Nishikawa R M, Yaffe M J
Med Phys. 1985 Jan-Feb;12(1):32-9. doi: 10.1118/1.595781.
The signal-to-noise ratio (SNR) and the detective quantum efficiency (DQE) have been experimentally determined as a function of spatial frequency for several mammographic film-screen systems. These two parameters were determined from our measurements of noise power spectra and sensitometric properties of each system along with modulation transfer function (MTF) data for the screens which were obtained from others. From the noise power spectra, it was found that film noise contributes significantly to the total noise of mammographic film-screen systems, comprising 30%-50% of the total noise at 1 cycle/mm and as much as 75% at 5 cycles/mm. All systems had approximately the same SNR below 1.5 cycles/mm, but differed at higher frequencies due to differences in screen MTF and in the gradient of the film's sensitometric curve. The DQE curves varied between systems at all frequencies, however, due to differences in system speed, MTF, and gradient. Generally, the DQE of mammographic film-screen systems is between 10%-30% at frequencies below 1 cycle/mm and decreases to about 1% between 8 and 12 cycles/mm. Compared to film-screen systems used in general radiography, mammographic systems have similar DQE values at low frequencies, but are superior at higher frequencies.
已经通过实验确定了几种乳腺X线胶片-增感屏系统的信噪比（SNR）和量子探测效率（DQE）作为空间频率的函数。这两个参数是根据我们对每个系统的噪声功率谱和感光特性的测量以及从其他来源获得的增感屏调制传递函数（MTF）数据确定的。从噪声功率谱中发现，胶片噪声对乳腺X线胶片-增感屏系统的总噪声有显著贡献，在1周期/毫米时占总噪声的30%-50%，在5周期/毫米时高达75%。所有系统在低于1.5周期/毫米时具有大致相同的SNR，但在较高频率时由于增感屏MTF和胶片感光曲线梯度的差异而有所不同。然而，由于系统速度、MTF和梯度的差异，DQE曲线在所有频率下在不同系统之间都有所变化。一般来说，乳腺X线胶片-增感屏系统在低于1周期/毫米的频率下DQE在10%-30%之间，在8至12周期/毫米之间降至约1%。与普通放射摄影中使用的胶片-增感屏系统相比，乳腺X线系统在低频时具有相似的DQE值，但在高频时更优。
