What is PET-CT?
PET-CT is a new precise diagnostic tool to visualize certain types of cancers and their metastases. It is not only possible to image cancer itself but also its activity. The method is particularly useful to monitor the effect and success of therapeutic interventions. The PET-CT investigation pinpoints the exact position, size, activity and spreading of cancer in the entire body.
Smallest cancer cells and metastases are visualized.
The PET-CT examination is the combination of two diagnostic imaging procedures, i.e. Positron Emission Tomography (PET) and Computed Tomography (CT). The imaging devices differ in their functions, thus providing different pictures and information.
In certain diagnostic set-ups, data supplied by PET and CT complement each other ideally. To link these technologies, PET was developed into combined PET-CT. Body structures and functional data are integrated into one image, thus increasing diagnostic precision.
Positron Emission Tomography has been applied successfully for more than 15 years as a diagnostic procedure of nuclear medicine. For this examination very small amounts of radiopharmaceuticals, so-called tracers, are introduced into the body. Their distribution is different in different kinds of body cells and is visualized with the help of the PET camera.
Computed Tomography is an established procedure of radiology to examine body regions layer by layer and provide cross-sections. This results in an exact, highly detailed visualization of the body with precise anatomic images of the region being examined.
What is new about PET-CT?
By means of a PET examination, neither the exact site of cancer cells nor the exact location of pathological changes may be determined. It is the combination of PET and CT procedures which solves this challenge. In a PET-CT, both examinations are performed at the same time with one camera, i.e. providing both PET and CT views. Data obtained are summarized in a fusion image, supplying significant visualizations where the PET image is superimposed with a CT "map". Cell areas high in metabolic activity can be allocated precisely to a tissue layer or an organ and remarkable PET findings can be assessed with greater safety. Based on a PET-CT scan, a tumor may be removed with highest precision or tissue may be removed with greatest focus.
This procedure provides a clear added value both for patients and attending doctors.
How does the procedure work?
The radioactive tracer emits positrons as it decays. These positively charged elementary particles are unstable, releasing energy as they "disappear". This energy can be measured with a detector and serves as a basis to compute computer images. The greater the amount of the substance administered reaching a cell, the clearer this cell is visualized. Most tumor cells consume more sugar than healthy cells. If they are "fed" with radiomarked glucose, they emit increasing radiation, thus providing a clear distinction from healthy tissue in PET images. Tissue that has a high rate of metabolism and a high consumption of sugar appears as especially dark spots on black-and-white PET images, and as especially bright spots on color images.
Studies have shown that the diagnostic accuracy of PET-CT is considerably higher than that of both procedures PET and CT performed separately.
In addition to optimal diagnostics, the patient benefits from having to undergo only one single examination procedure with a marked reduction in investigation time.
- PET-CT combines the advantages offered by PET and CT, thus proving particularly valuable in the exact diagnosis of cancers.
- Best diagnostic safety with lowest radiation exposure and shortest examination period.
- Difficult oncological questions can be answered with PET-CT.
- PET-CT-examinations reveal the exact position, size, activity and spreading of tumors inside the body.
- PET-CT examinations support the attending doctor in treatment plannign tailored to the patient's cancer care needs.
- The doctor's office is headed by the internationally recognized radiologist and specialist in nuclear medicine OA Dr. Martin Heinisch.
Before a PET-CT scan, a mildy radioactive substance, a so-called tracer, is administered to the patient. Usually, glucose radiomarked with fluorine is used for that purpose. Chemically, the radiopharmaceutical is called fluorine-18-deoxyglucose, abbreviated FDG. However, other radiomarked substances playing an important role in the metabolism of tumor cells may also be used. With a special measuring device, the detector, radiation emitted by the substance accumulated in the tissue can be recorded.
PET and CT are performed in immediate succession with the same device. The examination period in the device is about 20 minutes. The entire time period of the investigation, including the preparation period, is about two hours since radiomarked glucose takes about one hour to enrich in the whole body. During the examination procedure, you lie down on a bed moving into the opening of the PET-CT device. The opening is wide and the tube is short so that you will not feel enclosed and are able to stay in constant contact with medical staff. However, you will have to lie without moving and relax so that images easy to assess can be produced.
Main areas of application
Early diagnosis and therapy planning
In one single examination procedure, PET-CT can reveal whether a tumor has already spread to other parts of the body or not. During cancer treatment, PET-CT can monitor as early as after one or two cycles of chemotherapy whether the treatment has been successful. If glucose consumption in metastases is reduced, the therapy is effective. However, if it continues to stay high, early alternatives may be sought to improve the patient's chances.
In follow-up examinations, a PET-CT scan serves to find out whether a tumor has regrown or any subsequent metastates have developed.
PET-CT examinations are applied to reveal the following malignant tumor diseases:
- Pulmonary carcinoma (lung cancer)
- Mammary carcinoma (breast cancer)
- Colorectal carcinoma (bowel cancer)
- Melanoma (black skin cancer)
- Malignant lymphoma (cancer of the lymphatic system)
- Tumors in the head/neck (e.g. larynx cancer)
- Carcinoma of the oesophagus (oesophageal cancer)
- Carcinoma of the pancreas (pancreatic cancer)
- Carcinoma of the thyroid gland (thyroid cancer)
- Cervical carcinoma, endometrial carcinoma (cervical cancer)
- Ovarian carcinoma (ovaria cancer)
- Carcinoma of the bladder (bladder cancer)
- Prostatic carcinoma (prostate cancer)
It is up to the attending doctor to decide whether and when PET-CT is an appropriate examination method.
Are there risks from a PET-CT scan?
Regardless of the combination of two investigative imaging procedures, radiation exposure is slightly lower that that involved in a single computed tomography. The radiopharmaceuticals administered have a very short half-life. It is 110 minutes for the most frequently used substance, FDG, so-called fluorine-deoxyglucose. Half-life is the amount of time required for radioactivity to fall to half its value as measured at the beginning of the time period. Therefore, radiation exposure is reduced rapidly. Since such substances accumulate directly in target organs, low amounts of tracer are sufficient. The tracer's components (glucose) are metabolized normally and have no effects on the body.
As in all examination procedures using ionizing radiation, the radiation amount in PET has to be considered in relation to the information gathered.
PET-CT will only be applied if the doctor assesses the diagnostic benefit to be higher than the radiation risk.
The radiation dose used in PET with radioactive glucose (FDG) amounts to about 5-7 mSv. The CT component in PET-CT involves about 2-13 mSv compared to a radiation dose in contrast-enhanced CT of about 20 mSv. Accordingly, radiation exposure in a PET-CT scan frequently corresponds to the about triple dose of average natural annual radiation exposure found in the European population (about 3 mSv per year). The risk of any potential side-effects caused by radiation is therefore negligibly small.
No allergic or toxic side-effects of FDG are known which are excluded by the extremely low dose of injected FDG in the range of picomol or nanomol itself.
However, PET-CT is contraindicated during pregnancy and breast-feeding.