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Introduction
Positron emission tomography (PET) is one of the fastest growing techniques in nuclear medicine today. Fluoro-deoxyglucose (18F-FDG) is an analog of glucose and, as such, a versatile radiopharmaceutical with major applications in oncology, neurology, and cardiology. Clinically 18F-FDG PET is most widely used for cancer detection that tumors were seen as hypermetabolic lesions by an increase in tracer uptake 1. The availability of various radiotracers labeled with positron emitters currently enables even the quantitative assessment of not only the glucose and protein tissue metabolism but also the extent of enzyme expression, receptor density, the presence and degree of neurotransmitter activity, blood flow, tissue hypoxia and angiogenesis. This enables molecular alterations to be revealed even when structural and morphological changes are unidentifiable or difficult to identify. Many papers have demonstrated both the relevant impact of FDG PET (as a molecular imaging technique enabling early assessment of molecular alterations invivo) on early diagnosis, staging of many cancers and the superior accuracy of the technique compared with conventional diagnostic methods for pre-treatment evaluation, therapy response evaluation and relapse identification. In particular PET was found useful in identifying lymph nodal and metastatic spread, thus altering patient management in more than 30% of cases 1, 2. PET images show functional information, however they provide limited anatomical data, which in regions such as the head and neck, mediastinum and pelvic cavity is a significant drawback 2, 3. The exact localization of lesions may also be difficult in some cases on the basis of PET images alone. In many cases, the studies are interpreted with the help of anatomic information in X-ray CT and magnetic resonance (MR) images 3. However, image fusion is often difficult or impossible, as CT or MR examinations are not always available. When they are, they may have been performed at different times or may not be appropriate for an effective comparison. It should also be borne in mind that even when optimal images are available, complex software is required for image fusion, which creates numerous technical problems and requires anything but short turn-around times. The significant impact of these problems on clinical practice has prompted the manufacturers of imaging devices to develop a hybrid device (PET/CT) consisting of a single patient bed, a high quality PET scanner and a multislice CT device 4. In the last 2 years, PET imaging in oncology has been migrating from the use of dedicated PET scanners to the use of PET/CT tomographs. According to a recent market study, sales of PET/CT scanners have surpassed those of dedicated PET scanners by 65% since 2003 and sales of PET/CT scanners are anticipated to grow by more than 95% over the next few years 5.
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