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

医学影像学方法测量肝脏灌注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，也可用于肝移植术后监测。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，它非常容易受到运动的影响，这在测量腹部时由于呼吸而非常突出。在之前的DFG项目（“ASLiver”）中，我们开发了解决方案，允许在自由呼吸下获得ASL肝脏。虽然这个初步的项目显示了肝脏ASL运动补偿的原理验证发展，推动了最先进的技术，但在使用ASL作为定量肝脏灌注的稳健措施之前，还有许多挑战。在这个综合性的项目提案中，将对定量灌注评估的整个工作流程进行修订和评估，包括通过获取多te数据扩展传统的单室模型进行灌注建模，从而实现生理交换过程的可视化。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，并推进当前背景抑制和脂肪饱和度的状态。然后将最终序列嵌入到涵盖参考扫描和运动校正的自动工作流程中。这将允许获得高质量的肝脏ASL图像，使肝脏生理过程建模取得进展，由于肝脏解剖结构复杂，目前仍缺乏黄金标准。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，可以服务于全新的维度，需要解决许多挑战。这将为不使用造影剂或电离辐射的肝脏生理过程提供新的见解，并为临床应用ASL在肝脏中的应用做好准备。

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.