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Prosthetic graft occlusion is most frequent in the early postoperative period when the luminal surface is highly thrombogenic. It is generally believed that graft maturation ultimately results in a non-thrombogenic surface. The accumulation of 111-indium-labelled autologous platelets in Dacron aortofemoral grafts has been measured 1 week following surgery and at intervals of 6 months to 1 year. Platelets from 9 patients were labelled with 111-indium oxine and re-injected. Isotope emissions over the graft and a reference site (aortic arch) were measured daily for 8 days and gamma camera images taken on alternate days. Graft thrombogenicity was calculated as the daily rise in the graft: reference ratio of emissions. All grafts, regardless of age, accumulated platelets and were imaged by gamma camera. Mean thrombogenicity (+/- s.e.mean) 1 week after surgery was 0.21 +/- 0.04 compared with 0.08 +/- 0.03 at follow-up (P less than 0.01). The platelet survival during the early study was reduced at 6.8 +/- 0.6 days but recovered to a value of 8.6 +/- 0.8 days (P less than 0.01) at follow-up. Further grafts, 2, 5 and 9 years old, were studied and all accumulated platelets, especially near the anastomoses. Platelet accumulation on Dacron grafts does diminish with time but persists beyond the period of altered platelet survival and perhaps indefinitely.

Prosthetic femoropopliteal grafts attract platelet thrombus and often occlude in the months following implantation. Hence a technique to measure the in vivo thrombogenicity of different vascular substitutes in patients has been developed. In 28 patients the rate of accumulation of 111-indium-labelled platelets in saphenous vein, polytetrafluoroethylene (PTFE) and double velour Dacron femoropopliteal grafts was studied. One week postoperatively autologous 111In-labelled platelets were injected and the isotope emissions over the graft and contralateral leg counted. Graft thrombogenicity was calculated as the daily rise over 7 days in the ratio of counts over the graft to those over the contralateral leg. Mean thrombogenicity index (+/- s.e.mean) was greatest in the Dacron grafts at 0.24 +/- 0.03 which compared with 0.13 +/- 0.02 in PTFE (P less than 0.05). Saphenous vein was markedly less thrombogenic than either prosthetic graft with a mean index of only 0.025 +/- 0.01 (P less than 0.01). Platelet survival failed to differentiate the three graft materials, demonstrating that the direct measurement of 111In platelet deposition was a more sensitive technique.

The relationship between the rate of 111In-platelet deposition on vascular grafts and subsequent thrombosis has been examined in patients undergoing femoropopliteal by-pass. Sixty-seven patients undergoing femoropopliteal by-pass using vein, Dacron or PTFE were randomized to aspirin plus dipyridamole (ASA/DPM) or placebo. Autologous 111In-platelets were injected in the second postoperative week and Thrombogenicity Index (TI) calculated as the mean daily rise in the ratio of radioactivity graft/contralateral thigh. Graft patency was assessed to 1 year. Mean (+s.e.m.) TI at 1 week in 21 grafts that occluded within 12 months was 0.19 +/- 0.018 compared with 0.07 +/- 0.009 in the 38 that remained patient (P less than 0.001). Grafts with a TI less or greater than the median had a 90 per cent or 39 per cent cumulative 1-year patency, respectively (P less than 0.001). In the prosthetic grafts ASA/DPM reduced mean TI from 0.17 +/- 0.02 to 0.11 +/- 0.01 (P less than 0.02) and enhanced 1-year patency from 36 to 67 per cent (P less than 0.05). Following femoropopliteal by-pass TI related to subsequent graft patency. Radiolabelled platelet deposition therefore provides a guide as to how new materials or antithrombotic drugs may influence clinical graft thrombosis. Platelet inhibition reduced both graft thrombogenicity and subsequent occlusion.

The extensive morbidity and mortality of intra-abdominal abscess is mainly due to the delay in a diagnosis. The diagnostic accuracy of 111In-labelled mixed leucocytes with gamma imaging has been investigated in 100 consecutive patients including 34 following surgery and 36 with inflammatory bowel disease. White cell scans were performed 24 h following injection of autologous 111In-labelled leucocytes and were compared with clinical outcome where abscess was only diagnosed when pus either discharged or was drained at operation. Gamma images detected 28 of the 30 abscesses with no false positives giving 93 per cent sensitivity and 100 per cent specificity. Loculi of pus were identified in 11 of the 36 patients with inflammatory bowel disease with no errors in interpretation. Inflammation was reported in 15 of the remaining 25 patients with known but not necessarily active inflammatory bowel disease. 111In-labelled leucocyte imaging provides a rapid, safe and precise method for detecting intra-abdominal abscess even in the presence of inflammatory bowel disease.

A radionuclide method for detecting established thrombi at all sites in the lower limb would have several advantages. Autologous platelets were labelled with 150 microCi (5.5 MBq) indium-111-oxine and re-injected into patients who were imaged with a gamma camera and data processed by a medical computer. Areas of increased uptake on imaging were correlated with the sites of thrombi identified by bilateral ascending venography. Venography in 27 patients identified 12 unilateral and 5 bilateral thrombi. On the day following the re-injection of labelled platelets, imaging identified thrombi at 13 sites in 24 limbs giving an overall correlation with venography of 84.4 per cent, correlation for the calf and thigh being 79.5 per cent and 89.1 per cent respectively. In the thigh 57.1 per cent of thrombi were identified by imaging and 52.9 per cent in the calf. Activity over thrombi was at least 20 per cent higher than in adjacent areas or at similar sites in the contralateral leg. Herapin therapy is considered to affect the detection of deep vein thrombus adversely by this technique. The technique offers a useful method for the diagnosis of both early and established thrombi at any site in the lower limb.

A technique for monitoring pancreatic allografts in man is presented. The method utilizes 111-indium labelled autologous platelets and provides quantitative and qualitative analysis of uptake of the tracer by the graft. Five patients without any significant accumulation of radiolabelled platelets in their transplants had an uneventful recovery and left hospital with satisfactory graft function. The three patients who suffered graft failure showed abnormal uptake of the tracer. This presented as a diffuse platelet accumulation within the transplanted pancreas in the case of acute rejection, or as a focal accumulation in two cases of venous thrombosis. Minor complications such as perigraft haematoma can also be diagnosed using this technique. We suggest that 111-indium labelled platelets provide a valuable diagnostic aid in the management of pancreatic transplant recipients.