Kertész Hunor, Conti Maurizio, Panin Vladimir, Cabello Jorge, Bharkhada Deepak, Beyer Thomas, Papp Laszlo, Jentzen Walter, Cal-Gonzalez Jacobo, Herraiz Joaquín L, López-Montes Alejandro, Rausch Ivo
QIMP Team, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Währinger Gürtel 18-20, 1090, Vienna, Austria.
Siemens Medical Solutions USA, Inc., Knoxville, TN, USA.
EJNMMI Phys. 2022 Aug 19;9(1):56. doi: 10.1186/s40658-022-00482-y.
To evaluate the effect of combining positron range correction (PRC) with point-spread-function (PSF) correction and to compare different methods of implementation into iterative image reconstruction for I-PET imaging.
Uniform PR blurring kernels of I were generated using the GATE (GEANT4) framework in various material environments (lung, water, and bone) and matched to a 3D matrix. The kernels size was set to 11 × 11 × 11 based on the maximum PR in water and the voxel size of the PET system. PET image reconstruction was performed using the standard OSEM algorithm, OSEM with PRC implemented before the forward projection (OSEM+PRC simplified) and OSEM with PRC implemented in both forward- and back-projection steps (full implementation) (OSEM+PRC). Reconstructions were repeated with resolution recovery, point-spread function (PSF) included. The methods and kernel variation were validated using different phantoms filled with I acquired on a Siemens mCT PET/CT system. The data was evaluated for contrast recovery and image noise.
Contrast recovery improved by 2-10% and 4-37% with OSEM+PRC simplified and OSEM+PRC, respectively, depending on the sphere size of the NEMA IQ phantom. Including PSF in the reconstructions further improved contrast by 4-19% and 3-16% with the PSF+PRC simplified and PSF+PRC, respectively. The benefit of PRC was more pronounced within low-density material. OSEM-PRC and OSEM-PSF as well as OSEM-PSF+PRC in its full- and simplified implementation showed comparable noise and convergence. OSEM-PRC simplified showed comparably faster convergence but at the cost of increased image noise.
The combination of the PSF and PRC leads to increased contrast recovery with reduced image noise compared to stand-alone PSF or PRC reconstruction. For OSEM-PRC reconstructions, a full implementation in the reconstruction is necessary to handle image noise. For the combination of PRC with PSF, a simplified PRC implementation can be used to reduce reconstruction times.
评估正电子射程校正（PRC）与点扩散函数（PSF）校正相结合的效果，并比较将不同方法应用于迭代图像重建以进行I-PET成像的情况。
使用GATE（GEANT4）框架在各种材料环境（肺、水和骨）中生成均匀的I的PR模糊核，并将其与三维矩阵匹配。基于水中的最大PR和PET系统的体素大小，将核大小设置为11×11×11。使用标准的OSEM算法、在前向投影之前实施PRC的OSEM（OSEM+PRC简化版）以及在前向和后向投影步骤中均实施PRC的OSEM（完整实施）（OSEM+PRC）进行PET图像重建。在包含分辨率恢复、点扩散函数（PSF）的情况下重复进行重建。使用在西门子mCT PET/CT系统上采集的填充有I的不同体模对这些方法和核变化进行验证。对数据进行对比度恢复和图像噪声评估。
根据NEMA IQ体模的球体大小，OSEM+PRC简化版和OSEM+PRC分别使对比度恢复提高了2% - 10%和4% - 37%。在重建中包含PSF后，PSF+PRC简化版和PSF+PRC分别使对比度进一步提高了4% - 19%和3% - 16%。PRC的益处在低密度材料中更为明显。OSEM-PRC和OSEM-PSF以及完整和简化实施的OSEM-PSF+PRC显示出相当的噪声和收敛性。OSEM-PRC简化版显示出收敛速度相对较快，但代价是图像噪声增加。
与单独的PSF或PRC重建相比，PSF和PRC的组合可提高对比度恢复并降低图像噪声。对于OSEM-PRC重建，在重建中进行完整实施对于处理图像噪声是必要的。对于PRC与PSF的组合，可使用简化的PRC实施来减少重建时间。
