PET-MR: Hybrid Molecular and Anatomical Imaging
PET shows where cells are metabolically active; MRI shows where that is, with fine soft-tissue detail.
Why combine them
PET provides molecular/metabolic information (e.g. FDG uptake) but limited anatomy. Traditionally paired with CT (PET-CT), it can instead be paired with MRI. MRI adds far better soft-tissue contrast and functional data (DWI, perfusion) and less ionising radiation than the CT component.
Lower radiation and superior soft-tissue contrast make PET-MR especially appealing in children and in regions where MRI excels (brain, pelvis, liver).
Where it helps most
- Oncology: local staging where soft-tissue detail matters (pelvic, head & neck, liver and some paediatric tumours).
- Neurology: epilepsy focus localisation, dementia and neuro-oncology, combining metabolic and structural/functional data.
- Cardiac: inflammation/sarcoid and viability studies in selected centres.
Practical notes
PET-MR is complex and less widely available than PET-CT, with longer acquisitions and technical challenges (MR-based attenuation correction). It is chosen when its specific strengths change management, not as a routine replacement for PET-CT.
Sources
- Ehman EC et al. PET/MRI: where might it replace PET/CT? J Magn Reson Imaging 2017;46:1247–62.
Educational summary for clinicians; availability and indications vary by centre. Not medical advice.
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