Open AccessLock-in functional near-infrared spectroscopy for measurement of the haemodynamic brain response
Author(s) -
Stanisław Wojtkiewicz,
Karolina Bejm,
Adam Liebert
Publication year - 2022
Publication title -
biomedical optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.362
H-Index - 86
ISSN - 2156-7085
DOI - 10.1364/boe.448038
Subject(s) - functional near infrared spectroscopy , noise (video) , computer science , diffuse optical imaging , near infrared spectroscopy , sensitivity (control systems) , optics , brain cortex , detector , artificial intelligence , physics , neuroscience , electronic engineering , telecommunications , iterative reconstruction , engineering , biology , prefrontal cortex , medicine , cognition , image (mathematics)
Here we show a method of the lock-in amplifying near-infrared signals originating within a human brain. It implies using two 90-degree rotated source-detector pairs fixed on a head surface. Both pairs have a joint sensitivity region located towards the brain. A direct application of the lock-in technique on both signals results in amplifying common frequency components, e.g. related to brain cortex stimulation and attenuating the rest, including all components not related to the stimulation: e.g. pulse, instrumental and biological noise or movement artefacts. This is a self-driven method as no prior assumptions are needed and the noise model is provided by the interfering signals themselves. We show the theory (classical modified Beer-Lambert law and diffuse optical tomography approaches), the algorithm implementation and tests on a finite element mathematical model and in-vivo on healthy volunteers during visual cortex stimulation. The proposed hardware and algorithm complexity suit the entire spectrum of (continuous wave, frequency domain, time-resolved) near-infrared spectroscopy systems featuring real-time, direct, robust and low-noise brain activity registration tool. As such, this can be of special interest in optical brain computer interfaces and high reliability/stability monitors of tissue oxygenation.