BME PhD Prospectus Defense: Alexander C. Howard

Title: "peckle Contrast Optical Spectroscopy for Image Reconstruction, Physiological Characterization, and Metabolic Measurements"

Advisory Committee: Xiaojun Cheng, PhD (Co-Advisor), Biomedical Engineering, Boston University David A. Boas, PhD (Co-Advisor), Biomedical Engineering, Boston University Darren Roblyer, PhD (Chair), Biomedical Engineering, Boston University Maria A. Franceschini, PhD, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital Stefan A. Carp, PhD, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital

Abstract: Cerebral blood flow (CBF) and the cerebral metabolic rate of oxygen (CMRO2) are altered in stroke, traumatic brain injury, and Alzheimer's disease, but existing optical methods are limited. Functional near-infrared spectroscopy does not directly measure CBF, and traditional diffuse correlation spectroscopy's single-speckle detection constrains its scalability to imaging arrays. Speckle contrast optical spectroscopy (SCOS) achieves a higher signal-to-noise-ratio than diffuse correlation spectroscopy, making high-density optical CBF imaging practical. This dissertation establishes the mathematical foundation for speckle contrast optical tomography image reconstruction and applies it to produce the first group-level reconstructed CBF brain maps during a cognitive task in fifteen adults. Building on this foundation, it characterizes how systemic physiology modulates SCOS blood flow signals across a whole-hemisphere array to inform noise correction and regression design and combines SCOS with functional near-infrared spectroscopy with a multi-channel array to reconstruct the first images of CMRO2 from optical measurements in humans, demonstrating the feasibility of concurrent imaging of cerebral blood flow, hemoglobin, and oxygen metabolism.