Electromagnetic field applicator array with integral field sensors for implicit correction of mutual coupling and mismatch

[0001] The present invention relates to systems for creating specific electromagnetic field conditions in specific areas in space, or for focusing electromagnetic energy in a dielectric facility with improved control.

[0002] The ability to create specific electromagnetic field conditions is a basic requirement in many medical applications, from imaging to therapy. The present invention applies to both of these disciplines as well as to phased array antenna technology used in communications and detection applications.

[0003] One application of the present invention is to generate specific field conditions at certain locations in the human body to cause hyperthermia.

[0004] The National Cancer Institute of the US National Institutes of Health defines hyperthermia (also called heat therapy or therapeutics) as a type of cancer treatment in which body tissue is exposed to high temperatures (up to 45 ° C). Studies have shown that high temperatures can damage and kill cancer cells, generally with minimal damage to normal tissue. By killing cancer cells and damaging proteins and structures in cells, hyperthermia can cause shrinking of tumors.

[0005] The present invention relates to local hyperthermia, during which heat is delivered to a small area, such as a tumor. It is possible to use various techniques to provide energy to heat the tumor. In the context of the present invention, microwave or radio frequencies may be used to provide heat. Depending on the location of the tumor, there are several approaches to local hyperthermia. In the present case, an external approach is used to treat tumors. Energy is supplied using an applicator. The applicator is made of a number of elements that are located around or near the appropriate area, and the energy is focused on the tumor to increase its temperature, using phased array techniques. Hyperthermia is often used in combination with other types of therapy such as radiation therapy and / or chemotherapy. Hyperthermia is used as part of therapy in many types of cancer, including sarcoma, melanoma, and head and neck cancers, lung, esophagus, breast, bladder, rectum, liver, appendix, cervix and peritoneal lining (mesothelioma).

[0006] The antenna system is a phased antenna made of a number of small (smaller) radiating elements, each with its own power point. Phase antenna systems are electrically controlled, which means that the physical antenna can be stationary, but the array of antennas can be controlled by adjusting the amplitude and phase weighting of each element, so that it is focused towards the given area or in such a way that it allows locating objects in space . Phased systems can also be used to generate specific field conditions at certain locations in space or to concentrate radio frequency energy (FR) in dielectric objects to increase the temperature of a target area inside a dielectric object or patient, or to induce fields or currents in a patient to excite atoms , nerves or other cellular mechanisms.

[0007] The phased system can be used for hyperthermia by focusing RF energy in the patient in such a way that the temperature is increased. When a phased array is used for such a purpose, it is called an applicator because it applies energy to the patient. The phased array or applicator components are powered by a multichannel RF or microwave current source in which the phase and amplitude signals are mobile, so that RF or microwave energy can be concentrated in the target area or tumor. The number of layout elements and the arrangement of these elements relative to the target area determine the quality of focusing that can be obtained.

[0008] An example of RF hyperthermia will be used to illustrate the advantages of the invention. Although many systems for treating hyperthermia tumors have been proposed and used in the past, either alone or in combination with other therapies, there has generally been a lack of consistency and quality in therapy. In local hyperthermia, the most important is the ability to deliver or focus energy from the applicator to the target area, tissue or tumor. The entire target area should be sufficiently warm to achieve satisfactory therapy results. To ensure this, a good electromagnetic applicator and patient-specific models are most preferably used to plan and optimize therapy. This step of accurate prediction of energy deposition (and / or temperature rise) and its optimization for best tumor treatment was not present in hyperthermia systems and contributed to poor results. During the therapy itself, in which RF or microwave power is supplied to the hyperthermia system with amplitudes and excitation phases determined by the therapy plan, the key from the point of view of quality assurance is that the electromagnetic field generated by each element is monitored to determine whether the correct planned therapy.

[0009] Common to all phased antenna systems or hyperthermia applicators is the requirement of a multi-channel source that can generate high-power signals with precisely controlled amplitude and phase to be supplied to individual components generating an electromagnetic field. It is not important for the present invention which method is used to generate these signals.

[0010] Multi-component or phased applicators generally arrange system components around a patient with a water bolus filling the space between the patient and the system to provide surface cooling and for smaller reflections on the patient's surface. All US patents 4672980, 5251645 and 5441532 show typical phased applicators. Each includes elements arranged in a circular arrangement around the patient with individual antenna elements (or pairs of elements in US Patent 4672980) excited by an RF current source with controlled amplitude and phase. None of these systems actually measure the signals being delivered or any reflected power that reduces the effective radiation power. Therefore, these factors increase uncertainty. In field patents US 5251645 and 5441532, field sensors are located in and around the patient's body to measure the total applied field at these points, and it is claimed that using values ​​from these sensors, the excitation of the system can be controlled in such a way that energy is focused on the target . US Patent 4672980 uses a different approach in which temperature catheters are introduced into the patient and the system is controlled to maximize temperature rise in the target area. The disadvantage of both approaches is that the human body is highly inhomogeneous and there is no intuitive relationship between the excitation system used and the energy deposit model. Basically, these approaches assume that knowledge of the field and temperature at several points is a substitute for knowledge of radiation from each element of the system.

[0011] In the literature, Paulides et al., 2007, describe a typical prior art system in which the module and phase of the signals used for each applicator element are measured together with the reflected power, so that the controlled values ​​can be adjusted in such a way that the signals used in the light of reflections are as expected. When used with proper therapy planning, this system has the potential to perform satisfactorily. However, the system is based on a computer simulation model that fully defines the actual device, and there are no means available to fully account for changes in patient records in the applicator range for the impedance of the element and the element of mutual coupling of excitation.

[0012] In the broader context of phased circuits for other applications, US Patent 5867123 uses the technique of stimulating single elements and observing signals received by neighboring elements for embedded testing and failure analysis. Fulton and Chappell, 2009, review various calibration techniques for phased systems and argue that systems should be calibrated in an anechoic environment to determine the coupling matrix to allow compensation of reciprocal coupling in the system. In addition, it should be noted that internal electronic circuits can be implemented to monitor any change relative to the initial calibrated coupling or transfer path reinforcements, allowing adjustments to be made. Lee et al., 1992/3, introduced a transmission line (microline) to the antenna panel for coupling with each element so that the transmission and reception functions of the electronic circuits could be tested. The transmission line receives energy from all elements or introduces energy to all elements of the system simultaneously.

[0013] US 6208903 discloses a microwave applicator for the treatment of hyperthermia. In one embodiment, the device includes a plurality of circular segmented elements of a microstrip antenna, each of which includes a coaxial power supply in the geometrical center of the segment and a poorly coupled coaxial connector designed to sample the effective field under the segment. This system is limited to the generation of electromagnetic surface waves in tissue layers directly below the applicator. The signal from each of the individual sampling connections is sequentially delivered to the phase-amplitude comparator using a single-pole microwave multi-stage switch. However, such coaxial sampling connections act as antennas with which signals can be coupled directly and are therefore subject to signal contamination by the fields of adjacent antenna elements. In addition, the use of one phase-amplitude comparator suggests quite large distances over which individual signals are conducted.

[0014] WO 2008/068485 a device disclosed for treating skin tissue with microwave radiation, aimed at providing a constant field strength on the treated surface, the treatment depth being limited to less than 5 mm. The phase of the individual components of the system is controlled only for the purpose of impedance matching, and not for handling any coupling of antenna elements.

[0015] US 4885589 discloses a radar array of phased circuits in which remotely placed transmit and receive modules associated with each grid element are connected to centrally located radar transmitter / receiver means using optical fibers, in particular to provide immunity to exposure to electromagnetic pulses.

[0016] US2008 / 0297402 discloses beveled systems and means for validating system functionality and / or calibration. A system element or additional element is used to compare previous measurements when it is used either as a transmitter or as a receiver, while the rest of the system elements are configured as either receivers or as transmitters, respectively, and measures the characteristic response. The principle of operation is based only on the transmitting signals delivered to the system element (s) or received at each receiving connection (measurement based on the connection), which do not reflect the total excitation of the element.

[0017] US2004 / 0061644 discloses integrating probes into a system to enable its calibration. The probes are radiation-coupled to many components of the system or the system element is radiation-coupled to multiple probes, depending on whether it is transmitting or receiving calibration.

[0018] WO2007 / 146175 focuses on calibrating the paths of transmitting and / or receiving beveled systems and does not apply to radiation components of the system.

Summary of the Invention [0019] Experience with therapies and the planning of radio frequency hyperthermia therapies, and knowledge of the nature defects of the systems discussed above have led to important modifications made to devices and control systems. These modifications greatly improve confidence and consistency in the field excitation provided. The present invention improves consistency by providing guaranteed field excitation from each antenna element of the system in the presence of reciprocal coupling, mismatches and reflections, and therefore the uncertainty is reduced. In addition, the invention makes it possible to more accurately determine the coupling matrix than when using impedance or scattering matrix measurements, enabling a form of homogeneous self-calibration that can be performed for each patient undergoing therapy. The key to obtaining a guaranteed field excitation determined by the treatment plan is the conclusion of sensors integrated in the antenna elements themselves, which measure the phase and amplitude of the current flowing in the metal elements or the field in the element based on the gaps. These sensors provide a proportional measure of excitation in the absence of mutual coupling or reflection. However, it is not necessary to take into account the mismatch or phase differences in the connection cables, because the actual current (or field) in the antenna is measured (measured). With mutual couplings and reflections, the sensors measure the sum of all excitations, regardless of their origin, and for this reason they can determine the field actually emitted. In turn, the excitation of each element and the measurement of the current (or field) in the excited antenna together with the coupled excitation of all other antennas will allow direct determination of the coupling matrix of the system.

[0020] US Patent 5867123 discussed above also excites each item in turn, but this is not used as a way to achieve self-calibration; even if that were the case, mismatching the elements would increase uncertainty. Lee et al., 1992/3, contains transmission lines introduced into the antenna panel, but the antenna detection capability is not individually identifiable, and no motivation or ability to determine antenna currents (or fields) due to either direct excitation or reciprocally excited . Hence, this system is used as a diagnostic tool rather than to control field excitation.

[0021] The present invention comprises a system of elements generating an electromagnetic field and in each of them integrates a sensor for measuring the phase and amplitude of the current flowing in a metal element (antenna or coil) or a field in a slotted element connected to a measuring device to enable measurement of both phase and amplitude of electrical signals from each of the sensors. In addition, because the signal received by each sensor is directly proportional to the phase and amplitude of the current or field in the associated electromagnetic field generating element, where the current or field is the total current or field whose amplitude and phase is the sum of both excitation supplied (from the source of radio frequency power) ) as well as secondary from mutual coupling and mismatch, hence the measured value represents ideal excitation in the absence of mutual coupling and mismatch. The invention therefore uses built-in sensors in the antenna to add additional functionality, e.g., direct excitation of each system element by a multi-channel radio or microwave power source with individually controlled amplitude and phase can be modified using a feedback controller, so that the total excitation measured by the built-in sensor (current in the metal element or field in the slot antenna), is the ideal excitation of the system, without coupling or mismatch, so that the overlap of the fields generated by each electromagnetic field generating element produces a specific distribution of the electromagnetic field in a defined volume or area. Implicit compensation of mutual coupling and mismatch without explicit knowledge, and calculations based on mutual coupling and mismatch called the coupling matrix, so that changes in the coupling matrix due to the presence of objects or their changes are naturally taken into account. In addition, by using the sequential excitation of each element, the invention can directly determine the exact matrix of mutual coupling of the system, even in the presence of changes in the source impedance and undefined cable lengths that can be useful in determining the initial excitation of the system of elements generating the electromagnetic field, so that feedback can get a pre-determined ideal system excitation.

Brief description of the attached drawings [0022]

Fig. 1 shows two adjacent components of the system (slots with a cavity in the back), one illustrating the incorporation of one potential implementation of the present invention.

Fig. 1a shows two adjacent components of the system (slots with a cavity in the back) with the cavity cover of one element removed.

Fig. 2 shows the entire phased array of the RF hyperthermia applicator without details of the small sensor elements.

Fig. 3 a multi-channel radio frequency power source.

Fig. 4 single-channel measuring device.

Fig. 5 shows the entire multi-channel transmitter system with phase and amplitude control and phase / amplitude detectors connected by a measuring rail to measurement and computer controllers.

Fig. 6 shows a radio frequency hyperthermia system in which a water bolus is shown to be placed between system components and the patient to reduce reflections and to facilitate surface cooling.

Technical description with reference to the accompanying drawings [0023] The invention relates to a system formed of five integral parts, the new features of some of these parts and the integration and use of them as a whole creates innovation. The first integral part are the elements generating the electromagnetic field, Fig. 1, which are arranged in a system of any geometry, Fig. 2. The arrangement of elements is connected to a source of radio frequency power, Fig. 3, which has a number of channels with independently computer-controlled phases and amplitudes. Integrated with each electromagnetic field generating element is a current (or field) detection element that produces an electrical output signal proportional to the generated electromagnetic field, each electrical signal being measured by a measuring device that measures both amplitude and phase, Fig. 4. Measurement data is sent via the measuring bus to the measurement controller. The control computer uses measurement data to control the radio frequency power source in such a way that the generated electromagnetic fields are required fields, the entire system and connections are shown in Fig. 5.

[0024] An illustrative application of the invention is the phased applicator system, Fig. 5, which can generate field conditions at certain locations in space or focus RF energy in dielectric objects. Direct measurement of currents or fields in metal, slit or coil elements 26 allows direct quantification of emitted or reactive fields generated by electromagnetic field generating elements. In particular, the invention provides the ability to covertly compensate for interference in the electromagnetic field generated due to mutual coupling and mismatch in the applicator system 19, without explicit coupling matrix measurements and the use of excitation correction from an 18 RF power source. The direct relationship between the current in the metal element (or field in the slotted element), the electrical output signal from the element 4 sensors and the emitted or reactive field can be determined in an experimental or numerical way.

[0025] The object of the invention is to provide improved means for determining the actual emitted or reactive near field of each element 26, Fig. 1, in an arrangement 19 of electromagnetic field generating elements for radio frequency hyperthermia applications, Fig. 2 and 6, wherein the direct load due to the patient, dielectric objects and other system components changes the coupling between and mismatch observed at the input connections of the 3 elements 26, or when the source impedance of the radio frequency source channels 11 is not well defined.

[0026] Another object of the invention is to provide higher levels of certainty that the actual excitation of the system from a multi-channel 18 RF power source is a planned excitation that provides better control of the quality of the field distribution generated by the system of 19 electromagnetic field generating elements. To this end, the generated electromagnetic field is measured, Fig. 4, using a measuring device, such as a vector voltmeter or a phase / quadrature demodulator with sufficient sensitivity. Additional circuits may be added as shown in Fig. 4, to allow self-calibration of the amplitude detectors and the phase facilitated by not only spreading by means of a local oscillator rail, but also the phase reference, which can be switched to the input to enable calibration and / or remove phase ambiguity, further reducing uncertainty.

[0027] In addition, the invention provides a new paradigm for the correction of reciprocal coupling, by implicitly measuring the generated electromagnetic field including reciprocal coupling and mismatch. Hence, actual and planned excitations have small deviations, in particular in the presence of variations that cannot be modeled when planning the procedure.

[0028] Furthermore, the invention does not limit the geometry or arrangement of the components 26 of the applicator system, Fig. 2, around or near the target area and can be used in any generic array of electromagnetic field generating elements 19. In particular, there is no limit to the proximity of dielectric objects, such as patients or other reciprocal joins or attributes that modify the matching of elements.

[0029] Although integrated current or field sensors 4, Fig. 1, implicitly include mismatch and reciprocal coupling, the invention allows the coupling matrix (describing the mismatch and reciprocal coupling) of the electromagnetic field generating applicator system to be directly determined with greater accuracy than standard techniques for calculating the coupling matrix from S parameters, with convenient no need to disconnect system 19 of the applicator from the radio frequency power source 19, Fig. 5 and connecting to a network analyzer. By excitation of each element 2 in turn, using a radio frequency power source and the measurements of necessary currents (or fields) 5 in all elements 2 using a measuring device 18, the coupling matrix can be determined more accurately, because the ideal output impedances of each amplifier 10 and the length of the connecting wires between the output 11 of the RF power source and the electromagnetic field generating element 3 are already naturally considered.

[0030] The invention, providing this very important information about the emitted or reactive field from each element 26 also provides the ability to detect which output channel 11 from the multi-channel power source 18 radio frequencies has been connected to which element 26 generating the electromagnetic field in the system 19 and thus eliminates the possibility of incorrect connection and the likelihood of completely incorrect therapy.

[0031] By integrating the measuring device 20 with each element 26, it becomes possible to apply individual identification of each electromagnetic field generating element enabling the allocation of individual calibrations of the measuring device-element combination. Hence, calibration data can be assigned to the right item for quality control, easy operation and safety. The calibration function can therefore provide accredited calibration that can be assigned to the item. Enabling the modularity of the entire system with interchangeable elements 26 and providing the "plug and play" function.

Description of the Preferred Embodiment [0032] The preferred embodiment can be described in the context of the RF hyperthermia applicator system, Fig. 5. This hyperthermia applicator system consists of both devices and computer control systems and these systems allow advanced application paradigms that illustrate the utility of the invention .

[0033] The hyperthermia applicator system shown in Fig. 5 takes the form of an annular applicator system made of electromagnetic field generating elements, Fig. 2, wherein the electromagnetic field generating elements, Fig. 1, are located around the body near the area to be heated. . It is not always the case that the elements must form the entire ring, but they can be located mainly on one side of the patient. However, in this particular arrangement, the E field vector of all elements should be mainly oriented in the same direction in the target area, but this is not a requirement in all system applications. The area between the applicator and the patient is filled with a water bolus, Fig. 6, with a defined shape that allows three things:

1. Miniaturization of the antenna elements thanks to the high dielectric constant.

2. Minimizing discontinuities between the antenna and the patient because the dielectric properties of water and tissue are more similar than those of air and tissue.

3. Ensuring cooling of the patient's skin, as high levels of specific energy absorption may appear on the body surface.

[0034] Slotted antennas with a recess at the back, Fig. 1, are selected as the elements generating the electromagnetic field in our preferred embodiment because they provide: Low profile, good polarization purity, accurate dimensions using photolithographic printed circuit fabrication techniques, ease of manufacture , resistant structure, relatively broadband response and high tolerance to environmental changes. In the case of slot antenna 2, the correct detection method is therefore to detect the field in the slot by means of small coupling loops 4. Loops 4 are small enough so that the amount of coupled power is small compared to the total, which can be hundreds of watts, supplied to the antenna connection 3 so that the field in the gap 2 remains undisturbed by the measurement.

[0035] Each slot element in the applicator is powered from a radio frequency power source with controlled phase and amplitude, Fig. 3. The fields in each slot element of the applicator due to its own excitations and fields coupled with other elements are detected 4 and measured using the device measuring 20 consisting of phase / amplitude detectors, Fig. 4, and the values ​​are sent to control system 21. In this case, the phase / quadrature demodulator 14 in connection with the pair of analog-to-digital converters 15 is used to measure the levels of the phase and quadrature voltage. The digital signal is then converted into a module and phase using the microprocessor 16 and sent to the measuring controller 21 using the measuring rail 17.

[0036] Control system 22 sets the amplitudes and phases 8 of the multi-channel power source 18 radio frequencies and measures the resulting fields 4 supplied from each element 26 and allows feedback control to ensure that the fields supplied are required fields.

[0037] A typical usage paradigm is that a validated numerical electromagnetic model of the applicator system 19 is used with a patient-specific EM model acquired from CT, MRI or other imaging data in the treatment planning software. In the treatment planning software, the target area or areas of the treatment and the optimal ideal excitation values ​​(or not ideal considering mutual coupling and mismatch based on the mutual coupling matrix for the model, which may or may not correspond exactly to the actual coupling matrix due to possible errors mentioned previously, from whose ideal excitation can be calculated) are acquired and the appropriate EM field is generated, SAR or temperature rise values ​​over the entire target area or areas.

[0038] The target excitations are then sent to the treatment control software and the patient is placed in the applicator 19 in the modeled position in the treatment planning. The water bolus is filled with purified water (called demonized water).

[0039] The measuring devices 20 are put into a calibration mode in which the RF switch 13 in Fig. 4 is switched in such a way that the input calibration reference signal from the rail 12 is measured by each measuring device to allow the device phase calibration as well as for removal ambiguity of the phase 42 quadrature phase splitter in the phase / quadrature demodulator 14.

[0040] Each channel 11 of the RF power source output of the multi-channel 18 RF power source is excited in turn to determine which applicator element 28 is connected to each output channel and to measure the fields / currents 4 induced in all elements to generate the actual mutual matrix coupling for system 19 during the procedure. In addition, phase shifts and amplitudes due to connection cables or differences in transmission channels can be eliminated or compensated by calibration. Phase shifts due to the variability of the impedance of the applicator relative to the ideal, e.g. due to the proximity of the patient and thus changes in dielectric constant in the immediate environment, are also eliminated.

[0041] The treatment begins with the delivery of 18 RF power to each element 26 based on the treatment planning, either based on ideal or corrected (using a coupling matrix) excitation, with actual excitation levels determined using 4 field monitoring and measurements 20 and controlled by feedback controller 27 to correct any deviation from the desired excitation levels. During the entire procedure, the total output power from each channel 11 can be controlled 8 and the correct relationships between the amplitudes and phases monitored and controlled to the correct value. Although the invention disclosed herein has been described by means of specific embodiments and their uses, many modifications and changes may be made to one of ordinary skill in the art without departing from the scope of the invention as set forth in the claims.

Items cited

US patents [0042]

US Patent 5251645 "Adaptive nulling hyperthermia array" Creators: Fenn, Alan J. (Wayland, MA) Legal successors: Massachusetts Institute of Technology (Cambridge, MA).

US Patent 4672980 "System and method for creating hyperthermia in tissue" Creators: Turner, Paul F. Legal successors: BSD Medical Corporation (Salt Lake City, UT)

US patent US5441532 and WIPO patent application WO / 1993/000132 "ADAPTIVE FOCUSING AND NULLING HYPERTHERMIA ANNULAR AND MONOPOLE PHASED ARRAY APPLICATORS", Creators: Fenn, Alan J. (Wayland, MA) Legal successors: Massachusetts Institute of Technology (Cambridge, MA) .

Other literature [0043]

Calibration techniques for digital phased arrays, Fulton, C .; Chappell, W .; Microwaves, Communications, Antennas and Electronics Systems, 2009. COMCAS 2009. IEEE

International Conference on Communications, Antennas and Electronic Systems. Publication year: 2009, pages: 1-10

A Built-In Performance-Monitoring / Fault Isolation and Correction (PM / FIC) System for Active Phased-Array Antennas, Kuan-Min Lee, Ruey-Shi Chu, and Sien-Chang Liu, IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, WOL. 41, NO. 11, NOVEMBER 1993

KM Lee, RS Chu, and SC Liu, "A performance monitoring / fault isolation and correction system of a phased array antenna using transmission-line signal injection with phase toggling method," IEEE AP-S 1992 Symposium Digest (Chicago, IL), July 18-25, 1992, vol. 1, pages 429-432.

Foundation of Research on Information Technologies in Society (IT'IS Foundation),

Switzerland

Pełmocnik:

EP 2 425 794 B1 Z-13726