High-Resolution and Contrast-Agent Free Perfusion Imaging of the Moving Liver by Combining 3D GRASE PROPELLER Arterial Spin Labeling MRI with Prospective Motion Correction Using Fat Signal

测量肝脏灌注的医学影像学方法有助于放射科医生早期发现原发性和转移性肝脏恶性肿瘤和肝硬化。此外，它还可用于肝移植术后的监测。目前使用磁共振成像（MRI）进行肝脏灌注成像的最新技术包括静脉注射造影剂，正如过去几年发现的那样，造影剂可以在大脑中积累。这表明有必要探索替代的、无造影剂的MRI技术来获得肝脏的定量灌注图像。动脉自旋标记（ASL） MRI在脑成像中已经建立，可以满足这些要求。然而，它极易受到运动的影响，这在测量腹部时非常突出。作为解决方案，我们建议结合使用前瞻性和回顾性运动矫正技术。前瞻性运动校正应使用，通过利用脂肪信号来校正扫描期间的刚性运动组件，以不干扰实际测量的磁化。弹性运动组件使用3D GRASE PROPELLER读出方案进行校正，该方案对每个旋转图像读出中的k空间中心进行过采样。在扫描过程中已经刚性对准的单个PROPELLER采集数据，然后可以回顾性地校正弹性运动。这是通过计算图像之间的变形场，并将它们组合成高分辨率的、运动校正的肝脏灌注加权图像来完成的。开发工作是通过建立一个运动幻影来支持的，这将有助于评估运动校正方法。在项目的最后阶段进行体内评估研究，以与使用呼吸屏息或呼吸门控序列的传统测量技术进行比较。

Medical imaging methods to measure liver perfusion help radiologists in the early detection of primary and metastatic hepatic malignancies and cirrhosis. Further, it can be used for post-operative monitoring of liver transplants. The current state of the art in liver perfusion imaging using Magnetic Resonance Imaging (MRI) includes the intravenous injection of contrast agents which, as it was discovered during the last years, can accumulate in the brain. This shows the necessity to explore alternative, contrast-agent free MRI techniques for acquiring quantitative perfusion images of the liver. Arterial Spin Labeling (ASL) MRI, which has already been established in brain imaging, could meet these requirements. It is, however, highly susceptible to motion which is very prominent when measuring the abdomen. As solution, we suggest utilizing a combination of prospective and retrospective motion correction techniques. Prospective motion correction shall be used to correct for rigid motion components during the scan by utilizing fat signal to not disturb the magnetization of the actual measurement. Elastic motion components are corrected using a 3D GRASE PROPELLER readout scheme that oversamples the k-space center in each rotated image readout. The single PROPELLER acquisitions that were already rigidly aligned during the scan can then be retrospectively corrected for elastic motion. This is done by calculation a deformation field between the images and combining them to high-resolution, motion-corrected perfusion-weighted images of the liver. The development work is supported by building a motion phantom that will help to evaluate the motion correction methods. An in-vivo evaluation study is performed during the last stage of the project for comparison to conventional measurement techniques using breathholds or respiratory gating of the sequence.