An imaging system comprises: a magnetic resonance scanner (30) having a cylindrical bore (36) defining a cylinder axis (D A ), the magnetic resonance scanner having a gradient coil (10, 10') defining an isocenter (64) within the bore and an isoplane (66) passing through the isocenter and oriented transverse to the cylinder axis; a ring of radiation detectors (60a, 60b, 60') arranged concentric with the cylindrical bore and configured to detect radiation emanating from within the bore; and a generally annular electronic circuit board (62, 62') arranged concentric with the cylindrical bore and centered on the isoplane, the generally annular electronic circuit board operatively connected with the ring of radiation detectors to generate electrical signals indicative of detection of radiation by the ring of radiation detectors.