CLAIMS

1. Method for localizing a region of interest (R) in a medium (M) in which cavitation occurs, the method comprising the steps consisting in:

- producing cavitation in the region of interest (R), the cavitation generating an acoustic signal,

- at each of at least three separate positions, detecting a cavitation signal (C) representative of the acoustic signal of the cavitation,

- for at least two pairs of cavitation signals (C), determining a delay between the cavitation signals (C) of each pair of cavitation signals (C),

- calculating a localization of the region of interest (R) based on the delays and the positions, the method being characterized in that the step of determining the delay comprises, for each pair of cavitation signals (C):

- incrementally shifting one of the cavitation signal (C) with respect to the other according to a time pitch,

- at each time pitch, comparing the cavitation signals (C),

- identifying a maximum inter-correlation time pitch as the time pitch at which the cavitation signals (C) overlap at a maximum,

- calculating the delay as a sum of the time pitches up to the maximum inter-correlation time pitch.

2. Method according to claim 1, wherein the step of calculating a localization of the region of interest (R) comprises:

- converting the delays in distance,

- for a number of point of a space including the region of interest, each point having determined coordinates (x, y), minimizing the cost-function

n

C (x, y) =∑ [(>! (x, y) - r_{i} (x, y)) - £_{i} f (1 )

i=2

with n integer greater than or equal to 3 is the number of positions,

e distance between the position i and the acoustic source

(the cavitation cloud),

^{ε} · : , the distance between the positions i and 1 determined from the conversion of the delays in distance.

3. Method according to claim 1, wherein the step of calculating a localization of the region of interest (R) comprises solving hyperbolic solutions defined by the following equation (2):

r^{2} = K_{t} - 2x_{iX} - 2y_{i}y + x^{2} + _y^{2} , l = l, ..., n (2)

with n integer greater than or equal to 3 is the number of positions,

distance between the position numbered i and a point

having coordinates (x, y) that are searched and corresponding to a position of the acoustic source (the cavitation cloud),

wherein the solving of hyperbolic solutions comprises:

- the delay measured between the positions i and 1 being r_{n} = r_{i}—r ,

r^{2} = (r_{i l} + r_{:} )^{2} and equation (2) corresponds to:

r + 2^1 + r? = K_{t} - 2x_{t}x - 2y + x^{2} + y^{2} (3)

- subtracting equation (2) to equation (3) so that

r^{2}_{A} + 2η = -2x. _{lX} - 2y _{l}y + K_{t} - K, (4)

with x _{l} = x_{i} - x_{x} and y_{iX} = y. - y,

- solving equation (4) in terms of x\ for n=3 that is:

' 2,1 K_{2} + K,

2 (5)

inserting equation (5) into equation (2) for i=l to obtain a quadratic equation in rl, substituting back the positive root into equation (5) to produce solutions in x and y- 4. Method according to any of claims 1 to 3, wherein the step of detecting the cavitation signal (C) comprises providing at least three hydrophones (11) at respective separate positions and directing the hydrophones (11) towards an area (V) including the region of interest (R).

5. Method according to any of claims 1 to 4, wherein the acoustic signal of the cavitation has at least one specific frequency, and wherein said method comprises, before the step of determining the delay, a step consisting in filtering each cavitation signal (C) with a bandwidth around the specific frequency, the bandwidth being preferably between 25 % and 75 % of the specific frequency and more preferably between 30 % and 60 % of the specific frequency.

6. Method according to any of claims 1 to 5, wherein the step of producing cavitation comprises emitting at least first and second ultrasound beams along first (Dl) and second (D2) directions intersecting at a focal point (P), the first and second ultrasound beams being adapted to generate cavitation in a focal area (V) around the focal point (P).

7. Method according to claim 6 when dependent on claim 4, wherein the step of detecting the cavitation signal (C) comprises directing the hydrophones (11) towards the focal area (V).

8. Method according to any of claims 6 and 7 when dependent on claim 5, wherein the first and second ultrasound beams have an emission frequency f_{e}, and wherein the specific frequency of the acoustic signal of the cavitation is between 0.4 x f_{e} and 0.6 x f_{e}.

9. Method according to any of claims 6 and 7 when dependent on claim 5, wherein the first and second ultrasound beams have an emission frequency f_{e}, and wherein the specific frequency of the acoustic signal of the cavitation is between 1.2 x f_{e} and 2.2 x f_{e}.

10. System (1) for localizing a region of interest (R) in a medium (M) in which cavitation occurs, the system (1) comprising:

- a cavitation device (5) configured to produce cavitation in the region of interest (R), the cavitation generating an acoustic signal,

- at least three sensors (11) arranged at respective separate positions and configured to detect a cavitation signal (C) representative of the acoustic signal of the cavitation,

- a processing unit configured to:

for at least two pairs of cavitation signals (C), determine a delay between the cavitation signals (C) of each pair of cavitation signals (C),

calculate a localization of the region of interest (R) based on the delays and the positions,the system being characterized in that to determine the delay, the processing unit is configured to, for each pair of cavitation signals (C):

- incrementally shift one of the cavitation signal (C) with respect to the other according to a time pitch,

- at each time pitch, compare the cavitation signals (C),

- identify a maximum inter-correlation time pitch as the time pitch at which the cavitation signals (C) overlap at a maximum,

- calculate the delay as a sum of the time pitches up to the maximum inter-correlation time pitch.

11. System (1) according to claim 10, wherein the sensors are hydrophones (11) directed towards an area (V) including the region of interest (R).

12. System (1) according to any of claims 10 and 11, wherein the acoustic signal of the cavitation has at least one specific frequency, and wherein the processing unit is configured to, before determining the delay, filter each cavitation signal (C) with a bandwidth around the specific frequency, the bandwidth being preferably between 25 % and 75 % of the specific frequency and more preferably between 30 % and 60 % of the specific frequency.

13. System (1) according to any of claims 10 to 12, wherein the cavitation device (5) comprises at least first (6) and second (7) ultrasound transducers configured to emit first and second ultrasound beams along first (Dl) and second (D2) directions intersecting at a focal point, the first and second ultrasound beams being adapted to generate cavitation in a focal area (V) around the focal point (P).

14. System (1) according to claim 13 when dependent on claim 11, wherein the hydrophones (11) are directed towards the focal area (V).

15. System (1) according to claim 14, wherein at least two hydrophones (11a, l ib) are mounted respectively onto the first (6) and second (7) ultrasound transducers.

16. System (1) according to any of claims 13 to 15 when dependent on claim 12, wherein the first (6) and second (7) ultrasound transducers are controlled to emit the first and second ultrasound beams having an emission frequency f_{e}, and wherein the specific frequency of the acoustic signal of the cavitation is between 0.4 x f_{e} and 0.6 x f_{e}.

17. System (1) according to any of claims 13 to 15 when dependent on claim 12, wherein the first (6) and second (7) ultrasound transducers are controlled to emit the first and second ultrasound beams having an emission frequency f_{e}, and wherein the specific frequency of the acoustic signal of the cavitation is between 1.2 x f_{e} and 2.2 x f_{e}.