Magnetic resonance apparatus including an rf magnetic flux guiding structure for improving the signal-to-noise ratio

Magnetic resonance apparatus, in which resonance is excited in use in magnetic resonant active nuclei in a region of an object in the presence of a main magnetic field, including a structure (13-16, 19-21, 30) with magnetic properties for guiding magnetic flux, the structure being made of a material having a magnetic permeability greater than that of free space at the frequency of nuclear magnetic resonance but being non-magnetic in steady magnetic fields, the material comprising an array of capacitive elements, the array exhibiting a predetermined magnetic permeability in response to incident electromagnetic radiation lying within a predetermined frequency band which includes the magnetic resonance frequency, wherein each capacitive element includes a conducting path and is such that a magnetic component of the electromagnetic radiation at the magnetic resonance frequency induces an electrical current to flow around said path and through said associated element, wherein the spacing of the elements is less than the wavelength of the radiation within the predetermined frequency band, and wherein the size of the elements and their spacing apart are selected such as to provide the magnetic permeability greater than that of free space at the magnetic resonance frequency.