Bernhard J. Schattka

Multimodal nonlinear optical imaging of atherosclerotic plaque development in myocardial infarction-prone rabbits.

Label-free imaging of bulk arterial tissue is demonstrated using a multimodal nonlinear optical microscope based on a photonic crystal fiber and a single femtosecond oscillator operating at 800 nm. Colocalized imaging of extracellular elastin fibers, fibrillar collagen, and lipid-rich structures within aortic tissue obtained from atherosclerosis-prone myocardial infarction-prone Watanabe heritable hyperlipidemic (WHHLMI) rabbits is demonstrated through two-photon excited fluorescence, second harmonic generation, and coherent anti-Stokes Raman scattering, respectively. These images are shown to differentiate healthy arterial wall, early atherosclerotic lesions, and advanced plaques. Clear pathological changes are observed in the extracellular matrix of the arterial wall and correlated with progression of atherosclerotic disease as represented by the age of the WHHLMI rabbits.

Spectroscopic assessment of cutaneous hemodynamics in the presence of high epidermal melanin concentration

BACKGROUND For individuals with lightly pigmented skin, early stage pressure ulcers appear as areas of redness, which have compromised microcirculation and do not blanch in response to pressure. The lack of a visible blanch (hemodynamic response) to pressure is a convenient diagnostic test for stage I sores. However, the blanch response is not visually apparent in people with highly pigmented skin color due to the overwhelming contribution of melanin to the reflectance of skin. METHODS A simple least squares projection operator method is described, which can separate the reflectance contributions from melanin and hemoglobin. The methodology was tested in a study population of 20 subjects with healthy skin. The study population was evenly divided into a lightly pigmented skin group (visible blanch response) and a highly pigmented skin group (no visible blanch response). RESULTS The hemodynamic response to pressure being applied to the skin could clearly be distinguished spectroscopically in both groups at a high level of statistical significance. CONCLUSION The specific aim of this work was directed towards developing a spectroscopic basis for distinguishing the healthy blanch response in a manner that was independent of skin pigmentation. However, the technique has a general application when optical hemodynamic measurements are being made over a diverse patient population or under conditions of varying pigmentation such as the seasonal changes in skin color.

Skin hydration by spectroscopic imaging using multiple near-infrared bands

Near-infrared spectroscopic methods have been developed to determine the degree of hydration of human skin in vivo. Reflectance spectroscopic imaging was used to investigate the distribution of skin moisture as a function of location. A human study in a clinical setting has generated quantitative data showing the effects of a drying agent and a moisturizer on delineated regions of the forearms of eight volunteers. Two digital imaging systems equipped with liquid-crystal tunable filters were used to collect stacks of monochromatic images at 10-nm intervals over the wavelength bands 650-1050 nm and 960-1700 nm. Images generated from measurements of water absorption-band areas at three different near-IR wavelengths (970, 1200, and 1450 nm) showed obvious differences in the apparent distribution of water in skin. Changes resulting from the skin treatments were much more evident in the 1200-nm and 1450-nm images than in the 970-nm ones. The variable sensitivity of the method at different wavelengths has been interpreted as being the result of different penetration depths of the infrared light used in the reflectance studies. Ex-vivo experiments with pigskin have provided evidence supporting the relationship between wavelength and penetration depth. Combining the hydration results from several near-IR water bands allows additional information on hydration depth to be obtained.

The Utility of near Infrared Imaging in Intra-Operative Prediction of Flap Outcome: A Reverse McFarlane Skin Flap Model Study

Skin flaps are complex procedures used extensively in reconstructive surgery that require post-operative monitoring to ensure that they do not fail. Near infrared (NIR) spectroscopic imaging is a convenient, non-invasive method for surgeons to examine flaps during surgery and in the early post-operative period. Using a reverse McFarlane skin flap model, we show that model-free chemometric methods as well as simple modified Beer-Lambert analysis of the NIR images provide insights into the blood supply to flaps and demonstrate that the technique can detect and localise perfusion-related complications as well as give real-time feedback to the surgeon as they try to resolve the complication. We also show that using estimates of tissue haemoglobin oxygen saturation, imaging measurements made during surgery and in the early post-operative period are highly predictive of the outcome of the flap tissue with specificities and sensitivities exceeding 85%.

Propagation properties of 1300-nm light in blood-saline mixtures determined through optical coherence tomography

Establishing when the amount of recorded multiple scattered signal becomes dominant is important for various clinical applications that require optical coherence tomography imaging through a turbid environment such as blood. The profiles of detected signals obtained by compounding coherence tomography images of flowing blood-saline mixtures with various blood concentrations are analyzed. The scattering properties of the studied mixtures influence the corresponding profiles of the recorded signal. Monte Carlo simulations of light propagation through environments with various scattering coefficients are used to support and to explain the experimental data.

Evaluating the health of compromised tissues using a near-infrared spectroscopic imaging system in clinical settings: lessons learned

The present and accepted standard for determining the status of tissue relies on visual inspection of the tissue. Based on the surface appearance of the tissue, medical personnel will make an assessment of the tissue and proceed to a course of action or treatment. Visual inspection of tissue is central to many areas of clinical medicine, and remains a cornerstone of dermatology, reconstructive plastic surgery, and in the management of chronic wounds, and burn injuries. Near infrared spectroscopic imaging holds the promise of being able to monitor the dynamics of tissue physiology in real-time and detect pathology in living tissue. The continuous measurement of metabolic, physiological, or structural changes in tissue is of primary concern in many clinical and biomedical domains. A near infrared hyperspectral imaging system was constructed for the assessment of burn injuries and skin flaps or skin grafts. This device merged basic science with engineering and integrated manufacturing to develop a device suitable to detect ischemic tissue. This device has the potential of providing measures of tissue physiology, oxygen delivery and tissue hydration during patient screening, in the operating room or during therapy and post-operative/treatment monitoring. Results from a pre-clinical burn injury study will be presented.

Skin hydration imaging using a long-wavelength near-infrared digital camera

Skin hydration is a key factor in skin health. Hydration measurements can provide diagnostic information on the condition of skin and can indicate the integrity of the skin barrier function. Near-infrared spectroscopy measures the water content of living tissue by its effect on tissue reflectance at a particular wavelength. Imaging has the important advantage of showing the degree of hydration as a function of location. Short-wavelength (650-1050 nm) near infrared spectroscopic reflectance imaging has previously been used in-vivo to determine the relative water content of skin under carefully controlled laboratory conditions. We have recently developed a novel spectroscopic imaging system to acquire image sets in the long-wavelength region of the near infrared (960 to 1700 nm), where the water absorption bands are more intense. The LW-NIR systems uses a liquid- crystal tunable filter in front of the objective lens and incorporates a 12-bit digital camera with a 320-by-240-pixel indium-gallium arsenide array sensor. Custom software controls the camera and tunable filter, allowing image sets to be acquired and displayed in near-real time. Forearm skin hydration was measured in a clinical context using the long- wavelength imaging system, a short-wavelength imaging system, and non-imaging instrumentation. Among these, the LW-NIR system appears to be the most sensitive at measuring dehydration of skin.

Applications of visible near-infrared spectroscopy and imaging in burn injury assessment

The major objective of the project is to develop a noninvasive method to assess thermal burns. Currently, the diagnosis relies primarily upon visual assessment of the injury by a burn specialist and/or plastic surgeon. The diagnosis is based on the surface appearance of the wound to determine the type or depth of the burn. Near IR spectroscopic measurements of injured tissue provide an objective means of distinguishing between surface and subsurface changes related to the tissue injury. An acute porcine model is employed to investigate the potential of near IR spectroscopy to accurately distinguish between burns of varying severity in the early postburn period. Parallel factor analysis is used to investigate the spectral changes related to burns of varying severity. Burn injuries drastically alter the physical and optical properties of the tissue. Thermal destruction of cutaneous vasculature disrupts perfusion and oxygen delivery to the affected tissue. Tissue blood oxygenation decreases with increased severity of the burn. The result demonstrate that near IR spectroscopy may provide a new tool for objective clinical assessment of burn injuries.

Near-infrared spectroscopic approach to assess tissue viability following a thermal injury

A recurrent problem in the assessment of thermal injuries is the ability to accurately identify the depth and extent of injury. Generally, the depth of a burn injury determines and is inversely related to the ability of the skin to restore and regenerate itself. Burns involve damage to the dermis in varying amounts, reducing the dermal blood supply and altering the skin hemodynamics. Near infrared spectroscopic imaging was used to non-invasively assess the changes that occur in the early (1-3 h) post-burn period. The study used an accurate porcine model to investigate the potential of near infrared spectroscopic imaging to accurately distinguish between burns of varying severity. Data analysis was carried out using a two-way and three-way data decompositions techniques to investigate the spectral changes related to burns. Burn injuries drastically alter the physical and optical properties of the tissue. Thermal destruction of cutaneous vasculature disrupts perfusion and oxygen delivery to the affected tissue. The results demonstrated that near infrared spectroscopic imaging might provide a new tool for an objective clinical assessment of burn injuries.