Method for determining phase advancement of transducer elements in high intensity focused ultrasound

• US 6,042,556 A
• Filed: 09/04/1998
• Issued: 03/28/2000
• Est. Priority Date: 09/04/1998
• Status: Expired due to Term

• Current Assignee: Washington University In St Louis
• Original Assignee: University of Washington
• Inventors: Beach, Kirk W., Plett, Melani I., Caps, Michael J., Brown, Katherine G.
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): MANTIS MERCADER, ELENI M
• Application Number:
  US09/148,754
• Time in Patent Office: 571 Days
• Field of Search: 601/2, 601/3, 600/437, 607/96
• US Class Current: 601/3
• CPC Class Codes: A61B 2017/22028 arrays, e.g. phased arrays
• CPC Class Codes: A61N 7/02 Localised ultrasound hyperthermia hyperthermia in general A61F7/00

Abstract

Phase of each transducer element of a high intensity focused (HIFU) transducer array is controlled to compensate for phase change introduced by varying velocity through differing tissue along a path towards a treatment volume. The echo of a specific harmonic of ultrasound pulses of moderate intensity and less than HIFU intensity are used to measure the propagation path transit time of each HIFU transducer element that will converge in a treatment volume through nonhomogeneous tissue. The moderate intensity is outside the linear region between molecular velocity fluctuations and pressure fluctuations. Thus, specific harmonic echoes are distributed in all directions from the treatment volume. Temporal delay in the specific harmonic echoes provide a measure of the propagation path transit time to transmit a pulse that will converge on the treatment volume.

Claims

1. A method for applying ultrasound energy through a nonhomogeneous mass to an identified treatment volume to provide ultrasonic therapy to the treatment volume, wherein application of ultrasound energy causes molecular velocity fluctuation and pressure fluctuation along a path from a source of ultrasound energy to the treatment volume, and wherein there is a threshold intensity level at the treatment volume of the applied ultrasound energy, above which a relationship between the molecular velocity fluctuations and the pressure fluctuations becomes nonlinear in the treatment volume, the method comprising the steps of:

configuring a first transducer array to define a first aperture, wherein the first transducer array is formed by a plurality of transducer elements;

while the first transducer array is configured to define the first aperture, transmitting a pulse of ultrasound energy from the first transducer array toward the treatment volume at a prescribed frequency and at a first peak intensity greater than the threshold intensity level at the treatment volume;

receiving echoes of the transmitted ultrasound energy at the first transducer array and at a second transducer array, the second transducer array having a plurality of transducer elements, wherein the echoes include ultrasound energy at a specific harmonic of the prescribed frequency;

for echoes received during an expected time window for receiving echoes from the treatment volume, comparing arrival time phase of the received echoes at the specific harmonic for each active element of the first transducer array and the second transducer array;

adjusting phase delay for received echoes for one or more elements of the second transducer array to achieve phase inversion; and

while phase inversion is applied to the second transducer array, transmitting ultrasound energy from the second transducer array to the treatment volume at a second intensity for achieving desired ultrasonic medical therapy of the treatment volume, wherein the second intensity at the treatment volume is greater than the first peak intensity at the treatment volume.

2. The method of claim 1, wherein the steps of transmitting, receiving and comparing are repeated until each active element of the second transducer array is optimally aimed at the treatment volume.

3. The method of claim 1, wherein the step of transmitting from the first ultrasound transducer array comprises emitting a pulse of less than 10 microseconds in duration.

4. The method of claim 1, wherein the first peak intensity is at least 500 mW/cm² SPTP.

5. The method of claim 1, wherein the first intensity is greater than 500 mW/cm² SPTP and the second intensity is at least 50 W/cm² SPTP.

6. The method of claim 1 applied to a patient, wherein the treatment volume is in an organ, and further comprising prior to the step of transmitting from the first transducer array, the steps of:

measuring amplitude of the received echoes;

deactivating first elements of the first transducer array which receive echoes having an amplitude less than a threshold amplitude, wherein the threshold amplitude serves to identify ultrasound-obstructed pathways; and

deactivating second elements of the second transducer array which receive echoes having an amplitude less than the threshold amplitude.

7. A method for applying ultrasound energy through a nonhomogeneous path to an identified treatment volume to provide ultrasonic therapy to the treatment volume, wherein application of ultrasound energy causes molecular velocity fluctuation and pressure fluctuation along a path from a source of ultrasound energy to the treatment volume, and wherein there is a threshold intensity level of the applied ultrasound energy at the treatment volume, above which a relationship between the molecular velocity fluctuations and the pressure fluctuations becomes nonlinear, the method comprising the steps of:

configuring a transducer array to define a first aperture, wherein the first transducer array is formed by a first plurality of imaging elements and a second plurality of treatment elements, the treatment elements capable of transmitting higher ultrasound power than the imaging elements, and wherein the first aperture includes at least multiple ones of the first plurality of imaging elements;

while the transducer array is configured to define the first aperture, transmitting a burst of ultrasound energy for a prescribed time from the transducer array toward the treatment volume at a prescribed frequency and at a first peak intensity greater than the threshold intensity at the treatment volume;

configuring the transducer array to define a second first aperture, wherein the second aperture includes at least multiple ones of the first plurality of imaging elements and multiple ones of the second plurality of treatment elements;

while the transducer array is configured to define the second aperture, receiving echoes of the transmitted ultrasound energy at the transducer array, wherein the echoes include ultrasound energy at harmonics of the prescribed frequency;

for echoes received during an expected time window for receiving echoes from the treatment volume, comparing arrival time phase of the received echoes at the prescribed frequency and the specific harmonic of the prescribed frequency for each active element of the transducer array;

adjusting phase delay for the received echoes for one or more of said elements of the transducer array to achieve phase inversion;

configuring the transducer array to define a third aperture, wherein the third aperture includes at least multiple ones of the second plurality of treatment elements; and

while phase inversion is applied to the transducer array, transmitting an ultrasound burst from the transducer array through the third aperture to the treatment volume, wherein the ultrasound burst is of a second peak intensity at the treatment volume for achieving desired ultrasonic medical therapy of the treatment volume, wherein the second peak intensity at the treatment volume is greater than the first peak intensity at the treatment volume.

8. The method of claim 7, wherein the steps of configuring a first aperture, transmitting, configuring a second aperture, receiving and comparing are repeated until each active element of the second transducer array is optimally aimed at the treatment volume.

9. The method of claim 7, wherein the step of transmitting from the ultrasound transducer array comprises emitting a pulse of less than 10 microseconds in duration.

10. The method of claim 7, wherein the first peak intensity is at least 500 mW/cm² SPTP.

11. The method of claim 7, wherein the first peak intensity is greater than 500 mW/cm² SPTP and the second peak intensity is at least 50 W/cm² SPTP.

12. The method of claim 7, applied to a patient, wherein the treatment volume is an organ, and further comprising prior to the step of transmitting from the transducer array, the steps of:

measuring amplitude of the received echoes;

deactivating elements of the transducer array which receive echoes having an amplitude less than a threshold amplitude, wherein the threshold amplitude serves to identify ultrasound-obstructed pathways.

13. An ultrasound system for applying ultrasound energy through a nonhomogeneous path to a treatment volume to provide ultrasonic therapy to the treatment volume, wherein application of ultrasound energy causes molecular velocity fluctuation and pressure fluctuation along a path from a source of ultrasound energy to the treatment volume, and wherein there is a threshold intensity level of the applied ultrasound energy at the treatment volume, above which a relationship between the molecular velocity fluctuations and the pressure fluctuations becomes nonlinear, the apparatus comprising:

a first transducer array configured to define a first aperture, the first transducer array having a plurality of transducer elements which transmit ultrasound energy at a prescribed frequency and at a first peak intensity greater than the threshold intensity at the treatment volume, the first aperture being formed by active elements of the first transducer array;

a second transducer array having a plurality of active transducer elements which receive echoes of the transmitted ultrasound energy at a specific harmonic of the prescribed frequency;

means for comparing phase of the echoes at the specific harmonic for each active element of the first transducer array and the second transducer array by measuring transit time for the transmitted ultrasound energy to propagate from the first transducer array to the treatment volume and echo back to the second transducer array while the second transducer array is aimed at the treatment volume; and

means for adjusting the phase of received echoes for one or more elements of the second transducer array so that each active element of the second transducer array is aimed at the treatment volume, wherein propagation transit time is applied as an advance time to each active element of the second transducer array to achieve phase inversion; and

wherein while phase inversion is applied to the second transducer array, ultrasound energy is transmitted from the second transducer array to the treatment volume at a second peak intensity for achieving desired ultrasonic medical therapy of the treatment volume, wherein the second peak intensity is greater than the first peak intensity at the treatment volume.

14. The system of claim 13, wherein a transmission of ultrasound energy from the first ultrasound transducer array comprises a pulse of less than 10 microseconds in duration.

15. The system of claim 13, wherein the first peak intensity is at least than 500 mW/cm² and the second peak intensity is at least 50 W/cm² SPTP.

16. The system of claim 13, further comprising a plurality of time delay lines coupled to the transducer array, each of the time delay lines being adjustable to introduce a select time delay for the transmission at a corresponding transducer element of the transducer array, and wherein the phase adjusting means adjusts the time delay of at least one time delay line to adjust the phase of the received echoes.

17. An ultrasound system for applying ultrasound energy through a nonhomogeneous path to a treatment volume to provide ultrasonic therapy to the treatment volume, wherein application of ultrasound energy causes molecular velocity fluctuation and pressure fluctuation along a path from a source of ultrasound energy to the treatment volume, and wherein there is a threshold intensity level of the applied ultrasound energy at the treatment volume, above which a relationship between the molecular velocity fluctuations and the pressure fluctuations becomes nonlinear at the treatment volume, the apparatus comprising:

a transducer array including a first plurality of imaging elements and a second plurality of treatment elements, the treatment elements capable of transmitting higher ultrasound power than the imaging elements;

a plurality of time delay lines coupled to the transducer array, each one of the plurality time delay lines being adjustable to introduce a select time delay respectively for transmission and reception at a corresponding transducer element;

means for defining a first aperture of the transducer array through which a burst of ultrasound energy is transmitted toward the treatment volume for a prescribed time at a prescribed frequency and at a first peak intensity greater than the threshold intensity at the treatment volume, the first aperture including at least multiple ones of the first plurality of imaging elements;

means for defining a second aperture of the transducer array through which echoes of the transmitted ultrasound energy are received, wherein the echoes include ultrasound energy at harmonics of the prescribed frequency, the second aperture including at least multiple ones of the first plurality of imaging elements and multiple ones of the second plurality of treatment elements;

means for testing for time error of the echoes at the prescribed frequency and the specific harmonic of the prescribed frequency;

means for reducing time error by adjusting respective time delay at the plurality of time delay lines to achieve phase inversion and aim the transducer array at the treatment volume; and

wherein while phase inversion is applied to the second transducer array, ultrasound energy is transmitted through a third aperture of the transducer array to the treatment volume at a second peak intensity at the treatment volume for achieving desired ultrasonic medical therapy of the treatment volume, wherein the second peak intensity is greater than the first peak intensity at the treatment volume, and wherein the third aperture includes at least multiple ones of the second plurality of treatment elements.

18. The system of claim 17, further comprising means for measuring propagation transit time for the ultrasound energy to propagate from the transducer array to the treatment volume and echo back to the transducer array, and wherein adjustment of respective time delay is achieved by applying the propagation transit times an advance time for each element of the transducer array.

19. The system of claim 17, wherein a transmission of ultrasound energy from the first ultrasound transducer array comprises a pulse of less than 10 microseconds in duration.

20. The system of claim 17, wherein the first intensity is at least 500 mW/cm² SPTP and the second intensity is at least 50 W/cm² SPTP.

21. A method for applying ultrasound energy through a nonhomogeneous mass to an identified treatment volume to provide ultrasonic therapy to the treatment volume, wherein application of ultrasound energy causes molecular velocity fluctuation and pressure fluctuation along a path from a source of ultrasound energy to the treatment volume, and wherein there is a threshold intensity level at the treatment volume of the applied ultrasound energy, above which a relationship between the molecular velocity fluctuations and the pressure fluctuations becomes nonlinear in the treatment volume, the method comprising the steps of:

transmitting a pulse of ultrasound energy from a first transducer toward the treatment volume at a prescribed frequency and at a first peak intensity greater than the threshold intensity level at the treatment volume;

receiving echoes of the transmitted ultrasound energy at the first transducer and at a second transducer, wherein the echoes include ultrasound energy at a specific harmonic of the prescribed frequency;

for echoes received during an expected time window for receiving echoes from the treatment volume, comparing arrival time phase of the received echoes at the specific harmonic for the first transducer and comparing arrival time phase of the received echoes at the specific harmonic for the second transducer;

adjusting phase delay of received echoes for the second transducer to achieve phase inversion; and

while phase inversion is applied to the second transducer, transmitting ultrasound energy from the second transducer to the treatment volume at a second intensity for achieving desired ultrasonic medical therapy of the treatment volume, wherein the second intensity at the treatment volume is greater than the first peak intensity at the treatment volume.

22. A method for focussing ultrasound energy through a nonhomogeneous mass to a treatment volume, the method comprising the steps of:

transmitting a pulse of ultrasound energy from a transducer toward the treatment volume;

receiving echoes of the transmitted ultrasound energy at the transducer, wherein the echoes include ultrasound energy at a specific harmonic of the prescribed frequency;

for echoes received during an expected time window for receiving echoes from the treatment volume, comparing arrival time phase of the received echoes at the specific harmonic;

adjusting phase delay of received echoes for the transducer to achieve phase inversion; and

while phase inversion is applied to the transducer, transmitting ultrasound energy from the transducer to the treatment volume.

23. The method of claim 22, further comprising the step of receiving echoes of the ultrasound energy while phase inversion is applied to perform medical diagnostic ultrasound imaging.

24. The method of claim 22, wherein the transmitting ultrasound energy to the treatment volume while phase inversion is applied is for achieving ultrasonic medical therapy of the treatment volume in which application of the ultrasound energy causes molecular velocity fluctuation and pressure fluctuation along a path from the transducer to the treatment volume, and wherein there is a threshold intensity level of the applied ultrasound energy at the treatment volume, above which a relationship between the molecular velocity fluctuations and the pressure fluctuations becomes nonlinear in the treatment volume.

25. An ultrasound system for applying ultrasound energy through a nonhomogeneous path to a treatment volume to provide ultrasonic therapy to the treatment volume, wherein application of ultrasound energy causes molecular velocity fluctuation and pressure fluctuation along a path from a source of ultrasound energy to the treatment volume, and wherein there is a threshold intensity level of the applied ultrasound energy at the treatment volume, above which a relationship between the molecular velocity fluctuations and the pressure fluctuations becomes nonlinear, the apparatus comprising:

a first transducer which transmits ultrasound energy at a prescribed frequency and at a first peak intensity greater than the threshold intensity at the treatment volume, the transducer and a second transducer receiving echoes of the transmitted ultrasound energy at a specific harmonic of the prescribed frequency;

means for comparing phase of the echoes at the specific harmonic for the first transducer by measuring transit time for the transmitted ultrasound energy to propagate from the first transducer to the treatment volume and echo back to the first transducer;

means for comparing phase of the echoes at the specific harmonic for the second transducer by measuring transit time for the transmitted ultrasound energy to propagate from the first transducer to the treatment volume and echo back to the second transducer;

means for adjusting the phase of received echoes for the second transducer so that the transducer is aimed at the treatment volume, wherein propagation transit time is applied as an advance time to the second transducer to achieve phase inversion; and

wherein while phase inversion is applied to the second transducer, ultrasound energy is transmitted from the second transducer to the treatment volume at a second peak intensity for achieving desired ultrasonic medical therapy of the treatment volume, wherein the second peak intensity is greater than the first peak intensity at the treatment volume.