CONTEXT: Cerebral tissue damage due to stroke occurs in two stages: Lack of blood causes initial damage, and delayed cell death, presumably by apoptosis, follows in neighboring regions. Dr. Francis Blankenberg, an associate professor of radiology and pediatric medicine at Stanford University, used technetium-99m-rh-Hynic-Annexin V, an imaging marker that binds to cells at an early stage of apoptosis, to identify at-risk tissue surrounding the initial damage caused by stroke. Tc-99m-rh-Hynic-Annexin V attaches to phosphatidylserine, a phospholipid that is expressed on the membranes of neuronal cells undergoing apoptosis and is viewed using SPECT.
RESULTS: Two patients received Tc-99m-rh-Hynic-Annexin V injections after experiencing a stroke. Dieffusion-weighted MR and SPECT images were obtained within 72 hours of the episode and again approximately one month later. T-99m-rh-Hynic-Annexin V identified the damaged area and showed substantial binding in the surrounding at-risk regions. After one month, Annexin V had dissipated and was virtually undetectable. Results were presented in June at the Society of Nuclear Medicine meeting.
IMAGE: Fusion diffusion MR/SPECT images illustrate Tc99m-rh-Hynic-Annexin V binding to cells undergoing apoptosis. Regions of highest binding appear red and yellow. Healthy brain tissue exhibits nearly zero Annexin V binding, in stark contrast to damaged neurons. The skull appears red and yellow because apoptosis, and subsequent Annexin V binding, is widespread in normal bone marrow.
IMPLICATIONS: Tc-99m-rh-Hynic-Annexin V may predict the extent of tissue damage and associated clinical impairments better than MR because it provides a biologically informed image, not merely a physical picture.