A Narrative Review on Clinical Applications of fNIRS

Abstract

Functional near-infrared spectroscopy (fNIRS) is a relatively new imaging modality in the functional neuroimaging research arena. The fNIRS modality non-invasively investigates the change of blood oxygenation level in the human brain utilizing the transillumination technique. In the last two decades, the interest in this modality is gradually evolving for its real-time monitoring, relatively low-cost, radiation-less environment, portability, patient-friendliness, etc. Including brain-computer interface and functional neuroimaging research, this technique has some important application of clinical perspectives such as Alzheimer's disease, schizophrenia, dyslexia, Parkinson's disease, childhood disorders, post-neurosurgery dysfunction, attention, functional connectivity, and many more can be diagnosed as well as in some form of assistive modality in clinical approaches. Regarding the issue, this review article presents the current scopes of fNIRS in medical assistance, clinical decision making, and future perspectives. This article also covers a short history of fNIRS, fundamental theories, and significant outcomes reported by a number of scholarly articles. Since this review article is hopefully the first one that comprehensively explores the potential scopes of the fNIRS in a clinical perspective, we hope it will be helpful for the researchers, physicians, practitioners, current students of the functional neuroimaging field, and the related personnel for their further studies and applications.

Keywords: Anesthetic depth monitoring; Assistive modality; Behavioral disorder; Functional near-infrared spectroscopy (fNIRS); Neurological disorder.

Fig. 1

fNIRS modality-based BOLD signal monitoring from the prefrontal cortex

Fig. 2

Anesthetic monitoring by the fNIR sensor alone (left figure). The combination of fNIRS and BIS system for anesthetic condition monitoring is given in the right figure. In the combination system, only the upper channels of the fNIRS system are considered [11]

Fig. 3

The position of the prefrontal cortex that shows the most significant activation regarding the emergence of consciousness during the anesthetic period. This area is equivalent to the channel number 11 of the 16 channel optodes of the fNIRS devices [19]

Fig. 4

The overall average changes in the concentration of HbO₂ of different groups during the verbal fluency test in the right parietal area of the brain. This figure is redrawn from the information found in [37]

Fig. 5

This figure represents the tasks (VFT and LN) and averaged change in [HbO₂] and [dHb]

Fig. 6

This figure represents the tasks (VFT and LN) and related averaged change in the concentration of HbO₂ and dHb of the patients who were medicated by atypical antipsychotics and compared with the control group

Fig. 7

The number of appropriate answers for panic disorder, major depressive disorder, and stable controls on the Word Fluency Test (WFT) during fNIRS

Fig. 8

Significance diagram of the category of panic disorders (right panel) and the major depressive disorders (left panel) compared with stable controls. The color bars on the right display gradient colors as a measure of significance

Fig. 9

The most affected ROI on the prefrontal cortex due to the effects of methylphenidate during the auditory oddball paradigm test by the ADHD children