Ablation Needle Trajectory Planning Method And Its Application System For CT-guided Liver Tumor Ablation

CT-guided liver tumor ablation has been used in clinic.The ablation applicator or needle percutaneously inserts into a tumor under the guidance of CT imaging,so as to destroy the tumor in situ by heating-induced coagulation necrosis within a few minutes.As an important part of thermal ablation,the needle(insertion)trajectory planning must be accurate and effective.However,it still relies on the personal experience of clinicians in clinical procedures.In this paper,the computer-aided planning method and system are studied to plan the needle trajectory for CT-guided liver tumor ablation.It includes three-dimensional(3D)reconstruction of critical structures(such as liver vessel)based on 3D segmentation results in CT images,the computer-aided needle trajectory planning method based on multiple clinical insertion constraints,and the implement of the needle trajectory planning system.It has important academic significance and potential application value.The main research work and innovations are as follows:1)A new method is proposed for automatic 3D liver vessel segmentation in computed tomography(CT)images by using an improved vesselness filter and an improved fuzzy connectedness(FC)methed.Firstly,an improved vesselness filter is designed by incorporating an adaptive sigmoid filter and a background-suppressing item.Secondly,the improved vesselness response is innovatively incorporated into the fuzzy affinity function of FC,which improves the segmentation performance of traditional FC in low-contrast CT images.Thirdly,the multi-threshold Otsu algorithm is used to initialize the improved FC parameters adaptively.It reduces the dependence of traditional FC on the number and distribution of seeds and alleviates the sensitivity of the traditional FC method to the initial parameters.Finally,the fuzzy scene is segmented to obtain the automatic 3D segmentation results of the liver vessel.The improved FC method for liver vessel segmentation is evaluated on 20 cases of CT images in 3Dircadb and 20 cases of CT images in Sliver07.The average accuracy,sensitivity,specificity and Dice coefficient of the improved FC method are 96.4%,73.7%,97.4%,and 67.3%(3Dircadb)and 96.8%,84.4%,97.6%,and 71.4%(Sliver07),respectively.The proposed FC method can segment complex and diverse liver vessel even in low contrast CT images.Comparing with the traditional FC,region growing and threshold level set,the proposed FC method achieves better segmentation performance and lower dependence on seeds and initial parameters.The proposed FC method may be used as a new method for automatic 3D segmentation of liver vessel in CT images.2)A new automatic method of needle(insertion)trajectory planning is proposed based on computer-aided processing of clinical insertion constraints.First of all,an improved cube mapping method is designed based on coordinate correction,which can perspectively project the abdominal anatomy information of patient to the surface of the external bounding box.Secondly,the computer algorithm is used to deal with the clinical hard constraints automatically.At the same time,the improved cube mapping method is used to the critical structures in abdomen,which divides the surface of the external bounding box into the applicable insertion zone and no-fly zone automatically.Finally,the computer algorithm is used to deal with the clinical hard/soft constraints to generate the normalized gray-scale constraint maps by using the improved cube mapping method.The normalized gray-scale constraint maps are weighted to plan the needle trajectory automatically.Based on 10 cases of 3D CT images in 3Dircadb(18 tumors),the automatic method of needle trajectory planning is qualitatively evaluated.After discussion with two clinicians,they believe that more than 78%of computer-aided needle trajectories are reasonable,and nearly 39%of those are superior to their own manual planning.The needle trajectory planning method proposed in this paper is different from those existing automatic/semi-automatic methods.Firstly,the number and quality(accuracy)of the alternative needle trajectories(the candidate trajectories for selecting the optimal needle insertion trajectory)generated in this paper are only positively related to the spatial sampling of the patient CT image.Comparing with the discrete deflection angle method(n=360~2or n=720~2)or the polygonal mesh surface rendering method(n?[2000-6000]),the number of alternative needle trajectories generated in this paper is exceeded at least one order of magnitude,and the quality is not limited by the 3D reconstruction accuracy of the patient abdominal skin.In addition,comparing with the exhaustive collision detection(at least 2000-6000 collision detection)or cylindrical projection based on perspective projection(at least dozens of times perspective projections)to plan the needle trajectory,the proposed improved cube mapping method only needs 6perspective projections to complete the corresponding task.Finally,some related researches interactively plan optimal needle trajectory by using the Pareto Optimal Concept,while our method can automatically obtain the optimal needle trajectory.To sum up,the proposed needle trajectory planning method has higher planning accuracy,lower complexity and no need for human interaction.It may be used in the planning process of CT-guided liver tumor ablation.3)A set of computer-aided needle trajectory planning system is designed for CT-guided liver tumor ablation.The system is mainly composed of two functional modules.On the one hand,it is the 3D segmentation and reconstruction module for critical structures,which realizes 3D segmentation and reconstruction of liver,liver tumor,liver vessel,skin,bone and lung.On the other hand,it is the needle(insertion)trajectory planning module,which realizes the automatic planning and interactive adjustment for the needle trajectory.At the same time,it also provides real-time planning parameters of the needle trajectory(e.g.space coordinates of insertion point and target point,and the evalution of the compliance degree of the needle trajectory relative to the clinical constraints).Part of the current surgical planning systems do not include the automatic/semi-automatic segmentation module of the critical structure.In addition,the needle trajectory planning function of some surgical planning systems only stays in the 3D reconstruction of abdominal anatomy scene.which still needs to interactively plan the needle trajcetory based on clinician experience.In contrast,our needle trajectory planning system improves the planning link for CT-guided liver tumor ablation.Two clinicians operate the system and perform the needle trajectory planning.They believe that the system can assist or guide clinicians to complete the needle trajectory planning for CT-guided liver tumor ablation and improve the accuracy and objectivity of planning process.