A laser speckle imaging technique for measuring tissue perfusion

Vasoreactivity of the optic nerve head, nailfold, and facial skin in response to cold provocation in normal-tension glaucoma patients

BACKGROUND

The dysfunction of optic nerve head (ONH) hemodynamics has been suggested to be involved in the pathogenesis of normal-tension glaucoma (NTG). The aim of this study was to compare vasoreactivity in the ONH, nailfold, and facial skin in response to cold-water provocation in NTG patients and healthy controls.

METHODS

We performed cold-water provocation in 14 eyes of 14 NTG patients and 15 eyes of 15 age-matched control subjects. Laser speckle flowgraphy-derived tissue-area mean blur rate (MT), skin blood flowmetry-derived pulse wave amplitude (PA), nailfold capillaroscopy-derived nailfold capillary diameter, and other clinical parameters were recorded at baseline and 4 and 6 min after the cold stimulus. We compared changes (as percentages) in these variables in the NTG and control subjects with a linear mixed-effects model and evaluated correlations between these changes with Spearman's rank correlation coefficient.

RESULTS

The interaction term between the NTG group (reference, control group) and the 4-min protocol step (reference, baseline) significantly affected the changes in MT, nailfold capillary diameter and PA (β = -9.51%, P = 0.017, β = -20.32%, P = 0.002; β =  + 18.06%, P = 0.017, respectively). The change in MT was positively correlated with the change in nailfold capillary diameter, and negatively correlated with the change in PA (r = 0.39, P = 0.036; r = -0.40, P = 0.031, respectively).

CONCLUSION

NTG patients showed abnormal vasoconstriction in the ONH and nailfold and vasodilation in the facial skin in response to cold-water provocation.

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.

Exploration of Chick Embryo and Chorioallantoic Membrane on Imaging Navigated Platforms for Anticancer Pharmaceutical Evaluations

Conforming to the current replace-reduce-refine 3Rs' guidelines in animal experiments, a series of explorative efforts have been made to set up operable biomedical imaging-guided platforms for qualitative and quantitative evaluations on pharmacological effects of tumor vascular-disrupting agents (VDAs), based on the chick embryos (CEs) with its chorioallantoic membrane (CAM), in this overview. The techniques and platforms have been hierarchically elaborated, from macroscopic to microscopic and from overall to specific aspects. A protocol of LED lamplight associated with a new deep-learning algorithm was consolidated to screen out weak CEs by using the CAM vasculature imaging. 3D magnetic resonance imaging (MRI) and laser speckle contrast imaging (LSCI) to monitor the evolution of CE and vascular changes in CAM are introduced. A LSCI-CAM platform for studying the effects of VDAs on normal and cancerous vasculature of CAM and possible molecular mechanisms has been demonstrated. Finally, practical challenges and future perspectives are highlighted. The aim of this article is to help peers in biomedical research to familiarize with the CAM platform and to optimize imaging protocols for the evaluation of vasoactive pharmaceuticals, especially anticancer vascular targeted therapy.

Role of aquaporin 5 and glandular blood flow in the acetylcholine-induced secretion of saliva in rats

To clarify the role of the aquaporin 5 (AQP5) in salivary secretion, we evaluated acetylcholine (ACh)-induced secretion in Sprague-Dawley (SD) rats, rats expressing a low level of AQP5 protein (AQP5/low SD) which developed from SD rats, and Wistar/ST rats. The salivary secretion in AQP5/low SD rats in response to infusions of low-dose ACh (60-120 nmol/min) was 27-42% of that in SD rats. By contrast, Wistar/ST rats exhibited comparable secretion to that of SD rats in response to low-doses ACh, despite their low-level expression of AQP5. Experiments using spectrofluorometry and RT-PCR demonstrated no differences in the ACh-induced Ca2+ responses or the mRNA expression of muscarinic receptor, Cl- channel, or cotransporter between these strains. These findings imply that factors other than the function of salivary acinar cells regulates the secretion in response to weak stimuli. Monitoring of the hemodynamics in the submandibular gland revealed that low-doses ACh induced different patterns of the fluctuations in the blood flow in these strains. The blood flow decreased below the resting level in AQP5/low SD rats, but remained mostly above the resting level in Wistar/ST rats. The present study reveals that the contribution of AQP5-dependent transport of water is altered by stimulus intensity and blood flow.

Photoplethysmographic Imaging of Hemodynamics and Two-Dimensional Oximetry

The review of recent papers devoted to actively developing methods of photoplethysmographic imaging (the PPGI) of blood volume pulsations in vessels and non-contact two-dimensional oximetry on the surface of a human body has been carried out. The physical fundamentals and technical aspects of the PPGI and oximetry have been considered. The manifold of the physiological parameters available for the analysis by the PPGI method has been shown. The prospects of the PPGI technology have been discussed. The possibilities of non-contact determination of blood oxygen saturation SpO2 (pulse saturation O2) have been described. The relevance of remote determination of the level of oxygenation in connection with the spread of a new coronavirus infection SARS-CoV-2 (COVID-19) has been emphasized. Most of the works under consideration cover the period 2010-2021.

Transient Thermal Response of Blood Vessels during Laser Irradiation Monitored by Laser Speckle Contrast Imaging

Real-time monitoring of blood flow and thrombosis formation induced by laser irradiation is critical to reveal the thermal-damage mechanism and successfully implement vascular-dermatology laser surgery. Laser speckle contrast imaging (LSCI) is a non-invasive technique to visualize perfusion in various tissues. However, the ability of the LSCI to monitor the transient thermal response of blood vessels, especially thrombus formation during laser irradiation, requires further research. In this paper, an LSCI system was constructed and a 632 nm He-Ne laser was employed to illuminate a Sprague Dawley rat dorsal skin chamber model irradiated by a 1064 nm Nd: YAG therapy laser. The anisotropic diffusion filtering (ADF) technique is implemented after temporal LSCI (tLSCI) processing to improve the SNR and temporal resolution. The speckle flow index is used to characterize the blood-flow velocity to reduce the computational cost. The combination of the tLSCI and ADF increases the temporal resolution by five times and the SNR by 17.2 times and 16.14 times, without and with laser therapy, respectively. The laser-induced thrombus formation and vascular damage during laser surgery can be visualized without any exogenous labels, which provides a powerful tool for thrombus monitoring during laser surgery.

Development and characterization of a chick embryo chorioallantoic membrane (CAM) based platform for evaluation of vasoactive medications

Among various anti-cancer therapies, tumor vascular disrupting agents (VDAs) play a crucial role, for which their off-targeting effects on normal vessels need also to be investigated. The purpose of this study was to set up an in-ovo platform that combines a laser speckle contrast imaging (LSCI) modality with chick embryo chorioallantoic membrane (CAM) to real-time monitor vascular diameters and perfusion without and with intravascular injection. Two eggshell windows for both observation or measurement and injection were opened. Dynamic blood perfusion images and corresponding statistic graphs were acquired by using a LSCI unit on CAMs from embryo date (ED) 9 to ED15. A dedicated fine needle catheter was made for slow intravascular administration over 30 min with simultaneous LSCI acquisition. To verify the connectivity between CAM vessels and the embryonic circulations in the egg, contrast-enhanced 3D micro computed tomography (μCT), 2D angiography and histology were executed. This platform was successfully established to acquire, quantify and demonstrate vascular and hemodynamic information from the CAM. Chick embryos even with air cell opened remained alive from ED9 to ED15. Through collecting LSCI derived CAM vascular diameter and perfusion parameters, ED12 was determined as the best time window for vasoactive drug studies. A reverse correlation between CAM vessel diameter and blood perfusion rate was found (p < 0.002). Intravascular infusion and simultaneous LSCI acquisition for 30 min in ovo proved feasible. Contrast-enhanced angiography and histomorphology could characterize the connectivity between CAM vasculature and embryonic circulation. This LSCI-CAM platform was proved effective for investigating the in-ovo hemodynamics, which paves the road for further preclinical research on vasoactive medications including VDAs.

OUP accepted manuscript

Aims

Adverse cardiovascular events have day/night patterns with peaks in the morning, potentially related to endogenous circadian clock control of platelet activation. Circadian nuclear receptor Rev-erbα is an essential and negative component of the circadian clock. To date, the expression profile and biological function of Rev-erbα in platelets have never been reported.

Methods and results

Here, we report the presence and functions of circadian nuclear receptor Rev-erbα in human and mouse platelets. Both human and mouse platelet Rev-erbα showed a circadian rhythm that positively correlated with platelet aggregation. Global Rev-erbα knockout and platelet-specific Rev-erbα knockout mice exhibited defective in haemostasis as assessed by prolonged tail-bleeding times. Rev-erbα deletion also reduced ferric chloride-induced carotid arterial occlusive thrombosis, prevented collagen/epinephrine-induced pulmonary thromboembolism, and protected against microvascular microthrombi obstruction and infarct expansion in an acute myocardial infarction model. In vitro thrombus formation assessed by CD41-labelled platelet fluorescence intensity was significantly reduced in Rev-erbα knockout mouse blood. Platelets from Rev-erbα knockout mice exhibited impaired agonist-induced aggregation responses, integrin αIIbβ3 activation, and α-granule release. Consistently, pharmacological inhibition of Rev-erbα by specific antagonists decreased platelet activation markers in both mouse and human platelets. Mechanistically, mass spectrometry and co-immunoprecipitation analyses revealed that Rev-erbα potentiated platelet activation via oligophrenin-1-mediated RhoA/ERM (ezrin/radixin/moesin) pathway.

Conclusion

We provided the first evidence that circadian protein Rev-erbα is functionally expressed in platelets and potentiates platelet activation and thrombus formation. Rev-erbα may serve as a novel therapeutic target for managing thrombosis-based cardiovascular disease.

Key question

Adverse cardiovascular events have day/night patterns with peaks in the morning, potentially related to endogenous circadian clock control of platelet activation. Whether circadian nuclear receptor Rev-erba is present in platelets and regulates platelet function remains unknown.

Key finding

We provide the first evidence that Rev-erba is functionally expressed in platelets and acts as a positive regulator of platelet activation/thrombus formation through the oligophrenin-1-mediated RhoA/ERM signalling pathway.

Take home message

Our observations highlight the importance of circadian clock machinery in platelet physiology and support the notion that Rev-erba may serve as a novel therapeutic target for managing thrombosis-based cardiovascular diseases.

Utilisation of Chick Embryo Chorioallantoic Membrane as a Model Platform for Imaging-Navigated Biomedical Research

The fertilised chick egg and particularly its chorioallantoic membrane (CAM) have drawn continuing interest in biomedicine and bioengineering fields, especially for research on vascular study, cancer, drug screening and development, cell factors, stem cells, etc. This literature review systemically introduces the CAM's structural evolution, functions, vascular features and the circulation system, and cell regulatory factors. It also presents the major and updated applications of the CAM in assays for pharmacokinetics and biodistribution, drug efficacy and toxicology testing/screening in preclinical pharmacological research. The time course of CAM applications for different assays and their advantages and limitations are summarised. Among these applications, two aspects are emphasised: (1) potential utility of the CAM for preclinical studies on vascular-disrupting agents (VDAs), promising for anti-cancer vascular-targeted therapy, and (2) modern imaging technologies, including modalities and their applications for real-time visualisation, monitoring and evaluation of the changes in CAM vasculature as well as the interactions occurring after introducing the tested medical, pharmaceutical and biological agents into the system. The aim of this article is to help those working in the biomedical field to familiarise themselves with the chick embryo CAM as an alternative platform and to utilise it to design and optimise experimental settings for their specific research topics.

Fourier transforms for fast and quantitative Laser Speckle Imaging

Laser speckle imaging is a powerful imaging technique that visualizes microscopic motion within turbid materials. At current two methods are widely used to analyze speckle data: one is fast but qualitative, the other quantitative but computationally expensive. We have developed a new processing algorithm based on the fast Fourier transform, which converts raw speckle patterns into maps of microscopic motion and is both fast and quantitative, providing a dynamnic spectrum of the material over a frequency range spanning several decades. In this article we show how to apply this algorithm and how to measure a diffusion coefficient with it. We show that this method is quantitative and several orders of magnitude faster than the existing quantitative method. Finally we harness the potential of this new approach by constructing a portable laser speckle imaging setup that performs quantitative data processing in real-time on a tablet.

Multi-exposure laser speckle contrast imaging using a video-rate multi-tap charge modulation image sensor

Multi-exposure laser speckle contrast imaging (MELSCI) systems based on high frame rate cameras are suitable for wide-field quantitative measurement of blood flow. However, high-speed camera-based MELSCI requires high power consumption, large memory, and high processing capability, which may lead to relatively large and expensive hardware. To realize a compact and cost-efficient MELSCI system, we discuss an application of the multi-tap CMOS image sensor originally designed for time-of-flight range imaging. This image sensor operated in the global shutter mode and every pixel was provided with multiple charge-storage diodes. Multiple images for different exposures were acquired simultaneously because exposure patterns were programmable to implement an arbitrary exposure duration for each tap. The frame rate was close to video frame rates (30 frames per second (fps)) regardless of the exposure pattern. The feasibility of the proposed method was verified by simulations that were performed with real speckle images captured by a high-speed camera at 40 kfps. Experiments with a four-tap CMOS image sensor demonstrated that a flow speed map was obtained at a moderate frame rate such as 35 fps for a moving ground glass plate and 45 fps for flowing Intralipose, which were linearly moved at speeds of 1-5 mm/s.

Laser speckle contrast imaging and quantitative fluorescence angiography for perfusion assessment

PURPOSE

Indocyanine green fluorescence angiography (ICG-FA) is an established technique for assessment of intestinal perfusion during gastrointestinal surgery, whereas quantitative ICG-FA (q-ICG) and laser speckle contrast imaging (LSCI) are relatively unproven. The study aimed to investigate whether the techniques could be applied interchangeably for perfusion assessment.

METHODS

Nineteen pigs underwent laparotomy, two minor resections of the small bowel, and anastomoses. Additionally, seven pigs had parts of their stomach and small intestine de-vascularized. Data was also collected from an in vivo model (inferior caval vein measurements in two additional pigs) and an ex vivo flow model, allowing for standardization of experimental flow, distance, and angulation. Q-ICG and LSCI were performed, so that regions of interest were matched between the two modalities in the analyses, ensuring coverage of the same tissue.

RESULTS

The overall correlation of q-ICG and LSCI evaluated in the porcine model was modest (rho = 0.45, p < 0.001), but high in tissue with low perfusion (rho = 0.74, p < 0.001). Flux values obtained by LSCI from the ex vivo flow model revealed a decreasing flux with linearly increasing distance as well as angulation to the model. The Q-ICG perfusion values obtained varied slightly with increasing distance as well as angulation to the model.

CONCLUSIONS

Q-ICG and LSCI cannot be used interchangeably but may supplement each other. LSCI is profoundly affected by angulation and distance. In comparison, q-ICG is minimally affected by changing experimental conditions and is more readily applicable in minimally invasive surgery.

Monitoring of functional blood flow on human hand due to effect of different treatments by laser biospeckle imaging

In the proposed work, we report on qualitative as well as quantitative biospeckle monitoring of functional blood flow on the human hand. Intensity-based algorithms namely generalized difference and our earlier proposed algorithm parameterized global-average Fujii have been approached for the first time to analyze various physiological changes due to effect of different treatments such as hot and cold water treatments on the palm which can be helpful in examining cardiovascular and related diseases. In addition, blood flow has been monitored for the first time on face scrub, beauty creams, and pain relief ointments applied over the back of the palm. It has been found that, on application of four beauty creams namely Fair & Lovely, Ponds White Beauty, Vicco Turmeric, and Lotus Herbals Safe Sun on the back of the palm, blood flow increases and becomes highest (mean activity, 154.87) for Fair & Lovely among the four beauty creams. In addition, pain relief ointments such as Volini, Fast Relief, Molid Gel, and Zandu Gel increase blood flow after their applications on the back of the palm and Volini gives maximum increase of average blood flow (31.59) and hence can be considered one of the best among the four ointments. It has been further concluded that the person having more hemoglobin (14) and higher blood pressure (120/90) may have more blood flow or mean activity (85.80). In addition, it has been also concluded that although hot and cold water treatments can be used for increment in blood flow, temperature should be retained according to need and sensitivity of the sample.

Vascular Occlusion in a Porcine Flap Model: Effects on Blood Cell Concentration and Oxygenation

Background:

Venous congestion in skin flaps is difficult to detect. This study evaluated the ability of tissue viability imaging (TiVi) to measure changes in the concentration of red blood cells (CRBC), oxygenation, and heterogeneity during vascular provocations in a porcine fasciocutaneous flap model.

Methods:

In 5 pigs, cranial gluteal artery perforator flaps were raised (8 flaps in 5 pigs). The arterial and venous blood flow was monitored with ultrasonic flow probes. CRBC, tissue oxygenation, and heterogeneity in the skin were monitored with TiVi during baseline, 50% and 100% venous occlusion, recovery, 100% arterial occlusion and final recovery, thereby simulating venous and arterial occlusion of a free fasciocutaneous flap. A laser Doppler probe was used as a reference for microvascular perfusion in the flap.

Results:

During partial and complete venous occlusion, increases in CRBC were seen in different regions of the flap. They were more pronounced in the distal part. During complete arterial occlusion, CRBC decreased in all but the most distal parts of the flap. There were also increases in tissue oxygenation and heterogeneity during venous occlusion.

Conclusions:

TiVi measures regional changes in CRBC in the skin of the flap during arterial and venous occlusion, as well as an increase in oxygenated hemoglobin during venous occlusion that may be the result of reduced metabolism and impaired delivery of oxygen to the tissue. TiVi may provide a promising method for measuring flap viability because it is hand-held, easy to-use, and provides spatial information on venous congestion.

Thermal injury of skin and subcutaneous tissues: A review of experimental approaches and numerical models

Thermal injury to skin and subcutaneous tissue is common in both civilian and combat scenarios. Understanding the change in tissue morphologies and properties and the underlying mechanisms of thermal injury are of vital importance to clinical determination of the degree of burn and treatment approach. This review aims at summarizing the research involving experimental and numerical studies of skin and subcutaneous tissue subjected to thermal injury. The review consists of two parts. The first part deals with experimental studies including burn protocols and prevailing imaging approaches. The second part deals with existing numerical models for burns of tissue and related computational simulations. Based on this review, we conclude that though there is literature contributing to the knowledge of the pathology and pathogenesis of tissue burn, there is scant quantitative information regarding changes in tissue properties including mechanical, thermal, electrical and optical properties as a result of burns that are linked to altered tissue morphology.

Soft tissue biological response to zirconia and metal implant abutments compared with natural tooth: microcirculation monitoring as a novel bioindicator

INTRODUCTION

Zirconia is often used for implant abutments for esthetics. The aim of this clinical study was to compare the effects of zirconia and metal abutments on periimplant soft tissue.

MATERIALS AND METHODS

Ten maxillary anterior implant patients, 5 with metal abutments and 5 with zirconia abutments, were enrolled in this trial. The soft tissue around the implant abutments was evaluated by 2-dimensional laser speckle imaging and thermography. The blood flow in soft tissue around natural teeth was also measured to correct for differences among the subjects.

RESULTS

Significantly greater blood flow was detected in the zirconia abutment group (95.64 ± 5.17%) relative to the metal abutment group (82.25 ± 8.92%) in free gingiva (P = 0.0317). Reduced blood flow (by almost 18%) was detected in the tissue surrounding metal abutments compared with the tissue surrounding natural teeth. The surface temperature showed no significant difference for all measurements.

CONCLUSIONS

These results suggest that blood flow in tissue surrounding zirconia abutments is similar to that in soft tissue around natural teeth. Moreover, zirconia abutments could be advantageous for the maintenance of immune function by improving blood circulation.

On the equivalence and differences between laser Doppler flowmetry and laser speckle contrast analysis

Laser Doppler flowmetry (LDF) and laser speckle contrast analysis (LASCA) both utilize the spatiotemporal properties of laser speckle patterns to assess microcirculatory blood flow in tissue. Although the techniques analyze the speckle pattern differently, there is a close relationship between them. We present a theoretical overview describing how the LDF power spectrum and the LASCA contrast can be calculated from each other, and how both these can be calculated from an optical Doppler spectrum containing various degrees of Doppler shifted light. The theoretical relationships are further demonstrated using time-resolved speckle simulations. A wide range of Monte Carlo simulated tissue models is then used to show how perfusion estimates for LDF and LASCA are affected by changes in blood concentration and speed distribution, as well as by geometrical and optical properties. We conclude that perfusion estimates from conventional single exposure time LASCA are in general more sensitive to changes in optical and geometrical properties and are less accurate in the prediction of real perfusion changes, especially speed changes. Since there is a theoretical one-to-one relationship between Doppler power spectrum and contrast, one can conclude that those drawbacks with the LASCA technique can be overcome using a multiple exposure time setup.

The asymmetric facial skin perfusion distribution of Bell's palsy discovered by laser speckle imaging technology

Bell's palsy is a kind of peripheral neural disease that cause abrupt onset of unilateral facial weakness. In the pathologic study, it was evidenced that ischemia of facial nerve at the affected side of face existed in Bell's palsy patients. Since the direction of facial nerve blood flow is primarily proximal to distal, facial skin microcirculation would also be affected after the onset of Bell's palsy. Therefore, monitoring the full area of facial skin microcirculation would help to identify the condition of Bell's palsy patients. In this study, a non-invasive, real time and full field imaging technology - laser speckle imaging (LSI) technology was applied for measuring facial skin blood perfusion distribution of Bell's palsy patients. 85 participants with different stage of Bell's palsy were included. Results showed that Bell's palsy patients' facial skin perfusion of affected side was lower than that of the normal side at the region of eyelid, and that the asymmetric distribution of the facial skin perfusion between two sides of eyelid is positively related to the stage of the disease (P <  0.001). During the recovery, the perfusion of affected side of eyelid was increasing to nearly the same with the normal side. This study was a novel application of LSI in evaluating the facial skin perfusion of Bell's palsy patients, and we discovered that the facial skin blood perfusion could reflect the stage of Bell's palsy, which suggested that microcirculation should be investigated in patients with this neurological deficit. It was also suggested LSI as potential diagnostic tool for Bell's palsy.

PulseCam: high-resolution blood perfusion imaging using a camera and a pulse oximeter

Measuring blood perfusion is important in medical care as an indicator of injury and disease. However, currently available devices to measure blood perfusion like laser Doppler flowmetry are bulky, expensive, and cumbersome to use. An alternative low-cost and portable camera-based blood perfusion measurement system has recently been proposed, but such camera-only system produces noisy low-resolution blood perfusion maps. In this paper, we propose a new multi-sensor modality, named PulseCam, for measuring blood perfusion by combining a traditional pulse oximeter with a video camera in a unique way to provide low noise and high-resolution blood perfusion maps. Our proposed multi-sensor modality improves per pixel signal to noise ratio of measured perfusion map by up to 3 dB and improves the spatial resolution by 2 - 3 times compared to best known camera-only methods. Blood perfusion measured in the palm using our PulseCam setup during a post-occlusive reactive hyperemia (PORH) test replicates standard PORH response curve measured using laser Doppler flowmetry device but with much lower cost and a portable setup making it suitable for further development as a clinical device.

Evaluation of liver function and electroacupuncture efficacy of animals with alcoholic liver injury by the novel imaging methods

Imaging methods to evaluate hepatic microcirculation (HM) and liver function (LF) by directly monitoring overall liver tissue remain lacking. This study establish imaging methods for LF that combines Laser speckle perfusion imaging (LSPI) and in vivo optical imaging (IVOI) technologies to investigate changes of hepatic microcirculation and reserve function in the animals gavaged with 50% ethanol (15 ml/kg·bw) for a model of acute alcoholic liver injury (ALI), and for evaluation of electroacupuncture (EA) effect. The liver blood perfusion and indocyanine green (ICG) distribution were observe by LSPI and IVOI separately. After EA, the livers were collected to measure the levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), thromboxane A (TXA₂), prostacyclin (PGI₂) and endothelin (ET). The acquisitions of newly established LSPI of liver and ICG in vivo fluorescence imaging (ICG-IVFI), combining the results of other indexes showed: hepatic microcirculation perfusion (HMP) significantly reduced, ICG metabolism reduced, and ALT/AST increased in animal model with acute ALI. EA can reverse these changes. The use of LSPI of liver and ICG-IVFI, which was novel imaging methods for LF established in this study, could display the LF characteristics of ALI and the EA efficacy.

A systematic review of objective burn scar measurements

BACKGROUND

Problematic scarring remains a challenging aspect to address in the treatment of burns and can significantly affect the quality of life of the burn survivor. At present, there are few treatments available in the clinic to control adverse scarring, but experimental pharmacological anti-scarring strategies are now beginning to emerge. Their comparative success must be based on objective measurements of scarring, yet currently the clinical assessment of scars is not carried out systematically and is mostly based on subjective review of patients. However, several techniques and devices are being introduced that allow objective analysis of the burn scar. The aim of this article is to evaluate various objective measurement tools currently available and recommend a useful panel that is suitable for use in clinical trials of anti-scarring therapies.

METHODS

A systematic literature search was done using the Web of Science, PubMed and Cochrane databases. The identified devices were then classified and grouped according to the parameters they measured. The tools were then compared and assessed in terms of inter- and intra-rater reproducibility, ease of use and cost.

RESULTS

After duplicates were removed, 5062 articles were obtained in the search. After further screening, 157 articles which utilised objective burn scar measurement systems or tools were obtained. The scar measurement devices can be broadly classified into those measuring colour, metric variables, texture, biomechanical properties and pathophysiological disturbances.

CONCLUSIONS

Objective scar measurement tools allow the accurate and reproducible evaluation of scars, which is important for both clinical and scientific use. However, studies to evaluate their relative performance and merits of these tools are scarce, and there remain factors, such as itch and pain, which cannot be measured objectively. On reviewing the available evidence, a panel of devices for objective scar measurement is recommended consisting of the 3D cameras (Eykona/Lifeviz/Vectra H1) for surface area and volume, DSM II colorimeter for colour, Dermascan high-frequency ultrasound for scar thickness and Cutometer for skin elasticity and pliability.

Low-Power CMOS Laser Doppler Imaging Using Non-CDS Pixel Readout and 13.6-bit SAR ADC

Laser Doppler imaging (LDI) measures particle flows such as blood perfusion by sensing their Doppler shift. This paper is the first of its kind in analyzing the effect of circuit noise on LDI precision which is distinctively different from conventional imaging. Based on this result, it presents a non-correlated-double-sampling (non-CDS) pixel readout scheme along with a high-resolution successive-approximation-register (SAR) analog-to-digital-converter (ADC) with 13.6b effective resolution (ER). Measurement results from the prototype chip in 0.18 μm technology confirm the theoretical analysis and show that the two techniques improve LDI sensing precision by 6.9 dB and 4.4 dB (compared to a 10b ADC) respectively without analog pre-amplification. The sensor's ADC occupies 518 μm×84 μm and is suitable for fast column parallel readout. Its differential non-linearity (DNL), integral non-linearity (INL), and input referred noise are +3.0/-2.8 LSB, +24/-17 LSB, and 110 μVrms respectively, leading to a Figure-of-Merit (FoM) of 23 fJ/state which makes it one of the most energy efficient image sensor ADCs and an order of magnitude better than the best reported LDI system using commercial high-speed image sensors.

Laser Speckle Contrast Imaging for Monitoring Changes in Microvascular Blood Flow

BACKGROUND/AIMS

Microvascular blood flow is essential for healing and predicts surgical outcome. The aim of the current study was to investigate the relation between fluxes measured with the laser speckle contrast imaging (LSCI) technique and changes in absolute blood flow. In addition, we studied the reproducibility of the LSCI technique when assessing the intra-abdominal microcirculation of the pig.

METHODS

During trial 1, a fish gill arch was mechanically perfused with heparinized fish blood under controlled stepwise-altered flow rates alongside mechanically induced movement artefacts. The microcirculation of the fish gill was simultaneously assessed with the LSCI technique. In trial 2, microcirculation was measured in the stomach, liver, and small intestine of 10 pigs by two observers.

RESULTS

A linear correlation was observed between flux and volumetric flow. During conditions of no volumetric flow, the high recording speed with the LSCI technique registered the movement artefacts as flow signals. The LSCI measurements showed good correlation and agreement between the two observers when assessing microcirculation in the stomach, liver, and small intestine (r2 = 0.857, 0.956, and 0.946; coefficients of variation = 6.0, 3.2, and 6.4%, respectively).

CONCLUSION

Due to the non-contact and real-time assessment over large areas, LSCI is a promising technique for the intraoperative assessment of intra-abdominal microcirculation. A linear correlation between flux and volumetric flow was found, in accordance with previous experimental studies. However, movement artefacts affect flux measurements, and the choice of the sampling speed must be made with care, depending on the given setting.

Relationship between the blood perfusion values determined by laser speckle imaging and laser Doppler imaging in normal skin and port wine stains

OBJECTIVE

Laser Doppler imaging (LDI) and laser speckle imaging (LSI) are two major optical techniques aiming at non-invasively imaging the skin blood perfusion. However, the relationship between perfusion values determined by LDI and LSI has not been fully explored.

METHODS

8 healthy volunteers and 13 PWS patients were recruited. The perfusions in normal skin on the forearm of 8 healthy volunteers were simultaneously measured by both LDI and LSI during post-occlusive reactive hyperemia (PORH). Furthermore, the perfusions of port wine stains (PWS) lesions and contralateral normal skin of 10 PWS patients were also determined. In addition, the perfusions for PWS lesions from 3 PWS patients were successively monitored at 0, 10 and 20min during vascular-targeted photodynamic therapy (V-PDT). The average perfusion values determined by LSI were compared with those of LDI for each subject.

RESULTS

In the normal skin during PORH, power function provided better fits of perfusion values than linear function: powers for individual subjects go from 1.312 to 1.942 (R(2)=0.8967-0.9951). There was a linear relationship between perfusion values determined by LDI and LSI in PWS and contralateral normal skin (R(2)=0.7308-0.9623), and in PWS during V-PDT (R(2)=0.8037-0.9968).

CONCLUSION

The perfusion values determined by LDI and LSI correlate closely in normal skin and PWS over a broad range of skin perfusion. However, it still suggests that perfusion range and characteristics of the measured skin should be carefully considered if LDI and LSI measures are compared.

Underlying mechanisms of urine storage dysfunction in rats with salt-loading hypertension

AIMS

Spontaneous hypertensive rats provide a genetic model for exploring the pathogenesis of urine storage dysfunction related to hypertension (HT). In humans, however, HT develops by both genetic and environmental factors including lifestyle factors such as a high-calorie diet, excessive salt intake and stress. We investigated the influence of salt-loading on bladder function and the underlying mechanisms of storage dysfunction related to HT.

MAIN METHODS

Six-week-old male Dahl salt-sensitive (DS) and Dahl salt-resistant (DR) rats were fed with a normal or high-salt diet for 12weeks. Micturition parameters were obtained from a metabolic cage. Whole bladders were excised from 18-week-old rats and distended in an organ bath. The releases of adenosine triphosphoric acid (ATP) and prostaglandin E2 (PGE2) from the distended bladder epithelia were measured. Changes in bladder blood flow (BBF) were determined with a laser-speckle-blood-flow imaging system.

KEY FINDINGS

An increase in mean blood pressure (BP) was noted only in DS rats after salt-loading. During the inactive (sleeping) period, voided volume per micturition gradually increased in DR rats fed a normal or high-salt diet and normal-diet DS rats, while it did not change in the DS rats fed a high-salt diet. Bladder distension significantly increased ATP and PGE2 release from the urothelium in DS rats fed a high-salt diet. BBF was significantly decreased in high-salt-diet DS rats.

SIGNIFICANCE

One mechanism behind the relationship between salt-sensitive HT and urine storage dysfunction may be an increase in ATP and PGE2 release from the urothelium via suppression of BBF.

High-resolution harmonics ultrasound imaging for non-invasive characterization of wound healing in a pre-clinical swine model

This work represents the first study employing non-invasive high-resolution harmonic ultrasound imaging to longitudinally characterize skin wound healing. Burn wounds (day 0-42), on the dorsum of a domestic Yorkshire white pig were studied non-invasively using tandem digital planimetry, laser speckle imaging and dual mode (B and Doppler) ultrasound imaging. Wound depth, as measured by B-mode imaging, progressively increased until day 21 and decreased thereafter. Initially, blood flow at the wound edge increased up to day 14 and subsequently regressed to baseline levels by day 21, when the wound was more than 90% closed. Coinciding with regression of blood flow at the wound edge, there was an increase in blood flow in the wound bed. This was observed to regress by day 42. Such changes in wound angiogenesis were corroborated histologically. Gated Doppler imaging quantitated the pulse pressure of the primary feeder artery supplying the wound site. This pulse pressure markedly increased with a bimodal pattern following wounding connecting it to the induction of wound angiogenesis. Finally, ultrasound elastography measured tissue stiffness and visualized growth of new tissue over time. These studies have elegantly captured the physiological sequence of events during the process of wound healing, much of which is anticipated based on certain dynamics in play, to provide the framework for future studies on molecular mechanisms driving these processes. We conclude that the tandem use of non-invasive imaging technologies has the power to provide unprecedented insight into the dynamics of the healing skin tissue.

Laser speckle contrast imaging reveals large-scale synchronization of cortical autoregulation dynamics influenced by nitric oxide

Synchronization of tubuloglomerular feedback (TGF) dynamics in nephrons that share a cortical radial artery is well known. It is less clear whether synchronization extends beyond a single cortical radial artery or whether it extends to the myogenic response (MR). We used LSCI to examine cortical perfusion dynamics in isoflurane-anesthetized, male Long-Evans rats. Inhibition of nitric oxide synthases by N(ω)-nitro-l-arginine methyl ester (l-NAME) was used to alter perfusion dynamics. Phase coherence (PC) was determined between all possible pixel pairs in either the MR or TGF band (0.09-0.3 and 0.015-0.06 Hz, respectively). The field of view (≈4 × 5 mm) was segmented into synchronized clusters based on mutual PC. During the control period, the field of view was often contained within one cluster for both MR and TGF. PC was moderate for TGF and modest for MR, although significant in both. In both MR and TGF, PC exhibited little spatial variation. After l-NAME, the number of clusters increased in both MR and TGF. MR clusters became more strongly synchronized while TGF clusters showed small highly coupled, high-PC regions that were coupled with low PC to the remainder of the cluster. Graph theory analysis probed modularity of synchronization. It confirmed weak synchronization of MR during control that probably was not physiologically relevant. It confirmed extensive and long-distance synchronization of TGF during control and showed increased modularity, albeit with larger modules seen in MR than in TGF after l-NAME. The results show widespread synchronization of MR and TGF that is differentially affected by nitric oxide.

Microvascular blood flow monitoring with laser speckle contrast imaging using the generalized differences algorithm

Laser speckle contrast imaging (LSCI) is a full-field optical technique to monitor microvascular blood flow with high spatial and temporal resolutions. It is used in many medical fields such as dermatology, vascular medicine, or neurosciences. However, LSCI leads to a large amount of data: image sampling frequency is often of several Hz and recordings usually last several minutes. Therefore, clinicians often perform regions of interest in which a spatial averaging of blood flow is performed and the result is followed with time. Unfortunately, this leads to a poor spatial resolution for the analyzed data. At the same time, a higher spatial resolution for the perfusion maps is wanted. To get over this dilemma we propose a new post-acquisition visual representation for LSCI perfusion data using the so-called generalized differences (GD) algorithm. From a stack of perfusion images, the procedure leads to a new single image with the same spatial resolution as the original images and this new image reflects perfusion changes. The algorithm is herein applied on simulated stacks of images and on experimental LSCI perfusion data acquired in three different situations with a commercialized laser speckle contrast imager. The results show that the GD algorithm provides a new way of visualizing LSCI perfusion data.

Multiresolution analysis of pathological changes in cerebral venous dynamics in newborn mice with intracranial hemorrhage: adrenorelated vasorelaxation

Intracranial hemorrhage (ICH) is the major problem of modern neonatal intensive care. Abnormalities of cerebral venous blood flow (CVBF) can play a crucial role in the development of ICH in infants. The mechanisms underlying these pathological processes remain unclear; however it has been established that the activation of the adrenorelated vasorelaxation can be an important reason. Aiming to reach a better understanding of how the adrenodependent relaxation of cerebral veins contributes to the development of ICH in newborns, we study here the effects of pharmacological stimulation of adrenorelated dilation of the sagittal sinus by isoproterenol on the cerebral venous hemodynamics. Our study is performed in newborn mice at different stages of ICH using the laser speckle contrast imaging and wavelet analysis of the vascular dynamics of CVBF. We show that the dilation of the sagittal sinus with the decreased velocity of blood flow presides to the stress-induced ICH in newborn mice. These morphofunctional vascular changes are accompanied by an increased variance of the wavelet-coefficients in the areas of endothelial and non-endothelial (KATP-channels activity of vascular muscle) sympathetic components of the CVBF variability. Changes in the cerebral venous hemodynamics at the latent stage of ICH are associated with a high responsiveness of the sagittal sinus to isoproterenol quantifying by wavelet-coefficients related to a very slow region of the frequency domain. The obtained results certify that a high activation of the adrenergic-related vasodilatory responses to severe stress in newborn mice can be one of the important mechanisms underlying the development of ICH. Thus, the venous insufficiency with the decreased blood outflow from the brain associated with changes in the endothelial and the sympathetic components of CVBF-variability can be treated as prognostic criteria for the risk of ICH during the first days after birth.

Vascular structure and function in the medial collateral ligament of anterior cruciate ligament transected rabbit knees

To determine if decreased vascular responsiveness in the medial collateral ligament (MCL) of anterior cruciate ligament transected (ACL-t) rabbit knees is due to pericyte deficiency associated with angiogenesis. Vascular responses to potassium chloride (KCl), phenylephrine, acetylcholine, and sodium nitroprusside (SNP) were evaluated in ACL-t rabbit knees (n = 6) and control knees (n = 5) using laser speckle perfusion imaging. Ligament degeneration was determined by ultrasound imaging. Vascular and pericyte volume were measured using quantitative immunohistochemical volumetric analysis using CD31 and α-smooth muscle actin antibodies with co-localization analysis. Perfusion was increased in the ACL-t rabbits 2.5-fold. Responsiveness to phenylephrine, SNP, and acetylcholine was significantly decreased in the ACL knee while no change in KCl responses was seen. MCL ultrasound imaging revealed decreased collagen organization, increased ligament thickness, and increased water content in the ACL-t MCL. Vascular Volume was increased fourfold in ACL deficient knees, while pericyte volume to endothelial volume was not changed. No difference in CD31 and α-SMA co-localization was found. Blood vessels in the MCL of ACL-t knees do not lack smooth muscle. The MCL vasculature can undergo constrictive response to KCl, but have impaired receptor mediated responses and impaired nitric oxide signaling.

Laser Doppler imaging as a tool in the burn wound treatment protocol

INTRODUCTION

The main treatment of burns is early excision of injured tissues.

AIM

TO COMPARE TWO DIFFERENT METHODS OF EXAMINATION OF BURNED PATIENTS: clinical burn depth examination (CDE) and laser Doppler imaging (LDI).

MATERIAL AND METHODS

A prospective randomized study of 57 burn patients treated in 2009-2011 was carried out. The burned patients were randomized into a CDE group and an LDI group. The CDE and LDI scan were performed 72 h after injury, with the second and third CDE and LDI scan on the 7(th) and 14(th) day after the burn. Age, sex, length of inpatient stay, cost of burn treatment, burn depth, cause and localization of the burns were analyzed between the two groups.

RESULTS

Fifty-seven patients were treated during 2 years. Thirty-two patients were in the CDE group and 25 patients were in the LDI group. Most of the patients were male (45 male vs. 12 female, p < 0.001). The age was similar between the males and the females (female: 46.4 ±16.9 years vs. male: 46.3 ±12.5 years; p = 0.11). The mean length of stay in hospital was significantly higher in the CDE group (47 ±34.4 day vs. 25 ±10.8 day; p = 0.005). The mean cost of treatment of burned patients was significantly higher in the CDE group.

CONCLUSIONS

The length of stay and cost of treatment of burn patients depends upon early diagnosis of the deep burns and well-timed surgical treatment of burn wounds.

Robust revascularization, despite impaired VEGF production, after meniscus allograft transplantation in rabbits

BACKGROUND

Little is known about vascularization restoration and vascular circulation after allogenic graft transplantation, which are both important prerequisites for optimal use of allograft meniscus transplantation.

PURPOSE

To study vascularization restoration through autograft and allograft meniscus models in Oryctolagus cuniculus.

STUDY DESIGN

Controlled laboratory study.

METHODS

Forty-eight rabbits at mature bone age were randomized to receive either an autograft or allograft after the meniscus of the left knee was completely resected. Vascularization, blood circulation, histological characteristics of the grafted meniscus and surrounding tissues, and vascular endothelial growth factor (VEGF) expression in the meniscus were assessed at 4, 8, and 12 weeks after allograft or autologous transplantation.

RESULTS

The grafted meniscus was in good condition and was well connected to the surrounding joint capsule, and no obvious damage of the joint cartilage at the tibial plateau was observed. Even though the revascularization pattern was similar in the 2 groups, the meniscus body showed vessel growth mainly at the adhesion margin for less than one-third of the meniscus transverse diameter, and no significant vascular distribution was found at the free margin. Blood circulation peaked after 8 weeks at the anterior and posterior horns and declined thereafter. This was mimicked by VEGF expression, which showed a progressive decrease with time, even though the vascular endothelial cells gradually increased over time. There were no statistical differences in the various assessments between the allograft and autograft groups.

CONCLUSION

At 12 weeks after meniscus allografting, the vascular circulation had almost recovered and gradual reconstruction of cells and fibers had begun, mimicking similar observations in the autograft group.

CLINICAL RELEVANCE

Our data provide test reference for clinical rehabilitation after meniscus autograft.

Laser Speckle Contrast Imaging: theory, instrumentation and applications

Laser Speckle Contrast Imaging (LSCI) is a wide field of view, non scanning optical technique for observing blood flow. Speckles are produced when coherent light scattered back from biological tissue is diffracted through the limiting aperture of focusing optics. Mobile scatterers cause the speckle pattern to blur; a model can be constructed by inversely relating the degree of blur, termed speckle contrast to the scatterer speed. In tissue, red blood cells are the main source of moving scatterers. Therefore, blood flow acts as a virtual contrast agent, outlining blood vessels. The spatial resolution (~10 μm) and temporal resolution (10 ms to 10 s) of LSCI can be tailored to the application. Restricted by the penetration depth of light, LSCI can only visualize superficial blood flow. Additionally, due to its non scanning nature, LSCI is unable to provide depth resolved images. The simple setup and non-dependence on exogenous contrast agents have made LSCI a popular tool for studying vascular structure and blood flow dynamics. We discuss the theory and practice of LSCI and critically analyze its merit in major areas of application such as retinal imaging, imaging of skin perfusion as well as imaging of neurophysiology.

Review of laser speckle-based analysis in medical imaging

Speckle pattern forms when a rough object is illuminated with coherent light (laser) and the backscattered radiation is imaged on a screen. The pattern changes over time due to movement in the object. Such time-integrate speckle pattern can be statistically analyzed to reveal the flow profile. For higher velocity the speckle contrast gets reduced. This theory can be utilized for tissue perfusion in capillaries of human skin tissue and cerebral blood flow mapping in rodents. Early, the technique was suffered from low resolution and computational intricacies for real-time monitoring purpose. However, modern engineering has made it feasible for real-time monitoring in microcirculation imaging with improved resolution. This review illustrates several modifications over classical technique done by many researchers. Recent advances in speckle contrast methods gain major interest, leading towards practical implementation of this technique. The review also brings out the scopes of laser speckle-based analysis in various medical applications.

Laser speckle contrast imaging of cerebral blood flow

Laser speckle contrast imaging (LSCI) has emerged over the past decade as a powerful, yet simple, method for imaging of blood flow dynamics in real time. The rapid adoption of LSCI for physiological studies is due to the relative ease and low cost of building an instrument as well as the ability to quantify blood flow changes with excellent spatial and temporal resolution. Although measurements are limited to superficial tissues with no depth resolution, LSCI has been instrumental in pre-clinical studies of neurological disorders as well as clinical applications including dermatological, neurosurgical and endoscopic studies. Recently a number of technical advances have been developed to improve the quantitative accuracy and temporal resolution of speckle imaging. This article reviews some of these recent advances and describes several applications of speckle imaging.

Immediate ACL reconstruction prevents microvascular pathophysiology in the uninjured MCL that is not fully reversed by delayed ACL reconstruction

Anterior cruciate ligament (ACL) injury induces maladaptive vascular responses that degrade medial collateral ligament (MCL) function. The purpose of this study was to determine if early or delayed ACL reconstruction can prevent or reverse the abnormal changes in vascular function that occur in the uninjured MCL after ACL injury. Twenty-four rabbits were divided into four groups (n = 6); control, ACL-deficient (ACL-X), immediate ACL reconstructed (ACL-IR) and delayed ACL reconstructed (ACL-DR). After 8 weeks, MCLs were assessed for blood flow, responses to acetylcholine (ACh) and phenylephrine (Phe) and autoregulatory responses, using laser speckle perfusion imaging. In ACL-X knees, blood flow in the MCL increased by 2.5-fold compared to control. MCL hyperemia was diminished in ACL-DR knees and was unaltered in ACL-IR knees. MCL vasculature was unresponsive to ACh and Phe in ACL-X. These responses were partially restored by ACL reconstruction. Autoregulatory responses were not significantly different between groups. ACL-DR decreased hyperemia in the MCL and partially attenuated abnormal MCL vascular responses. ACL-IR was more effective at preventing MCL hyperemia and preserving vascular responsiveness to ACh and Phe. This suggests that the vascular alterations in the uninjured rabbit MCL are largely caused by abnormal mechanical loading resulting from ACL deficiency and can be prevented through early reconstruction. Early ACL reconstruction could limit the progression of microvascular dysfunction of the MCL, and preserve physiological joint homeostasis. This might prevent joint degeneration and delay the progression of osteoarthritis.

A transmissive laser speckle imaging technique for measuring deep tissue blood flow: an example application in finger joints

BACKGROUND AND OBJECTIVE

Laser speckle perfusion imaging (LSPI) is a minimally invasive optical measure of relative changes in blood flow, providing real-time, high resolution, two-dimensional maps of vascular structure. Standard LSI imaging uses a light-reflective geometry that limits the measurement to a thin surface layer of 0.2-1 mm. The objective of this study was to test a new LSI instrument geometry with the laser source opposed to the image capture plane (light transmissive). Captured light then travels the entire tissue thickness (10-15 mm), sampling much deeper regions of interest than conventional optical imaging techniques.

STUDY DESIGN

Reflective-light (conventional) and transmissive-light LSI modes were used to measure finger joint blood flow during a timed tourniquet occlusion of the brachial artery in volunteer participants.

RESULTS

There was greatly increased visibility of vessels underlying the skin in the light-transmissive mode LSI mode. Established LSI algorithms were shown to still work in the light-transmissive mode, despite decorrelation due to finite laser coherence length and the light passing through a tissue thickness of 10-15 mm.

CONCLUSION

Transmissive LSI can be used to measure blood flow deep (10-15 mm) into tissues. This could be useful for non-invasive measurements of finger joint synovial blood flow in diagnosing and treating peripheral vascular disorders, such as rheumatoid arthritis.

Nephron blood flow dynamics measured by laser speckle contrast imaging

Tubuloglomerular feedback (TGF) has an important role in autoregulation of renal blood flow and glomerular filtration rate (GFR). Because of the characteristics of signal transmission in the feedback loop, the TGF undergoes self-sustained oscillations in single-nephron blood flow, GFR, and tubular pressure and flow. Nephrons interact by exchanging electrical signals conducted electrotonically through cells of the vascular wall, leading to synchronization of the TGF-mediated oscillations. Experimental studies of these interactions have been limited to observations on two or at most three nephrons simultaneously. The interacting nephron fields are likely to be more extensive. We have turned to laser speckle contrast imaging to measure the blood flow dynamics of 50-100 nephrons simultaneously on the renal surface of anesthetized rats. We report the application of this method and describe analytic techniques for extracting the desired data and for examining them for evidence of nephron synchronization. Synchronized TGF oscillations were detected in pairs or triplets of nephrons. The amplitude and the frequency of the oscillations changed with time, as did the patterns of synchronization. Synchronization may take place among nephrons not immediately adjacent on the surface of the kidney.

Integration of image exposure time into a modified laser speckle imaging method

Speckle-based methods have been developed to characterize tissue blood flow and perfusion. One such method, called modified laser speckle imaging (mLSI), enables computation of blood flow maps with relatively high spatial resolution. Although it is known that the sensitivity and noise in LSI measurements depend on image exposure time, a fundamental disadvantage of mLSI is that it does not take into account this parameter. In this work, we integrate the exposure time into the mLSI method and provide experimental support of our approach with measurements from an in vitro flow phantom.