Cardiovascular magnetic resonance of the arterial wall

Abstract

BACKGROUND Atherosclerosis is the single greatest cause of mortality and morbidity in the developed world. Cardiovascular magnetic resonance (CMR) is a non-invasive imaging technique which can interrogate the arterial wall and identify atherosclerotic disease. CMR can provide quantitative volumetric data of atherosclerosis burden which have begun to be used in clinical trials, however comparatively few studies have been performed. We aimed to validate this approach ex vivo, to use it to characterise a normal population in vivo, to further develop the methodology, and to apply the technique to novel ‘at risk’ populations. METHODS AND RESULTS We validated quantitative CMR arterial wall volume in post mortem carotid arteries against both a CMR comparator, and against histological data. For all correlations, R2 was greater than 0.95: (CMR v histology: lumen volume 354 vs 308mm3, p<0.01; arterial wall volume 388 vs 351 mm3, p<0.01; total volume 750 vs 665 mm3; p<0.01). We studied 100 normal subjects from age 20 to 69 to determine normal ranges and the effect of normal ageing. Wall volume and total vessel volume increased significantly with age in both sexes (p < 0.006), and this was more marked in males. The W/OW ratio also increased significantly with age (p < 0.001). We showed that a 3-dimensional CMR sequence performs 63% faster than a conventional 2-dimensional sequence, with twice the signal-to-noise ratio (SNR), and highly correlated results (vessel volume: difference = 1.7%, R2 = 0.93, p < 0.001; lumen volume: difference = 4.9%, R2 = 0.92, p < 0.001, wall volume: difference = 4.7%, R2 = 0.77, p < 0.001, W/OW ratio: difference = 5.8%, R2 = 0.30, p < 0.001). Finally, we characterised atherosclerotic burden and arterial health in two populations with Takayasu’s arteritis and systemic lupus erythematosus by CMR. Carotid arterial wall volume was elevated in both populations: TA = 1045mm3, SLE = 761mm3, normals = 640mm3, p < 0.001, and myocardial late gadolinium enhancement was found 27% of TA patients, and in 60% of those with SLE. CONCLUSIONS Cardiovascular magnetic resonance of the arterial wall is an accurate way of measuring carotid atherosclerosis burden. This thesis validates this approach, and provides valuable normal data. It compares new techniques with old, aiding technical development. Finally, it demonstrates how the technique can be used in practice in populations with accelerated atherosclerosis. These data indicate that arterial wall CMR is ready to be applied in larger clinical trials.