Quantitative myocardial perfusion scintigraphy with thallium-201 has provided an increase in accuracy of coronary artery disease detection. Myocardial uptake and clearance data based on thallium-201 kinetics in normal subjects is using in quantitative interpretation of myocardial perfusion scan. Exercise and pharmacologic stress make different hemodynamic effects and different myocardial uptake and clearance of thallium-201. Effect of background subtraction on thallium-201 myocardial perfusion scintigraphy may also be different due to different thallium-201 biokinetics in each type of stress used. This study was aimed to evaluate the effects of the background subtraction on myocardial thallium-201 biokinetics according to the type of stress used.

Fifteen healthy volunteers underwent planar thallium-201 myocardial perfusion imaging with peak treadmill exercise and intravenous infusion of dipyridamole, adenosine, or dobutamine. Each subject underwent another planar thallium-201 myocardial perfusion imaging at 4 hour later, as a redistribution imaging. Count densities from ROIs(regions of interest) drawn over left ventricle, lung, and liver were compared between before- and after background subtraction.

Before background subtraction, absolute myocardial thallium-201 uptake was greater after pharmacologic testing than exercise testing in both stress and redistribution imaging. Myocardial thallium-201 clearance was lower during pharmacologic stress than exercise. After background subtraction, myocardial thallium-201 uptake was higher during exercise than pharmacologic testing. The percentage change in clearance was higher with exercise testing, while the percentage change in uptake was higher with pharmacologic testing.

Thallium-201 uptake and clearance in heart and adjacent structure were different between adenosine, dipyridamole, dobutamine, and exercise testing. Background subtraction results in different myocardial uptake and clearance data due to different extracardiac uptake subtracted in each stress method. The diagnostic criteria for quantitative analysis of myocardial perfusion imaging must be specified for types of myocardial stress and processes used for background subtraction.