Research On Vibration Assisted Cutting Mechanism And Cutting Characteristic Of Tissue In Biopsy Sampling

With the rise and rapid development of interventional therapy,higher and higher requirements is put forward to percutaneous puncture technology.As the interventional treatment has the advantage of simple,safe,effective,less complications,small trauma,significantly shorter hospitalization time,The interventional therapy develops rapidly and becomes more and more popular among the patients.Compared with the extracting tissue from the body,percutaneous biopsy technique has the advantages of small trauma,quick recovery and low infection rate.It becomes the main way to extract the suspected tissue of cancer for cytological diagnosis.However,during the biopsy process,the biopsy needle could miss the the suspected tissue of cancer because the needle tip bends due to the uneven force and the soft tissue is deformed due to the force from needle.During the sampling process,many factors lead to low sampling accuracy and poor sampling performance instability,which could led to misdiagnosis of the examples.Vibration-assisted inseriton technique can reduce the insertion force,reduce the bending of the needle tip,improve the sampling performance and improve the sampling precision.It is a potential biopsy technique.In this paper,we focus on the interaction mechanism between needle and soft tissue during vibration assisted puncture and studying the dynamic characteristics during needle inserting into soft tissue,studying The effects of different vibration types on the mechanical and sampling performance of soft tissue are discussed,and the sampling parameters are determined and optimized.The theory of vibration-assisted cutting soft tissue and the mechanism of interaction between needle and tissue is studied deeply.The kinematics and mechanics between needle and tissue are analyzed and the relevant models are established.The kinematic analysis of the biopsy needle during the insertion process was carried out.At the situation of the needle inserting soft tissue with and without vibration assist,The formula of the tip speed and the displacement were deduced.The theoretical analysis shows that there is a moving back and re-cutting process when the vibration velocity is greater than the feed rate.When the vibration velocity is less than the feed rate,needle does not move back and recut the tissue.The tip speed of the biopsy needle is deduced by iterative method.The biopsy needle insertion process is divided into three stages.The biopsy force of each stage is analyzed and the mechanical model is established.The second stage during needle insertion was divided into hollow needle insertion and solid needle insertion.These two cases were analyzed separately,and the mechanical models were established.Combining the mechanism of the metal cutting,the relationship between the tip speed and the insertion force is deduced when the hollow needle is inserted into tissue.The theoretical analysis shows that the increase of the tip speed leads to the increase of the deformation rate of soft tissue at the needle tip and the increase of insertion force.Based on the LuGre friction model,the friction between the soft tissue and the needle was analyzed.The results show that the frictional force increases with the increase of the velocity when the needle inserts without the vibration,and the friction force changes with the relationship between insertion speed and the vibration parameters under the vibration assisted puncture condition.In the vibration-assisted puncture condition,increasing the vibration frequency or increasing the vibration amplitude can reduce the friction force when |vi|<ωA for a given feed rate vi;increasing the vibration frequency or the amplitude can increase the Coulomb friction,thereby increase the friction,when | vi |>ωA.The effect of vibration on soft tissue fracture was analyzed.Based on energy method,the formulas of the soft tissue fracture toughness are deduced.The influence of vibration on the stress intensity factor of soft tissue is analyzed.The theoretical analysis shows that the stress intensity factor of soft tissue crack increases and then decreases with the vibration frequency increasing when the vibration mode is longitudinal vibration,The effects of insertion speed on insertion force and frictional force during puncture were studied with gelatin phantom and liver.The results show that the insertion force increases with the insertion speed because the deformation rate of the tissue or the gelatin prosthesis at needle tip increases when the insertion speed increases.The friction increases with the increase of the puncture speed.The effect of speed on the fracture toughness of soft tissue was studied by cutting the gel phantom by unit cutting tool.The results show that the fracture toughness of soft tissue increases with the increase of cutting speed,and the fracture toughness increases faster with the speed when the velocity is small,the fracture toughness of the soft tissue increases slowly with the cutting speed when the velocity is large.The effect of insertion speed on the sampling performance was studied by puncturing the liver with hollow biopsy needle and analyzing the puncture hole.The results show that the area of the puncture hole decreases first and then increases when the insertion speed increases.The effect of speed on the circularity of the area is not very obvious.The vibration-assisted sampling device was introduced and its performance was tested.It was found that the amplitude of the vibration-assisted sampling device decreased with the increase of the frequency when the input voltage was the same.When the vibration frequency is the same,the amplitude increases as the input voltage increases.The bionic vibration parameters are extracted based on the principle of bionics after determining the ordinary vibration parameters.The effects of of dinary vibration and bionic vibration on the maximum insertion force and friction force were studied by vibration-assisted inserting the gel phantom.The results show that the maximum insertion force increases with the increase of vibration frequency when the amplitude is the same under normal vibration assisted puncture.Under the conditions of bionic vibration,the maximum insertion force increases with the increase of gel phantom thickness.Under different insertion speed,the influence of bionic vibration on the maximum insertion force is different.The influence of bionic vibration on puncture friction is consistent with the theoretical analysis.The influence of vibration frequency on fracture toughness was studied by cutting gel phantom under different ordinary vibration.The results show that the dynamic fracture toughness is not changed obviouswhen the vibration amplitude is constant and the vibration frequency is increased.Effects of vibration frequency on sampling characteristics was researched by different frequency vibration-assisted insertion.The experimental results show that the puncture hole area and the crack length increase at first and then decrease because the dynamic intensity factor increases at first and then decreases when the vibration frequency increases.The effects of vibration frequencies on the needle tip bending were studied through inserting the needle into gel phantom with vibration.The results show that the bending of the needle tip decreases with the increase of the vibration frequency when the vibration frequency is increased,which is helpful to improve the sampling precision.The ultrasonic vibration sampling platform was built and the performance of the ultrasonic vibration sampling device was tested.After testing,it was found that with the input voltage of a certain ultrasonic vibration system increasing,the power of the ultrasonic vibration system increases and the vibration amplitude increase.The force model was established based on the fracture mechanics and the influence of the vibration amplitude on the insertion force and the the specimen characristics was researched.The experimental results show that the maximum insertion force and friction force decrease when the ultrasonic frequency is constant and the amplitude increases.The effect of ultrasonic vibration amplitude on the sum of tear force and expansion force is small.The dynamic fracture toughness of the material decreases and the crack length increases with the amplitude increasing.The effect of ultrasonic vibration on maximal puncture force and sampling performance was studied.The experimental results show that the amplitude decreases and the maximum insertion force increases with the increase of vibration frequency,under the same input voltage.Under the same voltage condition,the area of the puncture hole formed by ultrasonic vibration insertion tends to decrease and the roundness of the puncture hole area increases with the increase of the frequency.The effects of insertion speed,vibration frequency,needle diameter and tip surface number on the maximum puncture force,friction force and sampling performance were studied by means of orthogonal test and range analysis and variance analysis on the test results.The optimal combination of parameters for each index is obtained and the degree of influence of each test factor on each index was determined.Through the verification test,the correctness of the optimal parameter combination is verified,and the purpose of parameter optimization is achieved.