Technique and apparatus for ultrasound therapy

• US 6,589,174 B1
• Filed: 10/20/2000
• Issued: 07/08/2003
• Est. Priority Date: 10/20/2000
• Status: Expired due to Term

• Current Assignee: Sunnybrook and Women's College Health Sciences Centre
• Original Assignee: Sunnybrook and Women's College Health Sciences Centre
• Inventors: Chopra, Rajiv, Bronskill, Michael J.
• Primary Examiner(s): Jaworski, Francis J.
• Assistant Examiner(s): Pass, Barry
• Application Number:
  US09/692,448
• Time in Patent Office: 991 Days
• Field of Search: 600/459, 600/439, 600/411, 601/2
• US Class Current: 600/439
• CPC Class Codes: A61B 17/2251 characterised by coupling elements between the apparatus, e.g. shock wave apparatus or locating means, and the patient, e.g. details of bags, pressure control of bag on patient
• CPC Class Codes: A61B 2018/1861 with an instrument inserted into a body lumen or cavity, e.g. a catheter
• CPC Class Codes: A61N 2007/0073 using multiple frequencies
• CPC Class Codes: A61N 2007/0078 with multiple treatment transducers
• CPC Class Codes: A61N 2007/025 interstitial
• CPC Class Codes: A61N 7/02 Localised ultrasound hyperthermia hyperthermia in general A61F7/00
• CPC Class Codes: B06B 1/067 which is used as, or combined with, an impedance matching layer
• CPC Class Codes: G10K 11/02 Mechanical acoustic impedances; Impedance matching, e.g. by horns; Acoustic resonators
• CPC Class Codes: G10K 9/122 using piezoelectric driving means G10K9/121 takes precedence

Abstract

The present invention is directed to an imaging-compatible device for insertion into a region of tissue under image guidance, which employs ultrasound energy for the generation of thermal lesions. Coagulation can be confined to particular sectors in tissue through rotational control of the device. The depth of coagulation can be controlled through simultaneous modulation of the operating frequencies and powers. Described is a device which comprises a transducer located within a housing suitable for tissue insertion. The transducer comprises at least one piezoceramic element with at least one acoustic matching layer comprising a high acoustic impedance material for generating acoustic energy in narrow passbands around multiple resonant frequencies with high acoustic efficiency. The magnitude and frequency of the electrical power delivered to each element can be manipulated simultaneously providing control over the 3-dimensional shape of the thermal lesion created in tissue.

Claims

1. A device for thermal coagulation of tissue comprising:

(a) a multifrequency ultrasound transducer for providing acoustic energy at multiple discrete frequencies, said transducer having at least one matching layer comprising a high acoustic impedance material relative to soft tissue and having an acoustic impedance comparable to the acoustic impedance of the transducer for generating acoustic energy at discrete frequencies with high efficiency of acoustic energy transmission;

(b) a housing for said transducer;

(c) means for delivery of variable frequency and power to said transducer; and

,

(d) an acoustic window.

2. A device according to claim 1 further comprising a motor control system and means to control frequency and power of ultrasound simultaneously and independently, wherein said motor control system provides rotational control of the device to isolate heating to parts of tissue, the means to control frequency and power allow for adjustment of the depth of thermal coagulation.

3. A device according to claim 2 wherein the transducer is a single element transducer with multiple matching layers.

4. A device according to claim 2 wherein the transducer is a multi-element transducer with individual elements between about 6-20 wavelengths in length, each of which comprises said at least one matching layer.

5. A device according to claim 2 wherein the transducer is a phased array transducer, with elements less than about 1 wavelength in length.

6. A device according to claim 2 wherein at least three transducers are incorporated into the device wherein at least one of each of which comprises:

(a) a single element transducer with multiple matching layers;

(b) a multi-element transducer with individual elements between about 6-20 wavelengths in length;

or

(c) a phased array transducer with less than about 1 wavelength in length.

7. A device according to claim 1 wherein the at least one matching layer comprises a ¼

wavelength front matching layer of a high acoustic impedance material, capable of delivery of acoustic energy at two discrete frequencies.

8. A device according to claim 1 wherein the at least one matching layer comprises a ½

wavelength front matching layer of high acoustic impedance material, capable of delivery of acoustic energy at three discrete frequencies.

9. A device according to claim 8 wherein the material is PZT.

10. A device according to claim 9 which is constructed of MR-compatible materials chosen from a metal, ceramic or a polymer.

11. A device according to claim 10 wherein the material is a metal and is brass, copper, or stainless steel.

12. A device according to claim 11 wherein the material is a polymer which is Poly(ether ether ketone)PEEK.

13. A device as claimed in claim 2 wherein said housing comprises tube means for infusing a therapeutic agent into a patient.

14. A device of claim 2 further comprising an acoustically transparent catheter.

15. A device according to claim 1, wherein the high acoustic impedance material has an acoustic impedance similar to that of the transducer.

16. A device according to claim 1, wherein the multiple discrete frequencies are separated by a factor of at least two.

17. A device according to claim 1, wherein the at least one matching layer comprises a ¼

wavelength matching layer of a high acoustic impedance material and a ¼

wavelength intermediate acoustic impedance matching layer, capable of delivery of acoustic energy at three discrete frequencies.

18. A device according to claim 1, wherein the at least one matching layer comprises a ½

wavelength matching layer of a high acoustic impedance material and a ¼

wavelength intermediate acoustic impedance matching layer, capable of delivery of acoustic energy at four discrete frequencies.

19. A method for interstitial ultrasound thermal therapy of tissue comprising:

(a) determining target tissue volume from images;

(b) planning a route of insertion for a device and a heating regime based on the images, the heating regime comprising a sequence of scan rates, transmission frequencies and powers as a function of device angle;

(c) inserting the device into a desired location for the interstitial thermal coagulation of said target tissue volume, said device comprising a multifrequency ultrasound transducer for providing acoustic energy at multiple discrete frequencies at high efficiency, said transducer having at least one matching layer comprising a high acoustic impedance material relative to soft tissue and having an acoustic impedance comparable to the acoustic impedance of the transducer;

(d) implementing the heating regime by delivering the acoustic energy to the target tissue volume from the device, the acoustic energy having various frequencies selected from the multiple discrete frequencies, and by rotating and translating the device for producing a thermal lesion conformal to said target tissue volume; and

(e) assessing the thermal lesion with imaging.

20. A method according to claim 19 wherein the transducer of the device is a single element transducer with multiple matching layers.

21. A method according to claim 20 wherein the at least one matching layer comprises a ¼

wavelength front matching layer of a high acoustic impedance material, capable of delivery of acoustic energy at two discrete frequencies.

22. A method according to claim 21 wherein the material of the transducer is PZT.

23. A method according to claim 22 wherein the device is constructed of MR-compatible materials chosen from a metal, ceramic or a polymer.

24. A method according to claim 23 wherein the material of the device is a metal and is brass, copper, or stainless steel.

25. A method according to claim 23 wherein the material is a polymer which is Poly(ether ether ketone)PEEK.

26. A method according to claim 20 wherein the at least one matching layer comprises a ½

wavelength front matching layer of high acoustic impedance material, capable of delivery of acoustic energy at three discrete frequencies.

27. A method according to claim 19 wherein the transducer of the device is a multi-element transducer with individual elements between about 6-20 wavelengths in length, each of which comprises said at least one matching layer.

28. A method according to claim 19 wherein the transducer of the device is a phased array transducer, with elements less than about 1 wavelength in length.

29. A method according to claim 19, wherein at least three transducers are incorporated into the device wherein at least one of each of which comprises:

(a) a single element transducer with multiple matching layers;

(b) a multi-element transducer with individual elements between about 6-20 wavelengths in length;

or

(c) a phased array transducer with less than about 1 wavelength in length.

30. A method as claimed in claim 19 wherein the housing of the device comprises tube means for infusing a therapeutic agent into a patient.

31. A method of claim 19 where the device further comprises an acoustically transparent catheter.

32. A method according to claim 19, wherein step (d) further comprises varying power of the acoustic energy for adjusting depth of penetration of the acoustic energy.

33. A method according to claim 19, wherein step (d) further comprises varying the frequency by at least a factor of two.