No description available.

No description available.

Several medical imaging techniques are capable of producing tomographic images, corresponding to cross-sections through the body. A stack of adjacent sections contains three dimensional information about the organs of interest, and this can be presented on a two dimensional screen using shaded surface techniques. In order to facilitate the routine use of such images, algorithms and techniques were developed on a conventional medical imaging computer system in a hospital environment. Several object representation schemes were compared, and two new schemes were devised. The 'solid binary object' technique facilitated exploration of the interior of an object, while the 'ordered surface list' technique enabled real time display of object surfaces. Several shading algorithms were compared, and a local polynomial fitting routine was devised. This was found to be superior to other methods using objective evaluation of the accuracy of surface normal estimations, and subjective evaluation of the corresponding image appearance. The techniques developed were applied to a variety of data obtained using xray computed tomography, nuclear magnetic resonance and emission computed tomography. For display of myocardial tomograms, a technique was devised for superposition of colour coded coronary arteries, showing their relationship to observed perfusion defects. For display of time varying images of the heart, a rapid display routine was developed to enable ventricular wall motion to be evaluated from any angle. Colour display techniques were also applied to this data to produce single images which incorporated kinetic as well as morphological information. The results obtained have confirmed that shaded surface images can be produced using computers currently available in hospital imaging departments. Interactive object modification and real time object display can be achieved without requiring special hardware.

This thesis is concerned with the development of MOS charge-coupled device (CCD) technology for future applications in X-ray astronomy. Of particular interest is increased detection efficiency of high energy X-ray photons and increased pixel readout speed for large area sensors. Chapter 2 reviews the generation of X-rays, methods for extra-terrestrial X-ray observations, detectors and provides an overview of X-ray astronomy missions. Chapter 3 discusses the CCD and introduces some of the recent technological developments that improve their overall performance for optical and X-ray photon detection. Chapter 4 presents the basic laboratory equipment and methods used to carry out the experimental work of this thesis. Chapter 5 presents the characterisation of new high resistivity devices that were manufactured by e2v technologies during the work of this thesis. Chapter 6 describes a method for estimating the depletion depth of a CCD by analysing the X-ray event patterns that are generated in CCD image data. Chapter 7 presents the equipment developed and experimental measurements taken to evaluate the high energy X-ray quantum efficiency of a high resistivity CCD. Finally, Chapter 8 describes the ongoing development and characterisation of low noise ASICs that are intended for use in future X-ray astronomy missions.

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No description available.

In computed radiography (CR) images, dose reduction up to 0.10 mGy is possible in chest radiography without image manipulation.  A lower dose of 0.06 mGy can be achieved when image manipulation is used for detection of lesions in the mediastinum.  Both clarity and detectability in the mediastinum improved by between 48 to 66% with image manipulation.  Abdominal images showed a significant difference at 2.69 mGy for the soft tissue area, suggesting caution in further dose reduction.  Image quality in the spinal area was improved significantly by 21 – 78.6% (for clarity) and 3 to 77% (for detectability) when image manipulation was employed. Comparatively, the image quality at the low doses studied was better for the film screen radiography than both processed and unprocessed CR images suggesting that low doses achieved in FSR may not be applicable to CR.  This difference may be attributed to the differences in the image receptors’ response to high photon energies, and the reduced number of x-ray quanta which produce lower subject contrast in FSR and reduced signal to noise ratio (SNR) as a result of increased noise in CR. Nigerian clay in its natural and salted forms cannot be used in radiation dosimetry in diagnostic radiology.  Paraffin wax/MgSO₄.6H₂0, and rice-gelatine (<i>rigel</i>) combinations as well as rice and gelatine used separately, have shown tissue equivalent x-ray attenuation at tube potentials above 80 kVp.  Paraffin wax/MgSO₄.6H₂0 and <i>rigel </i>can therefore be used as tissue substitutes.  Low patient entrance surface doses achieved in FSR may not produce equivalent image quality when applied to imaging with CR systems.  With respect to dose reduction, both modalities show the possibility of further dose reduction below current dose values by about 40% (chest) and 20% (abdomen), respectively, when used alone.

Fast Field-Cycling (FFC) MRI allows the magnetic field to be switched during an imaging scan. FFC-MRI can be used to exploit a characteristic of contrast agents, i.e. the variation of its spin-lattice relaxation time (T1) or rate (R1= 1/T1) with magnetic field in order to increase contrast. Contrast agents play an essential role in MRI, allowing improved diagnosis and delineation of diseased tissue. However, the R1, and hence the effectiveness of contrast agents, varies significantly with magnetic field. Thus, Fast Field-Cycling (FFC) MRI can be used to take advantage of this variation to improve image contrast, allowing more sensitive detection of the agent. In this project new contrast agents, developed by a collaborating group (Invento S.r.l., Italy) were investigated for use with FFC-MRI. R1 dispersion curves of samples containing a range of contrast agents were first obtained using both a commercial relaxometer and a home-built whole-body FFC-MRI system, and the accuracy of the home-built FFC-MRI system was verified. The magnetisation behaviour of these samples during field-cycling pulse sequences was modelled in order to predict the pulse sequence parameters necessary for maximum T1 contrast. Images were obtained, using a number of novel imaging techniques developed on the home-built whole-body FFC-MRI system, and also, using standard T1 weighted imaging on a 3 T Philips clinical MRI scanner. A new FFC-MRI imaging method, ΔR1 mapping was employed to show an increase in contrast using a novel Mn2+ based liposomal contrast agent compared with T1 weighted images at 5 mT, 59 mT and 3 T. The low concentrations of Mn2+ based liposomal contrast agents used with ΔR1 mapping indicate suitability for molecular imaging

Magnetisation Transfer Contrast (MTC) is a well-established magnetic resonance imaging (MRI) contrast-generating mechanism, and is widely used for clarifying MR-invisible macromolecular information indirectly via MR-detectable free protons using an offresonance pre-saturation radiofrequency (RF) pulse (or MT pulse). As a result of MT pulse irradiation, magnetisation between both proton pools is exchanged and the signal intensity of mobile protons is decreased in relation to the amount of macromolecules. MTC MRI is normally implemented at a fixed magnetic field; however, it may be useful to evaluate changes of the MT effect as a function of magnetic field (B0). In order to explore fielddependent MTC experiments using a single MR instrument, two techniques are required, which enable simultaneously shifting both B0 and the resonance frequency of an RF coil (f0) during MT pulse irradiation and returning them to the original condition during MR data acquisition. Switching of B0 is achieved by fast field-cycling (FFC). FFC is a novel technique allowing B0 to shift between levels rapidly during the pulse sequence. This makes it possible to perform a number of beneficial field-dependent studies and/or to provide new MR contrast mechanisms. Switching of f0 requires an actively frequencyswitchable RF coil. This coil was designed and constructed for frequencies at and below 2.5 MHz proton Larmor frequency. The design employed PIN diodes, and enabled switching f0 between five different values. Using these techniques and tools, fielddependent MTC experiments were carried out with a control sample and samples with different concentrations of agarose gel. Due to the absence of macromolecules in the control, the MT effect was almost zero, whereas the MT effect observed in agarose samples increased with increasing concentration of macromolecules. Furthermore, MT effects ((for a given set of MT pulse conditions) were larger at higher B0.

This thesis details the development of a novel microwave breast imaging system based on a faceted metallic chamber using magnetic field data in an air background. The chamber is simulated showing benefits over a cylindrical chamber. The use of magnetic scattered-field data collected on the inner surface of the chamber is shown to provide better reconstruction results compared to electric field data for breast tissue phantoms. Shielded half-loop probes are selected for use in the new system and prototypes are constructed. These probes are sensitive to magnetic fields and reject electric fields. An experimental faceted chamber is also constructed and used with the probes to image simple homogeneous targets as well as a simple breast phantom. Several possible measurement techniques and calibration methods for the new system are analyzed. Tumour detection in the simple breast phantom in an air background is achieved, validating the performance of the novel system. / February 2017