Cancer is a major health problem and a leading cause of death in the world even if adequately treated. It will continue to be a chronic and debilitating disease. The key to improving the overall quality of life and to decrease lingering morbidity in cancer depends on continuous monitoring of disease activity, accurate staging, early detection of recurrence and initiation of appropriate and effective treatment. Obviously, there are very complex undertakings in spite of major advances in recent years in medical imaging and other diagnostic initiatives. By now it has become clear that structural imaging with CT and MRI suffers from many shortcomings and cannot be relied upon solely for optimal management of these patients. Positron emission tomography (PET) is a molecular imaging technology which utilizes tracers for assessing metabolic and biochemical pathways in a non-invasive and quantitative manner. By now, its role in oncology is well established by its ability to assess and characterize the metabolic and functional parameters of malignant tissues [1, 2]. PET/CT and PET-MR fusion imaging is emerging as the most effective multimodality approach and a significant advance for examining patients with cancer. The unique advantage of combined molecular and structural information provided by these multimodalities is to exploit the advantages of both and evaluate their role in many complex settings [3]. A large number of radiolabeled compounds targeting specific molecules or biochemical pathways have been and continue to be synthesized and validated as PET tracers. The leading tracer that is being widely used is 18F-fluorodeoxyglucose (FDG). The concept of the FDG technique was born in 1973 and was tested in 1976 at the University of Pennsylvania and ever since the critical role of molecular imaging in medicine emerged around the globe. This glucose analogue imitate glucose metabolism in the healthy and diseased tissue [4]. The idea behind using FDG in cancer is that the malignant cells are characterized by enhanced glucose consumption [5]; hence FDG-PET imaging allows detection and characterization of cancer based on the presence and the degree of 18F-FDG uptake. The evolution of FDGPET from a basic science and experimental undertaking to a powerful clinical modality has lead down a strong foundation for molecular imaging as a new specialty in medicine.