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Title: T1-mapping as a novel technique for myocardial tissue characterisation using cardiovascular magnetic resonance : from method development to clinical validation and application
Author: Ferreira, Vanessa Melanie
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2013
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Cardiovascular magnetic resonance (CMR) is superior to other cardiac imaging modalities in its ability to perform multiparametric myocardial tissue characterisation. Commonly applied techniques include T2-weighted (T2W) imaging for detecting oedema and late gadolinium contrast enhancement imaging for detecting fibrosis, allowing characterisation of most cardiac conditions encountered in the clinical setting. While these techniques have proven useful, conventional MR images acquired by these techniques are displayed on an arbitrary scale and only semi-quantitative with some inherent deficiencies. Quantitative techniques, such as T1-mapping, allow direct quantification of tissue properties and may circumvent many of the issues of conventional MR imaging, with potential to offer more insight into diseased myocardium. Although T1-mapping has been well-established for brain T1-mapping, cardiac T1-mapping has been slow to mature due to technical and practical challenges. The aim of this thesis was to develop a novel method for cardiac T1-mapping that is robust and clinically applicable so that cardiac T1-mapping can transition from a research tool into clinical practice. Further, cardiac T1-mapping using this new technique was validated in normal and disease states, including its ability to detect regional and global myocardial oedema and acute myocarditis. This work developed a novel MR sequence for cardiac T1-mapping, named Shortened Modified Look-Locker Inversion Recovery (ShMOLLI). The conventional method (MOLLI) required 17 heart-beats (a 17 second breath-hold for a patient with a heart rate of 60 bpm) for the acquisition of one slice of T1-map. This is difficult to achieve for patients, especially those who are acutely ill and if whole heart coverage (~8 slices) were desired. One of the goals in the design of ShMOLLI was to bring the breath-hold time down to below 10 seconds so that patients may tolerate the protocol. The design of ShMOLLI was successful in breaching the 10-second breath-hold time without compromising the accuracy of T1 measurements compared to the conventional method; further, unlike MOLLI, ShMOLLI did not exhibit increasing error with increasing T1 or heart rates, making it advantageous in measuring long T1 values and at fast heart rates. These features of ShMOLLI make it a very attractive method ready for clinical application. The ShMOLLI method was then further applied to disease states, starting with models of acute myocardial oedema. ShMOLLI T1-mapping was performed in patients with acute stress-induced cardiomyopathy (model of global oedema) and in patients with regional oedema without infarction, and compared to T2W imaging. T1-mapping demonstrated an excellent diagnostic performance compared to the T2W methods in detecting acute myocardial oedema, whether it was global or regional. ShMOLLI T1-mapping was well-tolerated by acute cardiac patients and showed promise in its application to other conditions in which oedema would be a major component in the pathophysiology. ShMOLLI T1-mapping was next applied to patients presenting with acute myocarditis, in which oedema and inflammation are major components. Compared to the conventional MR methods of T2W and LGE imaging, T1-mapping again showed superior diagnostic performance to T2W imaging and equivalent performance to LGE imaging in detecting acute myocarditis. Further, T1-mapping was able to detect a larger extent of injury compared to both of these methods, and provided topographic information such as the non-ischemic patterns of injury similar to that seen on LGE imaging, but without the need for exogenous contrast agents. In conclusion, this thesis reports the development of a novel method for cardiac T1-mapping, its validation and clinical application to detect myocardial oedema and characterise acute myocarditis without the need for exogenous contrast agents. ShMOLLI T1-mapping holds promise in quantitative tissue characterisation in a wide range of myocardial diseases.
Supervisor: Neubauer, Stefan ; Robson, Matthew D. ; Karamitsos, Theodoros D. Sponsor: Alberta Innovates Health Solutions, University of Oxford Clarendon Fund
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Cardiovascular disease ; Medical Sciences