Published: August 15, 2011 r2011 American Chemical Society 7424 dx.doi.org/10.1021/ac201467v | Anal. Chem. 2011, 83, 7424–7430 ARTICLE pubs.acs.org/ac Active DLP Hyperspectral Illumination: A Noninvasive, in Vivo, System Characterization Visualizing Tissue Oxygenation at Near Video Rates Karel J. Zuzak,* ,†,‡,§ Robert P. Francis, ‡,^ Eleanor F. Wehner, ‡ Maritoni Litorja, z Jeffrey A. Cadeddu, † and Edward H. Livingston †,‡ † University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, Texas 75390, United States ‡ University of Texas at Arlington, 501 West First Street, Arlington, Texas 76019, United States § Digital Light Innovations, DLi, 4501 Spicewood Springs, Rd., Suite 1000, Austin, Texas 78759, United States ^ Raytheon Elcan Optical Technologies, 1601 N. Plano Road, Richardson, Texas 75081, United States z National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, United States b S Supporting Information O ptical methods have been aiding clinicians for centuries in detecting, diagnosing, and monitoring disease. For example, the field of microscopy is commonly used in pathology, while specialized surgical microscopes help surgeons perform delicate neurosurgery. Slit lamps and fundus cameras image the eye’s retina, and endoscopes can be inserted through the umbilicus, the navel, or through natural orifices such as the esophagus or rectum reducing the need for large surgical incisions. More recently, the fields of chemical physics, specifically spectroscopy, are being combined with remote satellite imaging technology for delivering an image in which each pixel measures chemical information from the tissue. 1,2 Initial systems integrated a spectrometer into the beam path of a microscope for collecting optical spectra and fluorescence information used for assessing tissue, for example, identifying cancerous cells based on their spectroscopy. 3À5 Interest for imaging vasculature changes per- fusing the skin of patients undergoing clinical and surgical procedures led to building a portable and robust system based on solid state electro-optics. The resulting Hyperspectral Ima- ging System, using visible light, correctly imaged a decrease in the percentage of oxyhemoglobin, HbO 2 , as a biomarker for visualiz- ing ischemic tissue, modeled by briefly restricting blood flow into a finger. 6 Subsequent clinical studies successfully imaged micro- vascular changes in the oxygenation of hemoglobin in response to nitric oxide inhibition, inhalation, and stimulation. 7,8 In addition to absorbing visible light, the metalloprotein hemoglobin also Received: June 13, 2011 Accepted: August 15, 2011 ABSTRACT: We report use of a novel hyperspectral imaging system utilizing digital light processing (DLP) technology to noninvasively visualize in vivo tissue oxygenation during surgi- cal procedures. The system’s novelty resides in its method of illuminating tissue with precisely predetermined continuous complex spectra. The Texas Instruments digital micromirror device, DMD, chip consisting of 768 by 1024 mirrors, each 16 μm square, can be switched between two positions at 12.5 kHz. Switching the appropriate mirrors controls the intensity of light illuminating the tissue as a function of wavelength, active spectral illumination. Meaning, the tissue can be illuminated with a different spectrum of light within 80 μs. Precisely, predetermined spectral illumination penetrates into patient tissue, its chemical composition augments the spectral properties of the light, and its reflected spectra are detected and digitized at each pixel detector of a silicon charge-coupled device, CCD. Using complex spectral illumination, digital signal processing and chemometric methods produce chemically relevant images at near video rates. Specific to this work, tissue is illuminated spectrally with light spanning the visible electromagnetic spectrum (380 to 780 nm). Spectrophotometric images are detected and processed visualizing the percentage of oxyhemoglobin at each pixel detector and presented continuously, in real time, at 3 images per second. As a proof of principle application, kidneys of four live anesthetized pigs were imaged before, during, and after renal vascular occlusion. DLP Hyperspectral Imaging with active spectral illumination detected a 64.73 ( 1.5% drop in the oxygenation of hemoglobin within 30 s of renal arterial occlusion. Producing chemically encoded images at near video rate, time-resolved hyperspectral imaging facilitates monitoring renal blood flow during animal surgery and holds considerable promise for doing the same during human surgical interventions.