Frequency domain functional near infrared spectroscopic imaging for the assessment of human brain health

Perkins, Guy Antony ORCID: 0000-0002-0437-9324 (2024). Frequency domain functional near infrared spectroscopic imaging for the assessment of human brain health. University of Birmingham. Ph.D.

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Abstract

This thesis explores the use and development of frequency domain (FD) functional near infrared spectroscopy (fNIRS) and diffuse optical tomography (DOT) for use in the assessment of human brain health, with a focus on traumatic brain injury (TBI). The focus on TBI was chosen because TBI has the highest incident of all neurological disorders. TBI is caused when an external force impacts the head, causing an acceleration on the brain and depending on the magnitude and duration of this force, can have several minor and serious consequences on the brain. Currently TBI is graded, mild (mTBI), moderate (M-TBI) or severe (S-TBI) using a subjective assessment, the Glasgow coma scale, with supplementary imaging performed on S-TBI in the form of x-ray CT or MRI scans. These forms of imaging can not be done at the bedside, or outside of clinical environments, and in the case of MRI scans, can be resource expensive. In addition, the subjective assessments may be influenced by factors outside of the TBI itself, which means there exists an opportunity for portable, more resource efficient, objective assessment for TBI. The use of diffuse optics may present as a tool to supplement the aforementioned tools for the assessment of TBI and this thesis investigates the use of frequency domain diffuse optics of brain imaging, for the application of traumatic brain injury assessment. This thesis develops the use of FD fNIRS and DOT for functional brain imaging, which plays a role in assessing brain health. In the FD, light is emitted sinusoidally on the surface of the scalp, this light is then absorbed and scattered throughout tissue and some of that light is then detected. The measurements made are changes in the intensity (amplitude) and phase of the modulated light and it is these changes in intensity and more significantly phase that are crucial to unlocking the advantages of FD versus the much used continuous wave (CW) paradigm in diffuse optics. In CW measurements, only changes in intensity are measured, and it has been demonstrated that phase measurements actually sample deeper than intensity measurements. As well as sampling deeper and thus sampling the cortical tissue more than intensity, phase data is also less sensitive to superficial tissue changes. This thesis investigates and explores the use of phase and intensity data with FD measurements, showing that the inclusion of phase data when applied to functional brain imaging increases the contrast of measured brain activation for both fNIRS and DOT. This is performed with a specially designed workflow, to combine recent advancements of data analysis in fNIRS literature, such as short signal regression to minimise superficial tissue influence, optical subject specific registration for accurate placement of source-detector probes on the 3D subject model and a bespoke 3D printed probe holder for the subject neoprene helmet to perform standard and dual slope measurements. Through these design considerations, this workflow enables and enhances the demonstration of FD fNIRS and DOT for functional brain imaging. The final working chapter in this thesis demonstrates an experimental protocol for imaging S-TBI patients in the intensive care unit, using a lab based FD device and an injected contrast dye. It also provides insight into the challenges of imaging in this type of clinical environment. In addition, this thesis explores another unique aspect of phase data, that the distribution of sensitivity changes as a function of modulation frequency. Through simulations and then measurements on a phantom mimicking functional activation, it is shown that combining measurements of phase at different modulation frequencies increases the accuracy and resolution of DOT, unlocking the best performance of FD diffuse optics. These findings give the platform to FD fNIRS and DOT, in that when assessing human brain health, they provide a more accurate imaging of functional brain activation than the equivalent CW measurements, which could be vital for when assessing human brain health.

Type of Work:	Thesis (Doctorates > Ph.D.)
Award Type:	Doctorates > Ph.D.
Supervisor(s):	Supervisor(s) Email ORCID Dehghani, Hamid UNSPECIFIED orcid.org/0000-0003-4117-0412 Tino, Peter UNSPECIFIED UNSPECIFIED Lucas, Sam UNSPECIFIED UNSPECIFIED Cruse, Damian UNSPECIFIED UNSPECIFIED
Licence:	All rights reserved
College/Faculty:	Colleges > College of Engineering & Physical Sciences
School or Department:	School of Chemistry
Funders:	Engineering and Physical Sciences Research Council
Subjects:	Q Science > Q Science (General) Q Science > QA Mathematics > QA75 Electronic computers. Computer science R Medicine > R Medicine (General)
URI:	http://etheses.bham.ac.uk/id/eprint/15640

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