In vivo tracking of stem cells for clinical trials in cardiovascular disease.

Various stem cells hold promise for the treatment of human cardiovascular disease. Regardless of stem cell origin, future clinical trials will require that the location and number of such cells be tracked in vivo, over long periods of time. The problem of tracking small numbers of cells in the body is a difficult one, and an optimal solution does not yet exist. We review the many contrast agents and detectors that have been proposed for stem cell tracking during clinical trials, define the characteristics of an ideal imaging technology, and suggest future directions for research.