基于柱坐标B样条活动曲面模型的3D分割方法

3D Segmentation Based on Cylindrical B-Spline Active Surface Model

基于长轴和短轴系列核磁共振图像重建3D左心室内外表面是提取左心室基本形态参数以及左心室运动分析的基础.提出了柱坐标B样条主动表面(CBAS)模型,将其用于3D分割左心室内外膜表面.CBAS模型的等参曲线网格由B-snake模型组成,根据短轴、长轴成像平面在3D空间中的位置关系,网格中的节点在两幅短轴及长轴图像上寻找对应的边缘点,节点间的采样点则在单一的短轴或长轴图像上获得图像能量.首先利用改进的模糊Hough变换确定短轴图像中左心室心肌内外轮廓的大致位置,其次用其构建柱坐标B样条主动曲面模型的初始表面.对左心室表面的分割过程在柱坐标下进行,使得模型在SA图像及LA图像上形状的改变能够统一为一个参数的变化,减小了模型的复杂度.最后通过与手工分割结果的线性回归分析证明了方法的准确性.

Reconstruction of the surface of left ventricle （LV） is one of the challenging problems to analyze left ventricle＇s shape and motion. In this paper, a cylindrical B-spline active surface （CBAS） model is put forward. The model can be used to segment the LA （long axis） and SA（short axis ） tagged MR images to get the 3D surface of the LV. The model can be seen as a grid composed of B-snake contours. According to the relation of LA and SA image plane＇s position in the 3D space, one node of the grid synchronously finds the edge points in one SA image and one LA image, and the sample points between two nodes in the same direction calculate their image energies using only one SA or LA image. By using the cylindrical model, the deformation of the model on the SA planes or LA planes can be realized just by changing only one variable, which decreases the complexity of the model. In the paper, firstly, the fuzzy Hough transform is used to find the approximate position of the LV＇s contour. Secondly, the approximate contours are used to construct the initial surface of the CBAS model. Then, the model is utilized to segment the tagged MR image series and get the exact LV＇s surfaces. The experiment shows that the method can get exact 3D surfaces by being compared with manually outlined contours.