| Objective:To study the effect of different reconstruction and imaging conditions on the spatial resolution of PET image in PET/CT.Materials and methods:PET/CT equipment:Ge discovery ST-16 and discovery elite PET/CT.PET/CT images under different reconstruction and imaging conditions were obtained by using elliptic column resolution model.Acquisition conditions:① filter back projection method,iterative algorithm(VUE point HD),whether to use TOF and PSF technology.②In VPFX-S algorithm,the number of iterations is 2-10(interval is 2 times);reconstruction matrix:discovery st-16 type is 128×128,256×256,elite type is 128×128,192 ×192,256×256;cut-off frequency is 2.0mm-10.0mm(interval is 2.0mm);and whether attenuation correction is used.③ PET image acquisition uses list mode,the acquisition time is 6min,the interval is lmin;④whether there is bed overlap;⑤ whether there is scattering.The elliptical column resolution model was scanned by simulating clinical PET/CT scanning.Analyze the image on GE Xeleris workstation,calculate and select 5 layers of cross section in the reconstructed image,extract the section line data of each line source perpendicular to the outward direction of the rotation axis,that is,radial section line data,fit each section line data with Gaussian function,so as to obtain the radial expansion function of each line source,and calculate the full width at half maximum(FWHM)of each expansion function.FWHMx represents the radial spatial resolution.Results:under the condition of clinical collection and reconstruction,the spatial resolution of the central image before and after PSF was 4.95mm and 4.28mm respectively.The spatial resolution of the center image before and after TOF is 4.95mm and 5.19mm respectively.The spatial resolution of FBP is 4.63mm～7.45mm,and that of VUE point HD is 4.07mm～6.58mm.07 mm.If there is bed overlap,FWHM elite is 4.14 ±0.01mm,4.14±0.01mm,FWHMst-16 is 5.39 ± 0.19mm,5.38 ± 0.07mm.When the matrix is 256 ×256,192×192 and 128×128,the FWHM of the center is 4.07 ±0.18mm,4.25 ± 0.10mm and 4.73±0.08mm(Discovery Elite),respectively.The half width of the filter cut-off at the center of 2.0mm-10.0mm(interval 2.0mm)is 4.65 ±0.43mm,4.77±0.27mm,4.02±0.01mm,4.11±0.04mm and 9.94±0.01mm(discovery elite type),respectively.The FWHM of 2-10 iterations were 4.17±0.27mm,4.27 ±0.21mm,4.11 ±0.05mm,4.18 ± 0.04mm,4.12±0.06mm(Discovery Elite).If attenuation correction is used,the FWHM of discovery elite in the center is 4.14 ±0.01mm and 4.18 ±0.08mm,respectively.Conclusion:1)The use of PSF technology in PET/CT can effectively improve the spatial resolution of PET image,while TOF technology has no significant effect on the spatial resolution of PET.2)The reconstruction algorithm has a great influence on the spatial resolution of PET image,and the iterative VUE point HD algorithm is better than FBP algorithm.3)Under the same conditions,the spatial resolution of PET/CT image in water layer(scattering)is lower than that in air.4)When the filter cutoff is 6.0mm,the spatial resolution of Discovery Elite image is the best.5)Different acquisition time,iteration times,whether there is overlapping of beds and attenuation correction have no significant effect on pet spatial resolution.6)Under the same collection time and bed,the spatial resolution of elite image is improved by 40.57%compared with st-16 image. |
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