Moore S C, deVries D J, Nandram B, Kijewski M F, Mueller S P
Nuclear Medicine Service, V.A. Medical Center, West Roxbury, Massachusetts 02132, USA.
Med Phys. 1995 Jun;22(6):703-13. doi: 10.1118/1.597466.
A Bayesian estimator has been developed as a paradigm for human observer performance in detecting lesions of unknown size in a uniform noisy background. The Bayesian observer used knowledge of the range of possible lesion sizes as a prior; its predictions agreed well with the results of a six-observer perceptual study. The average human response to changes in collimator resolution, as measured by the detectability index, dA, was tracked by the Bayesian detector's signal-to-noise ratio (SNR) somewhat better than by two other estimation models based, respectively, on lesser and greater degrees of lesion size uncertainty. As the range of possible lesion sizes increased, the Bayesian detector's SNR decreased and the optimal collimator resolution shifted towards better resolution. An analytic approximation for the variance of lesion activity estimates (which included the same prior) was shown to predict the variance of the Bayesian estimator over a wide range of collimator resolution values. Because the bias of the Bayesian estimator was small (< 1%), the analytic variance estimate permitted a rapid and convenient prediction of the Bayesian detection SNR. This calculation was then used to optimize the geometric parameters of a two-layer tungsten collimator being constructed from crossed grids for a new imaging detector. A Monte Carlo program was first run to estimate all contributions to the radial point-spread function for collimators of differing tungsten contents and spatial resolution values, imaging 140-keV photons emitted from the center of a 15-cm-diameter, water-filled attenuator. The optimal collimator design for detecting lesions with unknown diameters in the range 2.5-7.5 mm yielded a system resolution of approximately 8.5-mm FWHM, a geometric collimator efficiency of 1.21 x 10(-4), and a single-septum penetration probability of 1%.
已开发出一种贝叶斯估计器，作为人类观察者在均匀噪声背景下检测未知大小病变的性能范例。贝叶斯观察者将可能病变大小范围的知识用作先验信息；其预测与一项六观察者感知研究的结果吻合良好。贝叶斯探测器的信噪比（SNR）对以可探测性指数dA衡量的人类对准直器分辨率变化的平均响应的跟踪，比分别基于较小和较大病变大小不确定性程度的另外两种估计模型稍好。随着可能病变大小范围的增加，贝叶斯探测器的SNR降低，最佳准直器分辨率向更高分辨率偏移。已证明病变活动估计方差的解析近似值（包含相同先验信息）能在广泛的准直器分辨率值范围内预测贝叶斯估计器的方差。由于贝叶斯估计器的偏差较小（<1%），解析方差估计允许快速方便地预测贝叶斯检测SNR。然后该计算用于优化为由交叉网格构成的用于新型成像探测器的双层钨准直器的几何参数。首先运行一个蒙特卡罗程序，以估计不同钨含量和空间分辨率值的准直器对径向点扩散函数的所有贡献，对从直径15厘米、充满水的衰减器中心发射的140千电子伏特光子进行成像。用于检测直径在2.5 - 7.5毫米范围内未知病变的最佳准直器设计产生了约8.5毫米半高宽的系统分辨率、1.21×10⁻⁴的几何准直器效率以及1%的单隔板穿透概率。
