量子斑点的维纳频谱与调制传递函数平方之间的比例关系。

Arimura H, Kubota H, Matsumoto M, Kanamori H

Department of Clinical Engineering, Hiroshima International University, Japan.

Phys Med Biol. 1999 May;44(5):1337-52. doi: 10.1088/0031-9155/44/5/318.

Rossmann proposed that the Wiener spectra of the quantum mottle of radiographs made using screen-film systems were proportional to the squares of the modulation transfer functions (MTFs) of the screen-film systems. On the other hand, Lubberts theoretically pointed out that the shape of the Wiener spectrum of the quantum mottle depended on the sum of the squares of the MTFs for different depths in the screen phosphor layer, rather than the square of the sum of the MTFs for the different depths, i.e. the square of the MTF of the screen-film systems. The purpose of this study is to experimentally investigate the proportionality between the Wiener spectra of the quantum mottle and the squares of the MTFs of screen-film systems using two screen-film systems having different screen thicknesses. For this purpose, we determined correction factors for the square of the MTF of the screen-film system in the Wiener spectrum of the quantum mottle at each spatial frequency when the Wiener spectral values of the screen mottle were separated into those of the quantum mottle and structure mottle. The correction factor is the ratio of the normalized Wiener spectrum of the quantum mottle to the square of the MTF of the screen-film system. As a result, for a thin screen, the correction factors were unity for all spatial frequencies; on the contrary, for a thick screen, the factor increased with spatial frequency. By calculating the theoretical correction factors using the models for the MTF and Wiener spectrum of the quantum mottle of Nishikawa and Yaffe based on Lubberts' theory, we verified that our experimental results agreed with Lubberts' theory. Furthermore, by obtaining the screen thickness dependence of the theoretical correction factors for the two screens, we showed that, for screens thinner than 0.02 mm, Rossmann's theory can be applied to the relationship between the Wiener spectrum of the quantum mottle and the MTF of the screen-film system, whereas for screens thicker than 0.02 mm, Lubberts' theory should be applied.

罗斯曼提出，使用增感屏 - 胶片系统制作的X线照片量子斑点的维纳频谱与增感屏 - 胶片系统调制传递函数（MTF）的平方成正比。另一方面，卢贝茨从理论上指出，量子斑点维纳频谱的形状取决于增感屏磷光层不同深度处MTF平方的总和，而不是不同深度处MTF总和的平方，即增感屏 - 胶片系统MTF的平方。本研究的目的是使用两种具有不同屏厚度的增感屏 - 胶片系统，通过实验研究量子斑点的维纳频谱与增感屏 - 胶片系统MTF平方之间的比例关系。为此，当屏斑点的维纳光谱值被分离为量子斑点和结构斑点的维纳光谱值时，我们确定了在每个空间频率下量子斑点维纳频谱中增感屏 - 胶片系统MTF平方的校正因子。校正因子是量子斑点归一化维纳频谱与增感屏 - 胶片系统MTF平方的比值。结果表明，对于薄屏，所有空间频率下的校正因子均为1；相反，对于厚屏，该因子随空间频率增加。通过基于卢贝茨理论使用西川和亚夫的量子斑点MTF和维纳频谱模型计算理论校正因子，我们验证了我们的实验结果与卢贝茨理论一致。此外，通过获得两种屏的理论校正因子对屏厚度的依赖性，我们表明，对于厚度小于0.02 mm的屏，罗斯曼理论可应用于量子斑点维纳频谱与增感屏 - 胶片系统MTF之间的关系，而对于厚度大于0.02 mm的屏，则应应用卢贝茨理论。