Research On Low-frequency Ultrasound Signals In Thoracic Imaging

Transmissive ultrasound imaging is expected to achieve online real-time monitoring of patients.The technology is not radioactive to the human body and can be used not only for the examination of diseases in the thoracic cavity,but also for subsequent data storage and analysis of the acoustic parameter values in tissues to track the treatment process and predict the development trend of the disease,which has great advantages in the early prevention of respiratory diseases.The ability of low-frequency band ultrasound to penetrate the thoracic cavity and lungs,which can be used for air and water content monitoring in the lungs,provides a theoretical basis for transmissive low-frequency ultrasound thoracic imaging.The thesis conducts research in the context of transmissive low-frequency ultrasound thoracic imaging technology.It mainly summarizes the working principle and system structure of transmission ultrasound imaging technology,establishes a thoracic cavity simulation model,builds an experimental measurement system for transmission low-frequency ultrasound imaging,and gives a method to apply multiple signal classification algorithms to pre-process ultrasound transmission data.Firstly,a thoracic cavity simulation model with the same acoustic properties as the human thoracic cavity was established by the finite element method,and the geometry of the simulation model was modeled after the human thoracic CT images.The model is set up with12 transceiver-transceiver transducers,each two transducers are separated by 30°,and 12 simulations are performed to achieve a 360° circular scan of the thoracic cavity through the transmit-receive mode of one transmitter and seven receivers,and the simulated transmission low-frequency ultrasound reception data can be obtained using this model.Secondly,an experimental measurement system was built that can be used for transmission low-frequency ultrasound thoracic imaging,and gelatin-thoracic cavity models in the lung inflation and lung deflation states were fabricated using materials with similar acoustic properties to human tissues,and the PGA460-EVM system was used for excitation of low-frequency ultrasound signals and acquisition of transmission-type reception data,and the same finite element simulation model was established by the one-shot seven-receive transmit-receive mode,the excitation and transmissive data acquisition of low-frequency ultrasound are performed at 12 locations,respectively.Finally,using a sound source identification algorithm,a method that can pre-process the ultrasonic received data is implemented,a mathematical model of the output signal of the received transducer array is derived,and the data derived from the simulation model and the measured data in the experimental system are processed using the data processing method,and the results show that the method can reduce the mean square error of the data and improve the signal-to-noise ratio of the data.