Diagnosis

Positron Emission Tomography (PET)

definition

Positron emission tomography (PET) is a special imaging examination method that can be used to make metabolic processes in the body visible. For this, the patient is given glucose with weak radioactive radiation via the vein, made visible with a measuring unit and the information is processed into a spatial image. The sugar is distributed in the body and accumulates, especially in tissues with an increased metabolic rate. In many cases, PET is combined with computed tomography (CT), which at the same time enables spatial imaging.The combined process of PET and CT is used, for example, to diagnose cancer, nervous and heart diseases.

When will the examination be carried out?

Positron emission tomography is most often used to clarify suspected cancer. The examination can also be helpful for the question of whether a cancer that has already been diagnosed has spread. A further indication arises in patients in whom a conspicuous structure has been determined in the course of a computed tomography (CT). PET can show whether this has increased metabolic activity (for example in the case of inflammation or cancerous ulcers) or whether the activity is reduced (for example in scar tissue). In addition, the PET examination is also suitable for monitoring therapy. If, for example, chemotherapy or radiation is carried out for a diagnosed cancer, PET can be used to examine whether the tumor focus (s) are getting smaller or disappearing completely. Even after tumor treatment has been completed, PET can be used as part of follow-up care to determine whether new cancerous ulcers have formed or not. Decisive for the question of whether a patient is indicated for a PET examination is an individual consideration in conjunction with the medical history and the other findings. In consultation with the attending physician, the benefits must be weighed against the stress and the risks of the examination.

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PET from the brain

The brain is the organ with the highest consumption of energy, including sugar. The metabolic activity of the individual brain areas can therefore be easily visualized with the help of positron emission tomography. PET can therefore contribute to the diagnosis of brain tumors, for example. These usually show a greatly increased accumulation of radioactively labeled sugar. The PET examination can also contribute to the diagnosis of the seizure disorder epilepsy. In episode-free phases, activity in the affected areas of the brain is reduced. Conspicuous PET findings are also possible in dementias such as Alzheimer's. The metabolic activity is also rather reduced here. However, the PET examination is not part of the standard diagnosis for these diseases. Therefore, the health insurance usually does not cover the costs. Whether positron emission tomography of the brain is appropriate must therefore be decided on an individual basis.

How PET works

With positron emission tomography, metabolic processes in the body can be made visible. For this purpose, a special variant of glucose is administered to the patient via the vein. This contains a component that releases radioactive radiation. The sugar accumulates within a short time, especially in tissue that has a high metabolic rate. This includes inflamed areas but also tumor cells and metastases. Some organs such as the heart and the brain also accumulate a lot of sugar due to their naturally high energy expenditure. With the help of a so-called PET scanner, the radiation emanating from the body can be recorded from outside and calculated with a connected computer. This allows possible areas with high radiation, i.e. with high sugar turnover, to be displayed. If, in addition to the PET examination, a computer tomography is carried out at the same time, a three-dimensional representation can show exactly in which body region there are areas with an increased metabolism. The doctor performing the examination (usually a nuclear medicine specialist) can assess whether it is a natural distribution or whether, for example, there could be indications of a cancerous ulcer.

preparation

In positron emission tomography, good preparation and compliance with various measures are decisive for good image quality and informative value. Current blood values (especially kidney, thyroid and sugar values) must be determined beforehand. Avoid any physical strain on the day before the examination. In addition, no more food should be consumed 12 hours beforehand. Only water and unsweetened tea are allowed to be drunk during this period. Medication should be taken as usual, with the exception of those that have a strong effect on blood sugar levels. The attending physician will give you recommendations on this. As with any imaging examination, it is also advisable to check any previous findings (CT, MRI, X-rays) bring along. Since the examination involves long waiting times, it is advisable to bring something to read. In some cases, the administration of a sedative can also be useful. In this case, an accompanying person should also be brought along for a PET examination that is carried out on an outpatient basis (not as part of an inpatient hospital stay).

Procedure of the investigation

In positron emission tomography, a vein access is first required. To do this, a small plastic cannula is usually placed and fixed in a vein in the crook of the arm. At the beginning of the examination, a small amount of the radioactively marked grape sugar is injected through this access. Afterwards, some saline solution and a diuretic agent are often given as an infusion (drip) through the venous access. You then have to wait about an hour so that the sugar can be distributed in the body via the blood system. It is very important that the patient sits as still as possible and avoids movements as much as possible. Every movement leads to an accumulation of sugar through muscle activity and can thus influence the test result. Patients who find it difficult to stand still because of nervousness or anxiety can be given a mild sedative. Then the actual examination begins with the PET scanner, which records the radiation emanating from the body. Here, too, the patient should lie comfortably and move as little as possible in order to prevent the images from blurring. The examination takes another 30 to 60 minutes. Unless a sedative has been administered, the patient is not affected in any way after the PET.

Evaluation of the images

The particles released during positron emission tomography are recorded by a special detector. A connected computer calculates the incoming information and generates an image that shows the metabolic activity. Areas with high activity are displayed brighter than those with low activity. Some organs such as the brain or the heart naturally consume a lot of energy and are therefore always clearly visible. In addition, the bladder and other urinary organs stand out because they show the radioactively labeled sugar particles excreted by the kidneys. Supposed over- or under-enrichment without relevance can also occur. The evaluation is therefore very complex and must be carried out by the attending physician (usually a specialist in nuclear medicine or radiology). He can assess whether there are any abnormal findings or not.

Investigation Risks

One risk posed by positron emission tomography is radiation exposure. However, this is very low with PET alone, since only a small amount of weakly radioactive substances is administered that disintegrates again in a short time. Radiation exposure is halved about every two hours after administration of the substance. However, since PET is often done in combination with computed tomography (CT), the risks can also be higher. For the CT, the body is exposed to significantly higher levels of radiation. Therefore, the benefit and risk must always be weighed before such an examination. Especially with children, a PET-CT examination should only be carried out in exceptional cases. Further risks exist if a contrast medium is to be used during the examination. In rare cases, this can lead to an intolerance reaction. Patients with thyroid disease can also be at risk from iodine-containing contrast media. Therefore, an up-to-date determination of the thyroid values must be carried out prior to a PET examination.

Duration of the PET

In most cases, positron emission tomography takes at least two hours. Of this, about 60 minutes make up the waiting time, which is necessary after administration of the radioactively marked grape sugar so that it can be distributed in the body. The actual examination, including the detection of the radiation emanating from the body by the PET scanner, takes about 30 to 60 minutes. In addition, there may be waiting times in advance and time for preparation, for example by talking to the doctor. If necessary, it is advisable to inquire in advance at the respective clinic or practice where the examination will be carried out about how much time should be planned.

Cost of a PET

The cost of a positron emission tomography examination is around € 1,000. A combined examination of PET and computed tomography (CT) costs around € 1,700. In the case of outpatient care, i.e. if the examination is not carried out as part of an inpatient hospital stay, the assumption of costs by the statutory health insurance (GKV) in Germany is currently under discussion. This is justified by the fact that PET cannot replace established and usually cheaper diagnostic methods, but can only supplement them. Only in the case of lung cancer and when clarifying the suspicion of this disease is the chance that the health insurance company will pay the costs. However, an application must be submitted to the health insurance company before the examination. A referral by the treating doctor alone is not sufficient. With private health insurance (PKV), the costs of a PET examination are more often covered. In any case, it is advisable to clarify in advance with the health insurance company (both statutory and private) whether the costs will be covered.

Further information

Further information on the subject of positron emission tomography: