Graduation Year

2022

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Electrical Engineering

Major Professor

Ashwin Parthasarathy, Ph.D.

Committee Member

Ramesh Ayyala, M.D.

Committee Member

Christopher Passaglia, Ph.D.

Committee Member

Ismail Uysal, Ph.D.

Committee Member

Jing Wang, Ph.D.

Keywords

Instrumentation, Interferometry, Preclinical, Speckle

Abstract

For label-free, non-invasive, wide field-of-view (FOV) imaging/monitoring of blood flow, speckle-based approaches are gaining popularity. However, to obtain quantitative flow information, speckle techniques rely on the multi-exposure scheme which requires complex, bulky, and expensive instrumentation, limiting its application to preclinical studies. This dissertation directly addresses these issues. In the first part of this dissertation, we report a novel single shot synthetic multi-exposure speckle imaging (syMESI) method to synthetically produce multi-exposure images from one short single exposure speckle image using spatial binning/averaging. We demonstrate that syMESI can reimagine conventional hardware based MESI, with low-cost single exposure laser speckle imaging (LSCI) instrumentation. We validate the syMESI algorithm with flow experiments on microfluidic channels, and by imaging cerebral blood flow in rodent brain in vivo. In the second part of this dissertation, we introduce a novel heterodyne instrument for imaging blood flow and new heterodyne laser speckle theory and model. We demonstrate that our new technique, can increase the signal-to-noise ratio (SNR) of blood flow measurements and can quantify flow images at low photon budget (<40 average detection intensity). These two techniques, transform traditional expensive multi-exposure method into a low-cost quantitative imaging tool, solving a decade long problem. Finally, we introduce a new diffuse optical instrument by combining a low coherence laser diode and a Mach-Zehnder interferometer, for obtaining dynamic properties (optical properties and blood flow). Our new instrument can provide deep tissue information by utilizing the diffusion theory of photon propagation. The capability to record path resolved diffuse optical measurements using a continuous (CW) laser source allows our instrument to operate at source-distance (S-D) separation of 2.5 cm or greater. As a proof of concept, we demonstrate results of intralipid phantom and in vivo arm-cuff occlusion. We believe, this new path-resolved instrument will enable researchers to uncover deep tissue optical properties information which cannot be performed with traditional diffuse correlation technique.

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