Abstract
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Objectives Tc-labelled myocardial perfusion agents are cleared by the liver and excreted by the biliary system. Increased liver, intestinal, or gastric activity may create a major problem in the visual and quantitative interpretation of the inferior wall, particularly at rest. The objective of the study is to determine when interpretation of the studies is affected by poor image quality.
Methods The SIMIND Monte Carlo code with the XCAT-phantom was used to simulate myocardial perfusion scintigraphy images. Inferior defects of 3 and 6% of the left ventricle were simulated. Extra-cardiac uptake was simulated using a spherical 4 cm hot spot with the same concentration of Tc as in the myocardium. The hot spot was placed below the heart, and the position was changed from 10 mm to 0 mm from the inferior cardiac wall, with 2 mm intervals. Images were created by simulating 32 angles in a 180 arc, starting from 45° right anterior oblique position and reconstructed using the OSEM algorithm with a gaussian post filter. The EXINI heart software was used to evaluate the extent and severity of the defects for the different defect sizes and distances to extra-cardiac uptake.
Results Severity started to decrease when the hot spot was closer to the heart than 6 mm, i.e. the spillout from the hot spot to the heart started to affect the computerized interpretation. For small defect sizes, the extent decreased when the hot spot was localized less than 6 mm from the heart (table 1).
Conclusions Extra-cardiac uptake starts to impair computerized interpretation of defect extent and severity when localized less than half of the spatial resolution (less than 6 mm from the heart)