Abstract
1772
Objectives: Due to its β-emitter (max 497 keV) and γ-emitters (208 keV, 11% and 113 keV, 6%) and its half life of 7 days Lu-177 is attractive for diagnostics and therapy in nuclear medicine. Due to the low γ-yields, it is favorable to include both photopeaks in planar imaging. However, the 113 keV photopeak suffers from severe scatter contamination. A scatter correction is suggested to include the 113 keV photopeak to increase both count statistics and contrast resolution with respect to 208 keV imaging only. Methods: A Jaszczak phantom containing 5 hollow spheres (11-33 mm) was used. The spheres were filled with 120 kBq/ml Lu-177. Planar imaging was performed for 5 scans, where the concentration of the water-equivalent background was 11, 14, 20, 28 and 42 kBq/ml, respectively. A double-headed gamma-camera (E.CAM, Siemens) was used. Two 15% energy windows were scanned around the photopeaks. Additional data through the 90-104 keV energy window were used for scatter correction of the low photopeak using a subtraction technique. Count statistics and target-to-background ratios (TBRs) were measured from the images for 3 situations: using the 208 keV photopeak (A), using the sum of the two photopeaks before (B) and after (C) scatter correction. Results: Averaged over the 5 experiments, statistics increased by 117% (sd 7%) for B, and by 52% (sd 4%) for C, with respect to A. Furthermore, TBR decreased by 4.2% (range 1.3-9.6%) for B, but increased by 4.2% (range 0.8-9.0%) for C, with respect to A. Conclusions: Merging of the two photopeaks of Lu-177 with an energy window for scatter correction results in a strong increase in count statistics and improvement of contrast resolution. The optimized protocol may be used to increase image quality or decrease scanning time by approximately one third.
- Society of Nuclear Medicine, Inc.