A combined MR and nuclear imaging device comprising an MRI device and an nuclear imaging device, wherein the nuclear imaging device is capable of operating with the magnetic field of the MRI device or in a region where the magnitude of the magnetic field is lesser. The combined system allows MRI examination and nuclear medicine examinations to be conducted quasi-simultaneously with no or minimal motion of the patient during the combined examination. The nuclear imaging device comprises nuclear detector modules capable of operating within a large magnetic field when the modules oriented in the direction of the field, and capable of operating in any direction when the magnitude of the field is below a certain threshold.