Multiparametric cardiac magnetic resonance imaging with motion compensation
Magnetic resonance imaging is a non-invasive imaging modality for the diagnosis of cardiovascular diseases. A broad range of diagnostic parameters can be obtained within a single examination, including information about morphology, physiology and tissue viability. Currently, qualitative contrast-enhanced imaging is the gold standard for the detection of myocardial pathologies by visual assessment. In such qualitative approaches healthy myocardium has to be present in the image to have a contrast between healthy myocardium and pathological areas. Therefore, only focal myocardial defects can be accurately diagnosed. Recently, it has been shown that T1-relaxation times can be used to characterize myocardial pathologies even if they are not localized but affect the entire myocardium (diffuse disease). Furthermore, T1 serves as a tissue specific quantitative diagnostic parameter which ensures comparability of different scans and allow for multi-center studies and monitoring of disease progression or treatment response even over a long period of time. T1 mapping relies on the acquisition of a number of qualitative T1-weighted images to encode the recovery of longitudinal magnetization, resulting in long acquisition times. However, a cardiac examination consists of multiple scans in order to obtain all information needed for diagnostics, such as cardiac function, leaving little room for additional scan time. This hinders its application in clinical practice. Therefore, fast and robust T1 mapping techniques have to be developed, without prolonging examination time or loss in accuracy or precision. Furthermore, cardiac T1 mapping is very challenging because of cardiac and respiratory motion. In this thesis, a multiparametric magnetic resonance imaging technique was developed to increase the efficiency of data acquisition. Using this approach, accurate T1 maps and functional images were obtained simultaneously without prolongation of the scan time. High-resolution T1 mapping was realized by advanced model-based image reconstruction that utilizes prior knowledge of T1 recovery to obtain accurate T1 estimation. By integration of cardiac motion correction techniques based on the reconstructed functional images, the scan duration was reduced by 50%, while precision of T1 mapping was increased. The presented techniques were evaluated in phantoms and feasibility was shown in healthy volunteers and in patients. The imaging approaches proposed in this thesis have been demonstrated to hold great promise for simultaneous imaging of multiple clinically relevant parameters by efficient data sampling and advanced image reconstruction methods. The multiparametric approach could be important for future directions in cardiovascular magnetic resonance imaging, because the fast and contrast-free examination allows for quantitative imaging in a short examination time.
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