THALLIUM-199 - A NEW RADIOPHARMACEUTICAL FOR MYOCARDIAL PERFUSION IMAGING

The efficacy of a new radionuclide, thallium-199 for myocardial scinti graphy was compared with conventional thallium-201 imaging. Owing to t he short half-life of thallium-199 (7.4 hours), when the injected dose of thallium-199 was increased to 200 MBq, the total dose reaching the critical organs was 3.6-15.5 times lower than with conventional nucli de, thallium-201. Studies were performed in a total of 177 patients. T he patients were divided into two groups (a) 17 patients with acute my ocardial infarction and (b) 160 patients undergoing coronary angiograp hy: 55 patients with no significant coronary artery disease and 105 pa tients with coronary disease. The sensitivity of the test was 92% with a specificity of 82% and overall predictive accuracy of 84%. Myocardi al images obtained with low and high energy collimators have similar p redictive accuracy. Perfusion defects were detected more frequently wi th increasing severity of angina. Myocardial infarction was characteri zed by persistent defects and myocardial ischaemia by redistribution o f thallium. Thallium-199 myocardial scintigraphy performed at rest can be used for the diagnosis of acute myocardial infarction and for the determination of infarct site and extent. Thallium-199 is a new myocar dial imaging agent, with a predictive accuracy for the diagnosis of co ronary artery disease similar to thallium-201, but a significantly red uced total body dose permits repeat studies with a reduced radiation d ose for the patient.