Method for mapping temperature rise using pulse-echo ultrasound

1. A method for mapping temperature rise of anatomical tissue using pulse-echo ultrasound, comprising the steps of:

a) obtaining a first signal of a first imaging ultrasound wave which has been reflected back from a region in the anatomical tissue at a first time;

b) obtaining a second signal of a second imaging ultrasound wave which has been reflected back from the region in the anatomical tissue at a later second time wherein the tissue has received at least some medical treatment by the second time;

c) computing first and second complex analytic signals from the first and second imaging signals;

d) computing the depth-dependent delay from the conjugate product of the first and second analytic signals;

e) generating an echo strain map from the slope of the depth-dependent delay;

f) using the echo strain map to estimate the amount of temperature rise from the first imaging signal to the second imaging signal; and

g) creating an image showing where temperature rise is occurring in the anatomical tissue.

2. The method of claim 1 , further comprising the step of spatially filtering the difference signal.

3. The method of claim 2 , further including the step of performing a thresholding operation to remove artifactual strain peaks.

4. The method of claim 1 , further including the step of multiplying a signal of an ultrasound imaging wave by a phase compensation function to compute a correlation coefficient indicating the reliability of the temperature estimation.

5. The method of claim 4 wherein the signal is the first imaging signal.

6. The method of claim 5 wherein the signal is the second imaging signal.

7. The method of claim 4 , further including the step of implementing windowed sums to provide a spatial map of the correlation coefficient.

8. The method of claim 7 wherein the windowed sums are two-dimensional.

9. The method of claim 1 , wherein the echo strain map representing the slope of the depth-dependent delay assumes a linear relationship between echo strain and temperature rise.

10. The method of claim 1 , wherein the echo strain map representing the depth-dependent delay assumes a non-linear relationship between echo strain and temperature rise.

11. The method of claim 10 wherein the non-linear relationship is derived from measurements of non-linear relationships between temperature, sound speed and thermal expansion.

12. The method of claim 10 wherein the non-linear relationship is derived empirically from calibration measurements in the anatomical tissue.

13. The method of claim 1 , wherein the medical treatment is ultrasound medical treatment.

14. The method of claim 1 , also including steps a) through g) for different regions to image the anatomical tissue, wherein the image includes medically-treated and medically-untreated regions of the anatomical tissue.

15. A method for mapping temperature rise of anatomical tissue using pulse-echo ultrasound, comprising the steps of:

a) obtaining a first set of frames comprising a plurality of imaging ultrasound wave signals which have been reflected back from a region in the anatomical tissue during a first period of time;

b) obtaining a second set of frames comprising a plurality of imaging ultrasound wave signals which have been reflected back from a region in the anatomical tissue at a later second time wherein the tissue has received at least some medical treatment by the second time;

c) averaging together the signals of the first set of frames to obtain an averaged first imaging signal;

d) averaging together the signals of the second set of frames to obtain an averaged second imaging signal;

e) computing first and second complex analytic signals from the first and second averaged imaging signals;

f) computing the depth-dependent delay from the conjugate product of the first and second analytic signals;

g) generating a strain map from the slope of the depth-dependent delay;

h) using the echo strain map to estimate the amount of temperature rise from the first averaged imaging signal to the second averaged imaging signal; and

i) creating an image showing where temperature rise is occurring in the anatomical tissue.

16. The method of claim 15 , further comprising the step of spatially filtering the difference signal.

17. The method of claim 15 , wherein the medical treatment is ultrasound medical treatment.

18. The method of claim 15 , also including steps a) through i) for different regions to image the anatomical tissue, wherein the image includes medically-treated and medically-untreated regions of the anatomical tissue.

19. A method for mapping temperature rise of anatomical tissue using pulse-echo ultrasound, comprising the steps of:

a) obtaining a first set of frames comprising a plurality of imaging ultrasound wave signals which have been reflected back from a region in the anatomical tissue during a first period of time;

b) obtaining a second set of frames comprising a plurality of imaging ultrasound wave signals which have been reflected back from a region in the anatomical tissue at a later second time wherein the tissue has received at least some medical treatment by the second time;

c) computing complex analytic signals from a selected frame from the first set of frames and a selected frame from the second set of frames;

d) computing the conjugate product of the complex analytic signals of step c);

e) repeating steps c) and d) until conjugate products have been computed for all of the frames of the first and second frame sets;

f) computing the average of the conjugate products of step e);

g) computing the depth-dependent delay from the averaged conjugate product of step f);

h) generating an echo strain map from the slope of the depth-dependent delay;

i) using the echo strain map to estimate the amount of temperature rise from the first averaged imaging signal to the second averaged imaging signal; and

j) creating an image showing where temperature rise is occurring in the anatomical tissue.

20. A method for mapping temperature change in anatomical tissue using pulse-echo ultrasound, comprising the steps of:

a) obtaining a set of frames comprising a plurality of imaging ultrasound wave signals which have been reflected back from a region in the anatomical tissue during a period of time;

b) computing complex analytic signals from the set of frames;

c) computing the conjugate product of a pair of adjacent frames of the set of frames;

d) repeating step c) until the conjugate products of all adjacent frames have been computed;

e) averaging the conjugate products of the adjacent frames of step d);

f) computing a depth-dependent delay map from the average conjugate product;

g) generating an echo strain map from the slope of the depth-dependent delay;

h) using the echo strain map to estimate the amount of temperature change from the first frame to the second frame; and

i) creating an image showing where temperature change is occurring in the anatomical tissue.

21. A method for mapping temperature rise of anatomical tissue using pulse-echo ultrasound, comprising the steps of:

a) obtaining a first signal of a first imaging ultrasound wave which has been reflected back from a region in the anatomical tissue at a first time;

b) obtaining a second signal of a second imaging ultrasound wave which has been reflected back from the region in the anatomical tissue at a later second time wherein the tissue has received at least some medical treatment by the second time;

c) computing first and second complex analytic signals from the first and second imaging signals;

d) computing the depth-dependent delay from the conjugate product of the first and second analytic signals;

e) generating an echo strain map from the slope of the depth-dependent delay;

f) using the echo strain map to estimate the amount of temperature rise from the first imaging signal to the second imaging signal;

g) creating an image showing where temperature rise is occurring in the anatomical tissue; and

h) repeating the method at least once by:

i) re-defining the second imaging signal obtained at step b) as the first imaging signal of step a);

ii) obtaining a new second imaging signal at step b); and

ii) repeating steps c) through g).