As can be understood from its name, PET/CT is an imaging device that is formed of the positron emission tomography and computerized tomography. PET/CT has opened an era in medical imaging and in year 2000, has been selected as the “innovation of the year” in medical world by TIME magazine.
As known, PET is a nuclear medicine method that is used for years and gives 3 dimensioned image of physiological processes of the body. However, since it does not give adequate anatomic data, the clinical interpretation and the determination of the lesion’s exact localization becomes hard.
The combination of PET device with CT removes this problem. PET/CT device provides the supply of anatomic and physiological data within one single session and improves the accuracy of the examination. Furthermore, as a result of using the CT component in the correction of attenuation, the examination has been accelerated at a certain value. The PET examination that was lasting for 1.5-2 hours with the previous generation PET scanners have been dropped to 20-30 minutes with the new generation PET/CT devices. This feature is a great improvement for the oncologic patients who cannot stay motionless for a long period of time.
Positron emitting radiopharmaceuticals are used for PET/CT examination. The one that is frequently used is 2-floro-2deoksi D-glucose that is shortly known as FDG (florodeoxy glucose). After FDG, a glucose analog, is taken into the cell, it is transformed into FDG-6-phospate with hexokinase enzyme. However, cannot progress to the other phases of glycolysis. As tumor cells, the cells that exhibit high metabolic activity are exposed to retention with this mechanism. Of course for viewing the metabolic activity by PET/CT scanner, FDG should be marked with a positron spreader (Flor-18).
F-18 is a radiopharmaceutical that has exactly 110 minutes halflife and it is a “cyclotron” product. After F-18 is obtained, it is conjugated to FDG through an automatized series of chemical reactions. The 110 minutes halflife of F-18 provides opportunity for the carriage of 18F-FDG. So, radioactive substance can be carried to the centers that do not have cyclotron but have PET/CT.
The radionuclide such as 82Rb, 11C, 13N that are used in PET/CT can only be used in centers that have cyclotron since their halflife is very short and there is no possibility of carriage.
For PET/CT, the patients should be fasting for 6 hours before the examination. The patients can have drugs except insulin or oral anti-diabetic. Since the endogenous glucose enters into competition with FDG in diabetic patients, the quality of the image can be sub-optimal. For this reason, before FDG injection, the blood glucose level is analyzed and generally over 180 mg/dL blood glucose levels, PET/CT is not recommended. Patients are scanned 1 hr postinjection.
Majority of PET/CT applications are used in oncology field. They are used in diagnosing and staging of pulmonary cancer, lymphoma, malign melanoma, head and neck tumors, breast cancer, colorectal cancers, esophageal and stomach tumors, gynecologic cancers, mesothelioma, primary bone tumors and primary unknown metastases and for the evaluation of the response to the treatment.
Another utilization field of PET/CT is the determination of the viable but hibernal tissue amount after myocardial infarction. In this indication, PET/CT is accepted as a gold standard.
PET/CT is also used for determining the epileptic focus for the evaluation of a surgery chance in refractory epilepsies in neurology and for early diagnosis of Alzheimer disease.
Following the utilization of new radiopharmaceuticals in PET/CT applications, the indications will be wider.
Please follow the following link for seeing the list of the indications which are currently approved and paid by social security institute
http://www.sgk.gov.tr/doc/teblig/SaglikUygulamaTebligi.html
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