The Signal Processing Of Medical Ultrasonic Image

Image quality assessment is dependent on Point Spread Function(PSF),in which,the width of the main lobe and side lobe level are important evaluation criteria.The most important part in medical ultrasonic imaging system is the beamformer. Beamforming includes receiving and transmitting beamforming, which determines resolution of image. Conventional Delay-And-Sum beamformer has been changed from analog mode to digital mode. Yet, the simple, direct method has its inherent disadvantages:the requirement of the sampling and storage is high, and thus cannot have ideal resolution. On this basis, here are some methods to control the beam. Such as dynamic aperture, large aperture will be used in the far field, small aperture will be used in near field respectively, which makes the lateral resolution of the image more uniform. Amplitude apodization, with window function, can effectively suppress sidelobes.Delay-And-Sum beamformer cannot realize the transmitting and receiving dynamic focusing practically. This paper shows the design of synthetic aperture imaging method. A reasonable design of transmit and receive aperture (synthetic focusing)can realize transmit and receive two-way dynamic focusing. It has better directivity, narrower main lobe and side lobe suppression effect is better. The simulation result shows that synthetic aperture performs much better than the traditional DAS or has equal performance at least.This paper also designs a minimum variance beamforming method, which is one method of adaptive beamforming and an improvement for the amplitude apodization, the weight of the signal is the signal correlation function instead of a simple window function in Delay-And-Sum beamformer. The method solves the contradiction between the the width of main lobe and side lobe level, using smaller aperture, but the penetration depth being deeper. In order to obtain higher frame rate, parallel beamforming is used, and will not reduce the image quality. This method has relatively good performance at high SNR, as the SNR decreases performance will be close to Delay-And-Sum beamformer. In addition, minimum variance beamforming requires more calculation...