Dept. of Radiol., State Univ. of New York, Syracuse, NY.
IEEE Trans Med Imaging. 1991;10(1):66-73. doi: 10.1109/42.75612.
Attenuation compensation for cone beam single-photon emission computed tomography (SPECT) imaging is performed by cone beam maximum likelihood reconstruction with attenuation included in the transition matrix. Since the transition matrix is too large to be stored in conventional computers, the E-M maximum likelihood estimator is implemented with a ray-tracing algorithm, efficiently recalculating each matrix element as needed. The method was applied and tested in both uniform and nonuniform density phantoms. Test projections sets were obtained from Monte Carlo simulations and experiments using a commercially available cone beam collimator. For representative regions of interest. reconstruction of a uniform sphere is accurate to within 3% throughout, in comparison to a reference image simulated and reconstructed without attenuation. High- and low-activity regions in a uniform density are reconstructed accurately, except that low-activity regions in a more active background have a small error. This error is explainable by the nonnegativity constraints of the E-M estimator and the image statistical noise.
用于锥束单光子发射计算机断层成像术（SPECT）的衰减补偿是通过包含在转移矩阵中的衰减的锥束最大似然重建来实现的。由于转移矩阵太大而无法存储在传统计算机中，因此 E-M 最大似然估计器使用射线追踪算法来实现，根据需要有效地重新计算每个矩阵元素。该方法已应用于均匀和非均匀密度体模中，并进行了测试。测试投影集是从使用商业上可用的锥束准直器的蒙特卡罗模拟和实验中获得的。对于代表性的感兴趣区域，与没有衰减的模拟和重建的参考图像相比，整个均匀球体的重建精度在 3%以内。在均匀密度中，高活性和低活性区域的重建是准确的，除了在更活跃的背景中有低活性区域的情况下，会有一个小误差。该误差可由 E-M 估计器的非负约束和图像统计噪声来解释。
