EFFECTS OF SCATTERING AND ABSORPTION ON LASER SPECKLE CONTRAST IMAGING

Laser Speckle Contrast Imaging (LSCI) is a real-time, non-invasive method in used to investigate blood flow and perfusion in biological tissues with high temporal and spatial resolution. A reduction in speckle contrast due to particle motion is the primary contrast mechanism in LSCI. Motion results in speckle fluctuations in time and reduces the contrast over a given camera integration period. There are a variety of parameters that effect contrast besides motion. The optical properties of the scattering medium are one of the parameters effecting LSCI values. Changes in blood hematocrit levels manifest as changes in optical properties. In this work, we explore the effects of different hematocrit levels on LSCI contrast values using fluid phantoms with varying optical properties. Herein, the combined effects of scattering and absorption coefficients on LSCI values are investigated using fluid phantoms. These fluid phantoms were designed to mimic the scattering and absorbing properties of blood with varying levels of hematocrit. The flow phantoms in our experiments contained different concentrations of glass microspheres (brand name Luxil) and India ink mixed with DI water. The different number of scatterers and absorbers in the phantoms mimic the scattering and absorption behaviors of blood with different number of red blood cells. An LSCI setup combined with a simple flow system was used in our experiments in order to investigate the effects of combined scattering and absorption coefficient of 121 samples with different concentrations of Luxil and India ink microspheres. The fluid phantoms were run in 2mm glass tubing on top of a plastic block using a mini peristaltic pump. An LSCI setup imaged the flow using a CCD camera. A MATLAB GUI controlled the pump and camera to provide near real-time contrast images of the flow. An 11x11 matrix of phantoms was created. Scattering coefficient was varied on the columns and absorption coefficient was varied on the rows such that the first element of the matrix is water and the last element contains the phantom with the maximum number of scatterers and absorbers. A hundred raw speckle images were recorded for each phantom experiment using the described optical setup. The experiments were conducted 3 times for each element of the matrix. The 11x11 results matrix displayed the average speckle image of all 300 raw speckle images. Additionally, the matrix was filled by the contrast images where contrast was defined as standard deviation of intensity over mean intensity. In order to compare the results numerically, we calculated the ratio of the contrast from the same size window of moving portion over the static portion of the phantoms. According to the results from LSCI experiments, an increase in scattering and absorption coefficients led to a reduction in contrast values of LSCI images. By increasing the number of scatterers and absorbers (equivalent to changing hematocrit level), the optical properties (scattering and absorption coefficient) increased, which led to a reduction in contrast value in the moving area. A negative slope linear curve describes the relationship between and scattering coefficient and between and absorption coefficient

Effects of Performance and Task Duration on Mental Workload during Working Memory Task

N-back is a working memory (WM) task to study mental workload on the prefrontal cortex (PFC). We assume that the subject’s performance and changes in mental workload over time depends on the length of the experiment. The performance of the participant can change positively due to the participant’s learning process or negatively because of objective mental fatigue and/or sleepiness. In this pilot study, we examined the PFC activation of 23 healthy subjects while they performed an N-back task with two different levels of task difficulty (2-, and 3-back). The hemodynamic responses were analyzed along with the behavioral data (correct answers). A comparison was done between the hemodynamic activation and behavioral data between the two different task levels and between the beginning and end of the 3-back task. Our results show that there is a significant difference between the two task levels, which is due to the difference in task complication. In addition, a significant difference was seen between the beginning and end of the 3-back task in both behavioral data and hemodynamics due to the subject’s learning process throughout the experiment

Effects of scattering and absorption on Laser Speckle Contrast Imaging

Laser Speckle Contrast Imaging (LSCI) is a real-time, non-invasive method in used to investigate blood flow and perfusion in biological tissues with high temporal and spatial resolution. A reduction in speckle contrast due to particle motion is the primary contrast mechanism in LSCI. Motion results in speckle fluctuations in time and reduces the contrast over a given camera integration period. There are a variety of parameters that effect contrast besides motion. The optical properties of the scattering medium are one of the parameters effecting LSCI values. Changes in blood hematocrit levels manifest as changes in optical properties. In this work, we explore the effects of different hematocrit levels on LSCI contrast values using fluid phantoms with varying optical properties. Herein, the combined effects of scattering and absorption coefficients on LSCI values are investigated using fluid phantoms. These fluid phantoms were designed to mimic the scattering and absorbing properties of blood with varying levels of hematocrit. The flow phantoms in our experiments contained different concentrations of glass microspheres (brand name Luxil) and India ink mixed with DI water. The different number of scatterers and absorbers in the phantoms mimic the scattering and absorption behaviors of blood with different number of red blood cells. An LSCI setup combined with a simple flow system was used in our experiments in order to investigate the effects of combined scattering and absorption coefficient of 121 samples with different concentrations of Luxil and India ink microspheres. The fluid phantoms were run in 2mm glass tubing on top of a plastic block using a mini peristaltic pump. An LSCI setup imaged the flow using a CCD camera. A MATLAB GUI controlled the pump and camera to provide near real-time contrast images of the flow. An 11x11 matrix of phantoms was created. Scattering coefficient was varied on the columns and absorption coefficient was varied on the rows such that the first element of the matrix is water and the last element contains the phantom with the maximum number of scatterers and absorbers. A hundred raw speckle images were recorded for each phantom experiment using the described optical setup. The experiments were conducted 3 times for each element of the matrix. The 11x11 results matrix displayed the average speckle image of all 300 raw speckle images. Additionally, the matrix was filled by the contrast images where contrast was defined as standard deviation of intensity over mean intensity. In order to compare the results numerically, we calculated the ratio of the contrast from the same size window of moving portion over the static portion of the phantoms. According to the results from LSCI experiments, an increase in scattering and absorption coefficients led to a reduction in contrast values of LSCI images. By increasing the number of scatterers and absorbers (equivalent to changing hematocrit level), the optical properties (scattering and absorption coefficient) increased, which led to a reduction in contrast value in the moving area. A negative slope linear curve describes the relationship between and scattering coefficient and between and absorption coefficient

Combined effects of scattering and absorption on laser speckle contrast imaging

© The Authors. Several variables may affect the local contrast values in laser speckle contrast imaging (LSCI), irrespective of relative motion. It has been suggested that the optical properties of the moving fluid and surrounding tissues can affect LSCI values. However, a detailed study of this has yet to be presented. In this work, we examined the combined effects of the reduced scattering and absorption coefficients on LSCI. This study employs fluid phantoms with different optical properties that were developed to mimic whole blood with varying hematocrit levels. These flow phantoms were imaged with an LSCI system developed for this study. The only variable parameter was the optical properties of the flowing fluid. A negative linear relationship was seen between the changes in contrast and changes in reduced scattering coefficient, absorption coefficient, and total attenuation coefficient. The change in contrast observed due to an increase in the scattering coefficient was greater than what was observed with an increase in the absorption coefficient. The results indicate that optical properties affect contrast values and that they should be considered in the interpretation of LSCI data

Effects of combined scattering and absorption coefficients on laser speckle contrast imaging

© 2015 SPIE. Laser Speckle contrast imaging (LSCI) is a non-invasive or minimally invasive method for visualizing blood flow and perfusion in biological tissues. In LSCI the motion of scattering particles results in a reduction in global and regional speckle contrast. A variety of parameters can affect the calculated contrast values in LSCI techniques, including the optical properties of the fluid and surrounding tissue. In typical LSCI where the motion of blood is of interests, optical properties are influenced by hematocrit levels. In this work we considered the combined effects of both the scattering and absorption coefficients on LSCI measurements on a flow phantom. Fluid phantoms consisting of various concentrations of neutrally buoyant ∼10 micron microspheres and India ink mixed with DI water were formulated to mimic the optical properties of whole blood with various levels of hematocrit. In these flow studies, it was found that an increase in μ \u3c inf\u3e a and/or μ \u3c inf\u3e s led to a decrease in contrast values when all other experimental parameters were held constant. The observed reduction in contrast due to optical property changes could easily be confused with a contrast reduction due to increased flow velocity. These results suggest that optical properties need to be considered when using LSCI to make flow estimates

Laser speckle contrast imaging is sensitive to advective flux

© 2016 The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. Unlike laser Doppler flowmetry, there has yet to be presented a clear description of the physical variables that laser speckle contrast imaging (LSCI) is sensitive to. Herein, we present a theoretical basis for demonstrating that LSCI is sensitive to total flux and, in particular, the summation of diffusive flux and advective flux. We view LSCI from the perspective of mass transport and briefly derive the diffusion with drift equation in terms of an LSCI experiment. This equation reveals the relative sensitivity of LSCI to both diffusive flux and advective flux and, thereby, to both concentration and the ordered velocity of the scattering particles. We demonstrate this dependence through a short series of flow experiments that yield relationships between the calculated speckle contrast and the concentration of the scatterers (manifesting as changes in scattering coefficient), between speckle contrast and the velocity of the scattering fluid, and ultimately between speckle contrast and advective flux. Finally, we argue that the diffusion with drift equation can be used to support both Lorentzian and Gaussian correlation models that relate observed contrast to the movement of the scattering particles and that a weighted linear combination of these two models is likely the most appropriate model for relating speckle contrast to particle motion

Review of Applications of Near-Infrared Spectroscopy in Two Rare Disorders with Executive and Neurological Dysfunction: UCD and PKU

Studying rare diseases, particularly those with neurological dysfunction, is a challenge to researchers and healthcare professionals due to their complexity and small population with geographical dispersion. Universal and standardized biomarkers generated by tools such as functional neuroimaging have been forged to collect baseline data as well as treatment effects. However, the cost and heavily infrastructural requirement of those technologies have substantially limited their availability. Thus, developing non-invasive, portable, and inexpensive modalities has become a major focus for both researchers and clinicians. When considering neurological disorders and diseases with executive dysfunction, EEG is the most convenient tool to obtain biomarkers which can correlate the objective severity and clinical observation of these conditions. However, studies have also shown that EEG biomarkers and clinical observations alone are not sensitive enough since not all the patients present classical phenotypical features or EEG evidence of dysfunction. This article reviews disorders, including two rare disorders with neurological dysfunction and the usefulness of functional near-infrared spectroscopy (fNIRS) as a non-invasive optical modality to obtain hemodynamic biomarkers of diseases and for screening and monitoring the disease

Assessment of incident intensity on laser speckle contrast imaging using a nematic liquid crystal spatial light modulator

© 2016 The Authors. Before laser speckle contrast imaging (LSCI) can be used reliably and quantitatively in a clinical setting, there are several theoretical and practical issues that still must be addressed. In order to address some of these issues, an electro-optical system that utilizes a nematic liquid crystal spatial light modulator (SLM) to mimic LSCI experiments was assembled. The focus of this paper is to address the issue of how incident intensity affects LSCI results. Using the SLM-based system, we systematically adjusted incident intensity on the SLM and assessed the resulting first-and second-order statistics of the imaged speckle to explain the corresponding spatial contrast values in both frozen and time-integrated speckle patterns. The SLM-based system was used to generate speckle patterns with a controlled minimum speckle size, probability intensity distribution, and temporal decorrelation behavior. By eliminating many experimental parameters, this system is capable of serving as a useful intermediary tool between computer simulation and physical experimentation for further developing LSCI as a quantitative imaging modality

Nematic liquid crystal spatial light modulator for mimicking laser speckle contrast imaging

© 2015 SPIE. Laser speckle contrast imaging (LSCI) is a non-or minimally-invasive modality for observing relative blood flow or perfusion. Recently, there has been an effort to use LSCI for truly quantitative blood flow measurements. However, this effort has been hampered not only by real theoretical issues, but also by challenges associated with numerous experimental parameters that can potentially impact the calculated contrast values. In this work, we present our efforts at using a nematic liquid crystal, phase-only, spatial light modulator (SLM) to mimic LSCI experiments with precisely controlled experimental parameters. This approach permits the rapid experimental investigation of numerous factors including: The effects of different flow models on LSCI contrast values; the effects of multiple decorrelation times in the same depth of field; the effects of \u27static\u27 scatterers; and the effects of camera settings relative to speckle decorrelation times, just to name a few. We have found that an SLM is a useful tool for the experimental investigation of LSCI that eliminates many of the experimental variables associated with typical flow model experiments or in vivo experimentation. LSCI experiments with SLMs are a useful intermediary between computer simulations and physical flow models

Optical vortex behavior in dynamic speckle fields

The dynamic behavior of phase singularities, or optical vortices, in the pseudo-phase representation of dynamic speckle patterns is investigated. Sequences of band-limited, dynamic speckle patterns with predetermined Gaussian decorrelation behavior were generated, and the pseudo-phase realizations of the individual speckle patterns were calculated via a two-dimensional Hilbert transform algorithm. Singular points in the pseudo-phase representation are identified by calculating the local topological charge as determined by convolution of the pseudo-phase representations with a series of 2 × 2 nabla filters. The spatial locations of the phase singularities are tracked over all frames of the speckle sequences, and recorded in three-dimensional space x; y; f, where f is frame number in the sequence. The behavior of the phase singularities traces \u27vortex trails\u27 which are representative of the speckle dynamics. Slowly decorrelating speckle patterns results in long, relatively straight vortex trails, while rapidly decorrelating speckle patterns results in tortuous, relatively short vortex trails. Optical vortex analysis such as described herein can be used as a descriptor of biological activity, flow, and motion. © 2012 Society of Photo-Optical Instrumentation Engineers (SPIE)