The role of near-infrared spectroscopy in Alzheimer's disease

Near-infrared spectroscopy (NIRS) is a noninvasive neuroimaging tool used to measure activation-induced changes in cerebral hemoglobin concentration. By this technique, changes in the optical absorption of light are recorded over time and are used to estimate the functionally evoked changes in cerebral oxyhemoglobin and deoxyhemoglobin concentrations that result from local cerebral vascular and oxygen metabolic effects during brain activities. Over the past decades, it has become a frequently used technique in psychiatry studies such as depression, schizophrenia, and Alzheimer's disease. Compared to positron emission tomography or magnetic resonance imaging, NIRS has the advantages of having higher temporal resolution, being easier to perform, and the ability to use portable equipment. Because of its growing popularity and promising perspectives in clinical applications, we review Alzheimer's disease-related studies using NIRS methodology in this article. The existing evidence shows that NIRS might have the potential to become either a disease- or syndrome-specific diagnostic tool in the future. However, larger studies with more study participants are needed to establish disease-specific sensitivity and specificity.