Method and system for microwave scanning of biological tissue

Abstract

Disclosed are systems and methods for microwave scanning of biological tissue that allow the tissue's response to a microwave signal to be measured without other unwanted signals, thereby eliminating the need for suboptimal filtering techniques. The collected signals can be conditioned using novel techniques. Disclosed are also systems and methods for reconstructing images of biological tissue that provide quantitative images related to the electrical properties of the tissue in a repeatable and stable manner.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 433,894, filed December 20, 2022, the entire contents of which are incorporated herein by reference in their entirety.

[0002] The present invention relates generally to scanning biological tissue, and more particularly to a method and system for microwave scanning of biological tissue. [Background technology]

[0003] Imaging and sensing of biological tissues by various techniques is desired to improve the detection and diagnosis of disease. Many of the advances in medical microwave imaging relate to breast imaging.

[0004] One technique for medical microwave imaging uses radar, in which reflections from tissue are focused to produce images that show where tissue properties change. Tomography is another technique that measures the signal transmitted through tissue, compares it to a signal generated by a model, and iteratively updates the model's properties until the measured and simulated signals match. Other techniques for imaging signals transmitted through tissue include intensity change tracking, holography, scattered power mapping, and time-delay spectroscopy.

[0005] In either case, there are challenges associated with (i) coupling microwave signals into tissue, (ii) recording very weak signal levels, and (iii) developing algorithms that can efficiently reconstruct images and interpret the results.

[0006] (i) When it comes to coupling microwave signals into biological tissue, challenges often arise from the large difference in electrical properties between tissue and air.

[0007] (ii) Regarding recording very low-level signals, another limiting aspect of microwave imaging relates to the extremely weak signals that may need to be detected. Such signals may be buried in other unwanted signals that must be removed for proper imaging. These unwanted signals may be reflections from the skin or other components in the imaging space. Complex algorithms can be employed to remove such spurious responses, but they often do not effectively extract the desired signal. Extracting small signals from large signals is a limiting factor, since it requires microwave receivers to have a significant dynamic range. The inability to extract small signals inherently limits the sensitivity of imaging or sensing systems.

[0008] (iii) Regarding developing algorithms capable of efficiently reconstructing images and interpreting the results, there are several limiting aspects of the algorithms employed to produce microwave images. Tomographic techniques involve evaluating the properties of a model in order to fit simulated signals to measurements. The model is iteratively updated until the measured and simulated signals match. This problem is inherently ill-conditioned, in part due to the multiple paths that the signal can take through the tissue, and often converges to an inaccurate solution. To avoid such cases, additional information is usually added, such as a range of property values ​​or information gathered by additional imaging modalities. This requires prior knowledge of the tissue, further complicating the already complex imaging algorithms.

[0009] With radar techniques, images do not measure actual properties but instead track locations where properties change. These changes may correspond to interfaces between healthy tissues, such as fatty and glandular tissue, in addition to any lesions or abnormalities present. Radar images typically contain multiple "hot spots" that require interpretation, related to the location of known lesions. Interpreting the intensity of the response is particularly difficult because the response is modified by several processing steps before forming the image. Like tomography, radar images benefit from additional information about the tissue, such as the range of properties, because this information improves focusing and detection.

[0010] For most of the microwave imaging approaches presented, a complication is the interpretation of the data. As highlighted above, tomography involves complex algorithms that may not converge to an exact solution, while radar images typically contain multiple responses that require interpretation. To incorporate microwave imaging into women's care pathways, it is important to correlate these images with the patient's medical history. Clinical imaging information typically consists of mammograms, as well as ultrasound and magnetic resonance imaging (MRI) used as diagnostic aids.

[0011] In most microwave scanners, patients are typically positioned face down, with the breast extending through a hole in the examination table. This position differs significantly from readily available mammograms, complicating comparison of microwave images with clinically available imaging data. Ultrasound images can be acquired for localized areas when examining abnormalities or with the patient in the supine position for automated breast ultrasound systems. Magnetic resonance imaging is used for patient subpopulations (e.g., women at high risk for breast cancer or undergoing tumor staging). MRI is characterized by a prone position but does not use a coupling fluid, as is customary with microwave scanning. Differences in breast geometry during microwave imaging, mammography, ultrasound, and MRI scans complicate interpretation of microwave breast images with clinically available information.

[0012] Other limitations of the prior art include signal clutter from other unwanted responses, low signal levels, and the ability to image only areas of the nipple that are proximal to the nipple. Many systems also rely on reflection-based imaging rather than mapping the properties themselves, revealing only the location of interfaces where properties change.

[0013] Therefore, there is a need for alternative devices and methods for imaging biological tissue with microwave signals that may alleviate at least some of the above-mentioned problems and limitations. The above background is provided solely to facilitate understanding of the art to which this disclosure pertains, and is not intended to be an admission that any technology is pertinent prior art. [Prior art documents] [Non-patent literature]

[0014] [Non-Patent Document 1] J. Bourqui and E. Fear, “System for Bulk Dielectric Permittivity Estimation of Breast Tissues at Microwave Frequencies”, IEEE Transactions on Microwave Theory and Techniques, Vol. 64, No. 9, September 2016. [Non-patent document 2] “Highly Accurate Debye Models for Normal and Malignant Breast Tissue Dielectric Properties at Microwave Frequencies,IEEE Microwave And Wireless Components Letters,Vol.17,No.12,December 2007 [Non-patent document 3] M. Lazebnik, M. Okoniewski, JHBooske and SCHagness, “Highly Accurate Debye Models for Normal and Malignant Breast Tissue Dielectric Properties at Microwave Frequencies,” in IEEE Microwave and Wireless Components Letters, vol.17, no.12, pages 822-824, December 2007, doi:10.1109 / LMWC.2007.910465 [Non-patent document 4] M. Lazebnik, M. McCartney, D. Popovic, CBWatkins, MJ Lindstrom, J. Harter, S. Sewall, A. Magliocco, JHBooske, M. Okoniewski, and SCHagness, “A large-scale study of the ultrawideband microwave dielectric properties of normal breast tissue obtained from reduction surgeries”, Phys Med Biol.21 May 2007;52(10):2637~56.doi:10.1088 / 0031-9155 / 52 / 10 / 001.Epub April 23, 2007 Summary of the Invention

[0015] In one aspect, disclosed is a system and method for microwave scanning of biological tissue that allows the response of biological tissue to a microwave signal to be measured without other unwanted signals, thereby eliminating the need for suboptimal filtering techniques. The collected signals can be conditioned using techniques described herein.

[0016] Disclosed in another aspect is a system and method for reconstructing images of biological tissue that provides quantitative images related to electrical properties of the tissue in a repeatable and stable manner.

[0017] According to one broad aspect, there is provided a method of microwave scanning of biological tissue, the method including: operating antenna elements in an antenna set, the antenna set comprising a transmitting antenna element in a transmitting antenna array and one or more receiving antenna elements in a receiving antenna array; operating at least one microwave transmitter to generate microwave interrogation signals for transmission into the biological tissue by the transmitting antenna elements; receiving, by at least one microwave receiver, one or more received microwave signals from each of the one or more receiving antenna elements; applying preconditioning to each received microwave signal to generate a corresponding conditioned microwave signal, the preconditioning separating tissue response characteristics from extraneous response factors; analyzing the conditioned microwave signals to determine one or more tissue response characteristics associated with the biological tissue; and generating an output based on the determined one or more tissue response characteristics.

[0018] In some embodiments, operating the antenna elements includes activating a first switch network to couple the transmit elements to at least one microwave transmitter and activating a second switch network to couple the one or more receive elements to at least one microwave receiver.

[0019] In some embodiments, the step of operating the antenna elements includes activating a microwave transmitter coupled to the transmitting antenna element and a microwave receiver coupled to the receiving antenna element.

[0020] In some embodiments, the biological tissue is placed in a scanning region between the transmitting and receiving antenna arrays and in contact with the antenna arrays.

[0021] In some embodiments, a dielectric coating material is coupled to one or more of the transmit antenna array and the receive antenna array and contacts the biological tissue within the scanning region.

[0022] In some embodiments, the dielectric coating material has a dielectric constant of less than 5 and a thickness of up to 2 mm, and more preferably has a dielectric constant of about 2.5 and a thickness of less than 0.5 mm.

[0023] In some embodiments, applying preconditioning to the microwave signal includes identifying a pair of transmit and receive antennas associated with the microwave signal, determining one or more placement parameters of the antenna array, and based on the determination, applying a path-specific correction factor to the microwave signal to generate a corrected microwave signal, and applying an antenna response compensation factor to the corrected microwave signal to generate an adjusted microwave signal.

[0024] In some embodiments, the per-path correction factors include correction factors for phase and amplitude corrections for each receive and transmit path associated with a transmit and receive antenna pair.

[0025] In some embodiments, the antenna array geometry parameters correspond to one or more of: (i) the positional spacing of antenna elements on each array surface; (ii) the axial spatial distance between antenna arrays; and / or (iii) the rotational orientation of the antenna.

[0026] In some embodiments, the antenna response compensation coefficients include an antenna gain compensation coefficient and a phase center compensation coefficient, and the antenna compensation coefficients are related to (i) the type of biological tissue and (ii) the geometry parameters of the antenna array.

[0027] In some embodiments, the antenna response compensation coefficients and path-specific correction coefficients are generated by a simulation tool that generates baseline compensation coefficients and baseline correction coefficients.

[0028] In some embodiments, each antenna array comprises a plurality of slot antenna elements, each slot antenna having its own shielding interface.

[0029] In some embodiments, each switch network includes one or more switch sub-networks and each antenna array includes one or more antenna sub-arrays.

[0030] According to another broad aspect, there is provided a system for microwave scanning of biological tissue, comprising: a transmit antenna array and a receive antenna array, each comprising a plurality of antenna elements, the antenna arrays separated along an axis by an axial separation to define a scan region for receiving the biological tissue; first and second switch networks, each coupled to a respective transmit antenna array and receive antenna array, the first switch network and second switch network comprising a plurality of switch elements; at least one microwave transmitter coupled to the transmit antenna array via the first switch network; and at least one microwave receiver coupled to the receive antenna array via the second switch network; and a controller coupled to the first and second switch networks and to the at least one microwave transmitter and the at least one microwave receiver, the controller operable to perform the method of any one of the preceding paragraphs.

[0031] According to another broad aspect, there is provided a system for microwave scanning of biological tissue, comprising: a transmit antenna array and a receive antenna array, each antenna array comprising a plurality of antenna elements, the antenna arrays separated by an axial separation along an axis to define a scan region for receiving the biological tissue; at least one microwave transmitter coupled to the transmit antenna array; at least one microwave receiver coupled to the receive antenna array; and a controller coupled to the at least one microwave transmitter and the at least one microwave receiver, the controller operable to perform the method of any one of the preceding paragraphs.

[0032] In some embodiments, the at least one microwave transmitter is a plurality of microwave transmitters, each coupled to a separate antenna element of a transmit antenna array, and the at least one microwave receiver is a plurality of microwave receivers, each coupled to a separate antenna element of a receive antenna array.

[0033] According to another broad aspect, there is provided an antenna assembly for use with a system for microwave scanning of biological tissue, comprising at least two antenna arrays separated by an axial separation along an axis to define a scanning region for receiving the biological tissue, and a dielectric covering material coupled to and covering each antenna array and in contact with biological tissue inserted into the defined imaging region.

[0034] In some embodiments, each antenna array comprises a plurality of slot antennas.

[0035] In some embodiments, each slot antenna has its own shielding interface.

[0036] In some embodiments, the dielectric coating material has a dielectric constant of less than 5 and a thickness of up to 2 mm, and more preferably has a dielectric constant of about 2.5 and a thickness of less than 0.5 mm.

[0037] In order that the above-mentioned features of the present invention may be understood in detail, several embodiments are shown in the accompanying drawings. It should be noted, however, that the accompanying drawings illustrate only typical embodiments of the present invention and therefore should not be considered as limiting the scope of the present invention. [Brief explanation of the drawings]

[0038] [Figure 1] 1 is a perspective view of an exemplary apparatus for microwave imaging in accordance with a disclosed example; [Figure 2A]1 is an exemplary two-dimensional (2D) reconstruction of the dielectric properties of exemplary breast tissue. [Figure 2B] 1 is an exemplary three-dimensional (3D) reconstruction of exemplary breast tissue. [Figure 3A] FIG. 1 is an isometric view of two curved antenna arrays and a mechanical system, according to some embodiments. [Figure 3B] FIG. 1 illustrates an isometric view of a tilted antenna array and mechanical system, according to some embodiments. [Figure 3C] FIG. 1 is an isometric view of an exemplary antenna array, according to some embodiments. [Figure 4A] FIG. 1 is a diagram of an exemplary microwave imaging system in accordance with a disclosed embodiment. [Figure 4B] FIG. 1 is a diagram of another exemplary microwave imaging system in accordance with disclosed embodiments. [Figure 5A] A diagram of two antenna arrays and the multiple signal paths extending between them. [Figure 5B] A two-dimensional view of two antenna arrays and the multiple signal paths extending between them. [Figure 6] FIG. 1 is an isometric view of an antenna array with multiple slot antennas integrated into the main printed circuit board (PCB). [Figure 7] FIG. 1 is a diagram of another exemplary antenna array comprising multiple slot antennas mounted on a main printed circuit board (PCB). [Figure 8A] 1A and 1B are diagrams of an example slot antenna and an exploded view of the slot antenna in accordance with the teachings herein. [Figure 8B] Various exemplary views of the slot antenna of Figure 8A, including a top plan view (top left), a perspective view (top right), a cross-sectional view (bottom left) along section line A-A' of the top left image, and a bottom perspective view (bottom right). [Figure 8C]FIG. 10 is a diagram of another exemplary slot antenna in accordance with the teachings herein. [Figure 8D] FIG. 1 illustrates an isometric view of a slot antenna integrated into a multilayer printed circuit board in accordance with some embodiments. [Figure 8E] FIG. 1 is an isometric view of a slot antenna and its microstrip feed, according to some embodiments. [Figure 8F] 1A-1C are top views of various possible slot shapes of a slot antenna, according to some embodiments. [Figure 9] 4 is a graph showing coupling between antenna elements with and without a coating. [Figure 10A] 10 is a diagram of a raised waveguide plate on top of a slot antenna according to some embodiments. [Figure 10B] FIG. 10B is a partially transparent view of the waveguide of FIG. 10A. [Figure 10C] 10B-10C show various views of the waveguide plate of FIG. 10A, including a front view (top left), a side view (top right), and a bottom view (bottom left). [Figure 11] FIG. 1 is a side view of a slot antenna and a thin dielectric covering for separating the skin from the radiating member, according to some embodiments. [Figure 12A] 1 is an exemplary graph showing the effect of applying a thin, low-permittivity dielectric coating to an antenna array. [Figure 12B] 10 is another exemplary graph showing the effect of applying a dielectric coating to an antenna array. [Figure 13A] 1 is an illustration of an exemplary method for scanning biological tissue using microwave signals. [Figure 13B] FIG. 1 illustrates an exemplary method for preconditioning a microwave signal. [Figure 13C] FIG. 10 is a diagram of another exemplary method for preconditioning a microwave signal. [Figure 14A] FIG. 1 is a diagram of an exemplary near-field radiation pattern in predominantly fatty tissue. [Figure 14B] FIG. 10 is a diagram of an exemplary near-field radiation pattern in tissue with a greater proportion of glands. [Figure 15A] FIG. 1 is a diagram of an exemplary near-field phase pattern in predominantly fatty tissue. [Figure 15B] FIG. 10 is an illustration of an exemplary near-field phase pattern in tissue with a greater proportion of glands. [Figure 16A] 10 is a graph plotting gain compensation for two different tissue types over different periods. [Figure 16B] 10 is a graph plotting phase center compensation for two different tissue types over different periods. [Figure 17A] 10 is a graph illustrating the correction resulting from using gain compensation for microwave signal attenuation. [Figure 17B] 10 is a graph illustrating the correction resulting from using phase center compensation on the phase of a microwave signal. [Figure 18A] Graph of the results of the dielectric constant correction using the signal when antenna response compensation is applied compared to the original signal, where the material properties are calculated using the Nicholson-Ross method. [Figure 18B] Graph of the results of conductivity correction using the signal after applying antenna response compensation compared to the original signal, where material properties are calculated using the Nicholson-Ross method. [Figure 19A] FIG. 1 is a diagram of an exemplary simulation model. [Figure 19B] 1 is a graph showing simulated versus measured results comparing the transmission coefficient with frequency when transmitting a microwave signal through canola oil (a lipid-mimicking liquid). [Figure 19C] 1 is a graph showing simulated versus measured results of the transmission coefficient compared to time when a microwave signal is transmitted through canola oil (a lipid-mimicking liquid). [Figure 19D] 10 is a histogram of the mean tissue permittivity calculated using 333 simulated signals transmitted through the body tissue model Group 1 "Low." [Figure 19E]10 is a histogram of the mean tissue permittivity calculated when antenna response compensation is applied to 333 simulated transmitted signals traveling through body tissue model Group 1 "Low." [Figure 19F] 1 is a histogram of the average permittivity of a glycerin-filled bag calculated using approximately 300 measured transmission signals. [Figure 19G] This is a histogram of the calculated average permittivity of a glycerin-filled bag when antenna response compensation is applied to approximately 300 measured transmitted signals. Antenna response compensation coefficients for Group 3 "Medium" are used. [Figure 19H] 1 is a histogram of the average permittivity of a water-filled bag calculated using approximately 300 measured transmission signals. [Figure 19I] 10 is a histogram of the average permittivity of a water-filled bag calculated when applying Group 1 Medium antenna response compensation to approximately 300 measured transmitted signals. [Figure 19J] 10 is a histogram of the average permittivity of a water-filled bag calculated when applying Group 3 Medium antenna response compensation to approximately 300 measured transmitted signals. [Figure 20] FIG. 2 is a simplified block diagram of hardware for an exemplary controller. DETAILED DESCRIPTION OF THE INVENTION

[0039] The disclosed embodiments relate to methods and systems for microwave scanning of biological tissue.

[0040] I. Definition The present invention generally relates to methods and systems for imaging biological tissue using microwave signals, preferably providing quantitative images of the electrical properties of biological tissue at microwave frequencies. Any term or phrase not expressly defined herein shall have a generally accepted definition as understood by one of ordinary skill in the art.

[0041] "Body tissue" refers to tissue of a living organism, including animal or human tissue. The body tissue may be any limb, head, neck, or torso; as a specific, non-limiting example, the body tissue is human breast tissue.

[0042] "Memory" refers to a non-transitory, tangible, computer-readable medium for storing information in a format readable by a processor and / or for storing instructions readable by a processor to implement an algorithm. The term "memory," even when used in the singular, includes multiple physically separate, operatively connected devices. Non-limiting types of memory include solid-state, optical, and magnetic computer-readable media. Memory may be non-volatile or volatile. Instructions stored by memory may be in multiple programming languages ​​known in the art, including, but not limited to, the C, C++, Python™, MATLAB™, and Java™ programming languages.

[0043] A "processor" refers to one or more electronic devices capable of reading and executing instructions stored in a memory and performing operations on data, which may be stored in a memory or provided in a data signal. The term "processor," even when used in the singular, includes multiple physically separate but operatively connected devices. Non-limiting examples of processors include devices referred to as microprocessors, microcontrollers, central processing units (CPUs), and digital signal processors. In some embodiments, the processing device comprises an embedded, stand-alone processor system, optionally connected to a standard computer. In some embodiments, the embedded processor system may comprise a microcontroller and a field programmable gate array (FPGA). The processor is associated with a memory containing instructions for performing the scanning and imaging steps described herein.

[0044] The frequency of "microwave" refers to electromagnetic (EM) waves in the microwave region, which are generally considered to be in the range of about 300 MHz to about 300 GHz, and corresponds to a wavelength in the range of about 1 m to 1 mm.

[0045] II. Overview 1 illustrates an exemplary apparatus 100 for microwave imaging of biological tissue (e.g., breast tissue) according to disclosed embodiments. As described herein, the apparatus 100 can use microwave signals to scan the tissue and determine various properties of the tissue.

[0046] 2A and 2B illustrate exemplary outputs that can be generated by the device 100, including two-dimensional (2D) image outputs (FIG. 2A) and / or three-dimensional (3D) image outputs (FIG. 2B) of biological tissue. In other embodiments, various other data outputs, such as a numerical score, can be generated.

[0047] As shown in Figure 1, the device 100 includes at least two opposing antenna arrays 102a, 102b. The antenna arrays 102a, 102b may be aligned along a common orientation axis 150a (Figure 3A) or may be oriented such that the antenna arrays 102a, 102b are directed toward each other or are otherwise separated by an axial spatial interval.

[0048] As used herein, the "axial spatial separation" (interchangeably referred to as "spatial separation" or "axial separation" or "separation" throughout) between antenna arrays 102a, 102b refers to the axial separation 152 (FIG. 3A) defined along orientation axis 150a between spaced-apart antenna arrays 102a, 102b. A gap (or void) 158 is defined by separation 152. In some embodiments, gap 158 is also referred to herein as scan region 158 (or "tissue scan region") because biological tissue requiring scanning can be inserted between region 158 and between the two antenna arrays 102.

[0049] As described in more detail herein, in some embodiments, each antenna array 102a, 102b may be segmented into two or more sub-antenna arrays. In this case, more than two antenna arrays are provided, and the multiple antenna arrays are also arranged facing each other. Furthermore, the antenna arrays 102a, 102b do not necessarily have to be vertically overlapping. For example, they may be arranged laterally or at any other desired angle relative to each other.

[0050] In one exemplary application in which the device 100 is used to scan breast tissue, a patient may be seated or standing and place their breast tissue between the opposing antenna arrays 102 a, 102 b and within the scan region 158. In other examples, other types of biological tissue may be placed between the opposing antenna arrays 102 a, 102 b.

[0051] As best shown in Figures 3A-3C, each antenna array 102a, 102b may be housed within a separate corresponding housing 104a, 104b. Each antenna array housing 104a, 104b may include a respective primary antenna surface 106 (Figure 3C) that contains the respective antenna array 102a, 102b and is configured to contact the tissue being scanned.

[0052] The primary antenna surface 106 may have any desired shape or configuration. In some instances, the primary surface 106 is substantially horizontal (FIG. 3C). Alternatively, as shown in FIG. 3A, the surface 106 may be curved or curved (e.g., concave). In this manner, the antenna array 102 itself may also be curved or curved. In at least one embodiment, the curvature of the primary surface 106 (and thus the antenna array 102) allows the array to better conform to the periphery of certain biological tissues (e.g., breast tissue).

[0053] Additionally or alternatively, the housing leading edge surface (110) may also be curved (FIG. 3A). This also allows the housing to better accommodate certain anatomy or body parts, including, but not limited to, the breast, chest, thorax, or head. For example, when imaging a human breast, it may be desirable for the leading edge (110) of the antenna array housing to conform to the curved surface of the thorax for greater comfort.

[0054] In at least one example, the antenna array housing (104) is covered with a microwave transparent cushioning (or deformable material) to improve the comfort of the device, for example, the cushioning may include foam or gel padding.

[0055] As described above, the antenna arrays 102a and 102b can be divided into multiple antenna sub-arrays. In this case, the housing 104 can also be divided into sub-housings, each housing housing a respective antenna sub-array. This allows, for example, for better conformance to the shape of the biological tissue being scanned. For example, four housings can be used with different adjustable angles to encompass various shapes, such as the human breast, neck, or head.

[0056] As illustrated in FIG. 3B, the antenna array housings 104a, 104b (and thus the antenna array 102) may be pivotable. For example, the housings 104a, 104b each pivot about a rotation axis 150b. The rotation axis 150b may be perpendicular to the orientation axis 150a. In this example, each housing 104 is pivotally mounted to a mounting arm 154. The pivoting allows the antenna arrays 102a, 102b to tilt forward or backward.

[0057] In some instances, the accuracy with which the antenna array 102 is positioned may be predetermined so that the device can be locked at a particular angle. In the case of imaging the breast, this position may correspond to the craniocaudal (CC) and mediolateral-oblique views.

[0058] The antenna arrays 102a, 102b may also be tilted to better conform to the shape of the anatomy being scanned and / or to increase the diversity of the recorded data. For example, the front-to-back angle and / or the lateral angle between the antenna arrays 102a, 102b may be adapted to the anatomy being scanned.

[0059] Referring again to Figure 1, the device 100 may include a mechanical system 108. The mechanical system 108 may be used to support and position the antenna housings 104a, 104b. A knob 110 may adjust the mechanical system 108 to adjust the axial spatial separation 152 between the opposing arrays 102a, 102b.

[0060] More specifically, the mechanical system 108 may hold two or more antenna arrays 102 oriented in an opposing manner such that the fields radiated by the antenna arrays 102 a, 102 b are directed toward the opposing array. The mechanical system 108 provides the ability to adjust the separation 152 ( FIG. 3A ) between the antenna arrays 102 a, 102 b to allow the biological tissue to be scanned to be inserted into the scanning region 158. The separation 152 can be adjusted or reduced by the mechanical system 108 so that the antenna arrays 102 a, 102 b contact the biological tissue to be scanned.

[0061] In at least one example, the mechanical system 108 provides a manual or motorized adjustment input for manually varying the separation 152 between the antenna arrays 102 a, 102 b. The mechanical system 108 may include a position indicator, such as a magnetic reader and magnetic strip, or other means for measuring the separation 152 between the arrays 102 a, 102 b and / or providing the ability to measure the position of one antenna array relative to another.

[0062] The mechanical system 108 may also control the rotation of the at least two antenna arrays 102a, 102b (FIG. 3B) about the axis of rotation 150b in a tilted position to provide different views of the biological tissue, as described above. The mechanical system 108 may provide a way to measure the angle at which the antenna arrays 102a, 102b are positioned.

[0063] In some instances, the mechanical system 108 may allow only one antenna array 102 to tilt while the other antenna array 102 is substantially fixed. For example, this feature may be utilized when there is an upper antenna array and a lower antenna array, where the upper one may be adjustable but the lower one is fixed.

[0064] The antenna array (102) may also have the ability to translate laterally (array assembly), allowing microwave measurements to be recorded at additional antenna element positions, thus effectively increasing the density of measurements. For example, if one of the two arrays is moved a distance equal to half the lateral distance between two adjacent antennas, readings obtained from one position can be combined with readings from the other position, effectively increasing the resolution of the array. In some instances, an actuation mechanism (not shown) is provided to move the antenna laterally.

[0065] As shown in Figure 1, the device 100 may also include a computer terminal 112. The computer terminal 112 may include a computer display screen 114 and an input interface 116 (e.g., a keyboard and / or a trackpad or mouse). The computer terminal 112 allows an operator to control the device.

[0066] As described herein, measurement protocols may be provided to guide the use of the device (110) in scanning (eg, imaging) biological tissue.

[0067] III. SYSTEM FOR MICROWAVE SCANNING OF BIOLOGICAL TISSUE 4A illustrates an exemplary microwave scanning system 400 according to disclosed embodiments. In some instances, the microwave scanning system 400 is incorporated into the microwave imaging device 100 (FIG. 1).

[0068] As shown, the microwave scanning system 400 includes at least two antenna assemblies 402a, 402b, each of which may be disposed within a respective antenna housing 104a, 104b.

[0069] Each antenna assembly 402 includes a corresponding antenna array 102a, 102b coupled to a corresponding switch network 404a, 404b. Each antenna array 102a, 102b includes a plurality of antenna elements 406 (e.g., two or more antenna elements) coupled to its respective switch network 404a, 404b. In operation, each antenna array 102a, 102b is activated to transmit (e.g., radiate) and / or receive microwave signals 414. In some instances, as discussed herein, the system 400 need not include a switch network 404 (FIG. 4B).

[0070] As noted above, one or both of the antenna assemblies 402 may include an antenna array 102a, 102b that is subdivided (e.g., segmented) into two or more subarrays. These antenna subarrays may also be coupled to the same corresponding switch network 404. In other instances, one or more switch networks 404 may also be segmented into two or more subnetworks. These subnetworks may be coupled to the same or different antenna arrays and / or antenna subarrays.

[0071] The antenna arrays 102a, 102b are positioned in opposing orientations along the orientation axis 150a and spaced apart to define a scanning region 158 extending along the separation 152. As discussed, the scanning region 158 may receive a biological tissue 412 (or any portion thereof) to be scanned, such as human breast tissue. In this manner, the opposing antenna arrays 102a, 102b are positioned axially on either side of the target tissue 412 to be scanned.

[0072] In some instances, the antenna housings 104a, 104b are adapted to be in contact with the target tissue 412. For example, the mechanical system 108 can be adjusted such that the spatial spacing 152 is adjusted to accommodate different sizes of biological tissue and bring the antenna housing 104—and thus the antenna array 102—into contact with the scanned tissue 412.

[0073] The system 400 also includes a microwave transceiver 416 coupled to the antenna array 406 via the switch network 404. A controller 418 is further provided, coupled to both the microwave transceiver 416 and the switch network 404.

[0074] Each of the microwave transceiver (416), switch network (404), and controller (418) is discussed in more detail herein below.

[0075] (i) Microwave transceiver In at least one example, the microwave transceiver (416) comprises (i) at least one microwave source transmitter (416a) for generating a microwave signal (414) to be transmitted (e.g., radiated) and at least one microwave receiver (416b) for consistently receiving the microwave signal (414).

[0076] In some instances, the microwave transmitter 416a and microwave receiver 416b are provided as separate units rather than being integrated into a single transceiver as shown.

[0077] The microwave transceiver 416 may also include multiple transmitters 416a and / or multiple receivers 416b. For example, the microwave transceiver 416 may include multiple transmitters 416a operating at different frequencies and capable of transmitting signals in parallel. Similarly, multiple receivers 416b may be provided for receiving signals simultaneously in parallel. In these examples, the switch networks 404a and 404b may not necessarily be provided.

[0078] For example, in FIG. 4B, multiple microwave transmitters (416a1) through (416a2) are shown, each connected to a separate antenna element (406) in the transmit antenna array (102a). n ) are provided. In addition, a plurality of microwave receivers (416b1) to (416b2) are provided, each connected to a separate antenna element (406) in the receiving antenna array (102b). n ) is provided.

[0079] Thus, in at least one example, there are as many microwave transmitters 416a as there are transmit antenna elements 406 in the transmit antenna array 102a. Additionally, there are as many microwave receivers 416b as there are receive antenna elements 406 in the receive antenna array 102b. At least the transmitters 416a may operate at the same and / or different frequencies.

[0080] Although FIG. 4B illustrates a single connection line between microwave transmitter (416a) and microwave receiver (416b) for ease of illustration, in practice the connection line would include a single connection line between each of microwave transmitters (416a1) through (416a n ) and microwave receivers (416b1) to (416b n ) to respective individual antenna elements (406) in the corresponding transmit antenna array (102a) and receive antenna array (102b).

[0081] In at least one example, a switch network 404 may be provided for one antenna array but not the other. Multiple transmitters 416 a and multiple receivers 416 b may be coupled to the same or different switch networks (or switch sub-networks). For example, if there are fewer microwave transmitters 416 a or microwave receivers 416 b than corresponding antenna elements 406, some microwave transmitters 416 a or microwave receivers 416 b may be coupled to the switch sub-network 414 while others are directly coupled to corresponding antenna elements 406.

[0082] In at least one example, the microwave transmitter (416a) is operable to generate microwaves in a frequency range of 100 MHz to 10.6 GHz, and in some examples, is operable to generate microwaves in a frequency range of 2 GHz to 8 GHz. Suitable microwave transceivers (416) are well known in the art.

[0083] (ii) Switch Network The switch networks 404a, 404b allow any antenna element 406 in each antenna array 102a, 102b to be coupled to either a microwave transmitter 416a or a microwave receiver 416b, which may be integrated into the transceiver 416. Thus, the switch networks 404a, 404b are used to select the transmit antenna element 406 and the receive antenna element 406.

[0084] For example, as shown in Figure 5, antenna array 102a may be designated as a transmit antenna array, while antenna array 102b may be designated as a receive array. In this case, switch network 404a may couple antenna elements 406a in transmit array 102a to microwave transmitter 416a. Furthermore, switch network 404b may individually couple each group 502 of antenna elements 406b in receive array 102b to microwave receiver 416b. Thus, antenna element 406a may be used to radiate (e.g., transmit) microwave signals, while groups 502 of antenna elements may be used to receive microwave signals.

[0085] As used herein, an "activated" antenna element (406) is an antenna element (406) that is coupled by the switch network (404) to either a microwave transmitter (416a) or a microwave receiver (416b), for example, within a microwave transceiver (416). In the case of Figure 4B, an "activated" antenna element is an antenna element that is directly coupled to an activated (e.g., activated) transmitter or receiver by the controller (418). More generally, an activated antenna element is an antenna element that is actively being used to transmit / receive signals.

[0086] Thus, a signal path 508 is defined between each pair of active transmit and receive antennas (FIG. 5A). That is, each signal path 508 is associated with a respective transmit and receive antenna element located in the opposing antenna array. As described in detail herein, a recognized advantage of the design of the antenna arrays 102a, 102b—in combination with the switch network 406—is the large number of different signal path options available.

[0087] In at least one example, if one antenna array (102) has 250 antennas (x) and the other array has 250 antennas (y), the available x antennas between different antenna pairs will be * There are potentially y (e.g., 62,500) different signal paths (see, e.g., FIG. 5B). Thus, the switch networks 404a, 404b are operated to connect to some or all of the available signal paths 508. In some instances, the scanning system 400 can select between about 1,500 and about 20,000 signal paths.

[0088] As described herein, providing a greater number of signal paths 508 improves the scanning resolution of the system 400. For example, different signal paths 508 may be generated to penetrate different cross-sectional portions (e.g., areas) of biological tissue located within the scan region 158. As the number of signal paths increases, a greater amount of data regarding tissue response may be obtained.

[0089] In at least one example, the switch networks 404 each include a plurality of microwave switches, as known in the art, connected to each antenna element 406 in a corresponding antenna array. The microwave switches are controllable, for example, by a controller 418, to selectively couple a particular antenna element 406 to either a microwave transmitter 416 a or a microwave receiver 416 b. In some examples, the microwave switches are solid-state microwave switches integrated within the antenna array's printed circuit board (PCB).

[0090] The switch networks 404a, 404b may incorporate multiple microwave transceiver integrated circuits mounted on the same PCB, with a transceiver connected to each antenna and the transceiver itself being switchable between transmit and receive modes.

[0091] (iii) Controller The controller 418 (FIG. 4A) can perform a variety of functions, including controlling the microwave transceiver 416 (e.g., transmitter 416a and / or receiver 416b) and controlling the switch networks 404a, 404b. In some instances, the controller 418 provides some signal processing and analysis functionality, as disclosed herein.

[0092] More specifically, the controller 418 operates the switch networks 404a, 404b to select pairs of antenna elements 406 in each array 102a, 102b to connect to a microwave transmitter 416a and / or a microwave receiver 416b, and each transmitting antenna element 406 may be separately paired with each of the multiple receiving antennas 406.

[0093] In another example where switch networks 404a, 404b are not necessarily provided (FIG. 4B), controller 418 may select microwave transmitters 416a1, 416a2, 416a3, 416a4, 416a5, 416a6, 416a7, 416a8, 416a9, 416b1, 416b2, 416b3, 416b4, 416b5, 416b6, 416b7, 416b8, 416b9, 416b10, 416b11, 416b12, 416b13, 416b14, 416b15, 416b16, 416b16, 416b17, 416b18, 416b19, 41 n ) and microwave receivers (416b1) to (416b n ) may be operable to control and correct.

[0094] For this reason, for ease of explanation, the remainder of this specification will refer to the system 400 as including a switch network 404, although it will be understood that all of the examples described using the system 400 of FIG. 4B may equally be reproduced by controlling, for example, one of the microwave transmitters 416 a and / or microwave receivers 416 b rather than a switch network to operate different antenna elements.

[0095] The controller 418 also operates the microwave transceiver 416 to generate and receive microwave signals via the operated antenna elements, and the controller 418 can process the received microwave signals to determine one or more tissue response characteristics (e.g., electrical characteristics) associated with the scanned biological tissue.

[0096] As described herein, and with reference to Figure 20, the controller (418) may include at least one processor (2002) coupled to a memory (2004). In some instances, the processor (2002) is also coupled to one or more of a communication interface (2006), an input interface (2008), an output interface (2010), and an input / output interface (2012).

[0097] Controller 418 may comprise or be otherwise incorporated within computer terminal 112 (FIG. 1). In other instances, controller 418 may be separate and coupled to computer terminal 112.

[0098] IV. Antenna Array The following provides a more detailed discussion of design arrangements for antenna arrays (102) that may be used alone or in combination with any of the features disclosed herein, including, for example, microwave imaging systems (400).

[0099] (i.) The placement of antenna elements in an antenna array As noted above, each antenna array (102) comprises a plurality of individual antenna elements (406) (FIG. 4A) distributed over the major surface (106) of the housing (104).

[0100] As described throughout this specification, a unique aspect of the scanning system 400 is the inclusion of multiple antenna elements 406 in each of the opposing antenna arrays 102, which allows the switch network 404 (FIG. 4A) (or microwave transmitter / receiver in FIG. 4B) to be controlled to switch between multiple signal paths 508 associated with different pairs of transmit and receive antenna elements, thereby providing higher resolution scanning of biological tissue.

[0101] Furthermore, the disclosed antenna assembly can scan large volumes of tissue while maintaining a fixed relative orientation and / or position of the antenna array (102). This is because the antenna array (102) generates multiple signal paths (508)—moving at different angles between different pairs of antennas (406)—allowing such signal paths (508) to penetrate different portions of the tissue. This eliminates the need for antenna assemblies that require movement or translation mechanisms to scan different regions of the tissue, thereby increasing scan times. In some instances, the antenna array (102) includes tens or hundreds of antenna elements (406), enabling multiple signal paths. In at least one example, the disclosed embodiments can scan large volumes of tissue in as little as 30 seconds.

[0102] Thus, the antenna elements 406 can be arranged in any desired pattern arrangement (e.g., FIG. 3C) around a given antenna array 102. By way of non-limiting example, some or all of the antenna elements 406 can be arranged in a pattern including a triangular grid (e.g., staggered), a square grid (e.g., aligned rows and columns), a rectangular grid (e.g., aligned rows and columns), or a hexagonal grid. Alternatively, or in addition, the antenna array 102 can have some or all of the antenna elements 406 arranged in an irregular pattern.

[0103] In at least one example, some or all of the antenna elements (406) in each antenna array (102) are slot antennas.

[0104] As best shown in Figures 6 and 7, a recognized advantage of using a slot antenna design is its compact design, which facilitates the packing of many (e.g., hundreds or thousands) of antennas into a small cross-sectional surface area, such as a PCB (502). In at least one example, the slot antenna design allows for 1680 slot antennas to reside in a 30 cm x 24 cm surface area. This design configuration is particularly well-suited for the disclosed applications because it facilitates the assembly of an antenna array (102) having a large number of antennas (406) that can be controlled by a switch network (404) (or by multiple microwave transmitters and receivers, as in Figure 4B) to generate many combinations of signal paths (508) during tissue scanning (Figures 5A-5B), thereby obtaining high-resolution tissue property response data from different portions of the scanned biological tissue. As explained further below, slot antennas are also less susceptible to the presence of closely spaced biological tissue.

[0105] Figure 6 illustrates an antenna array 102 in which the slot antennas 406 are integrated directly into the mounting substrate 502 (e.g., PCB 502) during manufacturing, while Figure 7 illustrates an antenna array 102 in which the slot antennas 406 are bonded (e.g., mounted or soldered) onto the mounting substrate 502 (e.g., PCB 502).

[0106] While any slot antenna design known in the art can be used, Figures 8A-8B illustrate a design for the slot antenna 406 used in the disclosed examples. The example in Figures 8A-8B can be used in conjunction with an antenna array in Figure 7, such as the slot antenna 406 coupled to the mounting substrate 502.

[0107] As shown, the illustrated slot antenna 406 can be elongated in a vertical orientation along an axis 850 between an upper surface 802a and a lower surface 802b. Although relative terms such as "upper" and "lower" are used throughout this specification, the disclosed slot antenna is not limited to any particular orientation.

[0108] The upper surface (802a) of each slot antenna may be exposed for transmitting and / or receiving microwave signals, while the lower surface (802b) may be attached to a substrate (e.g., PCB).

[0109] More generally, the slot antenna 406 can comprise a metallized substrate 804 in a surface of which a portion of the metallization has been removed to form the slot 806 (although for ease of illustration, the slot 806 is shown in FIG. 8A as being separate from the metallized substrate 804 on which it is formed). In an assembled state, the metallized substrate 804 forms the upper surface 802a of the slot antenna.

[0110] A slot 806 may be provided on the other side of the metallized substrate 804. A feed strip 808 (e.g., a microstrip line or stripline) oriented substantially perpendicular to the slot 806 may be located directly below or otherwise coupled to the substrate 804. The feed strip passes through the slot 806 and then terminates, forming a stub 808a. Many stub shapes can be used for both the microstrip feed and the slot. For example, a radial stub can be used to optimize the space used by the antenna element.

[0111] In some instances, the slot antenna (406) is mounted (e.g., fabricated or manufactured) on the surface of a thin dielectric constant substrate, such as a standard printed circuit board (PCB) laminate plastic, a specialized plastic, or a ceramic material.

[0112] As best shown in Figures 8A and 8D, the feed strip 808 may connect to further layers in the PCB stackup 502 through metallized vias 810. In this case, the thickness of the substrate below the microstrip may be electrically thicker (in terms of wavelength) than the substrate used for the slots.

[0113] In at least one example, vias 810 (FIG. 8A) connecting the feed strips 808 may extend to the top metallized substrate layer 804 (where the slots are located). In this example, the vias 810 can be used as measurement locations for probes to measure the response of the switch network 404 without the antenna response, as described below.

[0114] In some instances, the slot antenna (406) may have a slot (806) that widens in width (812) on either side of the feed strip (808) (FIG. 8A). This can be done to increase the bandwidth of the slot antenna, which may have limited bandwidth on its own. The ends of the feed strip may also be widened to form a wideband protrusion (808a), further increasing the bandwidth of the antenna.

[0115] The shape of the slot (806) may vary. For example, it may be a bowtie-shaped slot (FIG. 8E) or various shapes as shown in FIG. 8F. Generally, slot shapes that smoothly increase in slot width improve response. In at least one instance, the hourglass-shaped slot design in FIG. 8F (the right-most design) may provide the best performance.

[0116] For this reason, slot antennas (406) suitable for use in the present disclosure are preferably designed specifically for the intended frequency band (e.g., microwave) and specifically for use in contact with biological tissue. In at least one example, full magnetic field coupling is used to feed the slot (806), minimizing the parasitic inductance that a directly connected feed would exhibit. By avoiding parasitic induction, this increases the frequency band over which feed performance is acceptable.

[0117] As illustrated in FIG. 8A, the slot antenna (406) may be fabricated as a separate component. This may be done to simplify PCB stackup. An example of a separate component is shown in FIG. 8A using PCB technology and in FIG. 8B, which shows an example of a bowtie created on the ceramic cap surface. Such a separate component can be soldered to the PCB surface like any other component, as shown in FIG. 8C. FIGS. 8D and 8E illustrate the same slot antenna (406) design, but fully integrated within the PCB and mounting substrate (502).

[0118] 8A-8B, for the antenna array 102 to function properly, the closely spaced slot antenna elements 406 must be shielded from neighboring antennas, i.e., each slot antenna element 406 operates as independently as possible from surrounding antennas 406, especially its immediate neighbors.

[0119] Thus, in some instances, each slot antenna (406) further comprises a shielding interface (850) to provide electromagnetic shielding between adjacent and / or neighboring slot antennas and minimize coupling between the antennas. The antenna array (102) can then be designed with multiple closely spaced antennas (e.g., closely packed antennas) so that each antenna element (406) operates independently without interaction. As disclosed, this allows for the use of antenna arrays with many antennas that can be used to generate many signal paths and scan tissue with sufficient spatial sampling for high-resolution scanning. Shielding can also improve individual antenna performance, resulting in clearer signals being recorded.

[0120] In detail, the shielding requirement includes two aspects: (i) first, the antenna response of an antenna should not be affected by its neighbors, and (ii) second, the feed network should prevent signals from neighboring antennas from corrupting the signal in question.

[0121] In Figure 8A (and Figures 8D and 8E), the shielding interface (850) comprises a dielectric filler (812) surrounding the feed portion (808) and the feed via (810), and a ring of individually fabricated ground vias (814) around and within the outer periphery of the dielectric bore (812) (e.g., each extending between the upper surface (802a) and the lower surface (802b)).

[0122] In some instances, each ground via 814 may be metallized, thus creating a metal wall around the antenna and its feed, thereby reducing interaction between nearby antenna elements. For this reason, the feed vias 810 may be formed within the dielectric filler 812.

[0123] In the example of Figure 8A, a metal backing plate (814') may also be provided as part of the shielding interface (850) and coupled to the PCB. The metal backing plate (814') may have a small opening (816) for the feed via (810) to electrically connect to the PCB.

[0124] In other instances, the shielding interface 850 may comprise a continuous or partially continuous metallic enclosure (e.g., a cylindrical enclosure in place of the ground via 814) that encases the feed 808 and the via 810. In this example, no filler 812 is required, and the feed 808 and the via 810 may be surrounded by an air medium disposed within the metallic enclosure.

[0125] 9 shows a graph 900 of an exemplary effect of shielding slot antennas in an exemplary antenna array 102 and using a shielding interface 850. Graph line 902 shows the antenna coupling without the shielding, and graph line 904 shows the antenna coupling with the shielding. As shown, the shielding provides up to a 20 dB improvement, minimizing the coupling.

[0126] Maintaining sufficient isolation in the power distribution network can also be achieved by selecting microwave switches in the switch network (404) with strong port-to-port isolation and careful PCB routing.

[0127] Although the slot antennas 406 are illustrated as having a cylindrical shape, in other examples, the antennas 406 can have any other shape. For example, as illustrated in FIG. 8C, the slot antennas 406 can have a hexagonal shape. This allows the slot antennas 406 to be placed adjacent to one another (e.g., in a honeycomb pattern) in the antenna array 102, thereby increasing the spatial density in the antenna array 102 and providing additional signal paths between pairs of transmit and receive antennas.

[0128] In some instances, as shown in Figures 10A-10C, a waveguide structure 1002 may be coupled to the slot antenna 406, for example, to the upper surface 802a and the top of the substrate 804. The waveguide structure 1002 may include one or more ridges positioned on the slot antenna 406 and cover the slot 806 (Figure 10B). The waveguide 1002 may function to increase the directivity and gain of the antenna.

[0129] The raised waveguide (1002) portion may be of any geometric shape, for example, as shown in the figure, the waveguide (1002) may have a conical structure.

[0130] In at least one example, the waveguide structure (1002) has, at a minimum, a conductive material on its periphery or outer surface. The ridges (1004) face each other toward the waveguide cavity and complement the design of the slots (806). The ridges are close together at the slot locations and flare outward as they extend into the waveguide. In at least one example, the ridges (1004) may have a conductive coating to improve the transition from the slots (806) to the waveguide (1002).

[0131] The ridged waveguide may be made from a material, such as a specially engineered plastic or ceramic, that has a higher dielectric constant value than standard or conventional waveguide materials.

[0132] (ii.) Dielectric coating Although direct contact of the antenna arrays 102a, 102b with biological tissue can have positive effects (e.g., signals are coupled into the tissue without reflections), direct contact between the antenna metal coating and the tissue can negatively affect the efficiency of the antenna. Therefore, in some instances, a non-conductive (dielectric material) coating is placed between the antenna array 102 and the biological tissue to minimize the decrease in efficiency.

[0133] For example, as illustrated in Figure 11, each antenna array housing 104 may be covered by a thin dielectric (non-conductive) material 1102 (see also Figures 4A and 4B), which is coupled to and overlays (e.g., mounted on) the antenna array 102 and faces toward the scanning region 158.

[0134] When the biological tissue 412 is inserted into the scanning region 158, the dielectric material 1102 is positioned between the respective antenna array 102 and the biological tissue 412 (FIGS. 4A and 4B). For example, the dielectric material 1102 contacts and engages the skin 1104 surrounding the biological tissue to be scanned. The dielectric material 1102 may include any suitable non-conductive material, such as a polymer or ceramic.

[0135] More generally, the dielectric coating material (1102) is formed from a low dielectric constant material and is thin enough to promote coupling and prevent signal leakage around the biological tissue (412).

[0136] In at least one instance, the dielectric covering material (1102) is formed from a material having a dielectric constant of less than 5 and a thickness of up to 2 mm, and in some instances a dielectric constant of about 2.5 and a thickness of less than 0.5 mm, where the thickness of the material is defined along the axis (150a).

[0137] Figure 12A shows an exemplary graph 1200a illustrating the effect of a coating 1102 made of a material with a dielectric constant of 2.5 and a thickness of 0.4 mm on antenna arrays 102a, 102b without a coating (graph line 1202a) compared to antenna arrays 102a, 102b with a dielectric coating (graph line 1204a).

[0138] As shown in graph 1200a, an increase in the transmission coefficient of between 6 and 12 dB is observed for the antenna arrays 102a and 102b with the dielectric coating 1102 compared to the antenna array 102 without the dielectric coating 1102. Losing an additional 10 dB in the uncoated array can reduce the signal strength to the point where the signal is no longer recoverable, for example, from thermal noise. For reference, compensating for a 10 dB signal attenuation requires a 10-fold increase in measurement time to reduce the noise floor. This would increase the operation time from less than 30 seconds to 5 minutes, making it impractical for biomedical imaging.

[0139] FIG. 12B shows a graph 1200b comparing antenna arrays 102a, 102b with dielectric coatings 1102 having a thickness of 0.4 mm and various values ​​of permittivity. These values ​​include permittivity values ​​of 1 (1202b), 2.5 (1204b), 4 (1206b), 9 (1208b), and 15 (1210b). It can be observed that as the permittivity of the dielectric coating 1102 increases, the penetration at higher frequencies decreases. In particular, signals propagating through tissue experience greater attenuation at higher frequencies. Greater penetration at higher frequencies is crucial for enabling high sensitivity.

[0140] V. Exemplary Methods The following description relates to various exemplary methods for imaging biological tissue, according to disclosed embodiments.

[0141] Each of the described methods 1300a-1300c (FIGS. 13A-13C) can be performed by controller 418. In other instances, the methods may be performed by controller 418 alone or in combination with (e.g., coupled to) one or more external computing devices (e.g., servers).

[0142] (i.) The overall method FIG. 13A is a process flow diagram for an exemplary method 1300a of imaging biological tissue 412, for example, inserted in a scanning region 158 between two antenna assemblies 402a, 402b (FIG. 4A or 4B).

[0143] In 1302a, one or more antenna sets are selected for imaging the target biological tissue.

[0144] For example, as shown in Figure 5A, each antenna set 512 includes one transmit antenna element 406a and one or more corresponding receive antenna elements 406b associated with (e.g., assigned to) the transmit antenna element 406a. Thus, each antenna set 512 includes multiple antenna pairs, each antenna pair including a transmit antenna element 406a and one of the receive antenna elements 406b.

[0145] In some instances, the transmit antenna (406a) is selected from a first antenna array (102a), while one or more receive antennas (406b) are selected from a second antenna array (102b). It is also possible for the antennas to be selected from the same array.

[0146] More generally, as shown in FIG. 5A, each antenna set 512 may include one or more receive antennas 406b (and in some instances, two or more receive antennas 406b) that collectively form a receive antenna group 502. Accordingly, within each antenna set 512, each transmit antenna 406a is associated with a group 502 of receive antenna elements 406b. A receive antenna group 502 is an antenna positioned and installed to receive the most relevant transmitted microwave signal, both in terms of signal strength and geometric path.

[0147] As described herein, the purpose of defining receive antenna groups 502 is to simplify and speed up signal processing and analysis. Specifically, to simplify the complexity of signal analysis and thus increase the computational speed of the system, the system may ignore signals received by other antenna elements 406b in the receive antenna array 102b that are located outside of the receive group 502.

[0148] In some instances, a group of receive antennas 502 is determined by first identifying one opposing receive antenna element 406b (e.g., along axis 150a) that is directly opposite (FIG. 4A or 4B) the transmit antenna element 406a. Then, a predetermined number of receive antennas 406b, including and adjacent to the opposing receive antenna 406b, are selected for the group of receive antennas 502. In some instances, antenna elements 406 located within a 60 mm radius of the opposing receive antenna 406 are included in the group 502.

[0149] In another example, each antenna set (512) includes only a single transmit antenna (406) and a single receive antenna (406). Thus, in this example, the antenna group (502) includes only a single receive antenna (406).

[0150] In some instances, in 1302a, multiple antenna sets are determined for different transmit antennas 406a in the transmit antenna array 102a. For each transmit antenna 406a, one receive antenna group 502 is associated with that transmit antenna 406a to define a respective antenna set 512 for that transmit antenna 406a. Among different antenna sets 512, the receive antennas 406b included in each receive group 502 may overlap.

[0151] In at least one example, at 1302a, one antenna set 512 is selected for each transmit antenna 406a in the transmit antenna array 102a.

[0152] Thus, the determination in 1302a can be made in a variety of ways. In some instances, the selection of antenna elements in each antenna set 512 is determined manually in advance (e.g., by a system operator).

[0153] At 1304a, an antenna element 406 in one of the antenna sets 512 is activated.

[0154] For example, as shown in FIG. 4A, this involves operating a switch network (404a)—associated with the transmit antenna array (102a)—to couple the transmit antenna elements (406a) in the selected antenna set (512) to a microwave transmitter (416a).

[0155] Additionally, a switch network (404b) associated with the receive antenna array (102b) is operated to couple each of the receive antenna elements (406) in the associated group (502) of receive antennas to a microwave receiver (416b).

[0156] In some instances, switch network 404b is operated to couple one receive antenna 406b in group 502 to microwave receiver 416b at a time. In this case, actions 1306a through 1312a are repeated, whereby a different receive antenna 406b is coupled to microwave receiver 416b in each iteration. In other instances, all of the receive antennas in group 502 are coupled in parallel (e.g., simultaneously) to microwave receiver 416b.

[0157] 4B example—where switch network 404 is not provided—activating 1304a an antenna element in antenna set 512 involves activating a microwave transmitter 416a and a microwave receiver 416b associated with (e.g., coupled to) each antenna element that needs to be activated. Again, for receive antenna 406b, this may involve activating one microwave receiver 416b or operating multiple receivers in parallel.

[0158] At 1306a, a microwave transmitter 416a, for example, either alone or within a microwave transceiver 416, is operated to generate an interrogating microwave signal. The interrogating microwave signal is routed to a respective active transmitting antenna element 406a. The active transmitting antenna 406a accordingly transmits the interrogating microwave signal 414 such that the microwave signal passes through biological tissue 412 located within the scanning region 158 (FIGS. 4A and 4B).

[0159] At 1308a, the microwave signal 414 passes through the biological tissue 412, and each active group of receive antennas 502 receives a corresponding received microwave signal. As noted above, the receive antennas 502 may receive the microwave signals in parallel if they are active in parallel. In another example, if the microwave receivers 416b are active one at a time, each microwave receiver 416b receives a microwave signal from the transmit antenna during operation.

[0160] Thus, as shown in Figure 5A, each active receive antenna (406b) in a group (502) receives a corresponding receive microwave signal, each receive microwave signal corresponding to the interrogating microwave signal at a given active receive antenna (406b) after passing through biological tissue.

[0161] In this manner, multiple microwave signal paths (508) are defined between each pair of the one active transmitting antenna (406a) and one of the active receiving antennas (406b).

[0162] Each received microwave signal is then routed from the receive antenna (406b) to a microwave receiver (416b) for recording and further processing. In Figure 4A, the microwave signal is routed to the microwave receiver (416b) via a switch network (404b). In Figure 4B, the microwave signal is routed directly to the microwave receiver (416b) associated with the receive antenna (406b).

[0163] At 1310a, each received microwave signal—from each active receive antenna (406b)—is preconditioned to generate a corresponding conditioned microwave signal.

[0164] As shown in Figures 13B and 13C, signal preconditioning is used to correct for various error-inducing factors, including phase and amplitude correction and antenna radiation characteristic correction.

[0165] More generally, signal preconditioning is applied to each received signal from each active receive antenna 406b. As illustrated in Figures 13B and 13C, the preconditioning applied to a received signal is based on the characteristics of the signal path 508 associated with that received signal.

[0166] As explained above, a recognized technical advantage of defining each antenna set 512 to include only one group 502 or receive antenna element 406b is that operation 1310a is computationally efficient, i.e., signal preconditioning need only be applied to microwave signals received by a selected group of active receive antennas 406b that are positioned to receive the microwave signals most strongly (i.e., not every signal received by every antenna in the receive antenna array).

[0167] At 1312a, each of the conditioned microwave signals is analyzed to determine one or more tissue response characteristics (e.g., electrical tissue response characteristics) of the scanned biological tissue 412. In some instances, the one or more tissue characteristics are determined from the electrical tissue response characteristics (e.g., water content (and / or water state, such as bound water or free water), density of the biological tissue).

[0168] At 1314a, it is determined whether all antenna sets 512 have been activated. If not, the method returns to operation 1304a to activate the next antenna set, i.e., the next group 502 of transmit antennas 406a and their associated receive antennas 406b.

[0169] As used herein, each iteration of method 1300a using a different active antenna set 512 corresponds to a single "scan" of the biological tissue, and thus the method is repeated until all antenna sets have been activated and tissue response characteristics determined 1312a based on each scan.

[0170] As explained above, the system's ability to perform multiple scans using different combinations of antenna sets (512) allows for the generation of various signal paths (508) across different areas of a large volume of biological tissue (412) (FIG. 5B) and the rapid acquisition of corresponding tissue response data. This improves data resolution and system accuracy. The ability to respond to and scan through biological tissue using multiple signal paths is enhanced by using a slot antenna design, which allows for densely packed antennas (FIG. 7). Specifically, using a slot antenna design, each receive antenna group (502) can include multiple receive antennas (406b) positioned to receive strong microwave signals—via different signal paths.

[0171] As noted above, in some instances, the antenna array can be moved laterally and repositioned at different angles (FIG. 3B) to acquire data from different areas of the tissue. However, this may not always be necessary, as multiple signal paths—generated at different locations and extending at different angles—can scan different areas of a large tissue without having to move the antenna array around the tissue.

[0172] At 1316a, one or more outputs are generated based on the analysis and processing of the signals. The disclosure herein is not limited to the type or form of the output. For example, in at least one instance, the tissue response characteristics are visually represented in one or more output 2D or 3D images (FIGS. 2A and 2B). These images can be displayed, for example, on a display screen 114 (FIG. 1). The display screen 114 can be associated with or otherwise coupled to a controller 418.

[0173] (ii.) How to Precondition the Signal 13B shows a procedural flow diagram for an exemplary method 1300b of preconditioning a signal to generate a conditioned microwave signal, in which the intrinsic tissue response dependent on the microwave signal is included and the extraneous response is otherwise removed. In some instances, method 1300b is performed during operation 1310a in FIG. 13A.

[0174] More generally, method 1300b is applied to each received microwave signal at 1308a (FIG. 13A), i.e., within a given active antenna set 1304a, method 1300b is applied to each microwave signal transmitted by an active transmit antenna 406a and received by a given active receive antenna element 406b.

[0175] Thus, during one iteration of method 1300a (FIG. 13A), the method of FIG. 13B is applied independently to each received microwave signal (e.g., in FIG. 5A, each of the signals for each signal path 508) at each active receive antenna element 406b in the active antenna set.

[0176] Generally, in 1302b, the system first identifies the transmit and receive antenna pair associated with the received microwave signal, which allows the system to accurately determine the signal path 508 followed by the microwave signal, and which allows the system to determine the types of correction and compensation factors to apply in operations 1306b and 1308b.

[0177] In some instances, the determination at 1302b is based on knowing the settings of (i) the transmit switch network 404a, which indicates which transmit antenna 406a is associated with the microwave signal, and (ii) the receive switch network 404b, which indicates which receive antenna 406b received the microwave signal. Otherwise, in FIG. 4B, this information is known based on which microwave transmitters / receivers are activated at a given moment.

[0178] At 1304c, based on the determination at 1302b, the system determines configuration parameters for one or more antenna arrays. As described further herein, the configuration parameters can be used to precondition signals at 1306b and 1308b. In at least one example, the configuration parameters for the antenna arrays include:

[0179] (i) Positional location of the antenna elements in each array—in some instances, this data is stored in the controller's memory (2004) (FIG. 20). Positional location information can include the relative offset (e.g., x, y) of each antenna element in each array, and can also include vertical (z) offset, such as in the case of curved antenna arrays. Positional location is not necessarily expressed in Cartesian coordinates, for example, but can also be expressed in polar coordinates. Positional location information can also include the orientation of each antenna element in the array, for example, using Euler angles (e.g., ψ, θ, φ) representation.

[0180] (ii) The separation 152 between the antenna arrays 102 a, 102 b, which in some instances is predetermined or manually entered into the system. In other instances, as shown in FIGS. 4A and 4B , the controller 418 is coupled to one or more distance sensors 422 a that monitor the separation 152. For example, the distance sensor may be integrated into the mechanical system 108 and may include a magnetic reader that measures the position on a coded magnetic strip to measure the separation 152. Other distance sensors known in the art may be used, such as an optical line of sight sensor mounted on the housing 104.

[0181] (iii) The rotational position of the antenna arrays 102a, 102b (e.g., about an axis parallel to the axis of rotation 150b in FIG. 3B)—again, in some instances, this is predetermined or manually entered into the system. In other instances, as shown in FIGS. 4A and 4B, the controller 418 is coupled to one or more rotation sensors 422b (e.g., rotational position sensors as known in the art) that monitor the rotation of each antenna array. The rotation sensors may be coupled to the antenna housing 104, for example.

[0182] More generally, the antenna array geometry parameters can be used to determine the characteristics of the signal path associated with a received microwave signal.

[0183] Thus, as shown in FIG. 5A, each signal path (508) defined between the active transmit antenna (406a) and each active receive antenna (406b) may have different signal path characteristics.

[0184] Signal path characteristics include, for example, the signal path length (e.g., between associated transmit and receive antennas), the azimuth angle of incidence relative to the receive antenna, and the path offset relative to other antennas in the receive antenna array.

[0185] It will be appreciated that signal path characteristics are affected by the spatial placement of the antenna elements. That is, different arrays may be defined with different spacing offsets between the antenna elements. That is, the antenna elements 406 in different arrays 102 may be positioned differently around the periphery of the array. The spatial placement of the receive antenna elements in the array may affect the signal path characteristics for each receive antenna element.

[0186] Additionally, the signal path characteristics are affected by the separation (152) between the antenna arrays (FIG. 5A), which varies with at least the length and azimuth of the signal path. Furthermore, the rotation of the antenna arrays (FIG. 3B) can also vary with the length and azimuth of the signal path.

[0187] Thus, in at least one example, determining the signal path characteristics in 1304b involves first determining the separation 152 and / or rotational position of the antenna arrays 102a, 102b.

[0188] As described herein, the system can accommodate different separation and rotational positions of the antenna array, and the system can accommodate different biological tissues and generate an appropriate adjusted microwave signal. For example, two individuals may have different sized breasts—thus requiring adjustments to the spacing and rotational placement of the antenna array—yet the system accommodates this patient-specific adjustment and the factors that affect the characteristics of the signal path.

[0189] Based on the determinations at (1302b) and (1304b) and (1306b), one or more path-specific corrections are applied to the microwave signal to correct for phase and amplitude response and generate a corrected microwave signal. As described herein, phase and amplitude corrections are applied to correct for effects of measurement hardware and are applied to both transmit and receive antenna paths.

[0190] Subsequently, at 1308b, a path-specific antenna response compensation factor is applied to the corrected microwave signal to generate a corresponding adjusted microwave signal. The path-specific compensation factor removes the antenna response from the corrected microwave signal.

[0191] The conditioned microwave signal thus represents the biological tissue response, with the effects of the hardware measurements removed, which can then be used to more accurately determine various tissue properties, as described herein.

[0192] As explained above, operations 1306b and 1308b may be performed by digital signal processing using a processor in controller 418 (or any other external computing system).

[0193] Thus, as described herein, a unique aspect of the disclosed signal preconditioning methods is their reliance on a predetermined reference data set associated with correction and compensation coefficients. The use of the reference data set greatly simplifies the signal preconditioning process, allowing for increased computational and processing speeds when digitally filtering the signal. This, in turn, reduces the amount of time required to generate a desired output.

[0194] Next, operations 1306b and 1308b are described in more detail below.

[0195] (ii.a) Phase and amplitude correction In (1306b), phase and amplitude response corrections are applied to the received microwave signal.

[0196] More generally, the purpose of operation 1306b is to isolate and remove from the received microwave signal responses generated across (i) the transmit path extending between the microwave transmitter 416a and the particular active transmit antenna 406a associated with the microwave signal, and (ii) the receive path extending between the active receive antenna 406b associated with the received microwave signal and the microwave receiver 416b. In this way, the microwave signal is free from extraneous responses generated by the hardware.

[0197] In some instances, one or more path-specific correction factors are applied to the microwave signal, including (i) a first phase correction factor for the transmit path, (ii) a first amplitude correction factor for the transmit path, (iii) a second phase correction factor for the receive path, and (iv) a second amplitude correction factor for the receive path. It is understood that the correction factors are referred to as "path-specific" because they are different for different transmit / receive antennas.

[0198] Thus, the correction in operation 1306b may be applied using a predefined set of path-specific correction factors.

[0199] For example, the controller's memory 2004 (FIG. 20) may contain a reference data set (e.g., a reference look-up table) of correction integers consisting of known amplitude and phase correction factors for each transmit and receive path in the system 400.

[0200] For example, the reference data set may contain different phase and amplitude correction factors for each transmit path defined between (a) the microwave transmitter 416 a and (b) each transmit antenna element 406 a in the transmit antenna array 102 a. Additionally, the data set may also contain phase and amplitude correction factors for each receive path defined between (a) each microwave receive element 406 b in the receive antenna array 102 b and (b) the microwave receiver 416 b. In at least one example, the reference data set may also contain different phase and amplitude correction factors for different frequencies of the microwave signal, since these factors may be frequency dependent.

[0201] Thus, during 1306b, the system can—based on the transmit and receive antennas associated with the microwave signal 1302b—identify the specific transmit and receive paths associated with those antennas. The paths are then referenced to a correction factor dataset, which is then used to identify a "path-specific" correction factor associated with each path for both amplitude and phase correction. If multiple frequencies of microwave signals are used, the system can also identify known microwave frequencies being transmitted and determine the correction factors associated with those frequencies.

[0202] In at least one instance, a baseline correction factor data set is generated in advance by testing the system (400) using well-known vector network analyzer techniques.

[0203] For example, at some point prior to scanning the biological tissue, the path response between the microwave transceiver (416) and each antenna element (406) is measured using a two-port vector network analyzer. For example, the network analyzer is connected and reconnected between the antenna array's main port and the feed point of each antenna element (406). The measured path response (e.g., amplitude and phase) between the microwave transmitter and / or microwave receiver and each antenna element (406) is then recorded as a path-specific correction factor (e.g., a transfer function, as known in the art) associated with each antenna element in the fabricated array (102). In some instances, the data set includes the antenna element identifier and the associated transmit and / or receive path correction factor. This can be repeated for different signal frequencies to generate frequency-dependent correction factors.

[0204] Thus, when a two-port vector network analyzer is used to measure the path response, various techniques can be employed to accurately measure the path response, as known in the art. For example, the correction factors may be determined as a simple response calibration between the transmit and receive ports, or alternatively, they may be determined using an open-short-load calibration, a transmit-reflect-thru calibration, or any calibration technique known in the art.

[0205] In some instances, a specialized insertable probe is used to connect the network analyzer to the antenna feed point, or alternatively, a non-insertable probe (e.g., another antenna) may be used to externally couple to the antenna element 406 instead of an insertable probe.

[0206] In other instances, the path responses may be measured by one or more measurements of one or more reference materials or objects. Knowing the responses of the reference materials, the path responses for each antenna pair are extracted from the measured responses using a scattering matrix.

[0207] Thus, once operation 1306b is performed, the received microwave signal is corrected for amplitude and phase distortions, and a corrected microwave signal having corrected phase and amplitude characteristics is then generated.

[0208] (ii.b) Antenna response correction In (1308b), the antenna response is removed from the received microwave signal. The antenna response includes the antenna's radiation characteristics, including (i) the antenna's gain and (ii) the antenna's phase center.

[0209] Antenna Gain As is known in the art, the gain of an antenna determines the ability of a transmitting antenna element (406a) to convert input power into a radiated microwave signal, or alternatively, the ability of a receiving antenna element (406b) to convert a received microwave signal into output power.

[0210] In the ideal case, the transmit antenna (406a) converts 100 percent of the power supplied to it into a transmit microwave signal, and the receive antenna (406b) converts 100 percent of the received microwave signal into output power, regardless of the direction of incidence of the received microwave signal on the receive antenna.

[0211] However, in operation, the transmit and receive antenna elements do not exhibit perfect antenna gain. For example, the transmit antenna element 406a may not convert all of the power it receives (e.g., from the microwave transmitter 416a) into a transmit microwave signal. Similarly, the receive antenna element 406b may not convert the receive microwave signal into output power. Each antenna element will exhibit some degree of loss.

[0212] Importantly, for the receive antenna element (406b), the antenna gain is affected by the non-isotropic radiation pattern. More specifically, the radiation pattern from the transmit antenna (406a) in the active antenna set (512) (FIG. 5A) is often non-isotropic, such that microwave signals of the same amplitude incident on the receive antenna from various directions may result in different received powers at different receive antennas. Therefore, to properly extract tissue response, different "path-specific" (508) antenna gain compensation is applied to different microwave signals based on the characteristics of their unique signal paths.

[0213] Phase Center In addition to or as an alternative to antenna gain compensation, the antenna response compensation in (1308b) may also include phase center compensation.

[0214] The phase center of the transmitting antenna (406a) is the point in space from which the radiated signal appears to originate. This point is not necessarily at the physical center or edge of the antenna, or even on the surface of the radiating element itself. Therefore, eliminating the antenna response involves compensating for the distorted (e.g., non-ideal) location of the phase center of the transmitting antenna (406a). Phase center compensation is also path (508) specific, and therefore compensated for in the same way as gain.

[0215] Antenna response compensation coefficient In view of the above, at 1308b, for a given corrected microwave signal generated at 1306b, an antenna response compensation factor is applied to that signal to generate an adjusted microwave signal.

[0216] In at least one example, applying the antenna response compensation factor includes applying both (i) an antenna radiation gain compensation factor and (ii) a phase center position compensation factor, which are functions of frequency, antenna structure, and signal path (508) characteristics (e.g., azimuth and elevation angles of incidence).

[0217] In at least one example, the disclosed system can include a reference compensation coefficient data set (e.g., a reference data set) stored, for example, in the controller's memory 2004, that includes predefined gain and phase center compensations for each antenna structure in the system 400. In some examples, the gain and phase center compensations are associated with various azimuth and offset characteristics of the receive antenna relative to the transmit antenna. Thus, in 1308b, the correct compensation coefficients are selected in the reference data set based on the particular signal path characteristics identified in 1304b.

[0218] In some instances, the compensation coefficients also vary based on the signal path—the reference compensation coefficient data set may also include different compensation coefficients (e.g., gain and phase center) for different combinations of separation 152 (e.g., between antenna arrays) and / or rotational orientation of the antenna arrays (determined in 1304b based on the antenna array geometry parameters). Thus, in 1308b, the correct compensation coefficients are selected in the reference data set based on the separation distance and path orientation determined in 1304b.

[0219] In another example, the reference data set may contain compensation factors associated with various signal path lengths and azimuth angles of incidence, as well as signal frequencies.

[0220] It is also recognized that antenna response compensation varies significantly when the antenna arrays 102a, 102b are in contact with various biological tissues, including responses that vary between different types of tissue (e.g., breast vs. other tissues) and for the same tissue between different individuals.

[0221] Figures 14A and 14B illustrate the effect of different biological tissues on the antenna gain characteristics. Figure 14A shows the near-field radiation intensity pattern (1400a) in tissue that is predominantly fatty, while Figure 14B shows the near-field radiation intensity pattern (1400b) in tissue with a greater proportion of glandular tissue. The change in field strength of the antenna gain is clearly observed between the two radiation patterns.

[0222] Figures 15A and 15B illustrate the effect of different biological tissues on the phase center of the antenna. Specifically, phase is plotted for different tissue properties, even in the vicinity of the antenna. Figure 15A is the near-field phase pattern (1500a) for tissue that is predominantly fatty, while Figure 15B is the near-field phase pattern (1500b) for tissue with a greater proportion of glandular tissue. Again, clearly observed is the change in the shape of the phase, which results in a modified phase center depending on the position and / or orientation of the view relative to the antenna.

[0223] In view of the above, a technical challenge in using the disclosed antenna array configurations (e.g., FIGS. 4A and 4B) is to apply antenna response compensation to account for the different tissues being scanned.

[0224] To accommodate this, the compensation factor reference data set (eg, a reference chart) may also include different pre-defined compensation factors for different tissue types.

[0225] In some instances, the reference data set can include multiple sub-data sets (e.g., sub-reference maps) for each tissue type, and each sub-data set associated with each tissue type can include reference data related to tissue-specific antenna response coefficients, including (i) tissue-specific compensation coefficients defined for each antenna element, and (ii) tissue-specific compensation coefficients defined for various placement parameters (e.g., spatial spacing between antenna arrays and / or rotational orientation of antenna arrays).

[0226] Thus, in some instances, (1308c) the system may first determine the type of tissue being scanned, based on which the system may access the reference sub-dataset associated with that tissue type and determine the correct tissue-specific antenna response compensation coefficients, as described above.

[0227] In at least one instance, the antenna response compensation coefficients comprise a transfer function.

[0228] In at least one example, a reference data set of compensation coefficients is pre-generated by simulating the antenna design with various biological tissues using industry-standard simulation tools, with exemplary simulation criteria described below.

[0229] Specifically, the transmission coefficient between the antenna in contact with the tissue model is simulated for a range of array separations and / or array rotational orientations. Here, the transmission coefficient incorporates the effects of the antenna transfer functions for both the radiating and receiving antennas. The tissue model used may be represented in the simulation tool as a set of Debye models that describe the range of tissues to be expected. For each tissue model and each signal path (508) orientation, the transmission coefficient is simulated for multiple separations (152) and / or antenna rotational orientations. This allows the development of a model (a polynomial that is a function of separation and / or antenna rotational orientation) that describes the specific tissue placement of the antenna (path) and the necessary corrections for a specific material (tissue model).

[0230] Alternatively, instead of simulating the transmission coefficients between two antenna pairs, their detailed characterization can be performed by simulating the antenna transfer functions over a range of observation points in space from the antenna feed. The location of the observation points in space must match the locus of the path to which the compensation is applied. The actual antenna response compensation is then calculated by combining the antenna transfer functions for the radiating and receiving antennas. In this way, different tissue-specific compensation coefficients for each antenna element can be used. Other exemplary methods can also be employed.

[0231] Additionally or alternatively, a baseline compensation factor may be pre-measured by measuring the transmission coefficient between the two antennas over a range of path directions and various biological tissues.

[0232] For example, instead of simulation, measurements of a fluid-filled bladder representative of a range of biological tissues and at various separations 152 can be performed to determine the compensation coefficients. Compensation coefficients for the antenna radiation characteristics are then selected based on the tissue characteristics evaluated for each individual scan.

[0233] Thus, Figure 16A shows a graph (1600a) of antenna gain compensation for two different tissue types and when the signal paths have identical signal path characteristics, and Figure 16B shows a graph (1600b) of phase center compensation versus frequency for two different tissue types and when the signal paths have identical signal path characteristics.

[0234] 17A and 17B show graphs 1700a and 1700b illustrating the effect of correcting the attenuation and phase shift of the original signal using compensation for both gain and phase center. Specifically, these graphs show the resulting correction using gain compensation and phase center compensation.

[0235] In at least one example, the number of possible signal paths is significantly greater than the available compensation coefficient data, so if the compensation coefficients are not predetermined for a given signal path (for a given biological tissue), the compensation coefficients may be interpolated or extrapolated using techniques such as fitting a polynomial to the available data, and the resulting model allows correction coefficients to be obtained for a wide range of signal paths with different signal path characteristics.

[0236] In some embodiments, the correction of the antenna radiation characteristic is performed equally for all frequency points, individually for each frequency point, or equally for some frequency points and individually for other frequency points.

[0237] Therefore, the key to compensating for gain and phase is to thoroughly characterize the antenna response in a range of materials whose properties correspond to the desired properties of tissue. By removing the antenna properties from the measurement, the tissue response remains and can be used to determine the tissue response characteristics.

[0238] (ii.c) Determining predictions about tissue types Figure 13 is another process flow diagram for an exemplary method (1300c) for preconditioning a signal to generate a conditioned microwave signal, which is performed during operation (1310a) of Figure 13A.

[0239] In method 1300c, operations 1302c, 1304c, 1306c, and 1310c are similar to operations 1302b, 1304b, 1306b, and 1308b, respectively, of method 1300b. However, method 1300c also includes operation 1308c, which relates to determining the type of biological tissue being scanned before applying tissue-specific antenna response corrections.

[0240] More specifically, in various cases, the tissue 412 (FIGS. 4A and 4B) inserted into the scan region 158 may not be known precisely in advance. Thus, at 1308c, the system can predict the tissue type in real time or near real time. The system can then apply the correct antenna response compensation coefficients associated with that tissue type.

[0241] In at least one instance, determining the tissue type at 1308c involves initially determining tissue response characteristics, where this initial determination of tissue response characteristics is performed without the benefit of using a conditioned microwave signal that includes antenna response compensation and is intended solely to predict the tissue type.

[0242] In some instances, the measured tissue response characteristics may correspond to time delay characteristics of a microwave signal traveling through biological tissue. Exemplary methods for determining various tissue response characteristics, including time delay, are discussed in the next section.

[0243] Thus, the reference tissue property data set (e.g., stored in the controller's memory (2004) (FIG. 20)) can contain various reference tissue response properties for various biological tissues, and the system can then map the determined tissue response properties to the reference tissue properties to determine the biological tissue with the closest properties.

[0244] In at least one example, the baseline tissue response characteristics are generated by computer simulation. For example, simulations are generated for transmitting and receiving antennas in contact with various biological tissues, and their tissue response characteristics are predicted. A database may then contain a baseline lookup table of different tissue types and their predicted tissue response characteristics. Exemplary simulation conditions are further described below.

[0245] (iii.) Determine tissue response characteristics Exemplary tissue response characteristics of a target biological tissue that may be determined in operation 1312a (FIG. 13A) based on analyzing the conditioned microwave signal are discussed below.

[0246] In some instances, the tissue response characteristics include various electrical response characteristics of the scanned biological tissue, including, but not limited to, the tissue's permittivity, conductivity, attenuation, phase constant, and dielectric relaxation time characteristics.

[0247] For example, a method for determining magnetic permeability from time delay characteristics is described in J. Bourqui and E. Fear, “System for Bulk Dielectric Permittivity Estimation of Breast Tissues at Microwave Frequencies,” IEEE Transactions on Microwave Theory and Techniques, Vol. 64, No. 9, September 2016, which is incorporated herein by reference. As described in this reference, permittivity and conductivity characteristics can be determined based on the time delay characteristics.

[0248] In at least one example, the separation (152) between the active transmitting and receiving antennas is taken into account when determining the tissue response characteristics.

[0249] In some instances, tissue response characteristics are determined in the frequency domain, which then yields frequency-dependent electrical properties of the tissue. Frequency-dependent electrical properties include, by way of non-limiting example, permittivity, conductivity, attenuation constant, phase constant, or dispersive model parameters. Dispersive models may include a Debye model, which includes a static permittivity, an infinite permittivity, a static conductivity, and a dielectric relaxation time. Calculation of tissue properties in the frequency domain may be based on the phase and amplitude response of the signal in the frequency domain, or using well-known techniques such as the Nicholson-Ross-Weir method.

[0250] Electrical tissue properties can also be determined in the time domain. In this case, the frequency-domain microwave signal is converted to a time-domain signal. Discontinuities in the frequency-domain data may be removed by applying a window function before the time-domain conversion. The purpose of windowing is to improve the characteristics of the time-domain signal. Window functions include, but are not limited to, any known window function type, such as a flat-top window, a Hamming window, or a Tukey window, or low-pass filter responses, such as a Butterworth window, a Chebyshev window, or an elliptic window.

[0251] In at least one example, after converting the frequency domain signal to a time domain signal, the electrical property is determined by measuring the time delay and / or amplitude of the time domain signal.

[0252] More generally, as described in the above references, the time delay is evaluated as the peak in the time domain response corresponding to the group time delay, or from the rising edge of the time domain response corresponding to the first break. The time delay can be combined with the spacing between the arrays and the speed of light in a vacuum to estimate the permittivity. The amplitude of the time domain signal can be combined with the spacing between the arrays to estimate the conductivity.

[0253] In some embodiments, the method involves determining tissue response characteristics by using the difference between parameters extracted from the measured conditioned microwave signal and a reference microwave signal. The reference signal is measured with a material having known electrical properties and at the same separation and orientation as the antenna array. The reference material may comprise air, water, a mixture of water and glycerin, a mixture of Triton-X, water, and salt, any custom deformable material, or liquid with known electrical properties.

[0254] In at least one example, selected measurements of reference materials may be collected and used to create a model that predicts parameters extracted from the reference materials at various times. For example, time delay may be calculated from measurements of reference materials at various separations, and then a linear equation may be fitted to the time delay. This allows time delay to be predicted for additional separations without requiring specific reference measurements.

[0255] In some embodiments, the estimation method calculates the electrical properties by using the difference between microwave signals measured at various distances. This consists of subtracting the response measured at one distance from the response measured at another distance, resulting in a response corresponding to the compressed tissue without any other influences of the antenna or switch matrix.

[0256] In some embodiments, the estimation method calculates the electrical properties using a plane wave approach to calculate the permittivity and conductivity in the frequency domain.

[0257] For this reason, Figures 18A and 18B show graphs (1800a) and (1800b) of the final results after correcting the gain and phase center when the material properties are calculated using the Nicholson-Ross method.

[0258] (iv.) Generate output Below we consider the output generated in (1314a) (Figure 13A).

[0259] (iv.a) Combining tissue response properties In some instances, tissue response characteristics estimated at multiple transmit and receive antenna pairs are combined across a range of scanned biological tissue to generate an output (e.g., an output data set).

[0260] In at least one example, the system can define a two-dimensional data collection plane (550) (FIG. 5B). The data collection plane (550) can be equally spaced between the two arrays (550) and, in some examples, along a plane parallel to the two arrays. The system can then determine the intersection of each signal path (508) with the plane (550) based on the known signal path characteristics of each signal path. For example, this is shown in FIG. 5B as intersection point (552) of signal path (508'). Thus, any electrical properties of tissue determined from any signal path (508) traveling through tissue are mapped to a corresponding intersection point (552) on the plane (550). In this manner, each intersection point defines a "data point" (552) along the plane (550). This generates an output 2D data set characterizing the tissue response associated with multiple data points in the 2D horizontal plane (550). In other instances, the plane (550) can be defined at any other distance or angle relative to the two arrays.

[0261] Thus, if multiple tissue properties are determined at the same data point (552) associated with plane (550) (e.g., because multiple signal paths intersect at the same point), these tissue properties can be associated with that point separately or otherwise combined (e.g., an average of the tissue response property values).

[0262] In other instances, multiple planes can be defined and the process can be repeated to characterize the tissue response in 3D and generate 3D data sets along various planes (see, e.g., plane 550' and intersection 554). The 3D data sets may represent a collection of points generated by discretizing available paths in the space of interest. Thus, an infinite number of planes can theoretically be defined to generate 3D data with any desired resolution.

[0263] Interpolation can be performed on each of the 2D and 3D data sets to generate fill-in tissue properties for any point associated with any plane that is not quantified in the measured signal path.

[0264] (iv.b) Finding the characteristics of the tissue In some instances, the output may relate to determined tissue volume characteristics of the scanned biological tissue. The tissue may include, for example, water content, water status (bound water vs. free water), and ion concentration. These characteristics may be determined by relating at least one tissue electrical property or combination of tissue electrical properties along the microwave signal path to a particular tissue characteristic.

[0265] For example, a particular permittivity characteristic of a microwave signal can be mapped to a known water content ratio that correlates with a magnetic permeability characteristic. Thus, the electrical properties of tissue can be converted (e.g., mapped) to tissue features based on the known relationship between the tissue properties and the tissue features.

[0266] In some instances, as described above, for a 2D or 3D output data set, each 2D or 3D output data point can be mapped to a respective tissue property for that data point, thus generating a 2D or 3D tissue feature output.

[0267] (iv.c) Generate 2D and / or 3D images In some instances, the output corresponds to one or more images of the biological tissue, representing electrical properties and associated tissue features. For example, this may involve generating a visualization of a 2D or 3D tissue property dataset and / or a 2D or 3D tissue feature dataset, as described above (see, e.g., FIGS. 2A and 2B).

[0268] In some instances, imaging is performed in real time or near real time. Real-time imaging may be achieved by limiting the number of recorded frequency points and / or increasing measurement speed at the expense of reduced sensitivity. With sufficient processing power, the same algorithms presented herein may be used to reconstruct 2D images of the breast. Alternatively, the attenuation and phase shift values ​​of the adjusted frequency signals may be used to reconstruct qualitative 2D images of the breast.

[0269] (iv.d) Outputs related to tissue characterization In some instances, the microwave signal device may perform a method of analyzing images to characterize tissue and detect disease or response to treatment to obtain useful diagnostic information. For example, the analysis may include comparing images of two breasts, where the tissue distribution is expected to be symmetric. If one breast exhibits a localized increase in a characteristic, this may indicate breast disease.

[0270] In some embodiments, localized enhancement in an image may also be used to define regions of interest within the image that may be tracked over time and / or compared to similar regions in contralateral tissue. For example, comparing images over time may determine changes in tissue characteristics that indicate whether a disease is progressing or remitting over time, thereby indicating the success or failure of a particular treatment being administered.

[0271] In some embodiments, the method of analyzing the images comprises identifying signals exhibiting different characteristics between or within the two breasts. For example, the signal in a region of interest may be examined to identify differences in frequency content compared to signals in a region in the same breast, or compared to signals in a similar region in the opposite breast.

[0272] In some embodiments, methods for identifying signals with different characteristics may incorporate machine learning. This involves identifying characteristics of the time and / or frequency response of the measured signals to capture tissue responses and features that indicate changes over time. By extracting these characteristics and features for a new set of measurements, scans can be classified as consistent between breasts or within a breast over time, or changes can be identified.

[0273] In some embodiments, average image properties may be generated and correlated with tissue properties. For example, the average property of predominantly fatty tissue is predicted to be lower than that of predominantly glandular tissue. Density can be predicted from electrical property measurements by developing a model that maps average properties to tissue properties.

[0274] VI. Exemplary Measurement Protocol Below, various protocols are described that may be followed during measurements, e.g., scanning, of biological tissue using the microwave scanning system 400. These protocols may ensure that the position of the biological tissue does not change during scanning at different times.

[0275] In at least one example, the measurement protocol comprises enabling real-time imaging while the operator places the biological tissue 412 in the scan field 158 (FIGS. 4A and 4B). To assist the operator in repeating similar positions, an outline of the tissue's location from previous images may be displayed along with the real-time image, for example, on the display interface 114 (FIG. 1).

[0276] In some embodiments, the measurement protocol may provide real-time feedback to the operator while he or she is positioning the biological tissue within the array. To assist the operator in repeatable placement, an outline of the tissue's location from a previous image may be displayed along with an indication of the sensor currently in contact with the tissue. The indication of contact may be obtained by analyzing measurements at a subset or all of the frequency points.

[0277] The measurement protocol may also include automatic feedback to the operator to guide position corrections to ensure best tissue coverage and positional stability.

[0278] In at least one instance, the measurement protocol provides feedback regarding tissue positioning based on the positioning of the contralateral side. For example, in breast imaging, if the right breast is scanned in a craniocaudal view, positioning information is obtained from this scan to guide a subsequent scan of the left breast in a craniocaudal view.

[0279] In some embodiments, the measurement protocol ensures that the antenna array separation (152) (FIGS. 4A and 4B) does not vary when measuring the same biological tissue at different times. To accomplish this, the system guides the operator via the user interface to reproduce the separation from a previous measurement. This guidance consists of displaying the separation from the previous measurement and instructing the operator to adapt to that separation. The measurement protocol may include measurements at multiple separations (152), where the separation is modified by a small amount (compared to the overall spacing) between measurements without changing the tissue position.

[0280] The measurement protocol can also include obtaining multiple views of the tissue. The multiple views may be obtained by varying the angle of one or more of the arrays 102a, 102b, or by varying the position of all of the arrays 102a, 102b. The multiple views acquired are preferably from perspectives similar to those of other imaging devices. For example, the arrays 102a, 102b can be positioned to replicate the craniocaudal and mediolateral views used in mammography.

[0281] In at least one embodiment, the measurement protocol includes using similar or identical separations (152) when acquiring equivalent views of the contralateral tissue. As an example, if one breast is scanned in a craniocaudal view, the separation used for this breast is applied to the other breast of the same subject.

[0282] In some cases, the measurement protocol involves acquiring multiple scans of the same tissue, which may be done with or without varying the position of the tissue.

[0283] VII. EXEMPLARY SIMULATION PARAMETERS As discussed in FIGS. 13B and 13C, various simulations are performed to obtain the reference correction factors, more particularly the antenna response compensation factors.

[0284] In at least one example, simulation of the antenna array with various biological tissues to obtain the correction and compensation factors is performed using an industry standard simulation tool, which in at least one example includes Ansys™, HFSS™, CST™, or Sim4Life™.

[0285] 19A shows an example image obtained from an example simulation tool showing an example group 502 of simulated transmit antenna elements 406a and receive antenna elements 406b in a simulated system 400. A region 1902 is filled with simulated biological tissue.

[0286] In at least one example, the simulation is performed with a frequency sweep from 2 GHz to 8 GHz. The radiation boundary is placed on the side of the biological tissue, but the antenna is surrounded by a perfect electric conductor (PEC), similar to the structure of a real array. Feed is provided by direct feed vias (810) to capture all significant antenna effects.

[0287] In one approach to generating reference antenna response compensation coefficients, the transmission between the transmit antenna 406a and the set of receive antennas 502 may be simulated while a tissue model is placed in the region 1902 between the transmitter and receiver. As noted above, various known Debye models are known that model the permittivity and / or conductivity properties of various biological tissues and are input into the simulation tool. For example, a Debye model for breast tissue is described in "Highly Accurate Debye Models for Normal and Malignant Breast Tissue Dielectric Properties at Microwave Frequencies," IEEE Microwave and Wireless Components Letters, Vol. 17, No. 12, December 2007, which is incorporated herein by reference.

[0288] In another example, biological tissues are simulated using known Cole-Cole models for each tissue. More generally, various models describing a range of tissues that may be encountered may be used to determine antenna compensation coefficients. For example, tissue groups based on water content are defined in M. Lazebnik, M. Okoniewski, J.H. Booske, and S.C. Agness, "Highly Accurate Debye Models for Normal and Malignant Breast Tissue Dielectric Properties at Microwave Frequencies," in IEEE Microwave and Wireless Components Letters, vol. 17, no. 12, pp. 822-824, December 2007, doi:10.1109 / LMWC.2007.910465, which is incorporated herein by reference. This reference defines "Groups 1, 2, and 3" for high and low water content, respectively.

[0289] To further expand the number of models simulating tissues, each tissue grouping may be further expanded with two additional models describing upper and lower ranges with values ​​reflecting the original data found in M. Lazebnik, M. McCartney, D. Popovic, C.B. Watkins, M.J. Lindstrom, J. Harter, S. Sewall, A. Magliocco, J.H. Booske, M. Okoniewski, and S.C. Agness, “A large-scale study of the ultrawideband microwave dielectric properties of normal breast tissue obtained from reduction surgeries,” Phys Med Biol. 2007 May 21;52(10):2637-56. doi:10.1088 / 0031-9155 / 52 / 10 / 001. Epub 2007 Apr 23, which is incorporated herein by reference.

[0290] Thus, in the simulated environment, the distribution of the receive antenna set may mirror that of a particular antenna array (102). By simulating for various separations (152), the simulated model generates transmission data for a range of path directions that may be encountered during measurements. This transmission data is grouped using separation-independent path direction characteristics, such as path azimuth (angular orientation above the array plane) and path offset (lateral distance between the transmitter and receiver). Knowing the theoretical tissue response, the grouped transmission data is used to calculate antenna compensation coefficients (gain and phase center) valid for that particular tissue model. These antenna compensation coefficients are then fitted to a polynomial model that is a function of separation. By replicating these simulation steps with multiple tissue models, antenna compensation coefficients can be determined for other tissue properties.

[0291] In at least one example, during measurement, tissue properties are first evaluated to select appropriate antenna compensation coefficients that are valid for similar tissue properties, and then polynomials associated with the azimuth and offset of the corresponding paths are selected to calculate antenna compensation coefficients for any separation.

[0292] Therefore, a good fit between measurements and simulations is necessary for the disclosed techniques to work. Figures 19B and 19C, showing graphs (1900b) and (1900c), illustrate the degree of agreement between measurements and simulations of two antennas transmitting microwave signals passing through a bag filled with tissue-mimicking liquid (canola oil). As shown, the frequency-domain and time-domain representations show very good agreement, thereby validating the validity of the simulation model employed in this disclosure.

[0293] 19D-19F, showing graphs 1900d-1900j, illustrate the application of the disclosed techniques to a large amount of simulated data. The simulation contains one transmitter and a set of 37 receivers separated by low tissue in Group 1 (according to the above-cited references). The separation between the transmitter and receiver is swept between 40 and 80 mm in 5 mm increments. This results in a data set containing 333 signals. Antenna response compensation is applied using various tissue characteristics ("medium" tissue group 1) to mimic the case where correction factors tailored to the tissue group are not available.

[0294] Clearly observed in Figure 19D is the spread in the mean estimate of permittivity when no correction is applied, resulting in a coefficient of variation of 0.058. Figure 19E shows a histogram plot of the calculated mean permittivity when antenna response compensation is applied to 333 simulated transmitted signals passing through tissue model Group 1 "Low."

[0295] Next, when antenna response compensation is applied to the measured data, a bag of glycerin material is placed between the two arrays and the response is measured at a separation of 40 mm. Figure 19F shows the average permittivity calculated using the raw signal. Figure 19G shows the same data, but with antenna response compensation applied. The simulated antenna response compensation coefficients for Group 3 "Medium" are used because they have the permittivity closest to glycerin. Comparing the results, the average permittivity remains unchanged, but the coefficient of variation is reduced by a factor of two, demonstrating the effectiveness of this method.

[0296] In another example, a water-filled bag is placed between the antenna arrays and measured at a separation of 40 mm. Figures 19H-19J show the calculated permittivity for the original signal, the signal corrected with the "medium" coefficients of Group 1, and the signal corrected with the "medium" coefficients of Group 3, respectively.

[0297] The electrical property values ​​for water are significantly closer to the Group 1 "Medium" because the average permittivity of water is approximately 75 across the frequencies of interest, while the Group 1 "Medium" is approximately 45. On the other hand, the Group 3 "Medium" has an average permittivity of approximately 5, which is significantly different. In other words, the results without any compensation are shown in Figure 19F, the results of compensation with a reasonably appropriate coefficient are shown in Figure 19I, and the unfavorable results of compensation with an inappropriate coefficient are shown in Figure 19J. The estimates are more accurate with appropriate compensation, with the average permittivity value increasing from 72.8 to 76.7, and more importantly, the coefficient of variation is reduced from 0.085 to 0.034. A significantly narrower distribution is also evident. The opposite is true when an inappropriate compensation coefficient is used, as can be clearly seen in Figure 19J.

[0298] VIII. Exemplary Hardware Arrangements for Controllers 20 illustrates an exemplary electrical hardware configuration for the controller 418. As shown, the controller 418 may include a processor 2002 coupled to a memory 2004, as well as one or more of an input interface 2008, an output interface 2010, a communication interface 2006, and an input / output (I / O) interface 2012.

[0299] In some instances, the memory 2004 may contain various computer-executable instructions for performing the methods 1300a-1300c, or any portions thereof.

[0300] The input interface 2008 can include various devices for inputting data into the controller 418, such as a keyboard, a mouse, trackage, a virtual reality headset, a gesture recognizer, a voice command recognizer, or an augmented reality display. The input interface 2008 can be similar to the input interface 116 (FIG. 1).

[0301] The display interface 2010 can be an output interface (e.g., a liquid crystal display (LCD) screen) for displaying data. In some instances, the display interface 2010 comprises a display screen 114 (FIG. 1). In some instances, the display interface 2010 displays a user interface that allows an operator to communicate with the system.

[0302] In some instances, the input interface and the display interface may be one (e.g., a touch display screen).

[0303] The communications interface 2006 may include a cellular modem and antenna for wirelessly communicating data to a communications network. In some instances where the methods described above are performed using an external computing device (e.g., an external server), the external computing device communicates through the communications interface 2006 to receive and transmit data to the controller 418.

[0304] The input / output interface (2012) can be used to connect the controller (418) to other external devices, including the microwave transceiver (416) and the switch networks (402a), (402b).

[0305] Thus, those skilled in the art will understand that references herein to the controller (418) performing a function or operating in a particular manner imply that the processor (2002) is executing instructions (e.g., software programs) contained within the memory (2004) and, in some cases, sending or receiving inputs and outputs via one or more interfaces.

[0306] IX. Interpretation Aspects of the present invention may be described with reference to flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowcharts and / or block diagrams, and combinations of blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions that can be provided to a processor of a general-purpose computer, special-purpose computer, or other programmable data processing device to produce a machine, whereby the instructions, executed by the processor of the computer or other programmable data processing device, create means for performing the functions identified in one or more blocks of the flowcharts and / or block diagrams.

[0307] The flowcharts and block diagrams in the figures illustrate the structure, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code, including one or more executable instructions for implementing specific logical functions. It should also be noted that in some alternative implementations, the functions noted in the blocks may occur out of the order noted in the figures. For example, two blocks shown in succession may in fact be executed substantially in parallel, or the blocks may sometimes be executed in the reverse order, depending on the functionality involved. It should also be noted that each block of the flowcharts and / or block diagrams, and combinations of blocks in the flowcharts and / or block diagrams, may be implemented by a dedicated hardware-based system that performs a specific function or function, or by a combination of dedicated hardware and computer instructions.

[0308] The corresponding structure, material, acts, and their equivalents of all means or steps and functions within the scope of the claims appended hereto are intended to include any structure, material, or acts for performing the function in combination with other elements of the claim as specifically claimed.

[0309] References in the specification to "some embodiments," "one embodiment," "an embodiment," or "an embodiment" indicate that the described embodiment may include a particular aspect, feature, structure, or characteristic, but not every embodiment necessarily includes that aspect, feature, structure, or characteristic. Moreover, such phrases may, but do not necessarily, refer to the same embodiment referenced elsewhere in the specification. Furthermore, when a particular aspect, feature, structure, or characteristic is described in connection with an embodiment, it is within the knowledge of one of ordinary skill in the art to make changes to or associate such aspect, feature, structure, or characteristic, whether or not explicitly stated. In other words, any module, element, or feature may be combined with any other element or feature of different embodiments, unless expressly or inherently incompatible or specifically excluded.

[0310] It is further noted that the claims may be drafted to exclude any optional or preferred element. Accordingly, this statement is intended to serve as a prerequisite for using exclusive terminology, such as "solely," "only," etc., in connection with reciting claim elements or using a "negative" limitation. The terms "preferably," "preferred," "preferably," "optionally," "may," and similar terms are used to indicate that the stated item, state, or step is an optional (not required) feature of the invention.

[0311] The singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. The term "and / or" means any one of the items, any combination of the items, or all of the items with which the term is associated. The phrase "one or more" is readily understood by those of ordinary skill in the art, particularly when read within the context in which it is used.

[0312] The term "about" can refer to a variation of ±5%, ±10%, ±20%, or ±25% of the specified value. For example, "about 50" percent can include a variation of 45 to 55 percent in some embodiments. With respect to integer ranges, the term "about" can include one or two integers greater than and / or less than the recited integers at each end of the range. Unless otherwise indicated herein, the term "about" is intended to include values ​​and ranges near the recited range that are equivalent in terms of structure or function of the embodiment.

[0313] As will be understood by those skilled in the art, for any and all purposes, particularly with respect to providing a written description, all ranges described herein encompass any and all possible subranges and combinations of subranges, as well as the individual values ​​that make up that range, particularly integer values. The described ranges include each specific value, integer, decimal, or unit within the range. Any recited range can be readily recognized as fully describing and enabling the same range to be broken down into at least equal halves, thirds, quarters, fifths, or tenths. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third, and upper third.

[0314] As will be understood by one of ordinary skill in the art, phrases such as "up to," "at least," "greater than," "less than," "more than," "or greater than or equal to," etc., are all inclusive of the recited numbers, and such terms may be further broken down into subranges, as discussed above. Similarly, all ratios recited herein include all subratios falling within the broader ratio.

Claims

1. - operating antenna elements in an antenna set, the antenna set comprising a transmitting antenna element in a transmitting antenna array and one or more receiving antenna elements in a receiving antenna array; - activating at least one microwave transmitter to generate a microwave interrogation signal for transmission by said transmitting antenna element into the biological tissue; receiving, by at least one microwave receiver, one or more received microwave signals from each of said one or more receive antenna elements; - applying preconditioning to each of said received microwave signals to generate a corresponding conditioned microwave signal, said preconditioning separating tissue response characteristics from extraneous response factors; - analyzing the conditioned microwave signal to determine one or more tissue response characteristics associated with the biological tissue; generating an output based on the determined one or more tissue response characteristics; a method for microwave scanning of said biological tissue, said method comprising:

2. 2. The method of claim 1 , wherein the step of operating the antenna elements comprises activating a first switch network to couple the transmit elements to the at least one microwave transmitter and activating a second switch network to couple the one or more receive elements to the at least one microwave receiver.

3. 3. The method of claim 2, wherein the step of operating the antenna elements comprises: activating the microwave transmitter coupled to the transmitting antenna element; and activating the microwave receiver coupled to the receiving antenna element.

4. 4. The method according to claim 1, wherein the biological tissue is placed in a scanning region between the transmitting antenna array and the receiving antenna array and is in contact with the antenna array.

5. The method of claim 4 , wherein a dielectric covering material is coupled to one or more of the transmit antenna array and the receive antenna array and contacts the biological tissue within the scanning region.

6. 6. The method of claim 5, wherein the dielectric coating material has a dielectric constant of less than 5 and a maximum thickness of 2 mm, more preferably a dielectric constant of about 2.5 and a thickness of less than 0.5 mm.

7. The step of applying preconditioning to the microwave signal comprises: - identifying a pair of transmitting and receiving antennas associated with said microwave signals; - defining one or more configuration parameters of said antenna array; applying a path-specific correction factor to the microwave signal based on said determining to generate a corrected microwave signal; applying an antenna response compensation factor to said corrected microwave signal to produce an adjusted microwave signal; 7. The method of any one of claims 1 to 6, comprising:

8. The method of claim 7 , wherein the per-path correction factors include correction factors for phase and amplitude correction for each receive and transmit path associated with the pair of transmit and receive antennas.

9. 9. The method of claim 7 or 8, wherein the placement parameters of the antenna arrays correspond to one or more of: (i) the positional spacing of antenna elements on each array surface; (ii) the axial spatial distance between the antenna arrays; and / or (iii) the rotational orientation of the antennas.

10. 10. The method of claim 9, wherein the antenna response compensation coefficients include an antenna gain compensation coefficient and a phase center compensation coefficient, the antenna compensation coefficients being related to (i) the type of biological tissue and (ii) the placement parameters of the antenna array.

11. The method of claim 10 , wherein the antenna response compensation factors and per-path correction factors are generated by a simulation tool that generates baseline compensation factors and baseline correction factors.

12. 12. The method of claim 1, wherein each antenna array comprises a plurality of slot antenna elements, each slot antenna having its own shielding interface.

13. The method of claim 2 , wherein each switch network includes one or more switch subnetworks and each antenna array includes one or more antenna sub-arrays.

14. a transmitting antenna array and a receiving antenna array, each antenna array comprising a plurality of antenna elements; a transmit antenna array and a receive antenna array separated by an axial separation along an axis to define a scan region for receiving biological tissue; a first switch network and a second switch network, each coupled to a respective transmit antenna array and receive antenna array, said switch network comprising a plurality of switch elements; at least one microwave transmitter coupled to said transmit antenna array via said first switch network; at least one microwave receiver coupled to said receive antenna array via said second switch network; a controller coupled to the first switch network and the second switch network and to the at least one microwave transmitter and the at least one microwave receiver, the controller being operable to perform the method of any one of claims 1, 2 and 4 to 13; 1. A system for microwave scanning of biological tissue, comprising:

15. a transmitting antenna array and a receiving antenna array, each antenna array comprising a plurality of antenna elements; a transmit antenna array and a receive antenna array separated by an axial separation along an axis to define a scan region for receiving biological tissue; at least one microwave transmitter coupled to said transmitting antenna array; at least one microwave receiver coupled to said receive antenna array; a controller coupled to said at least one microwave transmitter and said at least one microwave receiver, said controller being operable to perform the method of any one of claims 1 and 3 to 13; 1. A system for microwave scanning of biological tissue, comprising:

16. 16. The system of claim 15, wherein the at least one microwave transmitter is a plurality of microwave transmitters, each coupled to a separate antenna element of the transmit antenna array, and the at least one microwave receiver is a plurality of microwave receivers, each coupled to a separate antenna element of the receive antenna array.

17. at least two antenna arrays separated by an axial separation along the axis to define a scanning region for receiving biological tissue; a dielectric covering material coupled to and covering each antenna array and in contact with said biological tissue inserted into the defined imaging region; 1. An antenna assembly for use with a system for microwave scanning of biological tissue, comprising:

18. 20. The antenna assembly of claim 17, wherein each antenna array comprises a plurality of slot antennas.

19. 20. The antenna assembly of claim 18, wherein each slot antenna comprises a respective shielding interface.

20. 20. An antenna assembly according to any one of claims 17 to 19, wherein the dielectric coating material has a dielectric constant of less than 5 and a maximum thickness of 2 mm, more preferably a dielectric constant of about 2.5 and a thickness of less than 0.5 mm.

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