Abstract
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Objectives Comparative simulation study was performed to find optimal acquisition parameter in 124I PET, in previous study. In this study, we compared the image characteristics between 124I and 18F using NEMA NU4-2008 and investigated the relationship between image quality and NECR for various energy windows.
Methods Spatial resolution was measured at various positions according to NEMA NU4 standards. Count rate performance including sensitivity, scatter fraction, NECR and image quality were also measured within 6 energy windows (250~550, 250~650, 250~750, 350~550,350~650 and 350~750 keV). To compare the sensitivity, NEMA NU2 like sensitivity phantom and method were used. For the measurement of scatter fraction and NECR, two NEMA scatter phantom were used and the data was acquired for 14 half-lives. For the measurement of image quality, NEMA NU4 image quality phantom filled with 124I or 18F solution and acquired for 20 min. Uniformity, recovery coefficient and spillover ratio(SOR) was measured.
Results The spatial resolution of 124I was 1.75, 1.49, 2.72 mm and those of 18F was 1.53, 1.50, 2.33 mm in radial, tangential, and axial direction, respectively. Volumetric resolution was 7.09 mm in 124I and 5.43 mm3 in 18F. Sensitivity was 3.84% in 124I and 9.83% in 18F within 250~750 keV. The lowest scatter fraction were 8% (mouse) and 21% (rat) in 18F and were 9% and 19% in 124I within 350~750 keV. For 18F, peak NECR could be obtained within 250~750 keV. 5.9% of highest uniformity was obtained within the same energy window. For 124I, peak NECR could be obtained within 350~750 keV. Although uniformity of 124I was similar under other energy windows, SOR for water was highest value of 1.27% within 350~750 keV. SOR for water and air were also higher when attenuation and scatter correction was not performed.
Conclusions Optimal PET acquisition parameter for 124I PET was obtained to enhance the image quality of 124I. This optimal energy window setting will be useful for I-124 PET studies