Ultrasound diagnostic apparatus
A transmission wave corresponding to an FM continuous wave having been subjected to an FM modulation processing is transmitted from a transmitting transducer. A pre-amplifier generates a reception RF signal and outputs the reception RF signal to a receiving mixer. The receiving mixer applies orthogonal detection to the reception RF signal to generate a complex signal. A reference signal supplied to each mixer in the receiving mixer is generated based on an FM continuous wave output from an FM modulator. The FM continuous wave output from the FM modulator is delayed by a delay circuit, and one signal is directly supplied to a mixer whereas the other signal is supplied to a mixer via a π/2 shift circuit. The delay circuit applies a delay processing in accordance with a depth of a target position within a living organism to the FM continuous wave.
1. An ultrasound diagnostic apparatus comprising:
a transmission signal processing section which outputs a modulated transmission signal that is a continuous wave having a frequency varied periodically;
a transmission/reception section which transmits ultrasound to a living organism based on the modulated transmission signal and receives a reflection wave from the living organism, thereby obtaining a reception signal;
a reception signal processing section which applies a demodulation processing to the reception signal by using a reference signal having a waveform that is substantially the same as a waveform of the modulated transmission signal to obtain a demodulated signal;
a delay processing section which adjusts a delay relationship between the reference signal and the reception signal; and
a Doppler information extraction section which extracts Doppler information from the demodulated signal,
wherein
the delay processing section performs a delay processing in accordance with a depth of a target position within the living organism to adjust the delay relationship between the reference signal and the reception signal and the demodulation processing is performed, thereby selectively extracting the Doppler information from the target position.
2. The ultrasound diagnostic apparatus according to claim 1 , wherein
at least one of the modulated transmission signal output from the transmission signal processing section and the reference signal to be used in the reception signal processing section is delayed to enhance a correlation between the reception signal from the target position and the reference signal, thereby selectively extracting the Doppler information from the target position.
3. The ultrasound diagnostic apparatus according to claim 2 , wherein
the at least one of the modulated transmission signal and the reference signal is delayed such that a phase of the reception signal from the target position and a phase of the reference signal are identical.
4. The ultrasound diagnostic apparatus according to claim 3 , wherein
the modulated transmission signal or the reference signal is delayed by a delay amount in accordance with a depth of the target position such that a phase of the reception signal from the target position and a phase of the reference signal are identical.
5. The ultrasound diagnostic apparatus according to claim 4 , wherein
the Doppler information is extracted from the target position while varying the delay amount to thereby shift the target position along a depth direction.
6. The ultrasound diagnostic apparatus according to claim 5 , wherein
the Doppler information is extracted from a plurality of positions through a subject section along the depth direction, by periodically varying the delay amount to thereby periodically shift the target position within the subject section along the depth direction.
7. The ultrasound diagnostic apparatus according to claim 6 , wherein
a velocity distribution of a fluid within the subject section is formed based on the Doppler information extracted from the plurality of positions in the subject section.
8. The ultrasound diagnostic apparatus according to claim 7 , wherein
a display image which includes an axis corresponding to a depth within the living organism, an axis corresponding to time, and an axis corresponding to a velocity of the fluid and which shows a state of a variation in the velocity distribution with time is formed.
9. The ultrasound diagnostic apparatus according to claim 1 , wherein
the Doppler information extraction section extracts, as the Doppler information, a Doppler signal component corresponding to a direct current signal component which is contained in the demodulated signal.
10. The ultrasound diagnostic apparatus according to claim 1 , wherein
the transmission signal processing section applies a frequency modulation processing to a carrier wave signal to generate the modulated transmission signal.
11. The ultrasound diagnostic apparatus according to claim 10 , wherein
the modulated transmission signal which is generated by the transmission signal processing section is delayed by a delay amount in accordance with a depth of the target position, to form the reference signal.
12. The ultrasound diagnostic apparatus according to claim 10 , wherein
a modulation signal to be used for the frequency modulation processing is delayed by a delay amount in accordance with the depth of the target position to obtain a delayed modulation signal, and the carrier wave signal is subjected to the frequency modulation processing by using the delayed modulation signal.
13. The ultrasound diagnostic apparatus according to claim 10 , wherein
a modulation index of the frequency modulation processing performed by the transmission signal processing section is adjusted to set a position resolution.
14. The ultrasound diagnostic apparatus according to claim 13 , wherein
the modulation index of the frequency modulation processing performed by the transmission signal processing section is a ratio of a maximum frequency deviation and a modulation frequency and is set to a value which is 1 or greater.
15. The ultrasound diagnostic apparatus according to claim 13 , wherein
the modulation index of the frequency modulation processing performed by the transmission signal processing section is a ratio of a maximum frequency deviation and a modulation frequency and is set to a value which is 30 or greater.
16. The ultrasound diagnostic apparatus according to claim 1 , wherein
the transmission signal processing section applies a phase modulation processing to a carrier wave signal to generate the modulated transmission signal.
17. The ultrasound diagnostic apparatus according to claim 1 , wherein the transmission signal processing section generates the modulated transmission signal based on data of a continuous wave having a frequency varied periodically.