Energy window based correction for septal penetration effects caused by impurities in cyclotron-produced Thallium-201

Abstract

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Objectives: Tl-201 is a SPECT tracer commonly used for assessing perfusion and viability of myocardial tissue as well as for tumor imaging. Tl-201 is cyclotron produced and can maximally contain 2.0 % Tl-200, 2.7 % Tl-202 and 0.3 % Pb-203 impurities. Previously we showed that contra-intuitive to the low percentage of this contamination, Tl-200 and Tl-202 significantly degrade Tl-201 images (Staelens EJNM 2008). In the study presented here we want to determine the optimal acquisition protocol settings for an energy window based correction method and its impact on the image quality.

Methods: Measurements were performed with an anthropomorphic phantom comprised of a cardiac insert with two solid defects. We used a custom modified PRISM 3000XP camera with a dual memory shared interface enabling list mode files.

Results: The measurements showed that the image degrading effect of these contaminations is mainly caused by septal penetration and down scatter of high energy photons resulting in detections with low spatial information content. Two additional energy windows at 100 keV and 200 keV can be acquired to correct for this persistent bias. Ongoing work is being performed to evaluate the gain in cold lesion contrast.

Conclusions: An energy window based correction for Tl-201 contamination during iterative reconstruction can improve contrast and quantitative accuracy. Based on experimental list mode data we were able to recommend protocol settings.