Computer aided diagnosis of early vascular disease from ultrasound images
This thesis consists of 2 separate ultrasound (US) based studies, performed with the common aim of improving the diagnosis of early vascular disease from US images.
Introduction: Flow mediated dilatation (FMD) is an endothelium-dependent process reflecting the dilatation of a conduit artery when it is exposed to increased blood flow and therefore increased shear stress. FMD requires a healthy endothelium and is depressed in those with cardiovascular risk factors. Current 2D US assessment is limited as a research tool only secondary to variable reproducibility, technical difficulties and difficulties determining true diameter measurement. To our knowledge this is the first study comparing 2D and 3D US assessment of FMD.
Methods: This was a cross sectional reproducibility study with 27 male patients. 2D and 3D FMD were performed on both study visits. Nitrate induced dilatation (NID) was performed as a control. We hypothesised that 3D US would eliminate the systematic underestimation of diameter that we believe occurs using 2D US. We believe this is secondary to probe malalignment errors occurring in 2D US that are eliminated using 3D US. Furthermore, we tested if 3D FMD is more reproducible than 2D FMD.
Results: We discovered 3D diameter to be greater than 2D diameter with between visit FMD correlation and reproducibility being similar in both 3D and 2D.
Conclusion: Findings suggest 3D US gives a greater and more accurate measurement of diameter, however this should be confirmed with an arterial phantom bench study comparing 2D and 3D US diameter measurements. With real-time high resolution 4D US likely to provide better temporal resolution, the advent of 4D FMD is only around the corner. This is likely to be more accurate, reproducible and user friendly than 2D and may soon find its way into clinical practice. We believe by identifying 3D US as a useful and comparable tool to 2D US in the assessment of FMD, this will provide a stepping stone for this to happen, thereby facilitating better quantification of endothelial function.
Introduction: Pre-eclampsia (PET) results in hypertension and proteinuria in pregnancy. It is associated with increased prevalance of cardiovascular risk factors and future cardiovascular risk, including increased intima-media thickness (IMT) and arterial stiffness. We used 2D US to assess for subtle alterations in vascular structure and function in young women with and without a history of gestational hypertension (GH) or PET.
Methods: This was a phase 2 cohort study of 40 women with at least 1 pregnancy in the last 5 years. Alterations in IMT distribution and compression patterns between the 3 groups were assessed according to multiple angles of insonation in the distal common carotid artery (CCA), and along the vascular tree (proximal versus distal CCA versus bifurcation (BIF) versus internal carotid artery (ICA)). Arterial stiffness within the proximal and distal CCA was also assessed. Using ANOVA we tested the hypotheses that the PET group would illustrate different values to the other groups.
Results: In women with a history of pre-eclampsia, IMT was greater in areas of the vascular tree with a predilection for atherosclerosis i.e. the medial wall of the common carotid artery and within the ICA. IMT compression in PET differed according to vascular tree and angle. Arterial stiffness was increased in the GH and PET groups with less compliant and distensible arteries in the distal CCA when compared to normotensives.
Conclusion: Women with PET have greater IMT than those without such a history. The pattern of IMT distribution by angle and along the vascular tree has been seen in previous studies, however to our knowledge never in such a group of asymptomatic women. A stepwise increase of IMT along the vascular tree was observed in the normal and GH groups with a subsequent decrease in IMT in the ICA, however, there was a further increase in IMT in the ICA in the PET group, suggesting an accelerated atherosclerotic process. Increased CCA stiffness in the PET and GH groups further supports this statement. Our results warrant further evaluation in other pre-eclampsia sufferers and perhaps similar asymptomatic groups using more novel non-invasive ultrasound techniques studying vascular wall structure and mechanics.