改进Demons算法的验证及其在4D-CT轮廓线推衍中的应用

Validation of an improved Demons deformable registration algorithm and its application in re-contouring in 4D-CT

目的研究一种改进的Demons变形配准算法,验证算法的有效性,评价配准算法的精度,并将其应用于4D-CT轮廓线的推衍。方法为加快收敛的速度和提高配准精度,将Demons算法的双向作用力进行重分配,并提出一个能量函数作为相似性测度,利用BFGS优化算法对能量函数进行优化,避免了经典算法中需指定迭代次数的缺陷。分别利用模拟形变CT图像与变形模体,分析和测量了配准算法的精度,并对该算法在4D-CT轮廓线推衍中的应用进行了评价。结果改进后的Demons算法与经典的Demons算法以及类似的变形配准算法相比,有较高的配准精度,推衍生成的轮廓线与人工勾画的轮廓线匹配程度高。结论变形配准是4D-CT中的一项关键技术,改进后的Demons算法应用于轮廓线的推衍有望大大治疗计划设计的轮廓勾画工作量,其配准精度能满足实际临床的需要。

Objective To validate the efficiency and accuracy of an improved Demons deformable registration algorithm and evaluate its application in contour recontouring in 4D-CT. Methods To increase the additional Demons force and reallocate the bilateral forces to accelerate convergent speed,we propose a novel energy function as the similarity measure,and utilize a BFGS method for optimization to avoid specifying the numbers of iteration. Mathematical transformed deformable CT images and home-made deformable phantom were used to validate the accuracy of the improved algorithm,and its effectiveness for contour recontouring was tested. Results The improved algorithm showed a relatively high registration accuracy and speed when compared with the classic Demons algorithm and optical flow based method. Visual inspection of the positions and shapes of the deformed contours agreed well with the physician-drawn contours. Conclusion Deformable registration is a key technique in 4D-CT,and this improved Demons algorithm for contour recontouring can significantly reduce the workload of the physicians. The registration accuracy of this method proves to be sufficient for clinical needs.