  The integration of positron emission tomography (PET) and magnetic resonance
imaging (MRI) has been an ongoing research topic for the last 20 years. This
paper gives an overview of the different developments and the technical
problems associated with combining PET and MRI in one system. After explaining
the different detector concepts for integrating PET-MRI and minimising
interference the limitations and advantages of different solutions for the
detector and system are described for preclinical and clinical imaging systems.
The different integrated PET-MRI systems are described in detail. Besides
detector concepts and system integration the challenges and proposed solutions
for attenuation correction and the potential for motion correction and
resolution recovery are also discussed in this topical review.
