Assessment of the human cutaneous microvasculature using optical coherence tomography: Proving Harvey's proof.

William Harvey proved the circulation of blood 400 years ago using a combination of ligature application and astute observation that presaged the existence of capillaries. Here we report findings, based on our development of a novel application of optical coherence tomography (OCT), that directly confirm the impact of cuff inflation on microvessels as small as ~30µm. By emulating Harvey's proofs, using cuff inflation at low pressure in the presence and absence of skin heating, we have imaged and quantified significant effects on microvascular diameter and density in humans in vivo. The application of cuff pressure significantly increased microvascular diameter (40.5 ± 4.6 vs 47.1 ± 3.9 µm, P = .01) and density (8.33 ± 4.3 vs 15.1 ± 4.9%, P < .01). These impacts were reversed by cuff deflation. Our study also showed the profound impacts of skin heating on microvessel diameter (46.7 ± 5.8 vs 70.6 ± 7.8 µm, P < .01) and density (14.2 ± 6.5 vs 43.2 ± 9%, P < .01) in vivo, which were further exacerbated by cuff inflation. Our approach to the direct visualization of the human skin microvasculature is non-invasive, safe, and easily applied. Future experiments might be directed at questions of microvascular physiology and pathophysiology, such as how different mammals thermoregulate and what impacts cardiovascular disease and diabetes have on microvascular structure and function.

Novel Noninvasive Assessment of Microvascular Structure and Function in Humans.

INTRODUCTION: Optical coherence tomography (OCT) is a novel high-resolution imaging technique capable of visualizing in vivo structures at a resolution of ~10 µm. We have developed specialized OCT-based approaches that quantify diameter, speed, and flow rate in human cutaneous microvessels. In this study, we hypothesized that OCT-based microvascular assessments would possess comparable levels of reliability when compared with those derived using conventional laser Doppler flowmetry (LDF). METHODS: Speckle decorrelation images (OCT) and red blood cell flux (LDF) measures were collected from adjacent forearm skin locations on 2 d (48 h apart), at baseline, and after a 30-min rapid local heating protocol (30°C-44°C) in eight healthy young individuals. OCT postprocessing quantified cutaneous microvascular diameter, speed, flow rate, and density (vessel recruitment) within a region of interest, and data were compared between days. RESULTS: Forearm skin LDF (13 ± 4 to 182 ± 31 AU, P < 0.05) and OCT-derived diameter (41.8 ± 6.6 vs 64.5 ± 6.9 µm), speed (68.4 ± 9.5 vs 89.0 ± 7.3 µm·s), flow rate (145.0 ± 60.6 vs 485 ± 132 pL·s), and density (9.9% ± 4.9% vs 45.4% ± 5.9%) increased in response to local heating. The average OCT-derived microvascular flow response (pL·s) to heating (234% increase) was lower (P < 0.05) than the LDF-derived change (AU) (1360% increase). Pearson correlation was significant for between-day local heating responses in terms of OCT flow (r = 0.93, P < 0.01), but not LDF (P = 0.49). Bland-Altman analysis revealed that between-day baseline OCT-derived flow rates were less variable than LDF-derived flux. CONCLUSIONS: Our findings indicate that OCT, which directly visualizes human microvessels, not only allows microvascular quantification of diameter, speed, flow rate, and vessel recruitment but also provides outputs that are highly reproducible. OCT is a promising novel approach that enables a comprehensive assessment of cutaneous microvascular structure and function in humans.

Optical coherence tomography in the assessment of acute changes in cutaneous vascular diameter induced by heat stress.

There are limited imaging technologies available that can accurately assess or provide surrogate markers of the in vivo cutaneous microvessel network in humans. In this study, we establish the use of optical coherence tomography (OCT) as a novel imaging technique to assess acute changes in cutaneous microvessel area density and diameter in humans. OCT speckle decorrelation images of the skin on the ventral side of the forearm up to a depth of 500 µm were obtained prior to and following 20-25 min of lower limb heating in eight healthy men [30.3 ± 7.6 (SD) yr]. Skin red blood cell flux was also collected using laser Doppler flowmetry probes immediately adjacent to the OCT skin sites, along with skin temperature. OCT speckle decorrelation images were obtained at both baseline and heating time points. Forearm skin flux increased significantly (0.20 ± 0.15 to 1.75 ± 0.38 cutaneous vascular conductance, P < 0.01), along with forearm skin temperature (32.0 ± 1.2 to 34.3 ± 1.0°C, P < 0.01). Quantitative differences in the automated calculation of vascular area densities (26 ± 9 to 49 ± 19%, P < 0.01) and individual microvessel diameters (68 ± 17 to 105 ± 25 µm, P < 0.01) were evident following the heating session. This is the first in vivo within-subject assessment of acute changes in the cutaneous microvasculature in response to heating in humans and highlights the use of OCT as an exciting new imaging approach for skin physiology and clinical research.

Regional assessment of LV wall in infarcted heart using tagged MRI and cardiac modelling.

A segmental two-parameter empirical deformable model is proposed for evaluating regional motion abnormality of the left ventricle. Short-axis tagged MRI scans were acquired from 10 healthy subjects and 10 postinfarct patients. Two motion parameters, contraction and rotation, were quantified for each cardiac segment by fitting the proposed model using a non-rigid registration algorithm. The accuracy in motion estimation was compared to a global model approach. Motion parameters extracted from patients were correlated to infarct transmurality assessed with delayed-contrast-enhanced MRI. The proposed segmental model allows markedly improved accuracy in regional motion analysis as compared to the global model for both subject groups (1.22-1.40 mm versus 2.31-2.55 mm error). By end-systole, all healthy segments experienced radial displacement by ~25-35% of the epicardial radius, whereas the 3 short-axis planes rotated differently (basal: 3.3°; mid: -1° and apical: -4.6°) to create a twisting motion. While systolic contraction showed clear correspondence to infarct transmurality, rotation was nonspecific to either infarct location or transmurality but could indicate the presence of functional abnormality. Regional contraction and rotation derived using this model could potentially aid in the assessment of severity of regional dysfunction of infarcted myocardium.

Imaging of skin birefringence for human scar assessment using polarization-sensitive optical coherence tomography aided by vascular masking.

We demonstrate the in vivo assessment of human scars by parametric imaging of birefringence using polarization-sensitive optical coherence tomography (PS-OCT). Such in vivo assessment is subject to artifacts in the detected birefringence caused by scattering from blood vessels. To reduce these artifacts, we preprocessed the PS-OCT data using a vascular masking technique. The birefringence of the remaining tissue regions was then automatically quantified. Results from the scars and contralateral or adjacent normal skin of 13 patients show a correspondence of birefringence with scar type: the ratio of birefringence of hypertrophic scars to corresponding normal skin is 2.2 ± 0.2 (mean ± standard deviation ), while the ratio of birefringence of normotrophic scars to normal skin is 1.1 ± 0.4 . This method represents a new clinically applicable means for objective, quantitative human scar assessment.

Assessment of human burn scars with optical coherence tomography by imaging the attenuation coefficient of tissue after vascular masking.

The formation of burn-scar tissue in human skin profoundly alters, among other things, the structure of the dermis. We present a method to characterize dermal scar tissue by the measurement of the near-infrared attenuation coefficient using optical coherence tomography (OCT). To generate accurate en face parametric images of attenuation, we found it critical to first identify (using speckle decorrelation) and mask the tissue vasculature from the three-dimensional OCT data. The resulting attenuation coefficients in the vasculature-masked regions of the dermis of human burn-scar patients are lower in hypertrophic (3.8±0.4 mm(-1)) and normotrophic (4.2±0.9 mm(-1)) scars than in contralateral or adjacent normal skin (6.3±0.5 mm(-1)). Our results suggest that the attenuation coefficient of vasculature-masked tissue could be used as an objective means to assess human burn scars.

Quantitative assessment of muscle damage in the mdx mouse model of Duchenne muscular dystrophy using polarization-sensitive optical coherence tomography.

Minimally invasive, high-resolution imaging of muscle necrosis has the potential to aid in the assessment of diseases such as Duchenne muscular dystrophy. Undamaged muscle tissue possesses high levels of optical birefringence due to its anisotropic ultrastructure, and this birefringence decreases when the tissue undergoes necrosis. In this study, we present a novel technique to image muscle necrosis using polarization-sensitive optical coherence tomography (PS-OCT). From PS-OCT scans, our technique is able to quantify the birefringence in muscle tissue, generating an image indicative of the tissue ultrastructure, with areas of abnormally low birefringence indicating necrosis. The technique is demonstrated on excised skeletal muscles from exercised dystrophic mdx mice and control C57BL/10ScSn mice with the resulting images validated against colocated histological sections. The technique additionally gives a measure of the proportion (volume fraction) of necrotic tissue within the three-dimensional imaging field of view. The percentage necrosis assessed by this technique is compared against the percentage necrosis obtained from manual assessment of histological sections, and the difference between the two methods is found to be comparable to the interobserver variability of the histological assessment. This is the first published demonstration of PS-OCT to provide automated assessment of muscle necrosis.

In vivo assessment of human burn scars through automated quantification of vascularity using optical coherence tomography.

In scars arising from burns, objective assessment of vascularity is important in the early identification of pathological scarring, and in the assessment of progression and treatment response. We demonstrate the first clinical assessment and automated quantification of vascularity in cutaneous burn scars of human patients in vivo that uses optical coherence tomography (OCT). Scar microvasculature was delineated in three-dimensional OCT images using speckle decorrelation. The diameter and area density of blood vessels were automatically quantified. A substantial increase was observed in the measured density of vasculature in hypertrophic scar tissues (38%) when compared against normal, unscarred skin (22%). A proliferation of larger vessels (diameter≥100 µm) was revealed in hypertrophic scarring, which was absent from normal scars and normal skin over the investigated physical depth range of 600 µm. This study establishes the feasibility of this methodology as a means of clinical monitoring of scar progression.

Ultrasound-guided optical coherence tomography needle probe for the assessment of breast cancer tumor margins.

OBJECTIVE: The purpose of this study was to evaluate a new imaging technique for the assessment of breast cancer tumor margins. The technique entails deployment of a high-resolution optical imaging needle under ultrasound guidance. Assessment was performed on fresh ex vivo tissue samples. CONCLUSION: Use of the ultrasound-guided optical needle probe allowed in situ assessment of fresh tissue margins. The imaging findings corresponded to the histologic findings.