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首页> 美国卫生研究院文献>Medical Physics >Estimation of the two-dimensional presampled modulation transfer function of digital radiography devices using one-dimensional test objects
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Estimation of the two-dimensional presampled modulation transfer function of digital radiography devices using one-dimensional test objects

机译：使用一维测试对象估算数字射线照相设备的二维预采样调制传递函数

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>Purpose: The 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.>Methods: Theory 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.>Results: The 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.>Conclusions: Overall, 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.
机译：>目的：医学成像设备的调制传递函数（MTF）通常是通过狭缝或边缘测试设备在垂直轴和水平轴附近进行正交一维（1D）测量的形式报告的。通过测量二维（2D）MTF，可以找到更完整的描述。已经提出了一些2D测试设备，但是与它们的使用有关的一些问题：（1）它们通常不可用； （2）他们可能需要很多图像； （3）结果的准确性可能降低； （4）实施起来可能特别麻烦。这项最新工作提出了将通用的一维测试设备用于对数字成像系统的二维预采样MTF进行实际和准确估计的方法。>方法：理论的发展和应用是为了确保对系统线进行足够的精细采样一维测试设备在近似垂直和水平方向以外的方向扩展功能。还推导了方法并以任意角度测试了缝隙不均匀性。在间接检测的平板系统[GE Revolution XQ / i（GE Healthcare，Waukesha，WI）]上，使用边缘测试对象在十个角度进行实验测量，并使用狭缝测试设备在三个角度进行实验测量，对技术进行了验证。通过基于基于一维边缘的MTF测量的Delaunay三角剖分的简单表面拟合和插值法来估算2D MTF。还使用来自假设的直接检测平板设备的模拟图像进行了合成验证。>结果：物理测量得出的二维MTF对于低于临界值的频率产生0.26％的平均相对精度误差（2.5 mm -1 ）和低于4 mm -1 的频率近似圆形对称。狭缝分析通常与边缘分析的结果一致，但两者在4 mm -1 以上的频率下显示出细微的差异。接近45°的狭缝测量显示出正方形像素孔径（0.2 mm××0.2 mm）导致的MTF径向不对称，正交1D MTF测量并不一定会意识到这一特性。在模拟实验中，基于狭缝和边缘的测量均解决了二维MTF中的径向不对称问题。 DC和截止频率（2.5 mm -1 ）之间的2D MTF中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相似。>结论：总体而言，用于MTF评估的1D测试设备的普遍可用性，可接受性，准确性和易实现性使其成为2D MTF的宝贵技术估计。

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