MULTIMODE ULTRASOUND FOCUSING FOR MEDICAL APPLICATIONS

• US 20100268088A1
• Filed: 04/17/2009
• Published: 10/21/2010
• Est. Priority Date: 04/17/2009
• Status: Active Grant

• Current Assignee: InSightec Ltd.
• Original Assignee: Insightec-Image-Guided Treatment Limited (InSightec Ltd.)
• Inventors: Vitek, Shuki, Prus, Oleg
• Granted Patent: US 8,617,073 B2
• Time in Patent Office: Days
• US Class Current: 600/459
• CPC Class Codes: A61B 8/0816 using echo-encephalography
• CPC Class Codes: A61B 8/14 Echo-tomography
• CPC Class Codes: A61B 8/4455 Features of the external shape of the probe, e.g. ergonomic aspects
• CPC Class Codes: A61B 8/485 involving measuring strain or elastic properties
• CPC Class Codes: A61N 2007/0056 Beam shaping elements
• CPC Class Codes: A61N 2007/0078 with multiple treatment transducers
• CPC Class Codes: A61N 7/02 Localised ultrasound hyperthermia hyperthermia in general A61F7/00

Abstract

Systems and methods for focusing ultrasound through the skull into the brain for diagnostic or therapeutic purposes may be improved by utilizing both longitudinal and shear waves. The relative contribution of the two modes may be determined based on the angle of incidence.

Claims

1. A method of delivering multimode ultrasound waves to a target through at least one tissue layer defining a first interface and a second interface, the waves having a shear component and a longitudinal component through the at least one tissue layer, the method comprising the steps of:

weighting energy contributions from the shear component and the longitudinal component based at least in part on an incident angle of the waves at the first interface;

computing phase shifts associated with the shear component and the longitudinal component; and

compensating for the phase shifts, based on the weightings, when delivering the ultrasound waves.

2. The method of claim 1 wherein the ultrasound waves are delivered by a phased array of transducers, the compensation step comprising adjusting outputs of the transducers in accordance with the phase shifts.

3. The method of claim 1 further comprising computing coefficients of attenuation associated with the longitudinal component and the shear component, and compensating for the attenuation when delivering the ultrasound waves.

4. The method of claim 1 further comprising computing a coefficient of reflection of the wave at the first interface, and compensating for the reflection when delivering the ultrasound waves.

5. The method of claim 1 wherein the weighting step is further based on a frequency of the ultrasound waves.

6. The method of claim 1 wherein the weighting step is further based on an acoustic response of the first layer.

7. The method of claim 1 wherein the compensating step is further based on at least one of a geometry, a thickness, a density, and an acoustic response of the first layer.

8. The method of claim 1 wherein the at least one tissue layer corresponds to a skull.

9. The method of claim 1 wherein the weighting step comprises:

determining a threshold angle; and

setting the energy contribution from the shear component to zero for incident angles smaller than the threshold angle; and

setting the energy contribution from the longitudinal component to zero for incident angles not smaller than the threshold angle.

10. The method of claim 1 wherein the weighting step further comprises:

determining a first threshold angle and a second threshold angle, the second threshold angle being greater than the first threshold angle;

setting the energy contribution from the shear component to zero for incident angles smaller than the first threshold angle; and

setting the energy contribution from the longitudinal component to zero for incident angles larger than the second threshold angle; and

computing the energy contributions from the shear component and the longitudinal component by interpolation for incident angles not smaller than the first threshold angle and not larger than the second threshold angle.

11. The method of claim 10 wherein the interpolation is linear.

12. The method of claim 1 wherein the weighting step is based on a relationship between energy contributions from the shear component and the longitudinal component determined empirically over a range of incident angles.

13. The method of claim 1 further comprising providing a model of the at least one tissue layer, and basing the compensation step on the model.

14. The method of claim 13 wherein the model comprises locally parallel layers.

15. The method of claim 13 wherein the model is obtained using at least one of computer tomography or magnetic resonance imaging.

16. The method of claim 1 wherein the ultrasound waves have a frequency in the range from 100 kHz to 400 kHz.

17. The method of claim 1 wherein the incident ultrasonic wave is purely longitudinal.

18. The method of claim 17 wherein the incident ultrasonic wave excites a longitudinal component and a shear component at the first interface.

19. The method of claim 18 wherein the shear component excites a longitudinal wave at the second interface.

20. A system for delivering multimode ultrasound waves to a target located inside an object that comprises at least a first layer defining a first interface and a second interface, the waves having a shear component and a longitudinal component through at least the first layer, the system comprising:

(a) a phased array of transducers arranged around the object;

(b) a controller for (i) receiving data about the object, its location relative to the transducers, and a location of the target, (ii) computing for each transducer, based on the data (1) an incident angle at which waves emanating from the transducer arrive at the first interface, (2) weightings of energy contributions from the shear component and the longitudinal component, based on the incident angle, and (3) phase shifts of the shear component and the longitudinal component, and (iii) computing phase shift compensations for the transducers based on the phase shifts of the shear components and the longitudinal components; and

a beam former in communication with the controller and the phased array of transducers for adjusting outputs of the transducers in accordance with the phase shift compensations computed by the controller.