Blood Flow Measurements Using Ultrasonic Pulsed Random Signal Doppler System

Two types of resolutions are of importance to pulsed ultrasonic Doppler blood-flow systems. These are the spatial resolution and the velocity resolution. The current pulsed ultrasonic Doppler system [1]-[6] suffer from their inherent lack of simultaneous range and velocity resolution. To overcome this limitation, a random signal pulsed Doppler ultrasonic system in which broadband Gaussian noise is used as the transmitted signal has been developed [7]-[13]. Since the range resolution and the bandwidth of the transmitted signal are inversely proportional an improvement in the range resolution is thus achieved. The velocity resolution is proportional to the bandwidth of the filter that is used to extract the Doppler frequencies and hence is improved by choosing a narrow-band filter. The lateral resolution of any ultrasonic Doppler system [1]–[13] depends upon the dimensions of the transducer face. This may be improved by focusing the ultrasonic beam with lenses; however, this increases the complexity of the system. In order to overcome this difficulty, a novel broadband dual element ultrasonic transducer has been developed [8]–[13]. The experimental results show that the lateral resolution of the dual element transducer is markedly superior to that of the existing single element transducers.