Dept. of Radiol. & Nuclear. Med., Univ. Hosp. Utrecht.
IEEE Trans Med Imaging. 1996;15(4):491-9. doi: 10.1109/42.511752.
The quality and quantitative accuracy of iteratively reconstructed SPECT images improves when better point spread function (PSF) models of the gamma camera are used during reconstruction. Here, inclusion in the PSF model of photon crosstalk between different slices caused by limited gamma camera resolution and scatter is examined. A three-dimensional (3-D) projector back-projector (proback) has been developed which models both the distance dependent detector point spread function and the object shape-dependent scatter point spread function of single photon emission computed tomography (SPECT). A table occupying only a few megabytes of memory is sufficient to represent this scatter model. The contents of this table are obtained by evaluating an analytical expression for object shape-dependent scatter. The proposed approach avoids the huge memory requirements of storing the full transition matrix needed for 3-D reconstruction including object shape-dependent scatter. In addition, the method avoids the need for lengthy Monte Carlo simulations to generate such a matrix. In order to assess the quantitative accuracy of the method, reconstructions of a water filled cylinder containing regions of different activity levels and of simulated 3-D brain projection data have been evaluated for technetium-99m. It is shown that fully 3-D reconstruction including complete detector response and object shape-dependent scatter modeling clearly outperforms simpler methods that lack a complete detector response and/or a complete scatter response model. Fully 3-D scatter correction yields the best quantitation of volumes of interest and the best contrast-to-noise curves.
当在重建过程中使用更好的伽马相机点扩散函数 (PSF) 模型时，迭代重建 SPECT 图像的质量和定量准确性会提高。在这里，研究了由于伽马相机分辨率有限和散射引起的不同切片之间的光子串扰如何包含在 PSF 模型中。已经开发了一种三维 (3-D) 投影仪反投影器 (proback)，它可以对单光子发射计算机断层扫描 (SPECT) 的距离相关探测器点扩散函数和物体形状相关散射点扩散函数进行建模。只需要占用几兆字节内存的表格就足以表示这种散射模型。该表的内容通过评估物体形状相关散射的解析表达式来获得。该方法避免了存储包括物体形状相关散射的完整 3-D 重建所需的全过渡矩阵的巨大内存需求。此外，该方法避免了需要冗长的蒙特卡罗模拟来生成这样的矩阵。为了评估该方法的定量准确性，已经对包含不同活动水平区域的充满水的圆柱体和模拟的 3-D 脑投影数据进行了锝-99m 的重建评估。结果表明，包括完整探测器响应和物体形状相关散射建模的完全 3-D 重建明显优于缺乏完整探测器响应和/或完整散射响应模型的简单方法。完全 3-D 散射校正可实现最佳的感兴趣容积定量和最佳的对比度噪声比曲线。
