We characterize a visible reflectance hyperspectral imaging system for noninvasive, in vivo, quantitative analysis of human tissue in a clinical environment. The subject area is illuminated with a quartz-tungsten-halogen light source, and the reflected light is spectrally discriminated by a liquid crystal tunable filter (LCTF) and imaged onto a silicon charge-coupled device detector. The LCTF is continuously tunable within its useful visible spectral range (525-725 nm) with an average spectral full width at half-height bandwidth of 0.38 nm and an average transmittance of 10.0%. A standard resolution target placed 5.5 ft from the system results in a field of view with a 17-cm diameter and an optimal spatial resolution of 0.45 mm. The measured reflectance spectra are quantified in terms of apparent absorbance and formatted as a hyperspectral image cube. As a clinical example, we examine a model of vascular dysfunction involving both ischemia and reactive hyperemia during tissue reperfusion. In this model, spectral images, based upon oxyhemoglobin and deoxyhemoblobin signals in the 525-645-nm region, are deconvoluted using a multivariate least-squares regression analysis to visualize the spatial distribution of the percentages of oxyhemoglobin and deoxyhemoglobin in specific skin tissue areas.

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We developed and characterized a new imaging platform for minimally invasive surgical venues, specifically a system to help guide laparoscopic surgeons to visualize biliary anatomy. This platform is a novel combination of a near-infrared hyperspectral imaging system coupled with a conventional surgical laparoscope. Intraoperative tissues are illuminated by optical fibers arranged in a ring around a center-mounted relay lens collecting back-reflected light from tissues to the hyperspectral imaging system. The system consists of a focal plane array (FPA) and a liquid crystal tunable filter, which is continuously tunable in the near-infrared spectral range of 650-1100 nm with the capability of passing light with a mean bandwidth of 6.95 nm, and the FPA is a high-sensitivity back-illuminated, deep depleted charge-coupled device. Placing a standard resolution target 5.1 cm from the distal end of the laparoscope, a typical intraoperative working distance, produced a 7.6-cm-diameter field of view with an optimal spatial resolution of 0.24 mm. In addition, the system's spatial and spectral resolution and its wavelength tuning accuracy are characterized. The spectroscopic images are formatted into a three-dimensional hyperspectral image cube and processed using principle component analysis. The processed images provide contrast based on measured spectra associated with chemically different anatomical structures helping identify the main molecular chromophores inherent to each tissue. The principal component images were found to image swine gallbladder and biliary structures from surrounding tissues, in real time, during cholecystectomy surgery. Furthermore, it is shown that surgeons can interrogate selected image subregions for their molecular composition identifying biliary anatomy during surgery and before any invasive action is undertaken.

Background-Vascular disease is commonly associated with reduced local synthesis of nitric oxide (NO) and impaired tissue perfusion. We introduce a novel noninvasive, visible-reflectance, hyperspectral imaging technique for quantifying the percentage of hemoglobin existing as oxyhemoglobin (HbO 2 ) as an index of skin tissue perfusion. Methods and Results-To simulate vascular endothelial dysfunction, N G -monomethyl-L-arginine (L-NMMA) was infused into the brachial arteries of 9 healthy subjects for 5 minutes to inhibit forearm NO synthesis, first with the subject breathing room air and subsequently during NO inhalation at 80 ppm for 1 hour. Blood flow was measured by venous occlusion plethysmography, and the percentage of HbO 2 perfusing skin tissue was imaged noninvasively with a visible-reflectance hyperspectral technique. L-NMMA reduced blood flow by 31.7Ϯ4.9% and percentage of HbO 2 by 6.5Ϯ0.1 (Pϭ0.002 and PϽ0.001 versus baseline, respectively). With subjects inhaling NO, blood flow fell during L-NMMA infusion by only 10.9Ϯ7.3%, and the percentage of HbO 2 decreased by 3.6Ϯ0.1 (Pϭ0.007 and PϽ0.001, respectively, versus room air L-NMMA responses). Conclusions-Visible-reflectance hyperspectral imaging demonstrates (1) a significant decline in the percentage of HbO 2 in skin tissue when blood flow is reduced after inhibition of forearm NO synthesis and (2) Key Words: peripheral vascular disease Ⅲ blood flow Ⅲ nitric oxide Ⅲ hemoglobin Ⅲ imaging M ore than 10 million Americans have diabetes mellitus, an important risk factor for cardiovascular disease. 1,2 In view of the morbidity and mortality associated with this condition, methods of early detection of vascular disease are needed to initiate appropriate treatment that might lead to an increased life expectancy and enhanced quality of life. Vascular endothelial dysfunction is common in type I and type II diabetes 3,4 and may result in vasoconstriction because of loss of endogenous synthesis of the vasodilating molecule nitric oxide (NO). 5 This, in turn, may compromise blood flow to the extremities of patients with diabetes and other diseases associated with vascular dysfunction, resulting in reduced tissue oxygenation and potentially leading to ulceration, infection, and loss of limb. An impediment to the appropriate clinical management of patients with peripheral arterial disease is the inability to monitor tissue perfusion noninvasively over time. We introduce a novel, noninvasive, visiblereflectance, hyperspectral imaging technique for assessing vascular endothelial dysfunction and its associated reduction in tissue hemoglobin oxygen saturation.Hemoglobin oxygen saturation may be measured by oximeters, although these devices are somewhat limited in usage. For example, a 2-wavelength transmission device restricts measurements to a single point, by which light is passed through either the finger or earlobe. 6 For application to other parts of the body (as, for example, the chest, forehead, or limbs), a transcutaneous reflectance oximeter was developed and f...