| 摘要 |
A method for receiving Doppler ultra sound signals at a high sample rate, at greater depths and from a large range gate size by increasing the length of time during which echoes can be received with respect to the time required to transmit the Doppler pulses that cause the echo signals to be created. According to a first embodiment of the invention, a Doppler pulse is transmitted for a time equal to the time required for an ultrasonic sound wave to travel from a transducer to a top of a range gate and back. Echo signals created in response to the long Doppler pulse are received for a time equal to the transmit time plus the time required for an ultrasonic sound wave to travel from the top of the range gate to a bottom of the range gate and back to the top of the range gate. In accordance with another aspect of the invention, each transducer element transmits a phase-shifted Doppler pulse, wherein the phase-shift is selected according to the time required for an ultrasonic sound wave to travel from the transducer element to a desired focal point. By simultaneously transmitting the phase-shifted Doppler pulses, the pulses arrive at different times at the focal point and constructively add. Echo signals created in response to the sum of the phase-shifted Doppler pulses can be sampled at substantially any rate to analyze the moving blood flow in the area of tissue defined by a range gat.
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