ORCID
https://orcid.org/0000-0002-7826-4159
Date of Award
12-18-2024
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Functional near-infrared spectroscopy (fNIRS) is a non-invasive imaging technique that measures hemodynamic responses in the brain, similar to functional magnetic resonance imaging (fMRI) but with distinct advantages. By utilizing near-infrared light, fNIRS can penetrate biological tissues and detect changes in oxygenated and deoxygenated hemoglobin. Additionally, fNIRS is portable, noninvasive and inexpensive. Within the realm of fNIRS, several measurement techniques exist, including Continuous Wave (CW), Frequency Domain (FD), and Time Domain (TD) methods. In this dissertation, we focused on the effects, fundamental principles and applications of FD designs. We provided the introduction in Chapter 1, and discussed the background theory and hardware setups in Chapter 2. In Chapter 3, The effects of modulation frequency on image quality as obtainable with FD-HD-DOT is investigated through simulations with a realistic noise model of functional activations in human head models, arising from 11 source modulation frequencies between CW and 1,000 MHz. Simulations were performed using five representative head models with a high-density regular grid of 158 light sources and 166 detectors and an empirically derived noise model. Functional reconstructions were quantitatively assessed with multiple image quality metrics including the localization error (LE), success rate, full width at half maximum (FWHM), and full volume at half maximum (FVHM). All metrics were evaluated against CW-based models. Compared to CW, localization accuracy is improved by >40% throughout brain depths of 13 - 25 mm below the surface with 300-500 MHz modulation frequencies. Additionally, the reliable field of view in brain tissue is enlarged by 35-48% within an optimal frequency of 300 MHz after considering realistic noise, depending on the dynamic range of the system. These results point to the tremendous opportunities in further development of high bandwidth FD-HD-DOT system hardware for applications in human brain mapping. In Chapter 4, we investigated the combined effects of two leading strategies to optimize DOT image quality, including (i) arrays of regular, interlacing, high-density (HD) grids of sources and detectors with closest spacing less than 15 mm, or (ii) source modulated light of order ~100 MHz. However, fundamental principles for how these crucial design parameters of array density and modulation frequency may interact have yet to be elucidated. Herein, we systematically evaluated how these design parameters effect image quality via multiple key metrics. Specifically, we simulated 32 system designs with realistic measurement noise and quantified localization error, spatial resolution, signal to noise, and localization depth of field for each of ~85,000 point spread functions in each model. We found that array density had a far stronger effect on image quality metrics than modulation frequency. Additionally, model fits for image quality metrics revealed that potential improvements diminish with regular arrays denser than 9 mm closest spacing. Further, for a given array density, 300 MHz source modulation provided the deepest reliable imaging compared to other frequencies. Our results indicate that both array density and modulation frequency affect the spatial sampling of tissue, which asymptotically saturates due to photon diffusivity within a turbid volume. In summary, our results provide comprehensive perspectives for optimizing future DOT system designs in applications from wearable functional brain imaging to breast tumor detection. Last, in Chapter 5, we investigated the relationship between the FD measurements and the structural characteristics of CSF within layered semi-infinite geometries. We further purposed a method to estimate the CSF depth and thickness using FD HD-DOT technologies.
Language
English (en)
Chair and Committee
Adam Eggebrecht
Committee Members
Hongyu An; Quing Zhu; Shankar Mukherji; Xi Wang; Zohar Nussinov
Recommended Citation
Fan, Weihao, "Sensitivity and Application of Frequency Domain High-density Diffuse Optical Tomography (FD HD-DOT)" (2024). Arts & Sciences Electronic Theses and Dissertations. 3386.
https://openscholarship.wustl.edu/art_sci_etds/3386