In vivo monitoring of apoptosis.

The biochemical and physiological processes involved in apoptosis were described from the perspective of detection by standard, clinical, noninvasive imaging modalities. The difficulties of monitoring apoptosis in vivo were discussed. Magnetic resonance imaging (MRI) approaches used to study apoptosis were surveyed. The cell shrinkage associated with apoptosis can be detected due to changes in tissue water T(2) and T(1)rho relaxation times and apparent diffusion coefficient (ADC). Magnetic resonance spectroscopy (MRS) approaches used to study apoptosis in vivo have largely centered on the formation of cytoplasmic lipid bodies, detected by 1H MRS, and metabolic/bioenergetic changes detected by 31P and 13C MRS. The most successful approach to in vivo mapping of apoptosis uses the high specific binding of annexin V or synaptotagmin I to phosphatidylserine (PS) that appears on the extracellular plasma membrane of cells during apoptosis. Technetium-99m (99mTc)-radiolabeling of the annexin V and superparamagnetic iron oxide (SPIO) labeling of the C2 domain of synaptotagmin I allow good in vivo apoptosis detection by gamma camera imaging and MRI, respectively.