Individual channel analog wall filtering to improve flow sensitivity in ultrasound imaging

• US 6,267,725 B1
• Filed: 09/13/1999
• Issued: 07/31/2001
• Est. Priority Date: 09/13/1999
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Dubberstein, David T.
• Primary Examiner(s): Jaworski, Francis J.
• Assistant Examiner(s): Imam, Ali M.
• Application Number:
  US09/395,343
• Time in Patent Office: 687 Days
• Field of Search: 600/437, 600/441-447, 600/454-458, 128/916, 367/7, 367/11, 367/130, 736/25, 736/26
• US Class Current: 600/443
• CPC Class Codes: A61B 8/06 Measuring blood flow measuring volume flow in general G01F, e.g. G01F1/66, G01F1/72; measuring speed of fluids in general G01P5/00
• CPC Class Codes: G01S 15/8979 Combined Doppler and pulse-echo imaging systems
• CPC Class Codes: G01S 15/8988 Colour Doppler imaging
• CPC Class Codes: G01S 7/52033 Gain control of receivers for seismic signals G01V1/245
• CPC Class Codes: G01S 7/52034 Data rate converters

Abstract

A method and an apparatus for wall filtering the receive signal in each receive channel of an ultrasound imaging system prior to analog-to-digital conversion. Large-amplitude echoes corresponding to stationary or very slow-moving tissue are removed before they saturate the inputs to the analog-to-digital converters (ADCs) in the receive channels. By first removing the wall signal, the gain of the TIC amplifier in the receive channel can be increased without saturating the (ADC). This additional amplification will increase the small flow signals, mapping them into higher bits of the ADC, thereby allowing more sensitive detection of weak blood flow in the human body.

Claims

1. A system for imaging flowing matter, comprising:

an array of transducer elements;

a receiver comprising a multiplicity of receive channels, each receive channel being coupled to a respective transducer element during first and second receive cycles for receiving first and second analog signals representing ultrasound echoes detected by said respective transducer element, and outputting a digital signal representing a difference between said first and second analog signals, and a beamsummer for beamsumming said digital signals output by said receive channels to form a flow vector which is a function of the velocity of flowing matter along a receive line;

a processor for deriving a flow image vector from said flow vector; and

a display subsystem for displaying a flow image having an image portion which is a function of said flow image vector.

2. The system as recited in claim 1, wherein said processor comprises an envelope detector.

3. The system as recited in claim 1, wherein said processor comprises a parameter estimator.

4. The system as recited in claim 1, wherein said transducer elements are piezoelectric transducer elements.

5. The system as recited in claim 1, wherein each receive channel comprises a pre-amplifier, a subtraction circuit, a time-gain control amplifier and an analog-to-digital converter arranged in series, and a receive signal reconstructing circuit arranged to receive an output from said analog-to-digital converter during said first receive cycle and to supply a reconstructed first analog signal to a first input of said subtraction circuit during said second receive cycle, said subtraction circuit having a second input coupled to an output of said pre-amplifier and having an output coupled to an input of said time-gain control amplifier.

6. The system as recited in claim 5, wherein said receive signal reconstructing circuit comprises memory for storing a receive vector derived from a signal output by said analog-to-digital converter during said first receive cycle and a digital-to-analog converter having an input coupled to said memory and having an output coupled to said first input of said subtraction circuit.

7. The system as recited in claim 6, wherein said receive signal reconstructing circuit further comprises a gain adjustment circuit arranged between said memory and the output of said analog-to-digital converter.

8. The system as recited in claim 6, wherein said receive signal reconstructing circuit further comprises a switch arranged between an output of said digital-to-analog converter and said first input of said subtraction circuit.

9. The system as recited in claim 1, wherein said receive channel circuitry comprises a pre-amplifier, a summation circuit, a time-gain control amplifier and an analog-to-digital converter arranged in series, and a receive signal reconstructing circuit arranged to receive an output from said analog-to-digital converter during said first receive cycle and to supply an inverted reconstructed first analog signal to a first input of said summation circuit during said second receive cycle, said summation circuit having a second input coupled to an output of said pre-amplifier and having an output coupled to an input of said time-gain control amplifier.

10. A receive channel in an ultrasound imaging system, comprising a pre-amplifier, a subtraction circuit, a time-gain control amplifier and an analog-to-digital converter arranged in series, and a receive signal reconstructing circuit arranged to receive an output from said analog-to-digital converter and to supply a reconstructed analog signal to a first input of said subtraction circuit, said subtraction circuit having a second input coupled to an output of said pre-amplifier and having an output coupled to an input of said time-gain control amplifier.

11. The receive channel as recited in claim 10, wherein said receive signal reconstructing circuit comprises memory for storing a digital signal derived from the output of said analog-to-digital converter and a digital-to-analog converter having an input coupled to said memory and having an output coupled to said first input of said subtraction circuit.

12. The receive channel as recited in claim 11, wherein said receive signal reconstructing circuit further comprises a gain adjustment circuit arranged between said memory and the output of said analog-to-digital converter.

13. The receive channel as recited in claim 12, wherein said receive signal reconstructing circuit further comprises a switch arranged between an output of said digital-to-analog converter and said first input of said subtraction circuit.

14. A receive channel in an ultrasound imaging system, comprising a pre-amplifier, a summation circuit, a time-gain control amplifier and an analog-to-digital converter arranged in series, and a receive signal reconstructing circuit arranged to receive an output from said analog-to-digital converter and to supply an inverted reconstructed analog signal to a first input of said summation circuit, said summation circuit having a second input coupled to an output of said pre-amplifier and having an output coupled to an input of said time-gain control amplifier.

15. A system for imaging flowing matter, comprising:

a transducer array comprising a multiplicity of transducer elements;

a transmitter coupled to said transducer array for pulsing selected transducer elements during first and second transmit firings to produce first and second transmit beams of wave energy focused at a transmit focal position;

a receiver comprising a multiplicity of receive channels respectively coupled to selected transducer elements of said transducer array for receiving a respective set of electrical receive signals transduced subsequent to each transmit firing, and a beamsummer for beamsumming receive vectors output by said receive channels, each receive channel comprising means for forming a flow vector which is a function of a difference between first and second receive signals acquired following said first and second transmit firings respectively, and said beamsummer forming a beamsummed flow vector from said flow vectors;

a processor for deriving a flow image vector from said beamsummed flow vector; and

a display subsystem for displaying a flow image having an image portion which is a function of said flow image vector.

16. A method for wall filtering receive signals in a receive channel of an imaging system, comprising the steps of:

(a) subjecting a first receive signal input to said receive channel to analog-to-digital conversion to form a receive vector;

(b) storing said receive vector;

(c) subjecting said receive vector to digital-to-analog conversion to form a reconstructed first receive signal;

(d) subtracting said reconstructed first receive signal from a second receive signal input to said receive channel to form a flow signal; and

(e) subjecting said flow signal to analog-to-digital conversion to form a flow vector.

17. The method as recited in claim 16, further comprising the steps of:

amplifying said first receive signal before analog-to-digital conversion;

attenuating said first receive vector before storing; and

amplifying said flow signal before analog-to digital conversion.

18. A method for wall filtering receive signals in a receive channel of an imaging system, comprising the steps of:

(a) subjecting a first receive signal input to said receive channel to analog-to-digital conversion to form a receive vector;

(b) inverting said receive vector;

(c) subjecting said inverted receive vector to digital-to-analog conversion to form a reconstructed inverted first receive signal;

(d) summing said reconstructed inverted first receive signal and a second receive signal input to said receive channel to form a flow signal; and

(e) subjecting said flow signal to analog-to-digital conversion to form a flow vector.

19. An imaging system comprising:

a transducer array comprising a multiplicity of transducer elements for transmitting wave energy in response to electrical activation and transducing returned wave energy into electrical signals;

a display monitor for displaying a flow image having an image portion which is a function of a flow image vector; and

a computer programmed to perform the following steps;

(a) activating transducer elements of said array to transmit focused wave energy during first and second transmit firings;

(b) forming first and second sets of receive signals from electrical signals output from said transducer elements subsequent to said first and second transmit firings respectively;

(c) for each pair of receive signals from said first and second sets corresponding to a respective transducer element, forming a respective flow vector which is a function of a difference between said pair of receive signals, said respective flow vectors forming a set;

(d) beamsumming said set of flow vectors to form a beamsummed flow vector;

(e) forming a flow image signal derived at least in part from said beamsummed flow vector; and

(f) sending said flow image signal to said display monitor.

20. An imaging system comprising:

a transducer array comprising a multiplicity of transducer elements for transmitting wave energy in response to electrical activation and transducing returned wave energy into electrical signals;

a transmitter coupled to said transducer array for pulsing selected transducer elements during first and second transmit firings to produce first and second transmit beams of wave energy focused at a transmit focal position;

a receiver comprising a multiplicity of receive channels respectively coupled to selected transducer elements of said transducer array for receiving first and second sets of electrical receive signals transduced subsequent to said first and second transmit firings respectively, each receive channel comprising means for forming a respective flow vector which is a function of a difference between a respective pair of receive signals from said first and second sets corresponding to a respective transducer element, said respective flow vectors from all receive channels forming a set, and said receiver further comprising a beamsummer for beamsumming said set of flow vectors to form a beamsummed flow vector;

a processor for deriving an image vector from said beamsummed flow vector; and

a display subsystem for displaying an image having an image portion which is a function of said image vector.

21. A method of flow imaging, comprising the steps of:

transmitting first and second beams of wave energy from transducer elements of an array forming a transmit aperture during first and second transmit firings respectively, said first and second beams being focused at a transmit focal position;

receiving first and second sets of receive signals subsequent to said first and second transmit firings respectively, each set comprising one receive signal for each transducer element in a receive aperture;

for each transducer element in said receive aperture, forming a respective flow vector which is a function of a difference between a respective pair of receive signals from said first and second sets corresponding to said respective transducer element, said respective flow vectors forming a set;

beamsumming said set of flow vectors to form a beamsummed flow vector;

deriving an image vector from said beamsummed flow vector; and

displaying an image having an image portion which is a function of said image vector.

22. The method as recited in claim 21, wherein said step of forming a respective flow vector comprises the steps of:

(a) subjecting a receive signal of said first set to analog-to-digital conversion to form a receive vector;

(b) storing said receive vector;

(c) subjecting said receive vector to digital-to-analog conversion to form a reconstructed receive signal of said first set;

(d) subtracting said reconstructed receive signal of said first set from a receive signal of said second set to form a flow signal; and

(e) subjecting said flow signal to analog-to-digital conversion to form said respective flow vector.

23. The method as recited in claim 21, wherein said step of forming a respective flow vector comprises the steps of:

(a) subjecting a receive signal of said first set to analog-to-digital conversion to form a receive vector;

(b) inverting said receive vector;

(c) subjecting said inverted receive vector to digital-to-analog conversion to form a reconstructed inverted receive signal of said first set;

(d) summing said reconstructed inverted receive signal of said first set from a receive signal of said second set to form a flow signal; and

(e) subjecting said flow signal to analog-to-digital conversion to form said respective flow vector.