Abstract
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Objectives The purpose of this study was to characteristic the performance of of time-of-flight (TOF) and high definition (HD) reconstruction on PET/CT image quality and spatial resolution.
Methods The NEMA body phantom (concentration of the background activity of 0.14μCi/ml) filled with 18F-FDG with a 4:1 activity concentration compared with the background uptake ratio was scanned following the NEMA NU2-2007 standard on uMI510.Furthmore, three 18F -FDG point sources (total activity of 77μCi)inside capillaries with internal diameter of 0.5 mm were placed at three transaxial positions and scanned. A list mode fully 3D attenuation-weighted ordered-subset-expectation-maximization (OSEM) was adopted to process the data with all necessary corrections as the reference setting for comparison(2 iterations for image quality experiment,4 iterations for spatial resolution experiment,24 subsets, 256X256 matrix sizes, acquisition time of 11 minutes for both).Other reconstruction algorithms (TOF+OSEM,HD+OSEM and TOF+HD+OSEM )were conducted in this experiment. Contrast, background variability ratio and accuracy of attenuation and scatter corrections were measured for image quality and transverse resolution at 1cm from the center and transverse radial,transverse tangential at 10cm were calculated by full width at half maximum (FWHM) for spatial resolution.
Results The contrast achieved 71.70%,60.60%, 64.80% and 60.39% of the group TOF+HD+OSEM, HD+OSEM, TOF+OSEM and OSEM, respectively. The background variability achieved 2.26%,2.31%,2.53% and 2.46% of the group TOF+HD+OSEM, HD+OSEM, TOF+OSEM and OSEM, respectively. The accuracy of attenuation and scatter corrections was 11.5% for TOF+HD+OSEM and 20.25% for OSEM. The transverse resolution at 1cm from the center were 2.01mm,2.01mm, 2.83mm and 2.76mm of the group TOF+HD+OSEM, HD+OSEM, TOF +OSEM and OSEM, respectively.
Conclusions It is suggested that contrast, background variability and accuracy of attenuation and scatter corrections with TOF+HD+OSEM were superior to other reconstructions. Moreover, the contrast of small lesions has been improved significantly by application of both TOF and HD technology. The spatial resolution of PET/CT imaging can be optimized by using OSEM with HD. It is more effective while increasing the number of iterations. Application of TOF has little effect on improvement of spatial resolution of PET/CT. It is suggested that use of HD, especially while increasing iteration properly , could improve the diagnostic capacity of small lesions.