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Report of the National Institute of Neurological Disorders and Stroke workshop on near infrared spectroscopy.

A workshop about near infrared spectroscopy (NIRS), an emerging technology used to measure cerebral oxygenation and blood flow, was sponsored by the Developmental Neurology Branch, Division of Convulsive, Developmental, and Neuromuscular Disorders of the National Institute of Neurological Disorders and Stroke in Bethesda, MD, on March 31 and April 1, 1992. This was an international work-shop designed to bring together experts in the development of this technology with clinical researchers. Topics covered included the history and background of the development of NIRS technology, experimental models for the use of NIRS, clinical experience with NIRS in the neonate and the intrapartum fetus, and current key research issues with regard to technology and clinical use.
 THE TECHNOLOGY
 Near infrared spectroscopy is a new application of an existing technology which can provide information about changes in cerebral oxygen saturation, cerebral blood flow and volume, and oxygen utilization in the brain. The technology has been used for a long time to monitor hemoglobin, but only more recently for cytochrome oxidase. It involves the same basic principle used in the pulse oximeter, which uses light in the visible range to detect changes in finger arterial oxygen saturation. The method is based on the fact that light in the near infrared range (700 to 1000 nm) can pass through skin, bone, and other tissues relatively easily and that there are characteristic absorption bands of oxygenated and deoxygenated hemoglobin, and of the mitochondrial enzyme cytochrome oxidase (or cytochrome AA3) in the near infrared range.
 When the near infrared beam is passed through tissue, a decrease in signal intensity results from the absorbance of the chromophores in the medium.