Robust Perfusion Imaging of the Moving Human Liver Using Arterial Spin Labeling MRI for Advanced Modelling of Liver Function

测量肝脏灌注的医学成像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，也有助于肝移植术后的监测。使用磁共振成像（MRI）的肝脏灌注成像的现有技术包括静脉内注射造影剂，如在过去几年中发现的，造影剂可以在大脑中积聚。这表明有必要探索替代的、无造影剂的MRI技术来获取肝脏的定量灌注图像。已经在脑成像中建立的动脉自旋标记（ASL）MRI可以满足这些要求。然而，它非常容易受到运动的影响，这在测量由于呼吸引起的腹部时非常突出。在之前的DFG项目（“ASLiver”）中，我们开发了允许在自由呼吸下采集肝脏ASL的解决方案。尽管该初步项目显示了肝脏ASL中运动补偿的原理验证发展，推进了最新技术水平，但在使用ASL作为定量肝脏灌注的稳健测量之前，还有许多挑战。在这个全面的项目提案中，将修订和评估评估定量灌注的整个工作流程，包括通过采集多TE数据扩展用于灌注建模的传统单室模型来可视化生理交换过程。这包括对ASL序列本身的改进，以受益于扫描加速和分割的最新技术，并提高背景抑制和脂肪饱和的当前状态。最终序列将被嵌入到自动工作流程中，包括参考扫描和运动校正。这将允许采集高质量的肝脏ASL图像，从而实现肝脏生理过程建模的进步，由于复杂的肝脏解剖结构，目前仍然缺乏黄金标准。关于如何正确分离两种血液供应的信号，确定标记效率或利用多TE数据，通过将交换过程纳入建模中，可以提供全新的维度，还有许多挑战需要解决。这将为在不使用造影剂或电离辐射的情况下观察肝脏的生理过程提供新的见解，并为在肝脏中使用ASL进行临床应用做好准备。

Medical imaging methods to measure liver perfusion help radiologists in the early detection of primary and metastatic hepatic malignancies and cirrhosis, but also in the 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 due to breathing. In a previous DFG project (“ASLiver”) we developed solutions to allow ASL acquisition of the liver under free breathing. Although this preliminary project showed proof-of-principle developments of motion compensation in liver ASL that advance the state-of-the-art, there are many challenges ahead before using ASL as a robust measure for quantitative liver perfusion. In this comprehensive project proposal, the whole workflow of assessing quantitative perfusion, including the visualization of physiological exchange processes by extending the conventional one-compartment model for perfusion modelling by acquiring multi-TE data, will be revised and evaluated. This includes improvements to the ASL sequence itself to benefit from state-of-theart techniques for scan acceleration and segmentation and advancing the current state of background suppression and fat saturation. The final sequence will then be embedded into an automatic workflow covering reference scans and motion correction. This will allow acquisition of liver ASL images with high quality, enabling advances in modeling the physiological processes in the liver, still lacking gold standards today due to the complex liver anatomy. There are many challenges to solve as to how to correctly separate the signal of the two blood supplies, determine the labeling efficiency or make use of multi-TE data that could serve a whole new dimension by incorporating exchange processes into the modelling. This will provide new insights into the physiological processes in the liver without use of contrast agents or ionizing radiation and prepare the use of ASL in the liver for clinical use.