X射线相位成像的最佳衬度

根据Zernike相衬观察法的基本思想和Fresnel–Kirchhoff衍射理论,采用傅里叶变换和卷积处理,考虑到临床实际,利用振幅近似和相位缓变条件,将X射线经过生物组织产生的相位改变转换成强度分布.在所导出的理论公式的基础上,作出相位衬度和吸收衬度与物平面到像平面距离的关系曲线.分析得到X射线相位衬度成像的最佳物像距离,并通过微聚焦X射线成像装置对蟑螂成像的实验加以验证,其结果表明理论所预言的成像最佳位置符合度较高.

Optimal Contrast for X-ray Phase-contrast Imaging

Based on Zernike phase-contrast observation and Fresnel-Kirchhoff diffraction theory, the phase changes can be transferred into intensity distribution by the Fourier transform and the convolution theorems. Considering the clinical conditions, the amplitude approximation and the moderate variation condition for phases are used in the calculation of the image distribution and the Fourier transform of the theoretical image intensity distribution formula is derived directly, rather than through the Fourier transform of the wave field itself. Then the curves of phase contrast and attenuation contrast are obtained according to the theoretical intensity formula. After the analysis of the curves, the optimal distance of object to the image is found and validated by the roach imaging experiment-employed mico focus X-ray source.