Klaus-Dietmar Merboldt1, Dirk Voit1, Martin Uecker1, 2, Jens Frahm3
1Biomed. NMR Forschung, Goettingen, Germany; 2Electrical Engineering and Computer Sciences, University of California, Berkeley, CA, United States; 3Biomedizinische NMR Forschungs GmbH am Max-Planck-Institut fr biophysikalische Chemie, Goettingen, Germany
Spatial information may be encoded as a differential phase - similar to the principles underlying velocity-encoded phase-contrast MRI - when a gradient is applied along a perpendicular dimension of a slab and if this dimension contains a MRI-visible object at only one spatial location. The situation applies to 3D mapping of planar (2D) structures with only two projection images and different spatial phase-encoding gradients. A combination with highly undersampled radial FLASH and image reconstruction by regularized nonlinear inversion allows for serial 3D mapping in real time and, e.g. a moving hand at 40 ms temporal resolution (25 fps). If the object is restricted to a linear (1D) structure its position can be localized even faster by the acquisition of only three phase-encoded projections as demonstrated for a rapidly rotating NMR-tube at a frame rate of 200fps .