Synthetic aperture imaging system and method using hybrid array

Abstract

A method of acousto-optical imaging can include receiving a first signal from a first sub-aperture of a sensor array. The first sub-aperture can include one or more array elements of a first type. The method can also include receiving a second signal from a second sub-aperture of the sensor array. The second sub-aperture can include one or more array elements of a second type different from the first type. In some variations, the array elements of the first type can be acoustic transducers (e.g., piezoelectric transducers) and / or the array elements of the second type can be optical sensors (e.g., optical resonators such as whispering gallery mode (WGM) resonators). The method can also include combining the first signal and the second signal to form a synthetic aperture of the sensor array.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Patent Application No. 63 / 075,727, filed September 8, 2020, the entirety of which is incorporated herein by reference. Technical Field

[0003] This disclosure generally relates to the field of ultrasound imaging, and more specifically to methods and apparatus that enable the formation of a synthetic aperture by combining signals from a hybrid array including an array of optical resonators and other sensors. The methods and apparatus disclosed herein include optical resonators with high sensitivity and high operating bandwidth to improve imaging performance. Background Technology

[0004] Ultrasound sensing is used in various industries, including medical imaging and medical diagnostics, due to several advantages. For example, ultrasound sensing utilizes ultrasound signals with significant penetration depth. Furthermore, ultrasound imaging is known to be an advantageous form of non-invasive imaging because it is based on non-ionizing radiation.

[0005] The various known ultrasonic transducers used in ultrasound imaging have many drawbacks. For example, some ultrasonic transducers are made of piezoelectric materials, such as lead zirconate titanate (PZT). However, the 6dB bandwidth of PZT materials is generally limited to only about 70%. Some composite PZT materials have slightly increased bandwidth, but still only achieve a maximum of about 80%. As another example, single-crystal materials are increasingly used to improve the performance of ultrasonic probes, but they have low Curie temperatures and are prone to variation. Another type of transducer material is silicon, which can be processed to build capacitive micromachined ultrasonic transducer (CMUT) probes with higher bandwidth. However, CMUT probes are not very sensitive or reliable. Furthermore, CMUT probes have several operational limitations. For example, CMUT probes are nonlinear sensors and are therefore generally unsuitable for harmonic imaging. In addition, CMUT probes require additional bias voltage to operate correctly. Therefore, there is a need for ultrasonic probes that include sensors with higher bandwidth and sensitivity. Summary of the Invention

[0006] In summary, in some variations, an apparatus for imaging a target may include one or more array elements of a first type forming a first sub-aperture, and one or more array elements of a second type, different from the first type, forming a second sub-aperture, wherein the first sub-aperture receives a first signal having a first phase, and the second sub-aperture receives a second signal having a second phase. The apparatus may also include a front end configured to generate a synthetic aperture at least partially by combining the first and second signals. In some variations, the front end may be configured to generate the synthetic aperture using one or more aspects of the methods described herein.

[0007] In summary, in some variations, a method for imaging a target may include receiving a first signal from a first sub-aperture of a sensor array, wherein the first sub-aperture comprises one or more array elements of a first type. The method may also include receiving a second signal from a second sub-aperture of the sensor array, wherein the second sub-aperture comprises one or more array elements of a second type different from the first type. The method may further include combining the first and second signals to form a composite aperture of the sensor array.

[0008] In some variations of this apparatus and method, the first type of array element can be a non-optical sensor configured to transmit sound waves, such as an acoustic transducer (e.g., a piezoelectric transducer or a capacitive micromechanical ultrasonic transducer (CMUT) sensor), and the second type of array element can be an optical sensor, such as a whispering gallery mode (WGM) sensor. The optical sensor can be / including microsphere resonators, micro-ring resonators, micro-ring resonators (e.g., having a circular or non-circular cross-sectional shape, such as a racetrack or ellipse), microbubble resonators, photonic integrated circuit (PIC) resonators, and / or microdisk resonators. In some cases, the first and second types of array elements can be configured to detect acoustic echoes corresponding to the transmitted sound waves.

[0009] In some variations, the method may further include phase matching of the first and second signals. To perform phase matching, a first delay may be applied to the first signal and / or a second delay may be applied to the second signal. In some cases, the first and / or second delays may be determined at least in part based on the difference between a first propagation time from one or more array elements of the first type to the imaged medium and a second propagation time from one or more array elements of the second type to the medium. Additionally, or alternatively, the first and / or second delays may be determined based on the thickness and sound velocity of the acoustic lens and / or the thickness and sound velocity of the acoustic matching layer. The first and / or second delays may be presented as delay curves that take into account the various differences between each array element and / or sub-element.

[0010] In some variations, the method may further include filtering the first and / or second signals to reduce noise in the signals and / or the frequency range of the matched signals. The filters may include bandpass filters, low-pass filters, high-pass filters, digital filters, and so on. In some variations, the method may further include amplifying the first and / or second signals according to an amplification gain to perform amplitude matching between the first and second signals. The amplification gain may be a preset value and / or determined based on the imaging depth. The amplification gain may include a constant value or a tensor comprising an amplification gain value that provides a specific gain for each array element.

[0011] The ultrasonic sensor array can be a 1D array, a 1.25D array, a 1.5D array, a 1.75D array, or a 2D array. In some variations, one or more array elements of a first type and one or more array elements of a second type can be arranged into a 1.25D array or a 1.5D array. Each of the 1.25D array or the 1.5D array can include a first row and a second row. The first row can include a first number of array elements, and the second row can include a second number of array elements. In some cases, the first number of array elements in the first row can be equal to the second number of array elements in the second row. For example, the first row and the second row can each include 128 array elements. In some cases, the first number of array elements in the first row can be different from the second number of array elements in the second row. For example, the first row can include 128 array elements, while the second row can include 192 array elements.

[0012] In some variations, the first signal may include a combination of signals originating from multiple array elements of the first type. Alternatively or additionally, the second signal may include a combination of signals originating from multiple array elements of the second type. Combining signals from similar types of array elements that are close to each other can reduce the dimensionality of the hybrid array (e.g., from a 1.5D array to a 1D array). Therefore, the hybrid array may require fewer filters and / or amplifiers.

[0013] In some variations, the method may include frequency matching, amplitude matching, and phase matching of the first and second signals in any suitable order. For example, the method may include frequency matching of the first and second signals, followed by amplitude matching, and then phase matching. As another example, the method may include phase matching, amplitude matching, and frequency matching of the first and second signals in sequence. After performing frequency matching, amplitude matching, and phase matching separately for each array element type, the first and second signals may be combined. This combination may involve coherent combination.

[0014] In some variations, the method may include selecting a first sub-aperture for transmitting an acoustic signal and a combination of a first sub-aperture and a second sub-aperture for receiving an acoustic echo in response to the acoustic signal. In some variations, the method may include selecting an element from one or more array elements of a first type for transmitting an acoustic signal, and selecting a combination of the first and second sub-apertures for receiving an acoustic echo in response to the acoustic signal. In some variations, the method may include selecting an angle (e.g., a steering angle) for transmitting the acoustic signal and / or receiving the acoustic echo. The above selection process may be repeated iteratively until all sub-apertures, array elements, and / or angles are fully covered.

[0015] In some variations, one or more of the second type of array elements may include one or more optical sensors embedded in the polymer structure. These optical sensors may be coupled to fiber optics to transmit a set of optical signals to a photodetector. The optical sensors may be configured to change the optical signals in response to acoustic echoes. Attached Figure Description

[0016] Figure 1 This is a block diagram of an exemplary synthetic aperture imaging system with a hybrid array.

[0017] Figure 2 This is a block diagram of an exemplary front end of a synthetic aperture imaging system with a hybrid array.

[0018] Figure 3 This is a block diagram of an exemplary front end of a synthetic aperture imaging system with a hybrid array.

[0019] Figure 4 This is a block diagram of an exemplary probe for a synthetic aperture imaging system with a hybrid array.

[0020] Figure 5 This is a schematic illustration of a hybrid array, which is an example of a synthetic aperture imaging system.

[0021] Figure 6 This is a schematic illustration of a hybrid array, which is an example of a synthetic aperture imaging system.

[0022] Figure 7 This is a schematic illustration of a hybrid array, which is an example of a synthetic aperture imaging system.

[0023] Figure 8 This is a schematic illustration of a hybrid array, which is an example of a synthetic aperture imaging system.

[0024] Figure 9 This is a schematic illustration of a hybrid array, which is an example of a synthetic aperture imaging system.

[0025] Figure 10 This is a schematic illustration of a hybrid array, which is an example of a synthetic aperture imaging system.

[0026] Figure 11 This is a flowchart of an exemplary method for performing synthetic aperture imaging using a hybrid array.

[0027] Figure 12 This is a flowchart of an exemplary method for performing synthetic aperture imaging using a hybrid array.

[0028] Figure 13 This is a flowchart of an exemplary method for performing synthetic aperture imaging using a hybrid array.

[0029] Figure 14 This is a block diagram of an exemplary method for performing synthetic aperture imaging using a hybrid array.

[0030] Figure 15 This is a block diagram of an exemplary method for performing synthetic aperture imaging using a hybrid array.

[0031] Figure 16 This is a block diagram of an exemplary method for performing synthetic aperture imaging using a hybrid array.

[0032] Figure 17 This is a block diagram of an exemplary method for performing synthetic aperture imaging using a hybrid array.

[0033] Figure 18 The example signal is shown, generated by two types of sensors in a hybrid array.

[0034] Figure 19An exemplary frequency response of two bandpass filters customized for two types of sensors in a hybrid array is shown.

[0035] Figure 20 An exemplary hybrid array window and its corresponding beammap are shown.

[0036] Figure 21 An exemplary synthetic aperture window of the hybrid array and its corresponding beam pattern are shown.

[0037] Figure 22 Exemplary delay curves for uniform arrays and hybrid arrays are shown. Detailed Implementation

[0038] This document describes and illustrates, in the accompanying drawings, various aspects and variations of the invention as non-limiting examples.

[0039] This document describes a method and apparatus for synthetic aperture imaging using an ultrasound probe with a hybrid array comprising multiple different types of array elements. The hybrid array described herein includes one or more array elements of a first type and one or more array elements of a second type (e.g., optical sensors, such as WGM optical resonators, etc.) that differ from the first type. Optical sensors offer high sensitivity and wide bandwidth when receiving ultrasound signals compared to other types of ultrasound sensors. One or more array elements of the first type (e.g., transducers, or non-optical subarrays) can be used to form a first set of signals. In parallel, one or more array elements of the second type (e.g., optical sensors in optical subarrays) are used to detect acoustic echoes that can be used to form the second set of signals. The second set of signals generated by the high-sensitivity and wide-bandwidth optical sensors can be used independently or combined with the first set of signals to form a further improved image. Due to the high sensitivity and wide bandwidth of the optical sensors, the images generated by the optical sensors can have improved spatial resolution, improved contrast resolution, improved penetration depth, improved signal-to-noise ratio (NSR), improved tissue harmonic imaging, and / or improved Doppler sensitivity.

[0040] Optical sensors do not generate ultrasonic signals, and therefore are used in hybrid arrays along with other transducers that do generate ultrasonic signals (e.g., piezoelectric transducers, CMUTs, etc.). Hybrid arrays can be arranged in various configurations and include sensor elements with varying noise levels, amplitude responses, phase delays, frequency ranges, and so on. Therefore, beamforming methods and apparatuses typically used for probes with one type of sensor cannot be used for probes using hybrid arrays employing multiple types of sensors.

[0041] For each hybrid array configuration, the beamforming method and algorithm can be customized to suit the configuration. Since both non-optical and optical subarrays can be used to receive ultrasonic echo signals, the receiving aperture of the hybrid array can be divided into multiple sub-apertures. For example, a first receiving sub-aperture (also referred to as a "non-optical aperture") may include one or more sensors that are not optical sensors. Furthermore, a second receiving sub-aperture (also referred to as an "optical sensor aperture") may include one or more optical sensors. The receiving aperture may include additional sub-apertures (e.g., a third sub-aperture, a fourth sub-aperture, etc.). Signals received from the sub-apertures can be combined by the receiving beamformer of the imaging system to produce a synthetic aperture, as further described below.

[0042] Using beamformers for synthetic aperture ultrasound imaging offers numerous advantages. For example, synthetic aperture ultrasound imaging can increase the aperture size without increasing the system channel count. Furthermore, it can increase the frame rate of ultrasound imaging without reducing the line density in the resulting images. As another example, synthetic aperture ultrasound imaging can improve image quality by enabling dynamic focusing for both transmission and reception.

[0043] Synthetic Aperture Imaging System

[0044] Figure 1This is a block diagram of an exemplary synthetic aperture imaging system 100 with a hybrid array. The synthetic aperture imaging system 100 includes a probe 125, an imaging system 160, and a display 170. The probe 125 may be coupled to the imaging system 160 (e.g., communicatively coupled). The probe 125 may receive and / or transmit a set of signals (e.g., electrical signals, optical signals, etc.) to the imaging system 160. The probe 125 may include a hybrid array 110 that may receive and / or transmit a set of signals (e.g., acoustic signals, etc.) to a medium to form an ultrasound image. The imaging system 160 may include a front end 140 and a rear end 150 that may jointly determine the physical parameters (e.g., time, position, angle, intensity, etc.) of the signals transmitted to the probe (e.g., via one or more transmit channels) and process the signals received by the probe 125 (e.g., via one or more receive channels) to form an image. Imaging system 160 may also be communicatively coupled to display 170 to send a set of signals (e.g., electrical signals, electromagnetic signals, etc.) to display 170. For example, in some variations, display 170 may be configured to display an image generated by imaging system 160 (e.g., in a graphical user interface (GUI)). Additionally or alternatively, imaging system 160 may receive signals from display 170. For example, display 170 may also include an interactive interface (e.g., touchscreen, keyboard, motion sensor, etc.) to receive commands from a user of synthetic aperture imaging system 100 to, for example, control the operation of synthetic aperture imaging system 100.

[0045] like Figure 1As shown, probe 125 may include a hybrid array 110, a multiplexer 120, and optical sensor cables 130. Hybrid array 110 may include one or more array elements of a first type (non-optical sensors, such as PZT transducers, CMUT transducers, etc.) and one or more array elements of a second type (optical sensors, such as WGM resonators). The non-optical transducers may be configured to transmit acoustic waves and, in some variations, to additionally receive and detect echo signals in response to the transmitted acoustic waves. The optical sensors may be configured to receive and detect echo signals with high sensitivity and wideband response. In some variations, probe 125 may be configured to iteratively scan the entire field of view using hybrid array 110. Doing so will generate images using optical sensors and / or non-optical transducers, as described in further detail below. The non-optical transducers in hybrid array 110 may be operatively coupled to multiplexer 120, which processes electrical signals transmitted and / or received between imaging system 160 and non-optical transducers. One or more array elements of the second type in the hybrid array 110 can be operatively coupled to an optical sensor cable 130, which processes optical signals transmitted and / or received between the imaging system 160 and the optical sensor.

[0046] The function of multiplexer 120 is to selectively connect individual system channels to desired array elements. Multiplexer 120 may include analog switches. The analog switches may include a plurality of high-voltage analog switches. Each analog switch may be connected to an individual system channel. Thus, multiplexer 120 can selectively connect individual system channels from a set of system channels of imaging system 160 to desired transducer elements of hybrid array 110.

[0047] Optical sensor cable 130 may include a dedicated optical path for sending and / or receiving optical signals to and from the optical sensor. Optical sensor cable 130 may include one or more optical waveguides, such as one or more fiber optic cables or one or more coaxial cables. The characteristics of optical sensor cable 130 may depend on the type of optical signal, the type of optical sensor, and / or the arrangement of the optical sensors. In some configurations, multiple optical sensors (e.g., an entire subarray of optical sensors, or any two or more optical sensors forming part of it) may be optically coupled to a single optical waveguide. Thus, signals from multiple optical sensors can be coupled into and communicated through a single optical waveguide. In some configurations, subarrays of optical sensors may be optically coupled to an array of optical waveguides at a 1:1 ratio (e.g., each optical sensor may be coupled to its own optical waveguide). Thus, optical signals from the subarrays of optical sensors can be coupled into one or more optical waveguides in optical sensor cable 130 and transmitted to imaging system 160 through these optical waveguides. Furthermore, in some variations, synthetic aperture imaging system 100 may include multiple optical sensor cables constructed as described above.

[0048] Imaging system 160 may include a front end 140 and a back end 150. Generally, front end 140 interfaces with probe 125 to generate an acoustic beam and receive electrical and / or optical signals. Back end system 153 may include one or more processors to process signals received from hybrid array 110 via front end to generate images, memory operatively coupled to the processors to store images, and / or communication interfaces to present images to a user (e.g., via a graphical user interface).

[0049] For example, display 170 may be operatively coupled to back-end system 150 of imaging system 160 to display a set of images generated by imaging system 160. In some variations, display 170 may additionally or alternatively include an interactive user interface (e.g., a touchscreen) and be configured to send a set of commands to imaging system 160 (e.g., pause, resume, etc.). In some variations, synthetic aperture imaging system 100 may also include a set of one or more auxiliary devices (not shown) for inputting or outputting information to synthetic aperture imaging system 100. This set of auxiliary devices may include, for example, one or more keyboards, one or more mice, one or more monitors, one or more webcams, one or more microphones, one or more touchscreens, one or more printers, one or more scanners, virtual reality (VR) head-mounted displays, one or more joysticks, one or more biometric readers, and / or similar devices (not shown).

[0050] Figure 2 This is a block diagram of an exemplary front end 140 of a synthetic aperture imaging system 100 with a hybrid array 110, where both non-optical and optical sensors can be used to detect ultrasound signals. Figure 2 As shown, in some variations, front-end 140 may include one or more probe interfaces 141, one or more transmitters 142, one or more receivers 143, one or more photoacoustic receivers 144, one or more transmit beamformers 146, and one or more receive beamformers 145. Transmit beamformer 146 may include one or more transmit channels, and receive beamformer 145 may include one or more receive channels. Each transmit or receive channel may be connected (e.g., via a set of wires, via a set of optical waveguides, etc.) to an array element of hybrid array 110. For example, transmit beamformer 146 may include 128 transmit channels, and receive beamformer 145 may include 256 receive channels.

[0051] Transmit beamformer 146 can generate various transmit waveforms based on the imaging mode. These waveforms can be amplified by transmitter 142 before being applied to the elements of probe 125 via probe interface 141. Probe interface 141 connects imaging system 160 to probe 125 of hybrid array 110, enabling probe 125 to transmit acoustic signals toward the imaging target. Receiver 143 receives echo signals in response to acoustic signals detected by non-optical sensors as input, processes these echo signals to generate a first set of digitized signals as output, and sends this output to receiver beamformer 145. Furthermore, photoacoustic receiver 144 receives echo signals in response to acoustic signals detected by optical sensors as input, processes these echo signals to generate a second set of digitized signals as output, and sends this output to receiver beamformer 145. Receiver beamformer 145 uses the first and second sets of signals to generate a receive beam.

[0052] Figure 3 This is a block diagram of an exemplary front end 140 of a synthetic aperture imaging system 100 with a hybrid array 110, where only the optical sensors of the hybrid array 110 are used to detect ultrasonic echo signals (i.e., non-optical sensors, such as those in the PZT subarray 113, are only used to transmit ultrasonic signals and not to detect echo signals). Figure 3As shown, the front end 140 may include a transmitter 142, a photoacoustic receiver 144, a transmit beamformer 146, and a receive beamformer 145. The transmitter 142 may be connected to or operatively coupled (e.g., via probe interface 141) to a non-optical sensor (e.g., a PZT subarray 113) to enable the non-optical array elements to transmit acoustic waves. The hybrid array of optical sensor subarray 115 can be used to detect echo signals and transmit them to the photoacoustic receiver 144. Figure 2 The variants shown are compared, due to the fact that in Figure 3 In the variant shown, no signal is detected by the non-optical sensor, so a separate receiver 143 associated with the non-optical sensor is not required to generate a signal based on acoustic echo. Therefore, the receive beamformer 145 uses the signal generated by the photoacoustic receiver 144 to generate the receive beam.

[0053] Figure 4 This is a block diagram of an exemplary probe 125 of a synthetic aperture imaging system 100 with a hybrid array 110. Probe 125 may include the hybrid array 110, one or more light sources 117, one or more thermal control units 119, one or more photodetectors 111, and one or more multiplexers 121. The light source 117 may generate continuous wave (CW) or pulsed light emission (stimulated emission, spontaneous emission, etc.). The light source 117 may further couple the light emission outward to one end of a waveguide medium (e.g., optical fiber, free space, photonic integrated circuit waveguide, etc.), which is optically coupled to an optical resonator of the optical sensor subarray 115. The photodetector 111 receives the outly coupled light from the optical resonator at the other end of the waveguide medium. Due to the presence of the optical resonator and acoustic vibrations (e.g., corresponding to reflected sound waves), the outly coupled light generally undergoes phase, amplitude, and / or spectral variations. The thermal control unit 119 of probe 125 can maintain a constant temperature for the optical resonator. In some cases, thermal control 119 can be used to stabilize the optical response of an optical resonator.

[0054] Hybrid Array

[0055] The hybrid array 110 comprises an array of sensor elements and can be configured for operation in a 1D, 1.25D, 1.5D, 1.75D, or 2D configuration, as further described below. Generally, the dimensionality of the ultrasonic sensor array relates to the range of elevation beamwidths (or elevation beam slice thicknesses) achievable when imaging with the ultrasonic sensor array, and to the degree of control the system has over the elevation beam aperture size, focus, and / or steering throughout the imaging domain (e.g., the entire imaging depth) of the sensor array. A 1D array has only one row of elements in the height dimension and a fixed elevation aperture size. A 1.25D array has multiple rows of elements in the height dimension and a variable elevation aperture size, but the elevation focus via the acoustic lens is fixed. A 1.5D array has multiple rows of elements in the height dimension, a variable elevation aperture size, and a variable elevation focus via electronic delay control. The 1.75D array is a 1.5D array with additional height beam steering capability. The 2D array has a large number of elements in both the lateral and height dimensions to meet the minimum spacing requirements for large beam steering angles.

[0056] In some variations, the synthetic aperture ultrasound imaging system can transform a 1.5D or 2D array configuration into a 1D array configuration. The hybrid array 110 may include a large number (e.g., 16, 32, 64, 128, 256, 1024, 4096, 8192, 16384, and / or similar numbers) of elements. In some variations, the hybrid array 110 may be arranged in a rectangular configuration and may include N×M elements, where N is the number of rows and M is the number of columns. The hybrid array 110 includes one or more array elements of a first type and one or more array elements of a second type, wherein the first type may be a transducer or other non-optical sensor configured to transmit ultrasound waves, and the second type may be an optical sensor, such as a WGM optical resonator. One or more array elements of the first type and one or more array elements of the second type may be positioned together in a rectangular arrangement, an arc arrangement, a circular arrangement, or a sparse array arrangement. For example, in some variations, the hybrid array may resemble any hybrid array described in U.S. Patent Application No. 63 / 029,044, which is incorporated herein by reference in its entirety. Furthermore, the hybrid array may be configured to perform harmonic imaging as described in U.S. Patent Application No. 63 / 046,888, which is incorporated herein by reference in its entirety.

[0057] The transducers(s) in the hybrid array 110 may include, for example, one or more leadzirconate titanate (PZT) transducers, one or more polymer thick film (PTF) transducers, one or more polyvinylidene fluoride (PVDF) transducers, one or more capacitive micromachined ultrasound transducers (CMUT) transducers, one or more piezoelectric micromachined ultrasound transducers (PMUT) transducers, one or more photoacoustic sensors, and one or more transducers based on single-crystal materials (e.g., LiNbO3(LN), Pb(Mg)). 1 / 3 Nb 2 / 3 )-PbTiO3(PMN-PT), and Pb(In 1 / 2 Nb 1 / 2 )-Pb(Mg 1 / 3Nb 2 / 3 Transducers of PbTiO3 (PIN-PMN-PT) and / or any sensor suitable for acoustic sensing.

[0058] Each optical sensor may be or may include an optical resonator, such as a microring resonator, microsphere resonator, micro-ring core resonator, microbubble resonator, fiber-based resonator, integrated photonic resonator, microdisk resonator, etc. In some variations, the optical sensor may include one or more WGM optical resonators. For example, in some variations, the optical sensor may be similar to any optical resonator described in PCT applications PCT / US2020 / 064094, PCT / US2021 / 022412, and PCT / US2021 / 033715, each of which is incorporated herein by reference. The optical sensor may include a closed loop of a transparent medium (e.g., glass, a transparent polymer, silicon nitride, titanium dioxide, or any other material suitably optically transparent at the operating wavelength of the optical resonator), which allows light of certain permitted frequencies to propagate continuously within the closed loop and stores the optical energy of the permitted frequencies of light within the closed loop. The above is equivalent to saying that an optical resonator can allow the propagation of modes that circulate around the outer periphery of the resonator, traveling on the concave surface of the optical resonator and corresponding to permitted frequencies (e.g., whispering corridor modes (WGM)). Each mode corresponds to the propagation of one of the permitted light frequencies. The permitted light frequencies and the quality factor of the optical resonator described herein can be based at least in part on the geometric parameters of the optical resonator, the refractive index of the transparent medium, and the refractive index of the environment surrounding the optical resonator. The resonant frequency of the optical resonator (e.g., due to the propagation of a set of WGMs) can have a high quality factor suitable for high-sensitivity sensing probes. In general, the sensitivity of an optical sensor can be improved by increasing the quality factor of the optical resonator. In particular, in some variations, the sensitivity can be controlled by the geometric parameters of the optical resonator. When used as an ultrasonic detector, the optical resonator can have low noise equivalent pressure and wide operating bandwidth. In some variations, when light propagating in an optical waveguide is coupled in an optical fiber and propagates in the outer periphery of the optical fiber, the optical resonator can include sensing nodes formed at the cross-sections of the optical fiber and the optical waveguide. In some variations, the optical sensor may include an integrated photonic optical resonator.

[0059] The space inside and / or around an optical resonator can be filled with an ultrasonic enhancement material, such as polyvinylidene fluoride, parylene, polystyrene, etc. Ultrasonic enhancement materials can improve the sensitivity of optical sensors. For example, an ultrasonic enhancement material can have a relatively high elastic optical coefficient, so that in response to the optical resonator receiving a set of ultrasonic echoes, the refractive index change of the ultrasonic enhancement material is greater than the refractive index change of the material(s) of the optical resonator(s) (e.g., when receiving mechanical stress or strain induced by that set of ultrasonic echoes).

[0060] Optical resonators can be coupled to the outside world to receive light, transmit light, and function in practice (e.g., for ultrasonic imaging or other sensing applications in acousto-optic systems). In some implementations, optical resonators can be operatively coupled to a light source (e.g., a laser, a tunable laser, an erbium-doped fiber amplifier, etc.) and / or a photodetector via optical fiber (e.g., tapered fiber). Optical sensor-based acousto-optic systems can directly measure ultrasound via the photoelastic effects and / or physical deformation of (one or more) resonators in response to ultrasonic waves (e.g., ultrasonic echoes). Therefore, an optical sensor can be considered a photoacoustic transducer capable of converting mechanical energy (e.g., acoustic energy) into optical energy. For example, in the presence of ultrasonic (or any pressure) waves, modes traveling through the resonator may experience spectral shifts or amplitude variations caused by changes in the resonator's refractive index and shape. Spectral variations can be readily monitored and analyzed in the spectral domain using a photodetector. Amplitude variations can also be detected by the photodetector. The photodetector ultimately converts the optical energy (i.e., optical signal) propagating in the optical resonator and optical fiber into electrical energy (i.e., electrical signal) suitable for processing by electronic circuitry. Furthermore, additional spatial and other information can be derived by monitoring and analyzing the optical response of the optical resonators within the hybrid array. This paper describes an exemplary hybrid ultrasound array.

[0061] In some variations, the hybrid array 110 may include one or more rows in the height dimension. For example, array elements (of the first and second types) may be collectively positioned in a rectangular array comprising several rows and several columns. In some variations, such as Figure 5 As shown, the hybrid array 110 may include three rows of elements in the height dimension. These three rows include one inner row and two outer rows. The two outer rows may be composed of a second type 114 (e.g., optical resonators, such as WGM optical resonators). The inner row may be composed of a first type 112 (e.g., PZT transducers or another type of transducer). The two outer rows may include an equal number of elements positioned in parallel in corresponding columns. Each pair of elements 114 positioned in the same column of the two outer rows may optionally be connected (e.g., electrically connected or electromagnetically coupled) to form a single combined outer element for a 1.25D array configuration or a 1.5D array configuration.

[0062] Although Figure 5A hybrid array 110 with three rows is depicted, but in some variations, the number of rows can be any odd number, such as 3, 5...2n+1, where n is an integer. In some variations, the first-type array elements 112 can be arranged in a central row of an odd number of rows. For example, a 1.5D array configuration may include 5 rows, with a PZT transducer row in the central row, two optical resonator rows adjacent to the central row, and two PZT transducer rows in the outermost row adjacent to the optical resonator rows. Having the central row include the transducers may be advantageous in some variations. For example, since the central row includes the first-type transducer elements 112 capable of performing both ultrasonic transmission and reception, the height apodization curve does not have a "dip" in the middle for both the transmission and reception modes of the transducer. Such a dip in the height apodization curve can degrade image quality and introduce image artifacts. Therefore, arranging the first-type transducer elements 112 in the central row (e.g., as shown in the diagram) is advantageous. Figure 5 (As shown) This can advantageously help avoid such degradation of image quality and image artifacts. However, in some variations, the hybrid sensor array may include an optical resonator in the center row.

[0063] In some variations, the number of rows can be any even number, such as 2, 4...2n, where n is an integer. For example, a 1.25D array configuration or a 1.5D array configuration may include at least two rows, with a first number of PZT transducer elements (or other transducer elements) in one row and a second number of optical sensor elements in another row. In some variations, the first and second numbers may be the same, while in other variations, the first and second numbers may be different (e.g., one row may include 128 array elements, while another row may include 192 array elements).

[0064] Figure 6 This is a schematic description of an exemplary hybrid array. Hybrid array 110 may include one or more array elements of a first type (e.g., a PZT transducer or another type of transducer) and one or more array elements of a second type (e.g., an optical sensor, such as a WGM resonator). Hybrid array 110 may include at least one row having at least one array element of the first type and at least one array element of the second type. Figure 6As shown, the hybrid array 110 may, for example, include a central row comprising at least one array element of a first type and at least one array element of a second type. For example, the central row may have a single array element of the second type, while other rows may have only array elements of the first type. The single array element of the second type may be an optical resonator with a wavelength approximately equal to or less than the wavelength of the transmitted sound wave. In some variations, using a single optical resonator can minimize the complexity of probe fabrication while leveraging the ultra-high sensitivity of the optical sensor to improve image quality.

[0065] Figure 7 This is a schematic description of an exemplary hybrid array. The hybrid array 110 may include two or more rows. Each of the two or more rows may have at least one array element of a first type (e.g., a PZT transducer or another type of transducer) and at least one array element of a second type (e.g., an optical sensor, such as a WGM resonator). The second type of array elements may be spatially distributed in a regular pattern or spatially distributed in an irregular pattern (e.g., a random pattern). A set of elements on the inner row and two outer rows may include optical resonators 114, and the remaining elements include first type 112, including, for example, one or more PZT transducers and / or one or more CMUT transducers. In some configurations, the spatial distribution of the positions of the optical resonators 114 may be random. In some configurations, the spatial distribution of the positions of the optical resonators 114 may follow an arrangement pattern (e.g., similarly, shifted one unit to the right between sensor elements and two units down between sensor elements). The size of the optical sensor may be smaller than or the same as the size of the first type 112.

[0066] Figure 8 This is a schematic description of an exemplary 1D hybrid array 110, comprising a single row containing multiple array elements or sensor elements. These multiple array elements may include at least one array element 112 of a first type (e.g., a PZT transducer or another type of transducer) and at least one array element 114 of a second type (e.g., an optical sensor, such as a WGM optical resonator). In some configurations, the spatial distribution of the first type (elements) 112 and the second type (elements) 114 may be random. In some configurations, the spatial distribution of the first type array elements 112 and the second type array elements 114 may follow an arrangement pattern. Compared to a conventional 1D array including only one type of sensor, the hybrid array may have improved performance in terms of sensing bandwidth and / or sensitivity due to the addition of an optical sensor.

[0067] Figure 9This is a schematic description of an exemplary 2D hybrid array 110 arranged in a rectangular configuration and comprising N×M sensor elements, where N is the number of rows and M is the number of columns, both of which are integers. In some implementations, the number of rows and / or columns may be greater than 31 rows and / or 31 columns. For example, the 2D hybrid array may comprise 64×96 = 6,144 sensor elements. The hybrid array 110 may comprise one or more array elements of a first type (e.g., PZT transducers or another type of transducer) and one or more array elements of a second type (e.g., optical sensors, such as WGM optical resonators), which may be collectively positioned in a rectangular arrangement. In some configurations, the spatial distribution of the first type 112 and the second type 114 may be random. In some configurations, the spatial distribution of the first type 112 and the second type 114 may follow an arrangement pattern.

[0068] Figure 10 This is a schematic description of an exemplary 2D hybrid array 110 in a sparse array configuration. Arranging the hybrid array 110 in a sparse array configuration, rather than a fully sampled arrangement, reduces the total number of sensor elements used to fabricate the hybrid array. For example, a sparse 2D array of the same size as a fully sampled 2D array might contain only 1000 sensor elements, while a fully sampled hybrid array would have 64 × 96 = 6,144 sensor elements. The hybrid array 110 may include one or more array elements of a first type (e.g., a PZT transducer or another type of transducer) and one or more array elements of a second type (e.g., an optical sensor, such as a WGM optical resonator), all positioned in a sparse array configuration. The spatial distribution of the first type array elements 112 and the second type array elements 114 can be random or follow a statistical distribution (e.g., a normal distribution, a Gaussian distribution, and / or a similar distribution). By using the sparse spatial distribution of the first type 112 and the second type 114 array elements, the generation of grating lobes in the image produced by the hybrid array can be reduced / prevented. The spatial distribution of the first type of array elements 112 can be the same as, similar to, or different from the spatial distribution of the second type of array elements 114. For example, the first set of positions of a group of optical sensors in the hybrid array 110 can have a uniform distribution, while the second set of positions of a group of PZT transducers in the hybrid array 110 can have a normal distribution.

[0069] Methods for performing synthetic aperture imaging

[0070] The following description Figures 11-17 The illustrations depict various aspects of an exemplary method for performing synthetic aperture imaging. The method for performing synthetic aperture imaging can be executed by a synthetic aperture computing device (not shown), which is a synthetic aperture imaging system (e.g., reference...). Figure 1A portion of and / or operatively coupled to the synthetic aperture imaging system 100 shown and described is included. The synthetic aperture computing device may include a set of electronic circuitry, such as a processor, memory, and a communication interface. The processor may include, for example, a hardware-based integrated circuit (IC) or any other suitable device to run or execute a set of instructions / code. For example, the processor may include a general-purpose processor, a central processing unit (CPU), an accelerated processing unit (APU), an application-specific integrated circuit (ASIC), a microprocessor, a field-programmable gate array (FPGA) chip, a graphics processing unit (GPU), a digital signal processing (DSP) chip, and so on. The memory may store, for example, code including instructions, to cause the processor to perform one or more processes or functions (e.g., signal filtering, signal amplification, phase matching, noise reduction, aperture selection, etc.). The memory may be / may include, for example, a memory buffer, random access memory (RAM), read-only memory (ROM), a flash drive, a secure digital (SD) memory card, and so on. The communication interface may be or may include a USB interface, a PCIe interface, or a hardware component operatively coupled to a processor and / or memory, and may enable the synthetic aperture computing device to communicate with components of the synthetic aperture imaging system and / or, in some variations, with external devices and / or networks of devices (e.g., the Internet).

[0071] A synthetic aperture computing device may include an application as software stored in memory and executed by a processor. For example, the application may include code that causes the processor to select an aperture, analyze signals, generate images, etc. Alternatively, the application may be implemented on a hardware-based device. For example, the application may include one or more digital circuits or one or more analog circuits that enable the synthetic aperture computing device to filter, amplify, and / or delay signals.

[0072] Figure 11This is a flowchart of an exemplary method for performing synthetic aperture imaging using a hybrid array configured to generate each ultrasound image frame on a serial, scan-line-by-scan basis. The synthetic aperture imaging system can begin performing synthetic aperture imaging after receiving an indication signal to start a new scan line. The synthetic aperture imaging system can then select one or more transmit apertures comprising one or more array elements of a first type (e.g., one or more PZT transducers). The synthetic aperture imaging system can then use a transmit beamformer (e.g., a reference beamformer)... Figure 2 The transmit channel of the transmit beamformer 146 (shown and described) is connected to a selected first-type array element. The synthetic aperture imaging system then selects one or more receive apertures that include one or more second-type array elements (e.g., one or more optical sensors). In some variations, the receive aperture may also include one or more first-type array elements. Generally, the selection of the receive aperture can be more complex than the selection of the transmit aperture, as there are at least three possible receive aperture types: a receive aperture with only first-type array elements, a receive aperture with only second-type array elements, or a receive aperture with a hybrid array of first-type and second-type array elements.

[0073] Once the transmitting and receiving apertures are selected and connected to the system channels, the front end of the synthetic aperture imaging system (e.g., reference) Figure 1 The front end 140, shown and described, emits an electrical signal to excite the array elements of the transmitting aperture to generate an acoustic signal (e.g., a pulse) and transmit the acoustic signal toward the imaged target. The receiving aperture then receives the acoustic echoes in response to these acoustic signals, generates a signal (e.g., an electrical signal) corresponding to the acoustic echoes, and sends these signals to the receiving beamformer at the front end. If the synthetic aperture imaging system includes more than one receiving aperture for the same transmitting aperture, the next (or more) receiving apertures will be selected to obtain additional acoustic echoes. Once all receiving apertures have been selected at least once and their corresponding signals acquired, the receiving beamformer can synthesize (e.g., coherent combination, phase matching, frequency matching, amplitude matching, summation, etc.) the signals generated from all receiving apertures. Subsequently, the system can repeat the loop through all receiving apertures for each transmitting aperture. Once all transmitting apertures have been selected at least once, the synthetic aperture imaging system synthesizes the signals generated from all transmitting apertures to produce a complete synthetic aperture that includes all receiving and transmitting apertures. The above process can be performed on each frame of ultrasound imaging for multiple scan lines. The synthetic aperture imaging system can then store each frame in memory and / or transmit the frame to a display included in or operatively coupled to the synthetic imaging system. The above process can be performed on multiple frames of ultrasound imaging.

[0074] Figure 12 This is a flowchart of an exemplary method for performing synthetic aperture imaging using a hybrid array configured to generate each ultrasound image frame from multiple scan lines in parallel processing. The synthetic aperture imaging system can begin performing synthetic aperture imaging after receiving an indication signal to start a new frame. The synthetic aperture imaging system can then select a first subframe of the complete frame. This subframe may include, for example, a subset of the scan lines that form the complete image frame (e.g., 32 scan lines). The synthetic aperture imaging system can then select the transmit aperture, receive aperture, and steering angle. The selected receive aperture can be composed entirely of array elements of the first type, entirely of array elements of the second type, or a hybrid array of the first and second types. Once the appropriate transmit and receive apertures for the subframe and steering angle have been selected and connected to the system channel, the front end of the synthetic aperture imaging system (e.g., reference) Figure 1 The front end 140 shown and described emits electrical pulses to excite the array elements of the transmitting aperture to generate acoustic signals (e.g., pulses), and transmits the acoustic signals through a target for radial imaging of the selected transmitting aperture(s). The selected receiving aperture(s) then receive acoustic echoes in response to these acoustic signals, generate signals corresponding to the acoustic echoes (e.g., electrical and optical signals), and send these signals to the receiving beamformer of the front end.

[0075] If the synthetic aperture imaging system needs to select multiple transmission angles for a subframe, additional steering angles can be selected to obtain additional acoustic echoes, and the above process can be repeated for each additional steering angle of the subframe. When all steering angles of the subframe have been selected at least once and the corresponding signals have been acquired, the receiving beamformer can coherently synthesize (e.g., coherently combine, phase-match, frequency-match, amplitude-match, sum, etc.) the signals generated from all steering angles of the subframe. Subsequently, the system can repeat the loop through all steering angles for each subframe. When all subframes have been selected at least once, the synthetic aperture imaging system can synthesize (e.g., coherently combine, phase-match, frequency-match, amplitude-match, sum, etc.) the signals generated from all subframes to generate a complete frame. The synthetic aperture imaging system can then store the frame in memory and / or send the frame to a display included in or operatively coupled to the synthetic aperture imaging system. The above process can be performed on multiple frames of ultrasound imaging.

[0076] Figure 13This is a flowchart of an exemplary method for performing synthetic aperture imaging using a hybrid array configured to generate each ultrasound image frame from multiple receiving apertures for each transmitting element intended for imaging operation (e.g., a first type of transducer, such as a PZT transducer, or another type of transducer). The synthetic aperture imaging system can begin performing synthetic aperture imaging after receiving an indication signal to start a new frame. The synthetic aperture imaging system can then proceed by using a transmitting beamformer (e.g., a reference beamformer)... Figure 2 The transmit channel of the transmit beamformer 146 shown and described is connected to a first transmit element to select the first transmit element. The first transmit element is a first type of array element capable of generating an acoustic signal. The synthetic aperture imaging system then selects one or more receive apertures, which include one or more second type array elements and may also include one or more first type array elements. There are three possible receive aperture types: a receive aperture with only first type array elements, a receive aperture with only second type array elements, or a receive aperture with both first type and second type array elements.

[0077] Once the transmitting element and receiving aperture are selected and connected to the system channel, the front end transmits an electrical signal to excite the transmitting element and generate an acoustic signal, which is then transmitted towards the imaged target. The receiving aperture then receives the acoustic echoes in response to these acoustic signals, generates a signal corresponding to the acoustic echoes, and sends these signals to the receiving beamformer at the front end. If the synthetic aperture imaging system includes more than one receiving aperture for the same transmitting element, additional receiving apertures are selected to obtain additional acoustic echoes associated with the transmission from that transmitting element. When all receiving apertures have been selected at least once and their corresponding signals have been acquired, the receiving beamformer can synthesize (e.g., coherent combination, phase matching, frequency matching, amplitude matching, summation, etc.) the signals generated from all receiving apertures for that transmitting element. The system can then repeatedly cycle through all transmitting elements used in imaging. When all transmitting elements are selected, the synthetic aperture imaging system can synthesize all transmitting elements to produce a synthetic aperture, generating a single frame or multiple frames. The synthetic aperture imaging system can then store one or more frames in memory and / or transmit those frames to a display included in or operatively coupled to the synthetic imaging system. This process can be performed to continuously scan the patient.

[0078] Figure 14This is a block diagram of an exemplary method for synthesizing acoustic data obtained using a hybrid array, based on several variations. As described herein, the hybrid array comprises one or more array elements of a first type (e.g., non-optical transducers) and one or more array elements of a second type (e.g., optical sensors, such as WGM optical resonators). Thus, the hybrid array generates both optical and non-optical signals. The optical and non-optical sensor signals may have different signal paths. Each optical and non-optical sensor has a different physical location within the hybrid array, and the optical resonator generally has a different frequency response, sensitivity, and amplitude compared to the non-optical sensor. Therefore, the signal from the optical resonator may require processing through different filters (e.g., low-pass filters, band-pass filters, high-pass filters, digital filters, etc.), amplifiers (e.g., digital amplifiers), and / or phase delays to compensate for its differences relative to the signal from the non-optical sensor before the optical and non-optical sensor signals can be effectively combined by a receiving beamformer.

[0079] For example, such as Figure 14 As shown, different bandpass filters can shape the waveforms of received optical sensor signals and non-optical sensor signals to improve detail resolution and signal-to-noise ratio (SNR). At least one optical sensor bandpass filter can be used to shape the received optical sensor signal, and at least one non-optical bandpass filter can be used to shape the received non-optical sensor signal (e.g., to make the optical sensor signal and non-optical sensor signal frequency-matched). The optical sensor bandpass filter and the non-optical bandpass filter can have different characteristics to account for the differences in frequency response between the optical resonator and the non-optical sensor. Because ultrasound signals propagate in soft tissue, the waveform or spectral shape of the ultrasound signal may vary with penetration depth. To account for this variation in waveform and spectral shape, synthetic aperture imaging systems can select filters based on penetration depth, waveform, and / or spectral shape.

[0080] Furthermore, different amplifiers can also provide gain values ​​and / or apodization profiles to the received optical and non-optical sensor signals to produce optimal or near-optimal beamforming patterns with minimal or near-minimum sidelobes. For example, at least one optical sensor digital amplifier can be used to provide appropriate gain and / or apodization profiles associated with the optical sensor signal, and at least one non-optical digital amplifier can be used to provide appropriate gain and / or apodization profiles associated with the non-optical sensor signal (e.g., to make the optical and non-optical sensor signals amplitude-matched). The gain and / or apodization profiles provided by the optical sensor digital amplifier may differ from those applied by the non-optical digital amplifier to account for the different sensitivities of the optical resonator and the non-optical sensor. The gain and / or apodization profiles may include preset and / or predetermined values ​​stored in the memory of the synthetic aperture imaging system. In some cases, the synthetic aperture imaging system can be configured to dynamically generate gain and / or apodization profiles. In some cases, the gain and / or apodization profiles of the amplifiers can be constant numbers or can be variable as a function of depth.

[0081] Furthermore, based on the position and / or positional differences between the optical resonator and / or non-optical sensor, different phase delays can be applied to the optical sensor signal and the non-optical sensor signal. An optical sensor delay unit can apply an appropriate phase delay to the optical sensor signal, and a non-optical delay unit can apply an appropriate phase delay to the non-optical sensor signal (e.g., to make the optical sensor signal and the non-optical sensor signal phase-matched). The phase delays applied by the optical sensor delay unit and the non-optical delay unit can be different to take into account the different positions of the optical resonator and the non-optical sensor. The phase delay can include a preset / predetermined value stored in memory. In some cases, the synthetic aperture imaging system can be configured to dynamically generate the phase delay (e.g., a phase delay profile). In some cases, the phase delay can also take other factors into account. For example, the phase delay can include a stored delay value based on the nominal or known acoustic lens thickness, and / or a dynamically stored delay value determined using an adaptive system configured to detect phase deviations and / or other defects in the acoustic lens and / or medium. In addition to the lens, both the optical sensor and the non-optical transducer can also include other layers (e.g., a matching layer, a coating layer, etc.) between the sensor surface and the patient body. Besides thickness considerations, sound velocity can also be another parameter when determining the final delay curve (one or more) of synthetic aperture beamforming.

[0082] After processing the received optical and non-optical sensor signals using the filters, amplifiers, and phase delays described above, the optical and non-optical sensor signals can be combined and transmitted to a receiving beamformer to form an image. In some variations, the combination of the optical and non-optical sensor signals can be a coherent combination.

[0083] Although Figure 14 The illustration depicts a specific sequence of signal processing (filtering, then amplification, then applying phase delay), but it should be understood that in some variations, the above signal processing steps can be performed in any suitable order. For example, Figure 15 This is a block diagram illustrating exemplary methods for synthesizing acoustic data obtained using a hybrid array, based on several variations. For example... Figure 15 As shown, instead of applying phase delay to both optical and non-optical sensor signals after filtering and amplification, a synthetic aperture imaging system can first apply phase delay, then amplification, and then filtering. As another example, in some variations, optical and non-optical sensor signals can be processed by applying phase delay, then performing filtering, and then amplification. In other words, synthesizing optical sensor signals with non-optical sensor signals from a hybrid array can include any permutation and combination of filtering, amplification, and applying phase delay.

[0084] Figure 16 This is a block diagram of an exemplary method for synthesizing acoustic data obtained using a hybrid array, based on several variations. The synthetic aperture imaging system can be configured to apply a first set of phase delays to the optical sensor signals using multiple respective optical sensor delay units (e.g., for each optical sensor signal) to achieve phase matching of all received optical sensor signals. The resulting phase-matched optical sensor signals can then be combined. Similarly, the synthetic aperture imaging system can be configured to apply a second set of phase delays to the non-optical sensor signals using multiple corresponding non-optical delay units (e.g., for each non-optical signal) to achieve phase matching of all received non-optical sensor signals. The resulting phase-matched non-optical sensor signals can then be combined. The synthetic aperture imaging system can be further configured to apply amplifier(s) and filters(s) to each of the combined optical sensor signals and the combined non-optical sensor signals, similar to the above reference. Figure 14 As described. For example, such as Figure 16As shown, the combined optical sensor signal can be further processed using at least one optical sensor digital amplifier and at least one optical sensor bandpass filter (in any order), and the combined non-optical sensor signal can be further processed using at least one non-optical digital amplifier and at least one non-optical bandpass filter (in any order), thereby matching the combined optical sensor signal and the combined non-optical sensor signal in amplitude and frequency response. The phase-matched, amplitude-matched, and / or frequency-matched optical sensor signal and non-optical sensor signal can be combined and conveyed to a receiving beamformer to form an image. (Refer to reference...) Figure 14 and Figure 15 Compared to the variants shown and described, Figure 16 Variants of this technology may have advantages in reducing the number of filters and amplifiers used in synthetic aperture imaging systems, thereby reducing manufacturing costs, and so on.

[0085] Figure 17 This is a block diagram of an exemplary method for synthesizing acoustic data obtained using a hybrid array, based on several variations. The synthetic aperture imaging system can be configured to synthesize a single element comprising one internal sub-element and two external sub-elements (e.g., reference). Figure 5 A 1.5D array is shown and described. Two external sub-elements can be of the same size and are positioned on each side of the internal sub-elements. Therefore, signals originating from the two external sub-elements can be combined (e.g., added) before applying delays (for high focusing) to these signals. After combining the signals from the two external elements, phase delays, amplifiers, and / or filters can be applied to the combined signals in any suitable order. Furthermore, signals originating from the internal sub-units can be individually amplified and filtered, and ultimately combined with the combined signals from the two external sub-units. Once the internal and external sub-elements of each element are synthesized as described above, the 1.5D or 2D array can be simplified to a 1D linear array for beamforming. Therefore, the number of phase delay processes can be significantly reduced. Although Figure 17 Three sub-elements (one internal sub-element and two external sub-elements) are described, but it should be understood that the process described above can be applied to systems comprising more than three sub-elements. For example, in some cases, the process described above can be applied to a 1.5D array having two or more sub-elements. For example, the element may include five sub-elements, seven sub-elements, and so on.

[0086] In some variations, reference Figure 17The described method can also be extended to more than one element. For example, two adjacent elements of a 1.5D array can be combined to be considered a single element, with a spacing equal to the sum of the spacings of the two adjacent elements. The resulting 1D array generated in this way has only half the number of elements as originally. More generally, n adjacent elements can be combined to form a larger element, thereby reducing the number of effective elements for the synthesized aperture by a factor of n, where n is an integer greater than 1.

[0087] In some variants, height beamforming is performed before lateral beamforming. However, in other variants, the order of beamforming can be reversed. That is, lateral beamforming can be performed before height beamforming.

[0088] Example

[0089] Figure 18 Exemplary signals generated by two types of sensors in a hybrid array are shown. The top-left plot (“Non-optical sensor echo signal”) shows the signal generated by the non-optical sensor in the time domain, and the bottom-left plot (“Optical sensor echo signal”) shows the signal generated by the optical resonator in the time domain. The top-right plot (“Spectrum of non-optical sensor echo signal”) shows the signal generated by the non-optical sensor in the frequency domain, and the bottom-right plot (“Spectrum of optical sensor echo signal”) shows the signal generated by the optical resonator in the frequency domain. As shown, the signal generated by the optical resonator differs from the signal generated by the non-optical sensor in amplitude, frequency, phase, and noise level. These variations in amplitude, frequency, phase, and noise level can be compensated for by applying amplifiers, filters, phase delays, and noise filters to the signal, as referenced above. Figures 14-17 As described.

[0090] Figure 19 An exemplary frequency response of the signal generated by a non-optical sensor and an optical resonator in a hybrid array is shown, along with the bandpass filter frequency response suitable for each frequency response when synthesizing the non-optical sensor signal and the optical sensor signal. Specifically, the dashed lines indicate the signal generated by the sensor in the frequency domain (similar to...). Figure 18 (As shown in the diagram). Furthermore, the solid lines illustrate the frequency responses of two Butterworth bandpass filters designed to handle signals generated by optical resonators (bottom diagram) and signals generated by non-optical sensors (top diagram). Figure 19 As shown, the optical sensor bandpass filter and the non-optical bandpass filter are determined to have different center frequencies and bandwidths, corresponding to the respective spectral responses (dashed lines) generated by the non-optical and optical resonators, respectively. For example, as Figure 19As shown in the figure below, the spectrum of the optical resonator has strong low-frequency components between approximately 0 and approximately 4 MHz, which can reduce the detail resolution of the final ultrasound image. Therefore, the bandpass filter used for the optical sensor signal is designed to attenuate these low-frequency components below approximately 4 MHz, thereby isolating the more valuable frequency components of the optical sensor signal for imaging purposes. However, when processing non-optical sensor signals, this 4 MHz cutoff frequency of the bandpass filter is too high to retain the useful frequency components between 3 and 4 MHz. Therefore, the bandpass filter used for non-optical sensor signals can be designed with a lower cutoff frequency (e.g., approximately 3 MHz) compared to the bandpass filter used for the optical resonator.

[0091] Figure 20 An exemplary hybrid array window and its corresponding beammap are shown. A beammap is a 1D beam pattern at a certain depth in the imaging plane. A beammap typically consists of a central main lobe and side lobes with lower peak values ​​on either side of the main lobe. The width of the main lobe determines the spatial resolution of the ultrasound image. The level of the side lobes determines the contrast resolution. In some cases, grating lobes may appear on the beammap when the element spacing is too large or the element sensitivity curves are periodically non-uniform. Grating lobes can produce undesirable image artifacts, including ghosting images.

[0092] Figure 20 The image shows three aperture window functions and their corresponding beammaps. The top left image (“Hybrid Array Window”) shows the beammap generated by the reference... Figure 8 The window function generated by the hybrid array configuration is shown and described. The inhomogeneity in the window function is caused by the difference in sensitivity between the optical resonators and non-optical sensors in the hybrid array. As shown in the upper right figure (“Hybrid Array Beammap”), the periodic inhomogeneous window produces two grating lobes with an amplitude of approximately -8.4 dB. The middle figures (“Corrected Hybrid Array Window” and “Corrected Hybrid Array Beammap”) illustrate that the grating lobes can be overcome by applying different digital amplification gains to the two types of sensors. Applying this digital amplification gain generates a uniform window function. Similar methods can be used to generate Gaussian-like apodization windows to reduce the sidelobes of the beammap, as shown in the two figures below (“Optimized Hybrid Array Window” and “Optimized Hybrid Array Beammap”). Figures 14-16 All three beamformer architectures shown can produce a unified window function. However, in some cases, only... Figure 14 and Figure 15 The beamformer architecture can generate arbitrary window functions.

[0093] Figure 21Exemplary synthetic aperture windows and their corresponding beammaps for hybrid arrays are shown. Three exemplary synthetic aperture (SA) window functions and their corresponding beammaps are shown. The two top images demonstrate why two or more sub-apertures must be properly synthesized to generate a good beammap. The top left image (“Inappropriate SA Window”) shows an inappropriate synthetic aperture window function. The beammap in the top right corner (“Inappropriate SA Beammap”) shows elevated sidelobes generated due to the gap between the two sub-apertures of the synthetic aperture window function. The two middle images (“Regular SA Window” and “Regular SA Beammap”) show a conventionally synthesized aperture, whose two sub-apertures are the same as those used for the synthetic aperture and corresponding beammap in the top left image. The sidelobes are significantly reduced compared to the beammap in the top right corner. The sidelobes can be further reduced by synthesizing two overlapping sub-apertures, as shown in the two images below. The synthetic aperture has a coarse apodization window, as shown in the bottom left image (“Overlapping SA Window”). The beammap obtained in the lower right figure (“overlapping SA beammap”) shows the reduced sidelobes due to the overlapping sub-apertures.

[0094] Figure 22 Exemplary delay curves for a uniform array and a hybrid array are shown. In some variations, the acoustic waves and / or signals may travel different signal paths before being added by the beamformer. For example, for a PZT sensor element, the acoustic waves and corresponding signals may travel through an acoustic lens and one or more matching layers before reaching the PZT sensor. On the other hand, for an optical resonator, the acoustic waves and corresponding signals may travel through acoustic lenses with different thicknesses and / or sound velocities and polymer layers with different thicknesses and / or sound velocities before reaching the optical resonator. The difference in signal paths can result in additional delay. This additional delay introduces phase errors in beamforming, thus reducing imaging performance, including detail resolution, contrast resolution, and signal-to-noise ratio (SNR). Therefore, the additional delay between the two sensor channels can be adjusted accordingly, such as... Figure 22 As shown and further described below.

[0095] The top graph (“Delay Curves for a Uniform Array”) shows the delay curves for the apertures of 64 elements with the same sensor. The bottom delay curve (“Delay Curves for a Hybrid Array”) is for the apertures of 64 elements with two different sensors, for example, reference [reference]. Figure 8 The hybrid array is shown and described. Additional fixed phase delays can be added to the non-optical channels or optical resonator channels to compensate for differences in signal paths between the two types of sensors. The delay profiles shown can be used for transmit and receive beamforming.

[0096] While synthetic aperture imaging methods and systems using hybrid arrays have been described in the context of ultrasound imaging, in some variations, synthetic aperture imaging methods and systems can be used in applications beyond ultrasound imaging. For example, in some cases, synthetic aperture imaging methods and systems can be used in metrology, signal processing, particle physics, remote sensing, aerospace applications, and / or similar applications.

[0097] The above description uses specific terminology for illustrative purposes to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that such specific details are not necessary for implementing the invention. Therefore, the above description of specific embodiments of the invention is given for illustrative and descriptive purposes. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed; obviously, many modifications and variations are possible in light of the above teachings. The embodiments were chosen and described to illustrate the principles of the invention and its practical application, thereby enabling others skilled in the art to utilize the invention and various embodiments with various modifications suitable for the particular intended use. The appended claims and their equivalents are intended to define the scope of the invention.

Claims

1. A method for acousto-optic imaging, comprising: Sending sound waves; A first signal is received from a first sub-aperture of a sensor array, wherein the first sub-aperture comprises one or more array elements of a first type; A second signal is received from a second sub-aperture of the sensor array, wherein the second sub-aperture comprises one or more array elements of a second type, the second type being different from the first type, wherein the second type is an optical sensor, and the array elements of the first type and the second type are configured to detect acoustic echoes corresponding to the transmitted sound waves; and The first signal and the second signal are combined using a receiving beamformer to obtain a combined signal for forming an image, wherein the combined signal comes from a composite aperture that includes the first sub-aperture and the second sub-aperture.

2. The method of claim 1, further comprising: Phase matching is performed on the first signal and the second signal.

3. The method as described in claim 2, wherein, Phase matching of the first signal and the second signal includes applying a first delay to the first signal or applying a second delay to the second signal, the first delay and the second delay being determined at least in part based on the difference between a first propagation time from the one or more array elements of the first type to the imaged medium and a second propagation time from the one or more array elements of the second type to the medium.

4. The method of claim 3, wherein, The first delay or the second delay is determined at least in part based on the thickness and sound velocity of the acoustic lens, or the thickness and sound velocity of the acoustic matching layer, or the thickness and sound velocity of each of the acoustic lens and the acoustic matching layer.

5. The method of claim 3, wherein, The first delay or the second delay is determined at least in part based on the transmit and / or receive focus.

6. The method of claim 1, further comprising: The first signal is filtered to reduce noise in the first signal, and the second signal is filtered to reduce noise in the second signal.

7. The method of claim 1, further comprising: The first signal or the second signal is amplified according to the amplification gain to perform amplitude matching between the first signal and the second signal.

8. The method of claim 7, wherein, The amplification gain is a preset value.

9. The method of claim 7, wherein, The amplification gain is determined at least in part based on the imaging depth.

10. The method of claim 1, further comprising: Frequency matching is performed on the first signal and the second signal.

11. The method of claim 2, wherein, The first signal is a combination of signals originating from a plurality of array elements of the first type, or the second signal is a combination of signals originating from a plurality of array elements of the second type, or both.

12. The method of claim 11, further comprising performing one or more of the following steps before performing phase matching on the first signal and the second signal: The first signal is generated by combining signals originating from multiple array elements of the first type or multiple array elements of the first and second types; and The second signal is generated by combining signals originating from multiple array elements of the second type or multiple array elements of the first and second types.

13. The method of claim 12, further comprising forming a larger effective array element from a plurality of array elements of the first type, a plurality of array elements of the second type, or a plurality of array elements of the first type and the second type.

14. The method of claim 12, further comprising reducing the effective number of array elements in the synthetic aperture.

15. The method of claim 12, further comprising reducing the effective dimension of the synthesized aperture.

16. The method of claim 15, wherein, The sensor array is a 1.5-dimensional (1.5D) array, and the method includes reducing the effective dimension of the synthetic aperture from 1.5D to 1D.

17. The method of claim 15, wherein, The sensor array is a 2D array, and the method includes reducing the effective dimension of the synthetic aperture from 2D to 1.5D.

18. The method of claim 1, further comprising: Frequency matching is performed on the first signal and the second signal; After frequency matching of the first signal and the second signal, amplitude matching of the first signal and the second signal is performed; and After frequency matching and amplitude matching of the first signal and the second signal, phase matching is performed on the first signal and the second signal.

19. The method of claim 1, further comprising: Phase matching is performed on the first signal and the second signal; After phase matching of the first signal and the second signal, amplitude matching of the first signal and the second signal is performed; and After performing phase matching and amplitude matching on the first signal and the second signal, frequency matching is then performed on the first signal and the second signal.

20. The method of claim 1, wherein, The combination of the first signal and the second signal is a coherent combination.

21. The method of claim 1, wherein, The optical sensor is an optical resonator.

22. The method of claim 21, wherein, The optical resonator is a Whispering Corridor Mode (WGM) optical resonator.

23. The method of claim 21, wherein, The optical resonator is a microbubble optical resonator, a photonic integrated circuit (PIC) optical resonator, a microsphere resonator, a micro-ring resonator, a micro-ring resonator, or a microdisk optical resonator.

24. The method of claim 1, wherein, The one or more array elements of the first type include piezoelectric transducers, single-crystal material transducers, piezoelectric micromechanical ultrasonic transducers (PMUTs), or capacitive micromechanical ultrasonic transducers (CMUTs).

25. The method of claim 1, further comprising: Select the first sub-aperture to transmit acoustic signals; and Choose either the first sub-aperture or the second sub-aperture to receive the acoustic echo in response to the acoustic signal.

26. The method of claim 1, further comprising: Select an element from one or more array elements of the first type to transmit an acoustic signal; and Choose either the first sub-aperture or the second sub-aperture to receive the acoustic echo in response to the acoustic signal.

27. The method of claim 1, further comprising: Select the angle used to transmit the acoustic signal; Send the acoustic signal; and Receive acoustic echoes in response to the acoustic signal.

28. The method of claim 1, wherein, The optical sensor is embedded in a polymer structure.

29. An apparatus for imaging a target, comprising: A transmitter used to send sound waves; One or more array elements of the first type forming the first sub-aperture; One or more array elements of a second type forming a second sub-aperture, the second type being different from the first type, the second type being an optical sensor, the array elements of the first type and the array elements of the second type being configured to detect acoustic echoes corresponding to transmitted sound waves, wherein the first sub-aperture receives a first signal having a first phase and the second sub-aperture receives a second signal having a second phase; as well as The front end includes a beamformer and is configured to obtain a combined signal for forming an image, wherein the combined signal comes from a composite aperture comprising a first sub-aperture and a second sub-aperture.

30. The apparatus of claim 29, wherein the front end is further configured to generate the synthetic aperture by performing phase matching on the first signal and the second signal.

31. The apparatus of claim 30, wherein, Phase matching of the first signal and the second signal includes applying a first delay to the first signal or applying a second delay to the second signal, the first delay and the second delay being determined at least in part based on the difference between a first propagation time from the one or more array elements of the first type to the imaged medium and a second propagation time from the one or more array elements of the second type to the medium.

32. The apparatus of claim 31, wherein, The first delay or the second delay is determined at least in part based on the thickness and sound velocity of the acoustic lens, or the thickness and sound velocity of the acoustic matching layer, or the thickness and sound velocity of each of the acoustic lens and the acoustic matching layer.

33. The apparatus of claim 31, wherein, The first delay or the second delay is determined at least in part based on the transmit and receive focus.

34. The apparatus of claim 29, wherein, The front end is further configured to generate the synthetic aperture by filtering the first signal to reduce noise in the first signal and filtering the second signal to reduce noise in the second signal.

35. The apparatus of claim 29, wherein, The front end is also configured to generate the synthetic aperture by amplifying the first signal or the second signal according to the amplification gain to perform amplitude matching between the second signal and the second signal.

36. The apparatus of claim 35, wherein, The amplification gain is a preset value.

37. The apparatus of claim 35, wherein, The amplification gain is determined at least in part based on the imaging depth.

38. The apparatus of claim 29, wherein, The front end is also configured to generate the synthetic aperture by frequency matching of the first signal and the second signal.

39. The apparatus of claim 29, wherein, The first signal is a combination of signals originating from multiple array elements of the first type, or the second signal is a combination of signals originating from multiple array elements of the second type.

40. The apparatus of claim 29, wherein, The front end is also configured to generate the synthetic aperture through the following steps: Frequency matching is performed on the first signal and the second signal; After frequency matching of the first signal and the second signal, amplitude matching of the first signal and the second signal is performed; and After frequency matching and amplitude matching of the first signal and the second signal, phase matching is performed on the first signal and the second signal.

41. The apparatus of claim 29, wherein, The front end is also configured to generate the synthetic aperture through the following steps: Phase matching is performed on the first signal and the second signal; After phase matching of the first signal and the second signal, amplitude matching of the first signal and the second signal is performed; and After performing phase matching and amplitude matching on the first signal and the second signal, frequency matching is then performed on the first signal and the second signal.

42. The apparatus of claim 29, wherein, The combination of the first signal and the second signal is a coherent combination.

43. The apparatus of claim 29, wherein, The optical sensor is an optical resonator.

44. The apparatus of claim 43, wherein, The optical resonator is a Whispering Corridor Mode (WGM) optical resonator.

45. The apparatus of claim 43, wherein, The optical resonator is a microbubble optical resonator, a photonic integrated circuit (PIC) optical resonator, a microsphere resonator, a micro-ring resonator, a micro-ring resonator, or a microdisk optical resonator.

46. ​​The apparatus of claim 43, wherein, The one or more array elements of the first type include piezoelectric transducers, single-crystal material transducers, piezoelectric micromechanical ultrasonic transducers (PMUTs), or capacitive micromechanical ultrasonic transducers (CMUTs).

47. The apparatus of claim 29, wherein, The front end is also configured to combine the first signal and the second signal by the following steps: The first sub-aperture is selected to transmit the acoustic signal; and Choose either the first sub-aperture or the second sub-aperture to receive the acoustic echo in response to the acoustic signal.

48. The apparatus of claim 29, wherein, The front end is also configured to combine the first signal and the second signal by the following steps: Elements are selected from one or more array elements of the first type to transmit acoustic signals; and Choose either the first sub-aperture or the second sub-aperture to receive the acoustic echo in response to the acoustic signal.

49. The apparatus of claim 29, wherein, The front end is also configured to combine the first signal and the second signal by the following steps: Select the angle used to transmit the acoustic signal; Send the acoustic signal; and Receive acoustic echoes in response to the acoustic signal.

50. The apparatus of claim 29, wherein, The one or more array elements of the first type and the one or more array elements of the second type comprise one or more rows in the height dimension.

51. The apparatus of claim 50, wherein, The one or more array elements of the first type and the one or more array elements of the second type comprise at least one row, and the at least one row comprises at least one array element of the first type and at least one array element of the second type.

52. The apparatus of claim 29, wherein the one or more array elements of the first type and the one or more array elements of the second type are in a 1D array.

53. The apparatus of claim 29, wherein the one or more array elements of the first type and the one or more array elements of the second type are in a 1.25-dimensional (1.25D) array.

54. The apparatus of claim 53, wherein, The one or more array elements of the first type and the one or more array elements of the second type are arranged in an array, wherein the array includes a first row having a first number of array elements and a second row having a second number of array elements.

55. The apparatus of claim 54, wherein, The first number of array elements in the first row is equal to the second number of array elements in the second row.

56. The apparatus of claim 54, wherein, The first number of array elements in the first row is different from the second number of array elements in the second row.

57. The apparatus of claim 29, wherein the one or more array elements of the first type and the one or more array elements of the second type are in a 1.5-dimensional (1.5D) array.

58. The apparatus of claim 57, wherein, The one or more array elements of the first type and the one or more array elements of the second type are arranged in an array, wherein the array includes a first row having a first number of array elements and a second row having a second number of array elements.

59. The apparatus of claim 58, wherein, The first number of array elements in the first row is equal to the second number of array elements in the second row.

60. The apparatus of claim 58, wherein, The first number of array elements in the first row is different from the second number of array elements in the second row.

61. The apparatus of claim 29, wherein the one or more array elements of the first type and the one or more array elements of the second type are in a 1.75-dimensional (1.75D) array.

62. The apparatus of claim 29, wherein the one or more array elements of the first type and the one or more array elements of the second type are in a 2D array.

63. The apparatus of claim 29, wherein, The one or more array elements of the second type include one or more optical sensors embedded in a polymer structure.

64. The apparatus of claim 29, wherein, The optical sensor is optically coupled to a fiber optic to send a set of optical signals to a photodetector.

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