Synthetic aperture imaging system and method using a mixed array

Abstract

The method of acousto-optic imaging may include receiving a first signal from a first subaperture of the sensor array. The first subaperture may include one or more array elements of a first type. The method may further include receiving a second signal from a second subaperture of the sensor array. The second subaperture may include one or more array elements of a second type different from the first type. In some variations, the first type of array element may be an acoustic transducer (e.g., a piezoelectric transducer) and / or the second type of array element may be an optical sensor (e.g., an optical resonator such as a whispering gallery mode (WGM) resonator). The method may further include combining the first signal and the second signal to form a synthetic aperture of the sensor array.

Description

Technical Field

[0001] Cross - Reference to Related Applications

[0001] This application claims the priority of U.S. Patent Application No. 63 / 075,727, filed on September 8, 2020, which is hereby incorporated by reference in its entirety.

[0002]

[0002] The present disclosure generally relates to the field of ultrasonic imaging, and more particularly, to methods and apparatuses that enable the formation of a synthetic aperture by combining signals from a hybrid array including an optical resonator and an array of other sensors. The methods and apparatuses disclosed herein include optical resonators having high sensitivity and high operating bandwidth to improve imaging performance.

Background Art

[0003]

[0003] Ultrasonic detection is used in various industries including medical imaging and medical diagnosis for many advantages. For example, ultrasonic detection utilizes ultrasonic signals having a significant depth of penetration. Further, ultrasonic imaging is known to be an advantageously non - invasive imaging modality since it is based on non - ionizing radiation.

[0004]

[0004] Various known ultrasonic transducers used for ultrasonic imaging have many drawbacks. For example, some ultrasonic transducers are made of piezoelectric materials such as lead zirconate titanate (PZT). However, the 6 dB bandwidth of PZT material is generally limited to only about 70%. Certain composite PZT materials have a slightly increased bandwidth, but still only achieve a maximum bandwidth of about 80%. As another example, single crystal materials are increasingly used to improve the performance of ultrasonic probes, but they have a low Curie temperature and are brittle. Another type of transducer material is silicon, which can be processed to construct capacitive micromachine ultrasonic transducer (CMUT) probes that can increase 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 not suitable for harmonic imaging. Furthermore, CMUT probes require an additional bias voltage to operate properly. Therefore, there is a need for ultrasonic probes that include sensors with higher bandwidth and sensitivity. [Overview of the project]

[0005]

[0005] Generally, in some modifications, the apparatus for imaging a target may include one or more array elements of a first type that form a first sub-aperture, and one or more array elements of a second type that, unlike the first type, form a second sub-aperture, the first sub-aperture receiving a first signal having a first phase, and the second sub-aperture receiving a second signal having a second phase. The apparatus may further include a front end configured to at least partially generate a composite aperture by combining the first signal and the second signal. In some modifications, the front end may be configured to generate a composite aperture using one or more embodiments of the method described herein.

[0006]

[0006] Generally, in some variations, a method for imaging a target may include the step of receiving a first signal from a first sub-aperture of a sensor array, wherein the first sub-aperture includes one or more array elements of a first type. The method may further include the step of receiving a second signal from a second sub-aperture of a sensor array, wherein the second sub-aperture includes one or more array elements of a second type different from the first type. The method may further include the step of combining the first signal and the second signal to form a composite aperture of the sensor array.

[0007]

[0007] In some variations of the apparatus and method, the first type of array element may be a non-optical sensor such as an acoustic transducer configured to transmit sound waves (e.g., a piezoelectric transducer or a capacitive micromachine ultrasonic transducer (CMUT) sensor), and the second type of array element may be an optical sensor such as a whispering gallery mode (WGM) sensor. The optical sensor may be / include a microsphere resonator, a microtroid resonator, a microring resonator (e.g., having a circular cross-sectional shape or a non-circular cross-sectional shape such as a racetrack or ellipse), a microbubble resonator, a photonic integrated circuit (PIC) resonator, and / or a microdisk resonator. In some cases, the first and second types of array elements may be configured to detect an acoustic echo corresponding to a transmitted sound wave.

[0008]

[0008] In some modifications, the method may further include the step of phase matching the first signal and the second signal. To phase match the signals, 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 delay and / or the second delay may be determined at least in part 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 delay and / or the second delay may be determined on the thickness and velocity of sound of the acoustic lens and / or the thickness and velocity of sound of the acoustic matching layer. The first delay and / or the second delay may be given as a delay profile that takes into account the various differences between each array element and / or sub-element.

[0009]

[0009] In some modifications, the method may further include a step of filtering the first signal and / or the second signal in order to reduce noise in the signal and / or to match the frequency range of the signal. The filters may include bandpass filters, lowpass filters, highpass filters and / or digital filters, etc. In some modifications, the method may further include a step of amplifying the first signal and / or the second signal with an amplification gain to amplitude match the first signal and the second signal. The amplification gain may be a preset value and / or may be determined based on the imaging depth. The amplification gain may include a constant value or may include a tensor of amplification gain values ​​that provide a specific gain to each array element.

[0010]

[0010] The ultrasonic sensor array may be a one-dimensional (1D) array, a 1.25-dimensional (1.25D) array, a 1.5-dimensional (1.5D) array, a 1.75-dimensional (1.75D) array, or a two-dimensional (2D) array. In some variations, one or more array elements of the first type and one or more array elements of the second type may be arranged in a 1.25D array or a 1.5D array. Each of the 1.25D array or the 1.5D array may include a first row and a second row. The first row may contain a first number of array elements, and the second row may contain a second number of array elements. In some cases, the first number of array elements in the first row may be equal to the second number of array elements in the second row. For example, the first row and the second row may each contain 128 array elements. In some cases, the first number of array elements in the first row may be different from the second number of array elements in the second row. For example, the first row may contain 128 array elements, and the second row may contain 192 array elements.

[0011]

[0011] In some modifications, the first signal may include a combination of signals from multiple array elements of the first type. Additionally or alternatively, the second signal may include a combination of signals from multiple array elements of the second type. By combining signals from similar types of array elements that are close to each other, the dimensionality of the mixed array can be reduced (e.g., from a 1.5D array to a 1D array). As a result, the mixed array may require fewer filters and / or amplifiers.

[0012]

[0012] 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 the steps of frequency matching, then amplitude matching, and then phase matching of the first and second signals. As another example, the method may include the steps of phase matching, amplitude matching, and frequency matching of the first and second signals in this order. After frequency matching, amplitude matching, and phase matching are performed separately for each type of array element, the first and second signals can be combined. This combination may include coherent combinations.

[0013]

[0013] In some modifications, the method may include the step of selecting a first sub-aperture for transmitting an acoustic signal and a combination of the first sub-aperture and a second sub-aperture for receiving an acoustic echo in response to the acoustic signal. In some modifications, the method may include the step of selecting elements from one or more array elements of a first type for transmitting an acoustic signal and a combination of the first sub-aperture and a second sub-aperture for receiving an acoustic echo in response to the acoustic signal. In some modifications, the method may include the step of selecting an angle (e.g., steering angle) for transmitting an acoustic signal and / or receiving an acoustic echo. The above selection process can be repeated iteratively until all sub-apertures, array elements, and / or angles are completely covered.

[0014]

[0014] In some modifications, one or more array elements of the second type may include an optical sensor embedded in a polymer structure. The optical sensor may be optically coupled to an optical fiber to transmit a set of optical signals to a photodetector. The optical sensor may be configured to modify the optical signals in response to an acoustic echo. [Brief explanation of the drawing]

[0015] [Figure 1]Block diagram of an exemplary synthetic aperture imaging system having a hybrid array. [Figure 2] Block diagram of an exemplary front end of a synthetic aperture imaging system having a hybrid array. [Figure 3] Block diagram of an exemplary front end of a synthetic aperture imaging system having a hybrid array. [Figure 4] Block diagram of an exemplary probe of a synthetic aperture imaging system having a hybrid array. [Figure 5] Schematic diagram of an exemplary hybrid array of a synthetic aperture imaging system. [Figure 6] Schematic diagram of an exemplary hybrid array of a synthetic aperture imaging system. [Figure 7] Schematic diagram of an exemplary hybrid array of a synthetic aperture imaging system. [Figure 8] Schematic diagram of an exemplary hybrid array of a synthetic aperture imaging system. [Figure 9] Schematic diagram of an exemplary hybrid array of a synthetic aperture imaging system. [Figure 10] Schematic diagram of an exemplary hybrid array of a synthetic aperture imaging system. [Figure 11] Flowchart of an exemplary method for performing synthetic aperture imaging using a hybrid array. [Figure 12] Flowchart of an exemplary method for performing synthetic aperture imaging using a hybrid array. [Figure 13] Flowchart of an exemplary method for performing synthetic aperture imaging using a hybrid array. [Figure 14] Block diagram of an exemplary method for performing synthetic aperture imaging using a hybrid array. [Figure 15] Block diagram of an exemplary method for performing synthetic aperture imaging using a hybrid array. [Figure 16] Block diagram of an exemplary method for performing synthetic aperture imaging using a hybrid array. [Figure 17]A block diagram of an exemplary method for performing synthetic aperture imaging using a hybrid array. [Figure 18] A diagram showing exemplary signals generated by two types of sensors in a hybrid array. [Figure 19] A diagram showing exemplary frequency responses of two bandpass filters adjusted to two types of sensors in a hybrid array. [Figure 20] A diagram showing exemplary hybrid array windows and their corresponding beam plots. [Figure 21] A diagram showing exemplary synthetic aperture windows of hybrid arrays and their corresponding beam plots. [Figure 22] A diagram showing an exemplary delay profile of a uniform array and an exemplary delay profile of a hybrid array.

Best Mode for Carrying Out the Invention

[0016]

[0037] Non-limiting examples of various aspects and variations of the present invention are described herein and shown in the accompanying drawings.

[0017]

[0038] This specification describes a method and apparatus for synthetic aperture imaging using an ultrasonic probe having a mixed array comprising several different types of array elements. The mixed array described herein comprises one or more array elements of a first type and one or more array elements of a second type different from the first type (e.g., optical sensors such as WGM optical resonators). Optical sensors have higher sensitivity and wider bandwidth in receiving ultrasonic signals compared to other types of ultrasonic sensors. One or more array elements of the first type (e.g., transducers, or non-optical sub-arrays) may 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 sub-arrays) may be used to detect acoustic echoes that can be used to form a second set of signals. The second set of signals generated by the highly sensitive, wideband optical sensors may be used independently or in combination with the first set of signals to form an improved image. Due to the high sensitivity and wide bandwidth of the optical sensor, the images produced by the optical sensor 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.

[0018]

[0039] Optical sensors do not generate ultrasonic signals and are therefore used together in mixed arrays with other transducers that do generate ultrasonic signals (e.g., piezoelectric transducers, CMUTs, etc.). Mixed arrays can be arranged in various configurations and may include sensor elements with varying noise levels, amplitude responses, phase delays, frequency ranges, etc. Therefore, beam shaping methods and devices commonly used for probes with one type of sensor cannot be used for probes using mixed arrays of multiple types of sensors.

[0019]

[0040] For each mixed array configuration, the beam shaping method and algorithm can be adjusted to suit the mixed array configuration. Since both non-optical and optical subarrays may be used to receive ultrasonic echo signals, the receiving aperture of the mixed array can be divided into multiple sub-apers. For example, the first receiving sub-aperture (also called the “non-optical aperture”) may include one or more sensors that are not optical sensors. Furthermore, the second receiving sub-aperture (also called the “optical sensor aperture”) may include one or more optical sensors. The receiving aperture may include additional sub-apers (e.g., a third sub-aperture, a fourth sub-aperture, etc.). The signals received from the sub-apers can be combined by the receiving beam shaper of the imaging system to generate a composite aperture, as will be further described below.

[0020]

[0041] Using a beam shaping device in synthetic aperture ultrasound imaging offers several advantages. For example, synthetic aperture ultrasound imaging can increase the aperture size without increasing the number of system channels. Furthermore, synthetic aperture ultrasound imaging can increase the frame rate of ultrasound imaging without reducing the linear density in the images produced by the imaging. As another example, synthetic aperture ultrasound imaging can improve image quality by achieving dynamic focusing for both transmission and reception.

[0021]

[0042] Synthetic aperture imaging system Figure 1 is a block diagram of an exemplary synthetic aperture imaging system 100 having a mixed array. The synthetic aperture imaging system 100 includes a probe 125, an imaging system 160, and a display 170. The probe 125 can be coupled to the imaging system 160 (e.g., communicatively coupled). The probe 125 can receive and / or transmit a set of signals (e.g., electrical signals, optical signals, etc.) to and from the imaging system 160. The probe 125 may include a mixed array 110 that can receive and / or transmit a set of signals (e.g., acoustic signals, etc.) to and from a medium to form an ultrasound image. The imaging system 160 may include a front-end 140 and a back-end 150 that can collectively determine the physical parameters (e.g., timing, position, angle, and / or 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. The imaging system 160 can also be communicatively coupled to the display 170 and transmit a set of signals (e.g., electrical signals, electromagnetic signals, etc.) to the display 170. For example, in some modifications, the display 170 can be configured to display the images generated by the imaging system 160 (e.g., in a graphical user interface (GUI)). Additionally or alternatively, the imaging system 160 can receive signals from the display 170. For example, the display 170 may further include an interactive interface (e.g., a touchscreen, keyboard, motion sensor, etc.) for receiving commands from a user of the synthetic aperture imaging system 100, such as for controlling the operation of the synthetic aperture imaging system 100.

[0022]

[0043] As shown in Figure 1, the probe 125 may include a mixed array 110, a multiplexer 120, and an optical sensor cable 130. The mixed array 110 may include one or more array elements of a first type (non-optical sensors such as PZT transducers and CMUT transducers) 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 modifications, they may be configured 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 broadband response. In some modifications, the probe 125 can be configured to iteratively scan across the field of view using the mixed array 110. By doing so, an image is generated using the optical sensors and / or non-optical transducers, as will be described in more detail below. The non-optical transducers in the mixed array 110 can be operably coupled to a multiplexer 120 that processes the transmitted and / or received electrical signals between the imaging system 160 and the non-optical transducers. One or more array elements of a second type within the mixed array 110 can be operably coupled to an optical sensor cable 130 that processes transmitted and / or received optical signals between the imaging system 160 and the optical sensor.

[0023]

[0044] The multiplexer 120 functions to selectively connect individual system channels to desired array elements. The multiplexer 120 may include analog switches. The analog switches may include a number of high-voltage analog switches. Each analog switch can be connected to an individual system channel. As a result, the multiplexer 120 can selectively connect individual system channels from a set of system channels of the imaging system 160 to desired transducer elements of the mixed array 110.

[0024]

[0045] The optical sensor cable 130 may include a dedicated optical path for transmitting and / or receiving optical signals to and from the optical sensor. The optical sensor cable 130 may include one or more optical waveguides, such as optical fiber cables or coaxial cables. The characteristics of the 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 a part thereof) can be optically coupled to a single optical waveguide. Thus, signals from multiple optical sensors can be coupled to a single optical waveguide and communicated by that single optical waveguide. In some configurations, the subarray of optical sensors may be optically coupled to an array of optical waveguides in a 1:1 ratio (e.g., each optical sensor may be coupled to its own optical waveguide). Thus, optical signals from the subarray of optical sensors can be coupled to one or more optical waveguides in the optical sensor cable 130 and thereby communicated to the imaging system 160. Furthermore, in some variations, the synthetic aperture imaging system 100 may include a plurality of optical sensor cables configured as described above.

[0025]

[0046] The imaging system 160 may include a front-end 140 and a back-end 150. Generally, the front-end 140 generates an acoustic beam and interfaces with the probe 125 to receive electrical and / or optical signals. The back-end system 150 may include one or more processors for processing signals received from the mixed array 110 via the front-end to generate an image, memory operably coupled to the processors for storing the image, and / or a communication interface for presenting the image to the user (e.g., via a graphical user interface).

[0026]

[0047] For example, the display 170 can be operably coupled to the backend system 150 of the imaging system 160 to display a set of images generated by the imaging system 160. In some modifications, the display 170 may additionally or alternatively include an interactive user interface (e.g., a touchscreen) and be configured to send a set of commands (e.g., pause, resume, etc.) to the imaging system 160. In some modifications, the synthetic aperture imaging system 100 may further include a set of one or more auxiliary devices (not shown) used to input information into or output information from the synthetic aperture imaging system 100. The set of auxiliary devices may include, for example, a keyboard, mouse, monitor, webcam, microphone, touchscreen, printer, scanner, virtual reality (VR) head-mounted display, joystick, biometric reader, etc. (not shown).

[0027]

[0048] Figure 2 is a block diagram of an exemplary front end 140 of a synthetic aperture imaging system 100 having a mixed array 110, which can detect ultrasonic signals using both non-optical and optical sensors. As shown in Figure 2, in some modifications, the front end 140 may include a probe interface 141, a transmitter 142, a receiver 143, a photoacoustic receiver 144, a transmitting beamformer 146, and a receiving beamformer 145. The transmitting beamformer 146 may include one or more transmitting channels, and the receiving beamformer 145 may include one or more receiving channels. Each transmitting or receiving channel may be connected to an array element of the mixed array 110 (e.g., via a set of wires, a set of optical waveguides, etc.). For example, the transmitting beamformer 146 may include 128 transmitting channels, and the receiving beamformer 145 may include 256 receiving channels.

[0028]

[0049] The transmitting beamformer 146 can generate various transmitting waveforms based on the imaging mode. The waveforms can be amplified by the transmitter 142 before being applied to the elements of the probe 125 via the probe interface 141. The probe interface 141 connects the imaging system 160 to the probe 125 having the mixed array 110 so that the probe 125 can transmit acoustic signals toward the object to be imaged. The receiver 143 can receive echo signals detected by non-optical sensors in response to the acoustic signals as input, process these echo signals to generate a first set of digitized signals as output, and transmit such output to the receiving beamformer 145. Furthermore, the photoacoustic receiver 144 can receive echo signals detected by optical sensors in response to the acoustic signals as input, process these echo signals to generate a second set of digitized signals as output, and transmit such output to the receiving beamformer 145. The receiving beamformer 145 uses the first set of signals and the second set of signals to generate a received beam.

[0029]

[0050] Figure 3 is a block diagram of an exemplary front end 140 of a synthetic aperture imaging system 100 having a mixed array 110, where only the optical sensors of the mixed array 110 are used to detect ultrasonic echo signals (i.e., non-optical sensors, such as sensors in the PZT subarray 113, are used only to transmit ultrasonic signals and not to detect echo signals). As shown in Figure 3, the front end 140 may include a transmitter 142, a photoacoustic receiver 144, a transmitting beamformer 146, and a receiving beamformer 145. The transmitter 142 may be connected to or operably coupled to non-optical sensors, such as the PZT subarray 113 (e.g., via a probe interface 141), so that the non-optical array elements can transmit acoustic waves. The optical sensor subarray 115 of the mixed array can be used to detect echo signals and communicate them to the photoacoustic receiver 144. In contrast to the modified example shown in Figure 2, in the modified example shown in Figure 3, signals are not detected by non-optical sensors, so a separate receiver 143 associated with the non-optical sensors to generate signals based on acoustic echoes is not required. Therefore, the receiving beam shaping unit 145 generates a received beam using the signal generated by the photoacoustic receiver 144.

[0030]

[0051] Figure 4 is a block diagram of an exemplary probe 125 of a synthetic aperture imaging system 100 having a mixed array 110. The probe 125 may include the mixed array 110, a light source 117, a thermal control unit 119, a photodetector 111, and a multiplexer 121. The light source 117 can generate continuous wave (CW) or pulsed emission (stimulated emission, spontaneous emission, etc.). The light source 117 can further outcouple the emission to one end of a waveguide medium (e.g., optical fiber, free space, photonic integrated circuit waveguide, etc.) optically coupled to the optical resonator of the optical sensor subarray 115. The photodetector 111 receives the outcoupled light from the optical resonator at the other end of the waveguide medium. The outcoupled light generally undergoes phase, amplitude, and / or spectral changes due to the presence of the optical resonator and acoustic vibrations (e.g., corresponding to reflected sound waves). The thermal control unit 119 of the probe 125 can maintain a constant temperature of the optical resonator. In some cases, the thermal control unit 119 can be used to stabilize the optical response of the optical resonator.

[0031]

[0052] Mixed array The mixed array 110 includes an array of sensor elements and can be configured to operate in one-dimensional (1D), 1.25-dimensional (1.25D), 1.5-dimensional (1.5D), 1.75-dimensional (1.75D), or two-dimensional (2D) array configurations, as further described below. Generally, the number of dimensions of the ultrasonic sensor array relates to the range of height beamwidth (or height beam slice thickness) achievable when imaging with the ultrasonic sensor array, and to the extent to which the system controls the height beam aperture size, focus, and / or steering of the sensor array over the entire imaging field (e.g., the entire imaging depth). A 1D array has only one row of elements with a height dimension and a fixed height aperture size. A 1.25D array has multiple rows of elements with height dimensions and variable height aperture sizes, but with a fixed height focus via an acoustic lens. A 1.5D array has multiple rows of elements with height dimensions, variable height aperture sizes, and variable height focus via electronic delay control. A 1.75D array is a 1.5D array with additional height beam steering capability. A 2D array has a large number of elements in both lateral and height dimensions to meet the minimum pitch requirements for large beam steering angles.

[0032]

[0053] In some variations, the synthetic aperture ultrasound imaging system can change a 1.5D array configuration or a 2D array configuration to a 1D array configuration. The mixed array 110 may contain a large number of elements (e.g., 16, 32, 64, 128, 256, 1024, 4096, 8192, 16384, etc.). In some variations, the mixed array 110 may be arranged in a rectangular configuration and may contain N × M elements, where N is the number of rows and M is the number of columns. The mixed array 110 includes one or more array elements of a first type and one or more array elements of a second type, where the first type may be transducers or other non-optical sensors configured to transmit ultrasound, and the second type may be optical sensors such as WGM optical resonators. The one or more array elements of the first type and one or more array elements of the second type may be collectively arranged in a rectangular, curved, circular, or sparse array. For example, in some modifications, the mixed array may be similar to any of the mixed arrays described in U.S. Patent Application No. 63 / 029,044, which is incorporated herein in its entirety by reference. Furthermore, the mixed array may be configured to perform harmonic imaging as described in U.S. Patent Application No. 63 / 046,888, which is incorporated herein in its entirety by reference.

[0033]

[0054] The transducers in the mixed array 110 include, for example, lead zirconate titanate (PZT) transducers, polymer thick film (PTF) transducers, polyvinylidene fluoride (PVDF) transducers, capacitive micromachine ultrasonic transducers (CMUT) transducers, piezoelectric micromachine ultrasonic transducers (PMUT) transducers, photoacoustic sensors, and 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 / 3 Nb 2 / 3It may include transducers based on )-PbTiO3(PIN-PMN-PT) and / or any sensor suitable for acoustic sensing.

[0034]

[0055] Each of the optical sensors may be / include an optical resonator such as, for example, a microring resonator, a microsphere resonator, a microtoroid resonator, a microbubble resonator, a fiber-based resonator, an integrated photonic resonator, or a microdisk resonator. In some modifications, the optical sensor may include one or more WGM optical resonators. For example, in some modifications, the optical sensor may be similar to any of the optical resonators described in PCT applications PCT / US2020 / 064094, PCT / US2021 / 022412, and PCT / US2021 / 033715, each of which is incorporated herein in whole. 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 that is appropriately optically transparent at the operating wavelength of the optical resonator) that allows several permissible frequencies of light to propagate continuously within the closed loop and stores the optical energy of the permissible frequencies of light within the closed loop. The above is equivalent to saying that an optical resonator can circulate around its circumference by moving along the concave surface of the optical resonator, allowing the propagation of modes corresponding to the allowable frequencies (e.g., whispering gallery modes (WGMs)). Each mode corresponds to the propagation of optical frequencies from the allowable optical frequencies. The allowable optical frequencies and quality factors of optical resonators described herein may 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 an optical resonator can have a high quality factor suitable for a highly sensitive detection probe (e.g., due to the propagation of a set of WGMs). In general, the sensitivity of an optical sensor can be improved by increasing the quality factor of the optical resonator. In particular, in some modifications, sensitivity can be controlled by the geometric parameters of the optical resonator. When used as an ultrasonic detector, an optical resonator can have a low-noise equivalent pressure and a wideband operating bandwidth. In some modifications, the optical resonator may include detection nodes formed in the cross-section of the optical fiber and the optical waveguide as light propagating through the optical waveguide couples within the optical fiber and propagates around the optical fiber. In some modifications, the optical sensor may include an integrated photonic optical resonator.

[0035]

[0056] The space inside and / or around the optical resonator may be filled with an ultrasonic-enhancing material, such as polyvinylidene fluoride, parylene, or polystyrene. The ultrasonic-enhancing material can increase the sensitivity of the optical sensor. For example, the ultrasonic-enhancing material may have a relatively high elastic-optical coefficient such that, in response to an optical resonator receiving a set of ultrasonic echoes (for example, when subjected to mechanical stress or strain induced by a set of ultrasonic echoes), the refractive index of the ultrasonic-enhancing material changes more significantly than the refractive index of the optical resonator material.

[0036]

[0057] An optical resonator may receive and transmit light (for example, for ultrasonic imaging or other detection applications in an acousto-optic system) and be coupled to the outside world in a practically useful manner. In some embodiments, the optical resonator may be operably coupled to a light source (e.g., a laser, a tunable laser, an erbium-doped fiber amplifier, etc.) and / or a photodetector via an optical fiber (e.g., a tapered optical fiber). An acousto-optic system based on an optical sensor can directly measure ultrasound by the photoelastic effect and / or physical deformation of a resonator in response to ultrasound (e.g., an ultrasonic echo). Thus, an optical sensor can be thought of as a photoacoustic transducer that can convert mechanical energy (e.g., acoustic energy) into optical energy. For example, in the presence of an ultrasonic (or any pressure) wave, the modes moving through the resonator may undergo spectral shifts or amplitude changes caused by changes in the refractive index and shape of the resonator. Spectral changes can be readily monitored and analyzed in the spectral region using a photodetector. Amplitude changes can also be detected by a photodetector. The photodetector ultimately converts the optical energy (i.e., optical signal) propagating through the optical resonator and optical fiber into electrical energy (i.e., electrical signal) suitable for processing by electronic circuits. Furthermore, additional spatial and other information can be derived by monitoring and analyzing the optical responses of the optical resonators between the mixed arrays. An exemplary mixed ultrasonic array is described herein.

[0037]

[0058] In some variations, the mixed array 110 may include one or more rows in its height dimension. For example, array elements (of the first and second types) may be arranged together in a rectangular array containing a number of rows and a number of columns. In some variations, as shown in Figure 5, the mixed array 110 may include three rows of elements in its height dimension. The three rows include one inner row and two outer rows. The two outer rows may consist of a second type 114 (e.g., optical resonators such as WGM optical resonators). The inner row may be formed of a first type 112 (e.g., PZT transducers or other types of transducers). The two outer rows may include an equal number of elements arranged parallel to the corresponding columns. Each pair of elements 114 arranged in the same columns of the two outer rows can be optionally connected (e.g., electrically connected or electromagnetically coupled) to form a single combined outer element in a 1.25-dimensional (1.25D) array configuration or a 1.5-dimensional (1.5D) array configuration.

[0038]

[0059] Figure 5 shows a mixed array 110 having three rows, but in some modifications, the number of rows may be any odd number such as 3, 5...2n+1, where n is an integer. In some modifications, the first type array element 112 may be located in the central row of a set of odd rows. For example, a 1.5D array configuration has five 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 rows adjacent to the optical resonator rows. In some modifications, it may be advantageous to include the transducer in the central row. For example, the central row includes the first type transducer element 112 capable of both transmitting and receiving ultrasound, so that the height apodization profile does not have a “dip” in the center for both the transmit and receive modes of the transducer. This dip occurring in the height apodization profile can degrade image quality and introduce image artifacts. Therefore, arranging the first type of transducer element 112 in the central row (for example, as shown in Figure 5) may preferably help avoid such degradation of image quality and image artifacts. However, in some modifications, the mixed sensor array may include an optical resonator in the central row.

[0039]

[0060] In some variations, the number of rows may 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, one row having a first number of PZT transducer elements (or other transducer elements) and the other row having a second number of optical sensor elements. In some variations, the first and second numbers may be the same, but in other variations, the first and second numbers may be different (for example, one row may contain 128 array elements and another row may contain 192 array elements).

[0040]

[0061] Figure 6 is a schematic diagram of an exemplary mixed array. The mixed array 110 may include one or more array elements of a first type (e.g., PZT transducers or other types of transducers) and one or more array elements of a second type (e.g., optical sensors such as WGM resonators). The mixed 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. As shown in Figure 6, the mixed array 110 may include, for example, a central row having at least one array element of the first type and at least one array element of the second type. For example, the central row may have a single array element of the second type, and the other rows may have only array elements of the first type. The single array element of the second type can be an optical resonator with a wavelength approximately equal to or smaller than the wavelength of the transmitted acoustic wave. In some modifications, the use of a single optical resonator can minimize the complexity of probe fabrication while taking advantage of the ultra-high sensitivity of the optical sensor for improved image quality.

[0041]

[0062] Figure 7 is a schematic diagram of an exemplary mixed array. The mixed 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 in a random pattern (e.g., a random pattern). A pair of elements in the inner row and two outer rows may include an optical resonator 114, and the remaining elements include a first type 112, for example, a PZT transducer and / or a CMUT transducer. In some configurations, the spatial distribution of the optical resonator 114 may be random. In some configurations, the spatial distribution of the optical resonator 114 may follow an arrangement pattern (e.g., one cell of the sensor elements is shifted to the right and two cells of the sensor elements are shifted down, if they are the same). The size of the optical sensor may be smaller than or the same as the size of the first type 112.

[0042]

[0063] Figure 8 is a schematic diagram of an exemplary 1D mixed array 110 including a single row containing multiple array elements or sensor elements. The 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 a displacement pattern. Compared to a conventional 1D array containing only one type of sensor, the mixed array can have improved performance in detection bandwidth and / or sensitivity due to the addition of optical sensors.

[0043]

[0064] Figure 9 provides a schematic description of an exemplary 2D mixed array 110 arranged in a rectangular configuration, which may contain 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 embodiments, the number of rows and / or columns may be greater than 31 rows and / or 31 columns. For example, the 2D mixed array may contain 64 × 96 = 6,144 sensor elements. The mixed array 110 may contain 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 can 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 a decomposed pattern.

[0044]

[0065] Figure 10 provides a schematic description of a typical 2D mixed array 110 in a sparse array configuration. By arranging the mixed array 110 in a sparse array configuration instead of a fully sampled arrangement, the total number of sensor elements used to manufacture the mixed array can be reduced. For example, a sparse 2D array of the same size as a fully sampled 2D array may contain only 1,000 sensor elements, compared to 64 × 96 = 6,144 sensor elements in a fully sampled mixed array. The mixed array 110 may include one or more array elements of a first type (e.g., PZT transducers or other types of transducers) and one or more array elements of a second type (e.g., optical sensors such as WGM optical resonators) collectively arranged in a sparse array configuration. The spatial distribution of the first type array elements 112 and the second type array elements 114 may be random or follow a statistical distribution (e.g., a normal distribution, a Gaussian distribution, etc.). By using a sparse spatial distribution of the first type 112 and the second type 114 array elements, the occurrence of grating lobes in images generated by the mixed array can be reduced / prevented. The spatial distribution of the first type array elements 112 may be the same as, similar to, or different from, the spatial distribution of the second type array elements 114. For example, the positions of a first set of optical sensors in the mixed array 110 may have a uniform distribution, and the positions of a second set of PZT transducers in the mixed array 110 may have a normal distribution.

[0045]

[0066] Method for performing synthetic aperture imaging Figures 11 to 17, described below, illustrate exemplary methods for performing synthetic aperture imaging. The method for performing synthetic aperture imaging may be performed by a synthetic aperture computing device (not shown) which is part of a synthetic aperture imaging system (e.g., synthetic aperture imaging system 100 illustrated and described with respect to Figure 1) and / or operably coupled to the synthetic aperture imaging system. The synthetic aperture computing device may include a set of electronic circuits, 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 for executing 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 the like. The memory may store code, for example, instructions for causing the processor to perform one or more processes or functions (e.g., filtering signals, amplification signals, phase matching, noise reduction, aperture selection, etc.). Memory may include, for example, a memory buffer, random access memory (RAM), read-only memory (ROM), a flash drive, or a secure digital (SD) memory card. The communication interface may be a USB interface, a PCIe interface, or a hardware component operably coupled to the processor and / or memory that enables communication with external devices and / or a network of devices (e.g., the Internet) in the components of the synthetic aperture computing device and synthetic aperture imaging system and / or in some variations thereof.

[0046]

[0067] A synthetic aperture computing device may include applications as software stored in memory and executed by a processor. For example, an application may include code that causes the processor to select an aperture, analyze a signal, generate an image, etc. Alternatively, an application may be implemented on a hardware-based device. For example, an application may include digital or analog circuits that cause the synthetic aperture computing device to filter a signal, amplify a signal, and / or delay a signal.

[0047]

[0068] Figure 11 is a flowchart illustrating an exemplary method of performing synthetic aperture imaging using a mixed array configured to generate each ultrasound image frame for each serial scanline. The synthetic aperture imaging system can begin performing synthetic aperture imaging after receiving an instruction signal to start a new scanline. The synthetic aperture imaging system can then select a transmit aperture containing one or more array elements of a first type (e.g., PZT transducers). The synthetic aperture imaging system can then connect the transmit channel of a transmit beamformer (e.g., transmit beamformer 146, illustrated and described with respect to Figure 2) to the selected array elements of the first type. The synthetic aperture imaging system can then select a receive aperture containing one or more array elements of a second type (e.g., optical sensors). In some modifications, the receive aperture may further include one or more array elements of the first type. In general, the selection of the receive aperture can be more complex than the selection of the transmit aperture, as there are at least three possible types of receive apertures: a receive aperture having only array elements of the first type, a receive aperture having only array elements of the second type, or a receive aperture having a mixture of array elements of the first and second types.

[0048]

[0069] Once the transmit and receive apertures are selected and connected to the system channel, the front end of the synthetic aperture imaging system (e.g., front end 140 shown and described with respect to Figure 1) sends an electrical signal to excite the array elements of the transmit aperture, generating an acoustic signal (e.g., a pulse) and transmitting the acoustic signal toward the imaging target. The receive aperture then receives an acoustic echo in response to these acoustic signals, generates a signal (e.g., an electrical signal) corresponding to the acoustic echo, and transmits the signal to the receive beamformer in the front end. If the synthetic aperture imaging system includes two or more receive apertures for the same transmit aperture, the next receive aperture is selected to acquire an additional acoustic echo. Once all receive apertures have been selected at least once and corresponding signals have been acquired, the receive beamformer can synthesize the signals generated from all receive apertures (e.g., coherent combination, phase matching, frequency matching, amplitude matching, sum, etc.). The system can then repeat the process of cycling through all receive apertures for each transmit aperture. Once all transmit apertures have been selected at least once, the synthetic aperture imaging system synthesizes the signals generated from all transmit apertures to produce a complete synthetic aperture containing all receive and transmit apertures. The process described above can be performed for multiple scan lines in each frame of the ultrasound image. The synthetic aperture imaging system can then store each frame in memory and / or transmit the frames on a display included in or operably coupled to the synthetic imaging system. The process described above can be performed for multiple frames of ultrasound images.

[0049]

[0070] Figure 12 is a flowchart illustrating an exemplary method of performing synthetic aperture imaging using a mixed array configured to generate each ultrasound image frame from multiple scan lines in parallel processing. The synthetic aperture imaging system can start performing synthetic aperture imaging after receiving a signal to initiate a new frame. The synthetic aperture imaging system can then select a first subframe of a complete frame. The subframe may include, for example, a subset of scan lines that form a complete image frame (e.g., 32 scan lines). The synthetic aperture imaging system can then select a transmit aperture, a receive aperture, and a steering angle. The selected receive aperture can be made up of only first-type array elements, only second-type array elements, or a mixed array element of first and second types. Once the appropriate transmit and receive apertures for the subframe and steering angle are selected and connected to the system channel, the front end of the synthetic aperture imaging system (e.g., front end 140 shown and described with respect to Figure 1) emits electrical pulses to excite the array elements of the transmit aperture, generating an acoustic signal (e.g., a pulse), and transmits the acoustic signal toward the imaging target through the selected transmit aperture. Next, the selected receiving aperture receives acoustic echoes in response to those acoustic signals, generates signals corresponding to the acoustic echoes (e.g., electrical and optical signals), and transmits the signals to the receiving beamformer at the front end.

[0050]

[0071] If the synthetic aperture imaging system needs to select multiple transmission angles for a subframe, additional steering angles may be selected to acquire additional acoustic echoes, and the process described above may be repeated for each additional steering angle of the subframe. Once all steering angles of a subframe have been selected at least once and corresponding signals have been acquired, the receiving beamformer can coherently synthesize (e.g., coherent combination, phase matching, frequency matching, amplitude matching, sum, etc.) the signals generated from all steering angles of the subframe. The system can then repeat the process of cycling through all steering angles of each subframe. Once all subframes have been selected at least once, the synthetic aperture imaging system can synthesize (e.g., coherent combination, phase matching, frequency matching, amplitude matching, sum, etc.) the signals generated from all subframes to produce a complete frame. The synthetic aperture imaging system can then store the frame in memory and / or transmit the frame to a display included in or operably coupled to the synthetic aperture imaging system. The process described above can be performed for ultrasound imaging of multiple frames.

[0051]

[0072] Figure 13 is a flowchart illustrating an exemplary method of performing synthetic aperture imaging using a mixed array configured to generate each ultrasound image frame from multiple receiving apertures for each transmitting element (e.g., a first type of transducer such as a PZT transducer or another type of transducer) intended to operate for imaging. The synthetic aperture imaging system can start performing synthetic aperture imaging after receiving a signal to initiate a new frame. The synthetic aperture imaging system can then select a first transmitting element by connecting the transmitting channel of a transmitting beamformer (e.g., a transmitting beamformer 146 illustrated and described with respect to Figure 2) to the first transmitting element. The first transmitting element is a first type of array element capable of generating an acoustic signal. The synthetic aperture imaging system then selects a receiving aperture which includes one or more array elements of a second type and may further include one or more array elements of the first type. There are three possible types of receiving apertures: receiving apertures which have only first type array elements, receiving apertures which have only second type array elements, or receiving apertures which have both first and second type array elements.

[0052]

[0073] 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, generate an acoustic signal, and transmit the acoustic signal toward the imaging target. The receiving aperture then receives an acoustic echo in response to these acoustic signals, generates a signal corresponding to the acoustic echo, and transmits the signal to the receiving beamformer in the front end. If the synthetic aperture imaging system includes two or more receiving apertures for the same transmitting element, an additional receiving aperture is selected to acquire additional acoustic echoes associated with the transmission from that transmitting element. Once all receiving apertures have been selected at least once and corresponding signals have been acquired, the receiving beamformer can synthesize (e.g., coherent combination, phase matching, frequency matching, amplitude matching, sum, etc.) the signals generated from all the receiving apertures of that transmitting element. The system can then repeat the process of cycling through all the transmitting elements used for imaging. Once all transmitting elements have been selected, the synthetic aperture imaging system can synthesize all the transmitting elements to generate a synthetic aperture to produce a single frame or multiple frames. The synthetic aperture imaging system can then store the frames in memory and / or transmit the frames to a display included in the synthetic imaging system or operablely coupled to it. The process described above may be performed for continuous scanning of the patient.

[0053]

[0074] Figure 14 is a block diagram of an exemplary method for synthesizing acoustic data obtained using a mixed array, with several modifications. As described herein, a mixed 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 mixed array generates optical and non-optical signals. The optical sensor signals and non-optical sensor signals may have different signal paths. Each of the optical and non-optical sensors has a different physical location within the mixed array, and the optical resonator generally has different frequency response, sensitivity, and amplitude compared to the non-optical sensor. As a result, the signal from the optical resonator may require processing via different filters (e.g., low-pass filters, band-pass filters, high-pass filters, and / or digital filters), amplifiers (e.g., digital amplifiers), and / or phase delays to compensate for the difference between the optical sensor signals and the non-optical sensor signals and the signal from the non-optical sensor before the optical sensor signals and non-optical sensor signals can be effectively combined by a receiving beam shaper.

[0054]

[0075] For example, as shown in Figure 14, different bandpass filters can shape the waveforms of the received optical sensor signal and non-optical sensor signal 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 (for example, so that the optical sensor signal and the non-optical sensor signal are frequency-matched). The optical sensor bandpass filters and non-optical bandpass filters may have different characteristics to account for the differences in the frequency responses of the optical resonator and the non-optical sensor. As the ultrasonic signal propagates through soft tissue, the waveform or spectral shape of the ultrasonic signal may change with penetration depth. To account for such variations in waveform and spectral shape, a synthetic aperture imaging system can select filters based on penetration depth, waveform, and / or spectral shape.

[0055]

[0076] Furthermore, different amplifiers can provide gain values ​​and / or apodization profiles to the received optical sensor signals and non-optical sensor signals to generate an optimal or near-optimal beam pattern with minimum or near-minimum sidelobes. For example, at least one optical sensor digital amplifier can be used to provide a suitable gain and / or apodization profile related to the optical sensor signal, and at least one non-optical digital amplifier can be used to provide a suitable gain and / or apodization profile related to the non-optical sensor signal (e.g., so that the optical sensor signal and the non-optical sensor signal are amplitude-matched). The gain and / or apodization profile 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 non-optical sensor. The gain and / or apodization profile 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 may be configured to dynamically generate the gain and / or apodization profile. In some examples, the gain and / or apodization profile of the amplifier may be a constant number or may be variable as a function of depth.

[0056]

[0077] Furthermore, different phase delays can be applied to the optical sensor signal and the non-optical sensor signal based on the position and / or position difference between the optical resonator and / or the non-optical sensor. 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 (for example, so that the optical sensor signal and the non-optical sensor signal are phase-matched). The phase delays applied by the optical sensor delay unit and the non-optical delay unit may differ to account for the different positions of the optical resonator and the non-optical sensor. The phase delay may include a preset / predetermined value stored in memory. In some cases, the synthetic aperture imaging system may be configured to dynamically generate the phase delay (e.g., a phase delay profile). In some cases, the phase delay may also account for other factors. For example, the phase delay may incorporate 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 aberrations and / or other defects of the acoustic lens and / or medium. In addition to the lens, both the optical sensor and the non-optical transducer may include other layers (e.g., matching layers, coating layers, etc.) between the sensor surface and the patient's body. Besides thickness considerations, acoustic velocity can be another parameter in determining the final delay profile for synthetic aperture beam shaping.

[0057]

[0078] After applying filters, amplifiers, and phase delays as described above to process the received optical and non-optical sensor signals, the optical and non-optical sensor signals are combined and communicated to a receiving beam shaper to form an image. In some modifications, the combination of optical and non-optical sensor signals may be a coherent combination.

[0058]

[0079] Figure 14 shows a specific sequence of signal processing (filtering, then amplification, then applying phase delay), but it should be understood that in some modifications, the above signal processing steps may be performed in any suitable order. For example, Figure 15 is a block diagram of an exemplary method for synthesizing acoustic data obtained using a mixed array, with some modifications. As shown in Figure 15, instead of applying phase delay to the optical sensor signal and non-optical sensor signal after filtering and amplification, the synthetic aperture imaging system may first apply phase delay, then amplification, and then filtering. As another example, in some modifications, the optical sensor signal and non-optical sensor signal may be processed by applying phase delay, then performing filtering, and then amplification. In other words, synthesizing an optical sensor signal with a non-optical sensor signal from a mixed array may involve any permutation of applying filtering, amplification, and phase delay.

[0059]

[0080] Figure 16 is a block diagram of an exemplary method for synthesizing acoustic data obtained using a mixed array, with several modifications. The synthetic aperture imaging system may be configured to apply a first set of phase delays to the optical sensor signals using a plurality of respective optical sensor delay units (for each optical sensor signal) to phase match all of the received optical sensor signals. The resulting phase-matched optical sensor signals can then be combined with each other. Similarly, the synthetic aperture imaging system may be configured to apply a second set of phase delays to the non-optical sensor signals using a plurality of respective non-optical delay units (for each non-optical signal) to phase match all of the received non-optical sensor signals. The resulting phase-matched non-optical sensor signals can then be combined with each other. The synthetic aperture imaging system may be configured to further apply amplifiers and filters to each of the combined optical sensor signals and combined non-optical sensor signals, as described above with respect to Figure 14. For example, as shown in Figure 16, the combined optical sensor signal may be further processed by 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 may be further processed by at least one non-optical digital amplifier and at least one non-optical bandpass filter (in any order), so that the combined optical sensor signal and the combined non-optical sensor signal are matched 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 communicated to a receiving beamformer to form an image. Compared to the modifications illustrated and described with respect to Figures 14 and 15, the modification in Figure 16 can have the advantage of reducing the number of filters and amplifiers used in the synthetic aperture imaging system, thereby reducing manufacturing costs, etc.

[0060]

[0081] Figure 17 is a block diagram of an exemplary method for synthesizing acoustic data obtained using a mixed array, with several modifications. The synthetic aperture imaging system may be configured to synthesize a single element comprising an inner sub-element and two outer sub-elements (e.g., a 1.5D array illustrated and described with respect to Figure 5). The two outer sub-elements may be of the same size and positioned on each side of the inner sub-element. Thus, the signals from the two outer sub-elements can be combined together (e.g., summed) before applying a delay (for height focusing) to their signals. After combining the signals from the two outer elements, phase delays, amplifiers, and / or filters can be applied to the combined signal in any appropriate order. Furthermore, the signals from the inner sub-element may be amplified and filtered separately and finally combined with the combined signal from the two outer sub-elements. Once the inner and outer 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 beam shaping. As a result, the number of phase delay processing steps can be significantly reduced. Figure 17 shows three sub-elements (one inner sub-element and two outer sub-elements), but it should be understood that the process described above may be applied to systems containing more than three sub-elements. For example, in some examples, the process described above may be applied to 1.5D arrays having two or more sub-elements. For example, the array may contain five sub-elements, seven sub-elements, and so on.

[0061]

[0082] In some variations, the technique described with respect to Figure 17 can be extended to multiple elements. For example, two adjacent elements in a 1.5D array can be combined such that their pitch is considered a single element equal to the sum of the pitches of the two adjacent elements. The resulting 1D array produced by such a technique has only half the number of elements as the original. More generally, n adjacent elements can be combined to form a larger element, thus reducing the number of effective elements in the combined aperture by a factor of n, where n is an integer greater than 1.

[0062]

[0083] In some modifications, height beam forming is performed before transverse beam forming. However, in some modifications, the order of beam forming may be reversed; that is, transverse beam forming may be performed before height beam forming.

[0063]

[0084] Examples Figure 18 shows exemplary signals generated by two types of sensors in a mixed array. The figure in the upper left corner ("Non-optical sensor echo signal") shows the signal generated by the non-optical sensor in the time domain, and the figure in the lower left corner ("Optical sensor echo signal") shows the signal generated by the optical resonator in the time domain. The figure in the upper right corner ("Spectrum of non-optical sensor echo signal") shows the signal generated by the non-optical sensor in the frequency domain, and the figure in the lower right corner ("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. Such variations in amplitude, frequency, phase, and noise level can be compensated for by applying amplifiers, filters, phase delays, and noise filters to the signals as described above with respect to Figures 14-17.

[0064]

[0085] Figure 19 shows exemplary frequency responses of signals generated by non-optical sensors and optical resonators in a mixed array, as well as appropriate bandpass filter frequency responses for each frequency response when the non-optical sensor signals and optical sensor signals are combined. Specifically, the dashed lines represent the signals generated by the sensors in the frequency domain (similar to those shown in Figure 18). Furthermore, the solid lines show the frequency responses of two Butterworth bandpass filters designed to process the signals generated by the optical resonator (lower figure) and the signals generated by the non-optical sensor (upper figure). As shown in Figure 19, the optical sensor bandpass filter and the non-optical bandpass filter are determined to have different center frequencies and bandwidths corresponding to their respective spectral responses (dashed lines) generated by the non-optical and optical resonators, respectively. For example, as shown in the lower plot of Figure 19, the spectrum of the optical resonator has strong low-frequency components of about 0 to about 4 MHz, which can reduce the fine resolution of the final ultrasound image. Therefore, the bandpass filter for the optical sensor signal is designed to attenuate these low-frequency components below about 4 MHz, thereby separating the more valuable frequency components of the optical sensor signal for imaging purposes. However, when processing non-optical sensor signals, such a 4 MHz cutoff frequency for a bandpass filter is too high and cannot maintain useful frequency components between 3 and 4 MHz. Therefore, bandpass filters for non-optical sensor signals can be designed with a lower cutoff frequency (e.g., around 3 MHz) compared to bandpass filters for optical resonators.

[0065]

[0086] Figure 20 shows an exemplary mixed array window and its corresponding beam plot. A beam plot is a 1D beam pattern at a certain depth in the imaging plane. A beam plot typically consists of a main lobe with a central lobe and side lobes, with low peak values ​​on either side of the main lobe. The width of the main lobe determines the spatial resolution of the ultrasound image. The levels of the side lobes can determine the contrast resolution. In some cases, if the element pitch is too large or the element sensitivity profile is periodically non-uniform, grating lobes may appear on the beam plot. Grating lobes can generate undesirable image artifacts, including ghost images.

[0066]

[0087] Three aperture window functions and their corresponding beam plots are shown in Figure 20. The upper left figure ("Mixed Array Window") presents the window function generated by the mixed array configuration illustrated and described with respect to Figure 8. The non-uniformity of the window function is caused by the difference in sensitivity between the optical resonators and non-optical sensors in the mixed array. As shown in the upper right figure ("Mixed Array Beam Plot"), the periodically non-uniform window generates two grating lobes with amplitudes of approximately -8.4 dB. The center figures ("Modified Mixed Array Window" and "Modified Mixed Array Beam Plot") show that the grating lobes can be overcome by applying different digital amplification gains to the two types of sensors. By applying such digital amplification gains, a uniform window function can be generated. Using a similar technique, a Gaussian apodization window can be generated to reduce the side lobes in the beam plot, as shown in the two lower figures ("Optimized Mixed Array Window" and "Optimized Mixed Array Beam Plot"). All three beamformer architectures shown in Figures 14–16 can generate a uniform window function. However, in some cases, only the beam shaping architectures shown in Figures 14 and 15 can generate arbitrary window functions.

[0067]

[0088] Figure 21 shows exemplary synthetic aperture windows for mixed arrays and their corresponding beam plots. Three exemplary synthetic aperture (SA) window functions and their corresponding beam plots are shown. The top two figures illustrate why two or more sub-apers must be properly synthesized to produce a good beam pattern. The top left figure ("Poorly Synthesized SA Window") shows a poorly synthesized aperture window function. The top right beam plot ("Poorly Synthesized SA Beam Plot") shows elevated side lobes generated due to the gap between the two sub-apers of the synthetic aperture window function. The two middle figures ("Conventional SA Window" and "Conventional SA Beam Plot") show conventional synthetic apertures with the same two sub-apers used for the synthetic aperture in the top left figure and the corresponding beam plot. The side lobes are significantly reduced compared to the top right beam plot. The side lobes can be further reduced by synthesizing two superimposed sub-apers, as shown in the two bottom figures. The synthetic aperture has a coarse apodization window, as shown in the bottom left figure ("Superimposed SA Window"). The resulting beam plot in the lower right figure ("superimposed SA beam plot") shows the reduction of side lobes due to the superimposed sub-apertures.

[0068]

[0089] Figure 22 shows exemplary delay profiles for a uniform array and a mixed array. In some modifications, sound waves and / or signals can travel through different signal paths before the signals are added by the beamformer. For example, in the case of a PZT sensor element, sound waves and the corresponding signals can travel through an acoustic lens and one or more matching layers before reaching the PZT sensor. On the other hand, in the case of an optical resonator, sound waves and the corresponding signals can travel through an acoustic lens with different thicknesses and / or sound velocities and a polymer layer with different thicknesses and / or sound velocities before reaching the optical resonator. Differences in signal paths can result in additional delays. Such extra delays introduce phase errors into beamforming, resulting in reduced imaging performance, including detail resolution, contrast resolution, and signal-to-noise ratio (SNR). Therefore, as shown in Figure 22 and further discussed below, extra delays between two sensor channels can be adjusted accordingly.

[0069]

[0090] The upper plot ("delay profile for a uniform array") shows the delay profile for an aperture with 64 elements of the same sensor. The lower delay profile ("delay profile for a mixed array") is for an aperture with 64 elements of two different sensors, such as a mixed array illustrated and described with respect to Figure 8. To compensate for the difference in signal paths between the two types of sensors, an additional fixed phase delay can be added to either the non-optical channel or the optical resonator channel. The delay profiles shown can be used for both transmit beam shaping and receive beam shaping.

[0070]

[0091] While synthetic aperture imaging methods and systems for mixed arrays are described in the context of ultrasound imaging, in some modifications, synthetic aperture imaging methods and systems can be used in applications other than ultrasound imaging. For example, in some cases, synthetic aperture imaging methods and systems can be used in measurement, signal processing, particle physics, remote sensing, aerospace applications, and more.

[0071]

[0092] The foregoing description uses specific nomenclature to provide a complete understanding of the invention for illustrative purposes. However, it will be apparent to those skilled in the art that specific details are not required to carry out the invention. Accordingly, the foregoing description of specific embodiments of the invention is presented for illustrative and explanatory purposes. They are not intended to be exhaustive or to limit the invention to the exact forms disclosed. Clearly, given the teachings above, many modifications and variations are possible. The embodiments are selected and described to illustrate the principles of the invention and its practical applications, thereby enabling other those skilled in the art to utilize the various embodiments with various modifications suitable for the invention and the specific applications it is intended for. The following claims and their equivalents are intended to define the scope of the invention.

Claims

1. A method of acoustic-optical imaging, A step of receiving a first signal from a first sub-aperture of a sensor array, wherein the first sub-aperture includes one or more array elements of a first type, A step of receiving a second signal from a second sub-aperture of the sensor array, wherein the second sub-aperture includes one or more array elements of a second type different from the first type, and the second type is an optical sensor. A step of combining the first signal and the second signal using a receiving beam shaping device to obtain a combined signal, wherein the combined signal is a signal from the combined aperture of the sensor array formed by the first sub-aperture and the second sub-aperture of the sensor array, A method that includes this.

2. Step of phase matching the first signal and the second signal. The method according to claim 1, further comprising:

3. The method according to claim 2, wherein the step of phase matching the first signal and the second signal includes the step of applying a first delay to the first signal or a second delay to the second signal, the first delay and the second delay being determined at least in part 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 according to claim 3, wherein the first delay or the second delay is determined at least in part on the thickness and sound velocity of the acoustic lens, or the thickness and sound velocity of the acoustic matching layer, or the respective thickness and sound velocity of the acoustic lens and the acoustic matching layer.

5. The method according to claim 3, wherein the first delay or the second delay is at least partially based on the transmit focus and / or receive focus.

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

7. Steps to amplify the first signal or the second signal with an amplification gain in order to amplitude match the first signal and the second signal. The method according to claim 1, further comprising:

8. The method according to claim 7, wherein the amplification gain is a preset value.

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

10. The step of frequency matching the first signal and the second signal. The method according to claim 1, further comprising:

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

12. Before the step of phase matching the first signal and the second signal, A step of generating the first signal by combining signals generated from a plurality of array elements of the first type, or a plurality of array elements of the first type and the second type, A step of generating the second signal by combining signals generated from a plurality of array elements of the second type, or from a plurality of array elements of the first type and the second type, The method according to claim 11, further comprising one or more of the above.

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

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

15. The method according to claim 12, further comprising the step of reducing the effective number of dimensions of the synthetic opening.

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

17. The method according to claim 15, wherein the sensor array is a two-dimensional (2D) array, and the method includes the step of reducing the effective number of dimensions of the composite aperture from 2D to 1.5 dimensions (1.5D).

18. The steps of frequency matching the first signal and the second signal, The first step of frequency matching the first signal and the second signal, followed by the step of amplitude matching the first signal and the second signal, After the step of frequency matching and amplitude matching the first signal and the second signal, the step of phase matching the first signal and the second signal, The method according to claim 1, further comprising:

19. A step of phase matching the first signal and the second signal, After the step of phase matching the first signal and the second signal, the step of amplitude matching the first signal and the second signal, After the step of matching the phase and amplitude of the first signal and the second signal, the step of matching the frequency of the first signal and the second signal, The method according to claim 1, further comprising:

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

21. The method according to claim 1, wherein the optical sensor is an optical resonator.

22. The method according to claim 21, wherein the optical resonator is a whispering gallery mode (WGM) optical resonator.

23. The method according to claim 21, wherein the optical resonator is a microbubble optical resonator, a photonic integrated circuit (PIC) optical resonator, a microsphere resonator, a microtoroid resonator, a microring resonator, or a microdisk optical resonator.

24. The method according to claim 1, wherein the one or more array elements of the first type include a piezoelectric transducer, a single-crystal material transducer, a piezoelectric micromachine ultrasonic transducer (PMUT), or a capacitive micromachine ultrasonic transducer (CMUT).

25. The steps include selecting the first sub-aperture for transmitting an acoustic signal, The steps include selecting the first sub-aperture or the second sub-aperture for receiving an acoustic echo in response to the acoustic signal, The method according to claim 1, further comprising:

26. A step of selecting an element from the one or more array elements of the first type to transmit an acoustic signal, The steps include selecting the first sub-aperture or the second sub-aperture to receive an acoustic echo in response to the acoustic signal, The method according to claim 1, further comprising:

27. The steps include selecting the angle for transmitting the acoustic signal, The steps include transmitting the aforementioned acoustic signal, The steps include receiving an acoustic echo in response to the aforementioned acoustic signal, The method according to claim 1, further comprising:

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

29. A device for imaging a target, One or more array elements of a first type that form a first sub-aperture, Unlike the first type, a second type of array element comprising one or more array elements forming a second sub-aperture, wherein the second type is an optical sensor, 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, A front end configured to obtain a combined signal by combining the first signal and the second signal using a receiving beam shaping device. Includes, The apparatus wherein the synthesized signal is a signal from a composite aperture of the sensor array formed by the first sub-aperture and the second sub-aperture of the sensor array.

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

31. The apparatus according to claim 30, wherein phase matching the first signal and the second signal includes applying a first delay to the first signal and a second delay to the second signal, wherein the first and second delays are determined at least in part 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 according to claim 31, wherein the first delay or the second delay is determined at least in part on the thickness and sound velocity of the acoustic lens, or the thickness and sound velocity of the acoustic matching layer, or the respective thickness and sound velocity of the acoustic lens and the acoustic matching layer.

33. The apparatus according to claim 31, wherein the first delay or the second delay is at least partially based on the transmit focus and the receive focus.

34. The apparatus according to claim 29, wherein the front end is further configured to generate the composite 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 according to claim 29, wherein the front end is further configured to generate the composite aperture by amplifying the first signal or the second signal with an amplification gain in order to amplitude match the first signal and the second signal.

36. The apparatus according to claim 35, wherein the amplification gain is a preset value.

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

38. The apparatus according to claim 29, wherein the front end is further configured to generate the composite aperture by frequency matching the first signal and the second signal.

39. The apparatus according to claim 29, wherein the first signal is a combination of signals generated from a plurality of array elements of the first type, or the second signal is a combination of signals generated from a plurality of array elements of the second type.

40. The aforementioned front end, The first signal and the second signal are frequency matched, After frequency matching the first signal and the second signal, amplitude matching the first signal and the second signal, After frequency matching and amplitude matching the first signal and the second signal, the first signal and the second signal are phase-matched, The apparatus according to claim 29, further configured to generate the aforementioned synthetic opening.

41. The aforementioned front end, The first signal and the second signal are phase-matched, After the first signal and the second signal are phase-matched, the first signal and the second signal are amplitude-matched. After matching the phase and amplitude of the first signal and the second signal, the first signal and the second signal are then frequency-matched. The apparatus according to claim 29, further configured to generate the aforementioned synthetic opening.

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

43. The apparatus according to claim 29, wherein the optical sensor is an optical resonator.

44. The apparatus according to claim 43, wherein the optical resonator is a whispering gallery mode (WGM) optical resonator.

45. The apparatus according to claim 43, wherein the optical resonator is a microbubble optical resonator, a photonic integrated circuit (PIC) optical resonator, a microsphere resonator, a microtoroid resonator, a microring resonator, or a microdisk optical resonator.

46. The apparatus according to claim 43, wherein the one or more array elements of the first type include a piezoelectric transducer, a single-crystal material transducer, a piezoelectric micromachine ultrasonic transducer (PMUT), or a capacitive micromachine ultrasonic transducer (CMUT).

47. The aforementioned front end, Select the first sub-aperture for transmitting an acoustic signal, By selecting the first sub-aperture or the second sub-aperture to receive an acoustic echo in response to the aforementioned acoustic signal, The apparatus according to claim 29, further configured to combine the first signal and the second signal.

48. The aforementioned front end, Select an element from the one or more array elements of the first type in order to transmit an acoustic signal. By selecting the first sub-aperture or the second sub-aperture to receive an acoustic echo in response to the aforementioned acoustic signal, The apparatus according to claim 29, further configured to combine the first signal and the second signal.

49. The aforementioned front end, Select the angle for transmitting the acoustic signal, The aforementioned acoustic signal is transmitted, By receiving an acoustic echo in response to the aforementioned acoustic signal, The apparatus according to claim 29, further configured to combine the first signal and the second signal.

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

51. The apparatus according to claim 50, wherein the one or more array elements of the first type and the one or more array elements of the second type include at least one row comprising at least one array element of the first type and at least one array element of the second type.

52. The apparatus according to 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 one-dimensional (1D) array.

53. The apparatus according to 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 according to 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, and 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 according to 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 according to 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 according to 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 according to 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, and 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 according to 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 according to 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 according to 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 according to 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 two-dimensional (2D) array.

63. The apparatus according to 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 according to claim 29, wherein the optical sensor is optically coupled to an optical fiber to transmit a set of optical signals to a photodetector.

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