WO2011144760A1

WO2011144760A1 - The system for suppression of hot spot regions in microwave heating

Info

Publication number: WO2011144760A1
Application number: PCT/EP2011/058363
Authority: WO
Inventors: Hana Trefna; Mikael Persson
Original assignee: Electromagnetic Consulting Sweden Ab
Priority date: 2010-05-21
Filing date: 2011-05-23
Publication date: 2011-11-24

Abstract

Example embodiments are directed towards a system, and corresponding method, for suppressing at least one hot spot region during a selective heating process of an enclosed structure. The method may comprise obtaining virtual electromagnetic propagation signals resulting from a virtual antenna located in a virtual model of the hot spot region. The virtual electromagnetic propagation signals may be time reversed in order to obtain signal characteristics of a real electromagnetic propagation signal. Using the signal characteristics, real electromagnetic propagation signals may be constructed, in combination with the corresponding time reversed signal obtained by placing a virtual antenna in the area of the desired heating, in the virtual model, and applied, through the use of a real life system, to the enclosed structure such that a desired area is selectively heated while an amount of energy absorption in the hot spot region is reduced, wherein the real life system comprises a plurality of real antennas externally surrounding the enclosed structure. Such a system may be used for hyperthermia and the treatment of tumors.

Description

THE SYSTEM FOR SUPPRESSION OF HOT SPOT REGIONS IN MICROWAVE HEATING

TECHNICAL FIELD

The example embodiments disclosed herein are directed towards a system and method for suppressing at least one hot spot region during a selective heating process of an enclosed structure.

BACKGROUND

Cancer is a leading cause of death worldwide, preceded only by cardiovascular diseases. To date, surgery is often the most effective cancer treatment, although radiation and chemotherapy are becoming increasingly effective. Radiation treatment is likely to become even more effective as the techniques for imaging and targeting cancer cells improve.

The degree of success and progress in cancer treatment does not correspond to the large resources invested. For example, the financial costs of cancer treatment in the USA was 72.1 billion dollars in 2004, up from 18.1 billion dollars in 1985, while during the same period, 5-year survival rate for all cancer sites, only increased from 54% to 66%. Cancer is estimated to account for almost 6% of the entire cost for treatment of diseases worldwide. It is increasingly clear that in order to improve the cancer cure-rates, the conventional oncological methods need to be combined with new treatment methods.

The use of heat as a complement to radiation therapy or chemotherapy seems to have potential advantages in cancer treatment. Research has also been performed in the area of microwave heating which provides a non-invasive method of treating tumors. SUMMARY

While microwave heating provides a non-invasive method for treating tumors, such systems are generally complex. Microwave heating systems and associated treatment planning typically require complex mathematical computation, thereby increasing the cost of such systems and reducing the speed at which these systems may operate.

Furthermore, the use of microwave heating also results in undesired hot spot regions in the body. Thus, at least one object of the example embodiments presented herein is to provide an efficient microwave heating system which is capable of suppressing hot spot regions. Some example embodiments may be directed towards a method for suppressing a hot spot region during a selective heating process of an enclosed structure. The method may comprise obtaining a virtual electromagnetic propagation signal that may result from a virtual antenna located in a virtual model of the hot spot region. The method may also comprise time-reversing the virtual electromagnetic propagation signal and obtaining signal characteristics of a real electromagnetic propagation signal. The method may further comprise constructing, in combination with the corresponding time reversed signal obtained by placing a virtual antenna in the area of the desired heating, in the virtual model, and applying the real electromagnetic propagation signal, which may be through the use of a real life system, to the enclosed structure such that a desired area is selectively heated while an amount of energy absorption in the hot spot region is reduced. The real life system may comprise a plurality of real antennas externally surrounding the enclosed structure.

In some example embodiments, the constructing and applying may further comprise applying uncorrelated weighting factors to the real antennas, the uncorrelated weighting factors may be determined as a function of energy absorption in the desired area and energy absorption suppression in the hot spot region.

In some example embodiments, the obtaining may further comprise correlating virtual electromagnetic propagation signals from the hot spot region and at least one other hot spot region with respect to phase and amplitude.

In some example embodiments, the constructing and applying may further comprise applying correlated weighting factors to the real antennas, wherein the correlated weighting factor is determined as a function of energy absorption in the desired area and energy absorption suppression in the hot spot region.

In some example embodiments, the obtaining may further comprise correlating virtual electromagnetic propagation signals from the hot spot region and at least one other hot spot region with respect to amplitude.

In some example embodiments, the constructing and applying may further comprise constructing a plurality of sets of the real electromagnetic propagation signals, wherein the plurality of sets are obtained by different methods of constructing. The method may further comprise applying each of the plurality sets of the real electromagnetic

propagation signals, in distinct heating schemes, in, for example, an alternating fashion.

In some example embodiments, the constructing and applying may further comprise weighting the plurality of real antennas such that the real electromagnetic propagation signals destructively interfere at the hot spot region. In some example embodiments, the weighting may further comprise determining a nulling pattern with the use of adaptive beamforming.

In some example embodiments the method may further comprise measuring a temperature of the hot spot region by determining conductivity and/or permeability values of each real antenna during different time intervals.

In some example embodiments, the selective heating process may be a

hyperthermia process, the desired area may be a tumor, the hot spot region may be healthy tissue, and the enclosed structure may be a human body.

In some example embodiments the applying may further comprise applying the real electromagnetic propagation signal as a pulsed signal comprising different frequencies.

In some example embodiments, the method may also comprise performing the obtaining, time-reversing, constructing, and applying in real time.

Some example embodiments may be directed towards a system for suppressing a hot spot region during a selective heating process of an enclosed structure. The system may comprise an obtaining unit that may be configured to obtain a virtual electromagnetic propagation signal, which may result from a virtual antenna located in a virtual model of the hot spot region. The system may also comprise a time-reversing unit that may be configured to time-reverse the virtual electromagnetic propagation signal and obtain signal characteristics of a real electromagnetic propagation signal. The system may also comprise a signaling unit that may be configured to construct and apply the real electromagnetic propagation signal, for example, through the use of a real life system, to the enclosed structure such that a desired area is selectively heated while an amount of absorption in the hot spot region is suppressed. The real life system may comprise a plurality of real antennas externally surrounding the enclosed structure.

In some example embodiments, the selective heating process may be a

In some example embodiments, the system may be configured to perform any of the method steps discussed above.

Some example embodiments may be directed towards a computer readable storage medium that may be encoded with computer executable instructions, wherein the instructions, when executed by a system for suppressing a hot spot region, may perform any of the method steps discussed above. BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particular description of the example embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the example embodiments.

FIG. 1 is an illustrative example of a selective heating system which may employ some of the example embodiments;

FIG. 2 is a hardware schematic of a selective heating system, according to some of the example embodiments;

FIG. 3 is a flow diagram of example operational steps which may be taken by the system of FIGS. 1 and 2;

FIGS. 4A-4D are system illustrations depicting signal propagation with the use of uncorrelated weighting factors, according to some of the example embodiments;

FIGS. 5A-5C are system illustrations depicting signal propagation with the use of correlation, according to some of the example embodiments; and

FIGS. 6A-6D are system illustrations depicting signal propagation with the use of amplitude correlation, according to some of the example embodiments. DETAILED DESCRIPTION

In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular components, elements, techniques, etc. in order to provide a thorough understanding of the example embodiments. However, it will be apparent to one skilled in the art that the example embodiments may be practiced in other manners that depart from these specific details. In other instances, detailed descriptions of well-known methods and elements are omitted so as not to obscure the description of the example embodiments.

Microwave heating may be used for hyperthermia therapy. Hyperthermia is a type of medical treatment in which body temperature is exposed to high temperatures to damage and kill cancer cells or to make cancer cells more sensitive to the effects of radiation and certain anti-cancer drugs.

Figure 1 provides an example of a typical hyperthermia system 10. The system 10 may comprise a sensor array 1 1 featuring a number of antennas 13 which may be configured to radiate microwave signals. The sensor array 1 1 may be placed around a patient's body part 15 which may be affected with a cancerous tumor 17.

In determining the optimal method of selective heating, calculations for each antenna may be performed. In the example provided by Figure 1 , the sensor array 1 1 features 12 antennas. Thus, 12 separate calculations are performed to determine the appropriate phase and amplitude of antenna which will yield the highest temperature at the appropriate location of the tumor 17. Moderations in the amplitude of the signals propagating from the antennas will affect the resulting temperature; while moderations in the phase will effect the location the signals will impact the patient's body.

During hyperthermia treatment, often undesired hot spot regions 19 may occur. The heating of the hot spot regions 19 may result in the destruction of healthy tissue. Thus, an optimal scheme needs to be found in which the tumor 17 is heated as efficiently as possible, while suppressing the amount of heat to the undesired hot spot regions 19. Such a scheme is typically found through the use of an optimization algorithm. In the example provided by Figure 1 , since there are 12 antennas the optimization algorithm will provide a calculation in the 12th dimensional space. Such a calculation is time consuming and mathematically complex. Thus, a need exists for finding an optimal heating scheme much more efficiently.

Figure 2 illustrates a microwave heating system according to some of the example embodiments presented herein. The microwave heating system of Figure 2 may comprise a virtual component 18 which may provide virtual modeling that may be used in determining an optimal heating scheme. The heating system may also comprise a real component 22 which may provide real electromagnetic propagation signals which may be used on the actual patient. It should be appreciated that the virtual 18 and real 19 system components may be comprised in a single system. Furthermore, it should be appreciated that the virtual 18 and real 22 system components may work simultaneously in order to provide real time results or performance alterations during the hyperthermia treatment.

The virtual 18 and real 22 components may each comprise a memory unit 21 and 29, respectively. The memory units 21 and 29 may be configured to store received and/or transmitted data or heating schemes, and/or executable program instructions. The memory units 21 and 29 may be any suitable type of computer readable memory and may be of volatile and/or non-volatile type. It should be appreciated that the virtual 18 and real 22 components may comprise a single shared memory unit.

The virtual component 18 may also comprise an obtaining unit 25. The obtaining unit 25 may be used for generating virtual electromagnetic propagation signals in the virtual model of the microwave heating system. The virtual component 18 may also comprise a time-reversing unit 27. The time-reversing unit 27 may be configured to time reverse the virtual propagation signals provided by the obtaining unit 25.

The real component 22 may comprise a signaling unit 33. The signaling unit 33 5 may be configured to construct and apply real electromagnetic propagation signals to be used by real antennas on an actual patient. The phase and amplitude of the real electromagnetic propagation signals may be provided with analysis performed by the obtaining 25 and/or time-reversing 27 units. The virtual 18 and real 22 components may also comprise general processing units 23 and 31 , respectively.

10 It should be appreciated that the obtaining unit 25, the time-reversing unit 27, the processing units 23 and 31 , and the signaling unit 33 need not be comprised as separate units. The obtaining unit 25, the time-reversing unit 27, the processing units 23 and 31 , and the signaling unit 33 may be comprised as a single processing unit or any number of computation units. The obtaining unit 25, the time-reversing unit 27, the processing units

15 23 and 31 , and the signaling unit 33 may be any suitable type of computation unit, e.g. a microprocessor, digital signal processor (DSP), field programmable gate array (FPGA), or application specific integrated circuit (ASIC).

Example operations of the microwave heating system of Figure 2 will now be discussed with the use of Figures 3-6D. Figure 3 illustrates a flow diagram illustrating

20 example operations which may be performed by the system of Figure 2. Figures 4A-6D illustrate example system configurations.

In determining an optimal heating scheme, first a virtual model of the treatment scenario may be created. A representation of such a scenario is provided in Figure 4A. As shown in Figure 4A, a virtual model of the portion of the patient 15v affected by the

25 tumor 17v is provided. The model may be compiled with the use of patient specific data and known tissue models. In determining an optimal heating scheme for the removal of the tumor, a virtual antenna 35v may be modeled as being located in the same position as the virtual tumor 17v, as is illustrated in Figure 4B.

An electromagnetic signal propagating from the virtual antenna 35v may also be

30 modeled. The modeled propagated signal represents a reversed optimal heating scheme for the tumor 17v. Specifically, the modeled propagated signal radiates out of the tumor 17v instead of towards the tumor, as would be the case during the actual treatment.

Through the use of time-reversal, the model may also provide propagation signal characteristics for each antenna 13v of an array 1 1 v which may be used by a similar real

35 system to duplicate a reverse signal of the virtual propagation signal provided by the virtual antenna 35v of Figure 4B. Thus, an optimal heating scheme may be determined with the use of one calculation. In contrast, prior art methods for finding an optimum heating scheme require separate calculations for each antenna of an antenna array.

As shown in Figure 4C, the virtual model, obtained through the use of the example embodiments, may also provide the affects on the patient from the array 1 1 v providing the time-reversed signal. As mentioned, some affects may comprise hot spot regions 19v where healthy tissue may be damaged. It should also be appreciated that the example embodiments need not utilize the placement of a virtual model in the tumor in order to obtain the heating affects on the patient. The heating affects on the patient may also be obtained using the optimization methods previously discussed.

An efficient method for determining the suppression or minimization of the hot spot regions is needed. Thus, some example embodiments may comprise obtaining a virtual electromagnetic propagation signal resulting from a virtual antenna 35v located in a virtual model of the hot spot region 19v (36), as is shown in Figure 4D. The obtaining unit 25 may be configured to model the electromagnetic propagation signal. The virtual signal provided by the obtaining unit 25 may represent a reversed modeled signal which may provide the greatest amount of heat to the heat region 19v.

Once the virtual electromagnetic propagation signal has been provided, some example embodiments may comprise time-reversing the virtual electromagnetic propagation signal and obtaining signal characteristics of a real electromagnetic propagation signal that may be applied by a real system (38). The time-reversing unit 27 may be configured to perform the time-reversing of the virtual electromagnetic

propagation signal. Thus, upon time-reversal signal characteristics that may be used by a real system, in real time, may be obtained which represent a heating scheme providing the greatest amount of heat to the heat region 19. It should be appreciated that adjustments, additions, or alterations to any heating schemes may also be performed in real time.

Once the time reversing has been completed, some example embodiments may comprise the constructing and application of the real electromagnetic propagation signal using the signal characteristics of the time-reversed virtual propagation signal (40). The construction and application may be performed by the signaling unit 33. It should be appreciated that there are various example embodiments which may be employed in the construction and application of the real electromagnetic propagation signals. Some of the embodiments will be presented herein below as an example. According to some of the example embodiments, the construction and application of the real electromagnetic propagation signal may comprise applying uncorrelated weighting factors to the real antennas 13. The application of uncorrelated weightings factors may affect the amplitude and phase of the signals provided by each of the real antennas 13. The method of uncorrelated weighting is further explained using the following equation:

where E'" is the total electromagnetic real propagation signal applied by antenna m, E"' is real propagation signal applied by a real antenna m which is determined with use of the original tumor T heating scheme (i.e., the heating scheme obtained by placing the virtual antenna in the virtual tumor 17v), N is the total number of hot spot regions, n is a summation index, w„is the uncorrelated weighting factor of the n^th hot spot region, and j¾" is real propagation signal associated with the n^th hot spot region and propagated by the m^th antenna (i.e., the heating scheme obtained by placing the virtual antenna in the virtual hot spot region 19v). Thus, as shown in equation (1 ), the heating scheme, which provides the greatest temperature to the hot spot regions, may be subtracted from the heating scheme which provides the greatest temperature to the tumor. In order to obtain an optimal heating level of the tumor, the subtraction may be weighted with the use of the uncorrelated weightings.

In deciding the value of the weighting factor to apply, the distance of the hot spot region from the tumor may be taken into account. For example, a larger weighting factor (e.g., close to or equal to one) may be employed if the distance between the hot spot region and tumor is large. Similarly, a smaller weighting factor (e.g. , close to zero) may be employed if the distance between the hot spot region and the tumor is small. The determination of large and small distances may depend on various factors, such as the treatment region, tumor position, and/or frequency of the propagation signals. In short, the weighting factors may be determined as a function of energy absorption in the desired area (e.g., the tumor) and energy absorption suppression in the hot spot region.

Upon the application of the uncorrelated weighting factors to the real antennas 13, the heating scheme will result in the hot spot region experiencing a reduced amount of heat absorption while the tumor region may experience little or not change from the optimal plan provided by the virtual model system (42). In some cases, a plurality of hot spot regions may be discovered with the use of the virtual model system, as illustrated in Figure 5A. If multiple hot spot regions are present, a correlation method may be employed. Accordingly, in some example embodiments the step of obtaining (36) may further comprise cross-correlating virtual electromagnetic propagation signals from each hot spot region (44). The cross-correlation of the obtained virtual electromagnetic propagation signals may have the affect of creating a single representative hot spot region form with a heating scheme may be obtained.

In performing the cross-correlation, virtual propagation signals may be determined by placing virtual antennas 34v and 35v in each hot spot region 19v and 20v, as shown in Figure 5B. The signals may thereafter be time-reversed and then cross-correlated. The cross-correlation may be performed by the obtaining unit 25. Upon cross-correlation, a representative hot spot region 37v may be obtained, as illustrated in Figure 5C.

Thereafter, correlated weighting factors may be applied to the real system antennas in an attempt to heat the tumor while suppressing the amount of heat from the representative hot spot region 37v, which corresponds to hot spot regions 19v and 20v. The cross- correlated heating scheme may be represented by the following equations:

¾ = ¾ * ^₂ (2)

E'" = E:_nK - w_nE^ (3) where represents the total real electromagnetic propagation signal associated with the representative, or correlated, hot spot region 37v at the m^th antenna, E"^ is the time- reversed or real electromagnetic propagation signal associated with the first hot spot region 19v at the m^th antenna, and s,™., is the time-reversed or real electromagnetic propagation signal associated with the second hot spot region 20v at the m^th antenna. E¹" represents the resulting real electromagnetic propagation signal for the final heating scheme at the m^th antenna, Ε'"._μ, represents the real electromagnetic signal propagation from the heating scheme obtained by only taking into account the tumor (i.e. , the heating scheme obtained by placing a virtual antenna in the virtual model of the tumor), and w_n \s the correlated weighting factor.

The correlated weighting factor may be used to adjust the amplitude and phase of the real electromagnetic propagation signals provided by the antenna array 1 1 (46).

Thus, similar to the uncorrelated weighting, the amount of heat absorbed by the hot spot region may be removed or suppressed, while having little impact of the heat absorption occurring in the tumor. It should be appreciated that the correlated weighting factor may be assigned in a similar manner as the uncorrelated weighting factor, as described above.

In some example embodiments, multiple hot spot regions may be correlated solely with respect to amplitude. An example of amplitude correlation is illustrated in Figures 6A-6D. As shown in Figure 6A, virtual modeling may provide an indication of the presence of multiple hot spot regions, for example hot spot regions 19v and 20v. As previously discussed, virtual electromagnetic propagation signals may be obtained from the various hot spot regions using virtual antennas placed within the hot spot region of the virtual model, for example virtual antennas 34v and 35v of Figure 6B (36). Once the virtual propagation signals are obtained, the obtained signals may be time reversed and correlated with respect to amplitude (48). The amplitude based correlation may yield a representative hot spot region 39v, as illustrated in Figure 6C. The amplitude based correlation may be expressed by the following equation:

where A"'_l represents the total amplitude of the correlated or real electromagnetic propagation signal resulting from the correlated representative hot spot region 39v at the m^th antenna, A"^ is the amplitude of the time-reversed or real electromagnetic

propagation signal associated with the first hot spot region 19v from the m^th antenna, and ™, is the amplitude of the time-reversed or real electromagnetic propagation signal associated with the first hot spot region 20v from the m^lh antenna. The resulting amplitude from the correlated representative hot spot region 39v may be utilized in creating a heating scheme.

In some example embodiments, two heating schemes may be employed with the use of amplitude correlation (50). The first heating scheme, illustrated in Figure 6D, may be represented by:

Heating Scheme _ 1 = Α"_η' _κ (5) where A'" , represents the amplitude of the time-reversed or real propagation signal at the m'^h antenna provided by time reversing virtual signals obtained with the use of a virtual antenna placed in the virtual model of tumor 17. The second heating scheme, illustrated by Figure 6C, may be represented by:

Healing _ Scheme _ 2 = A"'.„, + wA^ (6) where w represents the correlated weighting factor proportional to the severity of the hot spot region, and A'_n" represents the total amplitude of the time-reversed or real propagation signal resulting from the correlated representative hot spot region 39v at the m^th antenna.

Using the two heating schemes described above, a treatment method may be provided where the heating schemes are alternatively applied (52). The alternation of the two heating schemes allows for maximum heating of the tumor 17 while suppressing the heating applied to the hot spot regions and/or representative hot spot region. The two sets of data may be compiled by the signaling unit 33. Furthermore, the two sets of data may also utilize the original phase information.

It should be appreciated that the use of amplitude correlated data in obtaining a second heating scheme has been provided merely as an example. Any number of heating schemes may be employed, wherein the heating schemes may be obtained with the use of any of the example embodiments provided herein or any other embodiments which do not depart from the scope of the invention. Furthermore, it should be appreciated that one heating scheme may comprise the heating scheme obtained by placing a virtual antenna inside of the virtual model of the tumor (i.e., a heating scheme which does not account for any hot spot regions).

In determining the duration time spent on each heating scheme, an amount of energy absorption of the tumor and hot spot region may be monitored. The energy absorption may be determined by utilizing the real antennas 13 as sensors. In a sensor configuration, the antennas 13 may be utilized in a time-domain based microwave tomographic imaging procedure. Specifically, the antennas 13 may be configured to measure temperature dependent parameters, for example, conductivity and/or permeability. The measurements may be obtained during a period when propagation signals are not being transmitted.

During a measurement, one antenna may act as a transmitter while the other antennas of the array 1 1 may function as receivers. By comparing the transmitted signal with the signals received at each receiver antenna, the temperature dependent parameters may be obtained. The temperature dependent parameters may be utilized to determine temperature variances at different locations within the treatment area. It should be appreciated that any number of heating schemes may be constructed and utilized for treatment. The use of two heating schemes was merely presented as an example. It should be appreciated that any other means of energy absorption measurement may also be utilized. It should be appreciated while the correlation embodiments described above featured only two hot spot regions, the correlation methods may be employed with any number of hot spot regions. Use of the correlation methods may be beneficial when at least one hot spot region is located in close proximity to the tumor. However, it should be appreciated that the correlation methods discussed above may also be employed for hot spot regions located in greater distances from the tumor.

According to some of the example embodiments, the construction and application of the real electromagnetic propagation signal may comprise determining a nulling propagation signal pattern which may enable the destructive signal interference to occur at the hot spot region location (54). Such a signaling pattern may be determined with the use of adaptive beamforming. The adaptive beamforming may be provided with the use of an algorithm, for example similar to that which is used for in radar detection

applications. Once a nulling pattern has been determined, weighting factors may be applied to the real antennas in order to achieve the desired signaling affect (56).

According to some example embodiments, the real electromagnetic propagation signal may be in the form of a continuous wave or pulses. When utilizing a pulsed signal, the signal may comprise a number of frequencies. Employing a number of different frequencies may be beneficial as signals with different frequencies may provide different affects to the treatment process. As an example, consider a hyperthermia system that may be configured to operate in the range of 200MHz-1 GHz. Signals with higher frequency (e.g., higher than 400MHz) may provide sharper focus, but have a less effect on tumors located deep within the tissue. Comparatively, signals with lower frequencies (e.g., about 400MHz or less) may be more effective with tumors located deep within the tissue, but offer less focusing during treatment. It should be appreciated that the frequency ranges provided are merely examples as the determination of a high and low frequency is dependent on the treated region.

Various methods for the construction and application of the real electromagnetic propagation signals for hot spot region suppression have been discussed. It should be appreciated that all of these methods may be utilized in conjunction with one another. While an example has been provided which includes the use of two heating schemes being applied alternatively, it should be appreciated that any number of heating schemes may be employed. Furthermore, the plurality of heating schemes may obtained using any of the example embodiments discussed herein or any other embodiments which do not depart for the scope of the invention. It should be appreciated as different heating schemes are applied, the undesired hot spot regions will be given an opportunity to cool down, while the heating in the tumor may be continuously applied.

In the examples provided, hot spot regions have been discussed as regions in which large amounts of undesired heating occurs. It should be appreciated that a hot spot region may also comprise a region which is to be protected from heating. Examples of such regions may comprise the spinal cord, major organs, etc.

The example embodiments discussed above have been explained with the use of hyperthermia. However, it should be appreciated that the example embodiments may also be employed for suppressing hot spot regions while selectively heating any enclosed structure.

The above mentioned and described embodiments are only given as examples and should not be limiting to the present invention. Other solutions, uses, objectives, and functions within the scope of the invention as claimed in the below described patent claims should be apparent for the person skilled in the art.

Modifications and other embodiments of the disclosed invention(s) will come to mind to one skilled in the art having the benefit of the teachings present in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention(s) is/are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be comprised within the scope of this disclosure. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purpose of limitation.

It should be noted that the word "comprising" does not exclude the presence of other elements or steps than those listed and the words "a" or "an" preceding an element do not exclude the presence of a plurality of such elements. It should further be noted that any reference signs do not limit the scope of the claims, that the invention may be implemented at least in part by means of both hardware and software, and that several "means", "units" or "devices" may be represented by the same item of hardware.

The various embodiments of the present invention described herein is described in the general context of method steps or processes, which may be implemented in one embodiment by a computer program product, embodied in a computer-readable medium, including computer-executable instructions, such as program code, executed by computers in networked environments. A computer-readable medium may comprise removable and non-removable storage devices including, but not limited to, Read Only Memory (ROM), Random Access Memory (RAM), compact discs (CDs), digital versatile discs (DVD), flash memory, EEPROM, etc. Generally, program modules may comprise routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Computer-executable instructions, associated data structures, and program modules represent examples of program code for executing steps of the methods disclosed herein. Such instructions may be executed by the processing unit, e.g., central processing unit, microcontroller, microprocessor, field programmable gate array, application specific integrated circuit, digital signal processor, etc. The particular sequence of such executable instructions or associated data structures represents examples of corresponding acts for implementing the functions described in such steps or processes.

Claims

IMS

A method for suppressing at least one hot spot region during a selective heating process of an enclosed structure, the method comprising:

obtaining a virtual electromagnetic propagation signal resulting from a virtual antenna located in at least one virtual model of the at least one hot spot region; time-reversing the virtual electromagnetic propagation signal and obtaining signal characteristics of a real electromagnetic propagation signal; and

constructing, with the signal characteristics, and applying the real electromagnetic propagation signal, through the use of a real life system, to the enclosed structure such that a desired area is selectively heated while an amount of energy absorption in the at least one hot spot region is reduced, wherein the real life system comprises a plurality of real antennas externally surrounding the enclosed structure.

2. The method of claim 1 , wherein the constructing and applying further comprises applying uncorrelated weighting factors to the real antennas, the uncorrelated weighting factors being determined as a function of energy absorption in the desired area and energy absorption suppression in the at least one hot spot region.

3. The method of any of claims 1 -2, wherein the obtaining further comprises

correlating virtual electromagnetic propagation signals from the at least one hot spot region and at least one other hot spot region, or a region to be protected from heating, with respect to phase and amplitude.

4. The method of claim 3, wherein the constructing and applying further comprising:

applying correlated weighting factors to the real antennas, wherein the correlated weighting factor is being determined as a function of energy absorption in the desired area and energy absorption suppression in the at least one hot spot region.

5. The method of any of claims 1 -4, wherein the obtaining further comprises

correlating virtual electromagnetic propagation signals from the at least one hot spot region and at least one other hot spot region, or a region to be protected from heating, with respect to amplitude.

6. The method of any of claims 1 -5, wherein the constructing and applying further comprises weighting the plurality of real antennas such that the real electromagnetic propagation signals destructively interfere at the at least one hot spot region.

5 7. The method of claim 6, wherein the weighting further comprises determining a

nulling pattern with the use of adaptive beamforming.

8. The method of any of claims 1-7, the method further comprising measuring a

temperature of the at least one hot spot region by determining conductivity and/or

10 permeability values of each real antenna during different time intervals.

9. The method of any of claims 1 -8, wherein the constructing and applying further comprises:

constructing a plurality of sets of the real electromagnetic propagation signals, 15 wherein the plurality of sets are obtained by different methods of constructing; and applying each of the plurality of sets of the real electromagnetic propagation signals, in distinct heating schemes, in an alternating fashion.

10. The method of any of claims 1 -9, wherein the selective heating process is a

20 hyperthermia process, the desired area is a tumour, the at least one hot spot region is healthy tissue, and the enclosed structure is a human body.

1 1 . The method of any of claims 1 -10, wherein the applying further comprises applying the real electromagnetic propagation signal as a continuous wave or pulsed signal

25 comprising different frequencies.

12. The method of any of claims 1 -1 1 , further comprising performing the obtaining, time- reversing, constructing, and applying in real.

30 13. A system for suppressing at least one hot spot region during a selective heating process of an enclosed structure, the system comprising:

an obtaining unit configured to obtain a virtual electromagnetic propagation signal resulting from a virtual antenna located in a virtual model of the at least one hot spot region; a time-reversing unit configured to time-reverse the virtual electromagnetic propagation signal and obtain signal characteristics of a real electromagnetic propagation signal; and

a signaling unit configured to construct and apply the real electromagnetic propagation signal, through the use of a real life system, to the enclosed structure such that a desired area is selectively heated while an amount of energy absorption in the at least one hot spot region is suppressed, wherein the real life system comprises a plurality of real antennas externally surrounding the enclosed structure.

The system of claim 13, wherein the selective heating process is a hyperthermia process, the desired area is a tumour, the at least one hot spot region is healthy tissue, and the enclosed structure is a human body.

The system of any one of claims 13-14, wherein the system is configured to perform any of the method steps of claims 1 -9, 1 1 and/or 12.

A computer readable storage medium encoded with computer executable instructions, wherein the instructions, when executed by a system for suppressing at least one hot spot region, perform the method of any one of claims 1 -12.