Split dose thallium-201 dipyridamole imaging: A new technique for obtaining thallium images before and immediately after an intervention

A technique for performing thallium-201 imaging after two separate injections of the tracer, closely spaced temporally, was developed (split dose thallium technique). Thirty patients were studied; 23 had significant coronary artery disease and 7 did not. With the patient supine at rest, 1.0 mCi of thallium was injected intravenously and imaging was performed in the anterior and 50° left anterior oblique projections for a preset time. Immediately after acquisition of the rest images, without moving the camera head, an infusion of dipyridamole commenced at 0.14 mg/kg per min for 4 minutes. Two minutes after stopping the infusion, 1.0 mCi of thallium was injected intravenously and 50° left anterior oblique and anterior projection images were acquired. Two and a half to 3 hours after the dipyridamole infusion, myocardial imaging was repeated in the two projections. Images of the same projection were realigned using a computer image registration approach. The rest image was then subtracted from the realigned dipyridamole image to produce an image representing perfusion during dipyridamole-induced hyperemia (subtraction image).The subtraction images were of adequate quality for interpretation in 29 of 30 patients. The subtraction and rest images were displayed side by side and each of six segments interpreted as demonstrating normal thallium activity, or transient, persistent or combined transient/ persistent defect. Of 45 stenosed coronary arteries, 84% demonstrated thallium defects in appropriate segments. Of 42 normal coronary arteries, 98% demonstrated normal activity in the corresponding segments of the thallium images. The overall sensitivity and specificity of the subtraction versus rest thallium image technique for coronary artery disease were 91 and 100%, respectively.This study demonstrates that a split dose thallium imaging technique allows technically adequate imaging before and immediately after dipyridamole within a relatively short period of time. Future applications of the technique may include the assessment of myocardial perfusion before and immediately after exercise, coronary angioplasty and coronary thrombolysis with streptokinase and the evaluation of the impact of pharmacotherapy on regional myocardial perfusion