基于小波域树结构MRF的医学图像分割

Medical image segmentation based on tree-structured MRF in wavelet domain

针对医学图像分割中器官组织结构复杂重叠,且伴有噪声、局部容积效应、及伪影的问题,提出了小波域树结构MRF(wavelet tree-structured Markov random field,WTS-MRF)的医学图像分割算法。通过小波多分辨率分析描述医学图像的特征信息;在小波分解的每一尺度上定义相同的树结构MRF来表征医学图像特征信息间的联系。小波域树结构MRF模型包括层间小波系数四叉树结构和层内TS-MRF结构,层间小波系数结构具有一阶Markov性;层内TS-MRF模型,采用Potts模型对节点标号势函数建模,同标号的观测特征用高斯模型建模;最后,通过从低分辨率尺度到高分辨率尺度的递归运算、以及每一分辨率中从分类层次树的顶层向底层的递归来求解最大后验概率,实现医学图像分割。实验结果从视觉效果和定量分析两方面验证表明,文中算法能有效地提取图像的细节信息,比较完整地分割医学图像的目标区域,具有较高的分割精度和鲁棒性。

Medical image have the characteristics of the complex overlapping of organ and tissue, and accompanied by noise, local volume effect, artifact. So the traditional segmentation method is not ideal. To solve this problem, a medical image segmentation algorithm based on tree-structured MRF in wavelet domain （WTS-MRF） was proposed. For expressing medical im- age information. WTS-MRF model defines the same tree structure at every scale of wavelet decomposition. At the same time, wavelet transform has good directional selectivity, non-redundancy and multi-scale characteristics. Multiscale and multi direc- tion expression by wavelet decomposition improved the ability of TS-MRF to describe the non-stationary characteristics of images. Then, it can more accurately describe the statistical characteristics of images, and effectively extract the feature information of medical image. In the WTS-MRF model, there are two structures in the layer TS-MRF structure and the interlayer four fork tree structure of wavelet coefficient. The TS-MRF model is built in the layer, and the node potential function is modeled by Potts model. The Gaussian model is used to build the model for the observed characteristics with the same label. The interlayer wavelet coefficients have the property of first-order Markov. Finally, using recursion from low resolution scale to high resolution scale and from the top layer of a hierarchical tree to the bottom at each resolution get the result of the maximum a posteriori probability, to complete medical image segmentation. From two aspects of visual effect and quantitative analysis,the experiment results indicate that the algorithm not only can effectively extract the details but also can relatively completely extract target area of medical image,and has higher segmentation accuracy and robustness.