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The assessment of biomechanical modelling and PET/MR imaging in coronary atherosclerosis 10.17863/CAM.94121 Sun, Chang Graves, Martin The life-threatening acute coronary syndromes (ACSs) are caused mainly by the rupture of the coronary atherosclerotic plaques. Angiography-defined luminal stenosis is the only validated criterion for clinical decision making. However, post-mortem studies showed that only 14% of myocardial infarctions (MIs) were caused by plaques with >70% stenosis. Plaque vulnerability, characterised by morphological and compositional features, is more important than the luminal stenosis measurements. Mini-invasive virtual-histology intravascular ultrasound (VH-IVUS), optical coherence tomography (OCT), computed tomography angiography (CTA), magnetic resonance imaging (MRI) and positron emission tomography (PET) have been developed to characterise lesion morphology, composition, function and metabolism. However, the overall predictive power of an imaging-defined high risk feature for future ischaemic events is insufficient for clinical decision making. New biomarkers are therefore needed. Coronary atherosclerosis is a chronic inflammatory disease, and the plaque is subject to mechanical loading due to dynamic blood pressure and flow, as well as bending due to heart motion. The mechanical loading estimation and the inflammation quantification have the potential in generating new biomarkers for vulnerability assessment. An accurate mechanical analysis depends on many factors, such as material properties, loading conditions and modelling strategies. The influence of material properties and loading conditions has been widely studied, whilst modelling strategies are currently less investigated. A PET/MR system provides simultaneous anatomical and metabolic imaging. However, accurate attenuation correction is essential for quantitative PET reconstruction in the thorax, and the application of PET/MR in coronary imaging is limited due to the challenges of obtaining good quality images of the coronary vessels. The work presented in this thesis first investigates the influence of computation strategies and bending on the calculation of mechanical parameters, in particular, plaque structure stress (PSS). The hypothesis is that the 3D structure only finite element analysis (FEA) can accurately predict the PSS with good time efficiency, and bending is an important factor in coronary biomechanical analysis. Mechanical parameters calculated from the 3D fully coupled fluidstructure interaction (FSI) model with the patient-specific bending were used as references. 3D structure-only FEA showed a good agreement with the gold standard model and a shorter solution time (Chapter 3). The comparison of mechanical features with and without patientspecific coronary bending showed an increase in PSS due to the bending and revealed the importance of bending in coronary FEA (Chapter 4). For the imaging part, a hybrid bias correction method was proposed for the thoracic region using zero echo time (ZTE) images, which were converted to pseudo-CT images of the lung region. These images were integrated with the standard MR attenuation map to improve the accuracy of attenuation correction (AC) in PET reconstruction (Chapter 5). We hypothesise that non-Cartesian MR sequences could improve the coronary image quality in a PET/MR system, and the incorporation of ZTE based pseudo-CT in the lung can improve the PET attenuation correction. The imaging part of this work involved the development of 3D nonCartesian (spiral and radial) trajectory MR sequences for the PET/MR system (Chapter 6). Overall, the 3D structure only FEA with patient-specific bending can accurately estimate the coronary PSS with a reasonable computation time. The ZTE based pseudo-CT attenuation correction in the lung region can improve the accuracy of thoracic PET reconstruction. The application of non-Cartesian sequences for coronary imaging requires further development in the PET/MR system. University of Cambridge 2021-09-01 Thesis Doctoral Doctor of Philosophy (PhD) eng https://www.repository.cam.ac.uk/handle/1810/346701 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/11e72ff3-0602-4a62-8813-2d72b8d5cb80/download 45d36307482b12a505d6a66bd9f3a31b https://www.rioxx.net/licenses/all-rights-reserved/ Coronary atherosclerosis Biomechanics VH-IVUS DSA PET/MR Image processing MR attenuation correction