A patient imaging system includes a patient support table, an MRI system including a cylindrical magnet and a PET system including positron detectors mounted in a ring. The magnet defines a cylindrical bore for receiving the patient on the table where the magnet is mounted for rotation about a vertical axis on a slew ring carried on rails allowing longitudinal movement. The PET ring is mounted in the bore for longitudinal movement. The quench tube for the magnet passes through the slew ring with a rotary union at the axis. The shielding covers include a fixed upper part and a lower part which rotates about the axis with the magnet. The magnet is arranged in a two or three room diagnostic configuration in which a holding bay houses the magnet and the diagnostic patients are organized in the three rooms each cooperating with the magnet bay as the magnet is rotated.