胶片非线性特性对电子断层摄影术成像质量的影响

为了分析胶片的非线性特性对电子断层摄影术成像质量的影响,以Kodak4463(SO-163)型电子显微镜胶片为例,按照其成像光密度值与电子曝光量对数值之间的关系曲线(D-lgE曲线)对模型样品的线性投影像实施变换,并采用计算机仿真方法进行了三维重构.计算结果表明,随着最大曝光范围对应的D-lgE曲线片段的非线性度的增加,三维重构图像质量下降,尤其当最大曝光范围向D-lgE曲线的饱和区扩展时,三维重构的图像出现了严重失真的现象(重构图像与模型样品图像之间的相关系数从线性投影像对应的0.85减小到0.6以下).分析结果表明,调整样品的电子曝光量来改变胶片最大曝光范围在D-lgE曲线上的位置,可以降低胶片非线性特性对三维重构图像质量的影响,该研究结果对用胶片为记录媒体的电镜三维重构具有指导意义.

Simulation Study on Effect of Film Nonlinearity on Quality of Electron Tomography

To analyze the effect of the film nonlinearity on the quality of reconstructed image of electron tomography (ET), the nonlinear transform is performed on the linear projection of a model sample according to a D-lgE characteristic curve of the film, whose parameters are taken from the Kodak 4463 (SO-163) film, and the 3D reconstruction is worked out by computer simulation. The simulation results show that the quality of the reconstructed image decreases with the increase of the nonlinearity of the part of the D-lgE curve, which corresponds to the maximum exposure range. Especially, when the maximum exposure range extends to the saturation region of D-lgE curve, the reconstructed image appears to be distorted seriously and the correlation factor between the reconstructed image and the model sample may drop from 0.85, which corresponds to linear projection series, to a value below 0.6. It is also indicated that adjusting the electron exposure on the film, i.e. changing the position of the maximum exposure range on the D-lgE curve, can reduce the nonlinear effect of the film on 3D reconstructed image. This result is useful for ET when the film is used to record image data.