckle pulse wave signal was then compared with a photoplethysmographic signal both time and frequency domain. A total of thirty data-sets were acquired from 10 individuals. Subjects heart rate was identified with a root mean square error of 1.3 beats per minute. Signals similarity was evaluated using spectral coherence with an overall mean coherence of 0.63. Speckle contrast analysis is a newly commercialized technique to monitor microvascular blood flow. However, these results demonstrate the ability of the same technique to extract pulse waveform information. The inclusion of this feature in the current speckle devices is only associated with a slightly change in the signal processing techniques and video acquisition parameters but can be very useful in clinical context.
In the cardiovascular system, the macrocirculation and microcirculation—two subsystems—can be affected by aging. Laser speckle contrast imaging (LSCI) is an emerging noninvasive optical technique that allows the monitoring of microvascular function and can help, using specific data processing, to understand the relationship between the subsystems. Using LSCI, the goals of this study are: (i) to assess the aging effect over microvascular parameters (perfusion and moving blood cells velocity, MBCV) and macrocirculation parameters (pulse-wave velocity, PWV) and (ii) to study the relationship between these parameters. In 16 healthy subjects (20 to 62 years old), perfusion and MBCV computed from LSCI are studied in three physiological states: rest, vascular occlusion, and post-occlusive reactive hyperaemia (PORH). MBCV is computed from a model of velocity distribution. During PORH, the experimental results show a relationship between perfusion and age (R2=0.67) and between MBCV and age (R2=0.72), as well as between PWV and age at rest (R2=0.91). A relationship is also found between perfusion and MBCV for all physiological states (R2=0.98). Relationships between microcirculation and macrocirculation (perfusion-PWV or MBCV-PWV) are found only during PORH with R2=0.76 and R2=0.77, respectively. This approach may prove useful for investigating dysregulation in blood flow.
A system using laser speckle effect is proposed to segment images reflecting vibration movements of di use targets. Longitudinal movements are difficult to identify when simple imaging systems are used. The proposed system produces a two dimensional segmentation of the target and it is sensitive to longitudinal movements. The speckle effect, produced when coherent light is reflected and interferes when hitting rough surfaces, can be used in order to accomplish this purpose. A pattern with high and low intensity spots is observed depending on the illuminated scene. In our optical system, two silicone membranes are illuminated using a beam expanded laser source and their patterns are recorded using a video camera. One of the membranes experiences a longitudinal controlled movement while the remaining scene is still. Speckle data is processed using a temporal gradient and a regional entropy computation. This method produces a binary individual pixel classification. Four sets of parameters have been tested for the entropy computation and the area under the receiver operating characteristic (ROC) curve was used to select the best one. The selected set-up achieved a ROC value of 0.9879. A data set with 12 different membrane velocities was used to define the threshold that maximizes the classifier accuracy. This threshold was applied to a validation data-set composed by 4 sinusoidal movements with distinct velocities. The accuracy of this technique has achieved values between 92% and 97%. The results show that the target was accurately identified with the optical non-contact apparatus and the developed algorithm.
Laser Doppler flowmetry (LDF) signals give a peripheral view of the cardiovascular system. To better understand the
possible modifications brought by sleep apnea syndrome (SAS) in LDF signals, we herein propose to analyze the
complexity of such signals in obstructive SAS subjects, and to compare the results with those obtained in healthy
subjects. SAS is a pathology that leads to a drop in the parasympathetic tone associated with an increase in the
sympathetic tone in awakens SAS patients. Nine men with obstructive SAS and nine healthy men participated awaken in
our study and LDF signals were recorded in the forearm. In our work, complexity of LDF signals is analyzed through the
computation and analysis of their multifractal spectra. The multifractal spectra are estimated by first estimating the
discrete partition function of the signals, then by determining their Renyi exponents with a linear regression, and finally
by computing their Legendre transform. The results show that, at rest, obstructive SAS has no or little impact on the
multifractal spectra of LDF signals recorded in the forearm. This study shows that the physiological modifications
brought by obstructive SAS do not modify the complexity of LDF signals when recorded in the forearm.
The present work aims at comparing simulations of photon transport phenomena in biological multi-layered tissues by means of two methods: a finite element code and a Monte Carlo procedure. We apply these codes to model time-dependent light propagation in multi-layered media. The physical situation refers to the case of a narrow incident laser pulse of 1 ps duration acting upon the surface of the media. Time-resolved spectra are reported for different geometries and optical properties for high media. Here, codes are applied to simulate data acquired from measurements on tissues in extremities. The results of the study provide information to calibrate the finite element characteristics for future experiences including fluorescence events in multi-layered complex systems.
The potentialities offered by time-gated transillumination of inhomogeneous tissue slab media are numerically investigated in this paper. A finite element model is firstly presented in order to solve the time-dependent light transport in mutiple-scattering optical media containing different embedded objects. The numerical procedure is based on the Galerkin formulation added to an implicite finite difference scheme (Backward Euler) to integrate the resulting matrix formulation with respect to time. The meshed domain refers to Cartesian-coordinates system (x,y) such that the computational grid can be adapted to scan along the longitudinal coordinate x. It takes into account the boundary conditions relative to air-tissue interfaces. The use of the method is demonstrated by the forward computations of time-gated intensities, resulting from line scans across either partially absorbing or scattering cylindrical objects. The overall computations confirm that time-gating technique is very sensitive to local variations in optical properties that are due to hidden objects in turbid media. It is also shown that the lateral localization of these inclusions is enhanced when the time-gate width (Δt) is decreased to about 30 ps.
The depth-localization of fluorescent objects having different diameters and embedded within semi-infinite turbid tissue is determined with a model based on the finite element method. The work relies on the time to reach half of the maximum fluorescence intensity. The model is based on a set of two-dependent photon diffusion equations: - the transport of the pulsed laser source (duration 1 ps) and - the transport of the induced fluorescent light excited by the source. The coupling between these equations is due to a source term directly proportional to the scattered fluence rate at the same location. To solve this problem, the method proceeds following the Galerkin formulation added to an implicit finite difference scheme (Backward Euler) to integrate the resulting matrix formulation with respect to time. The meshed domain is axi-symmetrical and takes into account the boundary conditions relative to air-tissue interface. The different computational results show that the fluorescent signals can be used to provide time of flight information about the depth localization of a spherical tumor embedded in a turbid medium. These findings are in good agreement with experimental works.
Reactive hyperemia signals obtained with laser Doppler flowmetry are currently used to diagnose peripheral arterial occlusive diseases (PAOD). De-noising of such signals could lead to improved diagnoses. For this purpose, the principal components analysis is applied to signals acquired on PAOD and healthy subjects.
In the biomedical field, the laser Doppler flowmetry (LDF) technique is a non-invasive method to monitor skin perfusion. On the skin of healthy humans, LDF signals present a significant transient increase in response to a local and progressive pressure application. This vasodilatory reflex response may have important implications for cutaneous pathologies involved in various neurological diseases and in the pathophysiology of decubitus ulcers. The present work analyses the dynamic characteristics of these signals on young type 1 diabetic patients, and on healthy age-matched subjects. To obtain accurate dynamic characteristic values, a de-noising wavelet-based algorithm is first applied to LDF signals. All the de-noised signals are then normalised to the same value. The blood flow peak and the time to reach this peak are then calculated on each computed signal. The results show that a large vasodilation is present on signals of healthy subjects. The mean peak occurs at a pressure of 3.2 kPa approximately. However, a vasodilation of limited amplitude appears on type 1 diabetic patients. The maximum value is visualised, on the average, when the pressure is 1.1 kPa. The inability for diabetic patients to increase largely their cutaneous blood flow may bring
explanations to foot ulcers.
A computational model based on finite element method is derived to examine how the recorded time-dependent signals are related to the basic optical properties of a slab at both excitation and emission wavelengths. The model is based on a set of two time-dependent photon diffusion equations: -the transport of the pulsed laser source light (1 ps) and -the transport of the induced fluorescent light excited by the source. The coupling between these equations is due to a source term directly proportional to the scattered fluence rate at the same location. To solve this problem, the method proceeds following the Galerkin formulation, added to implicite finite difference scheme (Backward Euler) to integrate the resulting matrix formulation with respect to time. The meshed domain is two dimensional and takes into account the available boundary conditions relative to air-tissue interface (Robin boundary conditions). The computations are first carried out for a slab in which fluorophores are uniformly distributed, and afterwards devoted to the localization in depth of a fluorescent object (like a tumor) embedded within the slab.
The laser Doppler flowmetry technique has recently been used to report a significant transient increase of the cutaneous blood
flow signal when a local non-noxious pressure is applied progressively on the skin (11.1 Pa/s). The present work analyses the dynamic characteristics of this vasodilatory reflex response on anaesthetised rats. A de-noising algorithm using wavelets is proposed to obtain accurate values of these dynamic characteristics. The blood flow peak and the time to reach this peak are computed on the de-noised recordings. The results show that the mean time to reach the peak of perfusion is 85.3 s (time t = 0 at the beginning of the pressure application). The mean peak value is 188.3 arbitrary units (a.u.), whereas the mean value of the perfusion before the pressure application is 113.4 a.u. The mean minimum value obtained at the end of the experiment is 60.7 a.u. This latter value is, on the average, reached 841.3 s after the beginning of the pressure application. The comparison of the dynamic characteristics, computed with the de-noising algorithm on signals obtained in other situations, will give a better understanding on some cutaneous lesions such as those present on diabetic people.
Laser Doppler flowmetry is a non-invasive method used in the medical domain to monitor the microvascular blood cell perfusion through tissue. Most commercial laser Doppler flowmeters use an algorithm calculating the first moment of the power spectral density to give the perfusion value. Many clinical applications measure the perfusion after a vascular provocation such as a vascular occlusion. The response obtained is then called reactive hyperaemia. Target pathologies include diabetes, hypertension and peripheral arterial occlusive diseases. In order to have a deeper knowledge on reactive hyperaemia acquired by the laser Doppler technique, the present work first proposes two models (one analytical and one numerical) of the observed phenomenon. Then, a study on the multiple scattering between photons and red blood cells occurring during reactive hyperaemia is carried out. Finally, a signal processing that improves the diagnosis of peripheral arterial occlusive diseases is presented.
The goal of the present work is to analyse multiple scattering in laser Doppler blood flowmetry reactive hyperaemia experiments. For this purpose, three different kinds of outputs from a laser Doppler flowmeter are studied: the concentration of moving blood cells (CMBC), the linearised unfiltered flux and the unlinerised unfiltered flux. Three vascular occlusion lengths of time are observed on eight healthy volunteers. For each reactive hyperaemia experiment, the difference between the linearised unfiltered flux and the unlinearised unfiltered flux is calculated to examine the multiple scattering. The latter is considered as a function of time and compared to blood flux and concentration of erthrocyte variations. This work shows that, during reactive hyperaemia, the multiple scattering is predominant when the CMBC signal reaches its peak, the latter occurring at the peak of perfusion. However, very rapidly the multiple scattering becomes negligible whereas the CMBC and the linearised flux still take high values. Moreover, the longer the occlusion length of time, the longer the presence of the multiple scattering.
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