Positron-emitting tomography (PET) is a diagnostic procedure that is most commonly referred to as PET-scan, although nowadays almost all such scans are combined with computed tomography in one device. This is a hybrid nuclear and X-ray procedure that is mostly used to help treat patients with cancer. For certain types of cancer this procedure helps to assess the extent of the disease or presence of metastases. PET data may demonstrate changes in еру course of therapy earlier than other imaging tests. In certain types of cancer PET helps to predict treatment response. PET may help in choosing the most appropriate biopsy site and planning the radiation therapy.  

Combination of computed X-ray tomography and positron-emitting tomography in one procedure allows for simultaneous structural and functional assessment depending on the injected pharmaceutical drug. As in all nuclear medicine procedures, PET scan involves intravenous injection of a small amount of radioactive tracer.  For breast cancer the most commonly employed tracer is a labeled glucose. Cells and tissues need glucose to function, and most of the cancer cells require significantly more glucose, compared to normal cells. Due to this effect, most of the cancers are clearly seen on a PET scan.  Performing PET scan exposes the patient to a certain amount of ionizing radiation, both from CT and radiopharmaceutical PET portions. However, the risks of such exposure are usually outweighed by clinical benefits of the procedure. 

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