Estimation of the two-dimensional presampled modulation transfer function of digital radiography devices using one-dimensional test objects.
Estimation of the two-dimensional presampled modulation transfer function of digital radiography devices using one-dimensional test objects.
复制标题
使用一维测试对象估计数字射线照相设备的二维预采样调制传递函数。
DOI：
10.1118/1.4752442
复制
发表时间：
2012
期刊：
影响因子：
3.8
通讯作者：
Dobbins,JamesT
中科院分区：
文献类型：
--
作者：
Wells,JeredR;Dobbins,JamesT
目的医学成像设备的调制传递函数 (MTF) 通常以使用狭缝或边缘测试设备在垂直和水平轴附近进行的正交一维 (1D) 测量的形式报告。通过测量二维 (2D) MTF 可以找到更完整的描述。一些二维测试设备已经被提出，但它们的使用存在一些问题：（1）它们不普遍可用； (2) 他们可能需要很多图像； (3) 结果的准确性可能降低； (4)它们的实施可能特别麻烦。目前的工作提出了应用常用的一维测试设备来实际和准确地估计数字成像系统的二维预采样 MTF。方法理论的开发和应用是为了确保一维测试设备在近似垂直和水平以外的方向上对系统线扩展函数进行充分的精细采样。还导出并测试了任意角度狭缝不均匀性校正的方法。使用边缘测试物体在十个角度进行实验测量，并在间接检测平板系统上使用狭缝测试设备进行三个角度的实验测量来验证技术[GE Revolution XQ/i（GE Healthcare，沃科夏，威斯康星州）]。 2D MTF 通过简单的曲面拟合和基于 1D 边缘的 MTF 测量的 Delaunay 三角测量的插值来估计。还使用来自假设的直接检测平板设备的模拟图像进行了综合验证。结果从物理测量得出的 2D MTF 对于低于截止 (2.5 mm−1) 的频率产生了 0.26% 的平均相对精度误差，并且在低于 4 mm−1 的频率下近似圆形对称。虽然狭缝分析与边缘分析的结果大体一致，但两者在频率高于 4 mm−1 时表现出细微的差异。 45° 附近的狭缝测量揭示了由方形像素孔径 (0.2 mm × 0.2 mm) 导致的 MTF 径向不对称性，这一特性在正交 1D MTF 测量中不一定能被理解。在模拟实验中，基于狭缝和边缘的测量解决了 2D MTF 中的径向不对称性。 DC 频率和截止频率 (2.5 mm−1) 之间的 2D MTF 的平均绝对相对精度误差为 0.13%，平均相对精度误差为 0.11%。其他仿真结果与从物理数据得出的结果类似。结论总体而言，用于 MTF 评估的一维测试设备的普遍可用性、可接受性、准确性和易于实施性使其成为二维 MTF 估计的有价值的技术。
PurposeThe modulation transfer function (MTF) of medical imaging devices is commonly reported in the form of orthogonal one‐dimensional (1D) measurements made near the vertical and horizontal axes with a slit or edge test device. A more complete description is found by measuring the two‐dimensional (2D) MTF. Some 2D test devices have been proposed, but there are some issues associated with their use: (1) they are not generally available; (2) they may require many images; (3) the results may have diminished accuracy; and (4) their implementation may be particularly cumbersome. This current work proposes the application of commonly available 1D test devices for practical and accurate estimation of the 2D presampled MTF of digital imaging systems.MethodsTheory was developed and applied to ensure adequate fine sampling of the system line spread function for 1D test devices at orientations other than approximately vertical and horizontal. Methods were also derived and tested for slit nonuniformity correction at arbitrary angle. Techniques were validated with experimental measurements at ten angles using an edge test object and three angles using a slit test device on an indirect‐detection flat‐panel system [GE Revolution XQ/i (GE Healthcare, Waukesha, WI)]. The 2D MTF was estimated through a simple surface fit with interpolation based on Delaunay triangulation of the 1D edge‐based MTF measurements. Validation by synthesis was also performed with simulated images from a hypothetical direct‐detection flat‐panel device.ResultsThe 2D MTF derived from physical measurements yielded an average relative precision error of 0.26% for frequencies below the cutoff (2.5 mm−1) and approximate circular symmetry at frequencies below 4 mm−1. While slit analysis generally agreed with the results of edge analysis, the two showed subtle differences at frequencies above 4 mm−1. Slit measurement near 45° revealed radial asymmetry in the MTF resulting from the square pixel aperture (0.2 mm × 0.2 mm), a characteristic which was not necessarily appreciated with the orthogonal 1D MTF measurements. In simulation experiments, both slit‐ and edge‐based measurements resolved the radial asymmetries in the 2D MTF. The average absolute relative accuracy error in the 2D MTF between the DC and cutoff (2.5 mm−1) frequencies was 0.13% with average relative precision error of 0.11%. Other simulation results were similar to those derived from physical data.ConclusionsOverall, the general availability, acceptance, accuracy, and ease of implementation of 1D test devices for MTF assessment make this a valuable technique for 2D MTF estimation.