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SUMMARY Indium-111 ("'In) bound to 8-hydroxyquinoline can be used to label platelets without impairing their ability to participate in active thrombosis. The purpose of this study was to identify intracardiac thrombi using "'In platelet scintigraphy. Twenty-nine patients were studied. Twenty-one had discrete left ventricular aneurysms (group 1). The remaining eight patients (group 2) had normal or minimally narrowed coronary vessels (< 50%) and a global ejection fraction of 54 ± 14% (mean i SD) without segmental dysfunction on contrast ventriculography. Six of the eight patients with insignificant coronary disease had severe mitral valve disease requiring surgery. Each intravenous injection contained 3.4 ± 1.6 X 109 platelets labeled in a solution of acid citrate dextrose and saline (1:7, pH 6.5) with 454 ± 144 ,Ci (mean ± SD) "'In complexed to 8-hydroxyquinoline with a final labeling efficiency of 67 ± 17%. Platelet recovery at 15 minutes was 37.8 + 14.5% (mean i SD; n = 15). Imaging was performed in the anterior, left anterior oblique 450 and left lateral views (the right anterior oblique 450 view was included in all except patients 1-5 in group 1) on the day of injection and at 1-2-day intervals for a maximum of 8 days. In group 1, nine patients had abnormal areas of increased activity within the left ventricle. Four required aneurysmectomy and had left ventricular thrombi; a fifth died and at autopsy evidence of a thrombus was found. In four patients (the only patients in whom these data were obtained), surface thrombus "'In activity was at least 9.7 times greater than that of blood, noninvolved myocardium and deeper aspects of the thrombus. Twelve patients with aneurysms had normal scintiphotos. Six required aneurysmectomy and were negative for thrombi. All the patients in group 2 had negative platelet scintiphotos. The six patients who required mitral valve replacement had no thrombi at surgery. Therefore, the diagnostic accuracy of platelet scintigraphy (both groups) in the 17 patients in whom surgical or postmortem confirmation of thrombi could be obtained, five of whom had positive scintiphotos, was 100%. We conclude from this preliminary study that "1'In platelet scintigraphy promises to be a reliable method for the identification of left ventricular thrombi.INDIUM-111 ("'In) is a gamma-emitting radionuclide that emits two photons per disintegration with energies of 173 and 247 KeV and has a half-life of 67 hours. It is well suited for scintigraphic imaging. When bound to 8-hydroxyquinoline, it forms a lipidsoluble compound that is an effective platelet label and does not appear to affect the ability of the cell to participate in thrombus formation.' Therefore, platelets labeled in this way seem suitable for the detection of hematologically active intracardiac thrombi.Thirty to 70 percent5"8 of patients with left ventricular aneurysms, proved at autopsy or surgery, have mural thrombi. In clinical studies, systemic emboli occur in 6-13%5 9, 10 of patients with aneurysms, and the incidence is even higher...

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