Whole-body imaging of thallium-201 after six different stress regimens.

UNLABELLED: There are a number of stress techniques in common use for 201Tl myocardial imaging but few studies have been performed comparing the biodistribution of 201Tl in each case.
METHODS: We studied 36 normal patients after six different stress regimens by whole-body imaging, 40 min after 201Tl injection. The stress regimens were exercise, dipyridamole, adenosine or dobutamine alone in standard doses and exercise combined with a vasodilator (dipyridamole or adenosine).
RESULTS: Cardiac uptake expressed as a percentage of whole body uptake was greater for the vasodilators compared with exercise (p < 0.005), and this difference was unaffected by combining either vasodilator with exercise. Intermediate results were found with dobutamine. Heart-to-liver (p < 0.01) and abdomen (p < 0.05) ratios were greater for exercise compared with the vasodilators, and this difference was also unaffected by combining the exercise with either vasodilator. Heart-to-lung ratios were highest with any stress involving exercise (p < 0.05). The heart-to-background ratios with dobutamine were similar to the vasodilators.
CONCLUSION: Vasodilator infusion yields higher cardiac 201Tl uptake than exercise, but when given alone this results in poor heart-to-background ratios. Combining either vasodilator with exercise maintains the high cardiac uptake, but substantially improves the heart-to-background ratios to levels similar to exercise alone. Dobutamine stress produces an intermediate cardiac uptake, and heart-to-background ratios similar to the vasodilators. Therefore, optimal imaging conditions are obtained by stress which combines a vasodilator with exercise.