Doi K
Med Phys. 1977 Jan-Feb;4(1):15-20. doi: 10.1118/1.594378.
The basic theory of field characteristics is discussed. It is shown that the point spread function and optical transfer function (OTF) of geometric unsharpness at any arbitrary field position can be derived from those at the central beam position. At all locations in the radiation field, the OTF in a direction parallel to the x-ray tube cathode-target axis does not depend on the field position X, which is perpendicular to the tube axis, whereas the OTF in a perpendicular direction does not depend on the field position Y, which is parallel to the tube axis. The theoretical result is used to demonstrate the field characteristic of the uniform, square focal spot.
讨论了场特性的基本理论。结果表明，在任意场位置处几何不清晰度的点扩散函数和光学传递函数（OTF）可由中心束位置处的函数推导得出。在辐射场的所有位置，平行于X射线管阴极-靶轴方向的OTF不依赖于垂直于管轴的场位置X，而垂直方向的OTF不依赖于平行于管轴的场位置Y。理论结果用于证明均匀方形焦点的场特性。
