Diffraction Enhanced X-ray Imaging (DEI) uses synchrotron X-ray beams prepared and analyzed by perfect single crystals to achieve imaging contrast from a number of phenomena taking place in an object under investigation. The crystals used in DEI for imaging requires high precision positioning due to a narrow rocking curve. Typically, the angular precision required should be on the order of tens of nanoradians.<p>One of the problems associated with DEI is the inability to control, set, and fix the angle of the analyzer crystal in relation to the beam exiting the monochromator in the system. This angle is used to interpret the images acquired with an object present and the usual approach is to determine where the image was taken after the fact. If the angle is not correct, then the image is wasted and has to be retaken. If time or dose is not an issue, then retaking the image is not a serious problem. However, since the technique is to be developed for live animal or eventually human imaging, the lost images are no longer acceptable from either X-ray exposure or time perspectives.<p>Therefore, a mechanical positioning system for the DEI system should be developed that allows a precise setting and measurement of the analyzer crystal angles. In this thesis, the fundamental principles of the DEI method, the DEI system at the National Synchrotron Light Source (NSLS) and the sensitivity of the DEI system to vibration and temperature has been briefly studied to gain a better understanding of the problem. The DEI design at the NSLS was analyzed using finite element analysis software (ANSYS) to determine the defects in the current design which were making the system dimensionally unstable. Using the results of this analysis, the new analyzer support was designed aiming to eliminate the problems with the current design. The new design is much stiffer with the natural frequency spectrum raised about eight times. <p> This new design will improve the performance of the system at the National Synchrotron Light Source (NSLS) of Brookhaven National Laboratory, New York, USA and should assist in the development of a new DEI system for the Bio-Medical Imaging and Therapy (BMIT) beamline at the Canadian Light Source (CLS), Saskatoon, CANADA.

This work investigates the design, system integration, optimization, and evaluation of amorphous silicon (a-Si:H) active matrix flat panel imagers (AMFPI) for bio-medical applications. Here, two hybrid active pixel sensor (H-APS) designs are introduced that improve the dynamic range while maintaining the desirable attributes of high speed and low noise readout. Also presented is a systematic approach for noise analysis of thin film transistors (TFT) and pixel circuits in which circuit analysis techniques and TFT noise models are combined to evaluate circuit noise performance. We also explore different options of system integration and present measurement results of a high fill-factor (HFF) array with segmented photodiode.

This work investigates the design, system integration, optimization, and evaluation of amorphous silicon (a-Si:H) active matrix flat panel imagers (AMFPI) for bio-medical applications. Here, two hybrid active pixel sensor (H-APS) designs are introduced that improve the dynamic range while maintaining the desirable attributes of high speed and low noise readout. Also presented is a systematic approach for noise analysis of thin film transistors (TFT) and pixel circuits in which circuit analysis techniques and TFT noise models are combined to evaluate circuit noise performance. We also explore different options of system integration and present measurement results of a high fill-factor (HFF) array with segmented photodiode.

Diffraction Enhanced X-ray Imaging (DEI) uses synchrotron X-ray beams prepared and analyzed by perfect single crystals to achieve imaging contrast from a number of phenomena taking place in an object under investigation. The crystals used in DEI for imaging requires high precision positioning due to a narrow rocking curve. Typically, the angular precision required should be on the order of tens of nanoradians.<p>One of the problems associated with DEI is the inability to control, set, and fix the angle of the analyzer crystal in relation to the beam exiting the monochromator in the system. This angle is used to interpret the images acquired with an object present and the usual approach is to determine where the image was taken after the fact. If the angle is not correct, then the image is wasted and has to be retaken. If time or dose is not an issue, then retaking the image is not a serious problem. However, since the technique is to be developed for live animal or eventually human imaging, the lost images are no longer acceptable from either X-ray exposure or time perspectives.<p>Therefore, a mechanical positioning system for the DEI system should be developed that allows a precise setting and measurement of the analyzer crystal angles. In this thesis, the fundamental principles of the DEI method, the DEI system at the National Synchrotron Light Source (NSLS) and the sensitivity of the DEI system to vibration and temperature has been briefly studied to gain a better understanding of the problem. The DEI design at the NSLS was analyzed using finite element analysis software (ANSYS) to determine the defects in the current design which were making the system dimensionally unstable. Using the results of this analysis, the new analyzer support was designed aiming to eliminate the problems with the current design. The new design is much stiffer with the natural frequency spectrum raised about eight times. <p> This new design will improve the performance of the system at the National Synchrotron Light Source (NSLS) of Brookhaven National Laboratory, New York, USA and should assist in the development of a new DEI system for the Bio-Medical Imaging and Therapy (BMIT) beamline at the Canadian Light Source (CLS), Saskatoon, CANADA.

The development of a non-invasive method of visualizing gene expression in larger animals could revolutionize some aspects of gene research by opening up a wider variety of animal systems to explore; some of which may be better models of human systems. Presently, most gene expression studies employ Green Fluorescent Protein (GFP) transfected into the genome of the animal system. For larger animals, an x-ray equivalent of GFP would be desirable due to the high penetrating power of x-rays. A model gene modification system is to use the Sodium (Na) Iodide Symporter (NIS) which will cause the accumulation of iodine in cells which express the NIS. To non-invasively observe the dilute iodine accumulated by the cancer cells transfected with NIS in the head of small animals, such as a rat, two synchrotron-based imaging methods were studied: K-Edge Subtraction (KES) imaging and Fluorescence Subtraction Imaging (FSI).<p> KES needs wide monochromatic x-ray beams at two energies bracketing the K-edge of the contrast agent existing or injected in the tissues. The monochromatic beam in the synchrotron facility normally is prepared by a double crystal monochromator. The appearance of the azimuthal angle (tilt error) in the double crystal monochromator creates intensity variations across the imaging field. This misalignment was studied through another two synchrotron-based imaging methods, Diffraction Enhanced Imaging (DEI) and Multi-Image Radiography (MIR), which show this problem clearly in their processed images. The detailed analysis of the effect of the tilt error, how it affects the resulting images, and how to quantify such an error were presented in the thesis. A post processing method was implemented and the artifacts caused by the improper experimental settings were discussed.<p> With the wide monochromatic beam prepared by the double crystal monochromator, a sequence of KES experiments were done and the detection limit of KES was quantified at a projected amount of 17.5mM-cm iodine in a physical model of a rat head with a radiation dose of 2.65mGy. With the raster scan of the object relative to the monochromatic pencil beam, FSI was studied to obtain higher Signal to Noise Ratio (SNR) for local area and better detection limit compared to KES. The detection limit of FSI was measured as a projected amount of 2.5mM-cm iodine in the same physical rat head with a tolerable radiation dose of 24mGy. According to the comparison of these two imaging techniques with references to imaging time and area, radiation dose, spatial resolution, and SNR, it was concluded that these two imaging techniques can be used complementarily in imaging dilute contrast material. Due to the short imaging time and large imaging area, KES is used first to provide a global view of the object, locate the area of interest, do the preliminary diagnosis, and decide whether the further FSI is necessary. Due to its high SNR for the dilute sample, FSI can be used when the area of interest is known. The combination of these two imaging techniques will be very promising and powerful. To facilitate the comparison of KES and FSI, a quality factor was developed to evaluate the performance of the imaging system.<p> The measured detection limits in our experiments are far beyond the thyroidal iodine concentration of a rat (around 1mM). To further improve the performance of KES, a bent Laue crystal monochromator was designed to do the simultaneous iodine KES imaging which overcomes the artifacts in the iodine image caused by the temporal difference for a single set of images. The designed monochromator can provide two separated x-ray beams bracketing the K-edge of iodine at the same time with a very high spatial resolution which is only depends on the source size, a very high energy resolution which can almost compete with that of the double crystal monochromator, and an acceptable photon flux.

<p>The High Intensity Gamma-ray Source (HIGS) at Duke University is a world class Compton light source facility. At the HIGS, a Free-Electron Laser (FEL) beam is Compton scattered with an electron beam in the Duke storage ring to produce an intense, highly polarized, and nearly monoenergetic gamma-ray beam with a tunable energy from about 1 MeV to 100 MeV. This unique gamma-ray beam has been used in a wide range of basic and application research fields from nuclear physics to astrophysics, from medical research to homeland security and industrial applications.</p><p>The capability of accurately predicting the spatial, spectral and temporal characteristics of a Compton gamma-ray beam is crucial for the optimization of the operation of a Compton light source as well as for the applications utilizing the Compton beam. In this dissertation, we have successfully developed two approaches, an analytical calculation method and a Monte Carlo simulation technique, to study the Compton scattering process. Using these two approaches, we have characterized the HIGS beams with varying electron beam parameters as well as different collimation conditions. Based upon the Monte Carlo simulation, an end-to-end spectrum reconstruction method has been developed to analyze the measured energy spectrum of a HIGS beam. With this end-to-end method, the underlying energy distribution of the HIGS beam can be uncovered with a high degree of accuracy using its measured spectrum. To measure the transverse profile of the HIGS beam, we have developed a CCD based gamma-ray beam imaging system with a sub-mm spatial resolution and a high contrast sensitivity. This imaging system has been routinely used to align experimental apparatus with the HIGS beam for nuclear physics research. </p><p>To determine the energy distribution of the HIGS beam, it is important to know the energy distribution of the electron beam used in the collision. The electron beam energy and energy spread can be measured using the Compton scattering technique. In order to use this technique, we have developed a new fitting model directly based upon the Compton scattering cross section while taking into account the electron-beam emittance and gamma-beam collimation effects. With this model, we have successfully carried out a precise energy measurement of the electron beam in the Duke storage ring. </p><p>Alternatively, the electron beam energy can be measured using the Resonant Spin Depolarization technique, which requires a polarized electron beam. The radiative polarization of an electron beam in the Duke storage ring has been studied as part of this dissertation program. From electron-beam lifetime measurements, the equilibrium degree of polarization of the electron beam has been successfully determined. With the polarized electron beam, we will be able to apply the Resonant Spin Depolarization technique to accurately determine the electron beam energy. This on-going research is of great importance to our continued development of the HIGS facility.</p> / Dissertation

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<p>The Swedish field of digital X-ray imaging has since several years relied heavily on distributed information systems and digital storage containers. </p><p>To ensure accurate and safe radiological reporting, Swedish software-firm eCare AB delivers a system called Feedback—the first and only quality assurance IT support product of its kind. This thesis covers several aspects of the design and implementation of future versions of this software platform. </p><p>The focus lies on distributed directory services and models for secure and robust data propagation in TCP/IP networks. For data propagation, a new application, InfoBroker, has been designed and implemented to facilitate integration between Feedback and other medical IT support systems. The directory services, introduced in this thesis as the Feedback Directory Services, have been designed on the architectural level. A combination of CORBA and Java Enterprise Edition is suggested as the implementation platform.</p>

Digital radiography systems are important diagnostic tools for modern medicine. The images are produced when x-ray sensitive materials are coupled directly onto the sensing element of the detector panels. As a result, the size of the detector panels is the same size as the x-ray image. An alternative to the modern DR system is to image the x-ray phosphor screen with a lens onto a digital camera. Potential advantages of this approach include rapid readout, flexible magnification and field of view depending on applications. We have evaluated lens-coupled DR systems for the task of signal detection by analyzing the covariance matrix of the images for three cases, using a perfect detector and lens, when images are affected by blurring due to the lens and screen, and for a signal embedded in a complex random background. We compared the performance of lens-coupled DR systems using three types of digital cameras. These include a scientific CCD, a scientific CMOS, and a prosumer DSLR camera. We found that both the prosumer DSLR and the scientific CMOS have lower noise than the scientific CCD camera by looking at their noise power spectrum. We have built two portable low-cost DR systems, which were used in the field in Nepal and Utah. We have also constructed a lens-coupled CT system, which included a calibration routine and an iterative reconstruction algorithm written in CUDA.

The most promising technology for radiography is active matrix flat panel imaging systems (AMFPI). However, AMFPI systems are relatively expensive in comparison with conventional computed radiography (CR) systems. Therefore for general radiography applications low cost systems are needed, especially in hospitals and healthcare systems of the developing countries. The focus of this research is the fabrication and characterization of a low cost amorphous silicon metal-semiconductor-metal photodetector as a photosensitive element in a AMFPI systems. Metal-Semiconductor-Metal photodetectors (MSM-PD) are attractive as sensors due to their ease of fabrication and compatibility with thin film transistor fabrication process primarily because there is no p+ doped layer in comparison with conventional p-i-n photodiodes. We have reported low dark current lateral a-Si MSM-PD (lower than 20pA/mm2 ) with responsivity of 280mA/W and EQE of 65 percent to green light ( l = 525nm). These improvement are achieved by introduction of a PI blocking layer and operating the device at high electric field (15 V/µm). This new structure eliminates the need of p+ and n+ layers which makes this structure fully compatible with the a-Si:H TFT fabrication process and consequently a low cost flat panel imager. Further, in this study we have investigated the effect of the spacing and width of the comb structure in the proposed lateral a-Si MSM-PD to determine the best configuration. Moreover, a-Si MSM-PD with PI blocking layer shows a linear behaviour to the photon flux in the wide range of 200nW/cm2 - 300µW/cm2 intensity of the incoming light. In comparison to vertical p-i-n structures, the reported MSM lateral device shows gains in terms of dynamic range, ease of fabrication (no p+ layer) without any deterioration in EQE and responsivity. This results are promising and encourage the development of a-Si lateral MSM-PD for indirect conversion large area medical imaging applications and especially low cost flat.