利用定量相衬成像消除X射线同轴轮廓成像中散射的影响

Application of quantitative imaging to elimination of scattering effect on X-ray in-line outline imaging

在所有的相衬成像方法中,X射线同轴轮廓成像由于光路简单、不需要任何光学元件而备受关注.其缺点是无法直接消除散射的影响,从而限制了它在生物医学等领域中的应用.利用数字模拟方法研究了引入散射前后轮廓像的质量随样品到探测器距离的变化情况.模拟结果表明直接轮廓成像存在一个最佳成像距离,因而无法通过改变样品到探测器距离来减小散射的影响.利用定量相衬成像不受成像距离限制的特点,研究了远距离成像时散射的影响.结果表明,样品到探测器的距离增大到一个临界值时,散射对重构像的影响可降到一个极值,此时成像质量得到了明显改善.

X-ray in-line outline imaging （XILOI） attracts much attention in recent years, for its simple setup compared with other approaches. Unfortunately, scattering effect cannot be removed directly, which restricts seriously the applications of this method to fields like biomedical radiography. The scattering effect in XILOI was investigated by digital simulation, in which the sample- detector distance （SDD） was changed step by step. The results show that there is a best imaging distance for the direct outline imaging and it is impossible to eliminate the scattering by arbitrarily changing the distance in this case. This difficulty could be overcome by quantitative phase contrast imaging（QPCI）, in which SDD can be adjusted freely using a reconstruction algorithm. According to the investigation using QPCI, the scattering effect can be reduced to a minimum by increasing the SDD to a critical value, at which distinct improvement of the image quality can be achieved.