Thallium 201 for myocardial imaging: appearance of the normal heart

Thallium 201 myocardial perfusion images were obtained from 13 healthy adults after tracer administration both at rest and at maximal stress. On the rest injected scan, tracer was seen in left ventricular myocardium, liver and spleen. In two subjects with resting tachycardia, the right ventricular myocardium was slightly visualized after tracer injection at rest. When tracer was administered at stress, the left ventricular activity was more nearly homogeneous and the left ventricle was better defined on the scan. The left ventricle to lung background activity ratio increased from 2.4 at rest to 3.4 at stress. The right ventricular myocardium was seen on the stress injected scan. Phantom studies, performed to define the optimum position for visualization of lesions, showed that small lesions were best defined when seen either en face or in tangent. Scans should be performed at stress whenever possible and multiple views are essential.