Dynamic Contrast Enhanced Computed Tomography is an imaging tool that aids in evaluating functional characteristics in different stages of disease assessment: diagnostic, treatment effectiveness and monitoring. At the present time, following all the technological advances, there remains no universally validated method of quantitative, non-invasive, perfusion imaging. In order to address this challenge, certain quality assurance flow phantoms have been developed. This work presents the first step in the prospective framework of phantom simulations with the goal of enhancing the understanding of contrast agent kinetics. Existing knowledge about a two-compartmental fluid exchange phantom was used to validate the constructed computational fluid dynamics (CFD) simulation model. The sensitivity of various parameters, both in the geometric and computational domains, was determined. Finally, the model was employed to evaluate current perfusion parameter estimation models. This provides the groundwork for future phantom developments within the framework.

Dynamic Contrast Enhanced Computed Tomography is an imaging tool that aids in evaluating functional characteristics in different stages of disease assessment: diagnostic, treatment effectiveness and monitoring. At the present time, following all the technological advances, there remains no universally validated method of quantitative, non-invasive, perfusion imaging. In order to address this challenge, certain quality assurance flow phantoms have been developed. This work presents the first step in the prospective framework of phantom simulations with the goal of enhancing the understanding of contrast agent kinetics. Existing knowledge about a two-compartmental fluid exchange phantom was used to validate the constructed computational fluid dynamics (CFD) simulation model. The sensitivity of various parameters, both in the geometric and computational domains, was determined. Finally, the model was employed to evaluate current perfusion parameter estimation models. This provides the groundwork for future phantom developments within the framework.

Student Number : 8802466H - MSc research report - School of Physics - Faculty of Science / Medical ionising radiation sources give by far the largest contribution to the population dose from man-made sources. About 90% of this contribution is due to x-ray diagnostic procedures. Doses from diagnostic radiology procedures are nevertheless small and usually do not approach thresholds for deterministic effects. However, they must be accurately determined in order to maintain a reasonable balance between image quality and patient exposure. There is, thus, a need to establish quality assurance for diagnostic procedures that will provide the required clinical information in its optimal form and with minimum dose to the patient. In order to achieve this, dose measurements must be reproducible and the uncertainties associated with that measurement should be known. One of key factors for ensuring that appropriate levels of accuracy and long-term reproducibility of dose measurements are maintained is a calibration of the measuring equipment. The IEC (International Electrotechnical Commission) issued a standard IEC 61267 that deals with methods for generating radiation beams with radiation conditions which can be used under test conditions typically found in test laboratories for the determination of characteristics of medical diagnostic X-ray equipment. The document is currently being revised and publication of the new version is expected soon. Standard radiation qualities were established at a laboratory following the new IEC 61267 standard. Radiation qualities that characterize radiation beams emerging from the X-ray target (RQR qualities) were established. They were further filtered by Copper to obtain RQT beam qualities that simulate those used in Computed Tomography (CT). The spatial uniformity of a commercial CT dosimeter was then determined.

Spectral x-ray computed tomography (CT) is an important nascent imaging modality with several exciting potential applications. The research presented in this thesis separates into two primary areas with the common underlying theme of spectral CT; the first area is Compton scatter estimation and the second is interior tomography. First, the research is framed and outputs are identified. Background on the concepts used in the thesis is offered, including x-ray imaging and computed tomography, CT scanner architecture, spectral imaging, interior tomography and x-ray scatter. The mathematical background of techniques for image reconstruction from x-ray transmission measurements are presented. Many of the tools used to perform the research, both hardware and software, are described. An algorithm is developed for estimating the intensity of Compton scattered photons within a spectral CT scan, and a major approximation used by the algorithm is analysed. One proposed interior reconstruction algorithm is briefly evaluated; while this is not directly linked to spectral CT, it is related to the work on a novel hybrid spectral interior micro-CT architecture. Conclusions are summarised and suggestions for future work are offered. Scatter is known to cause artefacts in CT reconstructions, and several methods exist to correct data that has been corrupted by scatter. Compton scatter affects the energy of photons, therefore spectral CT measurements offer the potential to correct for this phenomenon more accurately than conventional measurements. A Compton scatter algorithm is developed and is found to match very well to Monte Carlo validation simulations, with the constraints that the object be at the micro-CT scale and that electron-binding effects are omitted. Development of the algorithm uses an approximation of the post-scatter attenuation to simplify the estimation problem and enable implementation. The consequences of this approximation are analysed, and the error introduced is found to be less than 5% in most biomedical micro-CT situations. Interior tomography refers to the incomplete data situation caused by the truncation of some or all CT projections, and is an active research area. A recently proposed interior reconstruction algorithm is evaluated with regard to its sensitivity to input error, and is found to have mediocre performance in this respect. Published results are not found to be reproducible, suggesting some omission from the published algorithm. A novel hybrid spectral interior architecture is described, along with an iterative reconstruction algorithm for hybrid data sets. The system combines a full field of view conventional imaging chain and an interior field of view spectral imaging chain to enable spectral measurement of a region of interest, and addresses some important limitations of spectral x-ray detectors; promising results are shown. Spectral reconstructions from interior data are shown to have sufficient information to distinguish two k-edge contrast agents (iodine and gadolinium) not only within the interior field of view but also beyond it. The architecture is further explored in the context of radiation exposure reduction, including testing of an analytical hybrid reconstruction algorithm.

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Registration is a key component for computer-navigated robot-assisted surgery. Invasive approaches such as fiducial-based and surface matching with mechanical probes are common but ultrasound may provide a non-invasive alternative. If an A-mode ultrasound transducer can be used to percutaneously select data points on the bones, a registration can be determined without needing any incision. This study investigates selecting an A-mode ultrasound transducer, calibrating it, analyzing the ultrasound signal, and using it to register a phantom sawbone tibia and femur as well as cadaveric specimens. This study is performed in conjunction with MAKO Surgical Corp.'s Tactile Guidance System™ (TGS™) at their headquarters and at The South Florida Spine Clinic for cadaveric experiments. The results for phantom and cadaveric ultrasound registrations compared to a mechanical probe approach demonstrate that A-mode ultrasound registration is a viable option for registration of the bones of the knee.

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Purpose: A time of flight approach to the analysis of 4D CT angiography is examined to calculate blood flow in arteries. Materials and Methods: Software was written to track contrast bolus TOF along a central vessel axis. Time density curves were analyzed to determine bolus time to peak at successive vessel cross-sections which were plotted against vessel path length. A line of best fit was plotted through the resulting data and 1/slope provided a measurement of velocity. Results: Validation was successful in simulation and in flow phantoms, though quality of results depended strongly on quality of curve fit. In phantoms and in vivo, accuracy and reproducibility of measurements improved with longer path lengths and, in vivo, depended on the avoidance of venous contamination. Conclusions: Quantitative functional intravascular information such as blood velocity and flow rate may be calculated from 4D CT angiography.

Purpose: A time of flight approach to the analysis of 4D CT angiography is examined to calculate blood flow in arteries. Materials and Methods: Software was written to track contrast bolus TOF along a central vessel axis. Time density curves were analyzed to determine bolus time to peak at successive vessel cross-sections which were plotted against vessel path length. A line of best fit was plotted through the resulting data and 1/slope provided a measurement of velocity. Results: Validation was successful in simulation and in flow phantoms, though quality of results depended strongly on quality of curve fit. In phantoms and in vivo, accuracy and reproducibility of measurements improved with longer path lengths and, in vivo, depended on the avoidance of venous contamination. Conclusions: Quantitative functional intravascular information such as blood velocity and flow rate may be calculated from 4D CT angiography.

This research was undertaken in order to investigate the robustness of the Anzai respiratory gating system. Tests were performed to verify the transfer of image data, to identify the method of gating and the accuracy of phase identification. It was found to have sizeable limitations which could result in either incorrectly gated images or serious artefacts. For these reasons it is recommended it be used under the guidance of a suitably qualified physicist.