Real-time liver motion compensation for MRgFUS.

MR-guided focused ultrasound (MRgFUS) is a non-invasive method by which tissue is ablated using ultrasound energy focused on a point. The procedure has proven effective for stationary targets (e.g. uterine fibroids) but has not yet been used for liver lesion treatment due to organ motion. We describe a method to compensate for organ motion to enable continuous application of ultrasound energy in the presence of target movement in the liver. The method involves tracking several salient features (typically blood vessels) in the vicinity of the target location. The location of the target point(s) themselves are updated using a thin plate spline (TPS) interpolation scheme. We demonstrate sub-pixel tracking accuracy on synthetic sequences and additionally show results on MRI sequences acquired on human subjects. Per-feature tracking times were measured to be 5.7ms with a standard deviation of 1.6ms, sufficient for real-time use.