PET/MRI

PET/MRI acquires PET and MRI simultaneously or sequentially using MR-compatible detectors, pairing PET's biological signal with MRI's superior soft-tissue contrast instead of CT. Because MRI adds no ionising radiation, the combined dose is lower than PET/CT, which is why it is valuable in paediatrics and in patients who need repeated scans. It is also used in brain tumours, prostate and pelvic cancers, where MRI already outperforms CT for local staging. In clinical use since 2010, it remains limited by cost, the small number of scanners and long acquisition times, and attenuation correction is harder than with CT because MRI does not directly measure tissue density. Whether the added detail changes management enough to justify the expense is still debated outside those niches. It is PET plus the best soft-tissue pictures, at lower radiation dose but with fewer machines available.