Effect of acquisition time and matrix on the image quality in integrated PET/MR

2725 Objectives Different reconstruction conditions may influence the PET image quality obtained from integrated PET/MR. The purpose of this work is to investigate the effects of different reconstruction factors such as acquisition time and matrix on PET image quality. Methods This study was carefully performed under controlled conditions according to National Electrical Manufactures Association (NEMA) IQ phantom experiment standard. The equipment was GE SIGNA PET/MR. NEMA IQ phantom was filled with a total activity of 4.14mCi of 18F-FDG well dissolved in water, and the sphere-to-background activity ratio was 4:1.Two largger balls were filled with cold water as controls. The PET/MR images were obtained under the lung area scan mode. Images were reconstructed under the following conditions: the reconstruction time were 2, 4, 8, and 11 minutes and the reconstruction matrix were 128×128, 192×192 and 256×256. According to the NEMA NU2-2007 standard, characteristics as contrast and background variability were elaborately calculated. Results By increasing the acquisition time from 2minutes to 11minutes, the image contrast increased from 62.43% to 65.46% when not applying Time of Flight (TOF) technique and from 76.10% to 79.76% when applying TOF. The background variability reduced from 12.14% to 8.88% without TOF and from 10.03% to 6.48% with TOF. The signal noise ratio (SNR) increased from 13.58 to 19.19 without TOF and from 19.19 to 32.06 with TOF. However, the background variability and SNR were remained unchanged between 8 minutes and 11minutes without TOF and there was a gradient change with TOF. By expanding the reconstruction matrix, the contrast increased from 55.28% to 63.19% without TOF and from 65.36% to 75.46% with TOF. The background variability reduced from 9.64% to 9.44% without TOF and from 8.12% to 7.90% with TOF. The SNR increased from 14.45 to 17.51 without TOF and from 20.37 to 24.06 with TOF. Conclusions Increasing acquisition time is an effective approach to improve the PET image quality. Moreover, TOF technique amplified the effect of time on increasing SNR, and improved the contrast of small lesions more significantly. The contrast, background variability and SNR could be optimized by applying larger reconstruction matrix, however, the difference was little between 192×192 and 256×256 reconstruction matrix.