Gravel Paul, Li Yusheng, Matej Samuel
Department of Radiology, University of Pennsylvania, Philadelphia, PA.
IEEE Trans Radiat Plasma Med Sci. 2020 Sep;4(5):603-612. doi: 10.1109/trpms.2020.2989209. Epub 2020 Apr 21.
Limited-angle data, such as data obtained from a dual-panel Breast-PET scanner, result in substantial image blur in directions coinciding with the missing cone of the image spectrum. On systems with time-of-flight (TOF) capabilities, this blur is reduced as given by the TOF uncertainty, with the image spectrum being correspondingly expanded into the missing spectral cone. Modeling of the TOF uncertainty in the reconstruction is expected to deconvolve this residual TOF blurring. We have however observed that, as a tradeoff, this TOF de-blurring process also introduces ringing artifacts at the edges, analogous to the edge effects observed with line-of-response (LOR) resolution modeling, which attempts to deconvolve the blur due to detector resolution effects. However, in the former case, the ringing artifacts are much wider due to the spatial extent of the TOF uncertainty as compared to the width of typical LOR resolution blur. We illustrate and investigate the effects of using matched, as well as under-modeled and over-modeled, TOF kernels on edge artifacts in reconstruction from limited-angle data, and compare them with TOF reconstructions of complete data. Although for the conventional data with full angular coverage the reconstruction is fairly insensitive to the exact size of the TOF kernel and TOF modeling does not produce ringing artifacts, it is not the case for the limited-angle data. We show that it is important to use some form of regularization of the TOF uncertainty deconvolution process within reconstruction of the limited-angle data, such as decreasing the TOF kernel size.
有限角度数据，例如从双面板乳腺正电子发射断层扫描仪获得的数据，会在与图像频谱缺失圆锥体一致的方向上导致显著的图像模糊。在具有飞行时间（TOF）功能的系统上，这种模糊会根据TOF不确定性而降低，图像频谱相应地扩展到缺失的频谱圆锥体中。预计在重建过程中对TOF不确定性进行建模将对这种残留的TOF模糊进行去卷积。然而，我们观察到，作为一种权衡，这种TOF去模糊过程也会在边缘处引入振铃伪影，类似于在响应线（LOR）分辨率建模中观察到的边缘效应，LOR分辨率建模试图对由于探测器分辨率效应导致的模糊进行去卷积。然而，在前一种情况下，由于TOF不确定性的空间范围与典型LOR分辨率模糊的宽度相比要大得多，振铃伪影要宽得多。我们展示并研究了使用匹配的、欠建模的和过建模的TOF核在有限角度数据重建中对边缘伪影的影响，并将它们与完整数据的TOF重建进行比较。尽管对于具有全角度覆盖的传统数据，重建对TOF核的确切大小相当不敏感，并且TOF建模不会产生振铃伪影，但对于有限角度数据则并非如此。我们表明，在有限角度数据的重建过程中，对TOF不确定性去卷积过程使用某种形式的正则化很重要，例如减小TOF核大小。
