【作者】 张丽慧；

【导师】 王广军；

【作者基本信息】 重庆大学 ， 动力工程及工程热物理， 2014， 博士

【摘要】 神经外科手术已进入微创时代。经鼻入路进入颅底进行肿瘤摘除手术，以鼻腔为天然通道，避免了开颅过程对正常组织结构造成的破坏，对患者的创伤小、术后恢复快，受到了神经外科界的广泛关注。骨头磨削是经鼻颅底肿瘤摘除手术中常见的和基本的手术操作之一，磨削过程产生的热量会对骨头及邻近的脑神经和血管结构等关键组织带来热损伤，而目前有关神经外科骨头磨削热问题的研究还非常少。本文采用实验和数值模拟相结合的方法，对采用微型球形磨具的骨头磨削过程的传热问题及其反问题进行了研究。建立了骨头磨削过程产热模型并对骨头磨削过程的瞬态温度场进行了数值模拟；在此基础上，结合磨削过程的实验研究结果，研究了磨削过程的瞬态热流强度及其空间分布的反演问题，并依据反演结果，重构了骨头磨削过程的三维瞬态温度场；通过磨削实验，研究了磨削过程电机占空比与磨削热之间的函数关系，初步建立了磨削热实时估算模型，为磨削过程骨头温度的实时监控奠定了基础；最后，对加入冷却液的磨削热问题进行了研究。本文的具体研究内容及获得的主要结果包括：(1)针对采用微型球形磨具的骨头磨削过程，借助于机械磨削理论估算了磨具与骨头接触表面的热流分配系数，建立了骨头磨削过程的三维瞬态有限元热分析模型，通过数值仿真试验讨论了磨具运动方向(±x方向运动和±y方向运动)、磨具与骨头的接触角(0°、15°和30°)以及磨削切深(0.10mm、0.25mm和0.40mm)等磨削条件对磨削区热源分布的影响，并分析了不同磨削条件下骨头的三维瞬态温度场。(2)进行了新鲜牛大腿皮质骨的骨头干磨削（未加冷却液）实验研究，获得了在8种不同磨削工况下测点的瞬态温度信息。利用实验研究结果和Active set优化方法反演了不同磨削工况下进入骨头的磨削热，在此基础上重构了不同磨削工况下骨头的三维瞬态温度场。结果表明，当接触角为30°，磨削切深为0.40mm，进给速度为20mm/min时，骨头的瞬时最高温度接近210°C；此时，若以50°C作为人体组织出现热损伤的临界值，沿横向方向(y方向)热损伤范围将扩散到离磨削槽约3mm的区域，沿深度方向(z方向)热损伤范围将扩散到磨削表面下3mm的位置。(3)根据磨削实验获得的电机脉冲宽度调制(PWM)信号，以及通过反演获得的进入骨头的磨削热，探索了磨削过程电机占空比与磨削热之间的函数关系。结果表明，电机占空比与磨削热之间具有良好的线性相关性；当磨具沿±y方向进给时，函数的线性斜率略低于磨具沿±x方向进给时的斜率。对于所选择的三种模型条件，利用该线性函数估算了骨头的磨削热并利用前述的磨削过程瞬态有限元热分析模型获得了骨头的瞬态温度场，并与实验过程中获得的测点温度响应进行了对比，验证了该线性函数模型的有效性。上述构造为实现磨削温度的实时监控创造了条件。(4)针对前述利用机械磨削理论的磨具与骨头接触表面的热流分配估算模型存在的问题，将骨头磨削热问题归结为具有未知分布式移动热源的非稳态传热问题，通过空间函数和时间函数的叠加，构造了磨削区热流密度的瞬态分布函数，并分别利用顺序函数法(SFSM)和序列二次优化(SQP)方法对磨具与骨头接触表面的瞬时平均热流密度和热流密度的瞬时分布函数进行同时反演。文中通过数值仿真实验对上述的瞬态分布热源反演方法的有效性进行了验证，并结合骨头磨削实验获得的实测温度信息，反演了实验过程磨具与骨头接触表面的瞬时分布热流，在此基础上对实验过程骨头的瞬态温度场进行了重构。(5)针对临床中常用的常温滴灌冷却技术存在的问题，设计了一种适用于骨头磨削的低温喷雾冷却实验系统。通过实验获得了磨削槽正下方0.5mm、1.0mm和1.5mm处被磨削骨头的瞬态温度。实验结果表明，当磨具向后进给，冷却液温度为3°C，喷雾流量为120ml/h时，低温喷雾冷却具有明显的预冷效果，磨削槽正下方0.5mm处最高平均温度约为21.0°C；当磨具向前进给时，由于喷嘴朝向限制了冷却液进入磨削区，磨削槽正下方0.5mm处最高平均温度约为70.0°C，无法获得理想的降温效果。进一步，根据实验测量结果，采用考虑对流换热的有限元热分析模型和传热学反问题方法重构了喷雾冷却条件下骨头的温度场。数值结果表明，采用低温喷雾冷却技术，当磨具向后进给时，能够明显抑制43°C的热损伤边界向磨削表面下方的扩散范围。更多还原

【Abstract】 Neurosurgery has entered the period of minimally invasive operation. Endoscopicendonasal approach, could avoid the damage to the normal tissues during the invasiveprocedures, thus has received extensively attention due to the less damage to humanbody and the fast recovery after operation. Bone grinding is common procedure in theneursurgery. The heat generated during the grinding process could bring thermaldamage to the key tissues, such as the bone and the adjacent cranial nerves, and thevascular structure. Till now, there are few researches concerning the thermal problem ofgrinding the neurosurgery bones.In this work, experimental and numerical simulation methods are combined tostudy the heat transfer in bone grinding using miniature spherical grinding tool. Thethermal model was established for the bone grinding process, and the transienttemperature field during this process was simulated. Using the experimental data ofbone grinding, the inverse problems were investigated on the transient heat fluxintensity and its spatial distribution. On the basis, the3-D transient temperature fieldduring bone grinding was reconstructed. The relationship between the duty cycle ratioof motor and the amount of heat flowing into bone during grinding was also studied,and a real-time model was preliminarily built to predict the grinding heat, whichestablished the foundation for the real-time monitoring of the temperature of boneduring the grinding. The heat transfer during grinding with the addition of cooling liquidwas investigated as well. The more detailed description of the research contents and theconclusions is as follows,(1) The heat flux distribution coefficient on the interface between bone andgrinding tool was determined based on mechanical grinding theory, and a3-D transientfinite element model was constructed for analyzing the temperature distribution duringbone grinding process using miniature spherical grinding tool. The effects of grindingconditions, such as motion direction of grinding tool (X direction and Y direction), thecontact angle (0°,15°and30°) between the grinding tool and the bone, and the cuttingdepth (0.10mm,0.25mm, and0.40mm), on the heat distribution in ground zone wasdiscussed with numerical simulation. Additionally, the3-D transient temperature fieldsof bone under different grinding conditions were analyzed as well.(2) The grinding experiments using fresh bovine cortical were carried out when no cooling is applied, and the measured temperature information was obtained for8grinding conditions. Then the optimization method of ‘Active set’ was utilized toinversely estimate the thermal conductivity of bone and the amount of heat entering tothe bone under different grinding conditions, and the3-D transient temperature fieldwas established. The results show that the instantaneous maximum temperature of thebone could reach up to210°C when the contact angle of tool is30°, the cutting depthand the feed rate are0.4mm and20mm/min, respectively. If50°C was set to be thecritical value for thermal damage of body tissue, the thermal damage could reach thearea of3mm from the surface of the grinding slot.(3) The relationship between the duty cycle ratio and the grinding heat wasexplored, on the basis of the PWM signal obtained from the grinding experiment andthe grinding heat entering the bones that calculated via the inversion method. A goodliner relationship was demonstrated between the duty cycle ratio and the grinding heat.It was found that the linear slope was slightly lower when the grinding tool moves alongthe x direction than that along the z direction. For the three selected grinding conditions,the linear function was used to predict the grinding heat, and the aforementionedtransient finite element thermal analysis model was utilized to get the transienttemperature field. By comparison with the temperature response obtained in experiment,the effectiveness of the linear function model was validated. All these results couldcontribute to the realization of the real-time monitoring of the grinding temperature.(4) The heat generation during bone grinding was considered as transient heattransfer problem with unknown distributed moving heat source, according to the existedproblems in the model of heat flux distribution within the interface between bone andgrinding tool, which was derived from the mechanical grinding theory. The transientdistribution function of heat flux in the grinding zone was constructed by combing thespatial and the time functions. Moreover, inversion was implemented for the transientaverage heat flux and the transient distribution function of heat flux on the interfacebetween bone and grinding tool using the sequential function specification method(SFSM) and the sequential quadratic programming method (SQP). The validity of theabove method was verified through numerical simulation. In addition, the transientdistribution of heat flux on the contact surface was inverted by integrating the real-timetemperature information obtained in the grinding experiments. The transienttemperature field during the measurement was inverted as well.(5) According to the disadvantages of room temperature irrigation technology commonly used in clinic, a cryogenic mist cooling experiment system was developedfor bone grinding. During experiment, transient bone temperature was measured at thelocation0.5,1.0, and1.5mm underneath the ground groove. The experimental resultsshow that when the grinding tool moves backward, the cryogenic (3°C) mist cooling at120ml/h flow rate has obvious pre-cooling effect, and the maximum averagetemperature measured at the location0.5mm beneath ground groove was about21.0°C; when the grinding tool moves forward, the position of the nozzle relative to thegrinding tool limits the coolant flowing to the ground zone, which results in poorcooling effect that the maximum average temperature measured at the location0.5mmbeneath ground groove was about70.0°C. Futher, with experimentally measuredtemperautre, the FEA thermal analysis model with convection heat transfer boundaryand inverse heat transfer method are applied to reconstruct the bone temperature fieldunder mist cooling. The numerical results indicate that with backward grinding motion,the cryogenic mist cooling technique can significantly surpress the43°C thermal injuryboundary propogating under the ground surface.更多还原