Apoptotic cell death: its implications for imaging in the next millennium

Apoptosis, also known as programmed cell death, is an indispensable component of normal human growth and development, immunoregulation and homeostasis. Apoptosis is nature's primary opponent of cell proliferation and growth. Strict coordination of these two phenomena is essential not only in normal physiology and regulation but in the prevention of disease. Programmed cell death causes susceptible cells to undergo a series of stereotypical enzymatic and morphologic changes governed by ubiquitous endogenous biologic machinery encoded by the human genome. Many of these changes can be readily exploited to create macroscopic images using existing technologies such as lipid proton magnetic resonance (MR) spectroscopy, diffusion-weighted MR imaging and radionuclide receptor imaging with radiolabeled annexin V. In this review the cellular phenomenon of apoptotic cell death and the imaging methods which can detect the process in vitro and in vivo are first discussed. Thereafter an outline is provided of the role of apoptosis in the pathophysiology of clinical disorders including stroke, neurodegenerative diseases, pulmonary inflammatory diseases, myocardial ischemia and inflammation, myelodysplastic disorders, organ transplantation, and oncology, in which imaging may play a critical role in diagnosis and patient management. Objective imaging markers of apoptosis may soon become measures of therapeutic success or failure in both current and future treatment paradigms. Since apoptosis is a major factor in many diseases, quantification and monitoring the process could become important in clinical decision making.