Review of recent advances in frequency-domain near-infrared spectroscopy technologies [Invited]

Abstract

Over the past several decades, near-infrared spectroscopy (NIRS) has become a popular research and clinical tool for non-invasively measuring the oxygenation of biological tissues, with particular emphasis on applications to the human brain. In most cases, NIRS studies are performed using continuous-wave NIRS (CW-NIRS), which can only provide information on relative changes in chromophore concentrations, such as oxygenated and deoxygenated hemoglobin, as well as estimates of tissue oxygen saturation. Another type of NIRS known as frequency-domain NIRS (FD-NIRS) has significant advantages: it can directly measure optical pathlength and thus quantify the scattering and absorption coefficients of sampled tissues and provide direct measurements of absolute chromophore concentrations. This review describes the current status of FD-NIRS technologies, their performance, their advantages, and their limitations as compared to other NIRS methods. Significant landmarks of technological progress include the development of both benchtop and portable/wearable FD-NIRS technologies, sensitive front-end photonic components, and high-frequency phase measurements. Clinical applications of FD-NIRS technologies are discussed to provide context on current applications and needed areas of improvement. The review concludes by providing a roadmap toward the next generation of fully wearable, low-cost FD-NIRS systems.

Aortic arch branch-prioritized reconstruction for type A aortic dissection surgery

“…If the blood flow in the femoral artery is not affected by dissection and the implementation of branch-priority technology is successful, it is necessary to evaluate the safety of cerebral perfusion. This can be achieved by monitoring the blood flow of the bypass and using near-infrared spectroscopy to observe cerebral oxygen saturation ( 19 ). It is worth noting that when using branch-priority technology, the perfusion flow during circulatory arrest may be greater than that of traditional selective cerebral or bilateral cerebral perfusion flow because the LSCA receives perfusion simultaneously.…”

Neural Plasticity Changes Induced by Motor Robotic Rehabilitation in Stroke Patients: The Contribution of Functional Neuroimaging

“…The analysis of a hemodynamic response, whose dynamics take at least 3 to 5 s, typically does not require high temporal resolution, but it can be useful for the study of transient hemodynamic activity [ 33 ]. Comparing fNIRS to fMRI, its primary disadvantages are its inferior spatial resolution (a few millimeters beneath the head) and insensitivity to subcortical areas [ 34 , 35 ]. This might be viewed as a minor drawback, though, as a substantial body of research suggests that walking involves cortical mechanisms [ 36 ], the motor system is organized across broad brain regions [ 37 ], and the cerebral cortex mirrors the function of subcortical structures [ 38 ].…”

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“…In general, NIRS is a desirable imaging technique for its rapidity in assessment, portability, and non-invasive nature [ 5 ]. Frequency-domain NIRS (FD-NIRS) provides information with respect to the absolute concentrations of oxygenated and deoxygenated hemoglobin (HbO and HHb), whereas the most commonly used technique, continuous-wave NIRS, makes more assumptions about the photons’ pathlengths, and provides information only on relative changes in chromophore concentrations [ 6 , 7 ]. Further, compared with time-domain NIRS, FD-NIRS portability is similar but more cost-efficient, which is imperative for clinical utility [ 6 , 7 , 8 ].…”