The Design, Simulation And Realization Of Ultrasonic Instrument For Non-invasive ICP Monitoring

A certain stress exists in cranial cavity of normal human, which is called intracranial pressure and it must be maintained within a certain range. Many craniocerebral diseases could give rise to intracranial hypertension(ICP), such as cerebral trauma, encephaledema, brain tumor, and so on. ICP is early signal for craniocerebral diseases and key factor for patient’s death. Furthermore, the risk of craniocerebral operations is much high. So, getting the change of ICP timely and seizing the best opportunity of craniocerebral operations is vital for saving patient’s lives.The invasive ICP monitoring method which is used usually in clinic at present might cause vice injure to patient, and it has many defects such as cross infection, etc. So, the non-invasive methods have been paid more importance to, It has already become research hotspot and development direction of ICP monitoring. The existing non-invasive methods monitor ICP indirectly and the monitoring object is closely related to ICP and easier to be measured. So, the greatest difficulty of non-invasive methods is establishing an accurate calculation model. While the calculation model for ICP needs much more knowledge, such as physiology etc. Another ubiquitous problem of all the present monitoring methods is that some practical applications in clinic are very difficult to realize, such as monitoring portably and movably when it need monitor real-time and in field for the site of accident or in the way to hospital. Since current situation and problems of present ICP monitoring method, it will have great research value and clinical significance that a brand-new ICP monitoring method is proposed based on ultrasonic technology.Acoustoelastic effect is usually used in ultrasonic stress measurement, which is refers to the relationship between wave velocity and stress. There has already been some research and preliminary application in acoustoelastic effect for measurement of solid residual stress. But the brain is soft matter. So, if acoustoelastic effect is used for ICP monitoring, which is the measurement of brain stress, a series of problems will need to be settled and some exploratory research must be conducted. In this paper, theoretical discussions and experimental researches will be carried out around following issues: if the brain could be looked as continuous medium when ultrasonic propagating, how to design out a model experiment which could simulate the mechanism of increasing ICP, acoustoelastic effect in soft matter such as brain, and so on. The main innovation works and conclusions in this paper are as follows:① After traversed and summarized most present main ICP monitoring methods, an ultrasonic ICP monitoring method is proposed according to the research status about ICP monitoring domestic and overseas and the problems existing in the current ICP monitoring method. Furthermore, theoretical method based on acoustoelastic effect is put forward.② According to craniocerebral biomechanical characteristic, simplified craniocerebral physical model is put forth. And constitutive model is simplified according to continuous medium hypothesis biomechanics.③ According to biomechanical characteristics of brain tissue, simulation materials of ultrasonic parameters required by the simulating model experiment for ultrasonic ICP non-invasive monitoring is confirmed. And in the first, a confirmatory experiment is designed for verifying acoustoelastic effect of experimental material which is used for simulating mechanical property of brain tissue. The results proved that soft matter has acoustoelastic effect like solid.④ According to the basic idea and overall plan of ultrasonic ICP non-invasive monitoring method, simulation experiment model of ICP monitoring which is similar to craniocerebral mechanical property is designed. Three-dimensional finite element modeling is established for the model and simulating calculation is conducted on the basis of acoustoelastic theory. Furthermore, theoretical calculating values are compared with experimental results. Since wave velocity is difficult to be acquired in the experiment, phase shift is adopted to replace wave velocity for measurement and computation. It is shown from the results that the calculated values fit well with the experimental results and the maximum error is no more than 5%. Consequently, it is feasible theoretically that acoustoelastic effect is used for non-invasive ICP monitoring.⑤ According to the results and conclusions gotten from the model experiment, a full digitalization prototype for non-invasive ICP monitoring is designed and it is tested in some preliminary clinical experiment. The clinical experimental results show that the non-invasive ICP monitoring method is effective and practical.