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.

Evaluation of Ventricular-vascular Coupling in Patients with Type 2 Diabetes Mellitus Using 2-Dimensional Speckle Tracking Imaging

The elastic and functional coupling of heart and vessels makes the stroke work （SW） of the heart optimal. Speckle tracking imaging （STI） can evaluate the myocardial strain and function. We studied ventricular-vascular coupling in 80 diabetic patients with different systolic function using STI. The patients were divided into two groups according to ejection fraction （EF）： the diabetes mel- litus with normal EF （DMN） group and the diabetes mellitus with abnormal EF （DMA） group. Forty-two volunteers served as control group. The relative wall thickness （RWT）, left ventricular mass index （LVMI）, stroke volume （SV）, SW, rate-pressure product （RPP）, systemic vascular resis- tance index （SVRI）, left ventricular end-systolic elastance （Ees）, effective arterial elasticity （Ea） and ventricular-vascular coupling index （VVI） were measured and calculated by conventional echocardi- ography. The longitudinal strain （LS） at basement （LSBA）, papillary muscle （LSvM） and cardiac apex （LSAv） was assessed with STI. It was found： （A） compared with control group, in DMN and DMA groups, LSBA, LSvM and LSAp decreased, and they were lower in DMA group. （B） VVI, RPP and SVRI increased, and they were higher in DMN group; Ees decreased, and it was lower in DMA group. （C） LSBA, LSpM, and LSAv had negative correlation with VVI. LSAp, RWT, LVMI and SW were independent predictors for VVI. The area under the receiver operating characteristic （ROC） curves was used for identification of DMA and DMN with LSBA, LSpM, and LSAp, and the area under the ROC of LSAp was the largest. This study supports that myocardial LS could reflect the ventricu- lar-vascular coupling. Different segments had an order to “respond to” the state of the coupling, and the cardiac apex might be the earliest.

Early prediction of myocardial viability after acute myocardial infarction by two-dimensional speckle tracking imaging

Background Identifying the transmural extent of myocardial necrosis and the degree of myocardial viability in acute myocardial infarction （AMI） is important clinically. The aim of this study was to assess myocardial viability using two-dimensional speckle tracking imaging （2D-STI） in patients with AMI. Methods 2D-STI was performed at initial presentation, three days, and six months after primary percutaneous coronary intervention （PCI） in 30 patients with AMI, who had a left anterior descending coronary artery （LAD） culprit lesion. In addition, 20 patients who had minimal stenotic lesions （〈 30% stenosis） on coronary angiography were also included in the control group. At six months dobutamine echocardiography was performed for viability assessment in seven segments of the LAD territory. According to the recovery of wall motion abnormality, segments were classified as viable or non-viable. Results A total of 131 segments were viable, and 44 were nonviable. Multivariate analysis revealed significant differences between the viable and nonviable segments in the peak systolic strain, the peak systolic strain rate at initial presentation, and peak systolic strain rate three days after primary PCI. Among these, the initial peak systolic strain rate had the highest predictive value for myocardial viability （hazard ratio： 31.22, P 〈 0.01）. Conclusions 2D-STI is feasible for assessing myocardial viability, and the peak systolic strain rate might be the most reliable predictor of myocardial viability in patients with AMI.

Ultrasound Speckle Tracking Imaging Contributes to Early Diagnosis of Impaired Left Ventricular Systolic Function in Patients with Type 2 Diabetes Mellitus

To investigate the value of ultrasound speckle tracking imaging （STI） in the assessment of the short-axis and long-axis systolic function of the left ventricle （LV） in patients with type 2 diabetes mellitus （DM）, 100 subjects with normal ejection fraction were studied, including 41 patients with DM only （DM group）, 22 patients with both DM and left ventricular hypertrophy （DH group）, and 37 healthy subjects （control group）. Left ventricle systolic function in the long axis defined as longitudinal strain, and that in the short axis defined as radial strain, apical and basal LV rotations, and LV twist were assessed respectively. The results showed that average peak strain in the long axis at basal, middle and apical levels, and global peak strain were significantly decreased in the patient groups when compared with the control group （P〈0.001 for each）. The parameters in DH group were significantly lower than those in DM group （P〈0.01 for each）. There were no significant differences in average radial peak strain in the short axis at different levels, and global peak strain among the three groups （P〉0.05）. Apical and basal LV rotations, and LV twist were greater in the patient groups than in the control group （P〈0.01 for each）. Basal LV rotation and LV twist were greater in DH group than those in DM group （P〈0.01）. It was concluded that STI may be used to identify early abnormalities in patients with type 2 DM that have normal left ventricular systolic function.

Assessment of Right Ventricular Free Wall Longitudinal Myocardial Deformation Using Speckle Tracking Imaging in Normal Subjects

To assess fight ventficular free wall longitudinal myocardium deformation and examine the changes with normal age by speckle tracking imaging （STI）, myocardial systolic peak strain （ε）, systolic peak strain rate （SRs）, early diastolic peak strain rate （SRe）, late diastolic peak strain rate （SRa）, the ratio of SRe/SRa were measured in the basal, middle and apical segments of right ventficular free wall in 75 healthy volunteers （age range： 21-71 y） by STI from the apical 4-chamber view. RV longitudinal strain and strain rate were highest in the basal segment of the free wall. Older subjects had lower early diastolic strain rate （SRe） than younger subjects, but they had higher late diastolic strain rate （SRa）. A negative correlation between age and the ratio of SRe/SRa was found in all RV free wall segments （r=-4）.466 - -0.614, P〈0.01）. It is concluded that RV diastolic strain rate changes with age and STI can be used for the study of RV myocardial deformation.

Assessment of Left Ventricular Global Twist in Essential Hypertensive Heart by Speckle Tracking Imaging

The left ventricular twist was evaluated by 2-dimensional ultrasound speckle-tracking imaging （STI） in 50 patients with hypertension with normal geometric left ventricle （LV） and 45 normal subjects as control group. The mean value of LV rotation was obtained at each plane Using STI. LV twist and twist velocity were defined as apical rotation/rotation rate relative to the base respectively. To adjust the intersubject differences in heart rates, the time sequence were normalized. The results showed that peak twist developed near the end of systole. Peak LV twist was significantly higher in patients with hypertension than normal controls （P〈0.001）. The diastolic untwisting mainly occurred in early diastole （=38%）. Compared with normal controls, untwisting rate （Untw R） in patients with hypertension was significantly reduced （P〈0.001）, and untwisting half-time （UHT） was significantly delayed （P〈0.05）. This study demonstrated that STI has a potential ability to evaluate the early change of heart function in patients with hypertension by measuring the twist of LV.

Laser speckle contrast imaging for monitoring of acutepancreatitis at ischemia-reperfusion injury of thepancreas in rats

The influence of ischemia-reperfusion(I/R)action on pancreatic blood flow(PBF)and the development of acute pancreatitis(AP)in laboratory rats is evaluated in vivo by using the laser speckle contrast imaging(LSCI).Additionally,the optical properties in norm and under condition of AP in rats were assessed using a modied integrating sphere spectrometer and inverse Monte Carlo(IMC)software.The results of the experimental study of microcirculation of the pancreas in 82 rats in the ischemic model are presented.The data obtained conrm the fact that local ischemia and changes in the blood°ow velocity of the main vessels cause and provoke acute pancreatitis.

Assessment of Age-related Changes in Left Ventricular Twist by Two-dimensional Ultrasound Speckle Tracking Imaging

To assess the normal value of left ventricular twist （LVtw） and examine the changes with normal aging by 2-dimensional ultrasound speckle-tracking imaging （STI）, 121 healthy volunteers were divided into three age groups： a youth group （19-45 y old）, a middle-age group （46-64 y old ） and an old-age group （≥65 y old）. Basal and apical short-axis images of left ventricular were acquired to analyse LV rotation （LVrot） and LVrot velocity. LVtw and LVtw velocity was defined as apical LVrot and LVrot velocity relative to the base. Peak twist （Ptw）, twist at aortic valve closure （AVCtw）, twist at mitral valve opening （MVOtw）, untwisting rate （UntwR）, half time of untwisting （HTU）, peak twist velocity （PTV）, time to peak twist velocity （TPTV）, peak untwisting velocity （PUV）, time to peak untwisting velocity （TPUV） were separately measured. The results showed that the normal LV performs a wringing motion with a clockwise rotation at the base and a counterclock- wise rotation at the apex （as seen from the apex）. The LVtw velocity showed a systolic counterclockwise twist followed by a diastolic clockwise twist. Peak twist develops near the end of systole （96%±4.2% of systole）. With aging, Ptw, AVCtw, MVOtw, HTU and PUV increased significantly （P〈0.05） and UntwR decreased significantly （P〈0.05）. However, no significant differences in TPUV, PTV and TPTV were noted among the 3 groups （P〉0.05）. It is concluded that LV twist can be measured non-invasively by 2-dimensional ultrasound STI imaging. The age-related changes of LVtw should be fully taken into consideration in the assessment of LV function.

Assessment of Left Ventricular Radial Deformation by Speckle Tracking Imaging

The left ventricular radial strain in the inner and outer layers was evaluated by using two-dimensional speckle tracking imaging （2DS）. Twenty-five piglets were studied. The short axis views were acquired. Peak systolic radial strain was measured from 6 circumferential points related to 6 standard segments in the inner and outer layers respectively using 2DS methods. The peak positive first derivative （dp/dt） of left ventricular pressure was compared to the radial strain from 2DS. The inner band showed higher peak radial strain values as compared to the outer band at all of the segments （P〈0.0001）, but the differences had significance just in anteroseptal, posterior, inferior and septal segments （P〈0.05）. Good correlation could be found between radial strain of inner and outer layers and peak dp/dt （P〈0.001）. These preliminary results showed that the degree of local deformation or wall thickening of the ventricular wall in its inner layer was more obvious than its outer layer. It is suggested that the 2DS technique is useful and sensitive for better understanding the regional and global myocar- dial motion and its relationship to the complex architecture of myocardium.

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.

Evaluation of Left Ventricular Rotation and Twist Using Speckle Tracking Imaging in Patients with Atrial Septal Defect

Speckle tracking imaging （STI） was employed to investigate the effect of right ventricular （RV） volume and pressure overload on left ventricular （LV） rotation and twist in 35 patients with atrial septal defect （ASD）, 18 of which with pulmonary hypertension, and 21 healthy subjects serving as controls. The peak rotations of 6 segments at the basal and apical short-axises and the average peak rotation and interval time of the 6 segments in the opposite direction during early systolic phase were measured respectively. LV twist versus time profile was drawn and the peak twist and time to peak twist were calculated. LV ejection fraction （EF） was measured by Biplane Simpson. Compared to ASD patients without pulmonary hypertension and healthy subjects, the peak rotations of posterior, inferior and postsept walls at the basal level were lower （P〈0.05）, and the average counterclockwise peak rotation of 6 segments at the basal level during early systolic phase was higher （P〈0.05）, and the average interval time was delayed （P〈0.05）. LV peak twist was also lower （P〈0.05）, and had a significant negative correlation with pulmonary arterial systolic pressure （r=-0.57, P=0.001）. No significant differences were found in LVEF among the three groups. It was suggested that although RV volume overload due to ASD has no significant effects on LV rotation and twist, LV peak twist is lower in ASD patients with pulmonary hypertension. Thus LV twist may serve as a new indicator of the presence of pulmonary hypertension in ASD patients.

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.

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.

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.

Left Ventricular Systolic Strain of the Cardiac Allograft Evaluated with Three-dimensional Speckle Tracking Echocardiography

Three-dimensional speckle tracking echocardiography was employed to evaluate the changes of left ventricular systolic strain in 23 heart transplant recipients at 1 st, 3rd, 6th and 12th month after heart transplantation, and 23 healthy subjects served as controls. The three-dimensional full-volume echocardiographic images of left ventricle were recorded and then were analyzed using EchoPAC software. The strain curves and peak systolic strain values for each segment and overall left ventricular wall were obtained. Left ventricular global peak longitudinal strain （GPSL）, global peak radial strain （GPSR）, global peak circumferential strain （GPSC） and global peak area strain （GPSA） were measured and then statistically analyzed. There were no significant differences in left ventricular ejection fraction （LVEF） and cardiac output （CO） between heart transplant recipients and controls. The GPSL in heart transplant recipients at 1st month after surgery was significantly lower than that in controls, but close to the normal value at 3rd month after surgery and later. The GPSC, GPSA and GPSR were significantly lower in heart transplant recipients at 1 st, 3rd, 6th and 12th month after surgery than those in controls. It is suggested that three-dimensional speckle tracking echocardiography can be used for monitoring changes of left ventricular systolic strains and evaluating left ventricular systolic function in cardiac allograft.