Department of Imaging Physics, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
Med Phys. 2009 Oct;36(10):4720-5. doi: 10.1118/1.3191245.
The antiscatter grid is an essential part of modern radiographic systems. Since the introduction of the antiscatter grid, however, there have been few methods proposed for acceptance testing and verification of manufacturer-supplied grid specifications. The grid ratio (r) is an important parameter describing the antiscatter grid because it affects many other grid quality metrics, such as the contrast improvement ratio (K), primary transmission (Tp), and scatter transmission (Ts). Also, the grid ratio in large part determines the primary clinical use of the grid. To this end, the authors present a technique for the nondestructive measurement of the grid ratio of antiscatter grids. They derived an equation that can be used to calculate the grid ratio from a single off-focus flat field image by exploiting the relationship between grid cutoff and off-focus distance. The calculation can be performed by hand or with included analysis software. They calculated the grid ratios of several different grids throughout the institution, and afterward they destructively measured the grid ratio of a nominal r8 grid previously evaluated with the method. They also studied the sensitivity of the method to technical factors and choice of parameters. With one exception, the results for the grids found in the institution were in agreement with the manufacturer's specifications and international standards. The nondestructive evaluation of the r8 grid indicated a ratio of 7.3, while the destructive measurement indicated a ratio of 7.53 +/- 0.28. Repeated evaluations of the same grid yielded consistent results. The technique provides the medical physicist with a new tool for quantitative evaluation of the grid ratio, an important grid performance criterion. The method is robust and repeatable when appropriate choices of technical factors and other parameters are made.
散射消除栅是现代射线照相系统的重要组成部分。然而，自从引入散射消除栅以来，对于制造商提供的栅规格的验收测试和验证，几乎没有提出什么方法。栅比(r)是描述散射消除栅的一个重要参数，因为它影响许多其他栅质量指标，如对比度改善比(K)、初级传输(Tp)和散射传输(Ts)。此外，栅比在很大程度上决定了栅的主要临床用途。为此，作者提出了一种用于非破坏性测量散射消除栅栅比的技术。他们推导出了一个方程，可以通过利用栅截止和离焦距离之间的关系，从单个离焦平面场图像计算栅比。计算可以手动进行，也可以使用包括的分析软件进行。他们计算了机构中几个不同栅的栅比，然后破坏性地测量了以前用该方法评估的标称 r8 栅的栅比。他们还研究了该方法对技术因素和参数选择的敏感性。除了一个例外，机构中发现的栅的结果与制造商的规格和国际标准一致。对 r8 栅的非破坏性评估表明，栅比为 7.3，而破坏性测量表明栅比为 7.53 +/- 0.28。对同一栅的重复评估得出了一致的结果。该技术为医学物理学家提供了一种新的工具，用于定量评估栅比，这是一个重要的栅性能标准。当选择适当的技术因素和其他参数时，该方法具有稳健性和可重复性。
