• Siemens Biograph mMR

For an examination with the most frequently used tracer, a slightly radioactively labelled "glucose", ^18F-FDG(fluorodeoxyglucose), it is necessary to appear for the examination on an empty stomach, i.e. not to have eaten anything or consumed any drinks containing sugar for up to 6 hours beforehand, as otherwise the examination results may be falsified.

Before the examination, there is an information session in which the doctor obtains important information about the patient's personal situation and explains the examination procedure in detail, such as the radiopharmaceutical used. The discussion is based on an information sheet which the patient is given beforehand to read through and complete (bring reading glasses if necessary).

All metal objects must be removed before the examination, as these could otherwise enter the very strong magnetic field of the MRI scanner and pose a risk of injury that should not be underestimated. Furthermore, electronic devices, wristwatches, credit or chip cards must not be placed near the device, as this could render them unusable or delete them.

It is also very important to inform us whether a pacemaker, artificial heart valves, cochlear implants or other metallic implants/foreign bodies are implanted in the body, as PET-MRI may then only be possible after special preparation or, in individual cases, not at all.

Before the examination, a few millilitres of a radioactively labelled substance, a so-called radiopharmaceutical (also known as a "tracer"), are injected into a vein. This is usually radioactively labelled glucose. Depending on the problem, other radiopharmaceuticals are also prepared for you, for example to visualise the prostate-specific membrane antigen PSMA (in patients with prostate carcinoma).

During the exposure time, which can last up to around an hour depending on the tracer, the radiopharmaceutical accumulates in areas of the body that have a particularly active metabolism or show certain surface characteristics. One example of this is cancer cells, which divide very frequently and therefore often have a very active metabolism.

After the exposure time, the examination takes place in the combined PET-MRI device, which appears very similar to a conventional MRI device. During the examination, the patient lies on their back; depending on the region being examined, light supports are required to improve the image quality. Noise reduction measures are also taken to minimise the (knocking) noises generated by the device during the examination. The examination itself takes between 25 and 90 minutes, depending on the question being asked.

As a hybrid device, PET-MRI is now able to detect the radiation emitted by the radiopharmaceutical (PET component) and, thanks to the high spatial resolution of MRI, assign it to the corresponding anatomical structures. In this way, the advantages of functional imaging and detailed anatomical images are combined in one device. The combination with MRI also enables a slightly lower radiation exposure compared to the combination with computer tomography, as MRI itself does not use ionising radiation to produce images.

Many studies show a significantly higher sensitivity and specificity with PET-MRI compared to PET and MRI as individual methods.

The radiopharmaceutical is rapidly excreted from the body after the examination. The duration depends heavily on the substance used; for common radiopharmaceuticals, the so-called half-life, i.e. the time after which half of the radioactive isotope has decayed, is between approx. 20 minutes and 120 minutes, for example.

Patients with diabetes mellitus:

Diabetics will also be contacted by telephone before the examination in order to coordinate the insulin application prior to the examination; this should usually take place at least 4 hours before the examination combined with an appropriate meal.

Patients with kidney disease:

Patients who are known to have kidney disease, such as chronic kidney failure, should have their current kidney values determined by their GP and bring them to the examination.

Depending on the problem, it may be necessary to administer MRI contrast medium (gadolinium-containing contrast medium) into the vein during the examination in order to better differentiate between the tissues. Overall, this is very well tolerated. However, if there is a very rare allergy to MRI contrast media, this must be reported in advance.

The administration of radiopharmaceuticals during pregnancy and breastfeeding should be avoided. Mothers are advised to stop breastfeeding for at least half a day after the examination. As glucose labelled with radioactive fluorine also passes into breast milk, PET scans are only carried out during breastfeeding if they cannot be avoided.