An apparatus for exposing a region of interest of an object, animal or person to an alternating magnetic field has a source of radio-frequency electromagnetic radiation arranged to provide the alternating magnetic field in an exposure volume defined by the apparatus, and a shield arranged between the source of radio-frequency electromagnetic radiation and the exposure volume. The shield includes a material that has a sufficient thickness and arrangement to reduce power deposition to at least regions outside of the region of interest of the object, animal or person during exposure in the exposure volume.
