Biophotonic methods in microcirculation imaging

GPER deficiency impedes murine myocutaneous revascularization and wound healing

Estrogens regulate numerous physiological and pathological processes, including wide-ranging effects in wound healing. The effects of estrogens are mediated through multiple estrogen receptors (ERs), including the classical nuclear ERs (ERα and ER β ), that typically regulate gene expression, and the 7-transmembrane G protein-coupled estrogen receptor (GPER), that predominantly mediates rapid "non-genomic" signaling. Estrogen modulates the expression of various genes involved in epidermal function and regeneration, inflammation, matrix production, and protease inhibition, all critical to wound healing. Our previous work demonstrated improved myocutaneous wound healing in female mice compared to male mice. In the current study, we employed male and female GPER knockout mice to investigate the role of this estrogen receptor in wound revascularization and tissue viability. Using a murine myocutaneous flap model of graded ischemia, we measured real-time flap perfusion via laser speckle perfusion imaging. We conducted histologic and immunohistochemical analyses to assess skin and muscle viability, microvascular density and vessel morphology. Our results demonstrate that GPER is crucial in wound healing, mediating effects that are both dependent and independent of sex. Lack of GPER expression is associated with increased skin necrosis, reduced flap perfusion and altered vessel morphology. These findings contribute to understanding GPER signaling in wound healing and suggest possible therapeutic opportunities by targeting GPER.

Sampling volume assessment for wearable multimodal optical diagnostic device

The process and results of numerical Monte Carlo simulation of optical radiation propagation in laser Doppler flowmetry (LDF) and fluorescence spectroscopy (FS) channels of a wearable diagnostic multimodal device are described in this paper. To achieve the goal, a multilayer skin model with different parameters of blood and melanin content and different distances between sources and radiation receivers was designed. The changes in the sampling (diagnostic) volume depending on the anatomical features of the biological tissues, as well as on the technical parameters of the device were shown. Depending on the scattering media optical properties and the source-detector configuration of the device, the diagnostic volume can range from 2 to 7 mm3 . The obtained results allow the formation of specialized medical and technical requirements for wearable multimodal devices implementing LDF and FS channels.

Towards Development of Specular Reflection Vascular Imaging

Specular reflection from tissue is typically considered as undesirable, and managed through device design. However, we believe that specular reflection is an untapped light-tissue interaction, which can be used for imaging subcutaneous blood flow. To illustrate the concept of subcutaneous blood flow visualization using specular reflection from the skin, we have developed a ray tracing for the neck and identified conditions under which useful data can be collected. Based on our model, we have developed a prototype Specular Reflection Vascular Imaging (SRVI) device and demonstrated its feasibility by imaging major neck vessels in a case study. The system consists of a video camera that captures a video from a target area illuminated by a rectangular LED source. We extracted the SRVI signal from 5 × 5 pixels areas (local SRVI signal). The correlations of local SRVIs to the SRVI extracted from all pixels in the target area do not appear to be randomly distributed, but rather form cohesive sub-regions with distinct boundaries. The obtained waveforms were compared with the ECG signal. Based on the time delays with respect to the ECG signal, as well as the waveforms themselves, the sub-regions can be attributed to the jugular vein and carotid artery. The proposed method, SRVI, has the potential to contribute to extraction of the diagnostic information that the jugular venous pulse can provide.

Sex differences in murine myocutaneous flap revascularization

Sex differences in susceptibility to ischemia/reperfusion injury have been documented in humans. Premenopausal women have a lower risk of ischemic heart disease than age-matched men, whereas after menopause, the risk is similar or even higher in women. However, little is known about the effects of sex on myocutaneous ischemia/reperfusion. To explore sex differences in wound revascularization, we utilized a murine myocutaneous flap model of graded ischemia. A cranial-based, peninsular-shaped, myocutaneous flap was surgically created on the dorsum of male and female mice. Physiological, pathological, immunohistochemical, and molecular parameters were analyzed. Flaps created on female mice were re-attached to the recipient site resulting in nearly complete viability at post-operative day 10. In contrast, distal full-thickness myocutaneous necrosis was evident at 10 days post-surgery in male mice. Over the 10 day study interval, laser speckle imaging documented functional revascularization in all flap regions in female mice, but minimal distal flap reperfusion in male mice. Day 10 immunostained histologic sections confirmed significant increases in distal flap vessel count and vascular surface area in female compared to male mice. RT-PCR demonstrated significant differences in growth factor and metabolic gene expression between female and male mice at day 10. In conclusion, in a graded-ischemia wound healing model, flap revascularization was more effective in female mice. The recognition and identification of sex-specific wound healing differences may lead to a better understanding of the underlying mechanisms of myocutaneous revascularization and drive novel discovery to improve soft tissue wound healing following tissue transfer for traumatic injury and cancer resection.

The tissue viability imaging system-Suitable method for discovering minimal skin changes in occupational screenings? Results of a cross-sectional field study

BACKGROUND

For early detection of initial skin changes in occupational screenings, only few objective assessment systems are available.

OBJECTIVES

With the aim of assessing an objective measurement method for hand eczema, we trialed the application of the tissue viability imaging (TiVi) system, quantifying erythema non-invasively by polarized light spectroscopy.

MATERIALS AND METHODS

In a field study with 625 employees of a semiconductor production company, 411 were exposed to prolonged wearing of occlusive gloves in the clean room. TiVi system and Hand Eczema Score for Occupational Screenings (HEROS), a quantitative skin score for the hands, were used, supplemented by a standardized personal interview.

RESULTS

TiVi values of 65 up to 246 for each hand (palm or back), for each participant summed to overall 289 up to 848 (median 389), were measured. Higher TiVi values were noted for men, smokers, and with increasing age. Correlation between TiVi and HEROS was only weak. Several factors like skin pigmentation, thickness of the skin, or tattoos seem to influence TiVi results.

CONCLUSIONS

The practical relevance of one-time measurements with the TiVi system in occupational screenings seems to be limited. Specifically, the TiVi system cannot replace dermatological examinations at the workplace. Notwithstanding, the application for other scientific purposes might be useful.

Photoacoustic Oxygenation Quantification in Patients with Raynaud's: First-in-Human Results

The purpose of this study was to investigate the use of photoacoustic imaging for quantifying fingertip oxygenation as an approach to diagnosing and monitoring Raynaud's phenomenon. After 30 min of acclimation to room temperature, 22 patients (7 patients with secondary Raynaud's associated to Scleroderma and 15 healthy controls) provided informed consent to undergo fingertip Doppler imaging and high-frequency photoacoustic imaging before and 5, 15 and 30 min after cold stimulus (submerged hand in a 15 °C water bath for 1 min). High-frequency ultrasound and photoacoustic imaging was performed on the nail bed of each patient's second through fifth finger on their dominant hand, using a Vevo 2100 LAZR system with an LZ-250 probe (Fujifilm VisualSonics, Toronto, ON, Canada) in oxy-hemoglobin quantification mode. During each exam, volumetric data across a 3-mm span of data was acquired to produce a volumetric image of percent oxygenation and hemoglobin concentration. Changes in fingertip oxygenation between Raynaud's patients and healthy volunteers were compared, using receiver operator characteristic (ROC) analysis. Photoacoustic signal was detected in both the nail bed and nailfold in all study participants. Doppler ultrasound resulted in poor differentiation of Raynaud's patients from healthy volunteers, with an area under the ROC curve (A_z) of 0.51. Photoacoustic imaging demonstrated improved accuracy at baseline (A_z = 0.72), which improved when quantifying normalized changes after cold stimulus (A_z = 0.89 5-min post stimulus, A_z = 0.91 15-min post stimulus, and A_z = 0.85 after stimulus). Oxygenation levels derived using photoacoustic imaging are able to identify patients with Raynaud's and safely evaluate their response to a cold stimulus over time.

Fabrication of a multilayer tissue-mimicking phantom with tunable optical properties to simulate vascular oxygenation and perfusion for optical imaging technology

Vast research has been carried out to fabricate tissue-mimicking phantoms, due to their convenient use and ease of storage, to assess and validate the performance of optical imaging devices. However, to the best of our knowledge, there has been little research on the use of multilayer tissue phantoms for optical imaging technology, although their structure is closer to that of real skin tissue. In this work, we design, fabricate, and characterize multilayer tissue-mimicking phantoms, with a morphological mouse ear blood vessel, that contain an epidermis, a dermis, and a hypodermis. Each tissue-mimicking phantom layer is characterized individually to match specific skin tissue layer characteristics. The thickness, optical properties (absorption coefficient and reduced scattering coefficient), oxygenation, and perfusion of skin are the most critical parameters for disease diagnosis and for some medical equipment. These phantoms can be used as calibration artifacts and help to evaluate optical imaging technologies.

Wearable speckle plethysmography (SPG) for characterizing microvascular flow and resistance

In this work we introduce a modified form of laser speckle imaging (LSI) referred to as affixed transmission speckle analysis (ATSA) that uses a single coherent light source to probe two physiological signals: one related to pulsatile vascular expansion (classically known as the photoplethysmographic (PPG) waveform) and one related to pulsatile vascular blood flow (named here the speckle plethysmographic (SPG) waveform). The PPG signal is determined by recording intensity fluctuations, and the SPG signal is determined via the LSI dynamic light scattering technique. These two co-registered signals are obtained by transilluminating a single digit (e.g. finger) which produces quasi-periodic waveforms derived from the cardiac cycle. Because PPG and SPG waveforms probe vascular expansion and flow, respectively, in cm-thick tissue, these complementary phenomena are offset in time and have rich dynamic features. We characterize the timing offset and harmonic content of the waveforms in 16 human subjects and demonstrate physiologic relevance for assessing microvascular flow and resistance.

Using Hawkeye from the Avengers to communicate on the eye

Superheroes, such as Iron Man, Captain America, Wonder Woman, Batman, and Hawkeye, have appeared in numerous films, displaying their range of incredible superpowers and abilities. Therefore, it is unsurprising that many people would not only wish to attain these powers, but also to learn about scientific accessibility to these powers. Popular culture characters such as superheroes can provide a unique platform for the communication of difficult scientific concepts. In the classroom, these characters can be used to communicate learning objectives to students in an interesting, fun, and accessible manner by taking advantage of student familiarity with the characters. Hawkeye, a member of the Avengers, is one such superhero who can be utilized by educators. His powers can be attributed in part to his advanced eyesight, which has physiological aspects in common with many birds of prey. Hence, Hawkeye can instigate discussion on the physiology of the human eye, while also allowing for comparison with other species, such as birds of prey, and reflection on advancements related to genetic engineering and wearable technologies. In addition, in my experience, Hawkeye has proven to be a highly suitable popular culture character for use in scientific communication and outreach.

Thermography-based blood flow imaging in human skin of the hands and feet: a spectral filtering approach

The determination of the relationship between skin blood flow and skin temperature dynamics is the main problem in thermography-based blood flow imaging. Oscillations in skin blood flow are the source of thermal waves propagating from micro-vessels toward the skin's surface, as assumed in this study. This hypothesis allows us to use equations for the attenuation and dispersion of thermal waves for converting the temperature signal into the blood flow signal, and vice versa. We developed a spectral filtering approach (SFA), which is a new technique for thermography-based blood flow imaging. In contrast to other processing techniques, the SFA implies calculations in the spectral domain rather than in the time domain. Therefore, it eliminates the need to solve differential equations. The developed technique was verified within 0.005-0.1 Hz, including the endothelial, neurogenic and myogenic frequency bands of blood flow oscillations. The algorithm for an inverse conversion of the blood flow signal into the skin temperature signal is addressed. The examples of blood flow imaging of hands during cuff occlusion and feet during heating of the back are illustrated. The processing of infrared (IR) thermograms using the SFA allowed us to restore the blood flow signals and achieve correlations of about 0.8 with a waveform of a photoplethysmographic signal. The prospective applications of the thermography-based blood flow imaging technique include non-contact monitoring of the blood supply during engraftment of skin flaps and burns healing, as well the use of contact temperature sensors to monitor low-frequency oscillations of peripheral blood flow.

Fabrication of a turbid optofluidic phantom device with tunable μa and μ's to simulate cutaneous vascular perfusion

Microfluidic devices are oftenly used to calibrate the imaging reconstruction, because they simulate the morphology of microvasculature. However, for lack of optical properties in microfluidics, the functional recovery of oximetry information cannot be verified. In this work, we describe the fabrication of a novel turbid optofluidic tissue phantom. It is designed to mimic the vascular perfusion and the turbid nature of cutaneous tissue. This phantom contains an interior hollow microfluidic structure with a diameter of ϕave = 50 μm. The microfluidic structure includes the geometry of an inlet, a river-like assay and an outlet. This structure can be perfused by hemoglobin solution to mimic the cutaneous micro-circulation. The multiple-layered phantom matrices exhibit the representative optical parameters of human skin cutis, namely the absorption coefficient μa and the reduced scattering coefficient . The geometry of the generated microfluidic structure is investigated by using Spectral-Domain Optical Coherence Tomography. This optofluidic phantom bridges the gap between tissue equivalent phantoms and Lab-On-Chip devices. Perspectively, this device can be used to calibrate a variety of optical angiographic imaging approaches.

Intraoperative monitoring of blood perfusion in port wine stains by laser Doppler imaging during vascular targeted photodynamic therapy: A preliminary study

OBJECTIVE

The objective of this study was to monitor blood perfusion dynamics of port wine stains (PWS) during vascular targeted photodynamic therapy (V-PDT) with laser Doppler imaging (LDI).

METHODS

The PWS lesions of 30 facial PWS patients received V-PDT, while the normal skins on the forearm of 5 healthy subjects were treated as light-only controls for comparison. Furthermore, two different PWS lesions in the same individual from each of 3 PWS patients successively received laser irradiation only and V-PDT, respectively. LDI was used to monitor intraoperative blood perfusion dynamics.

RESULTS

During V-PDT, the blood perfusion (278±96 PU) in PWS lesions for 31 of 33 PWS patients significantly increased after the initiation of V-PDT treatment, then reached a peak (638±105 PU) within 10min, followed by a slow decrease to a relatively lower level (515±100 PU). Furthermore, the time for reaching peak and the subsequent magnitude of decrease in blood perfusion varied with different patients. For light-only controls, an initial perfusion peak at 3min followed by a nadir and a secondary increase were found not only in normal skin, but also in PWS lesions.

CONCLUSION

The preliminary results showed that the LDI permits non-invasive monitoring blood perfusion changes of PWS lesions during V-PDT. There was a clear trend in blood perfusion responses during V-PDT and laser irradiation. The blood perfusion changes during treatment were due to V-PDT effects as well as local temperature increase induced by laser irradiation.

Near infrared image processing to quantitate and visualize oxygen saturation during vascular occlusion

The assessment of microcirculation spatial heterogeneity on the hand skin is the main objective of this work. Near-infrared spectroscopy based 2D imaging is a non-invasive technique for the assessment of tissue oxygenation. The haemoglobin oxygen saturation images were acquired by a dedicated camera (Kent Imaging) during baseline, ischaemia (brachial artery cuff occlusion) and reperfusion. Acquired images underwent a preliminary restoration process aimed at removing degradations occurring during signal capturing. Then, wavelet transform based multiscale analysis was applied to identify edges by detecting local maxima and minima across successive scales. Segmentation of test areas during different conditions was obtained by thresholding-based region growing approach. The method identifies the differences in microcirculatory control of blood flow in different regions of the hand skin. The obtained results demonstrate the potential use of NIRS images for the clinical evaluation of skin disease and microcirculatory dysfunction.

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.

Photoplethysmography Revisited: From Contact to Noncontact, From Point to Imaging

Photoplethysmography (PPG) is a noninvasive optical technique for detecting microvascular blood volume changes in tissues. Its ease of use, low cost and convenience make it an attractive area of research in the biomedical and clinical communities. Nevertheless, its single spot monitoring and the need to apply a PPG sensor directly to the skin limit its practicality in situations such as perfusion mapping and healing assessments or when free movement is required. The introduction of fast digital cameras into clinical imaging monitoring and diagnosis systems, the desire to reduce the physical restrictions, and the possible new insights that might come from perfusion imaging and mapping inspired the evolution of the conventional PPG technology to imaging PPG (IPPG). IPPG is a noncontact method that can detect heart-generated pulse waves by means of peripheral blood perfusion measurements. Since its inception, IPPG has attracted significant public interest and provided opportunities to improve personal healthcare. This study presents an overview of the wide range of IPPG systems currently being introduced along with examples of their application in various physiological assessments. We believe that the widespread acceptance of IPPG is happening, and it will dramatically accelerate the promotion of this healthcare model in the near future.

Speckle contrast optical spectroscopy, a non-invasive, diffuse optical method for measuring microvascular blood flow in tissue

We introduce a new, non-invasive, diffuse optical technique, speckle contrast optical spectroscopy (SCOS), for probing deep tissue blood flow using the statistical properties of laser speckle contrast and the photon diffusion model for a point source. The feasibility of the method is tested using liquid phantoms which demonstrate that SCOS is capable of measuring the dynamic properties of turbid media non-invasively. We further present an in vivo measurement in a human forearm muscle using SCOS in two modalities: one with the dependence of the speckle contrast on the source-detector separation and another on the exposure time. In doing so, we also introduce crucial corrections to the speckle contrast that account for the variance of the shot and sensor dark noises.

Speckle contrast optical tomography: A new method for deep tissue three-dimensional tomography of blood flow

A novel tomographic method based on the laser speckle contrast, speckle contrast optical tomography (SCOT) is introduced that allows us to reconstruct three dimensional distribution of blood flow in deep tissues. This method is analogous to the diffuse optical tomography (DOT) but for deep tissue blood flow. We develop a reconstruction algorithm based on first Born approximation to generate three dimensional distribution of flow using the experimental data obtained from tissue simulating phantoms.

Feasibility of capillary velocity assessment by statistical means using dual-beam spectral-domain Optical Coherence Tomography: a preliminary study

The assessment of vascular dynamics has been shown to yield both qualitative and quantitative metrics and thus play a pivotal role in the diagnosis and prognosis of various diseases, which may manifest as microcirculatory irregularities. Optical Coherence Tomography (OCT) is an established imaging modality which utilises the principle of optical interferometry to distinguish between spatial changes in refractive index and thus formulate a multi-dimensional representation of a specimen in vivo. Nonetheless, difficulties remain in obtaining accurate data (morphological and/or transient) in an environment which is subject to such large biological variability. In an effort to address the issue of angular dependence as with Doppler based analysis, a dual-beam Spectral-domain OCT system for quasi-simultaneous specimen scanning is described. A statistical based method of phase correlation is outlined which is capable of quantifying velocity values in addition to the ability to discern bidirectionality, without the necessity of angular computation.

The role of monocyte subsets in myocutaneous revascularization

BACKGROUND

The controlled recruitment of monocytes from the circulation to the site of injury and their differentiation into tissue macrophages are critical events in the reconstitution of tissue integrity. Subsets of monocytes/macrophages have been implicated in the pathogenesis of atherosclerosis and tumor vascularity; however, the significance of monocyte heterogeneity in physiologic neovascularization is just emerging.

MATERIALS AND METHODS

A cranial-based, peninsular-shaped myocutaneous flap was surgically created on the dorsum of wild-type mice (C57BL6) and populations of mice with genetic deletion of subset-specific chemokine ligand-receptor axes important in monocyte trafficking and function (CCL2(-/-) and CX3CR1(-/-)) (n=36 total; 12 mice per group, nine with flap and three unoperated controls). Planimetric analysis of digital photographic images was utilized to determine flap surface viability in wild-type and knockout mice. Real-time myocutaneous flap perfusion and functional revascularization was determined by laser speckle contrast imaging. Image analysis of CD-31 immunostained sections confirmed flap microvascular density and anatomy. Macrophage quantification and localization in flap tissues was determined by F4/80 gene and protein expression. Quantitative reverse transcription-polymerase chain reaction was performed on nonoperative back skin and postoperative flap tissue specimens to determine local gene expression.

RESULTS

Myocutaneous flaps created on wild type and CX3CR1(-/-) mice were engrafted to the recipient site, resulting in viability. In contrast, distal full thickness cutaneous necrosis and resultant flap dehiscence was evident by d 10 in CCL2(-/-) mice. Over 10 d, laser speckle contrast imaging documented immediate graded flap ischemia in all three groups of mice, functional flap revascularization in wild type and CX3CR1(-/-) mice, and lack of distal flap reperfusion in CCL2(-/-) mice. Immunostaining of serial histologic specimens confirmed marked increases in microvascular density and number of macrophages in wild type mice, intermediate increases in CX3CR1(-/-) mice, and no significant change in vessel count or macrophage quantity in CCL2(-/-) mice over the study interval. Finally, quantitative reverse transcriptase polymerase chain reaction demonstrated that the loss of function of chemokine ligand and receptor genes influenced the transcription of local genes involved in monocyte chemotaxis and wound angiogenesis.

CONCLUSIONS

In a graded-ischemia wound healing model, monocyte recruitment was severely impaired in CCL2(-/-) mice, resulting in failure of flap revascularization and concomitant cutaneous necrosis. Analysis of CX3CR1-deficient mice revealed adequate monocyte recruitment and revascularization for flap survival; however, the myeloid cell response and magnitude of neovascularization were dampened compared with wild type mice.

'Go with the flow ': a review of methods and advancements in blood flow imaging

Physics has delivered extraordinary developments in almost every facet of modern life. From the humble thermometer and stethoscope to X-Ray, CT, MRI, ultrasound, PET and radiotherapy, our health has been transformed by these advances yielding both morphological and functional metrics. Recently high resolution label-free imaging of the microcirculation at clinically relevant depths has become available in the research domain. In this paper, we present a comprehensive review on current imaging techniques, state-of-the-art advancements and applications, and general perspectives on the prospects for these modalities in the clinical realm.

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.

Dynamic microvascular responses with a high speed TiVi imaging system

TiVi technology presents a high resolution, low speed methodology for imaging microcirculation. Recently, the TiVi system was adapted to produce a high speed system capable of analysing dynamic responses from human tissues at a frame rate of 30 frames per second. We present results based on this system by investigating dynamic responses such as arterial pulsations both from a controlled flow model and in vivo tissue sites. We also quantify the effects of sympathetic vasomotion, a biological effect which is evident in many tissue sites, and show that the effects of arterial pulsations and vasomotion on the resulting TiVi time traces are easily determined.

In vivo imaging of the microcirculation of the volar forearm using correlation mapping optical coherence tomography (cmOCT)

Correlation mapping optical coherence tomography (cmOCT) is a recently proposed technique that extends the capabilities of OCT to enable mapping of vasculature networks. The technique is achieved as a processing step on OCT intensity images that does not require any modification to existing OCT hardware. In this paper we apply the cmOCT processing technique to in vivo human imaging of the volar forearm. We illustrate that cmOCT can produce maps of the microcirculation that clearly follow the accepted anatomical structure. We demonstrate that the technique can extract parameters such as capillary density and vessel diameter. These parameters are key clinical markers for the early changes associated with microvascular diseases. Overall the presented results show that cmOCT is a powerful new tool that generates microcirculation maps in a safe non-invasive, non-contact technique which has clear clinical applications.

The importance of engraftment in flap revascularization: confirmation by laser speckle perfusion imaging

BACKGROUND

The delivery of proangiogenic agents in clinical trials of wound healing has produced equivocal results, the lack of real-time assessment of vascular growth is a major weakness in monitoring the efficacy of therapeutic angiogenesis, and surgical solutions fall short in addressing the deficiency in microvascular blood supply to ischemic wounds. Therefore, elucidation of the mechanisms involved in ischemia-induced blood vessel growth has potential diagnostic and therapeutic implications in wound healing.

MATERIALS AND METHODS

Three surgical models of wound ischemia, a cranial-based myocutaneous flap, an identical flap with underlying silicone sheeting to prevent engraftment, and a complete incisional flap without circulation were created on C57BL6 transgenic mice. Laser speckle contrast imaging was utilized to study the pattern of ischemia and return of revascularization. Simultaneous analysis of wound histology and microvascular density provided correlation of wound perfusion and morphology.

RESULTS

Creation of the peninsular-shaped flap produced a gradient of ischemia. Laser speckle contrast imaging accurately predicted the spatial and temporal pattern of ischemia, the return of functional revascularization, and the importance of engraftment in distal flap perfusion and survival. Histologic analysis demonstrated engraftment resulted in flap revascularization by new blood vessel growth from the recipient bed and dilatation of pre-existing flap vasculature.

CONCLUSIONS

Further research utilizing this model of graded wound ischemia and the technology of laser speckle perfusion imaging will allow monitoring of the real-time restitution of blood flow for correlation with molecular biomarkers of revascularization in an attempt to gain further understanding of wound microvascular biology.

Section-illumination photoacoustic microscopy for dynamic 3D imaging of microcirculation in vivo

We developed section-illumination photoacoustic microscopy capable of dynamic in vivo imaging of microvessels as small as 30 microm in diameter. The section illumination improved the elevational resolution while an ultrasound array provided the in-plane axial and lateral resolutions. Using the imaging system, we monitored the wash-in dynamics of Evans Blue in the microcirculation of mouse ears at 249 Hz 2D and 0.5 Hz 3D image acquisition rates. Such observation allowed us to differentiate the arterioles from the venules. In the future, the technology may be used to study angiogenesis, diabetes-induced vascular complications, and pharmacokinetics.

A minimally invasive human in vivo cutaneous wound model for the evaluation of innate skin reactivity and healing status

Individual variability in skin reactivity and healing capacity after trauma are important clinical issues. The aims were to develop an in vivo, human wound model based on a standardised minimal skin injury and to demonstrate therapeutic effect of simple wound therapies in terms of morphological wound outcome with changes in skin blood perfusion as a quantified indicator of wound healing. In a series of experiments, wounds were induced on the normal forearm skin of volunteers using a blood collection lancet. This was well tolerated. Wounds were assessed by naked eye examination or laser Doppler perfusion imaging (LDPI) at baseline and at up to 6 further time points up to 96 h in control wounds and wounds treated by commonly used occlusive dressing options. Assessment by clinical observation with 10x magnification showed over 96 h a progression of erythema, surface crust, a new keratinisation layer and finally healed areas. LDPI quantifying wound erythema showed a peak at 24 h and near normal levels at 96 h. Inter-individual variability was evident but intra-individual variability was much less pronounced. Wounds treated with occlusion showed a statistically significant more rapid return to baseline blood perfusion as measured by LDPI compared to controls supported by favourable healing parameters in the clinical assessment. The paper exemplifies use of non-invasive, bioengineering technique for quantification of individual innate variability in skin reactivity, wound healing capacity and therapeutic effect in a well-tolerated in vivo, human, minimal skin trauma model.

Tissue viability (TiVi) imaging: temporal effects of local occlusion studies in the volar forearm

Tissue Viability (TiVi) imaging is a promising new technology for the assessment of microcirculation in the upper human dermis. Although the technique is easily implemented and develops large amounts of observational data, its role in the clinical workplace awaits the development of standardised protocols required for routine clinical practice. The present study investigates the use of TiVi technology in a human, in vivo, localized, skin blood flow occlusion protocol. In this feasibility study, the response of the cutaneous microcirculation after provocation on the volar surface of the forearm was evaluated using a high temporal-low spatial resolution TiVi camera. 19 healthy subjects - 10 female and 9 male - were studied after a localized pressure was applied for 5 different time periods ranging from 5 to 25 seconds. Areas corresponding to 100 x 100 pixels (2.89 cm(2)) were monitored for 60 seconds prior to, during and after each occlusion period. Our results demonstrated the removal of blood from the local area and a hyperaemic response supporting the suitability of TiVi imaging for the generation of detailed provocation response data of relevance for the physiological function of the skin microcirculation in health and disease.

The skin pathergy test: innately useful?

Pathergy is the term used to describe hyper-reactivity of the skin that occurs in response to minimal trauma. A positive skin pathergy test (SPT), characterised by erythematous induration at the site of the needle stick with a small pustule containing sterile pus at its centre, is among the criteria required for a diagnosis of Behçet's disease (BD) and in certain population has been shown to be highly specific for this condition. Problems with standardising the induction manoeuvre for the SPT as well as the method of assessment of the response have limited the usefulness of the SPT in the clinical setting. Extensive investigation into histopathological and immunological aspects of pathergy has led to a number of hypotheses relating to the aetiology of the skin pathergy reaction and the disease itself, but the cause is considered to be unknown. Pathergy lesions, the development of new skin lesions or the aggravation of existing ones following trivial trauma, are also reported in pyoderma gangrenosum and has been noted in other neutrophilic dermatoses such as Sweet's syndrome. The response of such patient groups to the systematic application of the SPT has not been described. We propose that a new way of considering the pathergy reaction is to see it as an aberration of the skin's innate reactivity from a homeostatic reactive mode closely coupled to tissue healing to an abnormal destructive/inflammatory mode. Our understanding of BD and other similar conditions would profit by more detailed mechanistic knowledge of skin homeostasis to minimal trauma in both health and disease through a more structured and systematic use of the SPT.

Comparison of instruments for investigation of microcirculatory blood flow and red blood cell concentration

The use of laser Doppler perfusion imaging (LDPI) and laser speckle perfusion imaging (LSPI) is well known in the noninvasive investigation of microcirculatory blood flow. This work compares the two techniques with the recently developed tissue viability (TiVi) imaging system, which is proposed as a useful tool to quantify red blood cell concentration in microcirculation. Three systems are evaluated with common skin tests such as the use of vasodilating and vasoconstricting drugs (methlynicotinate and clobetasol, respectively) and a reactive hyperaemia maneuver (using a sphygmomanometer). The devices investigated are the laser Doppler line scanner (LDLS), the laser speckle perfusion imager (FLPI)-both from Moor Instruments (Axminster, United Kingdom)-and the TiVi imaging system (WheelsBridge AB, Linkoping, Sweden). Both imaging and point scanning by the devices are used to quantify the provoked reactions. Perfusion images of vasodilatation and vasoconstriction are acquired with both LDLS and FLPI, while TiVi images are acquired with the TiVi imager. Time acquisitions of an averaged region of interest are acquired for temporal studies such as the reactive hyperaemia. In contrast to the change in perfusion over time with pressure, the TiVi imager shows a different response due its measurement of blood concentration rather than perfusion. The responses can be explained by physiological understanding. Although the three devices sample different compartments of tissue, and output essentially different variables, comparisons can be seen between the three systems. The LDLS system proves to be suited to measurement of perfusion in deeper vessels, while FLPI and TiVi showed sensitivity to more superficial nutritional supply. LDLS and FLPI are insensitive to the action of the vasoconstrictor, while TiVi shows the clear boundaries of the reaction. Assessment of the resolution, penetration depth, and acquisition rate of each instrument show complimentary features that should be taken into account when choosing a system for a particular clinical measurement.

Review of laser speckle contrast techniques for visualizing tissue perfusion

When a diffuse object is illuminated with coherent laser light, the backscattered light will form an interference pattern on the detector. This pattern of bright and dark areas is called a speckle pattern. When there is movement in the object, the speckle pattern will change over time. Laser speckle contrast techniques use this change in speckle pattern to visualize tissue perfusion. We present and review the contribution of laser speckle contrast techniques to the field of perfusion visualization and discuss the development of the techniques.