Abstract
Attenuation correction (AC) is required for accurate quantitative evaluation of small animal PET data. Our objective was to compare three AC methods in the small animal Clairvivo-PET scanner. The three AC methods involve applying attenuation coefficient maps generated by simulating a cylindrical map (SAC), segmenting the emission data (ESAC), and segmenting the transmission data (TSAC), imaged using a 137Cs single-photon source. Investigation was carried out using a 65 mm uniform cylinder and an NEMA NU4 2008 mouse phantom, filled with water or tungsten liquid, to mimic bone. Evaluation was carried out using the difference of the segmented map volume from the known cylindrical phantom volume, the recovery of the radioactivity concentration, and the line profiles. The optimal transmission scan time for achieving accurate AC using TSAC was determined using 5, 10, 15, 20, and 25 min transmission scan time. The effects of scatter correction and reconstruction algorithms on ESAC were investigated. SAC showed the best performance but was unable to correct for different tissues and the scanner bed, and faced difficulty with correct positioning of the attenuation coefficient map. ESAC was affected by scatter correction and reconstruction algorithm, and may result in poor boundary delineation, and hence was unreliable. TSAC showed reasonable performance but required further optimization of the default segmentation setting. A minimum transmission scan time of 20 min is recommended for Clairvivo-PET using 137Cs source to ensure that sufficient transmission counts are obtained to generate accurate attenuation coefficient map.
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Acknowledgements
The authors would like to thank Dr. Tetsuro Mizuta and Dr. Takayuki Kikuchi from Shimadzu Corp., Japan for their help and advice in this study. This study was funded by the Grants-in-Aid for Scientific Research (B) (No. 26293133) and (C) (No. 15K08707) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japanese Government.
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Nai, YH., Ose, T., Shidahara, M. et al. 137Cs transmission imaging and segmented attenuation corrections in a small animal PET scanner. Radiol Phys Technol 10, 321–330 (2017). https://doi.org/10.1007/s12194-017-0407-4
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DOI: https://doi.org/10.1007/s12194-017-0407-4