Advances in Functional Near‐Infrared Spectroscopy: Physical Principles and Expanding Applications in Neuroscience

ABSTRACT Functional near‐infrared spectroscopy (fNIRS) is an imaging technique that uses near‐infrared light to monitor blood oxygen level changes in the cerebral cortex and noninvasively study brain function. This review provides an overview of the expanding applications and physical principles of fNIRS to enhance understanding of its imaging process and promote awareness of its broad applicability and potential. We systematically searched PubMed, Web of Science, and Google Scholar, analyzing studies on fNIRS applications in psychiatry, neurology, education, and multimodal imaging. We also introduce the imaging principles of continuous wave fNIRS, frequency domain fNIRS, time domain fNIRS, and diffuse optical tomography fNIRS (including high‐density diffuse optical tomography). These studies have demonstrated the potential of fNIRS technology in measuring cerebral hemodynamics with high temporal and spatial resolution. The results of this review indicate that fNIRS is a versatile neuroimaging tool with great potential in research and clinical applications.