This dissertation describes the design and implementation of the first line-field MMOCT system. The system is composed of a LF-OCT system that uses a novel, supercontinuum light source and an optical design which together achieve the best combination of speed, sensitivity, and resolution of any LF-OCT system to date [50]. The LF-OCT system was then converted to a LF-MMOCT system with additional hardware and software components. This LF-MMOCT system has a speed comparable to the fastest reported volumetric throughput of any MMOCT system to date, with the potential be offer a further order of magnitude improvement in speed. After optimizing the imaging parameters to achieve the best possible magnetic SNR, the system was used to demonstrate the first detection of a single magnetic point particle using MMOCT and to measure a vibration amplitude consistent with the theoretical value. The ability to detect single magnetic point particles provides a necessary proof of concept that LF-MMOCT may be used for endogenous magnetite detection in the excised tissue from animals that are known to use geomagnetic navigation. The future work needed to prepare the system for endogenous magnetite detection is described at the end of Chapter 4. The broader impacts and potential utility of this work are described in the following paragraphs.
We demonstrated the ability of the second version of the LF-OCT system to image dynamic biological samples. The line-illumination combined with the high-speed camera, the excellent SNR, and the high axial resolution allowed us to image beating cilia of human
bronchial epithelial cells in a unique way. Rather than having to study a single A-line in time as in Ref [69], we were able to examine the dynamic behavior of the cilia across an entire 2D
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cross-sectional image because, in this system, each A-line is well correlated with the subsequent A-line in time. The study of ciliary beat frequency is of great interest for the study of human respiratory diseases such as cystic fibrosis and chronic obstructive pulmonary disorder. The ability to spatially map changes in the ciliary beat frequency over some cross-sectional area is useful for the study of mucociliary clearance, an indicator of the health of the airway. Future uses of the version 2 LF-OCT design presented here include not only further study of beating cilia in human airway cells, but any dynamic biological sample that can be studied in an in vitro
scenario. For example, the motility of cancer cells in response to certain chemotherapy drugs is another process studied by our lab (using a point-scanning OCT system) that requires high-speed imaging and the ability for subsequent frames to be well correlated in time. Motility is a metric of healthy cell activity so it is used to study the efficacy of certain drugs [103,104].
The development of the MMOCT frame-by-frame imaging scheme demonstrated an improvement in MMOCT imaging speed by decoupling the spatial dimension X from the magnet modulation in time. Although we were not the first to publish this method, we developed the method independently and in parallel with Ahmad et al [20]. While increasing the MMOCT framerate, this method maintains the same Fe sensitivity as the previously published line-by-line MMOCT imaging scheme. Higher MMOCT imaging speed is essential for volumetric MMOCT. This new imaging scheme makes MMOCT a more viable method for applications such as
endogenous magnetite detection, in which large volumes of tissue must be imaged. It was also essential for the development of a LF-MMOCT system: because all A-lines are recorded
simultaneously in the line-field configuration, line-by-line MMOCT is not possible with LFOCT. The LF-MMCOT system presented here is the first demonstration of an MMOCT system with the line-field configuration and the first MMOCT using a supercontinuum light source. By
combining the imaging speed improvement of the line-field configuration with the frame-by- frame imaging scheme and the high-power supercontinuum light source (which gives high optical SNR and high axial resolution) we built a system with the potential to be the fastest MMOCT system to date and one that has a sufficiently fine resolution and sufficiently high magnetic sensitivity to detect single, magnetic point particles. We have optimized the MMOCT imaging parameters to produce the highest magnetic SNR possible at kilohertz framerates. This is a key step on the path to endogenous magnetite detection.
We also present a summary of three optical designs with the subsequent figures of merit of the optical imaging system. This makes the LF-OCT system adaptable for different
applications. For example, a LF-MMOCT system built using the version 2 optical design would offer increased SNR and increased resolution homogeneity across the entire imaging region of interest if a sacrifice in transverse resolution is acceptable. This may be the preferred setup for applications in which the goal of the MMOCT imaging is to detect the presence of multiple particles rather than single, point-like particles. One such application is the detection of magnetic gold nanorods which may be used to measure the porosity of mucus or other polymers by
relating the diffusion of the magnetic gold nanorods to the polymer pore size [105,106]. In summary we have designed, built, characterized, and optimized a novel imaging system with the potential to be used for a wide variety of biological and biomedical applications currently under investigation by this lab and by our collaborators.
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