Elicia Kohlenberg

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.

Assessment of Local Hemodynamics in Periodontal Inflammation Using Optical Spectroscopy

BACKGROUND Among the newly emerging diagnostic approaches for periodontitis, optical spectroscopy is a promising complementary diagnostic tool. The objective of this study is to verify the reproducibility of this method at a geographically distinct location (Suzhou, China) to a broader patient population using similar instrumentation to that in a previous report. METHODS Using a portable optical near-infrared spectrometer, optical spectra were obtained, processed, and evaluated from healthy (n = 62), gingivitis (n = 98), and periodontitis (n = 47) sites from a total of 51 patients. A modified Beer-Lambert unmixing model that incorporates a non-parametric scattering loss function was used to determine the relative contribution of oxyhemoglobin and deoxyhemoglobin to the overall spectrum. The balance between tissue oxygen delivery and oxygen use in periodontal tissues was then assessed. RESULTS Tissue oxygenation decreased significantly from healthy sites to sites with gingivitis (P <0.01) and between gingivitis and periodontitis (P = 0.015). This is largely caused by a significant increase in deoxyhemoglobin between normal and gingivitis (P <0.01) and a concomitant decrease in oxyhemoglobin between gingivitis and periodontitis (P = 0.02). CONCLUSION This study supports previous findings that tissue oxygenation as measured by optical spectroscopy is significantly decreased in periodontitis and that optical spectroscopy can simultaneously determine multiple inflammatory indices related to periodontal disease directly in gingival tissues in vivo.

Detecting intestinal ischemia using near infrared spectroscopy

Blood supply to the intestine can suddenly be interrupted. Acute mesenteric intestinal ischemia often requires invasive surgery to restore blood supply to the intestine. Early correction of vascular insufficiency is the most important factor in improving patient survival when confronted with acute mesenteric intestinal ischemia. A prolonged loss of blood flow results in irreversible damage to the intestine that can lead to death. It is also imperative that dead segments of the intestines be removed. Several subjective criteria are relied upon to differentiate viable from non-viable tissue, unfortunately, these criteria can lead to an inaccurate assessment. A porcine model of intestinal ischemia was used to determine the efficacy of using near infrared (NIR) spectroscopy to find ischemic segments of the intestine and detect the onset of reperfusion following resolution of vascular occlusion. Nine segments of intestine were identified and six were assigned to three treatment groups; (1) segments undergoing no vascular manipulations, (2) segments undergoing arterial/venous occlusion and (3) segments undergoing arterial/venous occlusion followed by reperfusion. The remaining segments were used as spacers and interposed between each of the ischemia segments. A classification model, using partial least square discriminant analysis, was built on the spectra collected from the segments with no vascular manipulations and the segments that were solely subjected to arterial/venous occlusion. The spectra collected from the intestinal segments that experienced both occlusion and reperfusion were used to test the classification model. The model was able to detect and distinguish ischemic intestinal tissue with a specificity and sensitivity exceeding 80% with an overall classification accuracy of 89%. The method appears to be well suited as an intra-operative assessment method when intestinal ischemia is a concern.

Label-free imaging of arterial tissues using photonic crystal fiber (PCF) based nonlinear optical microscopic system

Nonlinear optical (NLO) microscopy provides a minimally invasive optical method for fast molecular imaging at subcellular resolution with 3D sectioning capability in thick, highly scattering biological tissues. In the current study, we demonstrate the imaging of arterial tissue using a nonlinear optical microscope based on photonic crystal fiber and a single femto-second oscillator operating at 800nm. This NLO microscope system is capable of simultaneous imaging extracellular elastin/collagen structures and lipid distribution within aortic tissue obtained from coronary atherosclerosis-prone WHHLMI rabbits (Watanabe heritable hyperlipidemic rabbit-myocardial infarction) Clear pathological differences in arterial lumen surface were observed between healthy arterial tissue and atherosclerotic lesions through NLO imaging.

Near infrared hyperspectral imaging: the road traveled to a clinical burn application

The process of taking a concept to a clinical device begins with the idea for a technological solution to an unmet clinical challenge. Burns are one of the most destructive insults to the skin causing damage, scarring, and in some cases death. The approach most commonly used to evaluate burns is based on the appearance of the wound. This technique is somewhat subjective and unreliable, relying on clinical experience to assess the burn. Instrument based diagnostic techniques as an adjunct to current practices has the potential to enhance the quality and timeliness of decisions concerning wound assessment and treatment. Near Infrared Spectroscopy is a promising technique that can track changes within the tissue, and can therefore provide insight as to how deep the burn actually penetrates before visual signs become apparent. Preliminary bench and animal studies were used to prove the concept of a near infrared based method of burn assessment. This study demonstrated the ability of near infrared imaging to detect and monitor the hemodynamics of burn injuries in the early post-burn period. Based on this study, a pre-prototype near infrared spectroscopic system was built with the goal of developing a reliable yet simple system that could be used in a clinical setting. A pilot clinical study was designed and implemented at the Ross Tilley Burn Center (Toronto, Canada) in order to assess the feasibility of our strategy in the clinical realm. The goal of this preliminary clinical study was to determine if the pre-prototype could be integrated into the strict regiment of an active burn centre. Both the instrument performance in a clinical setting and the injury assessment based on the analysis of near infrared reflectance measurements were a success.

Atherosclerosis diagnostic imaging by optical spectroscopy and optical coherence tomography

Atherosclerosis is traditionally viewed as a disease of uncontrolled plaque growth leading to arterial occlusion. More recently, however, occlusion of the arterial lumen is being viewed as an acute event triggered by plaque rupture and thrombosis. An atheromatous plaque becomes vulnerable to sudden activation and/or rupture when a constellation of processes are activated by various trigger mechanisms. There is growing evidence that the vulnerability (i.e. susceptibility to rupture) and thrombogenic nature of the plaque need to be taken into account in the planning and treatment of the disease. X-ray fluoroscopy and intravascular ultrasound, the current clinical diagnostic tools are not capable of the providing a complete histological picture of the plaque region. Intravascular diagnostic imaging of coronary atherosclerotic plaques by optical means to assess plaque, patient risk and assist in planning treatment strategies represents the future in angioplasty treatment by interventional cardiologists. The techniques which will enable a clinically acceptable and reliable intravascular diagnostic platform are currently being investigated and compared to the clinical standard of histology. Currently, we are investigating the use of a number of optical and imaging techniques for biochemical analysis of arterial tissue including Raman, near infrared and fluorescence spectroscopies. Biochemical imaging will provide compositional information on collagen, elastin, lipid and thrombogenic by-products as well as gauging inflammation and tissue remodeling activity levels. To complement the functional biochemical imaging, optical coherence tomography will be provide structural morphological imaging. The synergistic combination of functional and structural imagery will provide the interventional cardiologist with a complete clinical picture of the atherosclerotic plaque region. The clinician can use this diagnostic information to plan a personalized treatment procedure based on the entire clinical presentation.

Spectroscopic detection of the blanch response at the heel of the foot: a possible diagnostic for stage I pressure ulcers

Pressure ulcers (sores) can occur when there is constant pressure being applied to tissue for extended periods of time. Immobile people are particularly prone to this problem. Ideally, pressure damage is detected at an early stage, pressure relief is applied and the pressure ulcer is averted. One of the hallmarks of pressure damaged skin is an obliterated blanch response due to compromised microcirculation near the surface of the skin. Visible reflectance spectroscopy can noninvasively probe the blood circulation of the upper layers of skin by measuring the electronic transitions arising from hemoglobin, the primary oxygen carrying protein in blood. A spectroscopic test was developed on a mixed population of 30 subjects to determine if the blanch response could be detected in healthy skin with high sensitivity and specificity regardless of the pigmentation of the skin. Our results suggest that a spectroscopic based blanch response test can accurately detect the blanching of healthy tissue and has the potential to be developed into a screening test for early stage I pressure ulcers.

Optical spectroscopic assessment of free flap circulatory impairment

Free flaps are used to reconstruct tissue damaged by injury. Circulatory impairment of the free flap is the leading cause of a failed flap surgery. This study demonstrates that optical spectroscopy can detect early signs of circulatory impairment and distinguish between arterial or venous blockage. An epigastric flap model is used to mimic conditions of both arterial and venous circulatory impairment. Animals were divided into three groups 1.) arterial occlusion (n=5), 2.) venous occlusion (n=4), and 3.) control (n=5). A classifier was applied to the reflectance data to determine whether there were consistent differences between the three study groups. The classifier was able to distinguish between arterial occlusion, venous occlusion and healthy flaps with a 95% accuracy. Measures of hemoglobin oxygen saturation and blood volume were derived from the same reflectance data. Oxygenation of the flap was significantly lower during venous or arterial occlusion compared to control flaps. Blood volume of the free flap went up significantly following venous blockage while blockage of the artery cause a significant drop in blood volume. Combining the predictions of the classifier and examining the oxygenation and blood volume parameters reliably detected circulatory impairment of the free flap.

Spectroscopic assessment of ischemic bowel

Optical reflectance spectroscopy and imaging was used to investigate regional intestinal hemodynamics in a porcine model of ischemic bowel. Sections of the small intestine were divided into control and A-V occulsion groups and monitored.