Penney B C, King M A, Schwinger R B, Baker S P, Stritzke P, Doherty P W
Department of Nuclear Medicine, University of Massachusetts Medical Center, Worcester 01605.
Med Phys. 1987 Sep-Oct;14(5):849-58. doi: 10.1118/1.596123.
Image restoration using the constrained least-squares (CLS) method theoretically adapts to the image being processed. In addition, it only requires knowing the modulation transfer function of the imaging system when applied to nuclear medicine images. Prompted by these observations, a systematic evaluation of the effects of the form of the "coarseness function" [C(f)] used by the CLS method has been conducted. Nine C(f)'s are evaluated using an observer preference and a normalized mean-squared error (NMSE) criterion. This evaluation is conducted for three modulation transfer functions and a wide range of count levels. The results of the subjective studies support using the form of C(f) which has been most widely employed in previous studies, i.e., the form designed to minimize the energy in the second derivative of the restored image. A different form of C(f) is generally found to be optimal by the mean-squared error criterion. The CLS method is then compared to: (1) no processing, (2) count-dependent smoothing, and (3) count-dependent Metz restoration. When evaluated using objective measurements of error and contrast, the CLS method is found to be slightly inferior to the best method, Metz restoration. However, CLS restoration is found to be equal to or better than the other methods when judged by the results of observer preference studies.
使用约束最小二乘法（CLS）进行图像恢复理论上适用于正在处理的图像。此外，当应用于核医学图像时，它只需要知道成像系统的调制传递函数。受这些观察结果的启发，对CLS方法所使用的“粗糙度函数”[C(f)]形式的效果进行了系统评估。使用观察者偏好和归一化均方误差（NMSE）标准对九个C(f)进行了评估。针对三种调制传递函数和广泛的计数水平进行了此评估。主观研究结果支持使用先前研究中使用最广泛的C(f)形式，即旨在最小化恢复图像二阶导数能量的形式。通过均方误差标准通常会发现一种不同的C(f)形式是最优的。然后将CLS方法与以下方法进行比较：（1）不进行处理，（2）依赖计数的平滑处理，以及（3）依赖计数的梅茨恢复。当使用误差和对比度的客观测量进行评估时，发现CLS方法略逊于最佳方法，即梅茨恢复。然而，根据观察者偏好研究的结果判断，发现CLS恢复等于或优于其他方法。
