Department of Medical Physics and Biomedical Engineering, Tehran University of Medical Sciences, Tehran, Iran.
Research Center for Molecular and Cellular Imaging (RCMCI), Tehran University of Medical Sciences, Tehran, Iran.
Jpn J Radiol. 2020 Mar;38(3):231-239. doi: 10.1007/s11604-019-00914-3. Epub 2020 Jan 1.
The present study aims to assess the impact of acquisition time, different iterative reconstruction protocols as well as image context (including contrast levels and background activities) on the measured spatial resolution in PET images.
Discovery 690 PET/CT scanner was used to quantify spatial resolutions in terms of full width half maximum (FWHM) as derived (i) directly from capillary tubes embedded in air and (ii) indirectly from 10 mm-diameter sphere of the NEMA phantom. Different signal-to-background ratios (SBRs), background activity levels and acquisition times were applied. The emission data were reconstructed using iterative reconstruction protocols. Various combinations of iterations and subsets (it × sub) were evaluated.
For capillary tubes, improved FWHM values were obtained for higher it × sub, with improved performance for PSF algorithms relative to non-PSF algorithms. For the NEMA phantom, by increasing acquisition times from 1 to 5 min, intrinsic FWHM for reconstructions with it × sub 32 (54) was improved by 15.3% (13.2%), 15.1% (13.8%), 14.5% (12.8%) and 13.7% (12.7%) for OSEM, OSEM + PSF, OSEM + TOF and OSEM + PSF + TOF, respectively. Furthermore, for all reconstruction protocols, the FWHM improved with more impact for higher it × sub.
Our results indicate that PET spatial resolution is greatly affected by SBR, background activity and the choice of the reconstruction protocols.
本研究旨在评估采集时间、不同迭代重建协议以及图像上下文（包括对比水平和背景活动）对 PET 图像中测量空间分辨率的影响。
使用 Discovery 690 PET/CT 扫描仪，以半高全宽（FWHM）的形式直接从空气中嵌入的毛细管和 NEMA 体模的 10mm 直径球体来定量空间分辨率。应用不同的信号与背景比（SBR）、背景活动水平和采集时间。使用迭代重建协议重建发射数据。评估了各种迭代和子集（it×sub）的组合。
对于毛细管，更高的 it×sub 获得了改进的 FWHM 值，PSF 算法的性能优于非 PSF 算法。对于 NEMA 体模，通过将采集时间从 1 分钟增加到 5 分钟，对于 it×sub 32（54）的重建，具有 OSEM、OSEM+PSF、OSEM+TOF 和 OSEM+PSF+TOF 的固有 FWHM 分别提高了 15.3%（13.2%）、15.1%（13.8%）、14.5%（12.8%）和 13.7%（12.7%）。此外，对于所有重建协议，FWHM 随着更高的 it×sub 而得到更大的改善。
我们的结果表明，PET 空间分辨率受 SBR、背景活动和重建协议选择的影响很大。
