In Vivo Thromboscintigraphy With Indium-111-Labeled Platelets In A Dog-Catheter Model

Autologous platelets from mongrel dogs have been labeled with 200-400 μCi Indium-111 complexed to oxine using the technique of Thakur, McAfee and others. Intraarterial thrombogenesis was studied in vivo by advancing a polyethylene angiographic catheter from a femoral into a carotid artery, then serially imaging the catheter over periods of 0.5-3 hours by scintillation camera with interfaced computer. Quantitative uptake was derived from computer processing of the studies, and compared with in vitro In-111 counts and clot weight obtained at various times by catheter excision. Labeled platelets were injected prior to or at periods of 2 or 24 hours after catheter insertion in order to evaluate both forming and preformed thrombus. Platelet In-111 radioactivity was found to peak at 30-80 minutes in newly forming thrombus and to fall thereafter. In vitro In-111 activity correlated well with wet clot weight.In-111 (% inj. dose) = 0.00209 × (mgm clot) + 0.00091 (r = 0.882) (n = 24)In vivo correlation was also linear, but with a broader scatter of data points. At the peak, In-111 uptake was 0.06044). 019% of i.d. per cm of catheter by in vitro measurement, and clot weight was 27.9±5.6 mgm per cm. Preformed thrombus picked up substantially less of the label (2 hr: 0.017±0.011% i.d./cm; 24 hr: 0.00245).001% i.d./cm) (n=6) and was not imageable in vivo. The study documents the effectiveness of this new platelet radiolabel for quantitative in vivo scintigraphy of newly forming thrombus, which can be useful for comparison of different anti-thrombogenic regimens and different biomaterials. It also indicates, however, the problems that can be anticipated in attempting to image established thrombus in vivo.