A SIMPLE METHOD FOR DETERMINING THE MODULATION TRANSFER-FUNCTION IN DIGITAL RADIOGRAPHY
A SIMPLE METHOD FOR DETERMINING THE MODULATION TRANSFER-FUNCTION IN DIGITAL RADIOGRAPHY
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DOI：
10.1109/42.126908
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发表时间：
1992-03-01
影响因子：
10.6
通讯作者：
OHTSUKA, A
中科院分区：
文献类型：
--
作者：
FUJITA, H;TSAI, DY;OHTSUKA, A
提出了一种确定数字射线成像(DR)系统中预采样调制传递函数(MTF)的简单方法，该方法包括探测器的不清晰度和采样孔径的影响。用这种方法，预先采样的MTF是由一次曝光中用一个略微倾斜的狭缝获得的“精细采样”的LSF的傅里叶变换确定的。由于有效采样距离比DR系统的原始采样距离小得多，因此可以消除混叠对MTF计算的影响。将该方法应用于计算机射线照相(CR)系统的预采样MTF的测量，讨论了其方向相关性、指数外推的影响以及不同采样距离的影响。我们证明了在模拟屏幕-胶片系统中常用的多缝曝光和LSF尾部指数外推技术可以用于DR系统。此外，我们还利用铅盘方法测定了眩光分数，以估算主要由“眩光”引起的低频下降的分量。结果表明，眩光分数值在5~6.5%之间，与采样距离有一定的相关性。
We developed a simple method for determining the presampling modulation transfer function (MTF), which includes the unsharpness of the detector and the effect of the sampling aperture, in digital radiographic (DR) systems. With this method, the presampling MTF is determined by the Fourier transform of a "finely sampled" LSF obtained with a slightly angulated slit in a single exposure. Since the effective sampling distance becomes much smaller than the original sampling distance of the DR system, the effect of aliasing on the MTF calculations can be eliminated. We applied this method to the measurement of the presampling MTF of a computed radiographic (CR) system and discussed the directional dependence, the effect of exponential extrapolation, and the effect of different sampling distances. We showed that the technique of multiple slit exposure and exponential extrapolation of the LSF tail, which has been commonly used in analog screen-film systems, can be employed in DR systems. Furthermore, we determined the glare fraction, by means of a lead-disk method, in order to estimate the component of low-frequency drop mainly due to "glare." The results showed that the value of glare fraction was 5-6.5% and slightly dependent on the sampling distance.