An investigation of the imaging performance of CCD based x-ray detectors for digital mammography

This thesis describes the imaging performance of a prototype digital mammography system based upon charge coupled devices (CCDs). The imaging performance of these detectors is dependent upon the configuration of the detector. In this thesis the performance of 14 different detector configurations are studied for use in digital mammography. Experimental evaluations of factors which affect the performance of imaging systems such as quantum detection efficiency, dynamic range, modulation transfer function (MTF(f)) and Noise power spectrum (NPS) were performed. The use of spatial frequency dependent detective quantum efficiency DQE(f) to characterise the detectors in terms of signal to noise ratio transfer is described. It is shown that direct interactions of x-rays in the CCD act to reduce DQE(f) at high spatial frequencies and severely impair the detectors ability to detect small objects (250|im in diameter). The use of a sufficient thickness of fibre optic faceplate to couple the phosphor layer to the CCD is shown to remove these interactions and shows a corresponding increase in DQE(f) (at higher spatial frequencies) and the detector's ability to image smaller objects A subjective comparison of images of a breast phantom shows that images of superior quality were obtained with the prototype system compared with images produced using a conventional film-screen system, for a slight increase in dose. Improvements to the system and detector design are presented and will act to try to produce the same image quality for equivalent doses used in conventional mammography

Cardiac resynchronization therapy : advances in optimal patient selection

Despite the impressive results of cardiac resynchronization theraphy (CRT) in recent large randomized trials a consistent number of patients fails to improve following CRT implantation when the established CRT selection criteria (NYHA class III-IV heart failure, LV ejection fraction __35 % and QRS duration > 120 ms) were applied. For example, close analysis of the data from the MIRACLE trial revealed that 32% of patients did not improve or even worsened in NYHA class after 6 months of CRT. The presence of clinical non-responders to CRT has now been confirmed in several other studies and is usually around 30%. In addition, if response to CRT is defined using more objective parameters such absence of LV reverse remodeling or lack of improvement in LV ejection fraction on echocardiography at mid-term follow-up the number of non-responders is usually between 40-50%. In view of the unnecessary procedure risks and health care expenses in patients without response to CRT the percentage of non-responders among patients selected according to the current selection criteria is unacceptably high and should be reduced. Aim of the thesis: The relatively high number of patients without benefit from CRT (referred to as non-responders) indicates the need for refinement of the current selection criteria in order to 1] better identify those patients with the highest likelihood of response to CRT and 2] avoid device implantations in patients that are unlikely to respond to CRT. The aim of the current thesis was to improve and refine the current CRT selection criteria through the evaluation of the mechanismus underlying (non-) response to CRT.UBL - phd migration 201

K-edge Radiography and applications to Cultural Heritage

The present work of thesis is focused on application of X-ray K-edge technique to paintings. This technique allows one to achieve a topographic map of a pigment on the whole surface of the painting. The digital acquisition of radiographic images by using monochromatic X-ray beams allows to take advantage of the sharp rise of X-ray absorption coefficient of the elements, the K-edge discontinuity. Working at different energies, bracketing the K-edge peak, allows recognition of the target element. The K-edge radiography facility installed at Larix Laboratory, at Department of Physics in Ferrara, consists of a quasi-monochromatic X-ray beam obtained via Bragg diffraction on a mosaic crystal from standard X-ray source. In this work the K-edge technique and the facility used are illustrated. A characterization of the monochromatic beams in the energy range 7-40 KeV range and the elemental mapping on pictorial layers obtained are presented. At the end, a transportable facility for digital radiography is presented and some radiographic analysis of works of art performed are shown

Improvements to MOS CCD technology for future X-ray astronomy missions

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.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

Characterisation of cardiac structure and function in late adolescence and modification by adiposity and other cardiovascular risk factors

Cardiovascular disease remains one of the leading causes of death worldwide. However, a large proportion of research in the field focuses primarily on middle- to old- age, by which time much damage to the heart and vascular system has been incurred. The rationale for this research was to gain a clearer picture of cardiovascular health in late adolescence, prior to the onset of adulthood. In this thesis I characterise the cardiac structure and function of individuals from the ALSPAC cohort (average age 17.7 years) through analysing M-Mode, two dimensional and Doppler echocardiographic measures and haemodynamic, biochemical and anthropometric measures. Adiposity, sex and genetic predisposition are considered as key exposures which impact a range of cardiovascular outcomes. I consider the relationships of fat mass and lean mass with cardiovascular outcomes and the ways in which left ventricular mass indexation is affected by adiposity, lean mass, height and body surface area. I then discuss the roles which particular haemodynamic and biochemical biomarkers have in mediating associations between fat mass and left ventricular structural and functional outcomes. Finally I consider the influence which genes associated with body mass index have on key cardiovascular measures, including cardiac structural and functional measures. Adiposity has a direct and detrimental effect on cardiovascular health. My findings provide insights into the way in which adiposity affects the development of an adverse cardiometabolic phenotype from a comparatively young age and also have interesting implications for future research. Furthermore, they serve as another important reminder of the need for adiposity to be monitored throughout the life course

Steering electronics, module design and construction of an all silicon DEPFET module

High energy physics experiments require detectors with an excellent imaging performance. The innermost part is often a pixel vertex detector with 2D position readout. The DEPFET pixel detector is an option for the International Linear Collider and will be used in the Belle II experiment at the SuperKEKB accelerator in Japan. Two barrel layers will be installed in a very confined space and hence, a dense packaging of sensors, read-out and steering chips is mandatory. A hard radiation environment is influencing the electronics at the location close to the interaction point. The steering chips are controlling the DEPFET imaging devices. They need to provide fast signals to read-out the large sensitive areas in a high speed. Two generations of steering chips are characterized and tested for their radiation hardness in this work. A converter chip was designed to operate the read-out chip stand-alone, until the data compression chip is ready. The DEPFET detector modules will be build in the novel all-silicon approach, where the read-out and steering chips are mounted upside down directly onto the detector silicon. The silicon area is also used to interconnect the chips with the imaging devices and the cables. A thinned sensor area reduces the negative influences of the material on the particle tracks, but results in fragile devices. A flip-chip interconnection technology connects the chips to the detector and builds the all-silicon module. The technology has to be compatible with the thin and fragile DEPFET devices. Different flip-chip methods are evaluated in this dissertation. Many processes are only feasible for mass production and can’t adopt to the flexibility requirements in research and development. Two processes, the gold-stud and solder ball bumping, meet the requirements and were deployed in the scope of this work. Several test prototypes have been successfully built with these processes. Interconnecting the flip-chip mounted chips with the DEPFET array and the off-module cable connection on the detector modules is a further task addressed in this work. The special DEPFET technology limits the design complexity of the chip interconnection. A high power consumption of the read-out chips and the dense packaging of chips on the module are increasing the complexity furthermore. In summary, this work has provided an important contribution to the development of the novel high resolution DEPFET vertex detector concept and has advanced the construction of the Belle II pixel vertex detector