Device for monitoring HIFU treatment

Abstract

An ultrasound device is provided configured to perform HIFU treatment and detect the temperature distribution in a treatment area in real time during HIFU treatment. The device includes: an ultrasound probe comprising at least an array of piezoelectric transducers or CMUT transducers; a guiding device for the ultrasound probe; and a computing device configured to receive and store the raw ultrasound signals reflected by the tissue and acquired by each of the piezoelectric transducers or CMUT transducers, process the reflected raw ultrasound signals for generating an ultrasound image, and perform other processing on the raw ultrasound signals reflected by the tissue. The device is characterized in that a computer program configured to implement a method for determining the actual acoustic heating rate of the tissue is loaded onto the computing device, the method comprising the steps of: a) identifying a region of interest (15) within an ultrasound image (14) providing a treatment area (16); b) assigning an initial temperature distribution, through which the initial temperature... c) Distribute temperature values ​​to each point of the ROI, d) emit a high-intensity ultrasound beam (100) focused on a focal point (11) contained in the ROI at predetermined time intervals, followed by the emission of a broadband ultrasound pulse (200), and detect ultrasound signals reflected and / or emitted by the treated tissue, e) in order to obtain a reference spectrum (200s), perform a frequency transformation of the reflected ultrasound signal in response to the broadband ultrasound pulse (200s), f) repeat steps c) and d) iteratively to obtain a spectrum for each iteration, f) assume that when the spectrum (202s) detected in response to the broadband ultrasound pulse (202) includes multiple peaks (2021) not provided in the reference spectrum (200s), the temperature at the focal point (11) is equal to the predetermined temperature and function of the tissue in the treatment step, g) determine the actual acoustic heating rate Q based on the predetermined temperature and the intensity of the high-intensity ultrasound beam (100).

Description

Technical Field

[0001] This patent application, intended for industrial invention, relates to a method for treating tumor regions with high-intensity focused ultrasound (HIFU) in combination with monitoring of temperature distribution and the actual treatment area. Background Technology

[0002] There are many documents describing the treatment of tumor masses using high-intensity focused ultrasound (HIFU).

[0003] One of the main problems during HIFU treatment is determining the actual spatial temperature distribution in real time during the treatment.

[0004] US2015005634 describes an example of temperature monitoring by analyzing ultrasound signals reflected from tissue. Here, a method is described that utilizes changes in acoustic attenuation in tissue while the temperature is increased, and measures the temperature as a response to a high-temperature pulse by detecting temperature changes in the harmonics of the ultrasound signals reflected from tissue based on this effect.

[0005] However, in order to quantify the changes in harmonic parameters with temperature, the method requires calibration of the virtual tissue portion (model).

[0006] Clearly, the model used to study this problem (i) does not allow for consideration of heat diffusion phenomena related to body fluid circulation, and (ii) only partially approximates the true tissue characteristics because tissues in different body parts behave differently, and in the case of the same body part of interest, especially with reference to actual acoustic heating, the tissues of different subjects behave differently.

[0007] Technical issues

[0008] Other embodiments of non-invasive temperature measurement methods are described in US2020237234, US2019142513, US2019262074, and WO2019173138, but none of these embodiments solve the technical problem of measuring the spatial distribution of temperature by simply taking into account the specific characteristics of the tissue receiving HIFU treatment; all of these are performed in real time using unique ultrasound probes.

[0009] More generally, to the knowledge of the inventors, some problems related to the use of ultrasound signals for the diagnosis and treatment of tumors in various organs of the human body remain unresolved.

[0010] In fact, embodiments that allow the following processes to be performed using a unique ultrasound probe are unknown: (i) individualizing a tumor mass; (ii) verifying the correct positioning of the probe relative to the tumor mass; (iii) treating the tumor mass with HIFU; and (iv) verifying the extent of the actual treated area by real-time temperature monitoring. Summary of the Invention

[0011] Therefore, the object of the present invention is to provide a method for treating tumor masses that allows the following processes to be performed using a unique ultrasound probe: (i) personalizing the tumor mass; (ii) verifying the correct positioning of the probe relative to the tumor mass; (iii) treating the tumor mass with HIFU; and (iv) verifying the extension of the area actually treated by real-time temperature monitoring.

[0012] More specifically, the object of the present invention is to provide an ultrasound device and method that allows the measurement of the spatial distribution of temperature by simply taking into account the specific characteristics of the tissue receiving HIFU treatment (in particular the actual acoustic heating rate), all of which is done in real time using a unique ultrasound probe. Attached Figure Description

[0013] According to the reference appendix Figure 1 These and other advantages will become apparent from the detailed description of the invention in Figure 6. Figure 1 The image shown is an example of an ultrasound probe (1) located on the abdomen of a patient (2), which is only one application of the invention; Figure 2 The diagram shows the temperature change over time at the focal region after a HIFU treatment and operation cycle using the device according to the present invention; Figures 3-5 The present invention illustrates an example scheme of a method for treatment via HIFU according to the present invention; Figure 6a The spectrum of an organization without localized boiling and / or cavitation is shown in the figure; Figure 6b The spectrum of the tissue in which local boiling and / or cavitation are taking place is shown. Detailed Implementation

[0014] First of all, in the context of this patent application, "raw ultrasound signal" or "radio frequency ultrasound signal" means an ultrasound signal emitted by a probe and reflected by the human body to the same probe before it is processed in order to obtain an ultrasound image; however, unless otherwise specified, "ultrasound image" means a B-mode type ultrasound image obtained along the propagation plane of the ultrasound beam emitted by the probe.

[0015] However, it should be specified that "the original ultrasound signal corresponding to the defined ROI" means a portion of the original ultrasound signal that, after appropriate processing, produces an ultrasound image associated with the region of interest (ROI).

[0016] In fact, it is well known that because signals reflected from deeper tissues take longer to reach the probe after being reflected, the correlation between the position of each pixel in an ultrasound image and the ultrasound signal is implemented as a function of the time interval between ultrasound pulse emission and relative echo reception (the reflected signal).

[0017] Therefore, regardless of the nature of possible subsequent processing, in order to isolate the original ultrasound signal portion that produces a defined segment in the ultrasound image, the segmentation of the "original ultrasound signal corresponding to the defined ROI" occurs in the time domain.

[0018] However, unless otherwise specified, the ultrasonic probe used, as is well known in the prior art, refers to a probe comprising an array of piezoelectric transducers or CMUTs configured to emit multiple ultrasonic signals arranged side-by-side, such that a vertical line (“line of sight”) of the ultrasonic image corresponds to each signal, and the components of the side-by-side lines allow for the reconstruction of an ultrasonic image. For the sake of brevity and clarity, the processing performed on the ultrasonic signal is specified with reference to a single ultrasonic signal. It is evident, even in the absence of explicit specification, that all processing can be readily applied to multiple raw ultrasonic signals, each received by one of the piezoelectric transducers included in the ultrasonic probe.

[0019] However, the definition of a “point” for the original signal (radio frequency ultrasound signal) refers to the value of the original signal in a single sampling point: in a 20 MHz sampling, as a pure example, 20,000 points per millisecond of the acquired signal are obtained.

[0020] It is also specified that all the processing described below is performed by an echo recording device having at least an ultrasonic probe comprising an array of piezoelectric transducers or CMUTs and a suitable guiding device for the probe, a computing device for processing signals configured to generate signals transmitted through the probe and analyze signals received by the probe to obtain ultrasonic images, and a user interaction device including a graphical interface and control devices such as, for example, a keyboard and / or pointer devices.

[0021] The equipment used includes HIFU ultrasound probes of the type known in the prior art. Preferably, the probe includes an array of piezoelectric transducers or CMUTs configured to transmit and receive ultrasound signals of frequencies and intensities useful for ultrasound imaging, and an array of piezoelectric transducers configured to transmit high-intensity focused ultrasound signals.

[0022] These devices, as a whole, are known in the prior art and are commonly used in ultrasound technology. However, the ultrasound device specified for implementing the methods described below is configured to process the raw ultrasound signal (radio frequency ultrasound signal) for determining an ultrasound image, but also to store the raw ultrasound signal for implementing the following processing: a function not available in commercially available ultrasound imaging devices.

[0023] As previously stated, the problem addressed by this invention is to provide a method for treating tumor masses, which allows for the use of a unique ultrasound probe:

[0024] (i) Personalized tumor mass;

[0025] (ii) Define the area to be treated with HIFU;

[0026] (iii) Verify the correct positioning of the probe relative to the tumor mass used for HIFU treatment;

[0027] (iv) Treatment of tumor masses via HIFU;

[0028] (v) Verify the extent of the actual treatment area.

[0029] Tumor mass personalization can be implemented through automated organization classification methods or through manual personalization by physicians (i).

[0030] In addition to the buffer zone that may be further extended as determined by the physician, the definition of the area to be treated in point (ii) is presented to the physician as the area identified as a tumor. Clearly, the definition of this area can also be defined by the physician and highlighted on the ultrasound image via appropriate commands set on the echocardiography device.

[0031] It is well known that the effectiveness of HIFU treatment (positive if the treatment is applied to a tumor mass, and negative if the treatment is applied to healthy tissue) is related to the temperature reached by the tissue after treatment; therefore, there is a need for means to measure the average temperature reached by the tissue treated during treatment.

[0032] In fact, the key goal of all ablation therapy is to bring the temperature to and maintain it at 60–100°C throughout the entire volume of the tissue to be treated in order to induce coagulative necrosis.

[0033] It is said that in existing treatment systems, the temperature reached cannot be reliably assessed as a function of treatment time because the response to ultrasound penetration depends on the specific tissue under consideration and varies with different parts of the body and, in the case of the same site, with different patients.

[0034] In other words, the physical entity that provides acoustic heating to each tissue in response to HIFU treatment is not yet fully known a priori.

[0035] Conversely, the method according to the invention allows for monitoring of the actual temperature distribution in the ROI in a non-invasive manner and through unique ultrasound signal analysis throughout the entire duration of HIFU treatment.

[0036] exist Figure 3 The diagram shows a method of placing the probe (1) on the skin of a patient (2) by inserting a coupling gel (12).

[0037] exist Figure 3 The anatomical parts are deliberately omitted to imply that the method can be applied to various parts of the human body depending on the tissue or organ to be treated with HIFU.

[0038] It must be specified that, for simplicity, we will refer to the focal point (11) of the HIFU beam in the following text. This term means the center of the focusing volume. The focusing volume of the HIFU beam can be plotted in a two-dimensional ultrasound image by the focusing region. The focal point (11) shown below is the center of this focusing region.

[0039] It can be observed that probe (1) is configured as follows:

[0040] (i) In order to realize an ultrasound image (14) containing a region of interest (15), ultrasound pulses (200) are transmitted and received.

[0041] (ii) A high-intensity focused ultrasound beam (100) with its emission focus located at point (11) on the propagation axis (13) of the ultrasound beam.

[0042] (iii) Receive ultrasound signals reflected and / or emitted by the patient’s tissues after HIFU treatment.

[0043] Conveniently, the probe can be configured to use an array of both unique piezoelectric transducers or CMUT transducers to acquire ultrasound images and clearly detect ultrasound signals reflected and / or emitted by the patient's tissues at discrete times after HIFU treatment. Alternatively, the probe may comprise two arrays of transducers, one dedicated to HIFU treatment and the other dedicated to acquiring signals for ultrasound imaging.

[0044] In other words, the device is configured to implement the following loop:

[0045] - HIFU treatment is performed by emitting a high-intensity focused ultrasound beam (100).

[0046] - During the interruption between the emission of two focused ultrasound beams in HIFU treatment, a broadband ultrasound signal (200) is emitted and the reflected ultrasound signal is acquired.

[0047] For each reflected raw ultrasound signal, the device is also configured to calculate the spectrum (200s).

[0048] exist Figure 2 The figure shows a time series of high-intensity pulses (100, 101, 102) alternating with low-intensity pulses (200, 201, 202).

[0049] It is important to note how the temperature rises during each HIFU cycle; therefore, subsequent low-intensity pulses are applied to the tissue as the temperature gradually increases.

[0050] Figure 6 schematically shows the shape of the spectrum of the reflected signal in response to a low-intensity pulse for a temperature with no local boiling / cavitation (200s) and a temperature with local boiling / cavitation (202s) in progress.

[0051] Figure 3 To illustrate:

[0052] a) Areas that must be treated with HIFU (16);

[0053] b) Anatomical landmarks (P) identified within ultrasound images.

[0054] Figure 3 Two frames of reference are also shown:

[0055] c) A first Cartesian reference frame (x, y), where the coordinate x identifies the propagation line associated with a specific piezoelectric transducer or CMUT transducer in the array of piezoelectric transducers or CMUT transducers contained in the probe (1), and the coordinate y identifies the depth at which the point is located.

[0056] d) A polar coordinate system (r, z) originating from the focal point (11) of the HIFU ultrasound beam and whose z-axis coincides with the emission axis of the ultrasound pulse from the probe (1).

[0057] Therefore, in the ultrasound image plane, a second coordinate system (X, Y) originating from the marker point P can be defined. This second coordinate system (X, Y) is fixed on the patient's body, while the first two coordinate systems are integrated with the probe (1). It is clear that each point of the ROI (15) can be identified in each of the three coordinate systems mentioned, and each point can be identified in each of the three coordinate systems mentioned by means of a coordinate transformation having a formula known in the prior art.

[0058] After defining the coordinate system, assuming that the ultrasound probe (1) is still in a static position, the method for monitoring the temperature distribution after HIFU treatment can be determined first.

[0059] Therefore, assuming the initial temperature distribution allocated within the ROI, the temporal temperature change at each point in the ROI after HIFU treatment can be expressed by the heating-diffusion equation:

[0060] (1)

[0061] in:

[0062] K is the thermal diffusivity [m² / s];

[0063] I0(r, z) is the normalized profile of the spatial distribution of acoustic signal intensity, i.e., a matrix of values ​​between 0 and 1, which defines the spatial distribution of the intensity of the signal emitted by the probe in the reference frame (r, z).

[0064] Q is the actual acoustic heating rate, a scalar expressed in °C / s that correlates probe emission with actual tissue heating under specific conditions.

[0065] I0(r, z) is a characteristic of the ultrasound probe, and therefore it is known that once the ultrasound probe used is characterized, Q depends on several specific parameters, such as tissue absorption rate and tissue attenuation rate, which vary from patient to patient and from site to site, and are therefore unknown values.

[0066] The ability to accurately and in real-time determine the actual acoustic heating rate Q value for a particular patient allows for the calculation of the spatial and temporal distribution of temperature in the tissue of treatment interest via equation (1), which can be viewed in real-time through the graphical interface of the ultrasound machine, and allows the operator to implement treatment to avoid exceeding the temperature threshold, which is crucial for specific tissues close to the tissue of treatment interest.

[0067] This invention allows for the real-time and unique determination of the acoustic heating rate value Q of the specific tissue object being treated for each patient, and thus the determination of the spatial and temporal distribution of temperature.

[0068] In order to obtain the spatial temperature distribution, the device according to the present invention is configured to perform the following method:

[0069] a) Identify the region of interest (15) within the ultrasound image (14) that provides the area to be treated (16).

[0070] b) Assign an initial temperature distribution, through which temperature values ​​are assigned to each point of the ROI. Preferably, the initial temperature distribution is constant and equal to the patient's body temperature, and therefore typically equal to 37°C.

[0071] c) By holding the probe (1) in a static position, HIFU beams (100) focused on a focal point (11) contained within the ROI are emitted at predetermined time intervals, followed by the emission of broadband ultrasound pulses (200), and ultrasound signals reflected and / or emitted by tissue during the treatment step are detected. Preferably, but not limited to, the predetermined time intervals are between 0.5 seconds and 1 second.

[0072] d) In order to obtain a reference spectrum (200s), in response to the broadband ultrasonic pulse (200), a frequency transformation of the reflected ultrasonic signal is performed.

[0073] e) Iteratively repeat steps c) and d) to obtain the spectrum of each interaction.

[0074] f) Assuming that when the spectrum (202s) detected in response to a broadband ultrasound pulse (202) includes multiple peaks (2021) not provided in the reference spectrum (200s), the temperature at the focal point (11) is equal to a function of the predetermined temperature of the treated tissue,

[0075] Preferably, in the case of aqueous tissue, the predetermined temperature is equal to 100°C. The temperature can be determined during execution by testing tissue portions (models), for which the temperature can be measured directly.

[0076] g) Determine the actual acoustic heating rate Q based on the irradiated signal and the intensity of thermal diffusion.

[0077] Preferably, in order to obtain the Q value, the actual acoustic heating rate is calculated by iteratively solving equation (1);

[0078] h) Using the actual acoustic heating rate value (Q) determined at point g), the actual temperature distribution is obtained by calculating the temperature spatial distribution at the end of each time interval during which the tissue receives HIFU in steps d) to f) starting from the temperature spatial distribution assigned at point c) and through the heating diffusion equation.

[0079] In this way, the actual heating rate value Q specific to the treated tissue is determined, as well as the starting temperature distribution for the next treatment step.

[0080] In the first embodiment, the peak value can be personalized by implementing the next step for each iteration (2021):

[0081] f.1) Subtract the reference spectrum (200s) from the spectrum (202s) obtained after each HIFU treatment.

[0082] f.2) Personalize all frequencies (f1, f2, f3) where the difference between two spectra (202s, 200s) exceeds a predetermined threshold (e.g., 5dB).

[0083] f.3) If the difference between the spectra is lower than a second predetermined threshold (e.g., 3 dB), it is at least lower than the frequency (f1). The frequency of ) and at least higher than the frequency (f1) The frequency of ) is then classified into the frequency (f1) that was personalized as "peak" in the previous step.

[0084] Furthermore, preferably, in order to classify the frequency (f1) as a peak, the lower ( ) and higher ( The difference or ratio between frequencies is lower than a predetermined amount, thus introducing the test condition for peak amplitude.

[0085] It should be specified that the 100°C temperature at which a significant change in spectral shape occurs is reasonable, as this value is a good assessment of the temperature at which local boiling / cavitation may occur.

[0086] However, the entire operation was carried out with the equipment stationary and the HIFU beam continuously focused on a unique point within the ROI.

[0087] This means that only a very small area (ideally a point) of the tissue within the ROI (preferably at its geometric center) reaches a temperature of 100°C, while the entire surrounding volume reaches a lower temperature, thus ensuring the safety of the treatment.

[0088] The device is also configured to calculate multiple parameters relating to the shape of the spectrum of the original ultrasound signal reflected in response to each interruption of the transmission of the broadband ultrasound signal emitted during the transmission of the two focused ultrasound beams in HIFU treatment (particularly the portion of the original signal corresponding to the propagation path of the ultrasound signal including the focal point).

[0089] Therefore, after determining the temperature time distribution, it is possible to correlate the corresponding focal temperature with each calculated spectrum (200s, 202s).

[0090] Therefore, HIFU treatment can continue at other local points within the treatment area.

[0091] In this case, the device is configured to measure the temperature at the new position of the focus (1) relative to the probe via the following process:

[0092] - Calculate the spectrum of the original ultrasound signal reflected in response to the broadband ultrasound signal emitted during each interruption between the two focused ultrasound beams emitted in response to HIFU treatment, and therefore,

[0093] - Calculate the correlation coefficient of each spectrum associated with each temperature value.

[0094] Assume that the temperature value with a higher correlation coefficient for its spectrum is taken as the temperature value at the focal point.

[0095] In another embodiment, the correlation coefficients are provided in descending order, and the average temperature value associated with the highest correlation coefficient (e.g., the 5 highest correlation coefficients) is assumed to be the temperature value.

[0096] The conditions for verification at point f) require verification of whether boiling is observed at the focal point (11). Since the treated tissue is an aqueous medium, it is assumed in this method that boiling begins at approximately 100°C. The presence of boiling not only causes the tissue to reflect HIFU ultrasound pulses according to its own characteristics, but it also has its own ultrasound emission due to the pulses emitted by the formation of water vapor bubbles, which can be detected by spectral analysis. Clearly, the focal point must be located within the area to be treated to avoid damaging healthy tissue.

[0097] Furthermore, it is stipulated that in order to solve equation (1), in steps i) and j), the literature values ​​of the K parameter can be conveniently used, or it can be directly determined by a suitable tissue simulation model.

[0098] Without limiting the purpose of the invention, the K value used is preferably between 1,1E-07 m2 / s and 1,6E-07 m2 / s.

[0099] However, it is stipulated that, assuming boiling occurs first at the primis, the iterative solution of equation (1) at point i) is performed.

[0100] Equation (1) is solved using an attempt to find the value of Q. The method involves applying the initial temperature distribution from the start of treatment at time t=0 to the time t=t when boiling is detected by spectral analysis. boil Calculate the temperature distribution over all time intervals between t=t. Then, depending on the time interval at t=t... boil The Q value is modified based on the fact that the calculated temperature value at the focal point is higher or lower than 100°C, and the process is repeated until the difference between the calculated value and 100°C is lower than a predetermined threshold, such as 1°C.

[0101] like Figure 4 As shown, the indications related to the calculated temperature distribution can be graphically reproduced through a series of isotherms (17), which are graphically overlapped with the extension of the area to be treated, providing the operator with immediate and efficient feedback.

[0102] Furthermore, also with probe displacement, the proposed method allows for verification of the actual temperature distribution within the treatment area. For example... Figure 5 As shown, in fact, after the probe (1) is displaced, the position of the focal point (11) changes within the treatment area (16).

[0103] However, in the new ultrasound images ( The new location of the marker point (P) on the probe allows for the correct localization of the temperature spatial distribution values ​​calculated at the previous probe location, since their coordinates (X, Y) in the coordinate system originating from the marker point have not changed.

[0104] Therefore, in the method according to the invention, after each update of the temperature spatial distribution, which is conveniently implemented in the system (x, y) integrated with the ultrasonic probe, the temperature spatial distribution is transformed in the system (X, Y) originating from and integrated with the marker point.

[0105] After the probe is displaced, the reverse operation is performed by re-transforming the temperature spatial distribution from a system integrated with the marker point to a system integrated with the ultrasonic probe.

Claims

1. An ultrasound device configured to implement HIFU treatment and to detect in real time the temperature distribution in the treated area during HIFU treatment, said device comprising: - an ultrasound probe comprising at least an array of piezoelectric transducers or CMUT transducers; - guiding means of said ultrasound probe; - computing means configured to receive and store raw ultrasound signals reflected by a tissue and acquired by each of said piezoelectric transducers or CMUT transducers, to process the reflected raw ultrasound signals in order to generate ultrasound images and to implement other processing of said raw ultrasound signals reflected by said tissue, characterized in that a computer program configured to implement a method for determining the actual acoustic heating rate of a tissue is loaded on said computing means, said method comprising the following steps: a) identifying, within an ultrasound image (14), a region of interest ROI (15) in which a region to be treated (16) is provided, b) assigning a starting temperature distribution by which a temperature value is assigned to each point of the ROI, c) emitting, at predetermined time intervals, a high intensity ultrasound beam (100) focused on a focal point (11) contained in said ROI, followed by the emission of a first wideband ultrasound pulse (200) and the detection of ultrasound signals reflected and / or emitted by the treated tissue, said method further comprising the following steps: d) implementing, in response to said first wideband ultrasound pulse (200), a frequency transform of said reflected ultrasound signals in order to obtain a reference spectrum, e) iteratively repeating steps c) and d) so as to obtain a spectrum for each iteration, f) assuming that when the spectrum detected in response to a second wideband ultrasound pulse (202) comprises a number of peaks (2021) not provided in the reference spectrum, the temperature at the focal point (11) is equal to a predetermined temperature and a function of the intensity of the high intensity ultrasound beam (100), g) determining the actual acoustic heating rate Q from said predetermined temperature and the intensity of said high intensity ultrasound beam (100), and said device being configured to associate the respective focal point temperature with each spectrum calculated after the emission of each high intensity ultrasound beam (100).

2. The device according to claim 1, configured to measure the temperature distribution of the tissue receiving HIFU treatment at the focal point (11) with respect to the new position of said probe by the following procedure: - calculating the spectrum of the raw ultrasound signals reflected in response to the wideband ultrasound signals emitted during each interruption between the emission of two focused ultrasound beams of the HIFU treatment, - calculating the correlation coefficient with each spectrum associated with each temperature value, - assuming as the temperature value of the tissue at the focal point (11) the temperature value for which the correlation coefficient is highest for said spectrum.

3. The apparatus of claim 2, wherein, said device being configured to provide said correlation coefficients in descending order and to assume as the temperature value at the focal point (11) the average temperature value associated with the highest correlation coefficient, wherein said highest correlation coefficient is 5.

4. The apparatus of any of the preceding claims, wherein, said predetermined temperature is equal to 100°C.

5. The apparatus of claim 1, wherein, the temperature is determined during execution by a test on a portion of tissue for which the temperature can be directly measured.

6. The apparatus of claim 1 or 2, wherein, The actual acoustic heating rate is calculated by iteratively solving the heat diffusion equation with the temperature distribution assumed to be assigned at step b) as a starting condition.

7. The apparatus of claim 1 or 2, wherein, The peaks (2021) are personalized by implementing the following steps for each iteration: f.1) subtracting the reference spectrum from the spectrum obtained after each HIFU treatment, f.2) personalizing all frequencies (fl, f2, f3) for which the difference between the reference spectrum and the spectrum is higher than a predetermined threshold, f.3) classifying the frequency (fl) if there are frequencies (fl', fl") lower and higher than the frequency (fl) which have been personalized as "peaks" in the previous step for which the difference between the spectrum is lower than a second predetermined threshold.

8. The apparatus of claim 7, wherein, Further verifying that the difference or ratio between the frequency (fl') lower than the frequency (fl) and the frequency (fl") higher than the frequency (fl) is lower than a predetermined amount before classifying the frequency (fl) as a peak.

9. The device of claim 1 or 2, configured to display the temperature distribution of the tissue through a graphical user interface, through a series of isotherm curves (17) graphically overlaid on the ultrasound image with the extension of the region to be treated.

10. The device of claim 1 or 2, further configured to: - identify an anatomical marker point (P) within the ultrasound image (14), thereby identifying its position, - define a reference system (X, Y) integral with the anatomical marker point (P), - assign to each point of the ROI defining the temperature distribution the value of the coordinates in the reference system (X, Y) integral with the marker point (P), - displace the probe (1) in a new position in which the focal point is still contained within the region to be treated (16) and the marker point (P) is visible in a new ultrasound image (14') obtained by the probe (1) in the new position, - personalize the position of the ROI (15) and of the marker point (P) on the new ultrasound image (14'), - assign to each point of the ROI defining the temperature distribution the value of the coordinates in the reference system (x, y) integral with the probe, - view the temperature distribution overlaid with the new ultrasound image.

Images