Document Type

Thesis

Date of Award

2017

Keywords

Pure sciences, Applied sciences, Fluorescence, High-sensitivity, Light scattering, Photon transport, Tissue, Transimpedance amplifier

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical and Computer Engineering

First Advisor

Dr. Arkady M. Pertsov

Subject Heading(s)

Pure sciences; Applied sciences; Fluorescence; High-sensitivity; Light scattering; Photon transport; Tissue; Transimpedance amplifier; Electrical and Computer Engineering

Abstract

Part 1: High-Sensitivity Amplifiers for Detecting Fluorescence
Monitoring electrical activity and Cai 2+ transients in biological tissues and individual cells increasingly utilizes optical sensors based on voltage-dependent and Cai 2+-dependent fluorescent dyes. However, achieving satisfactory signal-to-noise ratios (SNR) often requires increased illumination intensities and/or dye concentrations, which results in photo-toxicity, photo-bleaching and other adverse effects limiting the utility of optical recordings. The most challenging are the recordings from individual cardiac myocytes and neurons. Here we demonstrate that by optimizing a conventional transimpedance topology one can achieve a 10-20 fold increase of sensitivity with photodiode-based recording systems (dependent on application). We provide a detailed comparative analysis of the dynamic and noise characteristics of different transimpedance amplifier topologies as well as the example(s) of their practical implementation.

Part 2: Light-Scattering Models for Interpretation of Fluorescence Data
Current interest in understanding light transport in cardiac tissue has been motivated in part by increased use of voltage-sensitive and Ca i2+-sensitive fluorescent probes to map electrical impulse propagation and Cai2+-transients in the heart. The fluorescent signals are recorded using such probes represent contributions from different layers of myocardial tissue and are greatly affected by light scattering. The interpretation of these signals thus requires deconvolution which would not be possible without detailed models of light transport in the respective tissue. Which involves the experimental measurements of the absorption, scattering, and anisotropy coefficients, μa, μ s, and g respectively.

The aim of the second part of our thesis was to derive a new method for deriving these parameters from high spatial resolution measurements of forward-directed flux (FDF). To this end, we carried out high spatial resolution measurements of forward-directed flux (FDF) in intact and homogenized cardiac tissue, as well as in intralipid-based tissue phantoms. We demonstrated that in the vicinity of the illuminated surface, the FDF consistently manifested a fast decaying exponent with a space constant comparable to the decay rate of ballistic photons. Using a Monte Carlo model we obtained a simple empirical formula linking the rate of the fast exponent to the scattering coefficient, the anisotropy parameter g, and the numerical aperture of the probe. The estimates of scattering coefficient based on this formula were validated in tissue phantoms. The advantages of the new method are its simplicity and low-cost.

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