Abstract
Functional near-infrared spectroscopy (fNIRS) has been utilized already around three decades for monitoring the brain, in particular, oxygenation changes in the cerebral cortex. In addition, other optical techniques are currently developed for in vivo imaging and in the near future can be potentially used more in human brain research. This paper reviews the most common label-free optical technologies exploited in brain monitoring and their current and potential clinical applications. Label-free tissue monitoring techniques do not require the addition of dyes or molecular contrast agents. The following optical techniques are considered: fNIRS, diffuse correlations spectroscopy (DCS), photoacoustic imaging (PAI) and optical coherence tomography (OCT). Furthermore, wearable optical brain monitoring with the most common applications is discussed.
Highlights
Conducting brain studies by electroencephalography (EEG), magnetoencephalography (MEG)and functional magnetic resonance imaging is a common practice in modern neuroimaging.Using EEG and MEG, signals generated by the neuronal activities can be measured with a time resolution of less than one millisecond
FNIRS, or diffuse optical spectroscopy (DOS), is mainly utilized for measuring oxygenation changes in the cerebral cortex that are linked to brain function
Normalized time-frequency analysis presented in vivo voltage-sensitive dye (VSD) response in the seizure group which was significantly distinguishable from the control groups at sub-mm spatial resolution
Summary
Conducting brain studies by electroencephalography (EEG), magnetoencephalography (MEG). Optical techniques, in addition to EEG, offer high potential due to their portability and adaptability [6] Complementing each other, these two methods have a growing interest especially to be utilized in wearable brain monitoring applications [7]. Related to fNIRS, diffuse correlations spectroscopy (DCS) provides a direct measure of blood flow dynamics, based on detection of scattering of photons due to red blood cells (RBCs) in blood flow [12] Both fNIRS and DCS still have a limited spatial resolution. PAI and OCT play an essential role in translational medical research when imaging and quantifying brain morphology and brain function on a microscopic scale These are commonly performed using rodent models, e.g., to study diseased brain. Wearable use of optical techniques in brain monitoring are discussed
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