Nishikawa R M, Yaffe M J
Department of Medical Biophysics, University of Toronto, Canada.
Med Phys. 1990 Sep-Oct;17(5):887-93. doi: 10.1118/1.596572.
We have examined the effect of screen-structure, optical-detector, and secondary-quantum noise sources on detective quantum efficiency, DQE(f). This was done by using experimental measurements of screen-structure and optical-detector noise in combination with a theoretical model which predicts x-ray quantum and secondary-quantum noise for different optical and physical properties of a phosphor screen. The reduction in DQE(f) from noise sources other than x-ray quantum noise depends on the noise power spectra (NPS) of these other sources relative to the x-ray quantum NPS. Even though x-ray quantum noise may be the dominant noise source at low spatial frequencies, it decreases relatively rapidly with increasing frequency so that other noise sources, which may be small at low frequencies, dominate. Our model predicts that DQE(f) can be increased, at spatial frequencies less than 4 mm-1, by changing the optical properties of the screen even though modulation transfer function MTF(f) may decrease. Furthermore, if screen and optical-detector noise decrease with increasing frequency and secondary-quantum noise sufficiently small, then DQE(f) will also be improved at frequencies greater than 4 mm-1.
我们研究了屏结构、光学探测器和二次量子噪声源对探测量子效率DQE(f)的影响。这是通过对屏结构和光学探测器噪声进行实验测量，并结合一个理论模型来完成的，该理论模型可预测磷光屏不同光学和物理特性下的X射线量子噪声和二次量子噪声。除X射线量子噪声外，其他噪声源导致的DQE(f)降低取决于这些其他源的噪声功率谱（NPS）相对于X射线量子NPS的情况。尽管在低空间频率下X射线量子噪声可能是主要噪声源，但随着频率增加它会相对迅速地降低，以至于在低频时可能较小的其他噪声源会占据主导。我们的模型预测，即使调制传递函数MTF(f)可能降低，但在空间频率小于4 mm-1时，通过改变屏的光学特性仍可提高DQE(f)。此外，如果屏和光学探测器噪声随频率增加而降低且二次量子噪声足够小，那么在频率大于4 mm-1时DQE(f)也会得到改善。
