Imaging Vascular Grafts In vivo with lndium-111-Labeled Platelets

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Abstract
Platelets labeled with 111In were used to visualize polytetrafluoroethylene (PTFE) bypass grafts in vivo and to quantitate platelet deposition vs. time. The grafts were inserted into the femoral and carotid arteries of dogs and were 1st exposed to unlabeled blood for 0-3 h. They were then imaged for up to 5 days. An index of activity, designed to correct for isotope decay and changing levels of background, was used to quantitate platelet deposition. Grafts exposed to unlabeled blood for, at most, 1 h were visible immediately. When labeled platelets were administered to the circulation after at least 2 h, grafts became visible only after 3 days. Continuous imaging of fresh implants, showing that platelet deposition does not increase monotonically with time, was used to explain this phenomenon. The interpretation of nuclear images of synthetic grafts depends on the delay between establishing flow in the grafts and the administration of labeled platelets.