The invention relates to a method and an apparatus for measuring the position and the orientation of an interventional device within a magnetic resonance imaging apparatus, the magnetic resonance image apparatus providing a static magnetic field B.sub.0 and magnetic field gradients with known magnetic flux densities and directions. The invention includes attaching a Faraday sensor to the interventional device, the Faraday sensor being connected to an optical measuring device. The method also includes using the optical measuring device for measuring the rotation of the plane of polarization of linearly polarized light in the Faraday sensor, while exposing the interventional device: (i) to the static magnetic field B.sub.0, and (ii) to the field gradients in all three directions of space in addition to the static magnetic field B.sub.0. The method also includes determining the position and the orientation of the interventional device by evaluating the measured rotation of the plane of polarization of the linearly polarized light.