**7.2.3 Positron emission tomography (PET)**

Positron emission tomography is a nuclear medicine technique that produces high resolution tomographic imaging through the detection of high energy photon pairs emitted during positron decay (Costelloeet al., 2009). This method was initially developed in 1960s, but has largely been used as a research tool. However, PET can provide useful information for clinical practice. The images generated by PET represent the metabolic activity of the underlying tissues and can therefore distinguish benign from malignant lesions on the basis of differences in metabolic activity. Similarly, it can identify recurrent diseases in areas in which conventional scans are difficult to interpret because of prior treatment (Costelloeet al., 2009). PET represents the most advanced imaging technique, because it not only allows a three-dimensional image reconstruction, but also it can quantify the activity uptake (Fass, 2008). It combines the highest degree of sensitivity with a resolution of currently, 5-7 mm. The principal applied radionuclide for PET is Fluor-18 (18F) which is known for its ideal half-life to manage (1.83 h). The development of radiopharmaceutical [2-18F]-2-fluoro-2 deoxyglucose (18FDG) has been so far an important progress for PET imaging in oncology (Berghammer et al., 2001). 18FDG acts as a glucose analogue allowing for the visualization of glucose consumption, a metabolic process being massively enhanced in many malignancies (Einat & Moshe, 2010). PET has several advantages include (1) unlimited depth penetration; (2) whole body imaging possible, (4) quantitative molecular imaging and (5) can be combined with CT or MRI for anatomical information (Pysz et al., 2010). The disadvantage of PET is that it requires a conveniently located and expensive cyclotron and radiochemistry facilities to produce the short-half life isotopes and to incorporate these into suitable probe molecules (Fass, 2008).
