Nononcological musculoskeletal disorders are a major cause for patient consultations, and often cause diagnostic difficulties that can be overcome by advanced imaging methods. These include the sensitive detection of structural changes of soft tissue, which are often the cause of subsequent clinical problems, as well as the sensitive detection of metabolic and inflammatory processes that underlie structural changes. Therefore, PET/MRI may be the preferred approach for diagnosing musculoskeletal diseases in a single examination: PET can provide essential information on early metabolic changes in musculoskeletal disorders, while MRI provides the precise anatomical detail essential to characterize musculoskeletal disorders.

However, PET/MRI has only recently been introduced. Following the complete integration of the PET detection system based on simultaneous avalanche photodiodes with MRI by Siemens Healthineers,1 in 2013 GE HealthCare introduced an integrated PET/MRI system capable of performing whole-body PET using time-of-flight (TOF) technology. This system uses silicon photomultipliers directly coupled to lutetium yttrium oxyorthosilicate crystals as light detectors in the PET detection system.2 Clinically used whole-body PET/MRI systems, which combine PET with the excellent soft-tissue contrast of MRI, offer qualitative and quantitative accuracy comparable to that of PET/CT systems. However, implementing PET/MRI on a daily basis is neither cost- nor time-effective to gain the excellent resolution, and the deployment of PET/MRI scanners is therefore limited, which may explain the limited number of studies on PET/MRI in musculoskeletal diseases.

In this review article, technical considerations and various musculoskeletal disorders are discussed and placed in the context of MRI and PET imaging. Wherever possible, specific PET/MRI studies are mentioned, highlighting the value of integrated imaging for better diagnosis of musculoskeletal disorders. Clinical indications as well as MRI and PET protocols are summarized in Table 1.