Abstract
Decoding the human's brain functional architecture is the most profound and far-reaching scientific challenges of our time. Currently existing noninvasive brain imaging technologies are constrained by costly, bulky and fixed hardware that preclude imaging of the functioning brain in a wide range of temporal and naturalistic environments. This doctoral dissertation focused on designing and developing of a new generation portable, wearable, configurable, and wireless functional near-infrared spectroscopy (fNIRS) neuroimaging system that allows us to monitor and study brain function in a naturalistic environment. The developed optical system maps changes in chromophore concentration, oxy hemoglobin (HbO2) and deoxyhemoglobin (Hb) of the cortical surface of the brain in response to the human brain functions noninvasively. The fNIRS hardware system was designed based on the Internet-of-Things (IoT) platform using Intel Edison for onboard intelligence, configurability and data transmission. The analog and digital circuits were designed and developed. The fNIRS controlling unit consists of three printed circuit boards (PCBs) sandwiched together: (1) embedded system PCB, (2) analog circuit PCB and (3) digitization PCB. We programmed the system to perform highly complex operations such as montage configuration, sequential NIR light injection and low-intensity back-reflected diffused light measurement from the cortical area of the brain at two wavelengths, data conversion, computation, and wireless data transmission, etc. The portable fNIRS system was capable of transferring multi-channel fNIRS data to a computer in real-time. The fNIRS channels are combinations of light sources and detectors. The light-emitting diode (LED) and silicon photodiode (Si-PD) detector based fNIRS optodes (source and detector) were developed. We used modern design tools such as 3D printing and laser cutting to fabricate human-centered fNIRS optodes. Feedback was taken from participants of different groups throughout the iterative design process. Two types of fNIRS optodes were designed; one was based on forehead patch and the other was integrable into an electrode head cap that can be placed along with electroencephalography (EEG) electrodes. Our software architecture wirelessly connects the fNIRS system with a computer or Android tablet through WiFi and interacts to send configuration settings and also to receive fNIRS data in real-time. A host computer connects to the fNIRS control unit via authentication and performs bi-directional communication in real-time to instruct the fNIRS controller to operate in a synchronized manner. The host computer also simultaneously collects and processes the fNIRS signal, and displays hemodynamics responses. A MatLab-based graphical user interface (GUI) software was developed to control the
Highlights
Non-invasive neuroimaging technologies are becoming increasingly prevalent due to their bountiful clinical and research applications
We found that hemodynamic response to the cortical activity rises in response to the mental arithmetic over time
The goal of coupling multiple photodiodes and light-emitting diode (LED) to a scalp was achieved through the reliability, durability, and usability of this design
Summary
Non-invasive neuroimaging technologies are becoming increasingly prevalent due to their bountiful clinical and research applications. Brain monitoring systems electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS) are increasingly used for brain studies that involve participants are in their natural states or performing physical activities, because both of these technologies are portable [4]. Functional near-infrared spectroscopy (fNIRS) is an emerging brain imaging technology that non-invasively maps hemodynamic responses of the brain by measuring changes in oxygenated (HbO2) and deoxygenated (Hb) hemoglobin con-. The fNIRS systems use near-infrared (NIR) light sources and detectors operating in the wavelength range 600-900 nm [7] to measure the relative changes in oxygenated (HbO2) and deoxygenated (Hb) hemoglobin concentration [Fig. 43] in the cortical region of the brain [8, 6, 9, 10, 11]. Functional near-infrared spectroscopy is an emerging neuroimaging modality that can non-invasively map the hemodynamic response of the brain by measuring changes in oxygenated (HbO2) and deoxygenated (Hb) hemoglobin concentration on the cortical surface of the brain [6, 10]. Many fNIRS and hybrid EEGfNIRS studies have successfully used LDA for BCIs
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