Renal cortex microperfusion evaluated by laser speckle contrast imaging in an ex vivo perfused kidney model-A proof-of-concept study

BACKGROUND

Validated quantitative biomarkers for assessment of renal graft function during normothermic machine perfusion (NMP) conditions are lacking. The aim of this project was to quantify cortex microperfusion during ex vivo kidney perfusion using laser speckle contrast imaging (LSCI), and to evaluate the sensitivity of LSCI when measuring different levels of renal perfusion. Furthermore, we aimed to introduce LSCI measurements during NMP in differentially damaged kidneys.

METHODS

Eleven porcine kidneys were nephrectomized and perfused ex vivo. Cortex microperfusion was simultaneously monitored using LSCI. First, a flow experiment examined the relationship between changes in delivered renal flow and corresponding changes in LSCI-derived cortex microperfusion. Second, renal cortical perfusion was reduced stepwise by introducing a microembolization model. Finally, LSCI was applied for measuring renal cortex microperfusion in kidneys exposed to minimal damage or 2 h warm ischemia (WI).

RESULTS

Cortex microperfusion was calculated from the LSCI-obtained data. The flow experiment resulted in relatively minor changes in cortex microperfusion compared to the pump-induced changes in total renal flow. Based on stepwise injections of microspheres, we observed different levels of cortex microperfusion that correlated with administrated microsphere dosages (r2 = 0.95-0.99). We found no difference in LSCI measured cortex microperfusion between the kidneys exposed to minimal damage (renal cortex blood flow index, rcBFI = 2090-2600) and 2 h WI (rcBFI = 2189-2540).

CONCLUSIONS

Based on this preliminary study, we demonstrated the feasibility of LSCI in quantifying cortex microperfusion during ex vivo perfusion. Furthermore, based on LSCI-measurements, cortical microperfusion was similar in kidneys exposed to minimal and 2 h WI.

Laser Speckle Contrast Imaging Guides Needling Treatment of Vascular Complications from Dermal Fillers

BACKGROUND

Although laser Doppler imaging (LDI) accurately delineates a hypoperfused area to help target hyaluronidase treatment, laser speckle contrast imaging (LSCI) is more appropriate for assessing microvascular hemodynamics and has greater reproducibility than LDI. This study investigated the use of LSCI in the evaluation and treatment of six patients who developed vascular complications after facial dermal filler injections.

METHODS

The areas of vascular occlusion were accurately defined in real time by LSCI and were more precise than visual inspections or photographic evidence for guiding needling and hyaluronidase treatment.

RESULTS

All patients had achieved satisfactory outcomes as early as Day 2 of treatment and no procedure-related complications were reported after a median follow-up of 9.5 (7-37) days.

CONCLUSION

LSCI accurately and noninvasively delineated vascular occlusions in real time among patients experiencing complications of facial dermal filler injections. Moreover, LSCI was more accurate than visual and photographic evaluations. Clinicians can use LSCI to reliably follow-up therapeutic outcomes after salvage interventions for vascular occlusions.

LEVEL OF EVIDENCE IV

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Research on the classification of early-stage brain edema by combining intrinsic optical signal imaging and laser speckle contrast imaging

The early detection and pathological classification of brain edema are very important for symptomatic treatment. The dual-optical imaging system (DOIS) consists of intrinsic optical signal imaging (IOSI) and laser speckle contrast imaging (LSCI), which can acquire cerebral hemodynamic parameters of mice in real-time, including changes of oxygenated hemoglobin concentration ( Δ C HbO 2 ), deoxyhemoglobin concentration (ΔCHbR) and relative cerebral blood flow (rCBF) within the field of view. The slope sum of Δ C HbO 2 , ΔCHbR and rCBF was proposed to classify vasogenic edema (VE) and cytotoxic edema (CE). The slope sum values in the VE and CE group remain statistically different and the classification results provide higher accuracy of more than 93% for early brain edema detection. In conclusion, the differences of hemodynamic parameters between VE and CE in the early stage were revealed and the method helps in the classification of early brain edema.

Dual-exposure temporal laser speckle imaging for simultaneously accessing microvascular blood perfusion and angiography

Laser speckle contrast imaging (LSCI) has gained significant attention in the biomedical field for its ability to map the spatio-temporal dynamics of blood perfusion in vivo. However, LSCI faces difficulties in accurately resolving blood perfusion in microvessels. Although the transmissive detecting geometry can improve the spatial resolution of tissue imaging, ballistic photons directly transmitting forward through tissue without scattering will cause misestimating in the flow speed by LSCI because of the lack of a quantitative theoretical model of transmissvie LSCI. Here, we develop a model of temporal LSCI which accounts for the effect of nonscattered light on estimating decorrelation time. Based on this model, we further propose a dual-exposure temporal laser speckle imaging method (dEtLSCI) to correct the overestimation of background speed when performing traditional transmissive LSCI, and reconstruct microvascular angiography using the scattered component extracted from total transmitted light. Experimental results demonstrated that our new method opens an opportunity for LSCI to simultaneously resolve the blood vessels morphology and blood flow speed at microvascular level in various contexts, ranging from the drug-induced vascular response to angiogenesis and the blood perfusion monitoring during tumor growth.

Tracking and navigation of a microswarm under laser speckle contrast imaging for targeted delivery

Micro/nanorobotic swarms consisting of numerous tiny building blocks show great potential in biomedical applications because of their collective active delivery ability, enhanced imaging contrast, and environment-adaptive capability. However, in vivo real-time imaging and tracking of micro/nanorobotic swarms remain a challenge, considering the limited imaging size and spatial-temporal resolution of current imaging modalities. Here, we propose a strategy that enables real-time tracking and navigation of a microswarm in stagnant and flowing blood environments by using laser speckle contrast imaging (LSCI), featuring full-field imaging, high temporal-spatial resolution, and noninvasiveness. The change in dynamic convection induced by the microswarm can be quantitatively investigated by analyzing the perfusion unit (PU) distribution, offering an alternative approach to investigate the swarm behavior and its interaction with various blood environments. Both the microswarm and surrounding environment were monitored and imaged by LSCI in real time, and the images were further analyzed for simultaneous swarm tracking and navigation in the complex vascular system. Moreover, our strategy realized real-time tracking and delivery of a microswarm in vivo, showing promising potential for LSCI-guided active delivery of microswarm in the vascular system.

Cortical perfusion measurements with laser speckle contrast imaging during adenosine induced cardiac arrest for aneurysm clipping: a case report

Adenosine induced cardiac arrest (AiCA) is one of the methods used to facilitate microsurgical aneurysm clipping by providing more visibility and less pressure in the aneurysmal sac and neighboring vessels. We report the use of laser speckle contrast imaging (LSCI) during AiCA to monitor the changes in pulsation and perfusion on the cortical surface during adenosine induced cardiac arrest for aneurysm clipping surgery. Application of this technology for perfusion monitoring may improve workflow and surgical guidance and provide valuable feedback continuously throughout the procedure. ClinicalTrials.gov identifier: NCT0502840.

Real-time laser speckle contrast imaging for intraoperative neurovascular blood flow assessment: animal experimental study

The use of various blood flow control methods in neurovascular interventions is crucial for reducing postoperative complications. Neurosurgeons worldwide use different methods, such as contact Dopplerography, intraoperative indocyanine videoangiography (ICG) video angiography, fluorescein angiography, flowmetry, intraoperative angiography, and direct angiography. However, there is no noninvasive method that can assess the presence of blood flow in the vessels of the brain without the introduction of fluorescent substances throughout the intervention. The real-time laser-speckle contrast imaging (LSCI) method was studied for its effectiveness in controlling blood flow in standard cerebrovascular surgery cases in rat common carotid arteries, such as proximal occlusion, trapping, reperfusion, anastomosis, and intraoperative vessel thrombosis. The real-time LSCI method is a promising method for use in neurosurgical practice. This approach allows timely diagnosis of intraoperative disturbance of blood flow in vessels in cases of clip occlusion or thrombosis. Additionally, LSCI allows us to reliably confirm the functioning of the anastomosis and reperfusion after removal of the clips and thrombolysis in real time. An unresolved limitation of the method is noise from movements, but this does not reduce the value of the method. Additional research is required to improve the quality of the data obtained.

Enhancing blood flow prediction in multi-exposure laser speckle contrast imaging through ensemble learning with K-mean clustering

Purpose.Accurately visualizing and measuring blood flow is of utmost importance in maintaining optimal health and preventing the onset of various chronic diseases. One promising imaging technique that aids in visualizing perfusion in biological tissues is Multi-exposure Laser Speckle Contrast Imaging (MELSCI). MELSCI technique allows real-time quantitative measurements using multiple exposure times to obtain precise and reliable blood flow data. Additionally, the application of machine learning (ML) techniques can further enhance the accuracy of blood flow prediction in this imaging modality.Method.Our study focused on developing and evaluating Ensemble Learning ML techniques along with clustering algorithms for predicting blood flow rates in MELSCI. The effectiveness of these techniques was assessed using performance parameters, including accuracy, F1-score, precision, recall, specificity, and classification error rate.Result.Notably, the study revealed that Ensemble Learning with clustering emerged as the most accurate technique, achieving an impressive accuracy rate of 98.5%. Furthermore, it demonstrated a high recall of more than 91%, F1-score, the precision of more than 90%, higher specificity of 99%, and least classification error of 1.5%, highlighting its suitability and sustainability for flow prediction in MELSCI.Conclusion.The study's findings imply that Ensemble Learning can significantly contribute to enhancing the accuracy of blood flow prediction in MELSCI. This advancement holds substantial promise for healthcare professionals and researchers, as it facilitates improved understanding and assessment of perfusion within biological tissues, which will contribute to the maintenance of good health and prevention of chronic diseases.

Wide dynamic range measurement of blood flow in vivo using laser speckle contrast imaging

Significance

Laser speckle contrast imaging (LSCI) is a real-time wide-field technique that is applied to visualize blood flow in biomedical applications. However, there is currently a lack of relevant research to demonstrate that it can measure velocities over a wide dynamic range (WDR), which is critical for monitoring much higher and more pulsatile blood flow in larger size myocardial vessels, such as the coronary artery bypass graft, and visualizing the spatio-temporal evolution of myocardial blood flow perfusion in cardiac surgery.

Aim

We aim to demonstrate that the LSCI technique enables measuring velocities over a WDR from phantom experiments to animal experiments. In addition, LSCI is preliminarily applied to imaging myocardial blood flow distribution in vivo on rabbits.

Approach

Phantom and animal experiments are performed to verify that the LSCI method has the ability to measure blood velocities over a wide range. Our method is also validated by transit time flow measurement, which is the gold standard for blood flow measurement in cardiac surgery.

Results

Our method is demonstrated to measure the blood flow over a wide range from 0.2 to 635    mm / s . To validate the phantom results, the varying blood flow rate from 0 to 320    mm / s is detected in the rat carotid artery. Additionally, our technique also obtains blood flow maps of different myocardial vessels, such as superficial large/small veins, veins surrounded by fat, and myocardial deeper arteriole.

Conclusions

Our study has the potential to visualize the spatio-temporal evolution of myocardial perfusion in coronary artery bypass grafting, which would be of great benefit for future research in the life sciences and clinical medicine.

Dye-free visualisation of intestinal perfusion using laser speckle contrast imaging in laparoscopic surgery: a prospective, observational multi-centre study

INTRODUCTION

Intraoperative perfusion imaging may help the surgeon in creating the intestinal anastomoses in optimally perfused tissue. Laser speckle contrast imaging (LSCI) is such a perfusion visualisation technique that is characterized by dye-free, real-time and continuous imaging. Our aim is to validate the use of a novel, dye-free visualization tool to detect perfusion deficits using laparoscopic LSCI.

METHODS

In this multi-centre study, a total of 64 patients were imaged using the laparoscopic laser speckle contrast imager. Post-operatively, surgeons were questioned if the additional visual feedback would have led to a change in clinical decision-making.

RESULTS

This study suggests that the laparoscopic laser speckle contrast imager PerfusiX-Imaging is able to image colonic perfusion. All images were clear and easy to interpret for the surgeon. The device is non-disruptive of the surgical procedure with an average added surgical time of 2.5 min and no change in surgical equipment. The potential added clinical value is accentuated by the 17% of operating surgeons indicating a change in anastomosis location. Further assessment and analysis of both white light and PerfusiX perfusion images by non-involved, non-operating surgeons showed an overall agreement of 80%.

CONCLUSION

PerfusiX-Imaging is a suitable laparoscopic perfusion imaging system for colon surgery that can visualize perfusion in real-time with no change in surgical equipment. The additional visual feedback could help guide the surgeons in placing the anastomosis at the most optimal site.

Laser speckle contrast imaging, an alternative to laser doppler imaging in clinical practice of burn wound care derivation of a color code

OBJECTIVE

To develop a color code and to investigate the validity of Laser Speckle Contrast Imaging (LSCI) for measuring burn wound healing potential (HP) in burn patients as compared to the reference standard Laser Doppler Imaging (LDI).

METHOD

A prospective, observational, cohort study was conducted in adult patients with acute burn wounds. The relationship between mean flux measured with LDI and mean perfusion units (PU) measured with LSCI was expressed in a regression formula. Measurements were performed between 2 and 5 days after the burn wound. The creation of a LSCI color code was done by mapping the clinically validated color code of the LDI to the corresponding values on the LSCI scale. To assess validity of the LSCI, the ability of the LSCI to discriminate between HP < 14 and ≥ 14 days and HP < 21 and original ≥ 21 days according to the LDI reference standard was evaluated, with calculation of receiver operating characteristics (ROC) curves.

RESULTS

A total of 50 patients were included with a median age of 40 years and total body surface area burned of 6%. LSCI values of 143 PU and 113 PU were derived as the cut-off values for the need of conservative treatment (HP < 14 and ≥ 14 days) resp. surgical closure (HP < 21 and ≥ 21 days). These LSCI cut off values showed a good discrimination between HP 14 days versus ≥ 14 days (Area Under Curve (AUC)= 0.89; sensitivity 85% and specificity = 82%) and a good discrimination between HP 21 days versus ≥ 21 days (AUC of 0.89, sensitivity 81% and specificity 88%).

CONCLUSION

This is the first study in which a color code for the LSCI in adult clinical burn patients has been developed. Our study reconfirms the good performance of the LSCI for prediction of burn wound healing potential. This provides additional evidence for the potential value of the LSCI in specialized burn care.

Optimizing the precision of laser speckle contrast imaging

Laser speckle contrast imaging (LSCI) is a rapidly developing technology broadly applied for the full-field characterization of tissue perfusion. Over the recent years, significant advancements have been made in interpreting LSCI measurements and improving the technique's accuracy. On the other hand, the method's precision has yet to be studied in detail, despite being as important as accuracy for many biomedical applications. Here we combine simulation, theory and animal experiments to systematically evaluate and re-analyze the role of key factors defining LSCI precision-speckle-to-pixel size ratio, polarisation, exposure time and camera-related noise. We show that contrary to the established assumptions, smaller speckle size and shorter exposure time can improve the precision, while the camera choice is less critical and does not affect the signal-to-noise ratio significantly.

Comparing laser speckle contrast imaging and indocyanine green angiography for assessment of parathyroid perfusion

Accurate intraoperative assessment of parathyroid blood flow is crucial to preserve function postoperatively. Indocyanine green (ICG) angiography has been successfully employed, however its conventional application has limitations. A label-free method overcomes these limitations, and laser speckle contrast imaging (LSCI) is one such method that can accurately detect and quantify differences in parathyroid perfusion. In this study, twenty-one patients undergoing thyroidectomy or parathyroidectomy were recruited to compare LSCI and ICG fluorescence intraoperatively. An experimental imaging device was used to image a total of 37 parathyroid glands. Scores of 0, 1 or 2 were assigned for ICG fluorescence by three observers based on perceived intensity: 0 for little to no fluorescence, 1 for moderate or patchy fluorescence, and 2 for strong fluorescence. Speckle contrast values were grouped according to these scores. Analyses of variance were performed to detect significant differences between groups. Lastly, ICG fluorescence intensity was calculated for each parathyroid gland and compared with speckle contrast in a linear regression. Results showed significant differences in speckle contrast between groups such that parathyroids with ICG score 0 had higher speckle contrast than those assigned ICG score 1, which in turn had higher speckle contrast than those assigned ICG score 2. This was further supported by a correlation coefficient of -0.81 between mean-normalized ICG fluorescence intensity and speckle contrast. This suggests that ICG angiography and LSCI detect similar differences in blood flow to parathyroid glands. Laser speckle contrast imaging shows promise as a label-free alternative that overcomes current limitations of ICG angiography for parathyroid assessment.

Real-time laser speckle contrast imaging measurement during normothermic machine perfusion in pretransplant kidney assessment

OBJECTIVES

Normothermic machine perfusion (NMP) provides a platform for pre-transplant kidney quality assessment that is essential for the use of marginal donor kidneys. Laser speckle contrast imaging (LSCI) presents distinct advantages as a real-time and noncontact imaging technique for measuring microcirculation. In this study, we aimed to assess the value of LSCI in visualizing renal cortical perfusion and investigate the additional value of dual-side LSCI measurements compared to single aspect measurement during NMP.

METHODS

Porcine kidneys were obtained from a slaughterhouse and then underwent NMP. LSCI was used to measure one-sided cortical perfusion in the first 100 min of NMP. Thereafter, the inferior renal artery branch was occluded to induce partial ischemia and LSCI measurements on both ventral and dorsal sides were performed.

RESULTS

LSCI fluxes correlated linearly with the renal blood flow (R2  = 0.90, p < 0.001). After renal artery branch occlusion, absence of renal cortical perfusion could be visualized and semiquantified by LSCI. The overall ischemic area percentage of the ventral and dorsal sides was comparable (median interquartile range [IQR], 38 [24-43]% vs. 29 [17-46]%, p = 0.43), but heterogenous patterns between the two aspects were observed. There was a significant difference in oxygen consumption (mean ± standard deviation [SD], 2.57 ± 0.63 vs. 1.83 ± 0.49 mLO2 /min/100 g, p < 0.001), urine output (median [IQR], 1.3 [1.1-1.7] vs. 0.8 [0.6-1.3] mL/min, p < 0.05), lactate dehydrogenase (mean ± SD, 768 ± 370 vs. 905 ± 401 U/L, p < 0.05) and AST (mean ± SD, 352 ± 285 vs. 462 ± 383 U/L, p < 0.01) before and after renal artery occlusion, while no significant difference was found in creatinine clearance, fractional excretion of sodium, total sodium reabsorption and histological damage.

CONCLUSIONS

LSCI fluxes correlated linearly with renal blood flow during NMP. Renal cortical microcirculation and absent perfusion can be visualized and semiquantified by LSCI. It provides a relative understanding of perfusion levels, allowing for a qualitative comparison between regions in the kidney. Dual-side LSCI measurements are of added value compared to single aspect measurement and renal function markers.

Laser speckle contrast imaging based on spatial frequency domain filtering

We proposed a novel method to separate static and dynamic speckles based on spatial frequency domain filtering. First, the raw speckle image sequence is processed frame by frame through 2D Fourier transform, low-pass and high-pass filtering in the spatial frequency domain, and inverse Fourier transform. Then, we can obtain low- and high-frequency image sequences in the spatial domain. Second, we averaged both sequences in the time domain. After the above processing, we obtain the mean intensities of the dynamic and static speckle components in the spatial domain. Finally, we calculated the time-averaged modulation depth to map the 2-D blood flow distribution. Both phantom and vivo experiments demonstrated that the proposed method could effectively suppress the background non-uniformity and has the advantage of high computational efficiency. It also can effectively improve image contrast, contrast-to-noise ratio, and imaging dynamic range.

Real-time quantification of bowel perfusion using Laparoscopic Laser Speckle Contrast Imaging (LSCI) in a porcine model

BACKGROUND/PURPOSE

Real-time quantification of tissue perfusion can improve intraoperative surgical decision making. Here we demonstrate the utility of Laser Speckle Contrast Imaging as an intra-operative tool that quantifies real-time regional differences in intestinal perfusion and distinguishes ischemic changes resulting from arterial/venous obstruction.

METHODS

Porcine models (n = 3) consisted of selectively devascularized small bowel loops that were used to measure the perfusion responses under conditions of control/no vascular occlusion, arterial inflow occlusion, and venous outflow occlusion using laser speckle imaging and indocyanine green fluoroscopy. Laser Speckle was also used to assess perfusion differences between small bowel antimesenteric-antimesenteric and mesenteric-mesenteric anastomoses. Perfusion quantification was measured in relative perfusion units calculated from the laser speckle perfusion heatmap.

RESULTS

Laser Speckle distinguished between visually identified perfused, watershed, and ischemic intestinal segments with both color heatmap and quantification (p < .00001). It detected a continuous gradient of relative intestinal perfusion as a function of distance from the stapled ischemic bowel edge. Strong positive linear correlation between relative perfusion units and changes in mean arterial pressure resulting from both arterial (R2 = .96/.79) and venous pressure changes (R2 = .86/.96) was observed. Furthermore, Laser Speckle showed that the antimesenteric anastomosis had a higher perfusion than mesenteric anastomosis (p < 0.01).

CONCLUSIONS

Laser Speckle Contrast Imaging provides objective, quantifiable tissue perfusion information in both color heatmap and relative numerical units. Laser Speckle can detect spatial/temporal differences in perfusion between antimesenteric and mesenteric borders of a bowel segment and precisely detect perfusion changes induced by progressive arterial/venous occlusions in real-time.

Smartphone-Based Rigid Endoscopy Device with Hemodynamic Response Imaging and Laser Speckle Contrast Imaging

Modern smartphones have been employed as key elements in point-of-care (POC) devices due to remarkable advances in their form factor, computing, and display performances. Recently, we reported a combination of the smartphone with a handheld endoscope using laser speckle contrast imaging (LSCI), suggesting potential for functional POC endoscopy. Here, we extended our work to develop a smartphone-combined multifunctional handheld endoscope using dual-wavelength LSCI. Dual-wavelength LSCI is used to monitor the changes in dynamic blood flow as well as changes in the concentration of oxygenated (HbO2), deoxygenated (Hbr), and total hemoglobin (HbT). The smartphone in the device performs fast acquisition and computation of the raw LSCI data to map the blood perfusion parameters. The flow imaging performance of the proposed device was tested with a tissue-like flow phantom, exhibiting a speckle flow index map representing the blood perfusion. Furthermore, the device was employed to assess the blood perfusion status from an exteriorized intestine model of rat in vivo during and after local ischemia, showing that blood flow and HbO2 gradually decreased in the ischemic region whereas hyperemia and excess increases in HbO2 were observed in the same region right after reperfusion. The results indicate that the combination of LSCI with smartphone endoscopy delivers a valuable platform for better understanding of the functional hemodynamic changes in the vasculatures of the internal organs, which may benefit POC testing for diagnosis and treatment of vascular diseases.

Prediction of motion artifacts caused by translation in handheld laser speckle contrast imaging

Significance

In handheld laser speckle contrast imaging (LSCI), motion artifacts (MA) are inevitable. Suppression of MA leads to a valid and objective assessment of tissue perfusion in a wide range of medical applications including dermatology and burns. Our study shines light on the sources of these artifacts, which have not yet been explored. We propose a model based on optical Doppler effect to predict speckle contrast drop as an indication of MA.

Aim

We aim to theoretically model MA when an LSCI system measuring on static scattering media is subject to translational displacements. We validate the model using both simulation and experiments. This is the crucial first step toward creating robustness against MA.

Approach

Our model calculates optical Doppler shifts in order to predict intensity correlation function and contrast of the time-integrated intensity as functions of applied speed based on illumination and detection wavevectors. To validate the theoretical predictions, computer simulation of the dynamic speckles has been carried out. Then experiments are performed by both high-speed and low-framerate imaging. The employed samples for the experiments are a highly scattering matte surface and a Delrin plate of finite scattering level in which volume scattering occurs.

Results

An agreement has been found between theoretical prediction, simulation, and experimental results of both intensity correlation functions and speckle contrast. Coefficients in the proposed model have been linked to the physical parameters according to the experimental setups.

Conclusions

The proposed model provides a quantitative description of the influence of the types of illumination and media in the creation of MA. The accurate prediction of MA caused by translation based on Doppler shifts makes our model suitable to study the influence of rotation. Also the model can be extended for the case of dynamic media, such as live tissue.

Spectral analysis of laser speckle contrast imaging and infrared thermography to assess skin microvascular reactive hyperemia

BACKGROUND

Post-occlusive reactive hyperemia (PORH) test with signal spectral analysis coupled provides potential indicators for the assessment of microvascular functions.

OBJECTIVE

The objective of this study is to investigate the variations of skin blood flow and temperature spectra in the PORH test. Furthermore, to quantify the oscillation amplitude response to occlusion within different frequency ranges.

MATERIALS AND METHODS

Ten healthy volunteers participated in the PORH test and their hand skin temperature and blood flow images were captured by infrared thermography (IRT) and laser speckle contrast imaging (LSCI) system, respectively. Extracted signals from selected areas were then transformed into the time-frequency space by continuous wavelet transform for cross-correlation analysis and oscillation amplitude response comparisons.

RESULTS

The LSCI and IRT signals extracted from fingertips showed stronger hyperemia response and larger oscillation amplitude compared with other areas, and their spectral cross-correlations decreased with frequency. According to statistical analysis, their oscillation amplitudes in the PORH stage were obviously larger than the baseline stage within endothelial, neurogenic, and myogenic frequency ranges (p < 0.05), and their quantitative indicators of oscillation amplitude response had high linear correlations within endothelial and neurogenic frequency ranges.

CONCLUSION

Comparisons of IRT and LSCI techniques in recording the reaction to the PORH test were made in both temporal and spectral domains. The larger oscillation amplitudes suggested enhanced endothelial, neurogenic, and myogenic activities in the PORH test. We hope this study is also significant for investigations of response to the PORH test by other non-invasive techniques.

Real-time quantification of intestinal perfusion and arterial versus venous occlusion using laser speckle contrast imaging in porcine model

PURPOSE

Real-time intraoperative perfusion assessment may reduce anastomotic leaks. Laser speckle contrast imaging (LSCI) provides dye-free visualization of perfusion by capturing coherent laser light scatter from red blood cells and displays perfusion as a colormap. Herein, we report a novel method to precisely quantify intestinal perfusion using LSCI.

METHODS

ActivSight™ is an FDA-cleared multi-modal visualization system that can detect and display perfusion via both indocyanine green imaging (ICG) and LSCI in minimally invasive surgery. An experimental prototype LSCI perfusion quantification algorithm was evaluated in porcine models. Porcine small bowel was selectively devascularized to create regions of perfused/watershed/ischemic bowel, and progressive aortic inflow/portal vein outflow clamping was performed to study arterial vs. venous ischemia. Continuous arterial pressure was monitored via femoral line.

RESULTS

LSCI perfusion colormaps and quantification distinguished between perfused, watershed, and ischemic bowel in all vascular control settings: no vascular occlusion (p < 0.001), aortic occlusion (p < 0.001), and portal venous occlusion (p < 0.001). LSCI quantification demonstrated similar levels of ischemia induced both by states of arterial inflow and venous outflow occlusion. LSCI-quantified perfusion values correlated positively with higher mean arterial pressure and with increasing distance from ischemic bowel.

CONCLUSION

LSCI relative perfusion quantification may provide more objective real-time assessment of intestinal perfusion compared to conventional naked eye assessment by quantifying currently subjective gradients of bowel ischemia and identifying both arterial/venous etiologies of ischemia.

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

SIGNIFICANCE

Microfluidic flow phantom studies are commonly used for characterizing the performance of laser speckle contrast imaging (LSCI) instruments. The selection of the flow control system is critical for the reliable generation of flow during testing. The majority of recent LSCI studies using microfluidics used syringe pumps for flow control.

AIM

We quantified the uncertainty in flow generation for a syringe pump and a pressure-regulated flow system. We then assessed the performance of both LSCI and multi-exposure speckle imaging (MESI) using the pressure-regulated flow system across a range of flow speeds.

APPROACH

The syringe pump and pressure-regulated flow systems were evaluated during stepped flow profile experiments in a microfluidic device using an inline flow sensor. The uncertainty associated with each flow system was calculated and used to determine the reliability for instrument testing. The pressure-regulated flow system was then used to characterize the relative performance of LSCI and MESI during stepped flow profile experiments while using the inline flow sensor as reference.

RESULTS

The pressure-regulated flow system produced much more stable and reproducible flow outputs compared to the syringe pump. The expanded uncertainty for the syringe pump was 8 to 20 × higher than that of the pressure-regulated flow system across the tested flow speeds. Using the pressure-regulated flow system, MESI outperformed single-exposure LSCI at all flow speeds and closely mirrored the flow sensor measurements, with average errors of 4.6 % ± 2.6 % and 15.7 % ± 4.6 % , respectively.

CONCLUSIONS

Pressure-regulated flow systems should be used instead of syringe pumps when assessing the performance of flow measurement techniques with microfluidic studies. MESI offers more accurate relative flow measurements than traditional LSCI across a wide range of flow speeds.

Speed-resolved perfusion imaging using multi-exposure laser speckle contrast imaging and machine learning

SIGNIFICANCE

Laser speckle contrast imaging (LSCI) gives a relative measure of microcirculatory perfusion. However, due to the limited information in single-exposure LSCI, models are inaccurate for skin tissue due to complex effects from e.g. static and dynamic scatterers, multiple Doppler shifts, and the speed-distribution of blood. It has been demonstrated how to account for these effects in laser Doppler flowmetry (LDF) using inverse Monte Carlo (MC) algorithms. This allows for a speed-resolved perfusion measure in absolute units %RBC × mm/s, improving the physiological interpretation of the data. Until now, this has been limited to a single-point LDF technique but recent advances in multi-exposure LSCI (MELSCI) enable the analysis in an imaging modality.

AIM

To present a method for speed-resolved perfusion imaging in absolute units %RBC × mm/s, computed from multi-exposure speckle contrast images.

APPROACH

An artificial neural network (ANN) was trained on a large simulated dataset of multi-exposure contrast values and corresponding speed-resolved perfusion. The dataset was generated using MC simulations of photon transport in randomized skin models covering a wide range of physiologically relevant geometrical and optical tissue properties. The ANN was evaluated on in vivo data sets captured during an occlusion provocation.

RESULTS

Speed-resolved perfusion was estimated in the three speed intervals 0 to 1    mm / s , 1 to 10    mm / s , and > 10    mm / s , with relative errors 9.8%, 12%, and 19%, respectively. The perfusion had a linear response to changes in both blood tissue fraction and blood flow speed and was less affected by tissue properties compared with single-exposure LSCI. The image quality was subjectively higher compared with LSCI, revealing previously unseen macro- and microvascular structures.

CONCLUSIONS

The ANN, trained on modeled data, calculates speed-resolved perfusion in absolute units from multi-exposure speckle contrast. This method facilitates the physiological interpretation of measurements using MELSCI and may increase the clinical impact of the technique.

Feasibility and comparison of laparoscopic laser speckle contrast imaging to near-infrared display of indocyanine green in intraoperative tissue blood flow/tissue perfusion in preclinical porcine models

OBJECTIVE

To determine if laser speckle contrast imaging (LSCI) mitigates variations and subjectivity in the use and interpretation of indocyanine green (ICG) fluorescence in the current visualization paradigm of real-time intraoperative tissue blood flow/perfusion in clinically relevant scenarios.

METHODS

De novo laparoscopic imaging form-factor detecting real-time blood flow using LSCI and blood volume by near-infrared fluorescence (NIRF) of ICG was compared to ICG NIRF alone, for dye-less real-time visualization of tissue blood flow/perfusion. Experienced surgeons examined LSCI and ICG in segmentally devascularized intestine, partial gastrectomy, and the renal hilum across six porcine models. Precision and accuracy of identifying demarcating lines of ischemia/perfusion in tissues were determined in blinded subjects with varying levels of surgical experience.

RESULTS

Unlike ICG, LSCI perfusion detection was real time (latency < 150 ms: p < 0.01), repeatable and on-demand without fluorophore injection. Operating surgeons (n = 6) precisely and accurately identified concordant demarcating lines in white light, LSCI, and ICG modes immediately. Blinded subjects (n = 21) demonstrated similar spatial-temporal precision and accuracy with all three modes ≤ 2 min after ICG injection, and discordance in ICG mode at ≥ 5 min in devascularized small intestine (p < 0.0001) and in partial gastrectomy (p < 0.0001).

CONCLUSIONS

Combining LSCI for near real-time blood flow detection with ICG fluorescence for blood volume detection significantly improves precision and accuracy of perfusion detection in tissue locations over time, in real time, and repeatably on-demand than ICG alone.

Application of Laser Speckle Contrast Imaging (LSCI) for the Angiogenesis Measurement of Tumors in the Chorioallantoic Membrane (CAM) Model

Tumor angiogenesis is one essential aspect for the growth and metastasis of cancer cells, which means that adequate in vivo angiogenesis models are of utmost importance for the investigation of such diseases. The chick chorioallantoic membrane (CAM) model is one established method for this purpose and has already been used for research on multiple cancer types. One important part of the evaluation of tumors grafted onto the CAM is the measurement of tumor-induced angiogenesis. In order to address this central aspect, we utilized the novel PeriCam perfusion speckle imager (PSI) system high resolution (HR) model (Perimed AB, Järfälla, Sweden), which is based on laser speckle contrast imaging (LSCI) for the semiquantitative measurement of blood flow in the CAM model. This method enables a fast and accurate analysis of the angiogenesis of cell line tumors and primary tumors that are grafted onto the CAM. The proposed model can be regarded as a precursor model for personalized cancer therapy.

Correcting sampling bias in speckle contrast imaging

When performing spatial or temporal laser speckle contrast imaging (LSCI), contrast is generally estimated from localized windows containing limited numbers of independent speckle grains N_S. This leads to a systematic bias in the estimated speckle contrast. We describe an approach to determine N_S and largely correct for this bias, enabling a more accurate estimation of the speckle decorrelation time without recourse to numerical fitting of data. Validation experiments are presented where measurements are ergodic or non-ergodic, including in vivo imaging of mouse brain.

Mapping of Perfusion During Full-Thickness Blepharotomy Using Laser Speckle Contrast Imaging

PURPOSE

The aim of this study was to monitor how the blood perfusion in human upper eyelids is affected during full-thickness blepharotomy.

METHODS

Seven eyelids in 5 patients with upper eyelid retraction due to Graves' disease underwent full-thickness blepharotomy. Perfusion was measured using laser speckle contrast imaging in the eyelid margin and in the conjunctival pedicle.

RESULTS

Immediately following the procedure, a nonsignificant reduction in perfusion was observed in the skin of the pretarsal eyelid margin, being 66% of the initial value ( p = n.s.). However, a statistically significant decrease in perfusion, to 53% of the initial value ( p < 0.01), was seen in the central pedicle of the conjunctiva. There were no surgical complications such as infection, signs of ischemia, or bleeding.

CONCLUSIONS

In this study, eyelid perfusion was mapped during full-thickness blepharotomy for the first time using laser speckle contrast imaging. The results showed that perfusion is sufficiently preserved during surgery, probably due to the rich vascular supply in the periocular region, which may explain the low risk of postoperative complications such as ischemia and infection.

Hyperspectral and Laser Speckle Contrast Imaging for Monitoring the Effect of Epinephrine in Local Anesthetics in Oculoplastic Surgery

PURPOSE

Epinephrine is used in local anesthetics to induce vasoconstriction and thus reduce bleeding and prolong the anesthetic effect. Finding the optimal delay between the administration of the anesthetic and skin incision to ensure vasoconstriction and minimize bleeding is important and has recently become the subject of debate. This is the first study to assess blood perfusion and oxygen saturation (sO 2 ) simultaneously in response to a local anesthetic containing epinephrine in human oculoplastic surgery.

METHODS

A local anesthetic consisting of lidocaine and epinephrine (20 mg/ml + 12.5 μg/ml) was injected in the eyelids of 9 subjects undergoing blepharoplasty. The perfusion and sO 2 of the eyelids were monitored using laser speckle contrast imaging and hyperspectral imaging, respectively.

RESULTS

Laser speckle contrast imaging monitoring showed a decrease in perfusion over time centrally at the site of injection. Half-maximum effect was reached after 34 seconds, and full effect after 115 seconds, determined by exponential fitting. The drop in perfusion decreased gradually further away from the injection site and hypoperfusion was less prominent 4 mm from the injection site, with a spatially dependent half-maximum effect of 231 seconds. Hyperspectral imaging showed only a slight decrease in sO 2 of 11 % at the injection site.

CONCLUSIONS

The optimal time delay for skin incision in oculoplastic surgery is approximately 2 minutes after the injection of lidocaine with epinephrine. Longer delay does not lead to a further decrease in perfusion. As sO 2 was only slightly reduced after injection, the results indicate that the use of epinephrine is safe in the periocular region.

Laser speckle contrast imaging enables perfusion monitoring of the anterior segment during eye muscle surgery

We demonstrate that laser speckle contrast imaging can be used to monitor blood perfusion noninvasively during the detachment of ocular muscles, which may be a valuable tool for reducing the risk of anterior segment ischemia as a complication of strabismus surgery.

Laser Speckle Contrast Imaging of the Blood Perfusion in Glabellar Flaps Used to Repair Medial Canthal Defects

BACKGROUND

The glabellar flap is a common technique for surgical repair after tumor excision in the medial canthal area. However, the outcome may be affected by partial flap necrosis. Little is known about the impact of surgery on blood perfusion and the postoperative course of reperfusion due to the absence of reliable and noninvasive perfusion monitoring techniques. The aim of this study was to use a modern imaging technique to assess blood perfusion in glabellar flaps.

METHODS

Glabellar flaps were used to repair medial canthal defects following tumor excision in 7 patients. Blood perfusion was monitored using laser speckle contrast imaging: during surgery, immediately postoperatively (0 weeks), and at follow-up, 1, 3, and 6 weeks after surgery.

RESULTS

Perfusion decreased gradually along the length of the flap, and reached a minimum 15 mm from the flap base. Perfusion in the proximal 20 mm of the flap was completely restored after 1 week, while the distal part of the flap was gradually reperfused over 6 weeks. Both the functional and esthetic surgical outcomes were excellent.

CONCLUSIONS

The rapid reperfusion of the glabellar flap may be explained by its connection to the vascular network via the flap pedicle. In flaps longer than 20 mm, the distal part can be considered a free skin transplant, and a combination of a glabellar flap and a free skin graft could then be considered.

Dynamic Alterations in Blood Flow in Glaucoma Measured with Laser Speckle Contrast Imaging

PURPOSE

To assess the repeatability of blood flow velocity index (BFVi) metrics obtained with a recently Food and Drug Administration-cleared laser speckle contrast imaging device, the XyCAM RI (Vasoptic Medical, Inc), and to characterize differences in these metrics among control, glaucoma suspect, and glaucoma participants.

DESIGN

Prospective, observational study.

PARTICIPANTS

Forty-six participants: 20 control, 16 glaucoma suspect, and 10 glaucoma participants, 1 eye per participant.

METHODS

Key dynamic BFVi metrics-mean, peak, dip, volumetric rise index (VRI), volumetric fall index (VFI), time to rise (TtR), time to fall (TtF), blow-out time (BOT), skew, and acceleration time index-were measured in the optic disc, optic disc vessels, optic disc perfusion region, and macula in 4 imaging sessions on the same day. Intrasession and intersession variability were calculated using the coefficient of variation (CV) for each metric in each region of interest (ROI). Values for each dynamic BFVi variable were compared between glaucoma, glaucoma suspect, and control participants using bivariate and multivariate analysis. Pearson correlation coefficients were used to correlate each variable in each ROI with age, intraocular pressure, cup-to-disc ratio (CDR), mean deviation, pattern standard deviation, retinal nerve fiber layer thickness, and minimum rim width.

MAIN OUTCOME MEASURES

Coefficient of variation for the intrasession and intersession variability for each dynamic BFVi metric in each ROI and differences in each metric in each ROI between each diagnostic group.

RESULTS

Intersession CV for mean, peak, dip, VRI, VFI, TtR, and TtF ranged from 3.2 ± 2.5% to 11.0 ± 3.8%. Age, CDR, OCT metrics, and visual field metrics showed significant correlations with dynamic BFVi variables. Peak, mean, dip, VRI, and VFI were significantly lower in patients with glaucoma than in control participants in all ROIs except the fovea. These metrics also were significantly lower in glaucoma patients than glaucoma suspect patients in the disc vessels.

CONCLUSIONS

Dynamic blood flow metrics measured with the XyCAM RI are reliable, are associated with structural and functional glaucoma metrics, and are significantly different among glaucoma, glaucoma suspect, and control participants. The XyCAM RI may serve as an important tool in glaucoma management in the future.

High-resolution three-dimensional blood flow tomography in the subdiffuse regime using laser speckle contrast imaging

SIGNIFICANCE

Visualizing high-resolution hemodynamics in cerebral tissue over a large field of view (FOV), provides important information in studying disease states affecting the brain. Current state-of-the-art optical blood flow imaging techniques either lack spatial resolution or are too slow to provide high temporal resolution reconstruction of flow map over a large FOV.

AIM

We present a high spatial resolution computational optical imaging technique based on principles of laser speckle contrast imaging (LSCI) for reconstructing the blood flow maps in complex tissue over a large FOV provided that the three-dimensional (3D) vascular structure is known or assumed.

APPROACH

Our proposed method uses a perturbation Monte Carlo simulation of the high-resolution 3D geometry for both accurately deriving the speckle contrast forward model and calculating the Jacobian matrix used in our reconstruction algorithm to achieve high resolution. Given the convex nature of our highly nonlinear problem, we implemented a mini-batch gradient descent with an adaptive learning rate optimization method to iteratively reconstruct the blood flow map. Specifically, we implemented advanced optimization techniques combined with efficient parallelization and vectorization of the forward and derivative calculations to make reconstruction of the blood flow map feasible with reconstruction times on the order of tens of minutes.

RESULTS

We tested our reconstruction algorithm through simulation of both a flow phantom model as well as an anatomically correct murine cerebral tissue and vasculature captured via two-photon microscopy. Additionally, we performed a noise study, examining the robustness of our inverse model in presence of 0.1% and 1% additive noise. In all cases, the blood flow reconstruction error was <2  %   for most of the vasculature, except for the peripheral vasculature which suffered from insufficient photon sampling. Descending vasculature and deeper structures showed slightly higher sensitivity to noise compared with vasculature with a horizontal orientation at the more superficial layers. Our results show high-resolution reconstruction of the blood flow map in tissue down to 500  μm and beyond.

CONCLUSIONS

We have demonstrated a high-resolution computational imaging technique for visualizing blood flow map in complex tissue over a large FOV. Once a high-resolution structural image is captured, our reconstruction algorithm only requires a few LSCI images captured through a camera to reconstruct the blood flow map computationally at a high resolution. We note that the combination of high temporal and spatial resolution of our reconstruction algorithm makes the solution well-suited for applications involving fast monitoring of flow dynamics over a large FOV, such as in functional neural imaging.

Hydroxyl Ethyl Starch (HES) Preserves Intrarenal Microcirculatory Perfusion Shown by Contrast-Enhanced Ultrasound (Ceus), and Renal Function in a Severe Hemodilution Model in Pigs

ABSTRACT

Acute normovolemic hemodilution (ANH) is associated with low oxygen carrying capacity of blood and purposed to cause renal injury in perioperative setting. It is best accomplished in a perioperative setting by a colloid such as hydroxyl ethyl starch (HES) due its capacity to fill the vascular compartment and maintain colloidal pressure. However, alterations of intra renal microvascular perfusion, flow and its effects on renal function and damage during ANH has not been sufficiently clarified. Based on the extensive use of HES in the perioperative setting we tested the hypothesis that the use of HES during ANH is able to perfuse the kidney microcirculation adequately without causing renal dysfunction and injury in pigs. Hemodilution (n = 8) was performed by stepwise replacing blood with HES to hematocrit (Hct) levels of 20% (T1), 15% (T2), and 10% (T3). Seven control animals were investigated. Systemic and renal hemodynamics were monitored. Renal microcirculatory perfusion was visualized and quantified using contrast-enhanced ultrasound (CEUS) and laser speckle imaging (LSI). In addition, sublingual microcirculation was measured by handheld vital microscopy (HVM). Intrarenal mean transit time of ultrasound contrast agent (IRMTT-CEUS) was reduced in the renal cortex at Hct 10% in comparison to control at T3 (1.4 ± 0.6 vs. 2.2 ± 0.7 seconds, respectively, P < 0.05). Although renal function was preserved, the serum neutrophil gelatinase-associated lipocalin (NGAL) levels was higher at Hct 10% (0.033 ± 0.004 pg/μg protein) in comparison to control at T3 (0.021 ± 0.002 pg/μg protein. A mild correlation between CO and IRMTT (renal RBC velocity) (r -0.53; P = 0.001) and CO and NGAL levels (r 0.66; P = 0.001) was also found. Our results show that HES induced ANH is associated with a preserved intra renal blood volume, perfusion, and function in the clinical range of Hct (<15%). However, at severely low Hct (10%) ANH was associated with renal injury as indicated by increased NGAL levels. Changes in renal microcirculatory flow (CEUS and LSI) followed those seen in the sublingual microcirculation measured with HVM.

Functional imaging of human retina using integrated multispectral and laser speckle contrast imaging

A novel integration of retinal multispectral imaging (MSI), retinal oximetry and laser speckle contrast imaging (LSCI) is presented for functional imaging of retinal blood vessels that could potentially allow early detection or monitoring of functional changes. We designed and built a cost-effective, scalable, retinal imaging instrument that integrates structural and functional retinal imaging techniques, including MSI, retinal oximetry and LSCI. Color fundus imaging was performed with 470 nm, 550 nm and 600 nm wavelength light emitting diode (LED) illumination. Retinal oximetry was performed using 550 nm and 600 nm LED illumination. LSCI of blood flow was performed using 850 nm laser diode illumination at 82 frames per second. LSCI can visualize retinal and choroidal vasculature without requiring exogenous contrast agents and can provide time-resolved information on blood flow, generating a cardiac pulse waveform from retinal vasculature. The technology can rapidly acquire structural MSI images, retinal oximetry and LSCI blood flow information in a simplified clinical workflow without requiring patients to move between instruments. Results from multiple modalities can be combined and registered to provide structural as well as functional information on the retina. These advances can reduce barriers for clinical adoption, accelerating research using MSI, retinal oximetry and LSCI of blood flow for diagnosis, monitoring and elucidating disease pathogenesis.

Movement correction method for laser speckle contrast imaging of cerebral blood flow in cranial windows in rodents

Laser speckle contrast imaging (LSCI) is used in clinical research to dynamically image blood flow. One drawback is its susceptibility to movement artifacts. We demonstrate a new, simple method to correct motion artifacts in LSCI signals measured in awake mice with cranial windows during sensory stimulation. The principle is to identify a region in the image in which speckle contrast (SC) is independent of blood flow and only varies with animal movement, then to regress out this signal from the data. We show that (1) the regressed signal correlates well with mouse head movement, (2) the corrected signal correlates better with independently measured blood volume and (3) it has a (59 ± 6)% higher signal-to-noise ratio. Compared to three alternative correction methods, ours has the best performance. Regressing out flow-independent global variations in SC is a simple and accessible way to improve the quality of LSCI measurements.

Adaptive processing for noise attenuation in laser speckle contrast imaging

BACKGROUND AND OBJECTIVE

Blood vessel visualization is an essential task to treat and evaluate diseases such as port-wine stain. Laser Speckle Contrast Imaging (LSCI) have applications in the analysis of the microvasculature. However, it is often limited to superficial depths because the tissue among skin and microvasculature introduces noise in the image. To analyze microvasculature, traditional LSCI methods compute a Contrast Image (CI) by using a shifting window of fixed size and shape, which is inadequate in images with structures different types of morphologies in it, as happens in LSCI. This work aims to reduce the noise in the CIs to improve the visualization of blood vessels at high depths (> 300 μ m).

METHODS

The proposed method processes the CIs with analysis windows that change their size and shape for each pixel to compute the contrast representation with pixels more representatives to the region.

RESULTS

We performed experiments varying the depth of the blood vessels, the number of frames required to compute the representation, and the blood flow in the blood vessel. We looked for an improvement in the Contrast to Noise Ratio (CNR) in the periphery of the blood vessels using an analysis of variance. Finding that the adaptive processing of the contrast images allows a significant noise attenuation, translated into a better visualization of blood vessels. An average CNR of 2.62 ± 1 and 5.26 ± 1.7 was reached for in-vitro and in-vivo tests respectively, which is higher in comparison with traditional LSCI approaches.

CONCLUSIONS

The results, backed by the measured CNR, obtained a noise reduction in the CIs, this means a better temporal and spatial resolution. The proposed awK method can obtain an image with better quality than the state-of-the-art methods using fewer frames.

Blood Perfusion of Random Skin Flaps in Humans-In Vivo Assessment by Laser Speckle Contrast Imaging

BACKGROUND

The viability of random skin flaps (RSFs) depends on an adequate perfusion pressure to avoid necrosis. Laser speckle contrast imaging is a new method to monitor skin flap microcirculation.

OBJECTIVE

The authors aimed to use laser speckle contrast imaging in evaluating the correlation between the perfusion pressure and the length-to-width ratio (LTWR) of RSFs.

MATERIALS AND METHODS

Sixty patients submitted to flaps were included: 20 advancement, 20 rotation, and 20 transposition flaps. Laser speckle contrast imaging measurements of perfusion were obtained-after the flaps were planned, dissected, and sutured-from the base to the tip of the flaps, allowing the creation of plot charts and calculation of linear regression equations.

RESULTS

Perfusion consistently and significantly decreased with the dissection of all flaps. A significant correlation between LTWR and perfusion was observed in undermined and sutured stages; a mathematical model was then delineated, explaining objectively the drop of perfusion along LTWR, with statistical significance, in all flaps.

CONCLUSION

Laser speckle contrast imaging allows accurate, rapid, reproducible, and noncontact measurements of skin blood perfusion over RSF, ultimately leading to an optimization of skin flap planning. This study proves that variation of perfusion pressure along the flap is dependent on the LTWR in a linear decreasing function.

Depth resolution in multifocus laser speckle contrast imaging

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.

Ensemble averaging laser speckle contrast imaging: statistical model of improvement as function of static scatterers

The appearance of the common artifacts of laser speckle contrast imaging (LSCI), namely the granularity in flow rate estimation caused by static scatterers, is a well-known phenomenon. This artifact can be greatly reduced in spatial speckle contrast calculation using interframe decorrelated illumination, forcing true ensemble averaging. We propose a statistical model, which describes the effect of multiple image acquisitions on the contrast map quality when the illumination stable and when the illumination is decorrelated frame by frame. We investigate the improvement as a function of the ratio of dynamic and static scatterers by formulating a statistical distribution based model, using in simulation, flow phantom and in vivo experiments. Our main finding is that the ensemble averaging yields limited improvement in several practical cases due to the highly heterogeneous scatterer structure of living tissues.

Mixed scattering as a problem in laser speckle contrast analysis

Static scattering is detrimental to the accuracy of laser speckle contrast analysis (LASCA) measurements on skin when, instead of percentile change monitoring, absolute perfusion values are needed, e.g., for tissue injury examination. Perfusion values were calculated using two evaluation models, while changing the dynamic/static scattering ratio of monitored skin and tissue phantoms. Results were strongly affected by the significant increase of static contribution. Measurements on a modified tissue phantom showed that the changes in the measured perfusion values were mostly caused by the mixed scattering, which was omitted by the tested models. Dynamic ratio values obtained by multi-exposure LASCA could be used for perfusion data correction.

Multimodal imaging of laser speckle contrast imaging combined with mosaic filter-based hyperspectral imaging for precise surgical guidance

OBJECTIVE

To enable a real-time surgical guidance system that simultaneously monitors blood vessel perfusion, oxygen saturation, thrombosis, and tissue recovery by combining multiple optical imaging techniques into a single system: visible imaging, mosaic filter-based snapshot hyperspectral imaging (HSI), and laser speckle contrast imaging (LSCI).

METHODS

The multimodal optical imaging system was demonstrated by clamping blood vessels in the small intestines of rats to create areas of restricted blood flow. Subsequent tissue damage and regeneration were monitored during procedures. Using LSCI, vessel perfusion was measured, revealing the biological activity and survival of organ tissues. Blood oxygen saturation was monitored using HSI in the near-infrared region. Principal component analysis was used over the spectral dimension to identify an HSI wavelength combination optimized for hemodynamic biomarker visualization. HSI and LSCI were complimentary, identifying thrombus generation and tissue recovery, which was not possible in either modality alone.

RESULTS AND CONCLUSION

By analyzing multimodal tissue information from visible imaging, LSCI perfusion imaging, and HSI, a recovery prognosis could be determined based on the blood supply to the organ. The unique combination of the complementary imaging techniques into a single surgical microscope holds promise for improving the real-time determination of blood supply and tissue prognosis during surgery.

SIGNIFICANCE

Precise real-time monitoring for vascular anomalies promises to reduce the risk of organ damage in precise surgical operations such as tissue resection and transplantation. In addition, the convergence of label-free imaging technologies removes delays associated with the injection and diffusion of vascular monitoring dyes.

Reperfusion of Free Full-Thickness Skin Grafts in Periocular Reconstructive Surgery Monitored Using Laser Speckle Contrast Imaging

PURPOSE

Free skin grafts are frequently used in reconstructive surgery. However, little is known about the course of reperfusion due to the previous lack of reliable perfusion monitoring techniques. The aim of this study was to use state-of-the-art laser speckle contrast imaging to monitor free skin grafts in the periocular area.

METHODS

Seven patients needing surgery due to tumor removal or cicatricial ectropion in the periocular region underwent reconstructive surgery using free skin grafts from either the contralateral upper eyelid or the upper inner arm. The free skin grafts measured 10-30 mm horizontally and 9-30 mm vertically. Blood perfusion was monitored using laser speckle contrast imaging immediately postoperatively (0 weeks) and at follow-up after 1, 3, and 7 weeks.

RESULTS

All grafts were reperfused gradually during healing, the median value being 46% in the central part of the graft after 1 week and 79% after 3 weeks. The grafts were completely reperfused after 7 weeks. No difference was observed in the rate of reperfusion between the center and periphery of the grafts (p = not significant). The cosmetic and functional outcome was excellent in all but 1 patient, who developed ectropion that had to be surgically corrected.

CONCLUSIONS

Skin grafts in the periorbital area are fully reperfused after 7 weeks. The periocular area is known to be well-vascularized and thus forgiving to reconstructive surgery. Future investigations of the reperfusion of free skin grafts in other parts of the body or in higher-risk populations should be carried out.

Revascularization After H-plasty Reconstructive Surgery in the Periorbital Region Monitored With Laser Speckle Contrast Imaging

BACKGROUND

H-plasty reconstructive surgery is commonly used to close defects after tumor excision in the periorbital region. Revascularization of the bipedicle skin flaps is essential for healing. However, it has not previously been possible to study this revascularization in humans due to the lack of noninvasive perfusion monitoring techniques. The aim was to monitor perfusion in H-plasty flaps during surgery and during postoperative follow-up, using laser speckle contrast imaging.

METHOD

H-plasty, i.e., bipedicle random advancement skin flaps, was used for reconstruction of the eyelids after tumor removal in 7 patients. The median length and width of the skin flaps were 13 mm (range, 8-20 mm) and 10 mm (range, 5-11 mm), respectively. Blood perfusion was measured using laser speckle contrast imaging during surgery and at follow up 1, 3, and 6 weeks postoperatively, to monitor revascularization.

RESULTS

Immediately postoperatively, the perfusion in the distal end of the flaps had fallen to 54% (95% CI, 38%-67%). The perfusion then quickly increased during the healing process, being 104% (86%-124%) after 1 week, 115% (94%-129%) after 3 weeks, and 112% (96%-137%) after 6 weeks. There was no clinically observable ischemia or tissue necrosis.

CONCLUSIONS

Revascularization of the H-plasty procedure flaps occurs quickly, within a week postoperatively, presumably due to the existing vascular network of the flap pedicle, and was not dependent on significant angiogenesis. This perfusion study confirms the general opinion that H-plasty is a good reconstructive technique, especially in the periorbital region with its rich vascular supply.

Real-time visualization of renal microperfusion using laser speckle contrast imaging

SIGNIFICANCE

Intraoperative parameters of renal cortical microperfusion (RCM) have been associated with postoperative ischemia/reperfusion injury. Laser speckle contrast imaging (LSCI) could provide valuable information in this regard with the advantage over the current standard of care of being a non-contact and full-field imaging technique.

AIM

Our study aims to validate the use of LSCI for the visualization of RCM on ex vivo perfused human-sized porcine kidneys in various models of hemodynamic changes.

APPROACH

A comparison was made between three renal perfusion measures: LSCI, the total arterial renal blood flow (RBF), and sidestream dark-field (SDF) imaging in different settings of ischemia/reperfusion.

RESULTS

LSCI showed a good correlation with RBF for the reperfusion experiment (0.94  ±  0.02; p  <  0.0001) and short- and long-lasting local ischemia (0.90  ±  0.03; p  <  0.0001 and 0.81  ±  0.08; p  <  0.0001, respectively). The correlation decreased for low flow situations due to RBF redistribution. The correlation between LSCI and SDF (0.81  ±  0.10; p  <  0.0001) showed superiority over RBF (0.54  ±  0.22; p  <  0.0001).

CONCLUSIONS

LSCI is capable of imaging RCM with high spatial and temporal resolutions. It can instantaneously detect local perfusion deficits, which is not possible with the current standard of care. Further development of LSCI in transplant surgery could help with clinical decision making.

Successful Free Bilamellar Eyelid Grafts for the Repair of Upper and Lower Eyelid Defects in Patients and Laser Speckle Contrast Imaging of Revascularization

PURPOSE

It is generally believed that large eyelid defects must be repaired using a vascularized flap for 1 lamella, while the other can be a free graft. Recent studies indicate that the pedicle of a tarsoconjunctival flap does not contribute to blood perfusion. The purpose of this study was to explore whether large eyelid defects can be repaired using a free bilamellar eyelid autograft alone.

METHODS

Ten large upper and lower eyelid defects resulting from tumor excision were reconstructed using bilamellar grafts harvested from the contralateral or opposing eyelid. Revascularization of the flap was monitored during healing using laser speckle contrast imaging, and the surgical outcome was assessed.

RESULTS

The functional and cosmetic results were excellent. All grafts survived and there was no tissue necrosis. Only 1 patient underwent revision after 4 days as the sutures came loose. Two patients developed minimal ectropion but needed no reoperation. All patients were satisfied with the surgical results. Perfusion monitoring showed that the grafts were gradually revascularized, exhibiting 50% perfusion after 4 weeks and 90% perfusion after 8 weeks.

CONCLUSIONS

A free bilamellar eyelid graft appears to be an excellent alternative to the tarsoconjunctival flap procedure in the reconstruction of both upper and lower eyelid defects, especially in patients who cannot tolerate visual axis occlusion or the 2-stage procedure of the conventional staged flap procedure.

Improving imaging depth by dynamic laser speckle imaging and topical optical clearing for in vivo blood flow monitoring

Laser speckle contrast imaging (LSI) is a promising non-invasive full-field blood flow monitoring technique. However, it is still far from clinic practice due to insufficient contrast-to-noise ratio (CNR) and limited detection depth. In this study, an in vivo laser speckle imaging visualization system was constructed to observe the blood circulation on a dorsal skin. A dynamic laser speckle imaging (dLSI) scheme, other than traditional laser speckle contrast analysis method, was applied to separate the dynamic light scattering from the static one to increase the image CNR. Based on the theoretical optimization for dLSI, at least two pixels are required for speckle pattern sampling and a spatial window size of 7 × 7 was optimal to balance the spatial resolution and statistical accuracy. The in vivo experiment observation shows that the CNR is improved 8.4 times by dLSI. The blood vessels were more pronounced, and more capillaries can be observed than in traditional laser speckle contrast images. Topical optical clearing technique by thiazone was combined with dLSI to increase the sampling depth from 700 to 1000 μm.