Ultrasound systems and methods for real-time noninvasive spatial temperature estimation

1. A method for real-time noninvasive temperature estimation, the method comprising:

propagating ultrasound waves into tissue, wherein the ultrasound waves become nonlinear in the tissue;

detecting echoes of the ultrasound waves, wherein detecting the echoes comprises detecting a plurality of harmonics of the ultrasound waves; and

monitoring changes in tissue temperature in real-time during treatment using a spectral-based approach, wherein monitoring the changes comprises monitoring changes in the magnitude of at least one detected harmonic to estimate tissue temperature, and wherein greater attenuation of an individual harmonic correlates to an increase in the tissue temperature.

2. The method of claim 1 , further comprising:

providing a plurality of predefined changes in harmonic magnitudes that correspond with predefined changes in tissue temperature; and

correlating a change in the magnitude of a detected harmonic with a predefined change in tissue temperature to determine the tissue temperature.

3. The method of claim 1 wherein monitoring the changes in tissue temperature comprises monitoring tissue temperatures above 60° C. in real-time.

4. The method of claim 1 wherein:

the ultrasound waves become non-linear proximate to a focal region in the tissue;

monitoring the changes in tissue temperature comprises monitoring the tissue temperature at the focal region; and

the method further comprises monitoring changes in tissue temperature along at least a portion of a propagation path of the ultrasound waves to the focal region using a strain-based approach.

5. The method of claim 1 wherein monitoring the changes in tissue temperature further comprises estimating the changes in tissue temperature using a strain-based approach that correlates changes in the sound speed of the detected echoes to changes in tissue temperature, wherein faster sound speeds correlate to higher temperatures.

6. The method of claim 5 , further comprising:

weighting the changes in tissue temperature estimated by the spectral-based approach according to a first coefficient;

weighting the changes in tissue temperature estimated by the strain-based approach according to a second coefficient, wherein the second coefficient is different from the first coefficient; and

combining the weighted changes in tissue temperature to form a temperature profile of the tissue.

7. The method of claim 1 wherein:

propagating ultrasound waves into tissue comprises propagating high-intensity focused ultrasound (HIFU) waves toward a focal region in the tissue with a first array of first transducers, the first transducers comprising a piezocermaic material; and

detecting echoes of the ultrasound waves comprises detecting the echoes with a second array of second transducers, the second transducers comprising a piezopolymer material.

8. The method of claim 1 wherein detecting echoes of the ultrasound waves comprises performing wavelet signal processing to enhance the resolution of the harmonics in the echoes.

9. The method of claim 1 , further comprising modeling the tissue temperature as a three-dimensional temperature map.

10. A noninvasive temperature estimation system comprising:

an ultrasound source configured to transmit ultrasound waves that become nonlinear at a focal region in tissue;

means for detecting harmonics of the nonlinear waves; and

means for determining changes in tissue temperature at the focal region in real-time using changes in the magnitude of at least one detected harmonic to estimate the tissue temperature, wherein a greater attenuation of an individual harmonic correlates to a greater increase in the tissue temperature.

11. The system of claim 10 wherein the ultrasound source comprises:

a first array of first transducers, the first transducers comprising a first piezoelectric material configured to transmit nonlinear ultrasound waves; and

a second array of second transducers different from the first transducers, the second transducers comprising a second piezoelectric material configured to detect up to at least a third harmonic of the ultrasound waves.

12. The system of claim 10 wherein the ultrasound source comprises a piezopolymer material.

13. The system of claim 10 wherein the ultrasound source is configured to detect harmonics of the nonlinear waves and the sound speed of reflected ultrasound waves, the detected harmonics and sound speeds being used to determine the tissue temperature.