Blood Flow Measurements Using Ultrasonic Pulsed Random Signal Doppler System

Two types of resolutions are of importance to pulsed sonic system used to conduct transcutaneous blood flow ultrasonic Doppler blood-flow sYstemsThese are the Spatid studies should posess high spatial and velocity resolution. resolution and the velocity resolution. The current pulsed Doppler systems developed by Baker from their inherent lack of simultaneous range and velocity resoluc117 Peronneau c21, and Others [3]-[61 have been suction. To overcome this limitation, a random signal pulsed Doppler cessful in performing transcutaneous blood flow studies. ultrasonic system in which broad-band Gaussian noise is used as However, they suffer from their inherent lack of simulthe transmitted simal has been developed [71-[131. Since the taneous range and velocity resolution. Waag et d. [15], range resolution and the bandwidth of the transmitted signal are inversely proportional an improvement in the range resolution is [l61 have reported a system in which the continuous thus The velocity resolution is proportional to the bandtransmission of a carrier is phase modulated with a pseudowidth of the filter that is used to extract the Doppler frequencies random binary sequence. The improvement in the range and hence is improved by choosing a narrow-band filter. and velocitv resolution obtained with this system over the The current pulsed ultrasonic Doppler system [l]-[a] suffer The lateral resolution of any ultrasonic Doppler system [l]-1131 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 &e system. In order to overcome this difficulty, a novel broad-band 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.