An MRI system is presented utilizing a magnetic assembly of a kind which, when accommodated within a primary static reasonably homogeneous magnetic field created by the MRI system affects the static magnetic field to cause creation of a region of substantial non-homogeneity of the static magnetic field in the vicinity of the magnetic assembly. By this, a local static field gradient is created. The magnetic assembly comprises a passive magnetic element, which deforms a pattern of the static magnetic field, while not being a magnetic field source by to itself.