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

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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.