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

多回波梯度-回波磁共振成像（MRI）中T2*弛豫和场非均匀性的映射分别是对有效自旋-自旋弛豫时间（横向磁化的信号衰减）和非共振相位贡献的量化。一方面，T2*舒张是临床诊断脏器铁超载的有价值的生物标志物，也是注射造影剂后动态敏感性变化评估心肌氧合和组织灌注的有价值的生物标志物。另一方面，场的非均匀性是组织易感性制图和化学位移成像（例如水/脂肪分离）的基础。然而，目前T2*松弛和场非均匀性映射的程序要么需要长时间屏气和心电图（ECG）门控，要么由于数据欠采样而遭受图像伪影和不准确。为了克服这些限制，我们开发了一种高度欠采样的多回波径向快速低角度拍摄（FLASH）序列，该序列无需屏气或ECG门控即可连续采样数据。基于这种先进的采集技术，本项目的第一个目标是开发一种专门的基于模型的迭代重建技术，用于精确和精确的T2*松弛和场非均匀性映射。因此，第二个目标是动态研究人体心肌的氧合状态，并实现约60 ms的时间分辨率和1 mm的空间分辨率。

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.