Bowsher J E, Floyd C E
Department of Radiology, Duke University Medical Center, Durham, North Carolina 27710.
J Nucl Med. 1991 Jun;32(6):1285-91.
This paper studies the extent to which lesion contrasts and signal-to-noise ratios in maximum-likelihood, expectation-maximization estimates of SPECT images can be improved by considering Compton scattering when calculating the photon detection probability matrix. Matrices are generated using a Monte Carlo code that realistically models a SPECT imaging system. For cold lesions having true contrasts of one, thirty-six combinations of three lesion sizes, three lesion locations, and four projection-data count levels are considered. Both hot and cold, 2-cm-radius lesions having various values of true contrast are studied at a few count levels and lesion locations. With scatter in the matrix, scatter effects are completely removed from the central regions of lesions whose radius is greater than the full width at half maximum of the spatial resolution. Resolution recovery is initially slower but eventually superior. Percent improvements in contrast are greater for lower-contrast cold lesions and higher-contrast hot lesions. In most cases, signal-to-noise ratios are comparable or better. Correct absolute activity levels are obtained.
本文研究了在计算光子探测概率矩阵时考虑康普顿散射，能否提高单光子发射计算机断层扫描（SPECT）图像最大似然期望最大化估计中的病变对比度和信噪比。通过使用真实模拟SPECT成像系统的蒙特卡罗代码生成矩阵。对于真实对比度为1的冷病变，考虑了三种病变大小、三个病变位置和四个投影数据计数水平的36种组合。在几个计数水平和病变位置研究了具有不同真实对比度值的半径为2 cm的热病变和冷病变。当矩阵中存在散射时，对于半径大于空间分辨率半高宽的病变中心区域，散射效应被完全消除。分辨率恢复最初较慢，但最终更优。对比度的百分比改善对于低对比度冷病变和高对比度热病变更大。在大多数情况下，信噪比相当或更好。获得了正确的绝对活性水平。
