Molecular imaging is a novel field that combines the global anatomical/physiologic scale of currently available in vivo imaging modalities with the detailed molecular/cellular scale of biochemistry and cell and molecular biology, with the goal of obtaining a visual representation and characterization of biological processes at the cellular/sub-cellular level in living subjects. As such, molecular imaging represents a multidisciplinary effort exploiting the convergence of image-capture techniques, basic cell/molecular biology, chemistry, medicine, pharmacology, medical physics, biomathematics and bioinformatics into a new imaging paradigm.The approach could allow unraveling of complex disease pathways; diagnosis of disease at the earliest causative stages, characterized by the first signs of metabolic or molecular disturbance; and noninvasive real-time monitoring of disease progression and response to therapy in authentic physiologic environments.

Five imaging modalities have been adapted for molecular imaging applications: radionuclide imaging, including positron emission tomography (PET) and single photon emission tomography (SPECT); optical imaging (bioluminescence and fluorescence); magnetic resonance imaging (MRI); computed tomography (CT); and ultrasound (US).