Thallium-199: a new radiopharmaceutical for myocardial perfusion imaging.

The efficacy of a new radionuclide, thallium-199 for myocardial scintigraphy was compared with conventional thallium-201 imaging. Owing to the 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 nuclide, thallium-201. Studies were performed in a total of 177 patients. The patients were divided into two groups(a) 17 patients with acute myocardial infarction and (b) 160 patients undergoing coronary angiography: 55 patients with no significant coronary artery disease and 105 patients with coronary disease. The sensitivity of the test was 92% with a specificity of 82% and overall predictive accuracy of 84%. Myocardial images obtained with low and high energy collimators have similar predictive accuracy. Perfusion defects were detected more frequently with increasing severity of angina. Myocardial infarction was characterized by persistent defects and myocardial ischaemia by redistribution of 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 myocardial imaging agent, with a predictive accuracy for the diagnosis of coronary artery disease similar to thallium-201, but a significantly reduced total body dose permits repeat studies with a reduced radiation dose for the patient.