Medical ultrasonic imaging system with three-state ultrasonic pulse and improved pulse generator

• US 6,432,055 B1
• Filed: 06/30/2000
• Issued: 08/13/2002
• Est. Priority Date: 06/30/2000
• Status: Expired due to Term

• Current Assignee: Siemens Medical Solutions USA Incorporated (Siemens AG)
• Original Assignee: Acuson Corporation (Siemens AG)
• Inventors: Shifrin, Lazar, Maslak, Samuel H., Carp, Stuart L.
• Primary Examiner(s): Jaworski, Francis J.
• Assistant Examiner(s): Imam, Ali M.
• Application Number:
  US09/607,806
• Time in Patent Office: 774 Days
• Field of Search: 600/437, 600/442, 600/443, 600/447, 600/448, 604/22, 736/02, 736/03, 736/14, 736/25, 736/26, 367/7, 367/11, 367/130, 367/138, 367/153, 367/2, 310/317, 310/316.01
• US Class Current: 600/437
• CPC Class Codes: A61B 8/481 involving the use of contrast agent, e.g. microbubbles introduced into the bloodstream analysis of echo signal exploiting properties of a contrast enhancer in devices for short-range imaging with acoustic waves G01S7/52039
• CPC Class Codes: G01S 15/102 using transmission of pulses having some particular characteristics
• CPC Class Codes: G01S 15/895 characterised by the transmitted frequency spectrum
• CPC Class Codes: G01S 7/5202 for pulse systems
• CPC Class Codes: G01S 7/52038 involving non-linear properties of the propagation medium or of the reflective target
• CPC Class Codes: G01S 7/52041 detecting modification of a contrast enhancer, e.g. detecting the destruction of a contrast agent by an acoustic wave, e.g. loss of correlation diagnostic techniques involving the use of contrast agents A61B8/481
• CPC Class Codes: G01S 7/52046 Techniques for image enhancement involving transmitter or receiver image enhancement by image data processing G06T5/00

Abstract

A three-state, pulse width modulated, bipolar waveform is constructed by summing a first component with an inverted, time-shifted version of the first component. By properly selecting the time interval for the time shift of the second component, frequency filtering benefits can be obtained. The three-state waveform is generated by a switched voltage source that provides a low, constant source impedance for all three voltage states.

Claims

1. A transmit waveform generator for a medical ultrasonic imaging system, said generator comprising:

a primary transformer winding;

a first switching circuit coupled to both sides of the primary winding and operative to provide a low resistance path across the primary winding when the first switching circuit is in a closed-circuit state;

a secondary transformer winding inductively coupled with the primary transformer winding and adapted to be coupled with a transducer element;

said first switching circuit operative when in the closed circuit state to drive the transducer element to a baseline voltage.

2. The invention of claim 1 wherein the first switching circuit comprises first and second switches, each switch coupled between a respective side of the primary winding and a reference potential.

3. The invention of claim 1 further comprising a second primary winding inductively coupled to the secondary winding, said second primary winding coupled on one side to a voltage source and on the other side to a reference voltage via a second switching circuit;

said second switching circuit operative when in a closed-circuit state to drive the transducer element to a second voltage, said second voltage being positive relative to the baseline voltage.

4. The invention of claim 3 further comprising a third primary winding inductively coupled to the secondary winding, said third primary winding coupled on one side to a respective voltage source and on the other side to a respective reference voltage via a third switching circuit;

said third switching circuit operative when in a closed-circuit state to drive the transducer element to a third voltage, said third voltage being negative relative to the baseline voltage.

5. The invention of claim 4 wherein the second and third primary windings are coupled to the same voltage source and the same reference voltage.

6. The invention of claim 1 wherein the primary winding comprises first and second windings interconnected at a node, and wherein the invention further comprises a second switching circuit interconnecting the node to a voltage source.

7. The invention of claim 1 wherein the primary winding is connected to first and second nodes on respective sides of the primary winding, wherein the first switching circuit comprises first and second switches, each interconnecting a respective node to a respective reference potential, and wherein the invention further comprises;

a second switching circuit interconnecting the first node to a respective voltage source; and

a third switching circuit interconnecting the second node to a respective voltage source.

30. The invention of claim 1, 8, 20, 27, 28 or 29 wherein the second and third switching circuits comprise respective switches, each switch comprising a respective gate and a respective drain, and wherein the invention further comprises first and second capacitors, each capacitor coupled between the gate of a respective one of the switches and the drain of the other switch.

31. The invention of claim 1, 8, 20, 27, 28 or 29 further comprising means for applying neutralizing currents to the second and third switching circuits to reduce switching times.

46. The invention of claim 1, 8, 20, 27, 28, 29 or 41 wherein the transmit waveform generator drives the transducer element with only three discrete voltage levels.

47. The invention of claim 1, 8, 20, 27, 28, 29 or 41 wherein the transmit waveform generator drives the transducer element with no more than eleven discrete voltage levels.

48. The invention of claim 1, 8, 20, 27, 28, 29, 32 or 41 wherein the baseline voltage is substantially equal to 0VDC.

8. A transmit waveform generator for a medical ultrasonic imaging system, said generator comprising:

a set of input conductors adapted for connection to at least one voltage source;

an output conductor adapted for driving a transducer element;

a first switching circuit coupled with the output conductor and operative to drive the output conductor to a baseline voltage at a first source impedance;

a second switching circuit coupled with one of the input conductors and the output conductor and operative to drive the output conductor to a second voltage at a second source impedance, said second voltage being positive relative to the baseline voltage;

a third switching circuit coupled with one of the input conductors and the output conductor and operative to drive the output conductor to a third voltage at a third source impedance, said third voltage being negative relative to the baseline voltage;

wherein the largest of the first, second, and third source impedances is no more than four times the smallest of the first, second, and third impedances at a selected ultrasonic frequency.

9. The invention of claim 8 wherein the first, second and third source impedances are all less than about 70 ohms at the selected ultrasonic frequency.

10. The invention of claim 8 wherein the output conductor comprises a secondary transformer winding;

and wherein the first, second and third switching circuits are inductively coupled with the secondary winding by first, second and third primary transformer windings, respectively.

11. The invention of claim 10 wherein each of the windings comprises an equal number of turns.

12. The invention of claim 8 wherein the first, second and third switching circuits each comprise at least one respective N-channel switch.

13. The invention of claim 8 wherein the first, second and third switching circuits each comprise at least one respective switch, and wherein the switches are substantially identical.

14. The invention of claim 8 wherein each of the switching circuits comprises at least one respective switch and at least one respective switch driver, and wherein all of the switch drivers are connected to a common voltage level.

15. The invention of claim 14 wherein all of the switches are connected to the same common voltage level as are the switch drivers.

16. The invention of claim 8 wherein the largest of the first, second, and third source impedances is no more than three times the smallest of the first, second, and third source impedances at the selected ultrasonic frequency.

17. The invention of claim 8 wherein the largest of the first, second, and third source impedances is no more than two times the smallest of the first, second, and third source impedances at the selected ultrasonic frequency.

18. The invention of claim 8 wherein the first, second, and third source impedances are all less than 50 ohms at the selected ultrasonic frequency.

19. The invention of claim 8 wherein the first, second, and third source impedances are all less than 20 ohms at the selected ultrasonic frequency.

20. A transmit waveform generator for a medical ultrasonic imaging system, said generator comprising:

a set of input conductors adapted for connection to at least one voltage source;

an output conductor adapted for driving a transducer element;

a first switching circuit coupled with the output conductor and operative to drive the output conductor to a baseline voltage at a first source impedance;

a second switching circuit coupled with one of the input conductors and the output conductor and operative to drive the output conductor to a second voltage at a second source impedance, said second voltage being positive relative to the baseline voltage;

a third switching circuit coupled with one of the input conductors and the output conductor and operative to drive the output conductor to a third voltage at a third source impedance, said third voltage being negative relative to the baseline voltage;

wherein the largest of the first, second, and third source impedances differs from the smallest of the first, second, and third impedances by less than 70 ohms at a selected ultrasonic frequency.

21. The invention of claim 20 further comprising:

a transducer cable; and

a resistive element connected in series between the output conductor and the cable and characterized by a resistive impedance, wherein the first, second, and third source impedances are all less than the resistive impedance at the selected ultrasonic frequency.

22. The invention of claim 20 further comprising:

a transducer cable having a characteristic impedance;

wherein the first, second and third source impedances are all less than the characteristic impedance at the selected ultrasonic frequency.

23. The invention of claim 20 wherein the largest of the first, second, and third source impedances differs from the smallest of the first, second, and third source impedances by less than 50 ohms at the selected ultrasonic frequency.

24. The invention of claim 20 wherein the largest of the first, second, and third source impedances differs from the smallest of the first, second, and third source impedances by less than 30 ohms at the selected ultrasonic frequency.

25. The invention of claim 20 wherein the largest of the first, second, and third source impedances differs from the smallest of the first, second, and third source impedances by less than 10 ohms at the selected ultrasonic frequency.

26. The invention of claim 20 wherein the largest of the first, second, and third source impedances differs from the smallest of the first, second, and third source impedances by less than 5 ohms at the selected ultrasonic frequency.

27. A transmit waveform generator for a medical ultrasonic imaging system, said generator comprising:

a set of input conductors adapted for connection to at least one voltage source;

an output conductor adapted for driving a transducer element;

a first switching circuit coupled with the output conductor and operative to drive the output conductor to a baseline voltage at a first source impedance;

a second switching circuit coupled with one of the input conductors and the output conductor and operative to drive the output conductor to a second voltage at a second source impedance, said second voltage being positive relative to the baseline voltage;

a third switching circuit coupled with one of the input conductors and the output conductor and operative to drive the output conductor to a third voltage at a third source impedance, said third voltage being negative relative to the baseline voltage; and

a transducer cable coupled with the output conductor, wherein the transducer cable has a characteristic impedance;

wherein the first, second, and third source impedances are all less than the characteristic impedance at a selected ultrasonic frequency.

28. A transmit waveform generator for a medical ultrasonic imaging system, said generator comprising:

a set of input conductors adapted for connection to at least one voltage source;

an output conductor adapted for driving a transducer element;

a first switching circuit coupled with the output conductor and operative to drive the output conductor to a baseline voltage at a first source impedance;

a second switching circuit coupled with one of the input conductors and the output conductor and operative to drive the output conductor to a second voltage at a second source impedance, said second voltage being positive relative to the baseline voltage;

a third switching circuit coupled with one of the input conductors and the output conductor and operative to drive the output conductor to a third voltage at a third source impedance, said third voltage being negative relative to the baseline voltage; and

a transducer element coupled with the output conductor, wherein the transducer element has a characteristic impedance at an ultrasonic frequency;

wherein the first, second, and third source impedances are all less than the characteristic impedance at a selected ultrasonic frequency.

29. A transmit waveform generator for a medical ultrasonic imaging system, said generator comprising:

a set of input conductors adapted for connection to at least one voltage source;

an output conductor adapted for driving a transducer element;

a first switching circuit coupled with the output conductor and operative to drive the output conductor to a baseline voltage;

a second switching circuit coupled with one of the input conductors and the output conductor and operative to drive the output conductor to a second voltage, said second voltage being positive relative to the baseline voltage;

a third switching circuit coupled with one of the input conductors and the output conductor and operative to drive the output conductor to a third voltage, said third voltage being negative relative to the baseline voltage;

wherein the first switching circuit is switchable between an open-circuit state and a closed-circuit state;

wherein the first switching circuit is characterized by a first impedance at a selected ultrasonic frequency when switched to the closed-circuit state to drive the output conductor to the baseline voltage; and

wherein the first impedance dominates the first source impedance at the selected ultrasonic frequency when the first switching circuit is in the closed-circuit state.

32. A transmit pulse generating method for a medical ultrasound imaging system, said method comprising:

(a) driving an output conductor coupled with a transducer element to a baseline voltage at a first source impedance with a first switching circuit during a first portion of an ultrasonic pulse characterized by a center frequency f₀ and an associated center period τ

₀ for a time period no less than N*τ

₀/128, where N≧

1;

(b) driving the output conductor to a second voltage at a second source impedance with a second switching circuit during a second portion of the ultrasonic pulse, said second voltage being positive relative to the baseline voltage; and

(c) driving the output conductor to a third voltage at a third source impedance with a third switching circuit during a third portion of the ultrasonic pulse, said third voltage being negative relative to the baseline voltage;

wherein the largest of the first, second, and third source impedances is no more than four times the smallest of the first, second, and third source impedances at a selected ultrasonic frequency;

wherein at least one of (b) and (c) is performed before (a) and at least one of (b) and (c) is performed after (a).

33. The method of claim 32 wherein the second and third voltages are adapted for ultrasonic imaging at a first, lower level of bursting of blood-borne microbubbles, and wherein the method further comprises:

(d) increasing the second and third voltages in magnitude such that the second and third voltages are adapted to burst blood-borne microbubbles at a second, higher level of bursting; and

then

(e) repeating (a), (b) and (c) in an order selected such that at least one of (b) and (c) is repeated before (a) is repeated, and at least one of (b) and (c) is repeated after (a) is repeated.

34. The method of claim 32 wherein the second and third voltages are adapted to burst blood-borne microbubbles at a first, higher level of bursting, and wherein the method further comprises:

(d) decreasing the second and third voltages in magnitude such that the second and third voltages are adapted for ultrasonic imaging at a second, lower level of bursting of blood-borne microbubbles; and

then

(e) repeating (a), (b) and (c) in an order selected such that at least one of (b) and (c) is repeated before (a) is repeated, and at least one of (b) and (c) is repeated after (a) is repeated.

38. The method of claim 33, 34, 35 or 36 further comprising:

(f) introducing microbubbles into a tissue to be imaged prior to (d).

39. The method of claim 33, 34, 35 or 36 wherein the microbubbles contain a therapeutic agent.

40. The method of claim 32, 33, 34, 35 or 36 wherein the ultrasonic pulse of (a), (b) and (c) is characterized by a fundamental frequency, and wherein the method further comprises:

forming an image based on harmonic echoes of the ultrasonic pulse.

42. The invention of claim 32 or 41 wherein the source impedances of (a), (b) and (c) are all substantially equal at the selected ultrasonic frequency.

43. The invention of claim 32 or 41 wherein N≧

2.

44. The invention of claim 32 or 41 wherein N≧

4.

45. The invention of claim 32 or 41 wherein N≧

8.

35. A transmit pulse generating method for a medical ultrasound imaging system, said method comprising:

(a) driving an output conductor coupled with a transducer to a baseline voltage at a first source impedance with a first switching circuit during at least one of a period prior to an ultrasonic pulse and a period subsequent to the ultrasonic pulse;

(b) driving the output conductor to a second voltage at a second source impedance with a second switching circuit during at least one portion of the pulse, said second voltage being positive relative to the baseline voltage;

(c) driving the output conductor to a third voltage at a third source impedance with a third switching circuit during at least one other portion of the pulse, said third voltage being negative relative to the baseline voltage;

wherein the largest of the first, second, and third source impedances is no more than four times the smallest of the first, second, and third source impedances at a selected ultrasonic frequency.

36. The method of claim 35 wherein the second and third voltages are adapted for ultrasonic imaging at a first, lower level of bursting of blood-borne microbubbles, and wherein the method further comprises:

(d) increasing the second and third voltages in magnitude such that the second and third voltages are adapted to burst blood-borne microbubbles at a second, higher level of bursting; and

then

(e) repeating (a), (b) and (c).

37. The method of claim 35 wherein the second and third voltages are adapted to burst blood-borne microbubbles at a first, higher level of bursting, and wherein the method further comprises:

(d) decreasing the second and third voltages in magnitude such that the second and third voltages are adapted for ultrasonic imaging at a second, lower level of bursting of blood-borne microbubbles; and

then

(e) repeating (a), (b) and (c).

41. A transmit pulse generator for a medical ultrasound imaging system, said generator comprising:

(a) switching circuit means for driving an output conductor coupled with a transducer element to a baseline voltage at a first source impedance during a first portion of an ultrasonic pulse characterized by a center frequency f₀ and an associated center period τ

₀ for a time period no less than N*τ

₀/128, where N≧

1;

(b) switching circuit means for driving the output conductor to a second voltage at a second source impedance during a second portion of the ultrasonic pulse, said second voltage being positive relative to the baseline voltage; and

(c) switching circuit means for driving the output conductor to a third voltage at a third source impedance during a third portion of the ultrasonic pulse, said third voltage being negative relative to the baseline voltage;

wherein the largest of the first, second, and third source impedances is no more than four times the smallest of the first, second, and third source impedances at a selected ultrasonic frequency.

49. A method for applying voltages to a medical ultrasonic imaging system transducer, said method comprising:

(a) providing a two-state waveform W(t);

(b) offsetting W(t) by a selected time interval to form an offset waveform W1(t);

(c) switching a first voltage to the transducer in response to W(t) when W(t) is not equal to W1(t); and

(d) switching a second voltage to the transducer in response to W1(t) when W(t) is not equal to W1(t).

50. The method of claim 49 wherein the first voltage is positive and the second voltage is negative relative to a baseline voltage.

51. The method of claim 49 further comprising:

(e) switching a third voltage intermediate the first and second voltages to the transducer when W(t) and W1(t) are equal.

52. The method of claim 49 further comprising:

(e) varying the selected time interval.

53. A method for-applying voltages to a medical ultrasonic imaging system transducer, said method comprising:

(a) providing a two-state waveform W(t);

(b) offsetting W(t) by a selected time interval to form an offset waveform W1(t);

(c) during times when W(t) and W1(t) are equal, setting a first and second control signal to a first logic state and a third control signal to a second logic state;

(d) during times when W(t) and W1(t) are not equal, setting the first control signal in response to W(t), the second control signal in response to W1(t), and the third control signal to the first logic state;

(e) switching a first voltage to the transducer in response to the third control signal;

(f) switching a second voltage to the transducer in response to the first control signal, said second voltage being positive relative to the first voltage;

(g) switching a third voltage to the transducer in response to the second control signal, said third voltage being negative relative to the first voltage.

54. The method of claim 53 further comprising:

(a) varying the selected time interval.

55. A transmit pulse in a medical ultrasonic imaging system, said pulse comprising at least three voltage levels and comprising first and second components that add to form the pulse, said first component substantially corresponding to a square wave signal alternating between a baseline voltage V_B and a second voltage V_B+V, said second component corresponding to an inverted version of the square wave signal alternating between the baseline voltage V_B and a third voltage V_B−

V, time shifted by a selected time interval.

57. The invention of claim 55 or 56 wherein the baseline voltage V_B is substantially equal to 0VDC.

56. A pulse transmitter in a medical ultrasonic imaging system, said transmitter comprising:

a transducer; and

a transmit waveform generator operative to apply a transmit pulse to the transducer, said pulse comprising at least three voltage levels and comprising first and second components that add to form the pulse, said first component substantially corresponding to a square wave signal alternating between a baseline voltage V_B and a second voltage V_B+V, said second component corresponding to an inverted version of the square wave signal alternating between the baseline voltage V_B and a third voltage V_B−

V, time shifted by a selected time interval.