PET/MRI: paving the way for the next generation of clinical multimodality imaging applications.

Multimodality imaging and, more specifically, the combination of PET and CT has matured into an important diagnostic tool. During the same period, concepts for PET scanners integrated into an MR tomograph have emerged. The excellent soft-tissue contrast of MRI and the multifunctional imaging options it offers, such as spectroscopy, functional MRI, and arterial spin labeling, complement the molecular information of PET. The development of a fully integrated PET/MRI system is technologically challenging. It requires not only significant modifications of the PET detector to make it compact and insensitive to magnetic fields but also a major redesign of the MRI hardware.