PETMRI

PET-MRI is a hybrid imaging modality that combines positron emission tomography with magnetic resonance imaging, enabling simultaneous or sequential acquisition of metabolic and anatomical/functional data. It integrates metabolic information from PET with high-resolution MRI data to improve lesion detection, characterization, and localization.

In a PET-MRI system, a PET detector ring is integrated with an MRI gantry. State-of-the-art devices use silicon photomultipliers and time-of-flight reconstruction to improve sensitivity. Simultaneous PET and MRI data acquisition can reduce total scan time and improve coregistration, compared with sequential imaging.

A key challenge is attenuation correction for PET without CT; MRI-based attenuation maps are derived from Dixon or other sequences, with ongoing methods to include bone and better segmentation. Artifacts and hardware used for MRI or implants can affect accuracy.

Radiotracers include 18F-FDG (FDG) as a workhorse, along with neurodegenerative tracers (amyloid, tau), perfusion tracers, and receptor-targeted tracers; MRI provides diffusion, perfusion, spectroscopy, functional MRI, and high-resolution anatomical imaging.

Applications include neurology (Alzheimer's disease, epilepsy localization), oncology (staging, therapy response), and cardiology (myocardial viability, inflammation). In research, PET-MRI enables multimodal biomarker studies.

Compared with PET-CT, PET-MRI offers improved soft tissue contrast and reduced radiation exposure from MRI (though total dose includes the PET tracer) and better co-registration; downsides include higher cost, longer examination times, limited availability, and more complex safety considerations.

Future developments aim to shorten scans, improve MR-based attenuation correction, expand tracers, and enhance motion correction.