The gas phase vibrational overtone spectrum of propane is measured using conventional near infrared (NIR) spectroscopy for the ΔvCH=2–5 regions and intracavity dye laser photoacoustic spectroscopy (IDL-PAS) for the ΔvCH=5 and 6 regions. The peaks are assigned in terms of the local mode model. Experimental oscillator strengths are compared to values calculated for the CH-stretching components of the spectrum. The calculations use a harmonically coupled, anharmonic oscillator local mode model to obtain the vibrational wave functions, and ab initio MO calculations at the SCF level with a 6-31G* basis set to obtain the dipole moment function. The importance of intermanifold coupling is explored. The calculations can account for the fall-off in intensity with increasing v, and can give a reasonably quantitative account of the relative intensities of the individual peaks within a given vibrational manifold. The questions of the relative intensities of primary and secondary CH bonds, and of the relative intensities of different methyl CH bonds are also explored.

The diagnosis of burn depth is based on a visual assessment and can be subjective. Near-infrared (NIR) spectroscopic devices were used preclinically with positive results. The purpose of this study was to test the devices in a clinical setting using easily identifiable burn wounds. Adult patients with acute superficial and full-thickness burns were enrolled. NIR point spectroscopy and imaging devices were used to collect hemodynamic data from the burn site and an adjacent unburned control site. Oxy-hemoglobin and deoxy-hemoglobin concentrations were extracted from spectroscopic data and reported as oxygen saturation and total hemoglobin. Sixteen patients (n=16) were included in the study with equal numbers in both burn wound groups. Point spectroscopy data showed an increase in oxygen saturation (p<0.0095) and total hemoglobin (<0.0001) in comparison with the respective control areas for superficial burn wounds. The opposite was true for full-thickness burns, which showed a decrease in oxygenation (p<0.0001) and total hemoglobin (p<0.0147) in comparison with control areas. NIR imaging technology provides an estimate of hemodynamic parameters and could easily distinguish superficial and full-thickness burn wounds. These results confirm that NIR devices can successfully distinguish superficial and full-thickness burn injuries.

Abstract. 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 ͑WHHLMI͒ 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. Atherosclerosis is the primary cause of heart disease, stroke, and lower limb amputation worldwide. It is a progressive disease characterized by chronic inflammation of injured intima and is associated with fatty plaque deposits in the arteries.1,2 Early atherosclerosis cannot be reliably detected by current clinical methods, therefore the disease is often overlooked until at a more advanced stage. The development of new tools that provide greater sensitivity and specificity for early detection and differentiation of atherosclerotic plaques would help our understanding of early disease and help establish preventative regimens that would slow disease progression.Recently, nonlinear optical ͑NLO͒ microscopy has emerged as a powerful tool for tissue imaging. It is a labelfree method with high sensitivity and specificity for major extracellular molecules. Its optical sectioning capability presents a means of 3-D in vivo imaging that would be useful in the context of atherosclerosis diagnostics. Several studies have demonstrated imaging of arterial tissue using NLO microscopy, [3][4][5][6] including studies imaging atherosclerotic lesions using a multimodal coherent anti-Stokes Raman Scattering ͑CARS͒ microscope based on two tightly synchronized Ti:sapphire lasers and a swine animal model. 6,7 In our study, we demonstrate label-free visualization of the extracellular matrix of arterial lumen and atherosclerotic plaques using a photonic crystal fiber ͑PCF͒-based multimodal NLO microscope employing only a single femtosecond oscillator. Twophoton excited autofluorescence ͑TPEF͒ is able to specifically image extracellular elastin fibers, second harmonic generation ͑SHG͒, type-1 collagen fibrils, and CARS lipid-rich structure or extracellular lipids droplets in unstained bulk intact tissue, indicating the methods are particularly suited to understanding the role and interplay between these key extracellular molecules involved in plaque development.PCF-based CARS was recently reported as an alternative CARS imaging method in biology. 8,9 Because it only requires a single femtosecond laser, PCF-based CARS can be easily integrated into existing...

A femtosecond CARS-based nonlinear optical microscope was used to simultaneously image extracellular structural proteins and lipid-rich structures within intact aortic tissue obtained from myocardial infarction-prone Watanabe heritable hyperlipidemic rabbits (WHHLMI). Clear differences in the NLO microscopic images were observed between healthy arterial tissue and regions dominated by atherosclerotic lesions. In the current ex-vivo study, we present a single parameter based on intensity changes derived from multi-channel NLO image to classify plaque burden within the vessel. Using this parameter we were able to differentiate between healthy regions of the vessel and regions with plaque, as well as distinguish plaques relative to the age of the WHHLMI rabbit.

Near-IR spectroscopic methods have been developed to determine the degree of hydration of human skin in vivo. Noncontact 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 650-1050 and 960-1700 nm wavelength bands. Synthetic 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 the skin. Changes resulting from the skin treatments were much more evident in the long-wavelength images than in the short-wavelength ones. The variable sensitivity of the method at different wavelengths has been interpreted as being the result of different penetration depths of the IR light used in the reflectance studies.

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Infrared (IR) spectroscopy has previously been established as a means to accurately quantify several serum and urine metabolites, based upon spectroscopy of dry films. The same technique has also provided the basis to develop certain diagnostic tests, developed in the 'metabolomics' spirit. Here, we report on the further development of an integrated microfluidic-IR technology and technique, customized with the aim of dramatically extending the capabilities of IR spectroscopy in both analytical and diagnostic (metabolomic) applications. By exploiting the laminar fluid diffusion interface (LFDI), serum specimens are processed to yield product streams that are better suited for metabolic fingerprinting; metabolites are captured within the aqueous product stream, while proteins (which otherwise dominate the spectra of films dried from serum) are present in much reduced concentration. Spectroscopy of films dried from the aqueous stream then provides enhanced diagnostic and analytical sensitivity. The manuscript introduces an LFDI card design that is customized for integration with IR spectroscopy, and details the development of a quantitative assay for serum creatinine--based upon LFDI-processed serum samples--that is substantially more accurate (standard error of calibration, SEC = 43 micromol/L) than the corresponding assay based upon unprocessed serum specimens (SEC = 138 micromol/L). Preliminary results of diffusion modeling are reported, and the prospects for further optimization of the technique, guided by accurate modeling, are discussed.

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