Two kinds of body imaging — positron emission tomography and magnetic resonance imaging — have been combined for the first time in a single scanner. Combining the two types of scan in a single machine is difficult because the two systems interfere with each other. MRI scanners rely on very strong, very smooth magnetic fields that can easily be disturbed by metallic objects inside the scanner. At the same time, those magnetic fields can seriously affect the detectors and electronics needed for PET scanning.