Research On Coded Excitation In Ultrasound Color Flow Imaging System

Ultrasound color flow imaging system plays a significant role in medical ultrasound diagnostic devices. However, the tradeoff between penetration and axial resolution exists in traditional narrow-band and wide-band color flow imaging systems, which makes it a very difficult task to image blood flow within narrow vessels from deeper regions or through tissues with very severe attenuation. Recently, coded excitation technique has been widely used in medical ultrasound for its outstanding features of increasing the image quality, penetration and sensitivity. But its application in color flow imaging still lacks of in-depth and systematic research.In the dissertation, some key issues of coded excitation in color flow imaging are addressed. In order to lower the cost and optimize the system in practical application, the rules for decoding filter coefficients are studied in detail. The advantages and improvements of coded excitation in color flow imaging are further demonstrated using simulation and experiments on the designed and modified platform. Emboli detection using coded excitation power M-mode Doppler is also investigated.Coded excitation techniques that are suitable for color flow imaging are systematically studied in the thesis. Barker codes and other optimal binary codes are chosen as candidates for their good features. The structure of the transmit code sequence, the decoding filter design methods, as well as the factors that compromise the pulse compression results, are studied and analyzed. Then in-depth studies of baseband decoding filter design, and the rules of decoding filter coefficients according to different conditions that pertain to the relationship between the chip duration and demodulation frequency, which result in real, complex symmetric and complex asymmetric forms, are carried out.Simulation and experimental studies are used to validate the proposed coded excitation color flow imaging system. The experiment platform is constructed based on the modified single-element B-mode imaging system and the simulated flow circulation setup. Through simulations and experiments, not only the rules for decoding filter coefficient are verified, but also the advantages of coded excitation in solving the penetration and axial resolution tradeoff are fully demonstrated.To meet the demands of clinical applications, the significance, methods and problems of ultrasound emboli detection are investigated. The principles and difficulties of emboli detection using Transcranial Doppler and power M-mode Doppler are compared and analyzed. A novel emboli tracking method based on coded excitation power M-mode Doppler system is proposed and evaluated by theoretical analysis, simulation and experimental studies.