Anam Choirul, Naufal Ariij, Lubis Lukmanda E, Fujibuchi Toshioh
Department of Physics, Faculty of Sciences and Mathematics, Diponegoro University, Semarang, Central Java, Indonesia.
Department of Physics, Faculty of Sciences and Mathematics, Diponegoro University, Semarang, Central Java, Indonesia.
Phys Med. 2025 Jan;129:104876. doi: 10.1016/j.ejmp.2024.104876. Epub 2024 Dec 4.
This study aimed to develop a statistical approach for edge spread function (ESF) phase alignment to improve the accuracy of modulation transfer function (MTF) measurements at the edges of computed tomography (CT) images.
A statistical approach to ESF phase alignment was initiated by collecting ESF samples with poor phase alignment. One ESF sample was selected as the reference ESF and the other as the treated ESF. The treated ESF was then shifted by 10-pixels in the right and left directions with a 1-pixel increment at each shift. The mean squared error (MSE) for each shift was calculated between the shifted and reference ESF, and the position with the minimum MSE indicated the best phase alignment between the two ESFs. All shifted ESFs were averaged and differentiated to obtain a single-line spread function (LSF). The MTF was generated by Fourier transformation of the LSF. The MTFs from the shifted ESF and the non-shifted MTF from images of the ACR CT, point-computational, CTDI, and anthropomorphic phantoms were compared.
The MTF curves obtained after the phase alignment showed higher and more consistent results than those obtained before the alignment. The MTF curves obtained after phase alignment were comparable to those obtained from a point computational phantom. Our method showed improved accuracy in measuring spatial resolution compared to those without the edge-shifting method.
The results showed that a statistical approach for ESF phase alignment can overcome poor phase alignment and produce a more accurate MTF curve.
本研究旨在开发一种用于边缘扩展函数（ESF）相位对齐的统计方法，以提高计算机断层扫描（CT）图像边缘处调制传递函数（MTF）测量的准确性。
通过收集相位对齐不佳的ESF样本启动ESF相位对齐的统计方法。选择一个ESF样本作为参考ESF，另一个作为处理后的ESF。然后将处理后的ESF在左右方向上以每次1像素的增量移动10像素。计算每次移动后移动后的ESF与参考ESF之间的均方误差（MSE），MSE最小的位置表明两个ESF之间的最佳相位对齐。对所有移动后的ESF进行平均并求导以获得单线扩展函数（LSF）。通过对LSF进行傅里叶变换生成MTF。比较了移动后的ESF的MTF与ACR CT、点计算、CTDI和拟人化体模图像的未移动MTF。
相位对齐后获得的MTF曲线比对齐前获得的曲线具有更高且更一致的结果。相位对齐后获得的MTF曲线与从点计算体模获得的曲线相当。与未采用边缘移动方法的方法相比，我们的方法在测量空间分辨率方面显示出更高的准确性。
结果表明，ESF相位对齐的统计方法可以克服相位对齐不佳的问题，并产生更准确的MTF曲线。
