Insertion Mechanism Of Deep Brain Stimulation With Intracranial Microelectrodes

In deep brain stimulation (DBS) implanted electrodes is inserted into specific parts of the brain by stereotactic brain surgery. High frequency simulation can suppress the abnormal electrical activities of neurons and thus play a therapeutic role to certain neurological disorders. However, there are some serious complications and side effects of DBS. One of the most important reasons is microelectrode-positioning inaccuracy. To ensure insertion positioning accuracy and improve the therapy success rate, it is necessary to research on the microelectrode structures and precision positioning drive strategies suitable for one-time implantation, and to develop more reliable insertion equipments, in which the research on the mechanical properties and insertion mechanism of brain tissue is the key part. In this paper, using porcine brain as research object, the mechanical properties and insertion mechanism of brain tissue was studied through experiments, theoretical analysis and finite element simulation method.The brain model three-dimensional reconstruction technology was introduced, and the reconstruction scheme was planned. The 3D models of human brain and porcine brain were established from the digital brain model and MRI scan image respectively. The insertion path of deep brain electrode implantation was determined. The study suggested that the brains of human and porcine are similar in a certain degree. The insertion path to the first half is mainly gray matter, while the latter half is mainly white matter. Thus, it is feasible to study the procedure and mechanism of human brain electrode implantation by through porcine brain test.A multi-functional test platform was built to test the brain tissue. Strain-stress relationships for different strain rates in compression experiments were tested. A brain tissue quasi-linear viscoelastic model suitable for finite element analysis was built by using Odgen hyperelastic model for instantaneous mechanical characteristics and Prony series for viscoelastic properties. A novel method was developed to build the visco hyperelastic model, in which the elastic function and relaxation function were calculated separately by introducing a factor κ. It is suggested when the factor κ was chosen to be 10, the model is most consistent with the experimental data. A criteria was discussed and carried out to choose the order of relaxation Prony series. Due to the limited compression speed and test time, the short-time and long-time response can never be fully portrayed, therefore, in order to better describe the relaxation curve, the terms in Prony series can be simplified only if its influence on the test period is far less than 1. Thus, generally the application conditions of brain tissue model should not exceed the test maximum strain rate, and the analysis time should not exceed the test time. The model raised in the paper is suitable to the situation when analysis time is less than 20 s, and the strain rate is less than 1 s-1.In order to study the brain tissue insertion mechanism, insertion forces under different conditions were tested by performing insertion experiments. The force transformations and tissue deformations were discussed in different stages of insertion. It was found that with the increases of insertion speed, the puncture force did not change significantly, the puncture depth decreased while the peak insertion force increased; and with the increases of diameters of insertion needles, the puncture force, puncture depth and peak insertion force all increased. A model was built for the insertion process using energy analysis method. It is suggested during the insertion process, the work of insertion force on the tissue turned into four kinds of energy: elastic strain energy stored by tissue deformation, surface energy consumed by producing new surfaces, friction energy and other energy dissipation. The model explained the energy and force transformation in the view of energy, and revealed the brain tissue insertion mechanism. A finite element model of electrode inserting into brain was established. The tissue deformation and stress distribution near the needle tip was simulated, and the influences of different conditions were analyzed.