Rolland J P, Barrett H H, Seeley G W
University of Arizona, Optical Sciences Center, Tucson 85721.
Phys Med Biol. 1991 Aug;36(8):1091-109. doi: 10.1088/0031-9155/36/8/005.
The ideal observer represents a Bayesian approach to performing detection tasks. Since such tasks are frequently used as a prototype tasks for radiological imaging systems, the detectability measured at the output of an ideal detector can be used as a figure of merit to characterize the imaging system. For the detectability achieved by the ideal observer to be a good figure of merit, it should predict the ability of the human observer to perform the same detection task. Of great general interest, especially to the medical community, are imaging devices with long-tailed point spread functions (PSFs). Such PSFs may occur due to septal penetration in collimators, veiling glare in image intensifiers or scattered radiation in the body. We have investigated the effect that this type of PSF has on human visual signal detection and whether any improvement in performance can be gained by deconvolving the tails of the PSF. For the ideal observer, it is straightforward to show that the performance is independent of any linear, invertible deconvolution filter. Our psychophysical studies show, however, that performance of the human observer is indeed improved by deconvolution. The ideal observer is, therefore, not a good predictor of human observer performance for detection of a signal imaged through a long-tailed PSF. We offer some explanations for this discrepancy by using some characteristics of the visual process and suggest a standard of comparison for the human observer that takes into account these characteristics. A look at the performance of the non-prewhitening (npw) ideal observer, before and after deconvolution, also brings some good insight into this study.
理想观察者代表了一种执行检测任务的贝叶斯方法。由于此类任务经常被用作放射成像系统的原型任务，理想探测器输出端测得的可检测性可用作表征成像系统的品质因数。为了使理想观察者实现的可检测性成为一个良好的品质因数，它应该能够预测人类观察者执行相同检测任务的能力。具有长尾点扩散函数（PSF）的成像设备引起了广泛关注，尤其是在医学界。这种PSF可能是由于准直器中的隔板穿透、图像增强器中的杂散光或体内的散射辐射而产生的。我们研究了这种类型的PSF对人类视觉信号检测的影响，以及通过对PSF的尾部进行去卷积是否可以提高性能。对于理想观察者而言，很容易证明性能与任何线性、可逆的去卷积滤波器无关。然而，我们的心理物理学研究表明，去卷积确实提高了人类观察者的性能。因此，对于通过长尾PSF成像的信号检测，理想观察者并不是人类观察者性能的良好预测指标。我们通过利用视觉过程的一些特征对这种差异给出了一些解释，并提出了一种考虑这些特征的人类观察者比较标准。观察去卷积前后非白化（npw）理想观察者的性能，也为这项研究带来了一些深刻见解。
