Automated navigator tracker placement for MRI liver scans

Abstract

We present a new method for automated placement of a navigator tracker for MRI liver scans. The tracker is used for the navigator echo sequence. It localizes the region acquiring the MR signal to monitor respiratory motion. Accurate placement of the tracker at the boundary between the lung and liver while observing scout images is a complicated task for operators, adversely affecting their workflow. Our proposed method uses ensemble-based classifiers to detect pixels and a right landmark on the upper edge of the liver, following identification of the area containing the edge pixels in the superior/inferior direction. The navigator tracker location is computed from the peak location of the upward convex shape formed by the edge pixels after fitting to a quadratic function. Our method placed the navigator tracker with a mean error of 6.79 mm for the desired location in 126 volunteers. A computational time was approximately 3 s.