PETMR

PETMR is a hybrid imaging modality that combines positron emission tomography (PET) with magnetic resonance imaging (MRI) for simultaneous acquisition of metabolic and anatomical data. A radiotracer reveals metabolic processes, while MRI provides high-resolution soft-tissue detail and functional information, enabling precise correlation between physiology and structure.

PETMR systems integrate PET detectors within an MR scanner, allowing concurrent PET and MR data collection. The setup relies on MR-compatible detectors, shielding, and MR coils, enabling image co-registration without moving the patient between modalities.

Accurate attenuation correction is essential for quantitative PET. In PETMR, MR-based attenuation maps (MR-AC) replace CT data; developing reliable bone representation is a key challenge, with approaches including Dixon/segmentation, atlas methods, and ultrashort echo time sequences.

Compared with PET/CT, PETMR can reduce overall radiation exposure and offer superior soft-tissue contrast from MRI, along with simultaneous functional information. Drawbacks include higher cost, longer scan times, stricter safety requirements, and more complex workflow.

PETMR finds use in neurology (neurodegenerative diseases, epilepsy, brain tumors), oncology (radiotherapy planning and monitoring in brain, liver, pelvis), and cardiology (myocardial viability and perfusion). It supports research into multimodal biomarkers and treatment response.

While 18F‑FDG remains the most common tracer, many PETMR studies employ specialized tracers targeting hypoxia, proliferation, or receptors. Multimodal protocols often combine diffusion-weighted imaging or functional MRI with metabolic PET data.

Limitations include cost, limited availability, exposure to MRI-related risks (implants, claustrophobia), and ongoing challenges in motion management and data integration across modalities.