Study On Intracranial Insertion And Directional Control Of Electrode For Deep Brain Stimulation

Corresponding to low targeting accuary and severe brain injury due to lacking of inserting mechanisms,lag in inserting tools during sub-thalamic nucleus deep brain stimulation,mechanical properties of brain tissues on the implanting trajectory of sub-thalamic nucleus are investigated in this paper.Moreover,brain tissue responses to electrode insertion are analysed and regularties of brain tissue deformation and inserting forces are obtained.Kinds of inserting needles with different surface textures are designed and fabricated,the best morphology for antifriction is determined,and the effect mechanism is investigated.The frameless methodology through orthogonal orientation for planned intracranial trajectory is proposed,the corresponding automatic inserting platform is fabricated,and a brain-like transparent model is built.The effect to improve targeting accuracy of the frameless methodology is confirmed through inserting tests to the brain-like transparent model.Based on conditions of electrode insertion during sub-thalamic nucleus deep brain stimulation,mechanical properties of brain tissues within different regions on the implanting trajectory of sub-thalamic nucleus are investigated.The effects of small section compression to the whole brain by guide cannular before cortical surface puncture and the indentation-relaxation to regions on the implanting trajectory after cortical surface puncture are analysed.The mechanics model of inserting a whole brain and a viscoelastic model describing the average load trace of each region using Boltzmann hereditary integral are built.The whole brain sample for inserting tests is prepared and pre-puncture needle insertion tests are carried out.The brain slices containing a planned trajectory with large section and thickness are prepared and indentation-relaxation tests to six regions along the planned trajectory are made.Elastic mechanical properties of the whole brain and viscoelastic mechanical properties of brain tissues within different regions along a planned trajectory are obtained.Differences of mechanical properties of tested regions are investigated.It is turned out that the whole brain show linear or non-linear elasticity.The constant Young's modulus is 4.044 kPa,and the range of non-linear Young's modulus is 3.027 kPa-5.032 kPa.Brain tissues on the implanting trajectory show obvious viscoelasticity which can be discribled by Shear relaxation moduli G(t).The six regions can be classified into three categories,according to the regional shear moduli.Within each category,tissues have no significant difference.However,significant differences exist between categories.Due to causes of targeting error and brain injury,guide cannula insertion is investigated through single-insertion tests,and the replacement of a microrecording electrode with a definitive DBS electrode is investigated through two-insertion tests.Brain tissue deformation and inserting force during single-insertion tests and two-insertion tests are analysed.Inserting mechanisms are as follows:brain tissue deformation and inserting force along inserting direction are dominated.For single-insertion,the position of cortical surface varied regularly with the depth of needle tip,and inserting force has different characteristics during each inserting stage.Dimpling depths positively contribute to puncture forces.Variations in dimpling depths/puncture forces exhibit undulate with increasing insertion velocities.The method of finding a wave-valley can determine an optimal insertion velocity that is 2.5 mm/s to reduce dimpling depths/forces in pre-puncture insertion.Less frictional force can reduce brain deformation and inserting force in post-puncture insertion.For two-insertion tests,brain tissue deformation,inserting force and its slope during the second insertion are lower than the first one.Actual insertion depth during the second insertion is greater than the first one for the same absolute insertion depth.The antifrictional effect of micro-surface textures is introduced in the design of guide cannular and several inserting needles with surface textures are fabricated.The process parameters on the evolution of lines on 316L stainless-steel surface by nanosecond laser are optimized through orthogonal tests.For optimum nanosecond laser process parameters:power is 0.04 W,frequency is 75 KHz,scanning speed is 400 mm/s and the overscan is 2.Regions containing lines with distances of 0.2 mm,0.3 mm,0.4 mm and 0.5 mm are fabricated on 316L stainless-steel surface using these process parameters.Distances of 0.2 mm,0.3 mm and 0.4 mm are determined for 01.5 mm needles with surface textures,according to improvement of wettability of water drople.Needles with linear,annular and spiral surface textures are obtained.Single-insertion tests that porcine brains are inserted by textured needles and a smooth stainless-steel needle with inserting velocities of 2 mm/s,3 mm/s and 4 mm/s are carried out.Adhesions of brain tissues on the side wall of needles with different surface textures are compared.The increase rates of inserting friction for textured needles are compared with the smooth stainless-steel needle.It is turned out that there is no adhesion of brain tissues on the side wall of linearly textured needles,but adhesion of brain tissues exsits on annular and spiral textured needles.The linearly textured needle with distances of 0.2 mm has the best antifrictional effect.Compared with the smooth stainless-steel needle,the increase rates of inserting friction decrease by 22.4%?40%.The antifrictional effect mechanism of linearly textured needles is attributed to the better lubricant performance of capturing cerebrospinal fluid,due to improved wettability of surface with dense textures.Moreover,the contact area between the shaft and brain tissues is less for a needle with surface textures,so friction is lower.According to low targeting accuary and severe brain injury due to cerebral stereotactic apparatus with frame,the frameless extracranial methodology through orthogonal orientation for planned intracranial trajectory is proposed.The procedures of orthogonal orientation are shown out to make the planning path vertical.The corresponding automatic inserting platform is fabricated,and a brain-like transparent model is built.The planned path designed on the brain-like transparent model is adjused vertical using the frameless extracranial methodology through orthogonal orientation and the STN-like target is inserted.It is turned out that the implanting trajectory parallels well to the planned path.Moreover,the center of the STN-like target is touched precisely by the needle tip.For 50 mm tested length,the error between needle tip and target is only 0.146 mm.