Generally, medical imaging refers to the specialized techniques and instrumentation used to create images or information of the human body for clinical purposes or medical science (including the study of normal anatomy and function) [1] . For clinical purposes, medical images of specific tissues or organs are obtained to assist in diagnosing a disease or specific pathology.There are many medical imaging modalities and techniques which have been developed in the past few years. The discovery of X-rays by the German physicist Wilhelm Konrad Rontgen and their application to medical examination, new medical imaging methods and devices such as CT, PET, MRI and others promoted the rapid development of Medical Imaging Science and evoked revolutionary changes in traditional medical diagnosis and treatment. With the help of these methods and devices, the images of organs and tissues in the human body can be acquired non-invasively, so as to get more objective information of the body's physiological status and pathological changes, and finally to assist in diagnosis and treatment.The selection of an appropriate medical imaging modality is important for obtaining the target information for a successful pathological investigation. Anatomical structures can be effectively imaged with CT, MRI, ultrasound and optical imaging methods. Furthermore, information about physiological structures with respect to metabolic functions can be obtained through nuclear medicine SPECT and PET, ultrasound, optical fluorescence and several derivative protocols J. Tian, Molecular Imaging