CLINICAL INVESTIGATIONS Poststress Motionlike Artifacts Caused by the Use of a Dual-Head Gamma Camera for 201Tl Myocardial SPECT

When performing 201Tl myocardial SPECT using a dual-head gamma camera on patients after exercise stress, we have observed in some a sudden increase in the counting rate between the 16th and 17th images. This increase provoked motionlike artifacts, which increased the number of false-positive findings. The aim of our study was to determine possible causes for this leap in activity. Methods: We performed myocardial SPECT using a dual-head gamma camera on 110 patients after exercise stress: in 38 patients approximately 5 min after injection (group 1), in 43 patients approximately 14 min after injection (group 2), and in 29 patients twice, at approximately 5 and 20 min after injection (group 3). We also performed dynamic data acquisition for 10 min on 18 patients after exercise stress. We compared activity in the heart region in image series obtained after exercise stress and at rest. Results: Daily quality control tests eliminated the possibility of any malfunctions of the gamma camera. Careful image analysis showed no visible patient motion. Our results showed that upward creep of the heart could not be a cause of the described phenomenon. After exercise stress, a 5% activity leap in the heart region on the 16th and 17th frames was more frequent in group 1 than in group 2. Two consecutive acquisitions after exercise stress showed that the leap was 5% in 24 patients (83%) and 12 patients (41%) at the first and second acquisitions, respectively (group 3). In all patients, the leap was 5% at rest. Dynamic studies showed that the activity in the heart region steadily decreased in all patients after exercise stress. We suggest that decreasing 201Tl concentrations in myocardium or blood could be a major reason for the described artifacts. Conclusion: We proposed that the pharmacokinetics of 201Tl-chloride be evaluated within a short time after injection in humans after exercise stress. Now, in our department, we have begun acquisition approximately 12 min after 201Tl administration, and the abovementioned phenomenon has not appeared. However, to avoid the artifacts caused by early redistribution of 201Tl, acquisition must not begin too late.