(The) mean frequency extension and the spatial average methods in the 2-dimensional doppler systems using the DSP

Abstract

The use of ultrasound pulsed Doppler systems has become increasingly popular due to the advantages of ease measurements of blood velocity, volume blood folw, and irregularities of the circulatory system. With 2-dimensional color flow mapping systems these values and irregularities can be measured However, the 2-D Doppler systems have several problems, such as range ambiguity, low signal to noise ratio, and slow frame rate. The mean frequency aliasing problem originating from the pulse repetition frequency is one of major limitations in pulsed doppler systems. A conventional approach to resolving this problem is tracking the mean frequency close to and beyond the Nyquist frequency along the temporal axis. In this thesis, a new concept of tracking the mean frequency along the spatial axis is proposed. The proposed technique is fault tolerant by nature and more suitable for multigate and 2-D Doppler systems than conventional methods. The slow frame rate problem is resolved by using the spatial average which is a method to acquire more data samples for mean frequency estimation. In this thesis, spatial average method using the 2nd order sampling instead of quadrature sampling is also proposed. The simulation and experimental results show that the proposed methods have better performance than the conventional methods.