Using pressure-driven flow systems to evaluate laser speckle contrast imaging

Chronic imaging of cerebral blood flow (CBF) is an important tool for investigating vascular remodeling after injury such as stroke. Although techniques such as Laser Speckle Contrast Imaging (LSCI) have emerged as valuable tools for imaging CBF in acute experiments, their utility for chronic measurements or cross-animal comparisons has been limited. Recently, an extension to LSCI called Multi-Exposure Speckle Imaging (MESI) was introduced that increases the quantitative accuracy of CBF images. In this paper, we show that estimates of chronic blood flow are better with MESI than with traditional LSCI. We evaluate the accuracy of the MESI flow estimates using red blood cell (RBC) photographic tracking as an absolute flow calibration in mice over several days. The flow measures computed using the MESI and LSCI techniques were found to be on average 10% and 24% deviant (n=9 mice), respectively, compared with RBC velocity changes. We also map CBF dynamics after photo-thrombosis of selected cortical microvasculature. Correlations of flow dynamics with RBC tracking were closer with MESI (r=0.88) than with LSCI (r=0.65) up to 2 weeks from baseline. With the increased quantitative accuracy, MESI can provide a platform for studying the efficacy of stroke therapies aimed at flow restoration.

In the last decade, Laser Speckle Contrast Imaging (LSCI) has been proposed and validated for imaging cerebral blood flow at the rodent brain surface in vivo. The technique relies on the calculation of the spatial speckle contrast, which is related to the velocity of scatterers (red blood cells). The implementation of the technique requires a partial craniotomy so that the brain tissues of interest can be illuminated with a laser diode. However, the studies of changes in the microcirculation during disease progression or treatment require longitudinal studies (i.e. imaging is done repeatedly over weeks or even months). Practically, the less invasive way to obtain such data is to image through the thinned skull without a craniotomy. However the presence of static scatterers (skull) will affect the speckle calculation and produce a bias in the estimation of the microcirculation changes. An extension to LSCI, termed Multi-Exposure Speckle Imaging (MESI) was proposed and validated a few years ago that address these limitations. It relies on a model of the speckle contrast as a function of the exposure time and the proportion of static scatterers. Here, we used MESI with the aim of repeatedly imaging the olfactory bulb of mice models of obesity. First, we have developed a MESI set up which was characterized on microfluidic flow phantoms with different flow-rates and channel diameters to simulate blood flow in animal model characteristics. Second, we show that MESI can discriminate flows in the presence of static scatterers and it can measure flow changes consistently. Finally we provide an in vivo validation of the technique in mice with and without a craniotomy.

Laser speckle contrast imaging (LSCI) is a widefield imaging technique that enables high spatiotemporal resolution measurement of blood flow. Laser coherence, optical aberrations, and static scattering effects restrict LSCI to relative and qualitative measurements. Multi-exposure speckle imaging (MESI) is a quantitative extension of LSCI that accounts for these factors but has been limited to post-acquisition analysis due to long data processing times. Here we propose and test a real-time quasi-analytic solution to fitting MESI data, using both simulated and real-world data from a mouse model of photothrombotic stroke. This rapid estimation of multi-exposure imaging (REMI) enables processing of full-frame MESI images at up to 8 Hz with negligible errors relative to time-intensive least-squares methods. REMI opens the door to real-time, quantitative measures of perfusion change using simple optical systems.

The present study aims to develop a microfluidic system in combination with laser speckle contrast imaging (LSCI) for the study of erythrocyte dynamics under various physiological flow conditions. Microfluidic device was fabricated and red blood cell suspension was introduced at various flow rate controlled by a syringe pump. Relative blood velocity profile in the microfluidic chamber was obtained by LSCI in a real-time manner and correlated well with simulated results by computational fluid dynamics. A close correlation of relative blood velocity, inlet flow rate and blood viscosity were found using this microfluidic-based LSCI system. In addition, our platform also allows the demonstration of spatiotemporal variation of blood flow in response to magnet-induced magnetic nanoparticle (MNP) retention. The flow behaviour of erythrocytes with the presence of MNPs appeared to be closely correlated with the location of the magnet placement. Our microfluidic-based LSCI measurement represents a simple yet controllable experimental model for evaluating the variations in different hemorheological conditions in vitro and has a strong potential as an easy-to-use tool for investigating local MNP retention and hemodynamic changes.

A systematic and robust laser speckle contrast imaging (LSCI) method and procedure is presented covering the LSCI system calibration, static scattering removal, and measurement noise estimation and correction to obtain a true flow speckle contrast and the flow speed from single-exposure LSCI measurements. We advocate the use of as the speckle contrast instead of the conventional contrast K, as the former relates simply to the flow velocity and is with additive noise alone. We demonstrate the efficacy of the proposed true flow speckle contrast by imaging phantom flow at varying speeds, showing that (1) the proposed recipe greatly enhances the linear sensitivity of the flow index (inverse decorrelation time) and the linearity covers the full span of flow speeds from 0 to 40 mm/s; and (2) the true flow speed can be recovered regardless of the overlying static scattering layers and the type of speckle statistics (temporal or spatial). The fundamental difference between the apparent temporal and spatial speckle contrasts is further revealed. The flow index recovered in the spatial domain is much more susceptible to static scattering and exhibit a shorter linearity range than that obtained in the temporal domain. The proposed LSCI analysis framework paves the way to estimate the true flow speed in the wide array of laser speckle contrast imaging applications.

Purpose: Laser speckle contrast imaging (LSCI) provides an innovative approach to the non-invasive evaluation of systemic microvascular endothelial function. In the present work, we assessed skin microvascular reactivity in individuals with early onset coronary artery disease (EOCAD, diagnosis at less than 45 years of age) using LSCI coupled to pharmacological and physiological stimuli. Methods: Skin microvascular blood flow was continuously monitored in the forearm using LSCI. Acetylcholine (ACh) dose-response curves were performed using an iontophoresis micropharmacology system and post-occlusive reactive hyperemia (PORH) was analyzed after a 3-minute occlusion of blood flow to the forearm. Measurements of microvascular skin blood flow in arbitrary perfusion units (APU) were divided by mean arterial pressure to give cutaneous vascular conductance (CVC) in APU/mm Hg. The results were presented as mean ± SEM and were analyzed using two-tailed unpaired Student's t tests. Results: Fifty-eight patients with EOCAD aged 45±0.4 years (34 men) and 25 healthy age- and sex-matched individuals were included in the study. ACh- and PORH-mediated vasodilation was significantly reduced in EOCAD individuals. Area under the curve of ACh-induced vasodilation was of 6445±842 and 3975±540 APU/sec in controls vs. EOCAD, respectively; p=0.0087; figure 1). Increase in CVC resulting from PORH-induced vasodilation was of 0.46±0.03 and 0.38±0.02 APU/mmHg in controls vs. EOCAD, respectively; p=0.0182; figure 1). ![Figure][1] Conclusions: LSCI identifies systemic microvascular endothelial-dysfunction in individuals presenting with EOCAD and thus could be used as an early peripheral marker of the atherothrombotic disease. [1]: pending:yes

Laser speckle contrast imaging (LSCI) has been widely used in in vivo blood flow imaging. However, the effect of local scattering property (scattering coefficient µs) on blood flow speed estimation has not been well investigated. In this study, such an effect was quantified and involved in relation between speckle autocorrelation time τc and flow speed v based on simulation flow experiments. For in vivo blood flow imaging, an improved estimation strategy was developed to eliminate the estimation bias due to the inhomogeneous distribution of the scattering property. Compared to traditional LSCI, a new estimation method significantly suppressed the imaging noise and improves the imaging contrast of vasculatures. Furthermore, the new method successfully captured the blood flow changes and vascular constriction patterns in rats’ cerebral cortex from normothermia to mild and moderate hypothermia.

Laser Speckle Contrast Imaging (LSCI) is a flexible, easy-to-implement technique for measuring blood flow speeds in-vivo. In order to obtain reliable quantitative data from LSCI the object must remain in the focal plane of the imaging system for the duration of the measurement session. However, since LSCI suffers from inherent frame-to-frame noise, it often requires a moving average filter to produce quantitative results. This frame-to-frame noise also makes the implementation of rapid autofocus system challenging. In this work, we demonstrate an autofocus method and system based on a novel measure of misfocus which serves as an accurate and noise-robust feedback mechanism. This measure of misfocus is shown to enable the localization of best focus with sub-depth-of-field sensitivity, yielding more accurate estimates of blood flow speeds and blood vessel diameters.

The study of blood microcirculation is one of the most important problems of the medicine. This paper presents results of experimental study of cerebral blood flow microcirculation in mice with alloxan-induced diabetes using Temporal Laser Speckle Imaging (TLSI). Additionally, a direct effect of glucose water solution (concentration 20% and 45%) on blood flow microcirculation was studied. In the research, 20 white laboratory mice weighing 20-30 g were used. The TLSI method allows one to investigate time dependent scattering from the objects with complex dynamics, since it possesses greater temporal resolution. Results show that in brain of animal diabetic group diameter of sagittal vein is increased and the speed of blood flow reduced relative to the control group. Topical application of 20%- or 45%-glucose solutions also causes increase of diameter of blood vessels and slows down blood circulation. The results obtained show that diabetes development causes changes in the cerebral microcirculatory system and TLSI techniques can be effectively used to quantify these alterations.

We compare the performance of a water-head pump (WHP) system with that of a syringe pump (SP) system with respect to fluctuation, tunability, and transient response of flow rate. Despite its simplicity, the WHP system has not been as widely adopted as a means of microfluidic control as the SP system, partly because the transient and steady-state flow rates of a WHP in a microfluidic system have not been characterized in detail. We show that the flow-rate fluctuation of the WHP system is at least one order of magnitude smaller than that of the SP system, and that the two systems have similar flow-rate tunability on the order of 1 nL min−1 to 1 mL min−1. In addition, the pressure rise time of the WHP system is at least one order of magnitude faster than that of the SP system. As model experiments, we applied the WHP system to hydrodynamic focusing with a stable focused stream and to fast fluidic switching. The WHP system could be broadly useful versus the SP system and could enable precise, stable, and fast flow-rate control with minimal experimental setup.

The time and costs associated with preparing and administering small-volume injections using seven infusion systems were compared. Thirteen demographically diverse hospitals were chosen as study sites, all under a common protocol. The systems compared were the CRIS controlled-release infusion, minibag, frozen ready-to-use minibag, drug manufacturer-supplied piggyback, syringe pump, volume-control set, and ADD-Vantage systems. Care was taken to ensure that similar drugs (i.e., drugs with equivalent preparation steps) were studied in the same test systems at the hospitals. The mean preparation time for the CRIS controlled-release infusion system was significantly longer than the times for the frozen ready-to-use minibags and ADD-Vantage system and significantly shorter than the times for the minibag and syringe pump systems. Medication administration time for initial doses was found to be significantly shorter with the CRIS system than with the volume-control and ADD-Vantage systems; the time required to administer subsequent doses of small-volume injections was shorter with CRIS than with all other systems except the ADD-Vantage system. When total material costs plus the cost of labor involved in both pharmacy and nursing were combined, CRIS proved to be the least expensive system to use, primarily because of the time and cost savings associated with its use for administration of subsequent doses. Of the seven admixture systems studied, the CRIS system proved to be the least expensive to use when labor and material costs associated with preparation and administration of six doses of an injectable drug were considered.

With the advancement in microfluidic technology, fluid flow control for syringe pump is always essential. In this paper, a mechatronic syringe pump will be developed and customized to control the fluid flow in a poly-dimethylsiloxane (PDMS) microfluidic device based on a polyimide laminating film. The syringe pump is designed to drive fluid with flow rates of 100 and 1000 μl/min which intended to drive continuous fluid in a polyimide based microfluidic device. The electronic system consists of an Arduino microcontroller board and a uni-polar stepper motor. In the system, the uni-polar stepper motor was coupled to a linear slider attached to the plunger of a syringe pump. As the motor rotates, the plunger pumps the liquid out of the syringe. The accuracy of the fluid flow rate was determined by adjusting the number of micro-step/revolution to drive the stepper motor to infuse fluid into the microfluidic device. With the precise control of the electronic system, the syringe pump could accurately inject fluid volume at 100 and 1000 μl/min into a microfluidic device.

To evaluate the risk of retrograde embolization of flush solution in neonates and infants with routinely used electronic syringe pumps and infusion bag pump flush systems. With hospital Ethical Committee approval we studied intubated neonates and infants with a 24-GA radial arterial cannula. Fast flush boluses were delivered from the infusion bag pump flush system by opening the flow regulating device for two seconds at bag pump manometre pressures of 100, 200 and 300 mmHg. In the syringe pump flush system, fast flush bolus volumes of 0.5, 1.0, 1.5 and 2.0 mL were programmed on the electronic syringe pump and released by opening the flow regulating device for two seconds. A 12-MHz ultrasonic probe placed in the jugular fossa was used to detect white bubbles indicating retrograde embolization of flush solution into the ipsilateral subclavian and common carotid artery. Sixteen patients, aged from 1-105 days (median 22 days) were studied. In all patients retrograde embolization into the subclavian artery was detected at syringe pump bolus volumes of 0.5-1.5 mL and at 100-200 mmHg bag pump pressure. In nine of the 16 patients a positive signal was detected in the common carotid artery with 1.5-2.0 mL syringe pump bolus volumes and at 200-300 mmHg bag pump pressure. In neonates and infants, the standard practice of arterial fast bolus flushing using syringe pump and bag pump flush systems causes retrograde embolization of flush solution into the central arterial and even into the cerebral circulation. The mandatory limitation of fast flush bolus volumes and manometre pressures is urgent in order to reduce retrograde embolization of flush solution and the associated risks in these small patients.

Laser speckle contrast imaging (LSCI) can be used to evaluate blood flow based on spatial or temporal speckle statistics, but its accuracy is undermined by out-of-focus image blur. In this Letter, we show how the fraction of dynamic versus static light scattering is dependent on focus, and describe a deconvolution strategy to correct for out-of-focus blur. With the aid of a z-splitter, which enables instantaneous multifocus imaging, we demonstrate depth-resolved LSCI that can robustly extract multi-plane structural and flow-speed information simultaneously. This method is applied to in vivo imaging of blood vessels in a mouse cortex and provides improved estimates of blood flow speed throughout a depth range of 300µm.

A new technique that can increase the depth of field (DOF) for in vivo tissue imaging is presented. Extended DOF for the imaging of strongly scattering media is realized through combining laser speckle contrast imaging (LSCI) with light field (LF) microscopy. To the best of our knowledge, it is for the first time to combine these two imaging techniques into one system to provide enhanced functionality. The entire imaging process requires only one single detection with no mechanical adjustment involved. The feasibility and capability of the proposed technique is experimentally demonstrated in volumetric flow speed measurement.