Methods and systems for enhancing RF energy delivery during thermoacoustic imaging

Abstract

A method and system for enhancing radiofrequency energy delivery to a tissue region of interest. The method and system direct one or more RF energy pulses into the tissue region of interest by a radiofrequency (RF) applicator, the tissue region of interest comprising an object of interest and at least one reference separated by at least one boundary; detect at least one bipolar acoustic signal generated in the tissue region of interest in response to the RF energy pulse by an acoustic receiver, and process the at least one bipolar acoustic signal to determine its peak-to-peak amplitude; adjust the RF applicator to maximize the peak-to-peak amplitude of the bipolar acoustic signal generated in the tissue region of interest in response to the RF energy pulse generated by the adjusted RF applicator; and direct one or more RF energy pulses into the region of interest by the adjusted RF applicator.

Description

[0001] field

[0002] The present disclosure relates to thermoacoustic imaging, and in particular, to methods and systems for enhancing radio frequency (RF) energy delivery during thermoacoustic imaging.

[0003] background

[0004] 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 radio frequency (RF) pulses, that are directed into a subject to rapidly heat absorptive features within the subject, which in turn induce acoustic pressure waves that are detected using an acoustic receiver, such as one or more thermoacoustic or ultrasound 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] In order to direct RF pulses into a subject during thermoacoustic imaging, a radio frequency (RF) applicator 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 can lead to problems such as 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 lead 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] Although techniques for coupling RF applicators to tissue have been considered, improvements are still needed. It is therefore an object to at least provide novel methods and systems for enhancing radio frequency (RF) energy delivery during thermoacoustic imaging.

[0007] Overview

[0008] It should be understood that the Summary is provided to introduce a selection of concepts in simplified form that are further described below in the Detailed Description. The Summary is not intended to be used to limit the scope of the claimed subject matter.

[0009] Thus, in one aspect, a method for enhancing radio frequency energy delivery to a tissue region of interest is provided, the method comprising: (i) directing one or more RF energy pulses into the tissue region of interest using a radio frequency (RF) applicator, the tissue region of interest comprising an object of interest and at least one reference separated by at least one boundary; (ii) detecting using an acoustic receiver at least one bipolar acoustic signal generated in the tissue region of interest in response to the RF energy pulses, and processing the at least one bipolar acoustic signal to determine its peak-to-peak amplitude; (iii) adjusting the RF applicator to maximize the peak-to-peak amplitude of the bipolar acoustic signal generated in the tissue region of interest in response to the RF energy pulses generated by the adjusted RF applicator; and (iv) directing one or more RF energy pulses into the region of interest using the adjusted RF applicator.

[0010] In one or more embodiments, the method further comprises performing thermoacoustic imaging of the tissue region of interest using the adjusted RF applicator. The method may also comprise determining one or more parameters of the object of interest based on the thermoacoustic imaging, such as determining at least one of fractional fat content and temperature.

[0011] In one or more embodiments, adjusting the RF applicator includes at least one of: adjusting the distance between the RF applicator and the tissue region of interest; adjusting the impedance of the RF applicator; adjusting the volume of the waveguide of the RF applicator; and adjusting the temperature within the waveguide of the RF applicator.

[0012] In one or more embodiments, the boundary is located between at least two different types of tissues. The two different types of tissues may be, for example, one of the following: muscle and fat; blood vessels and fat; and liver tissue and kidney tissue.

[0013] According to another aspect, a system for enhancing RF energy delivery to a tissue region of interest is provided, the tissue region of interest comprising an object of interest and a reference separated by at least one boundary, the system comprising: a thermoacoustic imaging system, the thermoacoustic imaging system comprising: an adjustable radio frequency (RF) applicator, the adjustable RF applicator being configured to transmit RF energy pulses into the tissue region of interest and heat the tissue therein; and an acoustic receiver, the acoustic receiver being configured to receive a bipolar acoustic signal generated in response to heating of the tissue in the tissue region of interest; and one or more processors, the one or more processors being configured to: process the received bipolar acoustic signal during calibration of the RF applicator to determine a setting of the RF applicator that produces an acoustic bipolar signal having a maximum peak-to-peak amplitude.

[0014] In one or more embodiments, one or more processors are further configured to process bipolar acoustic signals received by the acoustic receiver in response to an RF energy pulse transmitted into the tissue region of interest using an RF applicator adjusted to the setting to determine one or more parameters of the object of interest, such as at least one of fractional fat content and temperature.

[0015] In one or more embodiments, the distance between the RF applicator and the tissue region of interest is adjustable.

[0016] In one or more embodiments, the adjustable RF applicator includes at least one tuning element configured to change the impedance of a waveguide of the RF applicator.

[0017] In one or more embodiments, the adjustable RF applicator includes a waveguide having an adjustable volume.

[0018] In one or more embodiments, the adjustable RF applicator includes at least one heating element configured to change the temperature within a waveguide of the RF applicator.

[0019] According to another aspect, an adjustable RF applicator is provided, comprising: a waveguide; at least one radio frequency (RF) transmitter, the at least one RF transmitter being positioned within the waveguide and configured to generate RF energy pulses, the waveguide being configured to guide the generated RF pulses toward a tissue region of interest; and at least one adjustable feature, the at least one adjustable feature being configured to manipulate a property of the waveguide to adjust the frequency of the guided RF energy pulses.

[0020] In one or more embodiments, the at least one adjustable feature is at least one tuning element extending into the waveguide, the extent to which the at least one tuning element extends into the waveguide being adjustable to change the impedance of the waveguide.

[0021] In one or more embodiments, the at least one adjustable feature is a volume adjustment feature configured to adjust an interior volume of the waveguide.

[0022] In one or more embodiments, the at least one adjustable feature is at least one heating element configured to change the temperature within the waveguide.

[0023] According to another aspect, a method for enhancing radiofrequency energy delivery to a tissue region of interest is provided, the method comprising: (i) directing one or more RF energy pulses into the tissue region of interest using a radiofrequency (RF) applicator, the tissue region of interest comprising an object of interest and at least one reference separated by at least one boundary; (ii) detecting, using an acoustic receiver, at least one bipolar acoustic signal generated in the tissue region of interest in response to the RF energy pulses, and processing the at least one bipolar acoustic signal to determine its peak-to-peak amplitude; (iii) adjusting the RF applicator; and (iv) using the adjusted (v) using the acoustic receiver to detect at least one bipolar acoustic signal generated in the tissue region of interest in response to the RF energy pulses generated by the adjusted RF applicator, and processing the at least one bipolar acoustic signal to determine its peak-to-peak amplitude; (vi) comparing the peak-to-peak amplitude determined at step (v) with a previously determined peak-to-peak amplitude; and (vii) repeating steps (iii), (iv) and (v) until the peak-to-peak amplitude of the at least one bipolar acoustic signal determined at step (v) is maximized. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Embodiments will now be described more fully with reference to the accompanying drawings, in which:

[0025] Figure 1 is a schematic diagram of the imaging system;

[0026] Figure 2 and Figure 3 is formed Figure 1 A perspective view of a radio frequency (RF) applicator of a portion of an imaging system;

[0027] Figure 2A is a perspective view of a radio frequency (RF) applicator with an insert removed;

[0028] Figure 3A is formed Figure 2 and Figure 3 a perspective view of a portion of an RF source of an RF applicator;

[0029] Figure 4 is a graph showing an exemplary bipolar acoustic signal;

[0030] Figure 5 is a graph showing an exemplary electric field strength decay curve;

[0031] Figure 6 It is shown by Figure 2 and Figure 3A graph of an exemplary flux (energy gradient) of an RF energy pulse emitted by an RF applicator of FIG.

[0032] Figure 7 is a flow chart of a method for enhancing radiofrequency delivery during thermoacoustic imaging;

[0033] Figure 8 is an exemplary tissue region of interest including an object of interest and a reference;

[0034] Figures 9 to 11 is based on Figure 7 An exemplary bipolar acoustic signal obtained by the method of

[0035] Fig.12 It shows that according to Figure 7 Method Use Figure 1 Imaging systems are used to image various parts of the human body.

[0036] Detailed description of embodiments

[0037] When reading in conjunction with the accompanying drawings, the aforementioned overview and the following detailed description of some examples will be better understood.As used herein, the element or feature introduced in the singular and preceded by the word "a" or "an" should be understood as not necessarily excluding the plural number of the element or feature.In addition, the reference to "one example" or "one embodiment" is not intended to be interpreted as excluding the existence of the additional examples or embodiments also in conjunction with the element or feature.In addition, unless explicitly stated to the contrary, "including (comprising)" or "having (having)" or "including (including)" with a specific characteristic element or feature or a plurality of elements or features of the example or embodiment may include additional elements or features without the characteristic.In addition, it should be understood that the terms "including", "having", "including" mean "including but not limited to", and the terms "including", "having" and "including" have equivalent meanings.

[0038] As used herein, the term "and / or" may include any and all combinations of one or more of the associated listed elements or features.

[0039] 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, directly connected, directly coupled, or directly contacting another element or feature, or there may be intermediate 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 intermediate elements or features.

[0040] 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.

[0041] Methods and systems for enhancing radio frequency (RF) energy delivery during thermoacoustic imaging are described below. Generally, the methods and systems utilize an RF applicator to obtain thermoacoustic data of tissue within a region of interest (ROI) of a subject. The thermoacoustic data is analyzed and the RF applicator is adjusted to enhance energy delivery to the tissue.

[0042] Now go to Figure 1 , an exemplary imaging system is shown and generally identified by reference numeral 20. As can be seen, the imaging system 20 includes a programmed computing device 22 communicatively coupled to an ultrasound imaging system 24 and a thermoacoustic imaging system 26. The ultrasound imaging system 24 and the thermoacoustic imaging system 26 are configured to obtain ultrasound image data and thermoacoustic image data, respectively, of a tissue region of interest ROI associated with a subject S.

[0043] The programming computing device 22 in this embodiment is a personal computer or other suitable processing device, including, for example, a processing unit, the processing unit including one or more processors, system memory (volatile and / or non-volatile memory), other non-removable or removable 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 22 may also include networking capabilities using Ethernet, Wi-Fi and / or other suitable network formats to achieve connection to a shared or remote drive, 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 22 for receiving operator input. A display device (not shown) such as one or more computer screens or monitors is coupled to the computing device 22 for displaying one or more generated images based on the ultrasound image data received from the ultrasound imaging system 24 and / or the thermoacoustic image data received from the thermoacoustic imaging system 26.

[0044] The ultrasound imaging system 24 includes an acoustic receiver in the form of an ultrasound transducer 28, which houses one or more ultrasound transducer arrays 30 configured to transmit sound waves into a region of interest ROI of the subject S. The sound waves directed into the region of interest ROI of the subject echo from the tissue within the region of interest ROI, where different tissues reflect the sound to different degrees. The echoes received by the one or more ultrasound transducer arrays 30 are processed by the ultrasound imaging system 24 and then transmitted to the computing device 22 as ultrasound image data for further processing and for presentation as an ultrasound image that can be interpreted by an operator. In this embodiment, the ultrasound imaging system 24 utilizes B-mode ultrasound imaging technology assuming a nominal sound speed of 1,540 m / s. Since ultrasound imaging systems are well known in the art, further details of the ultrasound imaging system 24 will not be further described here.

[0045] The thermoacoustic imaging system 26 includes an acoustic receiver in the form of a thermoacoustic transducer 32. The thermoacoustic transducer 32 accommodates one or more thermoacoustic transducer arrays 34 and a radio frequency (RF) applicator 36. However, it should be understood that the RF applicator 36 can be accommodated separately from the thermoacoustic transducer 32. The RF applicator 36 is configured to emit short RF energy pulses directed into tissue within a region of interest ROI of a subject. In this embodiment, the RF applicator 36 has a frequency between about 10 MHz and 100 GHz and has a pulse duration between about 0.1 nanoseconds and 10 nanoseconds. The RF energy pulses delivered to the tissue within the region of interest ROI heat the tissue, thereby causing acoustic pressure waves detected by the thermoacoustic transducer 32. The acoustic pressure waves detected by the thermoacoustic transducer 32 are processed and transmitted to the computing device 22 as thermoacoustic image data for further processing and for presentation as a thermoacoustic image that can be interpreted by an operator.

[0046] In this embodiment, the ultrasonic transducer 28 and the thermoacoustic transducer 32 are mechanically interconnected so that the spatial relationship between the one or more ultrasonic transducer arrays 30, the one or more thermoacoustic arrays 34, and the RF applicator 36 is known. The spatial relationship is set using the centerlines of the one or more ultrasonic transducer arrays 30, the one or more thermoacoustic transducer arrays 34, and the RF applicator 36. Each centerline is defined as the midpoint of the area of ​​the corresponding transducer array.

[0047] In this embodiment, the spatial relationship between the one or more ultrasound transducer arrays 30 and the one or more thermoacoustic transducer arrays 34 is such that the centerline of the one or more thermoacoustic transducer arrays 34 is disposed at a known angle α relative to the centerline (also referred to as the axial axis or ultrasound transducer array beam axis) of the one or more ultrasound transducer arrays 30. The spatial relationship between the one or more thermoacoustic transducer arrays 34 and the RF applicator 36 is such that the centerline of the RF applicator 36 is spaced apart from and generally parallel to the centerline of the one or more thermoacoustic transducer arrays 34.

[0048] The imaging system 20 exploits the known spatial relationship between the one or more ultrasound transducer arrays 30 and the one or more thermoacoustic transducer arrays 34 to improve thermoacoustic precision and accuracy.

[0049] The coordinate system of the one or more ultrasonic transducer arrays 30 of the ultrasonic transducer 28 and the coordinate system of the one or more thermoacoustic transducer arrays 34 of the thermoacoustic transducer 32 are mapped by the computing device 22 so that the acquired ultrasonic image and the thermoacoustic image can be registered. Alternatively, the thermoacoustic imaging system 26 can utilize the one or more ultrasonic transducer arrays 30 of the ultrasonic transducer 28 by disconnecting the one or more ultrasonic transducer arrays 30 from the ultrasonic transducer 28 and connecting the one or more ultrasonic transducer arrays 30 to the thermoacoustic transducer 32. As will be appreciated, by doing so, coordinate mapping between the one or more ultrasonic transducer arrays 30 and the one or more thermoacoustic transducer arrays 34 is not required.

[0050] Now go to Figure 2 , Figure 3 and Figure 3A , better showing the RF applicator 36. As can be seen, the RF applicator 36 includes a hollow, generally rectangular, open-ended housing 200 formed of a conductive material. An insert 202 formed of ceramic or other suitable material lines the inner surface of the housing 200. An adjustable backplane 204 is located within the insert 202, adjacent to one end of the housing 200. The adjustable backplane 204 closes one end of the insert 202 to define a partially enclosed space 206 within the insert 202. In this embodiment, the backplane 204 has a hole therein through which a threaded rod 208 extends. A nut 210 attached to the outer major surface of the backplane 204 can threadably engage the threaded rod 208. Rotation of the threaded rod 208 causes the nut 210 to travel along the threaded rod 208, and thus causes the backplane 204 to travel longitudinally within the insert 202. Depending on the direction of rotation of the threaded rod 208, the base plate 204 may be pushed in or out of the insert 202, thereby allowing adjustment of the volume of the partially enclosed space 206. Although not shown, a handle may be provided on the threaded rod 208 to facilitate its rotation.

[0051] Figure 2A is a perspective view of a radio frequency (RF) applicator with the insert removed. The insert 202, the threaded connector 234 to which the control electronics are connected, the flange 236 covering the base 238, and the RF applicator 36 are shown.

[0052] A heating element 214 and a temperature sensor 216 are housed in the space between the outer and inner surfaces of the housing 200. The temperature sensor 216 is configured to transmit temperature data to the computing device 22, the temperature data being indicative of the temperature within the partially enclosed space 206 of the insert 202. The heating element 214 is configured to receive a control signal from the computing device 22 and be energized when the temperature within the partially enclosed space 206 drops below a set threshold. In this manner, the temperature within the partially enclosed space 206 can be effectively controlled by the computing device 22 by comparing the temperature data received from the temperature sensor 216 with the set temperature and energizing the heating element 214 when necessary.

[0053] In this embodiment, the heating element 214 extends along the longitudinal edge of the insert 202. However, those skilled in the art will appreciate that variations are possible. The heating element 214 may of course be positioned at an alternative location in the space between the outer and inner surfaces of the housing 200. In addition, multiple heating elements 214 at various locations in the space between the outer and inner surfaces of the housing 200 may be employed. In this embodiment, the temperature sensor 216 is positioned beside the longitudinal edge of the insert 202, opposite the heating element 214. The temperature sensor 216 may of course be positioned at an alternative location in the space between the outer and inner surfaces of the housing 200. In addition, multiple temperature sensors 216 at various locations in the space between the outer and inner surfaces of the housing 200 may be employed.

[0054] In this embodiment, the RF applicator 36 also includes a plurality of tuning elements 220a and 220b spaced laterally and longitudinally along the housing 200. The tuning element 220a is generally centered along the housing 200 and includes a head 222a and a threaded rod 224a extending therefrom. Figure 2 , the tuning element 220b is on one side and behind the tuning element 220a and includes a head 222b and a threaded rod 224b extending therefrom. The heads 222a and 222b of the tuning elements are in the form of disks and are located outside the housing 200, adjacent to one of its major surfaces. The threaded rods 224a and 224b of the tuning elements pass through threaded holes in the housing 200 that are aligned with the holes in the insert 202 and extend into the partially enclosed space 206 of the insert 202. Each tuning element 220a, 220b can be adjusted by rotating the corresponding head of the tuning element in a clockwise or counterclockwise direction to increase or decrease the extent to which the threaded rod extends into the partially enclosed space 206. Although two tuning elements are shown, it will be understood by those skilled in the art that the RF applicator 36 may include a single tuning element or more than two tuning elements.

[0055] An RF source 230 having an RF transmitter 232 at one end configured to generate pulses of RF energy extends through aligned holes in the housing 200 and the insert 202 such that the RF transmitter 232 is suspended within the partially enclosed space 206 of the insert 202. The RF source 230 also includes a threaded connector 234 to which the control electronics are connected, and a flange 236 that covers a base 238 formed on the housing 200 and through which threaded fasteners pass and engage the base 238, thereby securing the RF source 230 to the housing 200.

[0056] The window 240 is positioned at the open end of the housing 200 and the insert 202. In this embodiment, the window 240 is in the form of a dielectric support and is configured to allow RF energy pulses emitted by the RF transmitter 232 to pass therethrough and exit the RF applicator 36.

[0057] During operation of the RF applicator 36, the RF transmitter 232 of the RF source 230 is adjusted to generate short RF energy pulses that enter the partially enclosed space 206 of the insert 202. The housing 200 and the insert 202, which act as waveguides, confine and guide the emitted RF energy pulses so that the RF energy pulses travel along the RF applicator 36 in the direction indicated by the arrow A and then travel out of the RF applicator through the window 240. Once the RF energy pulses travel out of the RF applicator 36 through the window 210, they are directed into the subject's body to deliver energy to tissue within the region of interest ROI of the subject S.

[0058] During operation of the RF applicator 36, the frequency of the RF energy pulses can be changed in a variety of ways. For example, using one or more of the tuning elements 220a, 220b, the RF applicator 36 can be tuned by inserting more or less of the threaded rod into the partially enclosed space 206 of the insert 202 to change the impedance of the waveguide. When the tuning elements 220a, 220b are adjusted so that only a small amount of their threaded rods extend into the partially enclosed space 206, the tuning elements 220a, 220b act as parallel capacitors. When the tuning elements 220a, 220b are adjusted to increase the amount of the threaded rod extending into the partially enclosed space 206, the capacitance increases. When the tuning elements 220a, 220b have been adjusted so that the amount of the threaded rod extending into the partially enclosed space 206 is greater than one-quarter of the wavelength in the waveguide defined by the housing 200 and the insert 202, the tuning elements 220a, 220b are equivalent to a series LC circuit and resonate. Further increasing the amount that the threaded rod extends into the partially enclosed space 206 of the insert 202 causes the impedance to change from capacitive to inductive.

[0059] Alternatively or in addition, the frequency of the RF energy pulses emitted by the RF applicator 36 may be adjusted by changing the temperature within the partially enclosed space 206 of the insert 202. Specifically, by increasing the temperature of the partially enclosed space 206 within the insert 202 using the heating element 214 and the temperature sensor 216, the frequency of the RF energy pulses emitted by the RF applicator 36 may be increased. By decreasing the temperature of the partially enclosed space 206 within the insert 202, the frequency of the RF energy pulses emitted by the RF applicator 36 may be decreased.

[0060] Alternatively or additionally, the frequency of the RF energy pulses emitted by the RF applicator 36 may be tuned or adjusted by moving the base plate 204, thereby changing the volume of the partially enclosed space 206 of the insert 202. As will be described, adjusting the frequency of the RF energy pulses may help enhance energy delivery during thermoacoustic imaging.

[0061] Thermoacoustic imaging can be used to contrast fat or adipose tissue with soft or lean tissue because they have lower conductivity and dielectric constant in RF than other soft or lean tissues that are rich in water and ions. Fat and adipose tissue also has a lower absorption coefficient than soft or lean tissues (such as muscle). Thus, during thermoacoustic imaging of a region of interest that includes a boundary between fat or adipose tissue and soft or lean tissue, a bipolar acoustic signal is generated that is received by the thermoacoustic transducer 32. This is because soft or lean tissue absorbs more heat than fat or adipose tissue, causing it to expand rapidly across the boundary and into the less expanded fat or adipose tissue, and then rapidly contract. The intensity or peak-to-peak value of the bipolar acoustic signal depends on the relative absorption characteristics of the fat or adipose tissue and the soft or lean tissue.

[0062] Figure 4 4. Exemplary bipolar acoustic signals 400, 405, and 410 are shown in FIG. The bipolar acoustic signals 400, 405, and 410 are generated in response to thermoacoustic imaging of a tissue region of interest ROI that includes a first tissue 420 and a second tissue 425 of a different type separated by a boundary 415. Dashed line 430 indicates a time point corresponding to boundary 415. The peak-to-peak amplitude of each bipolar acoustic signal 400, 405, and 410 is proportional to the difference in absorption coefficients of the first tissue 420 and the second tissue 425. Figure 4, the first tissue 420 is a kidney and has no fat. For the bipolar acoustic signal 400, the second tissue 425 is a fatty liver with a high fractional fat content. For the bipolar acoustic signal 405, the second tissue 425 is an unhealthy liver with a medium fractional fat content. For the bipolar acoustic signal 410, the second tissue 425 is a healthy liver with a low fractional fat content. It can be seen that the peak-to-peak value of the bipolar acoustic signal 400 is greater than the peak-to-peak value of the bipolar acoustic signals 405 and 410, and the peak-to-peak value of the bipolar acoustic signal 405 is greater than the peak-to-peak value of the bipolar acoustic signal 410. The difference in the peak-to-peak values ​​of the bipolar acoustic signals 400, 405, and 410 indicates the extent to which the first tissue 420 expands into the boundary 415 and the second tissue 425 before contracting.

[0063] Different tissues have characteristic dielectric properties at specific frequencies. The dielectric properties determine how much energy the tissue absorbs. When an RF energy pulse is transmitted through tissue, the RF energy pulse is attenuated. The amount of attenuation can be determined using the dielectric properties of the tissue and the physical properties of the tissue. Fatty tissue absorbs less energy than lean tissue. Therefore, fat tissue attenuates RF energy pulses less than normal tissue. Using these properties, the amount of attenuation of the tissue can be estimated, and this can be used to determine how much fat is in the tissue. In this way, adjusting the frequency of the RF energy pulses emitted by the RF applicator 36 can help enhance energy delivery during thermoacoustic imaging.

[0064] exist Figure 5 2 and 3. Exemplary electric field strength attenuation curves 500 and 505 are shown in FIG. Each electric field strength attenuation curve 500, 505 represents the electric field strength attenuation of tissues 510, 515, respectively, as a function of distance from the RF applicator 36 of the thermoacoustic imaging system 26. Tissue 510 associated with electric field strength attenuation curve 500 has a higher fat concentration than tissue 515 associated with electric field strength attenuation curve 505.

[0065] Figure 6 The flux (energy gradient) of the RF energy pulse generated by the RF applicator 36 as it leaves the waveguide defined by the housing 200 and the insert 202 is shown. The window 240 is located at the zero value of the X-axis and is centered at the zero value of the X-axis. It can be seen that the electric field strength decreases as the distance from the center of the RF applicator 36 increases. In this way, adjusting the distance between the RF applicator 36 and the tissue can help enhance energy delivery during thermoacoustic imaging.

[0066] The imaging system 20 exploits the relationship between the energy absorption characteristics of the different types of tissue being imaged, the adjustability of the RF applicator 36, and the distance between the RF applicator 36 and the tissue to enhance energy delivery during thermoacoustic imaging.

[0067] Now go to Figure 7 , a method for enhancing RF energy delivery during thermoacoustic imaging is shown. During the method, a region of interest ROI (step 710) is initially located within a subject S to be imaged, containing an object of interest and a reference separated by at least one boundary. In this embodiment, an ultrasound imaging system 24 is used to locate the region of interest ROI. Specifically, ultrasound image data obtained by the ultrasound imaging system 24 is transmitted to a computing device 22. The ultrasound image data is processed by the computing device 22, and a reconstructed ultrasound image is presented on a display device. The operator moves the ultrasound transducer 28 on the subject's body until the region of interest is located. When the region of interest is located, the computing device 22 overlays information associated with the angle of the centerline of one or more transducer arrays 30 of the ultrasound transducer 28 on the reconstructed ultrasound image on the display device. This information is used to provide feedback to the operator to ensure that the axial axis of the ultrasound transducer 28 is substantially perpendicular to the boundary between the object of interest and the reference.

[0068] exist Figure 8 An exemplary region of interest 800 including an object of interest 805 and a reference 810 is shown in FIG. In this embodiment, the object of interest 805 is the liver of a subject, and the reference 810 is the kidney of the subject. Figure 8 Also shown is an RF applicator 36 and a thermoacoustic transducer 32 .

[0069] At least one boundary between the object of interest and the reference is then identified in the reconstructed ultrasound image (step 720). In this embodiment, the operator uses an input device (such as a mouse coupled to the computing device 22) to identify the at least one boundary. Specifically, the operator draws a box that encompasses at least a portion of the object of interest 805, at least a portion of the reference 810, and the identified boundary between portions of the object of interest and the reference. The computing device 22 provides feedback to the operator via a display device to indicate the approximate angle between the box and the boundary to ensure that the box is approximately perpendicular to the boundary.

[0070] exist Figure 8 8. As can be seen, the frame 815 encompasses a portion of the object of interest 805 (liver), a portion of the reference 810 (kidney), and a boundary 820 between the object of interest 805 and the reference 810. The boundary 820 is selected at a specific location 825 where the liver and kidney are closely related to each other.

[0071] Then perform RF applicator calibration. During calibration, adjust the RF applicator 36 to generate short RF energy pulses. The RF energy pulses travel out of the waveguide defined by the housing 200 and the insert 202, through the window 240, and are directed into the region of interest 800 to deliver energy to the object of interest 805 and the reference 810 within the region of interest ROI. In response, a bipolar acoustic signal is generated that is detected by the thermoacoustic transducer 32 (step 730).

[0072] Since the angle α between the centerline of the one or more transducer arrays 30 of the ultrasound transducer 28 and the centerline of the one or more transducer arrays 34 of the thermoacoustic transducer 32 is known, the operator can adjust the position of the thermoacoustic transducer 32 relative to the subject's body so that the thermoacoustic imaging system 26 can obtain thermoacoustic image data of the region of interest at a desired imaging angle σ. The desired imaging angle σ causes the centerline of the one or more transducer arrays 34 of the thermoacoustic transducer 32 to extend through the boundary 820 between the object of interest 805 and the reference 810.

[0073] The bipolar acoustic signal is then transmitted to the computing device 22 for processing (step 740). In this embodiment, the computing device 22 is programmed to determine the peak-to-peak amplitude of the bipolar acoustic signal. Fig. 9 An exemplary bipolar acoustic signal 900 is shown in . As can be seen, bipolar acoustic signal 900 includes a peak-to-peak amplitude 910 .

[0074] The RF applicator 36 is then adjusted to thereby change the frequency of the emitted RF energy pulses (step 750). In this embodiment, the RF applicator 36 can be adjusted by rotating one or both of the tuning elements 220a and 220b to change the impedance of the waveguide, by moving the base plate 204 to change the volume of the partially enclosed space 206 of the insert 202, and / or by increasing or decreasing the temperature within the partially enclosed space 206 of the insert 202. In addition, the distance between the RF applicator 36 and the region of interest ROI can be increased or decreased (e.g., by moving the RF applicator to a different location on the patient's skin or pressing the applicator into the subject to compress the subject).

[0075] After the RF applicator adjustment, the RF applicator 36 is again adjusted to generate a short RF energy pulse that is directed into the region of interest 800 to deliver energy to the object of interest 805 and the reference 810 (step 760). The resulting bipolar acoustic signal generated in the tissue of the region of interest and received by the thermoacoustic transducer 32 is again transmitted to the computing device 22 for processing to determine the peak-to-peak amplitude of the bipolar acoustic signal (step 770). The computing device 22 then compares the peak-to-peak amplitude of the bipolar acoustic signal with the peak-to-peak amplitude determined in step 740 to determine whether the peak-to-peak amplitude has increased (step 780). Fig.10 1000 includes a peak-to-peak amplitude 1010 that is greater than that of the bipolar signal 900 ( Fig. 9 The peak-to-peak amplitude 910 of the embodiment shown in FIG. 1 is larger.

[0076] If the peak-to-peak amplitude increases, the process returns to step 730 and re-executes steps 730 through 770. These steps are performed iteratively until the acoustic bipolar signal having the maximum peak-to-peak amplitude is determined (step 790). Fig.11 An exemplary bipolar acoustic signal 1100 is shown having a maximum peak-to-peak amplitude 1110. It can be seen that the peak-to-peak amplitude 1110 is greater than the peak-to-peak amplitude 910 ( Fig. 9 ) and a peak-to-peak amplitude of 1010( Fig.10 ). At this stage, the RF applicator calibration is considered complete.

[0077] When the RF applicator 36 has been adjusted to maximize the peak-to-peak amplitude of the generated bipolar acoustic signal, the RF energy delivered to the region of interest ROI is considered to be enhanced, and the thermoacoustic imaging system 26 is determined to be in a condition for performing thermoacoustic imaging of the region of interest. The thermoacoustic imaging of the region of interest is then performed using the adjusted RF applicator 36, and the resulting bipolar acoustic signal generated in the tissue of the region of interest and received by the thermoacoustic transducer 32 is transmitted to the computing device 22 for processing (step 795). As will be understood, when the bipolar acoustic signal has been maximized, the imaging result is more accurate. The bipolar acoustic signal is then processed to determine one or more parameters of the object of interest (step 770). For example, the bipolar acoustic signal can be processed to estimate the fractional fat content of the object of interest, as described in U.S. Patent Nos. 9,888,879, 9,888,880 and 9,980,677, the relevant parts of which are incorporated herein by reference. As will be understood, the bipolar acoustic signal can be processed to determine other factors, such as the temperature of the tissue.

[0078] Those skilled in the art will appreciate that in embodiments, the computing device may be programmed to adjust the parameters of the RF applicator. For example, the computing device may be coupled to one or more actuators configured to adjust the tuning elements 220a, 220b and / or the threaded rod 308.

[0079] Those skilled in the art will appreciate that the above method can be performed on a phantom designed to simulate a region of interest. In this embodiment, the RF applicator can be adjusted to maximize the peak-to-peak amplitude of the bipolar acoustic signal before imaging the patient. In addition, the method can be performed on multiple phantoms of various sizes to simulate patients of different sizes.

[0080] Although in the embodiments the object of interest is described as the liver and the reference is described as the kidney, one skilled in the art will appreciate that thermoacoustic data may be obtained for other parts of the body. Fig.12 As shown, various parts of the body that can be imaged using the above-mentioned systems and methods include extracardiac / pericardial adipose tissue 1301, liver 1302, subcutaneous adipose tissue 1303, visceral adipose tissue 1304, subcutaneous gluteal and femoral adipose tissue 1305, perivascular adipose tissue 1306, myocardial fat 1307, pancreatic fat 1308, renal sinus fat 1309 and muscle fat 1310.

[0081] In another embodiment, the space enclosed by the insert 202, the base plate 204, and the window 240 may be partially or completely filled with a material that conducts RF energy pulses, such as a liquid, gel, ceramic, or putty. As will be appreciated, in this embodiment, the material that partially or completely fills the space may be heated or cooled, thereby increasing or decreasing the temperature within the insert 202. Thus, the frequency of the RF energy pulses may be adjusted.

[0082] Although the embodiments have been described above with reference to the accompanying drawings, those skilled in the art will appreciate that changes and modifications may be made without departing from the scope defined by the appended claims.

Claims

1. A method for enhancing radiofrequency energy delivery to a tissue region of interest, the method comprising: (i) transmitting one or more RF energy pulses by a radio frequency (RF) applicator into the tissue region of interest, the tissue region of interest comprising an object of interest and at least one reference separated by at least one boundary; (ii) detecting, by an acoustic receiver, at least one bipolar acoustic signal generated in the tissue region of interest in response to the RF energy pulses, and processing the at least one bipolar acoustic signal to determine its peak-to-peak amplitude; (iii) adjusting the RF applicator to maximize the peak-to-peak amplitude of a bipolar acoustic signal generated in the tissue region of interest in response to the RF energy pulses generated by the adjusted RF applicator; as well as (iv) transmitting, by means of the adjusted RF applicator, one or more pulses of RF energy into the tissue region of interest, Wherein adjusting the RF applicator comprises adjusting the impedance of the RF applicator by adjusting the extent to which at least one tuning element of the RF applicator extends into a waveguide of the RF applicator to change the impedance of the waveguide. 2 . The method of claim 1 , further comprising performing thermoacoustic imaging of the tissue region of interest using the adjusted RF applicator. 3 . The method of claim 2 , further comprising determining one or more parameters of the object of interest based on the thermoacoustic imaging. 4 . The method of claim 3 , wherein the one or more parameters of the object of interest include at least one of fractional fat content and temperature.

5. The method of claim 1, wherein adjusting the RF applicator further comprises adjusting at least one of: adjusting the distance between the RF applicator and the tissue region of interest; adjusting the volume of the waveguide of the RF applicator; and The temperature within the waveguide of the RF applicator is adjusted. The method of claim 1 , wherein the boundary is at a location between at least two different types of tissue.

7. The method of claim 6, wherein the two different types of tissue are one of the following: muscle and fat; blood vessels and fat; and Liver and kidney tissue.

8. A system for enhancing radiofrequency energy delivery to a tissue region of interest, the tissue region of interest comprising an object of interest and a reference separated by at least one boundary, the system comprising: A thermoacoustic imaging system, comprising: an adjustable radio frequency (RF) applicator configured to transmit RF energy pulses into the tissue region of interest and heat the tissue therein; and an acoustic receiver configured to receive a bipolar acoustic signal generated in response to heating of the tissue in the tissue region of interest; and One or more processors, the one or more processors configured to: processing the received dipole acoustic signal during calibration of the RF applicator to determine a setting of the RF applicator that produces an acoustic dipole signal having a maximum peak-to-peak amplitude, Wherein the extent to which at least one tuning element of the RF applicator extends into a waveguide of the RF applicator is adjustable to change the impedance of the waveguide.

9. The system of claim 8, wherein the one or more processors are further configured to: Bipolar acoustic signals received by the acoustic receiver in response to a pulse of RF energy transmitted into the tissue region of interest using the RF applicator adjusted to a setting are processed to determine one or more parameters of the object of interest.

10. The system of claim 9, wherein the one or more parameters of the object of interest are at least one of fractional fat content and temperature.

11. The system of claim 8, wherein a distance between the RF applicator and the tissue region of interest is adjustable.

12. The system of claim 8, wherein the RF applicator comprises a waveguide having an adjustable volume.

13. The system of claim 8, wherein the RF applicator comprises at least one heating element configured to change the temperature within a waveguide of the RF applicator.

14. A method for enhancing radiofrequency energy delivery to a tissue region of interest, the method comprising: (i) transmitting one or more RF energy pulses into the tissue region of interest using a radio frequency (RF) applicator, the tissue region of interest comprising an object of interest and at least one reference separated by at least one boundary; (ii) detecting, using an acoustic receiver, at least one bipolar acoustic signal generated in the tissue region of interest in response to the RF energy pulses, and processing the at least one bipolar acoustic signal to determine its peak-to-peak amplitude; (iii) adjusting the RF applicator; (iv) transmitting one or more RF energy pulses into the tissue region of interest using the adjusted RF applicator; (v) detecting, using the acoustic receiver, at least one bipolar acoustic signal generated in the tissue region of interest in response to the RF energy pulses generated by the adjusted RF applicator, and processing the at least one bipolar acoustic signal to determine its peak-to-peak amplitude; (vi) comparing the peak-to-peak amplitude determined at step (v) with a previously determined peak-to-peak amplitude; as well as (vii) repeating steps (iii), (iv) and (v) until the peak-to-peak amplitude of the at least one bipolar acoustic signal determined at step (v) is maximized, Wherein adjusting the RF applicator comprises adjusting the impedance of the RF applicator by adjusting the extent to which at least one tuning element of the RF applicator extends into a waveguide of the RF applicator to change the impedance of the waveguide.

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