Fujita H, Doi K, Giger M L
Med Phys. 1985 Nov-Dec;12(6):713-20. doi: 10.1118/1.595653.
We devised a new, simple technique for measuring the modulation transfer function (MTF) of a digital imaging system by using an image of an angulated slit. With this technique, the "presampling" analog MTF, which includes the geometric unsharpness, the detector unsharpness, and the unsharpness of the sampling aperture, can be measured even beyond the Nyquist frequency. A single-frame image of a slightly angulated slit was employed in order to obtain Fourier transforms of line spread functions at different alignments. The presampling MTF was determined by averaging the two Fourier transforms which we obtained from two extreme alignments (center and shifted) of the slit relative to the sampling coordinate. The presampling MTFs of our digital subtraction angiographic system were determined in two orthogonal directions for three different image-intensifier modes.
我们设计了一种新的简单技术，通过使用成角度狭缝的图像来测量数字成像系统的调制传递函数（MTF）。利用这种技术，即使超过奈奎斯特频率，也可以测量包括几何模糊、探测器模糊和采样孔径模糊在内的“预采样”模拟MTF。为了获得不同对齐方式下线扩散函数的傅里叶变换，采用了稍微成角度狭缝的单帧图像。预采样MTF是通过对我们从狭缝相对于采样坐标的两个极端对齐方式（中心和偏移）获得的两个傅里叶变换进行平均来确定的。我们在三种不同的图像增强器模式下，在两个正交方向上确定了数字减影血管造影系统的预采样MTF。
