Research And Design Of High Frequency Medical Ultrasound Imaging System

Medical ultrasound diagnostic instruments, because of its noninvasive, efficacy and low cost, are widely used in clinic. High-frequency (>20 MHz) ultrasound has demonstrated high spatial resolution on the submillimeter level, and can be applied to ophthalmology, dermatology, small animal imaging, and intravascular imaging. However, to get a high quality imaging, the development of high-frequency ultrasound transducers and high-frequency ultrasound imaging system is essential and challenging.In this thesis, two different types of high-frequency ultrasound single-element transducer:PIN-PMN-PT single-element transducer and PMN-PT\Epoxy 1-3 composite single-element transducer, are designed and fabricated. While the PIN-PMN-PT transducer reveals better thermal stability than PMN-PT transducer, the PMN-PT\Epoxy 1-3 composite transducer has lower acoustic impedance and higher electromechanical coupling coefficient.A high-frequency medical ultrasound imaging system for high-frequency ultrasonic arrays has been developed. The system can handle up to 64-element array transducers and excite 64 channels and receive simultaneously at 160 MHz sampling frequency with 12-bit precision. Field programmable gate array (FPGA) and massively parallel processor array (MPPA) are used for high-speed digital signal parallely processing. GPIO and PCI EXPRESS physical interface are used for high-speed data transfer. In addition, the frame of software system is built. By using modular structure, the system has highly flexibility and adaptability, can be easily extended and upgraded.Furthermore, the ultrasound beamforming technique is studied; the arithmetic for ultrasound transmition and receiving is discussed. Multi-channel digital ultrasound transmit is implemented in a Field programmable gate array (FPGA), and three proposal for the implementation of ultrasound receive beamforming are put forward. Among the three proposals, the architecture based on FPGA and MPPA reveals good performance, the delay can be reduced under 1 ns by using a FIR interpolation filter.Finally the testing results of the fabricated ultrasound transducers and imaging system are given. Results show that both the PIN-PMN-PT transducer and PMN-PT\Epoxy 1-3 composite transducer have superior performance and can be used for high-frequency ultrasound imaging. Results also show that the imaging system can successfully realize the multi-channel ultrasound transmit, receiving and signal acquisition, and the digital beamforming can achieve a high-speed fine delay.