The clinical use of platelet scintigraphy with 111-In-oxine

Functional and anatomic evaluation of carotid atherothrombosis. A combined study of indium 111 platelet scintigraphy and B-mode ultrasonography

We examined the relation between in vivo thrombogenicity and the morphology of carotid lesions to clarify the role of platelet deposition in carotid atherothrombosis. We evaluated 60 subjects (120 carotid bifurcations) who had at least one established risk factor for atherosclerosis by using indium 111 platelet scintigraphy and high-resolution B-mode ultrasonography. We evaluated platelet accumulation in the carotid arterial wall by means of a dual-tracer method that used In 111-labeled platelets and technetium 99m-labeled human serum albumin. The tracer accumulation was assessed both visually and semiquantitatively by using the platelet accumulation index, ie, the ratio of radioactivity of the amount of In 111-labeled platelets deposited on the vascular wall to the amount of radioactivity in labeled platelets circulating in the blood pool. The morphology of the carotid lesions was analyzed with B-mode ultrasonography in terms of the presence of ulceration, the maximum percent stenosis, the echogenicity of plaque, and the plaque score, which indicates the severity of systemic atherosclerosis. Platelet accumulation increased with increase in plaque score (P < .01), and the magnitude of platelet accumulation was significantly greater in lesions with ulceration than in those without (P < .05). The platelet accumulation index in vessels with plaque showed a very weak but significant correlation with maximum percent stenosis (r = .28, P < .05) and a stronger correlation with the unilateral plaque score (r = .42, P < .0001). Analysis of the echogenicity of plaque showed that heterogeneous plaque had a high frequency of accumulating platelets. Platelet accumulation was related to the surface characteristics and severity of carotid lesions, especially in the presence of ulceration.

Identification of intracardiac thrombi in stroke patients with indium-111 platelet scintigraphy

Platelet scintigraphy (PSC) with indium-111 labelled platelets has been confirmed as an adequate method for the detection of intracardiac thrombi in patients with heart disease. We performed PSC of the heart and the neck vessels in 27 stroke patients with suspected cardiac embolism and as control on 10 patients with atherosclerotic lesions of the carotid arteries without evidence of heart disease. The carotid PSC was positive in 6 of 10 patients with carotid disease, and twice in the 27 with suspected cardiac embolism. In these 27 the PSC of the heart indicated pathological conditions 13 times. Pathological platelet accumulations could be visualized in 3 cases in the atrial space, in 9 cases in the region of the left ventricle, and once at the aortic valve. Scintigraphy was negative in all 10 patients with atherosclerosis of the neck vessels. The two-dimensional echocardiography revealed pathological findings in 8 of the 13 patients with positive heart PSC (3 with intraventricular thrombi, 3 with valvular disease, 2 with decreased ventricular contractility) and was normal in the 10 control patients. Open-heart surgery was performed in 2 patients with pathological PSC and revealed an intracardiac thrombus. Three of 4 patients with positive atrial PSC showed mitral or aortic valve disease. These results suggest that PSC can provide a valuable method for detecting cardiac thrombi in stroke patients.

Dual isotope carotid scintigraphy in patients with amaurosis fugax attacks

A new dual isotope scintigraphic (DISC) examination of the carotid arteries consisting of simultaneous injections of 111In-labeled platelets and 99mTc-labeled red cells was performed on eight male patients suffering from amaurosis fugax attacks. In concordance with the angiographically proven high percentage of significant extracranial carotid disease in patients with amaurosis fugax, six of the eight patients examined had an increased platelet accumulation in the carotid artery clinically affected. In one patient with normal angiography and one amaurosis fugax attack the platelet scintigraphy even revealed a pathological platelet accumulation in the ipsilateral carotid artery. These findings confirm the hypothesis that most amaurosis fugax attacks are due to arterio-arterial emboli originating from atherosclerotic plaques of the carotid bifurcation.

Dual isotope scintigraphy in stroke patients

Platelet scintigraphy is a useful technique to detect atherosclerotic lesions of the neck vessels in stroke patients. The habitual one isotope technique causes false positive and false negative results due to circulating platelet-bound activity. To eliminate these confusing results we performed a dual isotope technique on 20 stroke patients. The new method consists of simultaneous injections of 111-Indium labelled blood platelets and 99mTc labelled red cells, and achieves a calculation of the ratio 111-In/99mTc. Thus the subtraction of the red cell blood flow image can render a pure thrombus formation visible. The habitual visually evaluated one isotope scintigraphy showed positive scans in 11 out of 20 patients, whereas under dual isotope scintigraphy 3 patients showed no 111-Indium excess after subtraction of the red cell image; they can thus be qualified as false positive. In the case of another patient with a visually negative image a thrombus formation could be observed after the subtraction procedure. It seems, that the dual isotope technique in platelet scintigraphy is a valuable refinement on the way to verifiable results.