Research On The Computer-Aided Surgery Planning For Lacrimal Passage

The lacrimal passage is situated in the naso-orbital-ethmoid region,it's the excretory system for tears. A lacrimal passage primary consists of five parts, namely lacrimal punctum, lacrimal duct, common canaliculus, lacrimal sac and nasolacrimal duct. The nasolacrimal duct is a channel in which tears from the eyes into the nasal cavity. The naso-orbital-ethmoid region's fracture would lead to the nasolacrimal duct be squeezed or broken, making it's excretory function abnormal, causing vision loss or even serious dysfunction. Due to the complex anatomy of this area, the fracture may result in multiple parts, different types of obstruction. Consequently, fully understand the injury before surgery is the key to the success of the surgery and the recovery of lacrimal passage's excretory function.With the continuous progress in science and technology, computer-aided technology's application in medical field has become increasing widespread. However, no research institution or commercial company has developed a full computer-aided lacrimal passage planning system currently. In this paper, we cooperate with Shanghai Ninth People's Hospital affiliated to Shanghai Jiao Tong University, present some researches on the computer-aided surgery planning for lacrimal passage, it mainly includes:(1) The conversion method between two-dimensional points and three-dimensional points. In the three-dimensional space, only sampling points on object's surface can be marked, to this end, this paper presents a method which can convert two-dimensional points into the corresponding three-dimensional points. So we can mark sampling points inside the object.(2) Re-ample the volume data along the axial direction of nasolacrimal duct. Because the CT scanning direction is not perpendicular to the axial direction of nasolacrimal duct, CT slices cannot accurately show the structure and shape information of nasolacrimal duct. So we first calculate the axial direction of nasolacrimal duct by using the conversion method between 2D points and 3D points proposed above, then generate a series of new 2D sectional images along the axial direction of nasolacrimal duct by interpolation.(3) Three-dimensional reconstruction of nasolacrimal duct and lacrimal sac. We first use active contour mode algorithm to segment re-sampled slices, then take advantage of contour-based and volume-based surface reconstruction method to complete the 3D reconstruction of normal nasolacrimal duct and lacrimal sac. Due to fractured nasolacrimal duct's contour is unclosed, we use the snake model and artificial interactive method to complete the two-dimensional segmentation of the nasolacrimal duct, and then use the shortest diagonal method to reconstruct the three-dimensional model of fractured nasolacrimal duct. The shortest diagonal algorithm is also improved in this paper.(4) Automatic segmentation method. In view of deformable mode's defect in interactive operations, this paper presents an automatic segmentation method which take advantage of the continuity between adjacent slices, the method use the convergent contour on a slice as the initial contour of the next slice, so the slice sequences can be segmented one by one.(5) Computer-aided analysis and measurement. After the reconstruction, we can clearly show the internal and external anatomy of lacrimal duct, fracture position of nasolacrimal duct and acrimal sac's displacement distance, on this basis, to achieve visual measurement, mark and bilateral symmetry.Computer-aided lacrimal passage planning system helps doctors analyze medical images, make surgery planning by using computer image, graphics and visualization technology, it also can improve the safety and accuracy of the surgery. The method proposed in this paper is useful in computer-aided diagnosis and surgery planning related to lacrimal passage.