Thallium-201 scintigraphic quantitation of regional flow disparity and subsequent redistribution in dogs

Although quantitative analysis of postexercise thallium-201 (201Tl) scintigrams has been employed clinically for the diagnosis of coronary disease, the precise relationship of the quantitated defects to microsphere determined blood flow has not been determined. Accordingly, 201Tl was injected during exercise in 12 control dogs and seven with left circumflex (LCf) artery stenosis. Gamma camera scanning was started 10 min after 201Tl injection and continued for 3 hr. In the control animals, scintigraphic 201Tl activities in left anterior descending (LAD) and LCf perfusion territories were equal 10 min after 201Tl injection and the loss of 201Tl activity over 3 hr was 54.3 +/- 3.4% and 57.0 +/- 3.6% (mean +/- s.e.e.) of initial LAD and LCf activity, respectively (p = N.S.). In the experimental group, LCf activity 10-14 min after 201Tl injection averaged 67.4 +/- 5.9% of LAD activity in the same heart (p less than 0.001). Furthermore, LCf activity in the experimental animals was significantly lower than LCf activity in the control dogs (p less than 0.005), while LAD activities were not different in the two groups. The ratio of LCf/LAD scintigraphic 201Tl activity immediately after exercise was linearly related to, but higher than, the ratio of regional blood flows at peak exercise (r = 0.88, p less than 0.001) as determined by microsphere injection. Scintigraphic redistribution was also correlated with directly measured redistribution determined by well counter analysis (r = 0.83, p less than 0.025). Thus, in this exercise model, quantitative 201Tl scintigraphy accurately assessed the initial postexercise flow disparity and subsequent redistribution.