Improving sampling depth of laser speckle imaging by topical optical clearing:A theoretical and in vivo study

The effect of optical cleaning method combined with laser speckle imaging(LSI)was discussed to improve the detection depth of LSI due to high scattering characteristics of skin,which limit its clinical application.A double-layer skin tissue model embedded with a single blood vessel was established,and the Monte Carlo method was used to simulate photon propagation under the action of light-permeating agent.808 nm semiconductor and 632.8 nm He–Ne lasers were selected to study the e®ect of optical clearing agents(OCAs)on photon deposition in tissues.Results show that the photon energy deposition density in the epidermis increases with the amount of tissue°uid replaced by OCA.Compared with glucose solution,polyethylene glycol 400(PEG 400)and glycerol can considerably increase the average penetration depth of photons in the skin tissue,thereby raising the sampling depth of the LSI.After the action of glycerol,PEG 400,and glucose,the average photon penetration depth is increased by 51.78%,51.06%,and 21.51%for 808nm,68.93%,67.94%,and 26.67%for 632.8 nm lasers,respectively.In vivo experiment by dorsal skin chamber proves that glycerol can cause a substantial decrease in blood°ow rate,whereas PEG 400 can signicantly improve the capability of light penetration without a®ecting blood velocity,which exhibits considerable potential in the monitoring of blood°ow in skin tissues.

Laser speckle contrast imaging to predict the effect of temporary spinal cord stimulation in postherpetic neuralgia patients: A prospective observational study

Temporary spinal cord stimulation(tSCS)can effectively reduce the pain and severity of postherpetic neuralgia(PHN).However,there are no effective and objective methods for predicting the effects of tSCS on PHN.Laser speckle contrast imaging(LSCI)is frequently used in neurology to evaluate the effectiveness of treatment.To assess the accuracy of LSCI in predicting the impact of tSCS on PHN,14 adult patients receiving tSCS treatments for spinal nerve-innervated(C6-T2)PHN participated in this observational study.Visual analog scale(VAS)assessments and LSCI bloodflow images of the-ngers were recorded after the tSCS procedure.The results showed that the VAS scores of all patients decreased signi-cantly.Moreover,the bloodflow index(BFI)values were signi-cantly higher than they were before the procedure.Increased bloodflow and pain alleviation were positively correlated.The-ndings indicated that spinal nerve PHN(C6-T2)was signi-cantly reduced by tSCS.Pain alleviation by tSCS was positively correlated with increased bloodflow in the hand.The effect of tSCS on PHN may thus be predicted using an independent and consistent indicator such as LSCI.

Laser speckle imaging and wavelet analysis of cerebral blood flow associated with the opening of the blood–brain barrier by sound

The cerebral blood flow（CBF） alterations related to sound-induced opening of the blood–brain barrier（BBB） in adult mice are studied using laser speckle contrast imaging（LSCI） and wavelet analysis of vascular physiology.The results clearly show that the opening of the BBB is accompanied by the changes of venous but not microvessel circulation in the brain. The elevation of the BBB permeability is associated with the decrease of venous CBF and the increase of its complexity. These data suggest that the cerebral veins rather than microvessels are sensitive components of the CBF related to the opening BBB.

A New Method for Evaluating Regional Cerebral Blood Flow Changes:Laser Speckle Contrast Imaging in a C57BL/6J Mouse Model of Photothrombotic Ischemia

The present study aimed to improve the processing of data acquired from laser speckle contrast imaging（LSCI） to provide a standardization method to explore changes in regional cerebral blood flow（r CBF） and to determine the correlations among r CBF, cerebral ischemic lesion volume and microvascular density over time in a focal ischemic region. C57BL/6J mice were subjected to focal photothrombotic（PT） ischemia. r CBF was measured using LSCI at different time points before and after PT ischemia through an intact skull. Standardized r CBF（Sr CBF）, defined as the ratio of r CBF measured in the ipsilateral region of interest（ROI） to that in the corresponding contralateral region, was calculated to evaluate potential changes. In addition, the volume of the ischemic lesion and the microvascular density were determined using Nissl staining and immunofluorescence, respectively. The relationships among the ischemic lesion volume, microvascular density and Sr CBF were analyzed over time. The results showed that the cortical r CBF measured using LSCI following PT ischemia in the C57BL/6J mice gradually increased. Changes in the cerebral ischemic lesion volume were negatively correlated with Sr CBF in the ischemic region. Changes in the microvascular density were similar to those observed in Sr CBF. Our findings indicate that LSCI is a practical technique for observing changes in murine cortical r CBF without skull opening and for analyzing the relationships among the ischemic lesion volume, microvascular density and Sr CBF following focal cerebral ischemia. Preliminary results also suggest that the use of LSCI to observe the formation of collateral circulation is feasible.

ASSESSMENT OF OPTICAL CLEARING INDUCED IMPROVEMENT OF LASER SPECKLE CONTRAST IMAGING

Laser Speckle Contrast Imaging(LSCI)plays an important role in studying blood flow,but suffers from limited penetration depth of light in turbid tissue.The strong scattering of tissue obviously reduces the image contrast which decreases the sensitivity to flow velocity.Some image processing or optical clearing methods have been proposed to lessen the deficiency,but quantitative assessment of improvement is seldom given.In this study,LSCI was applied to monitor the blood flow through a capillary embedded within various tissue phantoms at depths of 0.25,0.45,0.65,0.85 and 1.05 mm,and the flow velocity in capillary was controllable from 0 to 4mm/s.Here,glycerol,a common optical clearing agent,was mixed with Intralipid at different volume ratio to make the reduced scattering coefficient of tissue phantom decrease from 13.00 to 0.50 cm−1.The quantitative analysis demonstrates that the optical clearing method can obviously enhance the image contrast,imaging depth,and sensitivity to blood flow velocity.Comparing the Laser Speckle Contrast Analysis methods and the optical clearing method,we find that for typical turbid tissue,the sensitivity to velocity estimated by the Laser Speckle Temporal Contrast Analysis(LSTCA)is twice of that by the Laser Speckle Spatial Contrast Analysis(LSSCA);while the sensitivity to velocity estimated by using the two analysis methods has a 10-fold increase,respectively,if addition of glycerol makes the reduced scattering coefficient of tissue phantom decrease by 30%.Combining the LSTCA and the optical clearing method,the sensitivity to flow velocity will be further enhanced.

Hidden stage of intracranial hemorrhage in newborn rats studied with laser speckle contrast imaging and wavelets

Using the laser speckle contrast imaging and wavelet-based analyses,we investigate a latent("hidden")stage of the development of intracranial hemorrhages(ICHs)in newborn rats.We apply two measures based on the continuous wavelet-transform of blood flow velocity in the sagittal sinus,namely,the spectral energy in distinct frequency ranges and a multiscality degree characterizing complexity of experimental data.We show that the wavelet-based multifractal formalism reveals changes in the cerebrovascular blood flow at the development of ICH.

IN VIVO MAPPING BRAIN MICROCIRCULATION BY LASER SPECKLE CONTRAST IMAGING:A MAGNETIC RESONANCE PERSPECTIVE OF THEORETICAL FRAMEWORK

The fundamental limitations of most vascular-based functional neuroimaging techniques are placed by the fact how fine the brain regulates the blood supply system.In vivo mapping of the cerebral microcirculation with high resolution and sensitivity hence becomes unprecedentedly compelling.This paper reviews the theoretical background of the laser speckle contrast imaging(LSCI)technique and attempts to present a complete framework stemming from a simple biophysical model.Through the sensitivity analysis,more insights into the tool optimization are attained for in vivo applications.Open questions of the technical aspects are discussed within this unified framework.Finally,it concludes with a brief perspective of future research in a way analogous to the magnetic resonance imaging(MRI)technique.Such exploration could catalyze their development and initiate a technological fusion for precise assessment of blood flow across various spatial scales.

Separation of cortical arteries and veins in optical neurovascular imaging

Separation of arteries and veins in the cerebral cortex is of significant importance in the studies of cortical hemodynamics,such as the changes of cerebral blood flow,perfusion or oxygen con-centration in arteries and veins under different pathological and physiological conditions.Yet the cerebral vessel segmentation and vessel-type separation are challenging due to the complexity of cortical vessel characteristics and low spatial signal-to-noise ratio.In this work,we presented an effective full-field method to differentiate arteries and veins in cerebral cortex using dual-modal optical imaging technology including laser speckle imaging(LSI)and optical intrinsic signals(OIS)imaging.The raw contrast images were acquired by LSI and processed with enhanced laser speckle contrast analysis(eLASCA),algorithm.The vascular pattern was extracted and seg-mented using region growing algorithm from the eLASCA-based LSI.Meanwhile,OIS imageswere acquired altermatively with 630 and 870 nm to obtain an oxy hemoglobin concentration mapover cerebral cortex.Then the separation of arteries and veins was accomplished by Otsuthreshold segmentation algorithm based on the OIS information and segmentation of LSI.Finally,the segmentation and separation performances were assessed using area overlap measure(AOM).The segmentation and separation of cerebral vessels in cortical optical imaging have great potential applications in full-field cerebral hemodynamics monitoring and pathological study of cerebral vascular diseases,as well as in clinical intraoperative monitoring.

Monitoring of rhythms in laset speckle data

While the laser speckle imaging(LSI)is a powerful tool for multiple biomedical applications,suchas monitoring of the blood flow,in many cases it can provide additional information when combined with spatio-temporal rhythm analysis.We demonstrate the application of GraphicsProcessing Units(GPU)-based rhythm analysis for the post procesing of LSI data,discuss therelevant structure of GPU-based computations,test the proposed technique on surrogate 3D data,and apply this approach to kidney blood fiow autoregulation.Experiments with surrogate data demonstrate the ability of the method to extract information about oscillation patterns fromnoisy data,as well as to detect the moving source of the rhythm.The analysis of kidney dataallow us to detect and to localize the dymamics arising from autoregulation processes at the levelof individual nephrons(tubuloglomerular feedback(TGF)rhythm),as well as to distinguishbetween the TGF-active and the TGF-silent zones.

Laser speckle contrast imaging based on uniting spatiotemporal Fourier transform

We propose a laser speckle contrast imaging method based on uniting spatiotemporal Fourier transform.First,the raw speckle images are entirely transformed to the spatiotemporal frequency domain with a three-dimensional(3D)fast Fourier transform.Second,the dynamic and static speckle components are extracted by applying 3D low-pass and high-pass filtering in the spatiotemporal frequency domain and inverse 3D Fourier transform.Third,we calculate the time-averaged modulation depth with the average of both components to map the two-dimensional blood flow distribution.The experiments demonstrate that the proposed method could effectively improve computational efficiency and imaging quality.

Laser speckle contrast imaging compared with indocyanine green in renal perfusion of a porcine model

Background:When viewed under near-infrared light,indocyanine green(ICG)signal for kidney perfusion can be utilized in partial nephrectomy.Laser speckle contrast imaging(LSCI)uses coherent light to detect perfusion during real-time laparoscopic surgery.Materials and methods:Laser speckle contrast imaging or ActivSight,an imaging sensor adapter,was used during laparoscopy of an anesthetized porcine kidney model.ActivSight's"perfusion mode"and"quantification mode"displayed the blood flow as a heatmap and numerical signal intensity,respectively.Results:After the upper segmental renal artery was clamped,ICG was seen in the lower pole,and LSCI showed low unit(dark color)quantification and perfusion in the upper pole.Indocyanine green was retained in the lower pole after the upper segmental artery was unclamped,and LSCI perfusion was demonstrated in the entire kidney.Conclusions:Laser speckle contrast imaging is a dye-free,repeatable,real-time adjunct for renal parenchymal perfusion assessment applicable to minimally invasive renal surgery to complement the technology of ICG near-infrared fluorescence and advance digital surgery.

Sample entropy analysis of laser speckle fluctuations to suppress motion artifact on blood flow monitoring

Laser speckle imaging is a common technique to monitor blood flow.The fluctuations in speckle intensity can be related to the blood flow by calculating the speckle contrast,the ratio between the standard deviation of speckle fluctuations and the average intensity.However,this simple statistic calculation is easily affected by motion artifacts.In this study,we applied sample entropy analysis instead of calculating standard deviations of the speckle fluctuations.Similar to the traditional method,sample entropy-based speckle contrast increases linearly with flow rate but was shown to be more immune to sudden movements during an upper arm occlusion test.

DETECTING CEREBRAL ARTERIES AND VEINS:FROM LARGE TO SMALL

In this paper,a model-based reconstruction technique is proposed to simultaneously measure the relative deoxyhemoglobin concentration and the relative blood flow velocity in cerebral cortex.With the help of this model-based reconstruction technique,artifacts due to nonuniform laser illumination and curvature of cortex are efficiently corrected.The results of relative deoxyhemoglobin concentration and relative blood flow velocity are then used to detect and distinguish cerebral arteries and veins.In an experimental study on rat,cerebral blood vessels are segmented from the reconstructed blood flow image by Otsu multiple threshold method.Afterwards,arteries and veins are distinguished by a simple fuzzy criterion based on the information of relative deoxyhemoglobin concentration.

Histogram analysis of laser speckle contrast image for cerebral blood flow monitoring

Laser speckle contrast imaging （LSCI） is a powerful tool for blood flow mapping. In this paper, we described a simple algorithm based on histogram analysis of laser speckle contrast image to provide rapid differentiation between macro- and microcirculations. The algorithm was successfully verified by the study of blood flow in rat cortex under functional activation.

In vivo monitoring of microneedle-based transdermal drug delivery of insulin

Soluble microneedles(MNs)have recently become an eficient and minimally invasive tool in transdermal drug delivery because of their excellent biocompatibility and rapid dissohution.However,direct monitoring of structural and functional changes of MNs in vivo to estimate the efficieancy of insulin delivery is difficult.We monitored the dissolution of MNs to obtain structural imaging of MNs'changes by using optical coherence tomography(OCT).We also observed the effect of MNs on microvascular conditions with laser speckle contrast imaging(LSCIT)and measured the blood perfusion of skin to obtain functional imaging of MNs.We determined the performance of two soluble MN arrays made from polyvinyi alcohol(PVA)and polyvinyl alco-hol/polyvinylpyrolidone(PVA/PVP)by calculating the cross sectional areas of the micro-channels in mouse skin as a function of time.Moreover,the change in blood glucose before and after using MNs loaded with insulin was evaluated as an auxiliary means to demonstrate the ability of the soluble MNs to deliver insulin.Results showed that the structural imaging of these MNs could be observed in vivo via OCT in real time and the fumctional imaging of MNs could be showed using LSCI OCT and LSCI are potential tools in monitoring MNs structural and functional changes.

Characterization of cerebral blood flow dynamics with multiscale entropy

Based on the laser speckle contrast imaging(LSCI)and the multiscale entropy(MSE),we study in this work the blood flow dynamics at the levels of cerebral veins and the surrounding network of microcerebral vessels.We discuss how the phenylephrine-related acute peripheral bypertension is refected in the cerebral circulation and show that the observed changes are scale dependent,and they are signifcantly more pronounced in microcerebral vessels,while the macrocerebral dynamics does not demonstrate authentic inter-group distinctions.We also consider the permeability of blood-brain barrier(BBB)and study its opening caused by sound exposure.We show that alterations associated with the BBB opening can be revealed by the analysis of blood flow at the level of macrocerebral vessels.

Noninvasive in vivo study of NADH fluorescence and its real-time intrinsic dynamical changes: Experiments and seven-layered skin model Monte Carlo simulations

Reduced nicotinamide adenine dinucleotide(NADH)plays a crucial role in many biochemical reactions in human metabolism.In this work,a flow-mediated skin fluorescence(FMSF)-postocclusion reactive hyperaemia(PORH)system was developed for noninvasive and in vivo measurement of NADH fluorescence and its real-time dynamical changes in human skin tissue.The real-time dynamical changes of NADH fluorescence were analyzed with the changes of skin blood flow measured by laser speckle contrast imaging(LSCI)experiments simultaneously with FMSFPORH measurements,which suggests that the dynamical changes of NADH fluorescence would be mainly correlated with the intrinsic changes of NADH level in the skin tissue.In addition,Monte Carlo simulations were applied to understand the impact of optical property changes on the dynamical changes of NADH fluorescence during the PORH process,which further supports that the dynamical changes of NADH fluorescence measured in our system would be intrinsic changes of NADH level in the skin tissue.

Mesenteric traction syndrome in pigs:A single-blinded,randomized controlled trial

Background:Mesenteric traction syndrome is commonly observed in patients undergoing upper abdominal surgery and is associated with severe postoperative complications.A triad of hypotension,tachycardia,and facial flushing seems provoked by prostacyclin(PGI 2)release from the gut in response to mesenteric traction.The administration of nonsteroidal anti-inflammatory drugs(NSAID)inhibits PGI 2 release,stabilizing the hemodynamic response.Here,we examined the effect of mesenteric traction on splanchnic blood flow in pigs randomized to NSAID or placebo treatment.Materials and Methods:Twenty pigs were allocated to either ketorolac or pla-cebo treatment.Five minutes of manual mesenteric traction was applied.Plasma 6-keto-PGF1,a stable metabolite of PGI 2,hemodynamic variables,and regional blood flow(laser speckle contrast imaging)to the liver,stomach,small intestine,upper lip,and snout(laser Doppler flowmetry)were recorded prior to traction and 5 and 30 minutes thereafter.Results:Both groups of pigs presented a decrease in systemic vascular resistance(P.01),mean arterial blood pressure(P.001),and blood flow in the gastric an-trum(P.002).Plasma 6-keto-PGF1 did not increase in either group(P.195),and cardiac output,heart rate,central venous pressure,and blood flow to the liver,small intestine,upper lip,and snout remained unchanged.Conclusion:Mesenteric traction resulted in cardiovascular depression,including re-duced blood flow in the gastric antrum.Plasma 6-keto-PGF1 did not increase,and ketorolac administration did not alter the response to mesenteric traction.Furthers studies are needed to identify which substance is responsible for eliciting the cardio-vascular response to mesenteric traction in pigs.

Recent advances of optical imaging in animal stroke model

Stroke is a major health concern and an intensive research subject due that it is the major cause of death and the leading cause of disability worldwide. The past three decades of clinical disappointments in treating stroke must compel us to rethink our strategy. New effective protocol for stroke could greatly benefit from the advances in optical imaging technologies. This review focuses on the latest advance of applications of three optical imaging techniques in animal model of stroke, such as photoacoustic （PA） imaging, laser speckle contrast imaging （LSCI） and two-photon microscopy （TPM）. The potential roles of those techniques in the future of stroke management are also discussed.

激光散斑成像技术观察浮针治疗急性贝尔面瘫案:病例报道

One case of acute Bell’s palsy was reported and treated with Fu’s subcutaneous needling(FSN).Present symptoms:facial muscle stiffness on the right side,ptosis of labial angle,failure to frown the right eyebrow,the eyeball exposed about 2 mm when gently closing the eyes,air leaking when bulging the cheeks,drooling when brushing the teeth and gargling,and food retained in the cheek when eating.Western medicine diagnosis:peripheral facial palsy.Traditional Chinese medicine diagnosis:facial paralysis.The subcutaneous swaying movement and reperfusion action of FSN were adopted on the affected muscles and achieved the remarkably effects on incomplete closure of eyes and drooping of the mouth.The patient was recovered quickly.Before and after treatment,the laser speckle contrast imaging was used to observe the improvement of blood flow on the face,which provides the idea for the research and clinical practice of Fu’s subcutaneous needling in treatment of Bell’s palsy.