ABSTRACT
Medical imaging has undergone signi cant development over the past three to four decades. New imaging modalities have been introduced, the quality of images has improved greatly, and the variety of information that can be derived from these systems has increased, allowing excellent diagnosis of disease and monitoring of therapy. For example, magnetic resonance imaging (MRI) is used to visualize tumors, computed tomography (CT) can delineate the coronary arteries, ultrasound is used in prenatal checkups, and positron emission tomography (PET) is used as a readout for glucose metabolism. e information derived from such imaging is due to contrast in the images. e contrast may be manipulated by adjusting the imaging parameters in some techniques, such as MRI, but the introduction of exogenous agents to provide additional contrast has been very useful in all methods of imaging. In some techniques like PET or single photon emission tomography (SPECT), contrast agents are a prerequisite.
