Evaluation of Simultaneous Dual-radioisotope SPECT Imaging Using 18F-fluorodeoxyglucose and 99mTc-tetrofosmin

Objective(s): Use of a positron emission tomography (PET)/singlephotonemission computed tomography (SPECT) system facilitates the simultaneousacquisition of images with fluorine18 fluorodeoxyglucose (18FFDG) andtechnetium (99mTc)tetrofosmin. However, 18F has a short halflife, and 511keV Comptonscattered photons are detected in the 99mTc energy window.Therefore, in this study, we aimed to investigate the consequences of thesefacts.Methods: The crosstalk correction for images in the 99mTc energy windowinvolved the dual energy window (DEW) subtraction method. In phantomstudies, changes in the count of uniform parts in a phantom (due to attenuationfrom decay), signal detectability in the hotrod part of the phantom, and thedefect contrast ratio in a cardiac phantom were examined.Results: For 18FFDG in the stepandshoot mode, nearly a 9% difference wasobserved in the count of projection data between the start and end positionsof acquisition in the uniform part of the phantom. Based on the findings,the detectability of 12 mm hot rods was relatively poor. In the continuousacquisition mode, the count difference was corrected, and detectability of thehot rods was improved. The crosstalk from 18F to the 99mTc energy windowwas approximately 13%. In the cardiac phantom, the defect contrast in 99mTcimages from simultaneous dualradionuclide acquisition was improved byapproximately 9% after DEW correction; the contrast after correction wassimilar to acquisition with 99mTc alone.Conclusion: Based on the findings, the continuous mode is useful for 18FFDGacquisition, and DEW crosstalk correction is necessary for 99mTctetrofosminimaging.