Near-infrared Spectroscopy: Neonatal and Perinatal Applications

Abstract

After completing this article, readers should be able to: 1. Delineate the clinical benefits of near-infrared spectroscopy. 2. Describe the primary clinical applications of near-infrared spectroscopy. ### Development of Light-based Diagnostic Systems Transillumination, or the passage of light through the body, has been studied since the early 1800s. Attempts to image organs and tissues for the purpose of diagnosis and treatment have developed to the point that light-based monitoring in the form of pulse oximetry is used daily in hospitals and clinics. Transillumination of the head, first described in 1831 by Richard Bright, eventually would be recognized as the first light-based diagnostic technique to identify hydrocephalus. With modification, although still crude, it was used to diagnose intracranial hemorrhage in the neonate at a time before head ultrasonography was available and when computed tomography (CT) was extremely expensive and not widely available. In early devices, light in the visible part of the spectrum was employed; more recently, light over a narrower band of wavelengths has been used. In 1977, Jobsis showed that tissue absorption of near-infrared light at a wavelength of 700 to 1,000 nm was low enough to allow spectral measurements across the head of an animal with a diameter of 5 to 6 cm. The absorption of near-infrared light by particular pigments in the body changes as the oxygenation state of these pigments change. Thus, deoxyhemoglobin (Hb) absorbs light differently after it has bound oxygen and becomes oxyhemoglobin (HbO2). Cytochrome aa3, the terminal enzyme in the mitochondrial electron transport chain, also can be detected using near-infrared spectroscopy (NIRS). Measurement of cytochrome aa3 may allow assessment of oxygenation at the cellular level, with changes in oxidized and reduced cytochrome aa3 concentrations (redox state) indicating changes in molecular oxygen availability. The relative absorbances for HbO2 and Hb are unique at each wavelength (Fig. …