The formation of new vessels--a process known as angiogenesis--depends on a particular protein called v3 integrin. Albert J. Sinusas of the Yale University School of Medicine and his colleagues injected this signaling protein, which initiates a cascade of cellular processes including cell adhesion, migration and proliferation, into rats and dogs that had suffered injury-induced heart attacks. To determine where the protein ended up, the scientists tagged it with the radionuclide indium 111, which can be detected by its emission of a single gamma ray.
In injured regions of the animals' hearts, the team detected v3 integrin at levels four times higher than in normal tissues. What is more, when the researchers performed autopsies on their animal subjects, they found increased vascular growth associated with the high-protein areas. After establishing this correlation, they succeeded in taking single photon emission computed tomographic (SPECT) images to evaluate changes in angiogenesis over time in living animal subjects.
Such a noninvasive scan may one day be used by doctors to visualize the repair process as it occurs in their human patients. Moreover, when a clogged artery threatens to cause a heart attack, Sinusas says, "in the future, instead of a coronary bypass we are going to stimulate the heart to produce new vessels." SPECT imaging could be the best way to track the effectiveness of these treatments.