When performing nuclear magnetic resonance (NMR) it is desirable to maximise the available polarisation of the spin system in order to achieve optimal signal-to-noise ratios. One method of achieving this is via the process of spin-exchange optical pumping (SEOP). SEOP can be used to produce hyperpolarised (HP) noble gases, which possess numerous applications in the fields of science and medicine, ranging from spectroscopic imaging of porous media to Magnetic Resonance Imaging (MRI) of the human lungs. The SEOP process involves transfer of angular momentum from circularly polarised laser photons to the electrons of an alkali metal vapour. Noble gas nuclei can then be polarised via collisions with the alkali metal vapour. Ultra-low frequency Raman Spectroscopy may be used to perform rotational temperature measurements of a nitrogen buffer gas in these SEOP experiments in real-time, in an attempt to understand the poorly understood and highly complex system dynamics and energy transport processes. The work contained in this thesis aims to investigate the co-dependence of these dynamics, in order to characterise the SEOP process in greater detail for a variety of gas mixtures, temperatures and alkali metal targets. With this, it is hoped that HP noble gases may be produced with greater efficiency, achieving faster build-up rates and higher net magnetisation. In addition to in situ Raman spectroscopy, additional diagnostic techniques were implemented in order to illustrate the co-dependence of variables during the thermal exchange processes present in SEOP. Low-field NMR spectroscopy was utilised to determine the 129Xe net spin polarisation (P_Xe) as a function of time and position within the SEOP vessel, whilst near-infra-red (NIR) optical absorption spectroscopy allowed an estimate of the alkali metal polarisation and global pump laser power absorption to be determined. Additionally, initial studies into the use of optical absorption spectroscopy at various wavelengths for determination of the alkali metal number density are discussed. A chronology of experiments conducted using an `in-line', optically filtered Raman probe arrangement will be presented, culminating in the development of a fully automated, single-axis translational stage to perform rapid measurement of the rotational nitrogen temperature (T_N2) within the optical pumping cell with a high degree of temporal and spatial precision. The automated nature of the system facilitates a >3-fold improvement in the rate of thermal data acquisition, with greater ease and reliability than the previous manual method. In addition to pure rubidium, rotational temperature determination via Raman spectroscopy is demonstrated in a variety of rubidium/caesium hybrid alloy mixtures. In this way it may be possible to more efficiently utilise the greater spin exchange rate of caesium with 129Xe to achieve hybrid Rb/Cs cross-polarisation. The result of this is the first observation of 129Xe polarisation in a hybrid Rb/Cs system exceeding that of an equivalent pure Rb system under otherwise identical experimental conditions.

<p> One pathway for a new device to gain access to the marketplace requires demonstration that it is equivalent to, or substantially better than, a legally marketed device. To evaluate the equivalence of a medical imaging device, we propose measuring the intra- or inter-reader agreement in a reader study, where the clinicians (readers) make diagnoses on the medical images (cases) using both the new and old imaging devices. Such an endpoint, as well as its variance estimate, enable us to make a statistical inference on the equivalence of two devices. A method for multiple-reader multiple-case agreement analysis was presented in Gallas et al. (2016) for fully-crossed study designs, where every reader reads every case. In practice, having every reader read every case may be impossible when readers have a limited amount of time to participate in the study. One alternative study design is the split-plot study design, where both the readers and the cases are partitioned into a fixed number of groups, and each group of readers reads its own group of cases. In this thesis, we adapt the multiple-reader multiple-case agreement analysis method in Gallas et al. (2016) to analyze split-plot study designs, and propose a new variance estimator based on splitting the analysis across the groups. In each split sub-study, we compute an estimate, and then combine these estimates to obtain the final estimate for the full study. Our numerical studies show that the "split-analysis" variance estimator provides more accurate estimation of the variance of concordance measurements than the full-study-based method for unbalanced split-plot study designs.</p><p>

No description available.

No description available.

A testing method was to he developed based on previous experience on computer tomography. It has been known for some time that an image of a cross-section of an object could be reconstructed using projections or scans at different angles describing 180 degrees around the cross-section. Sound velocity, attenuation and sound reflection are the parameters used in ultrasonic computerised-tomography. The object under investigation in this work is a cylinder of acoustic properties like plastic enclosed in a steel casing. The task was to find defects in the cylinder and these defects were of a nature such, that echoes received from them are low and therefore the pulse echo technique cannot be used in their detection. A reconstruction method, based on the "Algebraic Reconstruction Techniques" (ART) is used here to detect these defects. The main achievements are that these recionstructions are obtained from constrained-scans, due to total reflection of ultrasound near the edge of the field, and a technique of obtaining an image with no background speckles. square An extensive computer simulation was done using a mathematical model of the object, which generated scan data similar to that obtained by actual experiment. Different processing techniques were tried to improve the image quality and testing reliability especially to remove the above mentioned problems. A successful method was chosen such that it will be easy to implement in a real testing situation. Successive marking of defect-free areas of the different scans resulted in a well defined defect structure. No-scan areas were identified by experiment and both the no-scan areas due to total reflection and those due to different modes of propagation received the same treatment. Using a marking technique together with the known coordinates of these areas an integrated image was obtained. The implementation of the system was done using a microcomputer together with a commercial flaw detector. The flaw detector was coupled to a digital counter to measure the transit time. The datawere acquired by interfacing the counter to the microcomputer. Data acquisition, control and processing together with the reconstruction programme constituted the software which was developed for this system.

The research described in this thesis involves the development of a video coding scheme which provides lossless Region Of Interest (ROl) coding specifically targeted toward the compression of thermal video sequences. In particular the scheme is designed to provide lossless coding of critical temperature data contained in thermal video sequences used within firefighting applications. High coding efficiency is achieved by the use of Discrete Cosine Transform (DCT) based lossy coding for non-critical areas of the video sequence. The research is divided into three key sections; an investigation into thermal video, the practical development of a novel scheme for selective lossless compression of thermal video containing critical temperature data, and the presentation and analysis of test results which demonstrate the effectiveness of the scheme. The scheme's multi-pass encoder stores data which enables the recovery of the losses which occur within critical thermal data as a result of the lossy DCT coding stage. This error recovery data is stored as codewords where each individual codeword is used to represent the error data for up to two pixels within the ROI. Efficient entropy coding of the error recovery data is achieved through a combination of a new adaptive reordering scheme followed by Run Length Coding (RLC) and Variable Length Coding (VLC). By storing these error recovery codes within the normally unused colour channels of a compressed video sequence, the compressed thermal video sequence can be transmitted as an MPEG-1, MPEG-2 and MPEG4 compliant bitstream. This novel storage mechanism allows the error recovery codes to be spatially mapped to the ROl data, and hence the scheme can benefit from the motion compensation facilities provided within the MPEG compliant bitstream. Decoding of the lossy video sequence can be carried out using any MPEG compliant decoder. Lossless ROl decoding can be carried out using the special decoder described in, and provided with, the thesis.

Coherent anti-Stokes Raman scattering (CARS) microscopy is considered as a powerful tool for non-invasive chemical imaging of biological samples. CARS microscopy provides an endogenous contrast mechanism that it is sensitive to molecular vibrations. CARS microscopy is recognized as a great imaging system, especially in vivo experiments since it eliminates the need for the contrast agents. In this thesis, CARS microscopy/spectroscopy is built from scratch by employing a single (Ti-Sapphire) laser source generating 65 femtosecond laser pulses centered at 800 nm wavelength. Two closely lying zero dispersion photonic crystal fiber (PCF) is used to generate the supercontinuum for the Stokes beam to generate CARS at 2885 cm-1 to match lipids rich vibrational frequency. XY galvanometers are used for laser raster scanning across the sample. The initial generation of CARS signal was in the forward direction. After guaranteeing a strong CARS signal, images for chemical and biological samples were taken. To achieve a multimodal imaging technique, CARS microscopy imaging system is combined with two- photon excitation fluorescent (TPEF) and second harmonic generation (SHG) imaging techniques, where various information was extracted from the imaged samples. Images with our CARS microscopy show a good resolution and sensitivity. The second part of my work is to reduce the footprint for this setup to make it more suitable for use in clinical applications. For that reason, I integrated a homebuilt endoscope and all fiber femtosecond laser source together to get a fiber based imaging system. Proof of principal for the integrated system is achieved by obtaining a reasonable agreement in accuracy and resolution to those obtained by the endoscope driven by Ti-sapphire laser.

Automatic image registration is the technique to align images in different coordinate systems to the same coordinate system which has found wide industrial applications for control automation and quality inspection. Focusing on the industrial applications where product models are available and transformations between models and images are global, this thesis presents the research works on two registration problems based on different features and different transformation models. The first image registration problem is a 2D/2D one with a 2D similarity transformation and based on geometric primitives selected from models and extracted from images. Featured-based methods using geometric primitives like point, line segment and circle have been widely studied. This thesis proposes a number of novel registration methods based on elliptic features, which include a point matching algorithm based on local search method for ellipse correspondence search and rough pose estimation, a numerical approach to refine the estimation result by using the non-overlapping area ratio (NAR) of corresponding ellipses and an elliptic are matching algorithm based on integral of squared distances (JSD) between points on corresponding arcs. The major advantage of JSD is that its optimal solution can be obtained analytically, which makes it applicable to efficient elliptic arc correspondence search. The second image registration problem is a 3D/2D one with an orthographic projection transformation and based on silhouette features. A novel algorithm has been developed and presented in this thesis based on a 3D triangular-mesh model, which can be applied to approximate a de facto NURBS model, and images in which silhouette features can be extracted. The algorithm consists of a rough pose estimation process with shape comparison methods and a pose refinement process with 3D/2D iterative closest point (ICP) method. The computer simulation results show that the algorithm can perform very effective and efficient 3D/2D registration.

Gamma rays may Interact with matter by a variety of processes, many of which give rise to secondary radiations. This thesis examines the possibility of performing tomographic imaging by means of these secondary photons using low-cost apparatus. The techniques are compared with each other and with transmission tomography, which plays such an Important role in modern diagnostic imaging. The progress of industrial tomography is reviewed as are techniques of Investigation using gamma ray scattering in both industry and medicine. Some new applications of a simple gamma ray CT scanner have been performed. A method of determining the spatial distribution of pure beta emitters in matter by performing tomographic imaging using the bremsstrahlung radiation produced by the beta particles has been demonstrated. This technique has been shown to permit imaging at depths in material greatly exceeding the range of beta particles in matter. All the imaging techniques using secondary radiation have displayed two principal limitations: long scanning times and poor quantitative accuracy. The low scanning rate results from the small number of secondary photons that are detected. The major contributing factors to poor accuracy are attenuation and the noise produced by unwanted in-scattering. The possible applications for secondary photon imaging have been briefly outlined and some suggestions for future work are included, Although techniques based upon Imaging using secondary radiation will not be able to compete with transmission CT in the vast majority of applications, they may prove valuable in a range of specialised fields.

Scattering from X-ray Mirrors deals with the the phenomena observed when x-rays are reflected from high quality mirror surfaces at grazing incidence. The presence of micro- irregularities in the reflecting surface causes power to be deviated away from the specular direction and into the wings of the angular distribution of radiation. Both theoretical and experimental investigations are presented. The two principal theories of the scattering of electromagnetic radiation are reviewed and are shown to produce identical results in the smooth surface limit. The scalar theory is further developed so as to be applicable to a scattering surface which can be described by an arbitrary surface height distribution function for any surface autocovariance function. The theoretical advances reported suggest a means by which the surface height distribution statistics of mirror surfaces might be derived from experimental scattering measurements. The experimental work in the thesis deals with a scattering experiment designed to test these theoretical developments. The development work involved in the construction of the Variable Angle Scattering Experiment (VASE) is presented and the anomalous results obtained from scattering measurements from two test flat x-ray mirrors are discussed. A shadowing model is devised to account for the anomalous results from the VASE. The shadowing model is then shown to be in good agreement with the VASE data and with data from other scattering experiments. The shadowing model, which provides a means of measuring the properties of pure mirror surfaces, is further developed to enable measurements of surface structure on mirrors which have become specked with small sparse contaminant features, thus allowing highly sensitive estimates of contaminant density and height to be made.