Research On The Method Of Ultrasonic Thermometry Based On The Signal Energy Of Pyroelectric Sensor

Ultrasonic thermometry has become a research hotspot in the field of medical non-invasive temperature measurement because of its high real-time performance,relatively low equipment price and less damage.According to the principle of thermometry,ultrasonic thermometry can be divided into four categories:the thermometry based on sound velocity,the thermometry based on nonlinear coefficient,the thermometry based on scattering coefficient and the thermometry based on attenuation coefficient.The thermometry based on sound velocity must accurately measure the echo pulse and is susceptible to motion,such as breathing.The thermometry based on nonlinear coefficient is difficult to measure in vivo.The spatial resolution of thermometry based on scattering coefficient is not enough.The temperature sensitivity of the attenuation coefficient is higher,and the attenuation coefficient is a commonly means of tissue characterization.Therefore,the thermometry based on attenuation coefficient has higher technical feasibility and greater clinical applicability,it is a research hotspot of ultrasonic non-invasive temperature measurement,so this paper uses it as the theoretical basis of thermometry.However,the current measurement method of the attenuation coefficient is to measure the amplitude change of the ultrasonic signal by the piezoelectric effect,which is easily affected by the scattering and the sound field distribution.In this paper,an ultrasonic thermometry method based on the signal energy of pyroelectric sensor is proposed.The pyroelectric effect of the PVDF film is used to measure the sound power,which used to represent the attenuation coefficient,and the influence of the sound field distribution on the measurement of attenuation coefficient is overcome.Then,the pyroelectric sensor is used to establish and demonstrate the model of ultrasonic,temperature and pyroelectric sensor,which is the basis for ultrasonic thermometry used pyroelectric sensors.The focus of this article is as follows:1.A model for measuring the sound power used pyroelectric sensors is established,the feasibility of pyroelectric sensor for measuring ultrasonic power is theoretically proved by sound field distribution,heat transfer equation and equivalent circuit.Based on the temperature coefficient of the attenuation,the method of measuring the sound power by pyroelectric sensor is used to establish the temperature measurement model of the ultrasonic,target's temperature and pyroelectric sensor,and its feasibility is discussed.2.According to the established model of temperature measurement,this paper uses COMSOL to simulate the model and the change of pyroelectric sensor output is observed.The response of the sensor is close to the inverse proportional relationship of the attenuation coefficient of the tissue,indicating the feasibility of the theory.The sensor is designed and manufactured according to the simulation results.3.Experiments are designed to prove the correctness of the theory.The experiments consist of three parts:The first is to determine the performance of the pyroelectric sensor,including stability and sensitivity;The second experiment was to verify the temperature dependence of the sound attenuation coefficient with pork;The third is to find the relationship between the sensor and the temperature through experiments,conduct temperature measurement experiments according to the obtained relationship,and compared with the measured values by the thermocouple.After the sensor's data is collected,the pyroelectric signal is obtained after preprocessing,and the signal characteristics are consistent with the prediction.The results of the analysis showed that the error of the measurement results of the sensor in the five sets of repetitive experiments are no more than 2.5%,and the stability is acceptable.The peak voltage of the sensor is proportional to the drive power of the transducer,which enables measurement of sound power.For transducers with different radiation areas,the measurement error of the sensor is 2.4%.It can be considered that the output of the pyroelectric sensor has little relationship with the characteristics of the sound beam.The temperature dependence of the attenuation coefficient was confirmed by the pork heating experiment,which is consistent with the previous research results.In the five experiments of heating pork,the temperature estimation based on signal energy is basically consistent with the thermocouple measurement,and the error range is between 0.01?and 3.95?.It is hoped that the research in this paper will be helpful to monitor tissue temperature.