Abstract: A magnetic field generator assembly (44) is configured to be associated with a table (20) supporting a body. The magnetic field generator comprises magnetic field transmitters (57A) that are thin (of minimal height) and transparent, or substantially transparent, to x-ray radiation. The magnetic field transmitters (57A) are configured to minimally obstruct components of an imaging system and to minimally interfere with image quality. A plurality of transmitters is arranged in a first layer of the assembly. Each transmitter (57A) comprises an elongate conductive element, such as a wire, arranged in a spiral form, such as a coil.