A Study on the Clinical Feasibility of Split Dose Thallium-201 Dipyridamole Scan in the Diagnosis of Angina Pectoris

A technique for Thallium-201 imaging after two separate injections of the tracer, which took less than I hour, was performed to evaluate if this technique could be used clinically as a noninvasive screening test of angina pectoris. 29 patients who complained of chest pain were included in this study: 18 patients were proven to have coronary artery disease by coronary angiography and 11 patients had normal coronary arteries. With the patient supine at rest, 1.0 mCi of Thallium was injected intravenously and imaging was performed in the anterior and 50degrees left anterior oblique projections for a preset time according to Okada's protocol. Immediately after acquisition of the rest images, without moving the camera head, an infusion of dipyridamole was done at the rate of 0.14 mg/Kg/min for 4 minutes. Two minutes after stopping the infusion, 1.0 mCi of Thallium was injected intravenously and 50degrees left anterior oblique and anterior projection images were acquired. Images of the same projection were realigned using computer image registration approach (PDP-11/34 computer of DEC company). The rest image was then subtracted from the realigned dipyridamole image to produce an image representing perfusion during dipyridamole induced hyperemia (subtraction image). The results were as follows; 1) All of the subtraction images were of adequate quality for interpretation. 2) 16 cases in 18 patients of angina pectoris and 1 case in 11 normal control showed perfusion defects, so the over all sensitivity and specificity of the subtraction versus rest Thallium image technique for diagnosis of angina pectoris were 89% and 91%, respectively. 3) All patients (8 cases) whose left ventriculography revealed abnormality of regional wall motion showed perfusion defects in corresponding segments. But qualitative analysis of Thallium image could not predict if the patient whose Thallium image revealed perfusion defect has abnormality of regional wall motion. 4) segmental analysis was performed to know the association between the site of coronary artery stenosis and the perfusion defects in Thallium scan, which revealed the sensitivities for detecting stenosis of LCX, LAD & RCA were 50-60% in range and the range of specificities were 89-92%. 5) Adverse effects of dipyridamole were headache (2 cases) and chest pain (4 cases) but aminophylline was not needed in any case. In conclusion, split dose Thallium dipyridamole scan can be used as a noninvasive screening test of angina pectoris reducing the total duration of imaging to less than one hour. Futher applications of this technique may include the assessment of myocardial perfusion before and immediately after coronary angioplasty and coronary artery bypass graft and the evaluation of the impact of pharmacotheraphy on regional myocardial perfusion.

Thallium scan in patients with coronary artery disease: A preliminary report.

Exercise thallium studies of forty-eight patients performed to evaluate coronary artery disease were reviewed. The results of the exercise thallium studies were compared to those of exercise ECG tests done simultaneously, and coronary arteriography performed 2 weeks to more than one year after. The sensitivity and specificity of exercise thallium study were 81.8 and 100 percent whereas those of exercise ECG test were 81.8 and 50 percent, respectively. Sites of abnormalities detected by coronary arteriography correlated with 77.8 percent of thallium studies, but 44.4 percent of exercise ECG tests. The results of exercise thallium studies and exercise ECG tests agreed in 81.3 percent of patients. Exercise thallium study is sensitive and specific and has good correlation with coronary arteriography. It is useful in detection of coronary artery disease, evaluation of extent of the diseased myocardium as well as potency of coronary artery bypass graft.