Positron emission tomography represents a nuclear medicine diagnostic procedure for evaluating metabolic processes within the human organism. The procedure is used primarily in oncology, cardiology, and neurology.
What is positron emission tomography?
Positron emission tomography is used in particular for the diagnosis and early detection of tumor diseases such as prostate cancer, thyroid and bronchial carcinomas, meningiomas, and pancreatic tumors. Positron emission tomography (PET) is a diagnostic imaging technique used in nuclear medicine to visualize metabolic processes in the human body. For this purpose, sectional images are produced with the aid of radioactively labeled biomolecules (radiotracers or radiopharmaceuticals) and a special camera, which are used to assess specific questions. The method is used in particular in oncology, cardiology and neurology. Because positron emission tomography functionally images the metabolic processes of the organism, in many cases it is combined with computed tomography (PET/CT), which provides additional morphologic or anatomic information.
Function, effect, and goals
Positron emission tomography is used in particular for the diagnosis and early detection of tumor diseases such as prostate cancer, thyroid and bronchial carcinomas, meningiomas, and pancreatic tumors. In addition, the procedure is used to check the success of cancer therapy and to detect possible metastases (daughter tumors). In neurology, positron emission tomography can be used to diagnose various brain disorders (including Parkinson’s disease, Huntington’s chorea, low-grade malignant gliomas, determination of the triggering focus in epilepsy) and to differentiate them from other diseases in terms of differential diagnosis. In addition, positron emission tomography enables an assessment of dementia-related degeneration processes. Visualization of myocardial perfusion and oxygen consumption by the heart muscle can be used within cardiology to check cardiac function and detect, for example, coronary circulatory disorders or heart valve defects. For this purpose, depending on the target organ, a specific radiotracer (for example, radioactively labeled glucose in the case of suspected tumor disease) is injected intravenously into the arm of the person concerned. After about one hour (50 to 75 minutes), the radiotracer has been distributed in the target cells via the bloodstream, so that the actual measurement can take place. When the radiotracer decays, positrons (positively charged particles) are released that are unstable and release energy during their decay, which is recorded by detectors arranged in a ring. This information is transmitted to a computer, which processes the obtained data into an accurate image. Depending on the metabolism of the specific cells, the radiolabeled biomolecules are absorbed to different degrees. The cell areas that show increased metabolism and correspondingly increased absorption of the radiotracer (including tumor cells) stand out from the surrounding tissue areas in the computer-generated image due to an increased glow, allowing a detailed assessment of the expression, stage, localization and extent of the specific disease present. During the examination, the affected person lies as still as possible on a couch to increase the significance of the examination result. Since muscle activity can also lead to increased absorption of the radiotracer, especially glucose, a sedative can be used if necessary to avoid stress or tension. Following positron emission tomography, a diuretic is also administered intravenously to ensure prompt excretion of the radiotracer. In addition, the organism should be supplied with sufficient fluids. As a rule, positron emission tomography is combined with computed tomography, which allows a more accurate and detailed evaluation and reduces the duration of the examination.
Risks, side effects and dangers
Although it is assumed that radiation exposure from the radiolabeled tracer is low (comparable to radiation exposure during computed tomography) and that the radioactive particles are promptly excreted, a potential health risk cannot be completely ruled out. Accordingly, an individual risk-benefit assessment should always take place prior to positron emission tomography. Positron emission tomography is contraindicated in pregnant women due to radiation exposure, to which the unborn child is generally sensitive. Rarely, an allergic reaction to the radiopharmaceuticals used can be observed, which can manifest itself in the form of nausea, vomiting, skin rash, itching, and shortness of breath. In very rare cases, circulatory problems may also be observed. In addition, a hematoma may occur in the area of the injection needle. Very rarely, the injection causes infections, secondary bleeding or injury to the nerves. The use of a diuretic substance following positron emission tomography may cause a drop in blood pressure and, if urinary flow is impaired, colic (spastic contractions). If an antispasmodic drug is used, glaucoma may temporarily worsen and dry mouth and discomfort during urination may occur. Glucose or insulin applied in advance of positron emission tomography may cause transient hyperglycemia or hypoglycemia in diabetic patients.
