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

DESCRIPTION

ELECTROMAGNETIC FIELD APPLICATION MATRIX WITH INTEGRAL FIELD SENSORS FOR IMPLIED CORRECT COUPLING CORRECTION AND INCOMPATIBILITY

Background of the invention

This invention relates to systems for creating specific electromagnetic field conditions within specific regions in space, or for focusing electromagnetic energy on dielectric objects with greater control.

The ability to create specific electromagnetic field conditions is a fundamental requirement in many medical applications from imaging to therapy. The present invention has applications in both disciplines as well as phased array technology applied for communications and detection applications.

An application of this invention is the generation of specific field conditions at certain locations in the human body for hyperthermia purposes.

National Cancer Institute of the US National Institutes of Health defines hyperthermia (also called thermal therapy or thermotherapy) as a type of cancer treatment in which body tissue is exposed to high temperatures. (up to 45 ° C). Research has shown that high temperatures can damage and kill cancer cells, usually with minimal damage to normal tissues. By killing cancer cells and damaging proteins and structures within cells, hyperthermia can shrink tumors.

This invention relates to local hyperthermia where heat is applied to a small region, such as a tumor. Various techniques can be used to provide energy to heat the tumor. In the context of the present invention either microwave or radio frequencies may be employed to apply 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 applied through an applicator. The applicator consists of a series of elements that are positioned around or near the appropriate region, and energy is focused on the tumor to increase its temperature using phased array techniques. Hyperthermia is often applied in combination with other therapies such as radiation therapy and / or chemotherapy. Hyperthermia has been performed as part of the treatment of many cancers, including sarcoma, melanoma, and cancers of the head and neck, brain, lung, esophagus, breast, bladder, rectum, liver, appendix, cervix, and peritoneal lining (mesothelioma).

A phased array antenna is an antenna made up of a series of small radiation elements, each with its own power point. Phased array antennas are electrically steerable, meaning that the physical antenna can be stationary although the antenna pattern can be manipulated by adjusting the amplitude and phase weighting of each element such that it is focused to a particular region or such. mode that allows the location of objects in space. Phased array can also be used to generate specific field conditions at certain locations in space or to focus radio frequency (RF) on dielectric objects to raise the temperature of a target region within the dielectric or patient object or to induce fields. and currents in a patient to stimulate atoms, nerves or other cellular mechanisms.

Phased array can be used for hyperthermia by concentrating RF energy on the patient such that the temperature is high. When a grouping by phase is used for this purpose, it is called an applicator where energy is applied to the patient. The scaled array or application elements are powered by a multi-channel or microwave RF energy source, where the phase and amplitude signals are agile such that the RF or microwave energy can be focused on a target region, or tumor. The number of array elements and placement of these elements with respect to the target region define the quality of focus that can be achieved.

An example of RF hyperthermia will be used to illustrate the benefits of the invention. Although many systems have been proposed and used in the past for the treatment of tumor hyperthermia, alone or in conjunction with other therapies, consistency and quality of treatment has generally been lacking. Of major importance in local hyperthermia is the ability to apply or focus energy from the applicator to the target region, tissue or tumor. To achieve satisfactory treatment results, the entire destination region must be sufficiently heated. To ensure this, a good electromagnetic applicator and patient-specific models are most preferably used to plan and optimize treatment. This step of accurately predicting energy deposition (and / or temperature rise) and optimizing such, for better tumor treatment has been lacking in hyperthermia systems and has contributed to poor outcomes. During treatment itself, where RF or microwave energy is applied to the hyperthermia matrix with the pacing and phase amplitudes, as determined from the treatment plan, is essential from a quality control point. view that the electromagnetic fields generated by each element are monitored to determine that the correct conceived treatment is effectively applied.

Common to all phased array antennas or hyperthermia applicators, is the requirement for a multichannel source that can generate powerful signals with precisely controlled amplitude and phase that feeds the individual electromagnetic field generator elements. It is not important for the present invention whose method is used to generate these signals.

Multi-elements or phased array applicators generally eliminate matrix elements around the patient with a bolus of water filling the space between patient and matrix to provide surface cooling and inferior reflections at the patient interface. U.S. Patent Nos. 4672980, 5251645 and 5441532 all show typical phased array applicators. Each has the elements arranged in a circular arrangement around the patient with the individual antenna elements (or pairs of elements in US Patent 4,672,980) stimulated by an amplitude-controlled, phase-controlled RF energy source. None of these systems measure the actual applied signals or any reflected power that would reduce the effective radiated power. These factors therefore increase uncertainty. In US 5251645 and 5441532, field sensors are placed in and around the patient's body to measure the field generally applied at these points and states that using the values ​​of these sensors the stimulation The matrix can be controlled such that energy is focused on the target. US 4672980 uses a different method of temperature measurement in which catheters are inserted into the patient and the system controlled to maximize temperature increase in the target region. The draw behind both approaches is that the human body is highly inhomogeneous and there is no intuitive relationship between applied matrix stimuli and the energy deposition pattern. In essence these approaches suppose that knowing the field or temperature at some points is a substitute for knowing the radiation of each matrix element.

In the literature, Paulides et al 2007 describe a typical state of the art system, where the amplitude and phase of the signals applied to each applicator element is measured together with the reflected energy, such that control values ​​can be adjusted such that The signals applied to the reflection light are as desired. When used with proper treatment planning this system has the potential for satisfactory performance. However, the system relies on a computer simulation model completely defining the actual device and is not available for the media taking into account changes in the patient record relative to the applicator for the element impedance and the pacing mutual coupling element .

In the broader context of phased arrays for other applications, US 5867123 uses a thrilling individual element technique and observing the signals received by adjacent elements to build fault testing and analysis. Fulton and Chappell, 2009, evaluating different calibration techniques for phased arrays and matrix states should be calibrated in an anechoic environment to determine the coupling matrix to allow for mutual coupling compensation in the matrix. In addition, it should be noted that internal electronic hardware may be introduced to track any changes from the initial calibrated coupling or transmit chain gains, allowing the correction to be applied. Lee et al, 1992/3, introduced a transmission line (microfite) to the antenna panel to attach to each element so that the transmission and reception function of the electronics can be tested. The transmission line receives energy from all elements or injects energy into all elements of the matrix simultaneously.

US 6208903 describes a microwave applicator for treating hyperthermia. In one embodiment, the apparatus comprises a plurality of circular patch antenna elements each having a coaxial feed at the geometric patch center and a loosely coupled coaxial port for sampling the effective field under the patch. This arrangement is limited to the generation of surface electromagnetic waves in tissue layers just below the applicator. The signal from each of the individual sampling ports is sequentially fed to an amplitude phase comparator via a single pole, multi-throw microwave switch. However, coaxial sampling ports act as antennas to which signals can be directly coupled and therefore are subject to a contamination signal from the field of neighboring antenna elements. In addition, using a single phase comparator instead of amplitude implies the longer distances that individual signals are conducted.

WO 2008/068485 discloses an apparatus for the treatment of microwave and radiation skin tissues for maintaining a constant field force on the treated surface, with a treatment depth limited to less than 5 mm. The phase of individual matrix elements is controlled for the purpose of corresponding single impedance, and not to deal with any mutual coupling of matrix elements.

US 4885589 discloses a phase clustered radar system where remotely situated transmit and receive associated with the modules of each array element is linked to the central location of the transmitter / receiver radar which consists of using the optical fibers, in particular, to ensure immunity to exposure to electromagnetic impulses.

US2008 / 0297402 describes phased arrays and means for functionality validation and / or matrix calibration. One matrix element, or an additional element, is used for comparison with previous measurements when used as a transmitter or receiver, while the rest of the matrix elements are configured as transmitters or receivers respectively and measure the characteristic response. The principle of operation is based only on transmission signals as fed to the matrix element (s) or received at each receiving port (port based measurements), which do not reflect the total element stimulation.

US2004 / 0061644 discloses the integration of probes into a matrix to allow their calibration. The probes are radially coupled to a plurality of matrix elements or a matrix element is radially coupled to a plurality of probes, depending on whether it is a calibration transmission or reception.

WO 2007/146175 relates to the calibration of the transmission and / or reception of strings of a phased array, and is not related to the irradiation elements of a matrix.

Summary of the Invention

The experience with radio frequency hyperthermia treatments and treatment planning and knowledge of the shortcomings of nature systems discussed above has led to important developments being made for control equipment and systems. These developments will greatly enhance safety and consistency through assured field stimulation. The present invention increases the consistency ensured by field stimulation from each antenna array element in the presence of mutual coupling, mismatch and reflections and, consequently, reduces uncertainty. In addition, the invention allows the coupling matrix to be determined more accurately than by using impedance or matrix dispersion measurements, allowing a form of self-calibration that can be performed for each patient undergoing treatment. . The key to achieving assured field stimulation as determined by the treatment plan is the inclusion of integrated sensors for the antenna elements themselves that measure the phase and amplitude of current flowing in the metal element or a field in a base element. slot. These sensors, in the absence of mutual coupling or reflections, provide a measure proportional to stimulation. However, there is no requirement to consider mismatches or phase differences in the connection cables, since it is the actual current (or field) at which the antenna is measured. With mutual coupling and reflections, the sensors measure the sum of all stimulations, regardless of their origin, and consequently allow the determination of the actual radiated field. The stimulation of each element in turn, and the measurement of current (or field) in the animated antenna along with coupled stimulation of all other antennas will allow the matrix coupling matrix to be directly determined.

US Patent 5867123 discussed above also stimulates each element in turn, but does not use this as a means to achieve self-calibration; even if it did, element incompatibility would increase uncertainty. Lee et al, 1992/3 includes transmission lines introduced into the antenna panel, but lack the ability to sense each antenna element individually, and does not reveal any motivation or ability to determine antenna currents (or fields) due to either direct or mutually coupled stimulation. Thus, this system is used as a diagnostic tool rather than for stimulation field control.

The present invention comprises an array of electromagnetic field generating elements and integrates into each sensor to measure the phase and amplitude of current flowing in a metal element (antenna or coil) or field in a base element slot connected to a measuring device. to allow measurement of both phase and amplitude of electrical signals from each of the sensors, on the other hand, because the signal captured by each sensor is directly proportional to the phase and amplitude of the current or field in the associated electromagnetic field generator element, where the current or field is total of the current field or whose amplitude and phase is the sum of both. applied stimuli (from radio frequency energy source) and secondary mutually engaging and incompatibility, therefore the measured value represents the optimal stimulation, in the absence of mutual coupling and incompatibility. This invention then utilizes sensors incorporated into the antenna to further enhance the functionality of, for example, direct stimulation of each matrix element, a multi-channel radio frequency, or microwave power source with a individually adjustable amplitude and phase, can be modified using a feedback controller such that full pacing, as measured by the built-in (current in a metal or the field of a slot based antenna) of the sensor is optimal matrix stimulation without coupling or offset so that the overlapping fields produced by each magnetic field generating element produce a specific electromagnetic field distribution in the volume or a defined region. Implicitly, correcting for mutual coupling and mismatch without explicit knowledge of, and based on calculation, mutual coupling and mismatch, called coupling matrix, such that changes in the binding matrix due to the presence of objects or changes thereof are inherently taken into account. Furthermore, by using sequential stimulation of each element, the invention can directly determine the exact matrix of the mutual coupling matrix, even in the presence of variations in source impedance and undefined cable lengths, which may be useful in determining initial stimulation. of the electromagnetic field matrix generating elements such that feedback can more quickly reach the predefined ideal matrix.

Brief Description of the Attached Drawings

Fig. 1: is illustrative of two adjacent matrix elements (supported cavity slots) one which shows the embodiment of a possible implementation of the present invention.

Fig. La Two adjacent matrix cavity elements (supported cavity slots), tracing a cavity of a cutting element

Fig. 2: is illustrative of a phased array RF hyperthermia applicator, detail of small sensor elements are not included.

Fig. 3 Multichannel radio frequency power source

Fig. 4. Single channel measuring device

Fig. 5 is illustrative of a whole system with phase transmitter and amplitude controlled multichannel transmitter and phase / amplitude detectors connected by a measurement bus to the measurement and computer controllers.

Fig. 6 is illustrative of a radio frequency matrix for hyperthermia wherein a bolus of water is shown for placement between the matrix elements and the patient to reduce reflection and facilitate surface cooling.

Technical Description with reference to the accompanying Drawings

The invention relates to a system consisting of five integral parts, it is the new features of some of these parts and the integration and use of them as a whole that provides the innovation. The first integral part of the electromagnetic field generate elements, figure 1, which are arranged in an array of arbitrary geometry, figure 2. The array of elements is connected to a radio frequency power source, Figure 3, which has a number of independently phase and computer amplitude controllable channels. Integrated into each magnetic field generating element is a current (or field) sensing element that produces an electrical output proportional to the electromagnetic field generated, each electrical signal is measured by a measuring device that measures amplitude and phase, Figure 4 . Measurement data is communicated via a measurement bus to a measurement controller. A control computer uses the measurement data to control the radio frequency energy source so that the generated electromagnetic fields are required fields, the entire system and the interconnections are shown in Figure 5.

An illustrative application of the invention is a phased applicator matrix system 19, figure 5, which can generate specific field conditions at certain locations in space or focus RF energy on dielectric objects. Direct measurement of currents or fields in metallic, slot or coil 26 elements allows direct quantification of the radiated or reactive fields generated by the electromagnetic field generating elements. More specifically, the invention provides the possibility of implicitly correct for the disturbances of the electromagnetic field generated by mutual coupling and incompatibility in the matrix applicator 19 without explicitly measuring the coupling matrix and applying a correction for the stimulation from the power supply. a radio frequency 18. The direct relationship between the current of a metal element (or field in a groove base element) to the electrical output from the radiated or reactive field element 4 sensors can be determined by experimental or numerical means.

An object of the invention is to provide an improved means of determining the radiated or reactive real field closer to each element 26, figure 1, in an element generating electromagnetic field matrix 19 for radio frequency hyperthermia applications, figures 2 and 6, where the immediate load, due to the patient, Dielectric objects and other system components change the coupling between and correspondence seen at input ports 3 of elements 26 or where the radio frequency source impedance power source channels 11 are not well characterized.

Another object of the invention is to provide higher levels of confidence that true variety stimulation from the multi-channel radio frequency energy source 18 is designed to ensure greater control of the field distribution generated by the generating matrix 19. of electromagnetic field quality elements. To enable this, the generated electromagnetic field is measured, Fig. 4, using a measuring device such as a voltmeter or phase / quadrature meter of the demodulator of sufficient sensitivity.

Additional circuits may be added, as shown in Figure 4, to allow self-calibration of the amplitude and phase detectors facilitated by not only distributing the local oscillator across a bus but also a phase reference that can be switched to input. to allow calibration and / or phase ambiguity removal further reducing uncertainty.

Furthermore, the invention provides a new paradigm for the mutual coupling matrix correction by implicit measurement of the electromagnetic field generated with the mutual coupling and mismatch accounted for. Therefore, actual and planned pacing does not have a low deviation, in particular in the presence of variations that could not be modeled during treatment planning.

Furthermore, the invention is not limited to the geometry or placement of the applicator matrix elements 26, Figure 2, around or near the target area and may be applied to any generic array of electromagnetic field generating elements 19. In particular There are no limits to the proximity of dielectric objects such as diseased or other mutual couplings or matching element modifying attributes.

Although the actual or field integrated sensors 4, figure 1, implicitly take into account incompatibility and mutual coupling, The invention allows the coupling matrix (which describes the inconsistency and mutual coupling) of the applicator matrix of electromagnetic field generating elements to be directly determined with greater precision than the standard technique of calculating the coupling matrix from S-parameters. and with the convenience of not having to disconnect the matrix applicator 19 from the radio frequency power source 18, figure 5, and connect it to a network analyzer. By stimulating each element 2 in turn using the radio frequency energy source and measuring the required currents (or fields) 5 on all elements 2 using the measuring device 18, the coupling matrix can be determined with More accurate than the non-ideal output impedances of each amplifier lengths 10 and connecting radio link between source output radio frequency 11 and electromagnetic field generator element 3 are inherently accounted for.

The invention while providing this very important information about the reactive or radiated field of each element 26 also gives the ability to detect which channel 11 output of the multichannel radio frequency power source 18 has been connected to which the generating electromagnetic field element 26 in matrix 19 and therefore rule out the possibility of an incorrect connection and the possibility of a treatment that is completely wrong.

With a measuring device 20 integrated with each element 26, it is possible to have an individual identity for each electromagnetic field generating element, allowing individual calibrations for the elementmeasuring combination device to be assigned. Therefore, the calibration data can be assigned to the correct element for quality control, ease of use and safety. A calibration facility that can therefore provide an accredited calibration that can be assigned to a particular element. Enabling the entire set 19 to be modular with replaceable elements 26 and provide plug and play capabilities.

Description of Preferred Embodiment

The preferred embodiment may be described in the context of an RF hyperthermia applicator system, Figure 5. This hyperthermia applicator system consists of hardware and computer control systems that allow the use of these paradigm systems illustrating the improved utility of the invention.

Hyperthermia applicator system illustrated in Figure 5 is in the form of a ring matrix applicator made of electromagnetic field generating elements, figure 2, where the electromagnetic field generating elements, figure 1,

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All elements should be predominantly aligned in the same direction within the target region, but this is not a requirement in all system applications. The region between the applicator and the patient is filled with a body of water, Figure 6, in a definite way that provides three things:

1. Miniaturization of antenna elements due to high dielectric constant.

2. Minimizing discontinuity between antenna and patient as the dielectric properties of water and tissue are much more similar than air and tissue.

3 To provide a cooling of the patient's skin as high levels of specific energy absorption can occur on the body surface.

Supported cavity slots, figure 1, are chosen as electromagnetic field generation elements in our preferred embodiment as they provide: low profile, good polarization purity, exact dimensions through printed photolithography circuit processing techniques, ease of use. manufacturing, robust structure, relatively wide response, and therefore tolerance to environmental changes. With an antenna slot 2 embodiment, then an appropriate method of detection is by detecting the field in the housing by means of small engaging loops 4. Loops 4 are small enough that the amount of coupled energy is small relative to the total, which could be 100 watts, which is applied to the antenna port 3, so that the field in compartment 2 remains undisturbed by the measurement.

Each slot element in the applicator is fed from a phase and amplitude controllable radio frequency energy source, figure 3. Fields in each slot element applicator due to their own stimulation and fields coupled from other elements are detected. and measured using 4 device measurements 20 consisting of a phase / amplitude detectors, figure 4, and the values ​​reported to a control system 21. In this case, a quadrature / phase demodulator 14 in conjunction with a pair of analog to digital converters of 15 is used to measure the in-phase and quadrature voltage levels. The digital signal is then converted to a magnitude and phase using microprocessor 16 and communicated to metering controller 21 via a metering bus 17.

control system 22 defines the amplitudes and phases of 8 of the multichannel radio frequency power source 18 and measures the resulting fields 4 applied from each element 26 and provides feedback control to ensure the fields applied are the required fields.

A typical use paradigm is that a numerically validated electromagnetic applicator matrix model 19 is used with a patient specific EM model derived from T, MRI, or other image data within treatment planning software. In the treatment planning software of the target region or regions for treatment is defined and optimal optimal stimulation values ​​(or non-optimal take into account mutual coupling and mismatch based on the mutual coupling matrix for the model, which may or may not match the actual coupling matrix, due to the possible errors previously mentioned from which the optimal stimulation can be calculated) the corresponding EM-field is derived, SAR the temperature elevation values ​​across the entire region or target regions generated.

The target pacings are then transferred to the patient control and treatment software placed on the applicator 19 in the position modeled in the treatment planning. Water bolus 25 is filled with demonized water.

The metering devices 20 are placed in calibration mode, where the RF switch 13 in figure 4 is switched such that the bus calibration input phase reference signal 12 is measured by each metering device to allow calibration of the device phase and also to eliminate phase ambiguity of the quadrature phase to be divided by 2 in the phase phase divider / quadrature demodulator 14.

Each radio frequency power source outputs 11 channels of the multichannel radio frequency power source 18 is in turn stimulated to determine which applicator element 26 is attached to each freckle channel and to measure the induced fields / currents 4 at all. the elements for generating the actual mutual coupling matrix for matrix 19 at the time of treatment. In addition, phase and amplitude compensated due to connecting cables or transmit channel differences can be eliminated or calibrated. Phase shifts due to variation in the ideal applicator element impedance, for example due to the proximity of the patient and consequently changing in the immediate environment dielectric constant, are also eliminated.

Treatment is initiated with the radio frequency power 18 being applied to each element 26 based on treatment planning, either based on optimal or corrected stimulation (using the coupling matrix), actual stimulation levels are determined using monitoring field 4 and measurement 20 is controlled by feedback controller 27 to correct any deviation from desired stimulation levels. Throughout the treatment the total mackerel power of each channel 11 can be controlled from 8 and the correct ratio between amplitudes and phase 20 monitored and controlled to the correct value. While the invention disclosed herein has been described by way of specific embodiments and applications thereof, numerous modifications and variations may be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.

References cited

US patents

United States Patent 5251645 Adaptive nulling hyperthermia array Inventors: Fenn, Alan J. (Wayland, MA) Assignee: Massachusetts Institute of Technology (Cambridge, MA). United States Patent 4672980 System and method for creating hyperthermia in tissue Inventors: Turner, Paul F. Assignee: BSD Medical

Corporation (Salt Lake City, UT) United States Patent US5441532 and WIPO Patent Application WO / 1993/000132 ADAPTIVE FOCUSING AND NULLING ANNUAL HYPERTHERMIA AND MONOPOLE PHASED ARRAY APPLICATORS, Inventors: Fenn, Alan J. (Wayland, MA) Assignee: Massachusetts Institute of Technology (Cambridge, MA).

Other Literature

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, Page (s): 1 -10 Built-In PerformanceMonitoring / 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, VOL. 41, NO. 11 NOVEMBER 1993

Κ Μ Lee, RS Chu, and SC Liu, 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,