High-speed phase-stable swept source optical coherence tomography: functional imaging and biomedical applications

In the past decades, the performance of swept source optical coherence tomography (SS-OCT) has experienced an unprecedented improvement which is mainly driven by the rapidly evolving laser technologies: the state-of-art SS-OCT is now tens of dB more sensitive, six orders of magnitude faster, and seeing ten times deeper than the original version of time domain OCT. Regardless of the abovementioned progress, the phase instability is always considered the biggest weakness of SS-OCT and the mainstream belief often states that the mechanical tuning mechanism of the swept source is to blame. In my study, I first developed a high-speed phase-stable SS-OCT based on a new-generation akinetic laser source, which is electrically tuned in wavelength, in the hope of reducing the phase noise to a shot-noise limited level. The experimental results turned out to be contradicted to the conventional phase noise theory, which inspires my discovery of a completely new interpretation for the phase noise in SS-OCT: I proposed that the timing jitter and scanning variability has to be taken into the consideration in the noise model as multiplicative noises. The theory was later validated by another SS-OCT using a different light source. This study for the first time articulated the phase noise’s origin and composition in the SS-OCT. Although the SS-OCT performs relatively worse in phase stability compared with its spectral-domain counterpart (SD-OCT), it is still valuable since it images at a much faster rate than SD-OCT. Therefore, a better temporal resolution could be achieved, which is particularly attractive in areas such as time lapse imaging. I therefore utilize the system along with other two systems to conduct ex vivo imaging on human tracheobronchial epithelium. It is shown that the SS-OCT system could achieve equally good performance in this task. Moreover, thanks to the higher temporal and temporal frequency resolution, finer structure within the frequency response of the ciliary motion is picked up by our system. During the study of ex vivo ciliary imaging, one of the challenges I was confronted with was the enormous amount of data generated by the SS-OCT, especially when high temporal frequency resolution is required. We thus came up with an idea of applying the compressive sensing (CS) to reduce the data size. Currently, we have demonstrated some preliminary results with using CS on reference k-clock channel compression. In the future, we will apply the same theory to compress the sample channel data, especially or time lapse OCT imaging

Coronal Loops: Observations and Modeling of Confined Plasma

Coronal loops are the building blocks of the X-ray bright solar corona. They owe their brightness to the dense confined plasma, and this review focuses on loops mostly as structures confining plasma. After a brief historical overview, the review is divided into two separate but not independent sections: the first illustrates the observational framework, the second reviews the theoretical knowledge. Quiescent loops and their confined plasma are considered, and therefore topics such as loop oscillations and flaring loops (except for non-solar ones which provide information on stellar loops) are not specifically addressed here. The observational section discusses loop classification and populations, and then describes the morphology of coronal loops, its relationship with the magnetic field, and the concept of loops as multi-stranded structures. The following part of this section is devoted to the characteristics of the loop plasma, and of its thermal structure in particular, according to the classification into hot, warm and cool loops. Then, temporal analyses of loops and the observations of plasma dynamics and flows are illustrated. In the modeling section starts some basics of loop physics are provided, supplying some fundamental scaling laws and timescales, a useful tool for consultation. The concept of loop modeling is introduced, and models are distinguished between those treating loops as monolithic and static, and those resolving loops into thin and dynamic strands. Then more specific discussions address modeling the loop fine structure, and the plasma flowing along the loops. Special attention is devoted to the question of loop heating, with separate discussion of wave (AC) and impulsive (DC) heating. Finally, a brief discussion about stellar X-ray emitting structures related to coronal loops is included and followed by conclusions and open questions.Comment: 75 pages, 17 figures, to be published in Living Reviews in Solar Physic

Development of an image guidance system for laparoscopic liver surgery and evaluation of optical and computer vision techniques for the assessment of liver tissue

Introduction: Liver resection is increasingly being carried out via the laparoscopic approach (keyhole surgery) because there is mounting evidence that it benefits patients by reducing pain and length of hospitalisation. There are however ongoing concerns about oncological radicality (i.e. ability to completely remove cancer) and an inability to control massive haemorrhage. These issues can partially be attributed to a loss of sensation such as depth perception, tactile feedback and a reduced field of view. Utilisation of optical imaging and computer vision may be able to compensate for some of the lost sensory input because these modalities can facilitate visualisation of liver tissue and structural anatomy. Their use in laparoscopy is attractive because it is easy to adapt or integrate with existing technology. The aim of this thesis is to explore to what extent this technology can aid in the detection of normal and abnormal liver tissue and structures. / Methods: The current state of the art for optical imaging and computer vision in laparoscopic liver surgery is assessed in a systematic review. Evaluation of confocal laser endomicroscopy is carried out on a murine and porcine model of liver disease. Multispectral near infrared imaging is evaluated on ex-vivo liver specimen. Video magnification is assessed on a mechanical flow phantom and a porcine model of liver disease. The latter model was also employed to develop a computer vision based image guidance system for laparoscopic liver surgery. This image guidance system is further evaluated in a clinical feasibility study. Where appropriate, experimental findings are substantiated with statistical analysis. / Results: Use of confocal laser endomicroscopy enabled discrimination between cancer and normal liver tissue with a sub-millimetre precision. This technology also made it possible to verify the adequacy of thermal liver ablation. Multispectral imaging, at specific wavelengths was shown to have the potential to highlight the presence of colorectal and hepatocellular cancer. An image reprocessing algorithm is proposed to simplify visual interpretation of the resulting images. It is shown that video magnification can determine the presence of pulsatile motion but that it cannot reliably determine the extent of motion. Development and performance metrics of an image guidance system for laparoscopic liver surgery are outlined. The system was found to improve intraoperative orientation more development work is however required to enable reliable prediction of oncological margins. / Discussion: The results in this thesis indicate that confocal laser endomicroscopy and image guidance systems have reached a development stage where their intraoperative use may benefit surgeons by visualising features of liver anatomy and tissue characteristics. Video magnification and multispectral imaging require more development and suggestions are made to direct this work. It is also highlighted that it is crucial to standardise assessment methods for these technologies which will allow a more direct comparison between the outcomes of different groups. Limited imaging depth is a major restriction of these technologies but this may be overcome by combining them with preoperatively obtained imaging data. Just like laparoscopy, optical imaging and computer vision use functions of light, a shared characteristic that makes their combined use complementary

Medical Ultrasound Imaging and Interventional Component (MUSiiC) Framework for Advanced Ultrasound Image-guided Therapy

Medical ultrasound (US) imaging is a popular and convenient medical imaging modality thanks to its mobility, non-ionizing radiation, ease-of-use, and real-time data acquisition. Conventional US brightness mode (B-Mode) is one type of diagnostic medical imaging modality that represents tissue morphology by collecting and displaying the intensity information of a reflected acoustic wave. Moreover, US B-Mode imaging is frequently integrated with tracking systems and robotic systems in image-guided therapy (IGT) systems. Recently, these systems have also begun to incorporate advanced US imaging such as US elasticity imaging, photoacoustic imaging, and thermal imaging. Several software frameworks and toolkits have been developed for US imaging research and the integration of US data acquisition, processing and display with existing IGT systems. However, there is no software framework or toolkit that supports advanced US imaging research and advanced US IGT systems by providing low-level US data (channel data or radio-frequency (RF) data) essential for advanced US imaging. In this dissertation, we propose a new medical US imaging and interventional component framework for advanced US image-guided therapy based on networkdistributed modularity, real-time computation and communication, and open-interface design specifications. Consequently, the framework can provide a modular research environment by supporting communication interfaces between heterogeneous systems to allow for flexible interventional US imaging research, and easy reconfiguration of an entire interventional US imaging system by adding or removing devices or equipment specific to each therapy. In addition, our proposed framework offers real-time synchronization between data from multiple data acquisition devices for advanced iii interventional US imaging research and integration of the US imaging system with other IGT systems. Moreover, we can easily implement and test new advanced ultrasound imaging techniques inside the proposed framework in real-time because our software framework is designed and optimized for advanced ultrasound research. The system’s flexibility, real-time performance, and open-interface are demonstrated and evaluated through performing experimental tests for several applications

Applying Artificial Intelligence Planning to Optimise Heterogeneous Signal Processing for Surface and Dimensional Measurement Systems

The need for in-process measurement has surpassed the processing capability of traditional computer hardware. As Industry 4.0 changes the way modern manufacturing occurs, researchers and industry are turning to hardware acceleration to increase the performance of their signal processing to allow real-time process and quality control. This thesis reviewed Industry 4.0 and the challenges that have arisen from transitioning towards a connected smart factory. It has investigated the different hardware acceleration techniques available and the bespoke nature of software that industry and researchers are being forced towards in the pursuit of greater performance. In addition, the application of hardware acceleration within surface and dimensional instrument signal processing was researched and to what extent it is benefitting researchers. The collection of algorithms that the field are using were examined finding significant commonality across multiple instrument types, with work being repeated many times over by different people. The first use of PDDL to optimise heterogenous signal processing within surface and dimensional measurements is proposed. Optical Signal Processing Workspace (OSPW) is presented as a self-optimising software package using GPGPU acceleration using Compute Unified Device Architecture (CUDA)for Nvidia GPUs. OSPW was designed from scratch to be easy to use with very little-to-no programming experience needed, unlike other popular systems such LabVIEW and MATLAB. It provides an intuitive and easy to navigate User Interface (UI) that allows a user to select the signal processing algorithms required, display system outputs, control actuation devices, and modify capture device properties. OSPW automatically profiles the execution time of the signal processing algorithms selected by the user and creates and executes a fully optimised version using an AI planning language, Planning Description Domain Language (PDDL), by selecting the optimum architecture for each signal processing function. OSPW was then evaluated against two case studies, Dispersed Reference Interferometry (DRI) and Line-Scanning Dispersed Interferometry (LSDI). These case studies demonstrated that OSPW can achieve at least21x greater performance than an identical MATLAB implementation with a further 13% improvement found using the PDDL’s heterogenous solution. This novel approach to providing a configurable signal processing library that is self-optimising using AI planning will provide considerable performance gains to researchers and industrial engineers. With some additional development work it will save both academia and industry time and money which can be reinvested to further advance surface and dimensional instrumentation research

Coded Aperture Imaging: novel approaches to high-energy high-resolution laboratory imaging

Rapid advancement is being made in laser driven x-ray and particle sources, pushing the boundaries in temporal duration, spatial and spectral distribution, and maximum energy. These advancements need to be complimented with development of imaging capabilities, in order to fully characterise and utilise the new source potential. Here, coded apertures are used to investigate novel approaches to high-energy high-resolution aperture based imaging. Firstly, coded aperture theory is applied to high-energy x-ray sources such as those generated using laser wakefield techniques. The coded aperture is compared to a single pinhole aperture, to discuss whether the prior assumption of highly attenuating substrates is required when using coded apertures. The coded aperture with scatter and partial attenuation included, dubbed a `CASPA', is demonstrated with a 511 keV source simulation, showing that the fully attenuating 18~mm thick tungsten substrate for a single pinhole can be replaced with a 250 um thick tungsten CASPA. Furthermore, the thin CASPA is not mechanism specific, and the physical processes behind the scatter and partial attenuation is found to be inconsequential as long as the combined result yields adequate hologram contrast for image decoding to occur. Secondly, an investigation is conducted into imaging with spectral and spatial information for applications such as laser-solid interaction hotspots. Combing coded apertures with Ross pair filters, a banded spectrally-resolving coded aperture is discussed, dubbed a `BaSCA', using multiple non-redundant array designs on a single aperture and single non-spectrally resolving detector. Finally, the application of a CASPA for imaging high-resolution high-energy neutron sources from inertial confinement fusion experiments is discussed. Using the National Ignition Facility at Lawrence Livermore National Laboratory as an example, a CASPA is designed for the 14.1 MeV neutrons, and reconstruction techniques discussed. In comparison to the currently implemented 20 cm thick gold grand array, it is suggested here that a 10 mm tungsten CASPA would suffice - potentially reducing manufacturing costs, increasing ease of implementation and field of view

Virginia Commonwealth University Courses

Listing of courses for the 2019-2020 year