title: A framework for correcting brain retraction based on an eXtended Finite Element Method using a laser range scanner.
abstract: BACKGROUND
  Brain retraction causes great distortion that limits the accuracy of an image-guided neurosurgery system that uses preoperative images. Therefore, brain retraction correction is an important intraoperative clinical application.
  
  
  METHODS
  We used a linear elastic biomechanical model, which deforms based on the eXtended Finite Element Method (XFEM) within a framework for brain retraction correction. In particular, a laser range scanner was introduced to obtain a surface point cloud of the exposed surgical field including retractors inserted into the brain. A brain retraction surface tracking algorithm converted these point clouds into boundary conditions applied to XFEM modeling that drive brain deformation. To test the framework, we performed a brain phantom experiment involving the retraction of tissue. Pairs of the modified Hausdorff distance between Canny edges extracted from model-updated images, pre-retraction, and post-retraction CT images were compared to evaluate the morphological alignment of our framework. Furthermore, the measured displacements of beads embedded in the brain phantom and the predicted ones were compared to evaluate numerical performance.
  
  
  RESULTS
  The modified Hausdorff distance of 19 pairs of images decreased from 1.10 to 0.76 mm. The forecast error of 23 stainless steel beads in the phantom was between 0 and 1.73 mm (mean 1.19 mm). The correction accuracy varied between 52.8 and 100 % (mean 81.4 %).
  
  
  CONCLUSIONS
  The results demonstrate that the brain retraction compensation can be incorporated intraoperatively into the model-updating process in image-guided neurosurgery systems.
authors.affiliation: Digital Medical Research Center, Fudan University, Shanghai , 200032, People's Republic of China, lip@smic.edu.cn.
authors.forename: Ping
authors.initials: P
authors.lastname: Li
authors.forename: Weiwei
authors.initials: W
authors.lastname: Wang
authors.forename: Zhijian
authors.initials: Z
authors.lastname: Song
authors.forename: Yong
authors.initials: Y
authors.lastname: An
authors.forename: Chenxi
authors.initials: C
authors.lastname: Zhang
mesh_terms: D000465:Algorithms; D001921:Brain / Q000601:surgery*; D020342:Finite Element Analysis; D006801:Humans; D007834:Lasers; D016014:Linear Models; D019635:Neurosurgical Procedures / Q000295:instrumentation*; D019047:Phantoms, Imaging