What is PET?
The principle of PET imaging is similar to other nuclear medicine imaging techniques. The patient receives a radiopharmaceutical and is then scanned with a PET scanner after a certain period. What makes PET unique is the type of decay from the radioisotopes used (positrons), which, when combined with the highly sensitive PET scanner, can reveal very small lesions.
Today, PET scanners are often combined with Computed Tomography (PET/CT) or Magnetic Resonance Imaging (PET/MRI) machines. The chemical elements used as radioisotopes allow for the labeling of substances that closely resemble naturally occurring compounds in the body. This enables the imaging of specific biochemical and physiological processes in tissues.
Depending on the procedure, the patient will receive the radiopharmaceutical either on a resting bed or directly at the examination table via intravenous injection. The waiting period before the examination, known as the "uptake time," should be spent in a relaxed state, with muscle exertion being avoided. If the procedure requires that the tracer is applied on the examination table, the patient should remain as still and relaxed as possible for up to 60 minutes. Otherwise, the examinations typically last between 15 and 30 minutes, with an additional uptake time of 30 to 45 minutes.
Usually, patients can continue their medication as normal. However, since the [18F]FDG scan typically requires a low blood glucose level, meaning the patient should be fasting, diabetics may need to temporarily stop their oral antidiabetic medications. Diabetics who require insulin can take their morning insulin as usual but should reduce the amount of carbohydrates in their breakfast or remain fasting and adjust their insulin dose accordingly. We ask that you inform us when referring a patient with diabetes mellitus and, if needed, consult with a physician at the PET center.
For an [18F]FDG-PET scan, the patient should have a baseline blood glucose level and be well-hydrated during the tracer application. The patient should fast for at least 5 hours before the examination but can consume plenty of non-sugary drinks, such as mineral water. Physical exertion should be avoided, and even chewing gum can significantly affect scans of the head and neck area.
The patient must be able to tolerate possibly long periods of lying on the examination bed. Besides potential pain relief for back discomfort, mild sedation may be necessary, as some patients may experience claustrophobia while in the scanner. For patients with reduced left ventricular function, it's important to note that lying flat for extended periods may cause considerable shortness of breath unless a forced diuresis is performed before the examination. Different preparations may be required for PET scans with other radiopharmaceuticals, so please consult with us. Due to the short half-life of radiopharmaceuticals, punctual arrival for the appointment is crucial.
The substance most commonly used in PET scans, [18F]FDG, is a glucose derivative and has no significant side effect potential. In rare cases, substances that could potentially cause allergic reactions are used, but they are administered in such small quantities that their side effect potential is minimal, similar to that of radiopharmaceuticals used in conventional nuclear medicine.
Due to the short half-lives of the radionuclides used in PET, the radiation exposure for both patients and staff on the wards is minimal.
Breastfeeding mothers should nurse their baby before the tracer application, then pump and discard the first portion of milk after the examination.
The distinctive feature of PET compared to other nuclear medicine imaging techniques is that the radiopharmaceuticals used are either "natural" compounds that the body cannot distinguish from those it absorbs through food or synthesizes itself, or they are labeled medications chemically identical to their non-radioactive counterparts. This similarity allows them to distribute in the body in the same way.
This enables precise assessment of metabolic processes in the body. For example, it can determine whether a mass following chemotherapy and radiation therapy still contains viable tumor cells or is merely scar tissue. In cardiology, PET can identify heart muscle tissue that could still benefit from vessel-opening procedures like dilation or bypass surgery. In neurology, PET can estimate the extent of seizure foci in cases of poorly controlled epilepsy and help define the target area for potential surgical resection.