Direct demodulation in ultrasound instruments

• US 5,437,281 A
• Filed: 05/04/1994
• Issued: 08/01/1995
• Est. Priority Date: 01/14/1992
• Status: Expired due to Term

• Current Assignee: Diasonics Ultrasound, Inc. (IDB Holding Corporation Limited)
• Original Assignee: Diasonics Ultrasound, Inc. (IDB Holding Corporation Limited)
• Inventors: Scheib, John P., Lin, Sheng-Tz
• Primary Examiner(s): JAWORSKI, FRANCIS J
• Application Number:
  US08/237,638
• Time in Patent Office: 454 Days
• Field of Search: 128/600.01, 128/600.07, 128/661.01, 73/625, 329/341, 329/343
• US Class Current: 600/443
• CPC Class Codes: G01S 15/8979 Combined Doppler and pulse-echo imaging systems
• CPC Class Codes: G01S 7/52025 for pulse systems G01S7/52034 takes precedence
• CPC Class Codes: G01S 7/52028 using digital techniques
• CPC Class Codes: G01S 7/52034 Data rate converters
• CPC Class Codes: G01S 7/5206 Two-dimensional coordinated display of distance and direction; B-scan display

Abstract

A direct digital modulator for demodulating ultrasound signals. The demodulator includes a baseband demodulator, a magnitude and differential phase generator, and a Doppler preprocessor. The demodulator further includes an interface for receiving a signal from an analog front end. The baseband demodulator utilizes a Hilbert transform to convert received ultrasound signals into analytic signals. The present invention compensates phase and frequency of the analytic signal in order to process the signal. The phase information in the signal is then extracted.

Claims

1. A digital demodulator for use in an ultrasonic imaging system having a front end for generating an ultrasound passband signal and display for displaying an ultrasound image, said demodulator comprising:

compensation means for performing phase and frequency compensation on said ultrasound passband signal signal, wherein said compensation means comprises a Hilbert transformer to convert the ultrasound passband signal to an analytic baseband signal, such that the ultrasound passband signal is converted to said analytic baseband signal that is phase and frequency compensated without affecting the phase, Doppler information and magnitude information contained therein.

2. A digital demodulator for use in a real-time ultrasonic imaging system having a front end for generating an ultrasound passband signal and a display for displaying an ultrasound image, said digital demodulator comprising:

transform means for receiving said ultrasound passband signal and generating an analytic baseband signal in response to said ultrasound signal; and

digital sampling mixer means for performing mixing by sampling of said analytic baseband signal to compensate the frequency and phase of said analytic baseband signal digitally, such that the ultrasound passband signal is converted to said analytic baseband signal without affecting the phase, Doppler information and magnitude contained therein.

3. The digital demodulator as defined in claim 2 wherein said transform means comprises a Hilbert transform.

4. The digital demodulator as defined in claim 2 wherein said sampling mixer means comprises:

mixer means for shifting said analytic signal to an analytic baseband signal; and

rotation means coupled to said mixer means and responsive to said analytic baseband signal, said rotation means for arbitrarily shifting the frequency of said analytic baseband signal.

5. A digital demodulator for use in a real-time ultrasonic imaging system having a front end for generating an ultrasound signal and display for displaying an ultrasound image, said demodulator comprising:

transform means for receiving said signal and generating an analytic signal in response to said ultrasound signal;

sampling mixer means for performing mixing by sampling of said analytic signal, such that the frequency and phase of said analytic signal is compensated; and

coordinate transform means for translating said analytic signal to polar coordinates, such that the magnitude information and phase information of said analytic signal are produced.

6. The digital demodulator as defined in claim 5 further comprising:

differential phase generator means responsive to said phase information and for generating a phase signal, said phase signal representing the phase difference between successive samples along the path of said analytic baseband signal; and

magnitude compression means responsive to said magnitude for compressing said magnitude of said analytic signal, said magnitude compression means generating said analytic signal having a compressed magnitude.

7. The digital demodulator as defined in claim 6 further comprising switching means for receiving said phase signal and said compressed magnitude signal, said switching means sending said phase signal to said display means when send switching means is in a first position and sending said compressed magnitude to said display means when said switching means is in a second position.

8. The digital demodulator as defined in claim 6 further comprising phase compression means responsive to said compressed magnitude signal, said phase compression means for compressing said phase signal when said magnitude of said analytic signal is below a predetermined level.

9. The digital demodulator as defined in claim 5 further comprising:

differential phase generator means responsive to said phase information and for generating a phase signal, said phase signal representing the phase difference between successive samples along the path of said analytic baseband signal; and

phase compression means responsive to said compressed magnitude signal, said phase compression means for compressing said phase signal when said magnitude of said analytic signal is below a predetermined level.

10. A digital demodulator :

for use in a real-time ultrasonic imaging system having a front end for generating an ultrasound signal and a display for displaying an ultrasound image, said demodulator comprising;

a Hilbert transformer for converting said ultrasound signal into an analytic signal;

a complex mixer coupled to said Hilbert transformer for shifting said analytic signal to baseband and to compensate for attenuated signals, such that a shifted analytic signal is generated;

a magnitude and differential phase generator responsive to said shifted analytic Signal to generate phase information and magnitude information for display; and

a Doppler preprocessor responsive to said shifted analytic baseband signal to extract Doppler data from said shifted analytic baseband signal for display.

11. A method for demodulating a signal from the front end of an ultrasound imaging apparatus comprising the steps of:

compensating the frequency and phase of said signal;

detecting the phase information along the path of said signal; and

displaying said phase information.

12. A digital demodulator for use in a real-time ultrasonic imaging system having a front end for generating an ultrasound signal and display for displaying an ultrasound image, said demodulator comprising:

transform means for receiving said signal and generating an analytic signal in response to said ultrasound signal using a Hilbert transform; and

sampling mixer means for performing mixing by sampling of said analytic signal, wherein said sampling mixer means comprises

mixer means for shifting said analytic signal to an analytic baseband signal; and

rotation means coupled to said mixer means and responsive to said analytic baseband signal, said rotation means for arbitrarily shifting the frequency of said analytic baseband signal, such that the phase and frequency of said analytic signal are compensated.

13. The digital demodulator as defined in claim 12 wherein said transform means comprises a Hilbert transform.

14. A digital demodulator for use in a real-time ultrasonic imaging system having a front end for generating an ultrasound signal and display for displaying an ultrasound image, said demodulator comprising:

transform means for receiving said signal and generating an analytic signal in response to said ultrasound signal; and

sampling mixer means for performing mixing by sampling of said analytic signal, such that the frequency of said analytic signal is compensated; and

coordinate transform means for translating said analytic signal to polar coordinates, such that the magnitude of said analytic signal is obtained.

15. The digital demodulator as defined in claim 14 further comprising:

magnitude compression means responsive to said magnitude for compressing said magnitude of said analytic signal, said magnitude compression means generating said analytic signal having a compressed magnitude.

16. A digital demodulator for use in a real-time ultrasonic imaging system having a front end for generating an ultrasound signal and a display for displaying an ultrasound image, said demodulator comprising:

a Hilbert transformer for converting said signal into an analytic signal;

a complex mixer for shifting said analytic signal to said baseband and further shifting said analytic signal to compensate for attenuation in said signal;

magnitude generation means responsive to said shifted analytic baseband for generating the magnitude information signal and the magnitude of said signal for said display; and

Doppler preprocessing means responsive to said shifted analytic baseband signal and for extracting Doppler data from said shifted analytic baseband signal, said display displays said Doppler data.

17. A digital demodulator for use in a real-time ultrasonic imaging system having a front end for generating an ultrasound signal and a display for displaying an ultrasound image, said demodulator comprising:

a baseband demodulator producing an analytic baseband signal in response to the ultrasound signal, wherein the baseband demodulator comprises

a Hilbert transformer converting said ultrasound signal into a first analytic signal;

a complex mixer coupled to the Hilbert transformer, wherein the complex mixer performs phase and frequency equalization by shifting said first analytic signal to baseband and moving a peak of said first analytic signal, thereby creating the analytic baseband signal; and

a generator coupled to the baseband demodulator, wherein the generator derives phase and amplitude information from said analytic baseband signal.

18. The digital demodulator defined in claim 17 wherein the complex mixer comprises a digital mixer.

19. The digital demodulator defined in claim 17 wherein the complex mixer shifts the first analytic signal to the baseband and then moves its peak to the center frequency.

20. The digital demodulator defined in claim 17 wherein the baseband demodulator produces the analytic baseband signal without affecting the phase, Doppler or magnitude information in the ultrasound signal.

21. The digital demodulator defined in claim 17 wherein the generator determines phase differences between successive samples of the said analytic baseband signal.

22. The digital demodulator defined in claim 17 wherein the generator comprises

a magnitude generator generating a signal indicative of magnitude in the analytic baseband signal;

and

a differential generator determining a phase difference between successive samples of the said analytic baseband signal.

23. The digital demodulator defined in claim 17 wherein the generator further comprises a transform for transforming the analytic baseband signal from rectangular coordinates to polar coordinates.

24. The digital demodulator defined in claim 17 wherein the generator comprises

a transform for transforming the analytic baseband signal from rectangular coordinates to polar coordinates having a magnitude (R) component and a phase component;

a magnitude generator coupled to the transform to generate a signal indicative of magnitude in response to the magnitude (R) component of the analytic baseband signal in polar coordinates; and

a differential generator coupled to the transform to determine a phase difference between successive samples of the said analytic baseband signal in response to the phase component of the analytic signal in polar coordinates.

25. The digital demodulator defined in claim 24 further comprising phase compression for preventing output of information indicative of the phase difference in response to the magnitude (R) component being below a predetermined threshold.

26. The digital demodulator defined in claim 17 further comprising a Doppler preprocessor responsive to said shifted analytic baseband signal and for extracting Doppler data from said shifted analytic baseband signal, said display displays said Doppler data.

27. The digital demodulator defined in claim 26 wherein the Doppler preprocessor evaluates phase change for a specific sample volume.

28. The digital demodulator defined in claim 17 wherein the Hilbert transformer comprises a finite impulse response filter.

29. The digital demodulator defined in claim 17 wherein the front end includes at least one transducer having a center frequency and wherein the Hilbert transformer comprises a complex bandpass filter with a sample rate that is a multiple of the center frequency.

30. The digital demodulator defined in claim 17 wherein the baseband demodulator further comprises a decimator.

31. The digital demodulator defined in claim 17 wherein the complex mixer comprises

a mixer coupled to receive the first analytic signal to shift the first analytic signal to create a second analytic signal centered on zero frequency;

and

a rotator coupled to receive the second analytic signal from the mixer to compensate for attenuation of high frequency components of the ultrasound signal.

32. The digital demodulator defined in claim 31 wherein the baseband demodulator further comprises a look-up table (LUT) coupled to rotator.