Date of Award

2016

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Biomedical Engineering (PhD)

Administrative Home Department

Department of Biomedical Engineering

Advisor 1

Sean J. Kirkpatrick

Committee Member 1

Michael C. Roggemann

Committee Member 2

Warren F. Perger

Committee Member 3

Keat G. Ong

Abstract

Laser Speckle Contrast Imaging (LSCI) is a real-time, non-invasive method in used to investigate blood flow and perfusion in biological tissues with high temporal and spatial resolution. A reduction in speckle contrast due to particle motion is the primary contrast mechanism in LSCI. Motion results in speckle fluctuations in time and reduces the contrast over a given camera integration period. There are a variety of parameters that effect contrast besides motion. The optical properties of the scattering medium are one of the parameters effecting LSCI values. Changes in blood hematocrit levels manifest as changes in optical properties. In this work, we explore the effects of different hematocrit levels on LSCI contrast values using fluid phantoms with varying optical properties.

Herein, the combined effects of scattering and absorption coefficients on LSCI values are investigated using fluid phantoms. These fluid phantoms were designed to mimic the scattering and absorbing properties of blood with varying levels of hematocrit. The flow phantoms in our experiments contained different concentrations of glass microspheres (brand name Luxil) and India ink mixed with DI water. The different number of scatterers and absorbers in the phantoms mimic the scattering and absorption behaviors of blood with different number of red blood cells. An LSCI setup combined with a simple flow system was used in our experiments in order to investigate the effects of combined scattering and absorption coefficient of 121 samples with different concentrations of Luxil and India ink microspheres. The fluid phantoms were run in 2mm glass tubing on top of a plastic block using a mini peristaltic pump. An LSCI setup imaged the flow using a CCD camera. A MATLAB GUI controlled the pump and camera to provide near real-time contrast images of the flow. An 11x11 matrix of phantoms was created. Scattering coefficient was varied on the columns and absorption coefficient was varied on the rows such that the first element of the matrix is water and the last element contains the phantom with the maximum number of scatterers and absorbers. A hundred raw speckle images were recorded for each phantom experiment using the described optical setup. The experiments were conducted 3 times for each element of the matrix. The 11x11 results matrix displayed the average speckle image of all 300 raw speckle images. Additionally, the matrix was filled by the contrast images where contrast was defined as standard deviation of intensity over mean intensity. In order to compare the results numerically, we calculated the ratio of the contrast from the same size window of moving portion over the static portion of the phantoms. According to the results from LSCI experiments, an increase in scattering and absorption coefficients led to a reduction in contrast values of LSCI images. By increasing the number of scatterers and absorbers (equivalent to changing hematocrit level), the optical properties (scattering and absorption coefficient) increased, which led to a reduction in contrast value in the moving area. A negative slope linear curve describes the relationship between and scattering coefficient and between and absorption coefficient.

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