Medical Imaging: Overview and the Importance of Contrast

Significant medical imaging techniques for in vivo use are magnetic resonance imaging (MRI), optical imaging techniques (including fluorescence), X-ray imaging techniques (including X-ray Computed Tomography, CT), gamma imaging techniques (including Single Photon Emission Computed Tomography, SPECT), positron emission tomography (PET), and ultrasound. The key requirement for any useful medical imaging technology is contrast, achieved either through some endogenous physical mechanism, or through the effects of some exogenous chemical agent, that permits one structure in the body to report a different signal than another. This chapter reviews briefly endogenous and exogenous contrast in medical imaging, and discusses how medical imaging is used.