CW and pulse Doppler diagnostic system

Abstract

In an interlaced pulse-echo and range-gated Doppler system, an ultrasound transmitter generates a train of constant repetition rate echo pulse interlaced with a Doppler pulse train of plural bursts. The time duration between each burst and the preceding range gate opening is held constant while the time to the successive range gate opening is automatically varied to provide a continuously variable PRF tracking of the console range gate depth setting. The power of the transmitted signal is internally varied in the same sense and the cutoff frequency of the receiver low pass tracking filters is varied in the opposite sense to optimize signal-to-noise ratio at various tissue inspection depths. Selectable turnable high pass filters normalized to low velocity roll-off eliminate artifact for peripheral or central vascular probes. The detection system operates in quadrature and includes a synchronous demodulator and a peak detector, and a level detector operative on peak detected signals. Transducer probes interchangeably usable in the system include within each probe a narrow band amplifier critically turned to the respective probe crystal to provide further S/N ratio improvement. The system is operable in CW or pulsed Doppler modes dependent on switch setting on the split crystal probe.