Towards free breathing 3D ASL imaging of the human liver using prospective motion correction.

Purpose: Measurements of liver perfusion yield valuable information about certain diseases like carcinomas and cirrhosis. To assess perfusion, noninvasive arterial spin labeling (ASL) MRI has the potential to become an important alternative to contrast agent-based methods. Unfortunately, ASL perfusion-weighted images are highly susceptible to breathing motion. This work presents a prospective motion-compensation technique, tackling breathing motion during ASL experiments of the human liver.

Methods: Feasibility of 3D pseudo-continuous ASL imaging under free breathing is investigated by using a prospective motion-compensation technique with fat signal in additional 2D-EPI navigators. The proposed technique is compatible with strong signal suppression, occurring in background-suppressed pseudo-continuous ASL imaging. An additional retrospective 2D elastic registration algorithm is proposed to correct for residual elastic deformations. The technique is validated in 8 healthy volunteers.

Results: The prospective technique allowed a significant reduction of the cranial-caudal liver shifts during free breathing pseudo-continuous ASL experiments. Additional 2D elastic image registration allowed reduction of cranial-caudal liver motion to levels of timed breathing protocols. Artifacts in perfusion-weighted images could be reduced when compared with free-breathing ASL images without motion correction.

Conclusion: The proposed technique is suitable for prospective compensation of liver motion in background-suppressed 3D pseudo-continuous ASL imaging. Future work focuses on further improving the quality of perfusion-weighted images.