Application of cardiac magnetic resonance myocardial deformation technique and T1 mapping : the value in evaluation of biventricular function and tissue characterization

Abstract

This thesis addresses the feasibility and diagnostic performance of two novel cardiac magnetic resonance (CMR) techniques: (1) T1 mapping – A CMR sequence characterising myocardial tissue. We used T1 mapping to assess for myocardial fibrosis in asymptomatic childhood cancer survivors (CCSs) post anthracycline chemotherapy. (2) Feature-tracking (FT), which involves post-processing of standard cine images to quantify myocardial deformation. In this thesis, we looked at FT’s accuracy and reliability to quickly identify patients with right ventricular (RV) systolic dysfunction (SysD) and to diagnose diastolic dysfunction (DD) using CMR. First study – Small studies and some without normal volunteer data suggested an increase in myocardial fibrosis in childhood cancer survivors (CCS) post anthracycline chemotherapy particularly in women. We carried out a larger study with normal volunteers to explore the severity of left ventricular (LV) fibrosis in asymptomatic CCS post-anthracycline treatment. 55 CCS and 42 age- and gender-matched controls were prospectively recruited. Our results demonstrated no significant difference in native T1, extracellular volume (ECV) and LGE volume between CCS and controls. Therefore there was no significant increase in myocardial diffuse and replacement fibrosis in asymptomatic CCSs. Female CCS and controls showed significantly higher native T1 and ECV values than their male counterparts. Multivariable linear regression analysis further confirmed sex was the only independent variable for both native T1 and ECV, suggesting the higher values for females were due to an intrinsic sex difference rather than a higher vulnerability to chemotherapy treatment. Second study - 29 patients with dilated cardiomyopathy were prospectively recruited. We investigated the accuracy of RV free-wall longitudinal strain (FLS) from CMR-FT, FLS and global longitudinal strain (GLS) from echocardiography speckle-tracking (STE) in determining RV global SysD compared with conventional techniques. The results showed CMR RV-FLS and STE RV-GLS correlated best with RVEF with excellent inter-/intraobserver reproducibility. Both variables showed good discriminative performance to infer impaired RV SysD with cut-off value provided. This study revealed clinical potential of CMR-FT and STE for a rapid evaluation of RV SysD with high accuracy and reproducibility, which were superior to conventional methods. Third study - 71 patients were retrospectively identified to explore the value of CMR-FT for diastolic dysfunction (DD) assessment. LV circumferential-diastolic strain rate (CDSR) showed the best accuracy to determine DD and agreed well with echocardiography, regardless of whether LVEF was preserved. CDSR inter/intra-observer reproducibility was excellent. The diagnostic accuracy of CDSR significantly outperformed conventional diastolic indices in phase-contrast (PC), including E/e’ and E/A ratio. Combined assessment of CDSR and PC-MRI significantly increased sensitivity for DD recognition, enabling a comparable diagnosis between CMR and current reference echocardiography. Our T1 mapping study in CCS post anthracycline chemotherapy showed no significant increase in myocardial fibrosis in CCS post-chemotherapy which was contrary to findings of previous smaller studies. It also emphasized the importance of taking account of T1 mapping values based on gender. CMR-FT showed feasibility and good clinical performance in detecting RV SysD and LV DD.