Analysis of pigmented skin lesions and malignant melanoma by Laser Doppler flowmetry - Report of different cases and further analysis by a neuronal network

BACKGROUND

Dermatoscopy is successfully used for the early diagnosis of suspicious skin lesions, however, correct diagnosis depends on training. There is evidence that wavelet analysis by Laser Doppler flowmetry (LDF) can identify malignant melanomas by their hypervascularization and changes in the capillary morphology.

OBJECTIVE

To show the capability of LDF in the distinction of melanomas and benign pigmented skin lesions based on data collected over 16 years.

METHODS

Evaluation of pigmented skin lesions was based on clinical information. The LDF measurements were taken. The suspect lesion was excised afterwards for histological work-up. Four case reports are presented. Data collected over 16 years was processed into a neuronal network to estimate the dignity of the lesion.

RESULTS

A total of 517 suspicious lesions were analyzed by LDF. In the histological work-up, 114 lesions turned out to be melanomas, whereas 403 benign naevi were secured. Specificity to detect melanomas was good based on the clinical information. The LDF increases the sensitivity of melanoma detection, which is also illustrated in four case reports.

CONCLUSION

In addition to clinical parameters, such as color and border, information from the LDF can help in the diagnosis of malignant melanomas. The LDF provides information on the vascularization of the skin lesion.

Space-directional approach to improve blood vessel visualization and temporal resolution in laser speckle contrast imaging

Blood flow is a parameter used to diagnose vascular diseases based on flow speed, blood pressure, and vessel size. Different techniques have been developed to estimate the relative blood flow speed and to improve the visualization of deep blood vessels; one such technique is laser speckle contrast imaging (LSCI). LSCI images contain a high level of noise mainly when deep blood vessels are imaged. To improve their visualization, several approaches for contrast computation have been developed. However, there is a compromise between noise attenuation and temporal resolution. On the one hand, spatial approaches have low spatial resolution, high temporal resolution, and significant noise attenuation, while temporal approaches have the opposite. A recent approach combines a temporal base with a directional process that allows improving the visualization of blood vessels. Nevertheless, it still contains a high level of noise and requires a high number of raw frames for its base. We propose, a space-directional approach focused on improving noise attenuation and temporal resolution for contrast computation. The results of reference approaches and the proposed one are compared quantitatively. Moreover, it is shown that the visualization of blood vessels in LSCI images can be improved by a general morphological process when the noise level is reduced.

Combined laser speckle imaging and fluorescent intravital microscopy for monitoring acute vascular permeability reaction

Optical clearing agents (OCAs) and many chemicals are widely used in functional diagnosis of skin tissues. Numerous studies are associated with the transcutaneous diffusion of OCA in epidermal, dermal, and hypodermal tissues, which results in changing their optical properties. In addition, an objective approach that is suitable for screening the influence of utilized OCA, as well as various chemical agents, synthetics, and nanomaterials, on blood and lymph flows is highly desirable. In our study, a highly sensitive laser speckle imaging (LSI) system and fluorescent intravital microscopy (FIM) were used team-wise to inspect the acute skin vascular permeability reaction in mouse ear during the local application of OCA on the skin surface. Fluorescent contrast material administrated intravenously was used for quantitatively assessing the intensity of vascular permeability reaction and the strength of skin irritation. The obtained results suggest that a combined use of LSI and FIM is highly effective for monitoring the cutaneous vascular permeability reaction, with great potential for assessment of allergic reactions of skin in response to interactions with chemical substances.

Laser Doppler Flowmetry to Study the Regulation of Cerebral Blood Flow by G Protein-Coupled Receptors in Rodents

A large body of evidence suggests that G protein-coupled receptors (GPCRs) play an important role in the regulation of peripheral vascular reactivity. Meanwhile, the extent of GPCR influence on the regulation of brain vascular reactivity, or cerebral blood flow (CBF), has yet to be fully appreciated. This is of physiological importance as the modulation of CBF depends on an intricate interplay between neurons, astrocytes, pericytes, and endothelial cells, all of which partaking in the formation of a functional entity referred to as the neurovascular unit (NVU). The NVU is the anatomical substrate of neurovascular coupling (NVC) mechanisms, whereby increased neuronal activity leads to increased blood flow to accommodate energy, oxygen, and nutrients demands. In light of growing evidence showing impaired NVC in several neurological disorders, and the fact that GPCRs represent the most important targets of FDA-approved drugs, it is of utmost importance to use experimental approaches to study GPCR-induced regulation of NVC for the future development of pharmaceutical compounds that could normalize CBF function. Herein, we describe a minimally invasive approach called laser Doppler flowmetry (LDF) that, when used in combination with a whisker stimulation paradigm in rodents, allows gauging blood perfusion in activated cerebral cortex. We comprehensively explain the surgical procedure and data acquisition in mice, and discussed about important experimental considerations for the study of CBF regulation by GPCRs using pharmacological agents.

Machine learning in multiexposure laser speckle contrast imaging can replace conventional laser Doppler flowmetry

Laser speckle contrast imaging (LSCI) enables video rate imaging of blood flow. However, its relation to tissue blood perfusion is nonlinear and depends strongly on exposure time. By contrast, the perfusion estimate from the slower laser Doppler flowmetry (LDF) technique has a relationship to blood perfusion that is better understood. Multiexposure LSCI (MELSCI) enables a perfusion estimate closer to the actual perfusion than that using a single exposure time. We present and evaluate a method that utilizes contrasts from seven exposure times between 1 and 64 ms to calculate a perfusion estimate that resembles the perfusion estimate from LDF. The method is based on artificial neural networks (ANN) for fast and accurate processing of MELSCI contrasts to perfusion. The networks are trained using modeling of Doppler histograms and speckle contrasts from tissue models. The importance of accounting for noise is demonstrated. Results show that by using ANN, MELSCI data can be processed to LDF perfusion with high accuracy, with a correlation coefficient R  =  1.000 for noise-free data, R  =  0.993 when a moderate degree of noise is present, and R  =  0.995 for in vivo data from an occlusion-release experiment.

Nicotinamide riboside has protective effects in a rat model of mesenteric ischaemia-reperfusion

Acute mesenteric ischaemia is a syndrome caused by inadequate blood flow through the mesenteric vessels, resulting in ischaemia and eventual gangrene of the bowel wall. Although relatively rare, it is a potentially life-threatening condition. The maintenance of haemodynamic stability, along with adequate oxygen saturation, and the correction of any electrolyte imbalance, are of the utmost importance. However, nicotinamide adenine dinucleotide (NAD) biosynthesis modulation by precursor introduction can also be a powerful tool for preventing injury. Nicotinamide riboside is a pyridine-nucleoside form of vitamin B3 that functions as a precursor to NAD+ . The present study investigated nicotinamide riboside's effect on endothelium functional state, microcirculation and intestinal morphology in acute mesenteric ischaemia and reperfusion. Mesenteric ischaemia was simulated after the adaptation period (15 minutes) by occluding the superior mesenteric artery for 60 minutes, followed by a reperfusion period of 30 minutes. The functional state of intestinal microcirculation was evaluated by laser Doppler flowmetry. Endothelial functional activity was studied by using wire myography. Intestinal samples were stained with haematoxylin and eosin for histological analysis. The results revealed that nicotinamide riboside protects the intestinal wall from ischaemia-reperfusion injury, as well as improving the relaxation function of mesenteric vessels. Nicotinamide riboside's protective effect in small intestine ischaemia-reperfusion can be used to reduce ischaemia-reperfusion injury, as well as to preserve intestinal grafts until transplant.

Effect of leg immersion in mild warm carbonated water on skin and muscle blood flow

Leg immersion in carbonated water improves endothelial-mediated vasodilator function and decreases arterial stiffness but the mechanism underlying this effect remains poorly defined. We hypothesized that carbonated water immersion increases muscle blood flow. To test this hypothesis, 10 men (age 21 ± 0 years; mean ± SD) underwent lower leg immersion in tap or carbonated water at 38°C. We evaluated gastrocnemius muscle oxyhemoglobin concentration and tissue oxygenation index using near-infrared spectroscopy, skin blood flow by laser Doppler flowmetry, and popliteal artery (PA) blood flow by duplex ultrasound. Immersion in carbonated, but not tap water elevated PA (from 38 ± 14 to 83 ± 31 mL/min; P < 0.001) and skin blood flow (by 779 ± 312%, P < 0.001). In contrast, lower leg immersion elevated oxyhemoglobin concentration and tissue oxygenation index with no effect of carbonation (P = 0.529 and P = 0.495). In addition, the change in PA blood flow in response to immersion in carbonated water correlated with those of skin blood flow (P = 0.005) but not oxyhemoglobin concentration (P = 0.765) and tissue oxygenation index (P = 0.136) while no relations was found for tap water immersion. These findings indicate that water carbonation has minimal effect on muscle blood flow. Furthermore, PA blood flow increases in response to lower leg immersion in carbonated water likely due to a large increase in skin blood flow.

Visualization of skin microvascular dysfunction of type 1 diabetic mice using in vivo skin optical clearing method

To realize visualization of the skin microvascular dysfunction of type 1 diabetic mice, we combined laser speckle contrast imaging and hyperspectral imaging to simultaneously monitor the noradrenaline (NE)-induced responses of vascular blood flow and blood oxygen with the development of diabetes through optical clearing skin window. The main results showed that venous and arterious blood flow decreased without recovery after injection of NE; furthermore, the decrease of arterious blood oxygen induced by NE greatly weakened, especially for 2- and 4-week diabetic mice. This change in vasoconstricting effect of NE was related to the expression of α1-adrenergic receptor. This study demonstrated that skin microvascular function was a potential research biomarker for early warning in the occurrence and development of diabetes. The in vivo skin optical clearing method provides a feasible solution to realize visualization of cutaneous microvessels for monitoring microvascular reactivity under pathological conditions. In addition, visual monitoring of skin microvascular function response has guiding significance for early diagnosis of diabetes and clinical research.

Visualization of skin microvascular dysfunction of type 1 diabetic mice using in vivo skin optical clearing method

To realize visualization of the skin microvascular dysfunction of type 1 diabetic mice, we combined laser speckle contrast imaging and hyperspectral imaging to simultaneously monitor the noradrenaline (NE)-induced responses of vascular blood flow and blood oxygen with the development of diabetes through optical clearing skin window. The main results showed that venous and arterious blood flow decreased without recovery after injection of NE; furthermore, the decrease of arterious blood oxygen induced by NE greatly weakened, especially for 2- and 4-week diabetic mice. This change in vasoconstricting effect of NE was related to the expression of α1-adrenergic receptor. This study demonstrated that skin microvascular function was a potential research biomarker for early warning in the occurrence and development of diabetes. The in vivo skin optical clearing method provides a feasible solution to realize visualization of cutaneous microvessels for monitoring microvascular reactivity under pathological conditions. In addition, visual monitoring of skin microvascular function response has guiding significance for early diagnosis of diabetes and clinical research.

Detecting Vascular Age Using the Analysis of Peripheral Pulse

Vascular ageing is known to be accompanied by arterial stiffening and vascular endothelial dysfunction, and represents an independent factor contributing to the development of cardiovascular disease. The microvascular pulse is affected by the biomechanical alterations of the circulatory system, and has been the focus of studies aiming at the development of non-invasive methods able to extract physiologically relevant features.

OBJECTIVE

proposing an approach for the assessment of vascular ageing based on a support vector machine (SVM) learning from features of the pulse contour.

METHODS

the supervised classifier was trained and validated over 20935 models of pulse wave, obtained with a multi-Gaussian decomposition algorithm, applied to laser Doppler flowmetry signals of 54 healthy, non-smoker subjects.

RESULTS

the multi-Gaussian model showed a mean R² of 0.98 and an average normalized root mean square error of 0.90, demonstrating the ability to reconstruct the pulse shape. Over 30 training and validation experiments, the SVM showed a mean Pearson's r of 0.808 between the rate of waves classified as old and the age of the subjects, along with an average area under the ROC curve of 0.953.

CONCLUSION

the SVM showed the capability to discriminate differently aged individuals.

SIGNIFICANCE

the proposed method might detect the ageing-related modifications of the vascular tree; furthermore, since diabetes promotes vascular alterations comparable to ageing, this approach may be also suitable for the screening of diabetic angiopathy.

Pulse waveform analysis on temporal changes in ocular blood flow due to caffeine intake: a comparative study between habitual and non-habitual groups

PURPOSE

To evaluate and compare the temporal changes in pulse waveform parameters of ocular blood flow (OBF) between non-habitual and habitual groups due to caffeine intake.

METHOD

This study was conducted on 19 healthy subjects (non-habitual 8; habitual 11), non-smoking and between 21 and 30 years of age. Using laser speckle flowgraphy (LSFG), three areas of optical nerve head were analyzed which are vessel, tissue, and overall, each with ten pulse waveform parameters, namely mean blur rate (MBR), fluctuation, skew, blowout score (BOS), blowout time (BOT), rising rate, falling rate, flow acceleration index (FAI), acceleration time index (ATI), and resistive index (RI). Two-way mixed ANOVA was used to determine the difference between every two groups where p < 0.05 is considered significant.

RESULT

There were significant differences between the two groups in several ocular pulse waveform parameters, namely MBR (overall, vessel, tissue), BOT (overall), rising rate (overall), and falling rate (vessel), all with p < 0.05. In addition, the ocular pulse waveform parameters, i.e., MBR (overall), skew (tissue), and BOT (tissue) showed significant temporal changes within the non-habitual group, but not within the habitual group. The temporal changes in parameters MBR (vessel, tissue), skew (overall, vessel), BOT (overall, vessel), rising rate (overall), falling rate (overall, vessel), and FAI (tissue) were significant for both groups (habitual and non-habitual) in response to caffeine intake.

CONCLUSION

The experiment results demonstrated caffeine does modulate OBF significantly and response differently in non-habitual and habitual groups. Among all ten parameters, MBR and BOT were identified as the suitable biomarkers to differentiate between the two groups.

Is laser speckle contrast analysis (LASCA) the new kid on the block in systemic sclerosis? A systematic literature review and pilot study to evaluate reliability of LASCA to measure peripheral blood perfusion in scleroderma patients

OBJECTIVES

A reliable tool to evaluate flow is paramount in systemic sclerosis (SSc). We describe herein on the one hand a systematic literature review on the reliability of laser speckle contrast analysis (LASCA) to measure the peripheral blood perfusion (PBP) in SSc and perform an additional pilot study, investigating the intra- and inter-rater reliability of LASCA.

METHODS

A systematic search was performed in 3 electronic databases, according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. In the pilot study, 30 SSc patients and 30 healthy subjects (HS) underwent LASCA assessment. Intra-rater reliability was assessed by having a first anchor rater performing the measurements at 2 time-points and inter-rater reliability by having the anchor rater and a team of second raters performing the measurements in 15 SSc and 30 HS. The measurements were repeated with a second anchor rater in the other 15 SSc patients, as external validation.

RESULTS

Only 1 of the 14 records of interest identified through the systematic search was included in the final analysis. In the additional pilot study: intra-class correlation coefficient (ICC) for intra-rater reliability of the first anchor rater was 0.95 in SSc and 0.93 in HS, the ICC for inter-rater reliability was 0.97 in SSc and 0.93 in HS. Intra- and inter-rater reliability of the second anchor rater was 0.78 and 0.87.

CONCLUSIONS

The identified literature regarding the reliability of LASCA measurements reports good to excellent inter-rater agreement. This very pilot study could confirm the reliability of LASCA measurements with good to excellent inter-rater agreement and found additionally good to excellent intra-rater reliability. Furthermore, similar results were found in the external validation.

All-optical photoacoustic Doppler transverse blood flow imaging

The method of measuring blood flow in photoacoustic microscopy usually relies on ultrasonic transducers in contact fashion, which is not favored in many applications, such as wound areas, burns, and anabrosis. Here we present a noncontact photoacoustic velocity measurement method to quantitatively map transverse blood flow based on the photoacoustic Doppler (PAD) bandwidth broadening method with an all-optical photoacoustic microscopy system. It is validated that the PAD bandwidth broadening is proportional to the transverse flow within a certain range. The transverse flow speed ranging from 0 to 5.5 mm/s, as well as sectional flow images, was obtained in the blood-mimicking flow phantoms. Furthermore, the blood flow image of the mouse ear demonstrates that the all-optical photoacoustic Doppler method can acquire the information of blood flow in vivo, which could significantly broaden the scope of applications for obtaining the blood flow velocity of the microvasculature in biomedicine.

Adaptable switching schemes for time-encoded multichannel optical coherence tomography

We introduce the approach of variable time encoding for multichannel optical coherence tomography (OCT). High-speed fiber optical switches are applied for sequential sample arm switching to enable quasisimultaneous image acquisition from three different orientation angles. In comparison with previous multichannel OCT (using simultaneous sample illumination), time-encoded multichannel OCT has no need for division of illumination power among the respective channels to satisfy laser safety requirements. Especially for ophthalmic applications-in particular retinal imaging, which the presented prototype was developed for-this advantage strongly influences image quality through an enhanced sensitivity. Nevertheless, time encoding comes at the cost of a decrease in imaging speed due to sequential channel illumination. For the typical multichannel OCT modality Doppler OCT, this results in a reduction of the maximum unambiguously determinable Doppler velocity. However, we demonstrate that this drawback can be overcome by adaptation of the illumination channel switching scheme. Thus, a re-extension of the maximum unambiguously determinable Doppler frequency to the full A-scan rate of the tunable light source is presented. The performance of the technique is demonstrated by flow phantom experiments and measurements of retinal blood flow in the eyes of healthy human volunteers.

ICP Versus Laser Doppler Cerebrovascular Reactivity Indices to Assess Brain Autoregulatory Capacity

BACKGROUND

To explore the relationship between various autoregulatory indices in order to determine which approximate small vessel/microvascular (MV) autoregulatory capacity most accurately.

METHODS

Utilizing a retrospective cohort of traumatic brain injury patients (N = 41) with: transcranial Doppler (TCD), intracranial pressure (ICP) and cortical laser Doppler flowmetry (LDF), we calculated various continuous indices of autoregulation and cerebrovascular responsiveness: A. ICP derived [pressure reactivity index (PRx)-correlation between ICP and mean arterial pressure (MAP), PAx-correlation between pulse amplitude of ICP (AMP) and MAP, RAC-correlation between AMP and cerebral perfusion pressure (CPP)], B. TCD derived (Mx-correlation between mean flow velocity (FVm) and CPP, Mx_a-correlation between FVm and MAP, Sx-correlation between systolic flow velocity (FVs) and CPP, Sx_a-correlation between FVs and MAP, Dx-correlation between diastolic flow index (FVd) and CPP, Dx_a-correlation between FVd and MAP], and LDF derived (Lx-correlation between LDF cerebral blood flow [CBF] and CPP, Lx_a-correlation between LDF-CBF and MAP). We assessed the relationship between these indices via Pearson correlation, Friedman test, principal component analysis (PCA), agglomerative hierarchal clustering (AHC), and k-means cluster analysis (KMCA).

RESULTS

LDF-based autoregulatory index (Lx) was most associated with TCD-based Mx/Mx_a and Dx/Dx_a across Pearson correlation, PCA, AHC, and KMCA. Lx was only remotely associated with ICP-based indices (PRx, PAx, RAC). TCD-based Sx/Sx_a was more closely associated with ICP-derived PRx, PAx and RAC. This indicates that vascular-derived indices of autoregulatory capacity (i.e., TCD and LDF based) covary, with Sx/Sx_a being the exception, whereas indices of cerebrovascular reactivity derived from pulsatile CBV (i.e., ICP indices) appear to not be closely related to those of vascular origin.

CONCLUSIONS

Transcranial Doppler Mx is the most closely associated with LDF-based Lx/Lx_a. Both Sx/Sx-a and the ICP-derived indices appear to be dissociated with LDF-based cerebrovascular reactivity, leaving Mx/Mx-a as a better surrogate for the assessment of cortical small vessel/MV cerebrovascular reactivity. Sx/Sx_a cocluster/covary with ICP-derived indices, as seen in our previous work.

Sympathetic ganglionectomy for facial blushing using application of laser speckle flow graph

OBJECTIVE

Endoscopic thoracic sympathectomy at the second rib level is considered effective as a therapeutic treatment for facial blushing. However, 10% to 15% of patients do not benefit from this intervention. No additional procedure has been developed for this disorder. Recently, ganglionectomy using application of laser speckle flow graph has been evaluated for the treatment of compensatory sweating. We report our results of ganglionectomy for facial blushing as a redo surgery.

METHODS

Between August 2012 and April 2017, 8 patients with facial blushing who underwent an initial sympathectomy reported symptom recurrence. Seven patients had undergone transection of the sympathetic trunk at the second rib and 1 patient had undergone transection of the sympathetic trunk at the second and third ribs. These patients were treated using ganglionectomy guided by application of laser speckle flow graph. After temporary decreases in facial skin blood perfusion were confirmed by stimulating the sympathetic ganglions, ganglionectomy was performed.

RESULTS

All patients' symptoms improved. There were no side effects, including deterioration of compensatory sweating, worsening of gustatory sweating, or Horner syndrome. There were no cases of mortality or conversion to open surgery.

CONCLUSIONS

This study shows the effectiveness of ganglionectomy for the treatment of facial blushing, representing a new treatment option for this condition. Considering the mechanism of facial blushing, it is important to recognize that ganglionectomy is effective after the interception of the sympathetic trunk on the cranial side.

[Effects of the Airway Obstruction on the Skin Microcirculation in Patients with Bronchial Asthma]

Background

Pulmonary hemodynamic disorders depend on the inflammatory phases and severity of the obstructive syndrome. However, the effect of asthma bronchial obstruction on the state of peripheral hemodynamics remains insufficiently known.

Aims

To study the effects of airway obstruction on skin blood flow parameters and its regulatory systems in patients with persistent atopic bronchial asthma in the remission state.

Materials and Methods

A comparative study of the skin peripheral blood flow in patients with bronchial asthma with severe airway obstruction (1st group) and without obstruction (2nd group) was conducted. 20 patients with confirmed diagnosis of atopic asthma of 50–74 years old participated in the study. All patients received basic therapy in a constant dosing of high doses of inhaled glucocorticosteroids/long-acting beta-2-agonists. The control group included 20 healthy volunteers without evidence of bronchial obstruction. The study lasted for 3 months. The forced expiratory volume in 1 s (FEV1) was used to evaluate the bronchial obstruction by spirometry technique. Skin blood perfusion changes were recorded by laser Doppler flowmetry at rest and in response to short-term local ischemia. Registered peripheral blood flow signals were examined using the amplitude temporal filtering in five frequency intervals to identify the functional features of the peripheral blood flow regulation systems.

Results

Consistent two-fold decrease of the oscillation amplitudes was found in the neurogenic interval at rest (p=0.031), as well as in the myogenic (p=0.043; p=0.031) and endothelial intervals (p=0.037; p≤0.001) both at rest and during the postocclusive reactive hyperemia respectively in the 1st group of patients with bronchial obstruction (FEV1 <80%) compared with the control group. No significant changes were revealed for skin blood flow parameters in the 2nd patient group (without obstruction, FEV1 >80%) in comparison to control subjects.

Conclusions

The presence of bronchial obstruction has a significant impact on the changes of the amplitudes of skin blood flow oscillations in patients with bronchial asthma in the myogenic, neurogenic and endothelial intervals.

Laser Doppler sensing for blood vessel detection with a biologically inspired steerable needle

Puncturing blood vessels during percutaneous intervention in minimally invasive brain surgery can be a life threatening complication. Embedding a forward looking sensor in a rigid needle has been proposed to tackle this problem but, when using a rigid needle, the procedure needs to be interrupted and the needle extracted if a vessel is detected. As an alternative, we propose a novel optical method to detect a vessel in front of a steerable needle. The needle itself is based on a biomimetic, multi-segment design featuring four hollow working channels. Initially, a laser Doppler flowmetry probe is characterized in a tissue phantom with optical properties mimicking those of human gray matter. Experiments are performed to show that the probe has a 2.1 mm penetration depth and a 1 mm off-axis detection range for a blood vessel phantom with 5 mm s^-1 flow velocity. This outcome demonstrates that the probe fulfills the minimum requirements for it to be used in conjunction with our needle. A pair of Doppler probes is then embedded in two of the four working channels of the needle and vessel reconstruction is performed using successive measurements to determine the depth and the off-axis position of the vessel from each laser Doppler probe. The off-axis position from each Doppler probe is then used to generate a 'detection circle' per probe, and vessel orientation is predicted using tangent lines between the two. The vessel reconstruction has a depth root mean square error (RMSE) of 0.3 mm and an RMSE of 15° in the angular prediction, showing real promise for a future clinical application of this detection system.

Processing methods for photoacoustic Doppler flowmetry with a clinical ultrasound scanner

Photoacoustic flowmetry (PAF) based on time-domain cross correlation of photoacoustic signals is a promising technique for deep tissue measurement of blood flow velocity. Signal processing has previously been developed for single element transducers. Here, the processing methods for acoustic resolution PAF using a clinical ultrasound transducer array are developed and validated using a 64-element transducer array with a -6 dB detection band of 11 to 17 MHz. Measurements were performed on a flow phantom consisting of a tube (580  μm inner diameter) perfused with human blood flowing at physiological speeds ranging from 3 to 25  mm  /  s. The processing pipeline comprised: image reconstruction, filtering, displacement detection, and masking. High-pass filtering and background subtraction were found to be key preprocessing steps to enable accurate flow velocity estimates, which were calculated using a cross-correlation based method. In addition, the regions of interest in the calculated velocity maps were defined using a masking approach based on the amplitude of the cross-correlation functions. These developments enabled blood flow measurements using a transducer array, bringing PAF one step closer to clinical applicability.

[Determining depth of burns using laser Doppler imaging]

Early accurate assessment of burn depth is important to determine the optimal treatment of burns (conservative versus surgery). Laser Doppler imaging (LDI) is a technique that allows accurate measurement of burn depth by measuring dermal perfusion. Although it has been demonstrated that LDI led to faster decisions as to whether or not to operate, this has not lead to shorter wound healing time or cost savings in Dutch burn care. LDI is used in all Dutch burn centres. In case of doubt about the depth of a burn in primary or secondary care, referral to a burn centre is advisable.

[Present-day possibilities of non-invasive control over microcirculation and metabolism in man]

The main function of the microcirculatory bed consists in maintaining tissue homeostasis at an optimal level irrespective of the effect of various external and internal factors. Of all types of metabolism (diffusive, filtration-reabsorption and vesicular), directly dependent on the haemodynamic parameters is filtration-reabsorption metabolism which provides exchange of water, low-molecular-weight and water-soluble substances at the opposite to the heart «pole» of the cardiovascular system. The present study was aimed at testing a hypothesis that activation of metabolic processes in man would be accompanied by alterations in haemodynamic parameters which may be registered by means of modern non-invasive methods of examination, i. e., laser Doppler flowmetry (LDF) and computer-assisted capillaroscopy (CCS). We used actovegin as an activator of metabolic processes. The study included acute pharmacological testing in apparently healthy volunteers (n=28), a course of taking actovegin in patients with cognitive dysfunctions on the background of arterial hypertension (n=60) and in patients with chronic ischaemia of the lower limbs (n=80). The obtained findings of LDF and CCS demonstrated that the known metabolic effects of actovegin (improved utilization of oxygen and glucose by tissues) were accompanied by an increase in the number of functioning capillaries, increased velocity of capillary blood flow with a decrease in the degree of hydration of the interstitial space, thus reducing the «blood-cell» distance for nutrients and products of tissue metabolism. Improvement of capillary blood flow was determined by a decrease in the tonicity of the capillary sphincters, thus leading to reduced arteriolar-venular shunting of blood with predominant supply to the capillary bed, improved NO-mediated regulation of the value of the lumen of the precapillary arterioles by the microvascular endothelium, improved reaction of resistant microvessels to various dilatation stimuli. The obtained results make it possible to draw a conclusion that modern non-invasive methods of study of human microcirculation (LDF and CCS) are informative not only for assessment of the functional state of the microcirculatory bed of the skin but make it possible to evaluate efficacy of the filtration-reabsorption mechanism of metabolism.

Photonic monitoring of treatment during infection and sepsis: development of new detection strategies and potential clinical applications

Despite the strong decline in the infection-associated mortality since the development of the first antibiotics, infectious diseases are still a major cause of death in the world. With the rising number of antibiotic-resistant pathogens, the incidence of deaths caused by infections may increase strongly in the future. Survival rates in sepsis, which occurs when body response to infections becomes uncontrolled, are still very poor if an adequate therapy is not initiated immediately. Therefore, approaches to monitor the treatment efficacy are crucially needed to adapt therapeutic strategies according to the patient's response. An increasing number of photonic technologies are being considered for diagnostic purpose and monitoring of therapeutic response; however many of these strategies have not been introduced into clinical routine, yet. Here, we review photonic strategies to monitor response to treatment in patients with infectious disease, sepsis, and septic shock. We also include some selected approaches for the development of new drugs in animal models as well as new monitoring strategies which might be applicable to evaluate treatment response in humans in the future. Figure Label-free probing of blood properties using photonics.

The use of laser Doppler flowmetry to evaluate oral soft tissue blood flow in humans: A review

The objective of this work is to define the conditions for improving the use of laser Doppler flowmetry (LDF) and to determine the limits for the use of this technique. This article systematically reviews the literature on the evaluation of oral soft tissue blood microcirculation by LDF. We analysed the available literature through October 2016 using the database resources Medline/PubMed, the Cochrane Oral Health Group Specialist Trials Register and the ISI Web of Knowledge. Several points emerged from this literature review The use of LDF involves specific constraints; however, the influence of different factors (temperature, tobacco, pressure etc.) must be adequately controlled when using LDF. LDF measurements of soft tissue within the oral cavity vary depending on the anatomical site. In dentistry, LDF can be used to track healing progress in periodontal surgery and to diagnose vascular flow changes in the connective tissue of mucosae covered by a removable prosthesis at an early stage prior to the onset of clinical inflammation signs.

Intraoperative continuous cerebral microcirculation measurement in patients with aneurysmal subarachnoid hemorrhage: preliminary data on the early administration of magnesium sulfate

BACKGROUND

In patients with subarachnoid hemorrhage (SAH), vasospasm remains one of the major complications. The application of intravenous magnesium sulfate (MgSO4) has been under discussion to prevent cerebral ischemia. Our aim was to examine the impact of early MgSO4 administration on local cerebral microcirculation during microsurgical clipping of SAH-related aneurysms.

METHODS

The non-invasive laser-Doppler spectrophotometry system "Oxygen-to-See (O2C)" was used in 14 consecutive patients (11 female, 3 male, median age 56.5±9.7 yrs) with aneurysmatic SAH. A subdural probe measured capillary venous oxygenation (SO2), relative hemoglobin content (rHb), blood cell velocity (velo) and blood flow (flow) in 7 mm tissue depth. Data samples were recorded as baseline immediately before intraoperative application of MgSO4 10% 50 mg/kg body weight and 10 min thereafter. The continuous MgSO4 infusion rate depended on blood pressure (mean arterial pressure > 60-65 mmHg) and lasted a maximum of 60 min.

RESULTS

MgSO4 was administered 2.8 (min. 1.6, max. 15.5) hours after onset of symptoms. Median flow increased significantly by 20.8% (5-68%, p = 0.001). Velo increased 4.9% (1-17%), rHb decreased 1.5% (3-34%) and SO2 decreased 9.4% (8-38%) by trend compared to the baseline values. FiO2 correlated positively with velo (rs = 0.712, p = 0.004), whereas arterial HCO3 correlated negatively with SO2 (rs = -0.599, p = 0.024). Of 14 patients, 2 had symptomatic vasospasm.

CONCLUSIONS

Our data suggest an increased cerebral blood flow after early intraoperative administration of MgSO4 in patients with SAH. Using a non-invasive laser-Doppler spectrophotometry system, this technique is feasible for continuous real-time monitoring of cerebral microcirculation.

TRIAL REGISTRATION

DRKS (German Clinical Trial Registry), DRKS00013047 , retrospectively registered on September 21st, 2017.