基于SHOT与目标函数对称ICP的低重叠率术前术中点云配准算法

Low overlap rate preoperative and intraoperative point cloud registration algorithm based on SHOT and symmetric objective function ICP

目的配准是术前影像引导的椎弓根螺钉内固定术中的重要环节。术前CT影像三维重建获得的点云和术中捕获的暴露部位点云重叠率低,易受噪声、遮挡等因素的干扰,使点云配准更具挑战性。本文采用局部特征和距离度量相结合的方式应对低重叠率配准问题。方法首先利用方向直方图描述子(signature of histograms of orientations,SHOT)和随机抽样一致算法(random sample consensus,RANSAC)提取并匹配几何特征相似的点,完成初始对齐。应用目标函数对称ICP,通过最小化对称化点到面目标函数得到最终变换矩阵。对来源于SpineWeb公开数据集的5组腰椎数据进行配准实验。结果术前术中点云配准实验中平均配准误差为0.128 mm,平均运行时间为5.750 s。结论实验结果验证了该算法在低重叠率术前术中点云配准中的有效性,使得外科医生能及时根据配准结果调整手术器械,从而提高椎弓根螺钉置入准确率。

Objective Registration is an important part of preoperative image-guided pedicle screw fixation.The point cloud obtained by the 3D reconstruction of the preoperative CT image and the point cloud of the exposed part captured during the operation have a low overlap rate and are easily interfered by factors such as noise and occlusion,which makes the point cloud registration more challenging.This paper adopts the combination of local geometric features and distance measurement to deal with the problem of low overlap registration.Methods Firstly,the points with similar geometric features were extracted and matched using the signature of histograms of orientations descriptor(SHOT)and the random sample consensus(RANSAC)to complete the initial alignment.Applying the objective function symmetric ICP algorithm,the final transformation matrix was obtained by minimizing the symmetric point-to-surface objective function.Registration experiments were performed on five groups of lumbar spine data from the SpineWeb public dataset.Results In the preoperative and intraoperative point cloud registration experiments,the average registration error was 0.128 mm,and the average running time was 5.750 s.Conclusions The experimental results verify the effectiveness of the algorithm in the preoperative and intraoperative point cloud registration with low overlap rate,which enables surgeons to adjust the surgical instruments according to the registration results in time,thus improving the accuracy of pedicle screw placement.