RESTRICTION OF THE IMAGING REGION FOR MRI IN AN INHOMOGENEOUS MAGNETIC FIELD

When magnetic resonance imaging in the vicinity of a metallic object (like, for instance, a metal implant), severe spatial perturbations of the static magnetic field occur. In order to suppress the back-folding of distant off-resonant signals into the region of interest, the imaging volume is spatially restricted by selection gradients applied concurrently with the excitation and the refocusing RF pulses in a spin echo sequence. The selection gradient applied during the excitation pulse has an amplitude and/or a polarity different from that of the selection gradient applied during the refocusing pulse so that the respectively selected slices in an off-resonance frequency versus spatial coordinate diagram become tilted with respect to one another. The applied imaging technique may of the SEMAC or MAVRIC type and may incorporate compressed sensing, parallel imaging, fat suppression and/or SVD-based noise reduction.