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

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.

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).

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.

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.