Radio frequency applicator for thermoacoustic imaging system

Abstract

A radio frequency applicator for a thermoacoustic imaging system is disclosed. The applicator includes: a waveguide having an internal radio frequency source, wherein the waveguide has an opening; an electromagnetic matching layer coupled to the waveguide and proximate to the opening; and a sound absorbing layer coupled to the matching layer.

Description

Technical Field

[0001] The present disclosure relates generally to thermoacoustic imaging, and more particularly to systems and methods for thermoacoustic imaging using a radio frequency applicator to preferentially modulate received signals. background

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] In high frequency systems, waveguides are often employed to guide electromagnetic waves or sound with minimal energy loss by limiting the expansion of electromagnetic waves propagating within the waveguide to one or two dimensions. Depending on the nature of the electromagnetic waves to be propagated, waveguides can take different forms. In many cases, filters are employed to allow electromagnetic waves at certain frequencies to pass and travel along the waveguide while rejecting electromagnetic waves at other frequencies. For example, when propagating radio frequency (RF) waves, hollow, open, conductive metal waveguides are often employed. In some cases, in order to provide the desired filtering, these hollow metal waveguides are equipped with solid inserts formed of high dielectric constant materials.

[0004] Waveguides, such as those described above, have been employed in thermoacoustic imaging systems. Thermoacoustic imaging is a form of imaging that provides information related to the thermoelastic properties of tissue. Thermoacoustic imaging uses short pulses of electromagnetic energy, such as RF pulses, that are directed into a subject to rapidly heat heat absorbing features within the subject, which in turn cause acoustic pressure waves that are detected using acoustic receivers, such as one or more thermoacoustic or ultrasonic transducer arrays. The detected acoustic pressure waves are analyzed by signal processing and processed for presentation as a thermoacoustic image that can be interpreted by an operator.

[0005] To direct RF pulses into a subject during thermoacoustic imaging, a radio frequency (RF) applicator employing a waveguide is coupled to tissue adjacent to a region of interest (ROI) within the subject to be imaged. Suboptimal coupling of the RF applicator to the tissue may cause problems (e.g., inefficient energy transfer, reduced heating rates, reduced signal strength, uneven energy deposition, tissue hot spots, tissue overheating, RF power supply damage, and poor image quality). Factors that contribute to suboptimal coupling of the RF applicator to the tissue include variability in subject size, size of tissue within the subject, geometry of tissue within the subject, composition of tissue within the subject, etc.

[0006] The strong electromagnetic fields inside the applicator and its immediate vicinity (the top layer of the medium to be imaged) and the high conductivity of the skin layers generate strong stray acoustic waves close to the front face of the applicator. Such clinically insignificant waves propagate through the tissue and mask the desired thermoacoustic signals from the various components, thus interfering with the measurement.

[0007] Many academic systems utilize a split configuration where the applicator is facing the acoustic sensor (opposite geometry) or at 90 degrees to the applicator (perpendicular geometry). The opposite geometry ensures that the interfering signal will arrive last, so it is temporarily separated from the signal of interest. The perpendicular geometry configuration ensures that only side scattered waves will reach the detector, greatly reducing the received interference.

[0008] However, the disadvantage of both of these configurations is that they deviate significantly from the standard of care, as reflection mode ultrasound requires separate handheld devices - applicator and detector. This would require considerable adaptation by the clinician, would be complex to operate, and would be highly susceptible to user manipulation. Furthermore, these geometries are often impractical to perform with handheld devices in a clinical setting and are more suited to whole-body small animal imaging. Overview

[0009] A radio frequency applicator for a thermoacoustic imaging system is disclosed, which comprises: a waveguide with an internal radio frequency source, wherein the waveguide has an opening; an electromagnetic matching layer coupled to the waveguide and close to the opening; and an acoustic absorption layer coupled to the matching layer.

[0010] In one embodiment, the electromagnetic matching layer has a real part of a dielectric constant of 5 to 65 and an imaginary part of a dielectric constant of 0 to 60 at a frequency range between 15 MHz and 2.5 GHz.

[0011] In one embodiment, the electromagnetic matching layer has an acoustic impedance greater than 3 MRayl (megaRayles) at a frequency range between 0.1 MHz and 20 GHz.

[0012] In one embodiment, the sound absorbing layer has a real part of a dielectric constant of 5 to 65 and an imaginary part of a dielectric constant of 0 to 60 at a frequency range between 15 MHz and 2.5 GHz.

[0013] In one embodiment, the sound absorbing layer has an acoustic impedance between 1.2 MRayl and 1.8 MRayl at a frequency range between 0.1 MHz and 20 GHz.

[0014] In one embodiment, the electromagnetic matching layer has a real part of a dielectric constant of 2 to 80 and an imaginary part of a dielectric constant of 0 to 60 at a frequency range between 1 MHz and 1000 MHz.

[0015] In one embodiment, the electromagnetic matching layer has an acoustic impedance greater than 1 MRayl at a frequency range between 0.01 Hz and 100 Hz.

[0016] In one embodiment, the sound absorbing layer has a real part of a dielectric constant of 2 to 80 and an imaginary part of a dielectric constant of 0 to 60 at a frequency range between 1 MHz and 1000 MHz.

[0017] In one embodiment, the sound absorbing layer has an acoustic impedance between 35 kRayl (kiloRayl) and 1 MRayl at a frequency range between 0.01 Hz and 100 Hz.

[0018] In one embodiment, the electromagnetic matching layer has a real part of a dielectric constant of 2 to 100 and an imaginary part of a dielectric constant of 0 to 60 at a frequency range between 3 kHz and 30 kHz.

[0019] In one embodiment, the electromagnetic matching layer has an acoustic impedance greater than 4 MRayl at a frequency range between 50 kHz and 500 kHz.

[0020] In one embodiment, the sound absorbing layer has a real part of a dielectric constant of 2 to 100 and an imaginary part of a dielectric constant of 0 to 60 at a frequency range between 3 kHz and 30 kHz.

[0021] In one embodiment, the sound absorbing layer has an acoustic impedance between 0.4 MRayl and 3 MRayl at a frequency range between 50 kHz and 500 kHz.

[0022] In one embodiment, the electromagnetic matching layer is formed of a high dielectric constant elastomeric material.

[0023] In one embodiment, the electromagnetic matching layer is formed of a ceramic material.

[0024] In one embodiment, the electromagnetic matching layer is formed from a composite material comprising high dielectric constant particles embedded in a solid matrix.

[0025] In one embodiment, the sound absorbing layer is formed from an open cell foam.

[0026] In one embodiment, the sound absorbing layer is formed from impregnated cork.

[0027] In one embodiment, the sound absorbing layer is formed by an acoustic anechoic absorber.

[0028] In one embodiment, the sound absorbing layer is formed of a rubber-based vibration isolating material.

[0029] This summary is provided merely to introduce certain concepts, and is not intended to identify key or critical features of the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] One or more embodiments will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 schematically illustrates an exemplary imaging system and an exemplary region of interest in a liver with blood vessels; Figure 2 An exemplary side view of a thermoacoustic application is shown; Figure 3 An exemplary split configuration thermoacoustic system is shown; Figure 4 A thermoacoustic system showing exemplary relative geometries; Figure 5 shows a cross-sectional side view of an embodiment of a radio frequency applicator; Figure 6 A cross-sectional side view of an embodiment of a thermoacoustic application is shown; Figure 7 shows a perspective view of an exemplary RF applicator; Fig. 8A and Figure 8B shows a perspective view of another exemplary radio frequency applicator; and Fig. 9A and Fig. 9B shows a perspective view of another exemplary radio frequency applicator; Fig.10 Another exemplary radio frequency applicator is shown; Fig.11 An exemplary radio frequency applicator is schematically illustrated, showing the directional flow of electromagnetic energy; and Fig.12 An exemplary radio frequency applicator is schematically illustrated, showing the directional flow of acoustic signals (acoustic energy). Detailed Description

[0031] References throughout this specification to "one embodiment," "an embodiment," or similar language mean that a particular feature, structure, or characteristic described in conjunction with the embodiment is included in at least one embodiment of the subject matter of the present disclosure. The appearance of the phrases "in one embodiment," "in an embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. The term "based on" is not exclusive and allows for being based on other factors not described unless the context clearly dictates otherwise. Additionally, in the subject description, the word "exemplary" is used to indicate use as an example, instance, or illustration.

[0032] Furthermore, unless explicitly stated to the contrary, an example or embodiment that “comprising” or “having” or “including” an element or feature or multiple elements or features having a particular property may include additional elements or features that do not have that property. Furthermore, it will be understood that the terms “comprising”, “having”, and “including” mean “including but not limited to”, and that the terms “including”, “having”, and “including” have equivalent meanings.

[0033] As used herein, the term "and / or" may include any and all combinations of one or more of the associated listed elements or features.

[0034] It should be understood that when an element or feature is referred to as being "on," "attached," "connected," "coupled," "contacting," etc., the element or feature may be directly on, directly attached to, directly connected to, directly coupled to, or directly contacting another element or feature, or there may be intervening elements. In contrast, when an element or feature is referred to as being, for example, "directly on," "directly attached," "directly connected," "directly coupled," or "directly contacting" another element or feature, there are no intervening elements or features.

[0035] It should be understood that spatially relative terms, such as "under", "below", "lower", "over", "above", "upper", "front", "back", etc., may be used herein to describe the relationship of an element or feature to another element or feature as shown in the figures for ease of description. However, the spatially relative terms may also encompass different orientations in use or operation in addition to the orientations depicted in the figures.

[0036] References herein to "examples" refer to one or more features, structures, elements, components, characteristics, and / or operating steps described in conjunction with the example being included in at least one embodiment and / or implementation of the subject matter of the present disclosure. Therefore, phrases throughout the present disclosure such as "an example," "another example," and similar language may, but do not necessarily, refer to the same example. Furthermore, a subject matter characterizing any one example may, but does not necessarily, include a subject matter characterizing any other example.

[0037] References to "configuration" herein refer to the actual state of configuration, which fundamentally relates an element or feature to the physical characteristics of the element or feature preceding the phrase "configured to."

[0038] Unless otherwise noted, the terms "first," "second," etc. are used herein merely as labels and are not intended to impose order, position, or hierarchy requirements on the items to which these terms refer. Furthermore, reference to a "second" item does not require or preclude the existence of lower-numbered items (e.g., a "first" item) and / or higher-numbered items (e.g., a "third" item).

[0039] As used herein, the terms "substantially" and "approximately" indicate that an amount is close to the stated amount, which still performs the desired function or achieves the desired result. For example, the terms "substantially" and "approximately" can refer to an amount within an engineering tolerance that will be readily understood by a person of ordinary skill in the art.

[0040] Various embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein the same reference numerals represent the same parts and components in the several views. Reference to the various embodiments does not limit the scope of the present invention, which is limited only by the scope of the appended claims. In addition, any examples set forth in this specification are not intended to be limiting and only set forth some of the many possible embodiments of the claimed invention.

[0041] Referring now to the drawings, wherein the depictions are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting these embodiments, Figure 1 An exemplary imaging system 100 is schematically shown and generally identified by the reference numeral 100. As can be seen, the imaging system 100 includes a programmed computing device 102 communicatively coupled to an ultrasound imaging system 104 and a thermoacoustic imaging system 106. The ultrasound imaging system 104 and the thermoacoustic imaging system 106 are configured to obtain ultrasound image data and thermoacoustic image data, respectively, of a region of interest 116. The components of the system 100 are shown in FIG. Figure 1 This illustration is for ease of description, and it should be appreciated that system 100 may include a number of additional imaging devices or sub-devices.

[0042] The programming computing device 102 can be a computer, server or other suitable processing device, including, for example, a processing unit including one or more processors, computer-readable system memory (volatile and / or non-volatile memory), other non-removable or removable computer-readable memory (e.g., hard drive, RAM, ROM, EEPROM, CD-ROM, DVD, flash memory, etc.), and a system bus that couples various computer components to the processing unit. The computing device 102 can also include networking capabilities using Ethernet, Wi-Fi and / or other suitable network formats to be able to connect to shared or remote drives, one or more networked computers or other networked devices. One or more input devices, such as a mouse and keyboard (not shown), are coupled to the computing device 102 for receiving operator input. A display device (not shown), such as one or more computer screens or monitors, is coupled to the computing device 102 for displaying one or more generated images based on ultrasound image data received from the ultrasound imaging system 104 and / or thermoacoustic image data received from the thermoacoustic imaging system 106. The programmed computing device 102 executes program code stored on the computer-readable system memory and / or other non-removable or removable computer-readable memory and performs methods according to the program code, as will be further described below.

[0043] The ultrasound imaging system 104 includes an acoustic receiver in the form of an ultrasound transducer 108, which houses one or more ultrasound transducer arrays configured to transmit sound waves into a region of interest 116. The sound waves directed into the region of interest 116 echo from the materials within the region of interest ROI, where different materials reflect sound to different degrees. The echoes received by the one or more ultrasound transducer arrays of the ultrasound transducer 108 can be processed by the ultrasound imaging system 104, and then transmitted to the computing device 102 as ultrasound image data for further processing and for presentation on a display device as an ultrasound image that can be interpreted by an operator. In one embodiment, the ultrasound imaging system 104 utilizes B-mode ultrasound imaging technology assuming a nominal sound speed of 1,540 m / s. Since ultrasound imaging systems are known in the art, additional details of the ultrasound imaging system 104 will not be further described herein.

[0044] The thermoacoustic imaging system 106 includes an acoustic receiver in the form of a thermoacoustic transducer 110. The thermoacoustic transducer 110 houses one or more thermoacoustic transducer arrays. A radio frequency (RF) applicator 112 may be housed together with the thermoacoustic transducer 110 or separately. The RF applicator 112 is configured to emit short pulses of RF energy that are directed into a region of interest ROI containing a blood vessel 128. In one embodiment, the RF applicator 112 has a frequency between about 10 MHz and 100 GHz and has a pulse duration between about 0.1 nanoseconds and 10 microseconds. The RF energy pulses delivered to the material within the region of interest 116 cause acoustic pressure waves (thermoacoustic multipole signals) within the region of interest 116 that are detected by the thermoacoustic transducer 110. The acoustic pressure waves detected by the thermoacoustic transducer 110 are processed and transmitted as thermoacoustic image data to the computing device 102 for further processing and for presentation on a display device as a thermoacoustic image that can be interpreted by an operator.

[0045] The coordinate system of the one or more ultrasonic transducer arrays of the ultrasonic transducer 108 and the coordinate system of the one or more thermoacoustic transducer arrays of the thermoacoustic transducer 110 are mapped by the computing device 102 so that the acquired ultrasound image and the thermoacoustic image can be registered. Alternatively, the thermoacoustic imaging system 106 can utilize the one or more ultrasonic transducer arrays of the ultrasonic transducer 108 by disconnecting the one or more ultrasonic transducer arrays from the ultrasonic transducer 108 and connecting the one or more ultrasonic transducer arrays to the thermoacoustic transducer 110. As will be appreciated, by doing so, coordinate mapping between the one or more ultrasonic transducer arrays and the one or more thermoacoustic transducer arrays is not required.

[0046] In one embodiment (such as Figure 1 ), the exemplary region of interest 116 contains blood vessels 128 and is located within a liver 230 of a human or animal body (patient) 114. The patient 114 includes skin 202 and a subcutaneous fat layer 218 and a muscle layer 220 adjacent to the liver 230.

[0047] In one embodiment, a radio frequency (RF) applicator 112 includes a waveguide with an internal RF source, wherein the waveguide has an opening. In various embodiments, the waveguide includes an antenna and an applicator, and / or components configured to deliver RF and / or microwave energy into tissue.

[0048] Figure 2 An exemplary RF applicator 112 and a thermoacoustic transducer 110 are shown in an exemplary application. Figure 2As shown, skin 202, fat (including subcutaneous fat) 204, muscle 220, and liver (or another organ) 230 are present in the patient. At the interface between the RF applicator 112 and the skin 202 (at Figure 2 ), the interface between the skin 202 and the fat 204 (shown as line "A" in FIG. Figure 2 204 and the muscle 220 (shown as line "B" in FIG. Figure 2 ”C”) and at the interface between the muscle 220 and the liver 230 (in Figure 2 Thermoacoustic signals are generated at the interfaces between the RF applicator 112 and the skin 202 and between the skin 202 and the fat 204 (e.g., Figure 2 The thermoacoustic signals generated at the interfaces between the fat 204 and the muscle 220 and between the muscle 220 and the liver 230 are undesirable and may interfere with the thermoacoustic signals generated at the interfaces between the fat 204 and the muscle 220 and between the muscle 220 and the liver 230. Therefore, the present disclosure describes embodiments that are configured to minimize the intensity (amplitude) of the thermoacoustic signals generated at the interfaces between the RF applicator 112 and the skin 202 and between the skin 202 and the fat 204, while minimizing the intensity (amplitude) of the thermoacoustic signals generated at the interfaces between the fat 204 and the muscle 220 and between the muscle 220 and the liver 230 (e.g., Figure 2 The signal strength (amplitude) generated at the interference lines C and D) is the largest. These embodiments are novel RF applicator 112 configurations.

[0049] Figure 3 A separated configuration (perpendicular geometry) embodiment of the thermoacoustic transducer 110 and the RF applicator 112 of the system 100 is shown. The perpendicular geometry configuration ensures that only side scattered waves will reach the detector, thereby greatly reducing received interference. In some embodiments, the RF applicator 112 is disposed at an angle of substantially 90 degrees relative to the thermoacoustic transducer 110, for example, at an angle of 75 degrees to 115 degrees relative to the thermoacoustic transducer 110.

[0050] Figure 4 An embodiment of the relative geometry of the thermoacoustic transducer 110 and the RF applicator 112 of the system 100 is shown. The relative geometry ensures that the interfering signal will arrive last, so it is temporally separated from the signal of interest.

[0051] Figure 5An exemplary cross-sectional side view of the RF applicator 112 with the sound absorbing layer 500 is shown. The RF applicator 112, skin 202, fat 204, muscle 220, liver 230, electromagnetic matching layer 502, cloth layer 504, and foam layer 506 are shown. In one embodiment, the sound absorbing layer 500 includes the cloth layer 504 and the foam layer 506. In one embodiment, the RF applicator 112 is pre-configured with the electromagnetic matching layer 502. In one embodiment, the electromagnetic matching layer 502 is integral with the applicator 112. In one embodiment, the electromagnetic matching layer 502 is coupled to the applicator by, for example, an adhesive. In one embodiment, the electromagnetic matching layer 502 is coupled to the insert 1010. As shown in FIG. Figure 5 As shown, the thermal acoustic signal is absorbed by the sound absorbing layer 500 (in Figure 6 The material in the image is reduced and absorbed as shown in line "E").

[0052] Figure 6 A cross-sectional side view of an embodiment of the thermoacoustic transducer 110 and the RF applicator 112 of the system 100 is shown. The RF applicator 112, the thermoacoustic transducer 110, and a patient having skin 202, fat 204, muscle 220, liver 230 are shown. The RF applicator 112 includes an electromagnetic matching layer 502, a cloth layer 504, and a foam layer 506. In one embodiment, the cloth layer 504 and the foam layer 506 constitute the sound absorbing layer 500.

[0053] Electromagnetic matching layer 502 is preferably configured to substantially match the electrical impedance of the target material (eg, tissue) without matching the acoustic impedance of the target (eg, tissue). The target material may include one or more of the following: skin 202 , subcutaneous fat layer 218 , muscle layer 220 , and liver 230 .

[0054] The fabric layer 504 preferably substantially matches the electrical and acoustic properties of the electromagnetic matching layer 502, and is used to connect the electromagnetic matching layer 502 and the foam layer 506. The foam layer 506 is preferably configured to substantially match both the electrical impedance of the tissue and the acoustic impedance of the tissue. Therefore, the combination of the electromagnetic matching layer 502, the fabric layer 504, and the foam layer 506 minimizes the acoustic transmission from the RF applicator 112, maximizes the transmission of RF energy to the tissue (e.g., the skin layer 202), and captures and disperses the RF energy at the interface of the RF applicator 112 and the skin 202 (at the interface of the RF applicator 112 and the skin 202). Figure 6 ”A”) and the interface of skin 202 and fat 204 (in Figure 6 The shape of the acoustic absorbing layer 500 (particularly the foam layer 506) helps to further disperse unwanted acoustic signals that may interfere with the desired imaging area (e.g., Figure 1 ROI shown) and from Figure 6 The signals emitted by the interference lines "C" and "D".

[0055] In various embodiments, the acoustic absorbing layer 500 includes a saline soaked open foam layer 506 with a cloth backing 504. The cloth 504 may have an adhesive layer that allows the cloth 504 to be adhered (permanently or temporarily, in various embodiments) on top of the applicator 112. The acoustic absorbing layer 500 can attenuate generated stray acoustic waves by: A) having strong acoustic scattering and / or absorption, which attenuates the waves generated at the interface between the layer 500 and the applicator 112 from propagating further into the tissue; B) reinforcing the spacing between the tissue (e.g., skin 202 and / or fat 204) and the applicator 112. When the electromagnetic field peaks near the front of the applicator 112 - this spacing reduces the electromagnetic field reaching the highly conductive skin layer; C) acting as an acoustic matching layer boundary around the applicator 112, thereby reducing strong acoustic reflections from this area; D) in one embodiment, the layer 500 is shaped to deflect the signal away from the shortest vertical position relative to the RF transmitter 110.

[0056] In one embodiment, the absorbent layer 500 has a cross-section in the shape of an arrow with an angle varying from 0-60 degrees and a central apex. In one embodiment, a portion of the absorbent layer 500 has a conical or partial conical shape. In various embodiments, the absorbent layer 500 includes a portion having a truncated cone, a pyramid, a truncated pyramid, or a parallelepiped shape.

[0057] Embodiments of system 100 having an RF applicator 112 with an acoustically absorbing layer 500 provide: (1) attenuation of stray signals; and (2) use of a single complementary layer to both electrically (via spacing) and acoustically (via matching and absorption) process signals generated at the surface of the applicator 112 and the skin surface.

[0058] In various embodiments, similar layers can also be applied to photoacoustic imaging. That is, matching the refractive index of the tissue while absorbing sound will reduce stray acoustic waves at the interface.

[0059] In various embodiments, the cloth backing 504 and adhesive layer are not required and may be replaced or removed. Formation of the layers is also not required.

[0060] In various embodiments, the RF applicator 112 includes a waveguide 702 having an internal RF source 1018. The waveguide preferably has an opening 1016. The acoustic absorbing layer 500 is sized and shaped to cover the opening 1016.

[0061] In one embodiment, foam layer 506 has a minimum thickness of 5 mm and a maximum thickness of 15 mm.

[0062] Figure 7A perspective view of an exemplary RF applicator 112 embodiment is shown. Figure 7 As shown, the RF applicator 112 may include an RF waveguide 702, an electromagnetic matching layer 502, a cloth layer 504, and a foam layer 506, which form an acoustic absorption layer 500. The exemplary acoustic absorption layer 500 is shown to have a tapered edge on the foam layer 506.

[0063] Fig. 8A and Figure 8B Another RF applicator embodiment is shown, which shows an exemplary shape of the sound absorbing layer 500. Fig. 8A and Figure 8B As shown, the sound absorbing layer 500 has a tapered side surface leading to a central edge (ie, a linear apex) on the front surface. In this embodiment, the sound absorbing layer 500 has an arrow cross-sectional shape.

[0064] Fig. 9A and Fig. 9B Another RF applicator embodiment is shown, which shows an exemplary shape of the sound absorbing layer 500. Fig. 9A and Fig. 9B As shown, the sound absorbing layer 500 has a rounded front surface, i.e., a convex central vertex. It is contemplated that a sound absorbing layer similar to Fig. 9A and Fig. 9B Other embodiments of the embodiments have a vertex in the central area of ​​the front surface of the sound absorbing layer 500.

[0065] Fig.10 A perspective view of another exemplary RF applicator 112 is shown. As can be seen, the RF applicator 112 includes a hollow, generally rectangular, open waveguide 702, which can be formed of a conductive metal material. A plinth 706 is disposed on a surface of the waveguide 702 adjacent one end of the waveguide. A central hole 1006 is disposed in the plinth 706 and extends through the surface of the waveguide 702. A flange 1008 can extend around the waveguide 702, adjacent the other end of the waveguide, and can be used to mount the RF applicator 112 within a thermoacoustic probe, which includes a thermoacoustic transducer 110 and can include an ultrasonic transducer 108.

[0066] A solid, low-loss, high dielectric constant insert 1010 formed of ceramic or other suitable material is positioned inside the waveguide 702 and may fill the interior volume of the waveguide 702. A recess 1012 is disposed in the high dielectric constant insert 1010 aligned with the hole 1006. In one embodiment, high dielectric constant refers to a real relative dielectric constant greater than 10, and low loss refers to a loss tangent less than 0.01.

[0067] Insert 1010 has a facing surface 1014 that is substantially flush with a waveguide opening 1016. Opening 1016 is configured for electromagnetic energy communication therethrough. Opening 1016 is rectangular, but various sizes and shapes of openings may be used in various embodiments, consistent with the electromagnetic energy communication through which the opening is configured.

[0068] An RF source 1030 having an RF transmitter 1018 at one end configured to generate pulses of RF energy extends through the hole 1006 and into the waveguide 702 such that the RF transmitter 1018 is suspended within the waveguide 702. The RF source 1030 also includes a threaded connector 704 to which control electronics can be connected. In one embodiment, the RF source 1030 is configured to engage a base 706 through which threaded fasteners pass. A mounting flange 1030 covers the base 706 to secure the RF transmitter 1018 within the waveguide 702. The RF transmitter 1018 serves as an internal radio frequency source for the waveguide 702.

[0069] In one embodiment, which may be desirable in medical applications enabling thermoacoustic measurements in tissue, the electromagnetic matching layer 502 has the following electromagnetic properties at a target frequency range between 15 MHz and 2.5 GHz: A) the real part of the dielectric constant is in the range of 5 to 65; and B) the imaginary part of the dielectric constant is in the range of 0 to 60.

[0070] For various applications, such as medical applications, the electromagnetic matching layer 502 may have the following acoustic properties at a target frequency range between 0.1 MHz and 20 GHz: A) a sound velocity greater than 2000 m / s; B) a velocity greater than 1500 kg / m 3 density; and C) an acoustic impedance greater than 3 MRayl (acoustic impedance is the speed of sound multiplied by the density).

[0071] For various applications, such as medical applications, the electromagnetic matching layer 502 can be formed from a high dielectric constant elastomer (e.g., Avient's Preperm®), a ceramic (e.g., National Magnetics' K-60®), and / or a composite material containing high dielectric constant particles embedded in a solid matrix (e.g., PPG's Des-K®).

[0072] For various applications, such as medical applications, the sound absorbing layer 500 may have the following electromagnetic properties at a target frequency range between 15 MHz and 2.5 GHz: A) the real part of the dielectric constant is in the range of 5 to 65; and B) the imaginary part of the dielectric constant is in the range of 0 to 60.

[0073] For various applications, such as medical applications, the sound absorbing layer 500 can have the following acoustic properties at a target frequency range between 0.1 MHz and 20 GHz: A) 0.3 dB / (cm*MHz) to 30 dB / (cm*MHz) sound attenuation; B) sound velocity between 1350 m / s and 1650 m / s; C) 900 kg / m 3 and 1100 kg / m 3 and D) an acoustic impedance from 1.2 MRayl to 1.8 MRayl, which is close to the acoustic impedance of tissue (1.5 MRayl) (acoustic impedance is the speed of sound multiplied by the density).

[0074] The sound absorbing layer 500 may be formed of open-cell foam because foam has high sound attenuation. In a separate embodiment, the open-cell foam may be soaked with saline or another liquid to change its acoustic and electromagnetic properties to match the reference range of the present disclosure.

[0075] In one embodiment, the sound absorbing layer 500 is formed of impregnated cork, wherein the particles used to impregnate it are selected in such a way that they adjust the cork to match the reference range of the present disclosure. In one embodiment, the sound absorbing layer 500 is a commercially available acoustic anechoic absorber (e.g., Aptflex® from Precision acoustics).

[0076] In one embodiment that may be desirable in through-the-earth thermoacoustic measurements, the electromagnetic matching layer 502 may have the following electromagnetic properties at a target frequency range between 1 MHz and 1000 MHz: A) the real part of the dielectric constant is in the range of 2 to 80; and B) the imaginary part of the dielectric constant is in the range of 0 to 60.

[0077] For various applications, such as through-the-earth thermoacoustic applications, the electromagnetic matching layer 502 may have the following acoustic properties at a target frequency range between 0.01 MHz and 100 GHz: A) a speed of sound greater than 500 m / s; B) a velocity greater than 2000 kg / m 3 density; and C) an acoustic impedance greater than 1 MRayl (acoustic impedance is the speed of sound multiplied by the density).

[0078] For various applications, such as through-the-earth thermoacoustic applications, it may be desirable for the electromagnetic matching layer 502 to be formed from a high dielectric constant elastomer (e.g., Avient's Preperm®), a ceramic (e.g., National Magnetics' K-60®), and / or a composite material comprising high dielectric constant particles embedded in a solid matrix (e.g., PPG's Des-K®).

[0079] For various applications, such as through-the-ground thermoacoustic applications, the sound absorbing layer 500 may have the following electromagnetic properties at a target frequency range between 1 MHz and 1000 MHz: A) the real part of the dielectric constant is in the range of 2 to 80; and B) the imaginary part of the dielectric constant is in the range of 0 to 60.

[0080] The sound absorbing layer 500 may have the following acoustic properties at a target frequency range between 0.01 Hz and 100 Hz: A) sound attenuation greater than 1 dB / (cm*kHz); B) sound velocity between 70 m / s and 700 m / s; C) sound velocity between 500 kg / m 3 With 1500kg / m 3 and D) an acoustic impedance (acoustic impedance is the speed of sound multiplied by the density) which should be between 35 kRayl and 1 MRayl.

[0081] The sound absorbing layer 500 may be formed from a variety of materials including Sorbothane® and / or other rubber-based vibration isolating materials such as Neoprene® and Nitrile®.

[0082] In one embodiment that may be desirable for performing underwater thermoacoustic measurements, the electromagnetic matching layer 502 has the following electromagnetic properties at a target frequency range between 3 kHz and 30 kHz: A) the real part of the dielectric constant is in the range of 2 to 100; and B) the imaginary part of the dielectric constant is in the range of 0 to 60.

[0083] For various applications, such as underwater thermoacoustic applications, the electromagnetic matching layer 502 has the following acoustic properties at a target frequency range between 50 kHz and 500 kHz: A) a sound velocity greater than 2000 m / s; B) a velocity greater than 2000 kg / m 3 density; and C) an acoustic impedance greater than 4 MRayl (acoustic impedance is the speed of sound multiplied by the density).

[0084] For various applications, such as underwater thermoacoustic applications, it may be desirable for the electromagnetic matching layer 502 to be formed from a high dielectric constant elastomer (e.g., Avient's Preperm®), a ceramic (e.g., National Magnetics' K-60®), and / or a composite material comprising high dielectric constant particles embedded in a solid matrix (e.g., PPG's Des-K®).

[0085] For various applications, such as underwater thermoacoustic applications, the sound absorbing layer 500 can have the following electromagnetic properties at a target frequency range between 3 kHz and 30 kHz: A) the real part of the dielectric constant is in the range of 2 to 100; and B) the imaginary part of the dielectric constant is in the range of 0 to 60.

[0086] The sound absorbing layer 500 may have the following acoustic properties at a target frequency range between 50 kHz and 500 kHz: A) sound attenuation from 3 dB / (cm*MHz) to 50 dB / (cm*MHz); B) sound velocity between 80 m / s and 2000 m / s; C) sound velocity at 500 kg / m 3 and 1500 kg / m 3 and D) should be an acoustic impedance from 0.4 MRayl to 3 MRayl (acoustic impedance is the speed of sound multiplied by the density).

[0087] For various applications, such as underwater thermoacoustic applications, it may be desirable for the sound absorbing layer 500 to be formed from Sorbothane® material and / or other rubber-based vibration isolation materials (such as, Neoprene® and Nitrile®) and high-density cork.

[0088] Fig.11 A cross-sectional side view of an embodiment is schematically shown to illustrate the directional flow of electromagnetic energy during use. RF energy 1102 is shown as being emitted from the RF applicator 112 and first passes through the electromagnetic matching layer 502, then through the acoustic absorption layer 500, and then is absorbed in the measured medium 1104. The measured medium 1104 can be tissue (medical applications), the ground (the earth, through-the-earth applications), or fresh or salt water (underwater thermoacoustics).

[0089] Fig.12 A cross-sectional side view of an embodiment is schematically shown to illustrate the directional flow of acoustic signals (acoustic energy). The RF applicator 112 emits unwanted RF applicator acoustic energy 1202, which is reflected back from the electromagnetic matching layer 502. In addition, the acoustic absorption layer 500 absorbs unwanted tissue acoustic energy 1204 emitted from the tissue 1104. The measured medium 1104 can be tissue (medical applications), ground (earth, through-the-earth applications), or fresh or salt water (underwater thermoacoustics).

[0090] Although the foregoing disclosure discusses illustrative embodiments, it should be noted that various changes and modifications may be made herein without departing from the scope of the described embodiments as defined by the appended claims. Therefore, the described embodiments are intended to include all such changes, modifications, and variations that fall within the scope of the appended claims. Furthermore, although the elements of the described embodiments may be described or claimed in the singular, the plural is contemplated unless a limitation to the singular is explicitly stated. Additionally, all or part of any embodiment may be used together with all or part of any other embodiment unless otherwise stated.

Claims

1. A radio frequency applicator for a thermoacoustic imaging system, the applicator comprising: a waveguide having an internal radio frequency source, wherein the waveguide has an opening; an electromagnetic matching layer coupled to the waveguide and proximate to the opening; as well as A sound absorbing layer is coupled to the matching layer.

2. The radio frequency applicator according to claim 1, wherein: The electromagnetic matching layer has a real part of a dielectric constant of 5 to 65 and an imaginary part of a dielectric constant of 0 to 60 in a frequency range between 15 MHz and 2.5 GHz.

3. The radio frequency applicator according to claim 1, wherein: The sound absorbing layer has a real part of a dielectric constant of 5 to 65 and an imaginary part of a dielectric constant of 0 to 60 in a frequency range between 15 MHz and 2.5 GHz.

4. The radio frequency applicator according to claim 1, wherein: The sound absorbing layer has an acoustic impedance between 1.2 MRayl and 1.8 MRayl at a frequency range between 0.1 MHz and 20 GHz.

5. The radio frequency applicator according to claim 1, wherein: The electromagnetic matching layer has a real part of a dielectric constant of 2 to 80 and an imaginary part of a dielectric constant of 0 to 60 in a frequency range between 1 MHz and 1000 MHz.

6. The radio frequency applicator according to claim 1, wherein: The sound absorbing layer has a real part of a dielectric constant of 2 to 80 and an imaginary part of a dielectric constant of 0 to 60 at a frequency range of 1 MHz to 1000 MHz.

7. The radio frequency applicator according to claim 1, wherein: The sound absorbing layer has an acoustic impedance of between 35 kRayl and 1 MRayl at a frequency range between 0.01 Hz and 100 Hz.

8. The radio frequency applicator according to claim 1, wherein: The electromagnetic matching layer has a real part of a dielectric constant of 2 to 100 and an imaginary part of a dielectric constant of 0 to 60 in a frequency range between 3 kHz and 30 kHz.

9. The radio frequency applicator according to claim 1, wherein: The sound absorbing layer has a real part of a dielectric constant of 2 to 100 and an imaginary part of a dielectric constant of 0 to 60 at a frequency range between 3 kHz and 30 kHz.

10. The radio frequency applicator according to claim 1, wherein: The sound absorbing layer has an acoustic impedance between 0.4 MRayl and 3 MRayl at a frequency range between 50 kHz and 500 kHz.

11. The radio frequency applicator according to claim 1, wherein: The electromagnetic matching layer is formed of a ceramic material.

12. The radio frequency applicator according to claim 1, wherein: The sound absorbing layer is formed of open-cell foam.

13. The radio frequency applicator according to claim 1, wherein: The sound absorbing layer is formed of impregnated cork.

14. The radio frequency applicator according to claim 1, wherein: The sound absorbing layer is formed by an acoustic anechoic absorber.

15. The radio frequency applicator according to claim 1, wherein: The sound absorbing layer is formed of a rubber-based vibration insulating material.

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