Quantitative T2* Relaxation and Field Inhomogeneity Mapping Using Multi-Echo Radial FLASH Magnetic Resonance Imaging and Model-based Iterative Reconstruction

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Mapping of T2* relaxation and field inhomogeneity in multi-echo gradient-echo magnetic resonance imaging (MRI) refers to the quantification of effective spin-spin relaxation times (signal decay of the transversal magnetization) and off-resonance phase contributions, respectively. On the one hand, T2* relaxation is a valuable biomarker for clinical diagnosis of organ iron overload as well as for the assessment of myocardial oxygenation and tissue perfusion by dynamic susceptibility changes after contrast injection. On the other hand, field inhomogeneity is the basis for tissue susceptibility mapping and chemical shift imaging (e.g. water/fat separation). However, current procedures for T2* relaxation and field inhomogeneity mapping either require lengthy breath holding and electrocardiography (ECG) gating, or suffer from image artifacts and inaccuracy due to data undersampling. To overcome these limitations, we have developed a highly undersampled multi-echo radial fast low angle shot (FLASH) sequence, which continuously samples data without the need of breath holding or ECG gating. Based on this advanced acquisition technique, the first goal of this project is to develop a dedicated model-based iterative reconstruction technique for accurate and precise T2* relaxation and field inhomogeneity mapping. Accordingly, the second goal is to dynamically study the oxygenation state of the human myocardium and to achieve a temporal resolution of about 60 ms and a spatial resolution of 1 mm.