Non-contrast-enhanced magnetic resonance imaging and computational fluid dynamics for carotid atherosclerosis

Atherosclerotic plaques of the carotid artery are considered to be one of the major risk factors for stroke. To efficiently and precisely characterise the major plaque components, a new magnetic resonance imaging (MRI) sequence has therefore been promoted in this project. Besides plaque components, haemodynamics also plays a critical role in the progress and rupture of atherosclerotic plaques. Therefore, a new methodology that combines computational fluid dynamics (CFD) with non-contrast-enhanced magnetic resonance angiography (MRA) has been developed in this study to provide quantitative haemodynamic analysis for the diagnosis of carotid atherosclerosis and assessment of the outcomes of surgery. In the first part of this research, a newly-developed plaque sequence termed 'MATCH' is introduced. The MATCH sequence has the advantages of short acquisition time and ability to identify plaque components. The MATCH sequence has been utilised to characterise the major plaque components, which include intraplaque haemorrhage (IPH), a large lipid-rich necrotic core, loose matrix, and calcification. The performance of MATCH in differentiating plaque components was compared with that of conventional multi-contrast MRI and confirmed by histological evidence in this study. The results indicate that the MATCH was comparable if not superior to conventional protocol in identification and quantification of major carotid plaque components. In the second part, the relationship between haemodynamics and carotid plaques with IPH was investigated. We hypothesised that haemodynamics plays a pivotal role in the development of IPH. For this purpose, the maximum wall shear stress (mWSS) at the surface of plaques was compared for the groups with and without IPH under different severities of carotid artery stenosis. The results demonstrated that the higher mWSS was exhibited in carotids with IPH for cases with stenosis less than 70%, and the magnitude of mWSS was positively correlated with the volume of IPH. However, there was no significant relationship between mWSS and IPH when the stenosis exceeded 70%. Our results indicate that mWSS i a promising parameter to evaluate plaque vulnerability for carotids with stenosis of less than70%. In the last part of this thesis, CFD simulation was performed to analyse blood flow changes after carotid endarterectomy (CEA). The morphological characteristics and haemodynamic parameters were compared before and after CEA, as well as for healthy carotids as a control group. The major haemodynamic parameters were restored after surgery in short-term followup. This study indicates that CFD analysis can provide valuable information for the evaluation of physiological functions after CEA.