Doi K, Loo L N, Chan H P
Radiology. 1982 Jul;144(2):383-93. doi: 10.1148/radiology.144.2.7089295.
Thirty-two focal spot sizes of four x-ray tubes were measured by the pinhole, star pattern, slit, and root-mean-square (RMS) methods under various exposure conditions. The modulation transfer functions (MTFs) and line spread functions (LSFs) were also determined. The star pattern focal spot sizes agreed with the effective sizes calculated from the frequencies at the first minimum of the MTF within 0.04 mm for large focal spots and within 0.01 mm for small focal spots. The focal spot size determined by the slit method was approximately equal to the width of the LSF at the cutoff level of 0.15 +/- 0.06 of the peak value. The RMS method provided the best correlation between the measured focal spot sizes and the corresponding image distributions of blood vessels. The pinhole and slit methods tended to overestimate the focal spot size, but the star pattern method tended to underestimate it. For approximately 90% of the focal spots, the average of the star and slit (or pinhole) focal spot sizes agreed with the RMS focal spot size within +/- 0.1 mm.
在各种曝光条件下，采用针孔法、星芒图案法、狭缝法和均方根（RMS）法对四个X射线管的32个焦点尺寸进行了测量。还测定了调制传递函数（MTF）和线扩展函数（LSF）。对于大焦点，星芒图案焦点尺寸与从MTF第一个最小值处的频率计算出的有效尺寸在0.04mm范围内相符；对于小焦点，在0.01mm范围内相符。狭缝法测定的焦点尺寸约等于LSF在峰值的0.15±0.06截止水平处的宽度。RMS法在测量的焦点尺寸与相应的血管图像分布之间提供了最佳相关性。针孔法和狭缝法往往高估焦点尺寸，而星芒图案法往往低估焦点尺寸。对于约90%的焦点，星芒图案法和狭缝法（或针孔法）焦点尺寸的平均值与RMS焦点尺寸在±0.1mm范围内相符。
