PET-MRI Scan

PET-MRI acquires a PET scan and an MRI scan at the same time in one machine. The PET part shows metabolic or receptor activity with a radioactive tracer such as FDG, PSMA or DOTATATE. The MRI part supplies the anatomical detail, with much better soft-tissue contrast than CT and no X-ray dose.

It is most helpful in the brain, pelvis, liver, head and neck, and in children and young adults who face many scans over the years, because total radiation is roughly halved compared with PET-CT. It is not better for everything. The lungs are seen less well than on CT, the examination is longer, and for most cancer staging PET-CT gives equivalent answers.

What PET-MRI Scan shows

Depending on the tracer, PET-MRI maps tumour activity against detailed MRI sequences, including diffusion and contrast-enhanced images. In prostate cancer, PSMA PET-MRI localises disease within the gland and in pelvic nodes. In the liver, it separates small metastases from benign lesions. In brain tumours, amino acid or FDG tracers help to tell recurrence from radiation damage. In epilepsy, it identifies the low-metabolism focus for surgical planning, and in dementia it combines amyloid or FDG patterns with volumetric MRI. It is also used for cervical, rectal and head and neck cancers, sarcoma, cardiac sarcoidosis and myocarditis.

When PET-MRI Scan is recommended

• Children, teenagers and young adults with lymphoma, sarcoma or other cancers needing repeated PET imaging
• Primary staging or recurrence of prostate cancer with PSMA tracers, where pelvic MRI is needed anyway
• Brain tumours, drug-resistant epilepsy and selected dementia work-ups
• Liver, pelvic and head and neck tumours where MRI is the preferred anatomical scan
• Patients who would otherwise need a separate PET-CT and MRI, to combine them in one visit

Grenzen und Situationen, in denen ein anderer Test besser ist:

• MRI-unsafe implants: many pacemakers and defibrillators, some aneurysm clips, cochlear implants, or metal fragments in the eye
• Lung nodules and lung cancer staging, which are better assessed with PET-CT
• Severe claustrophobia or inability to lie still for up to an hour
• Severe kidney impairment, if gadolinium contrast would be required
• Situations where PET-CT answers the question equally well and is more readily available

Wie man sich vorbereitet

• Complete the MRI safety questionnaire honestly, listing all implants, stents, surgery and tattoos
• For FDG: fast 4 to 6 hours, avoid exercise for 24 hours, and have diabetes well controlled; PSMA and DOTATATE tracers need no fasting
• Remove all metal, jewellery, hearing aids and medication patches
• Ask about mild sedation beforehand if you are claustrophobic; children may need general anaesthesia
• Bring previous imaging and treatment dates

Was passiert während des Tests

After the tracer injection you rest for 45 to 60 minutes. You then lie in the scanner tunnel, which is narrower and longer than a PET-CT ring, with receiver coils placed over the body and ear protection against the loud knocking. A whole-body study takes 30 to 60 minutes, and dedicated organ sequences may add time. Gadolinium contrast may be injected partway through. You must keep still throughout.

Ergebnisse und nächste Schritte

The study is read jointly by nuclear medicine and radiology specialists, and reports usually take 2 to 3 working days because there is more data to review. As with any PET study, suspicious findings often need biopsy confirmation. Ask for the images in DICOM format so they can be shown at a tumour board or to your surgeon at home.

• Test time: 2 to 3 hours in total, 30 to 60 minutes in the scanner
• Results ready: 2 to 3 working days
• Back to everyday activity: None, unless sedation is used

Sicherheit und Risiken

• Radiation from the tracer only, typically 3 to 8 mSv, about half that of PET-CT
• Heating or movement of metallic implants if safety screening is incomplete
• Reaction to gadolinium contrast, which is rare
• Claustrophobia and noise-related discomfort
• False positive and false negative results, as with PET-CT

Arranging PET-MRI Scan in Türkiye

Few centres in any country have a PET-MRI scanner, so availability may be a genuine reason to have it abroad. Travel for it only when a specialist has explained why PET-MRI, and not PET-CT with a separate MRI, is needed in your case, for example in a child requiring serial scans or for epilepsy surgery planning.

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