ORCID
https://orcid.org/0000-0002-5038-0262
Date of Award
2-2-2024
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Cerebral blood flow (CBF) is an important biomarker for indicating many brain diseases, such as stroke and traumatic brain injury. Therefore, the development of real-time CBF measures in the clinic is desired, and many techniques have been developed to measure CBF. However, the current standard techniques, including positron emission tomography (PET), arterial spin labeling magnetic resonance imaging (ASL-MRI), and computed tomography (CT) perfusion are limited to the high instrument cost, massive size, and the requirement of ionizing radiation, and thus are not able to map CBF at the bedside. Furthermore, these techniques offer only snapshots due to scanner logistics. An alternative optical modality is diffuse correlation spectroscopy (DCS); however, DCS requires a sensor with very high temporal resolution and has a lower signal-to-noise ratio (SNR) because it measures only one speckle at a time. Speckle contrast optical tomography (SCOT) is an attractive optical technique that can address the challenges in current CBF measurement techniques. SCOT offers a cost-efficient, radiation-free, and portable optical method for continuously mapping CBF. It also overcomes the SNR limitation in DCS by simultaneously aggregating many speckles. The current free-space design of SCOT has been shown to have similar results as in fMRI in phantoms and rodents. However, this design is difficult for imaging CBF in humans due to the focus challenge through a large region of the brain and the signal attenuation caused by hairs. Thus, this research focuses on developing a fiber-based SCOT to overcome these challenges. A fiber-based design can adapt to the complex shape of a head and can comb through the hairs to obtain a good signal. To investigate the unknown performance of a fiber-based SCOT in humans, we developed a computational modeling method to simulate the measurement and images of a fiber-based SCOT. In addition, to address to limitation of the current models that use only the homogeneous model and do not include system noise, we developed a reconstruction method based on an anatomical head model from MRI with five tissue layers and an array with 24 sources and 28 detectors with multiple noise models. Results show that including longer source-detector distances reduces the localization error of the SCOT reconstruction. Moreover, even though SCOT signals are smaller with increased exposure time, the SNR increases by 1000X by extending exposure time from 10 µs to 10 ms. In experimental results, we demonstrate that cost-efficient multi-mode fiber (MMF) bundles can be used to relay flow. Furthermore, speckle statistics can be used to distinguish speckle signals and noise. Finally, we demonstrate the feasibility of measuring pulsatile blood flow in humans through MMFs and show that they can be used to develop a SCOT system.
Language
English (en)
Chair and Committee
Shankar Mukherji, Joseph P. Culver
Committee Members
Hongyu An, Anders E. Carlsson, Timothy Holy
Recommended Citation
Lin, Chen-Hao, "Fiber-Based Speckle Contrast Optical Tomography in Humans" (2024). Arts & Sciences Electronic Theses and Dissertations. 3236.
https://openscholarship.wustl.edu/art_sci_etds/3236