Acousto-optic harmonic imaging with optical sensors

Abstract

The acousto-optic imaging system may include at least one transducer that transmits an ultrasound signal having a fundamental frequency f. The acousto-optic imaging system may include at least one optical sensor that may generate one or more optical responses upon receiving harmonically related ultrasound echoes corresponding to the transmitted ultrasound signal. For example, the one or more optical sensors may have a bandwidth ranging from at least f / M to Nf, where M and N are integers greater than 1.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Patent Application No. 63 / 046,888, filed July 1, 2020, which is incorporated by reference in its entirety.

[0002]

[0002] The present disclosure relates generally to the field of acousto-optic imaging, and more particularly to methods and devices involving optical sensors for ultrasound sensing and harmonic imaging. [Background technology]

[0003]

[0003] Ultrasound sensing is used in a variety of industries, including medical imaging, due to a number of advantages. For example, ultrasound sensing utilizes ultrasound signals that have a significant penetration depth. Furthermore, ultrasound imaging is known to be advantageously a non-invasive form of imaging because it is based on non-ionizing radiation.

[0004]

[0004] Conventional ultrasonic sensing is based on lead zirconate titanate (PZT), polymer thick film (PTF), polyvinylidene fluoride (PVDF), and capacitive micro-ultrasound. Transducer Conventional ultrasound sensing uses piezoelectric materials, such as CMUT (Compact Modular Utterances). However, one of the challenges associated with such conventional ultrasound sensing is their narrow bandwidth. Therefore, new and improved devices and methods are needed for ultrasound imaging modes involving various frequency harmonics to obtain higher resolution, better penetration, and fewer artifacts than the underlying imaging of conventional ultrasound sensing. Summary of the Invention

[0005] Generally, in some embodiments, an acousto-optic imaging system generates one or more ultrasound signals, each having a respective fundamental frequency (eg, fundamental frequency f). send At least one Transducer (e.g., one Transducer , 10 Transducer , 100 Transducer At least one Transducer is a piezoelectric Transducer , capacitive micro-ultrasound Transducer (CMUT), polymer thick film (PTF) Transducer , photoacoustic Transducer , piezoelectric micro-ultrasonics Transducer The acousto-optic imaging system may include a PMUT. send At least one optical sensor (e.g., 1 optical sensor, 10 optical sensors, 100 optical sensors, etc.) with a broadband acoustic response that generates one or more optical responses upon receiving a fundamental frequency, superharmonic, ultraharmonic, subharmonic, or differential harmonic ultrasonic echo corresponding to an ultrasonic signal.

[0006]

[0006] The fundamental frequency is the original send It can be defined as the frequency of the ultrasonic signal. A superharmonic can be defined as an integer multiple of the original transmitted or fundamental frequency. For example, the second superharmonic is 6 MHz when the fundamental frequency is 3 megahertz (MHz). An ultraharmonic can be defined as a frequency higher than the fundamental frequency but that is not a superharmonic. For example, when the fundamental frequency is 3 MHz, one possible ultraharmonic is 4.5 MHz. A subharmonic is a frequency that is a multiple of the original transmitted frequency or fundamental frequency. send It can be defined as a frequency or a fraction of the fundamental frequency. For example, if the fundamental frequency is 3 MHz, one possible subharmonic is 1.5 MHz. (For example, if there is at least one Transducer By send will be) send When an ultrasound signal contains multiple frequencies (e.g., two frequencies), in some cases the nonlinear medium being imaged by the acousto-optic imaging system may also generate so-called differential harmonics. For example, sendIf the ultrasound signal includes both 3 MHz and 5 MHz frequencies, one possible differential harmonic can include the 5-3=2 MHz frequency. In some cases, at least one optical sensor (e.g., a whispering gallery mode (WGM) optical resonator, a microbubble resonator, a microsphere resonator, or a microdisk resonator) can include a closed loop of one or more optically transparent materials with an acoustic response bandwidth ranging from at least f / M to Nf, where M and N are integers greater than 1. By leveraging such a broadband acoustic response of the at least one optical sensor, the acousto-optic imaging system can use the fundamental frequency, subharmonics, ultraharmonics, superharmonics, and / or differential harmonics of the ultrasound signal. As a result, such devices are less complex and can be easily mass-produced in a cost-effective manner.

[0007] In some embodiments, the at least one optical sensor may generate at least a portion of one or more optical responses upon receiving an ultrasonic echo having a superharmonic frequency of at least Qf, where Q is an integer of 3 or greater (e.g., 3f, 6f, 11f, etc. (superharmonic frequency)). Further, the at least one optical sensor may generate at least a portion of one or more optical responses upon receiving an ultrasonic echo having a frequency of 2f or f. Similarly, the at least one optical sensor may generate at least a portion of one or more optical responses upon receiving an ultrasonic echo having a subharmonic frequency of f / R, where R is an integer of 2 or greater (e.g., f / 2, f / 5, f / 8, etc.).

[0008] In some embodiments, the at least one optical sensor may generate at least a portion of one or more optical responses upon receiving ultrasonic echoes having an ultraharmonic frequency of at least Qf, where Q is a non-integer number greater than 1 (e.g., 1.5f, 2.5f, 3.33f, etc.). Similarly, the at least one optical sensor may generate at least a portion of one or more optical responses upon receiving ultrasonic echoes having a subharmonic frequency of f / R, where R is a non-integer number greater than 1 (e.g., f / 1.5, f / 2.75, f / 4.33, etc.).

[0009] In some embodiments, at least one Transducer may generate a first ultrasonic signal having a first fundamental frequency f1 and a second ultrasonic signal having a second fundamental frequency f2. Furthermore, the at least one optical sensor may generate, at least in part, one or more optical responses upon receiving ultrasonic echoes corresponding to frequencies of the one or more linear combinations nf1 + mf2. The parameters n and m represent integers selected such that the linear combination nf1 + mf2 is a positive number. However, the parameters n and m may include negative or positive integers. Thus, the linear combination may be the difference between a multiple of the first fundamental frequency and a multiple of the second fundamental frequency, or the sum of a multiple of the first fundamental frequency and a multiple of the second fundamental frequency.

[0010] In some embodiments, the acousto-optic imaging system may include a computer-readable medium storing code representing instructions for generating an image based on one or more optical responses of at least one optical sensor. The computer-readable medium may provide the instructions for generating the image, for example, by calculating a magnitude of each ultrasonic echo in the at least one optical sensor based on the changes, and further by executing code for converting the magnitude of each ultrasonic echo into a pixel value for display.

[0011] In some embodiments, the change may indicate a spectral shift. The at least one optical sensor may be highly sensitive such that each optical response includes at least one spectral resonance feature with a full width at half maximum (FWHM) smaller than the spectral shift. In some cases, the at least one optical sensor may include several spectral response features (e.g., tens of spectral response features, hundreds of spectral response features, etc.) with a high quality factor (Q factor). Each of the several spectral response features may be smaller than the spectral shift detected to form an image using the at least one optical sensor.

[0012] In some embodiments, the at least one optical sensor may have an effective refractive index and wall thickness capable of propagating a set of whispering gallery modes (WGMs) in the at least one optical resonator. Further, the at least one optical sensor may be coupled to one or more optical waveguides (e.g., optical fibers, integrated optical circuit waveguides, etc.) for propagating multiple optical signals to one or more optical detectors.

[0013] In some embodiments, the change in the spectral response characteristic of the at least one optical sensor may be caused by a change in the effective refractive index of the at least one optical sensor due to a photoelastic effect of the at least one optical sensor upon receiving the ultrasonic echo. In some embodiments, the at least one optical sensor may be embedded in a polymer structure having an effective refractive index lower than the effective refractive index of the at least one optical sensor.

[0014] In some embodiments, the method of acousto-optic imaging includes: Transducer Ultrasonic signals are transmitted via the medium send The method may further include: sendand generating one or more optical responses via the at least one optical sensor upon receiving harmonic or subharmonic ultrasonic echoes corresponding to the ultrasonic signal, wherein the at least one optical sensor may have a bandwidth ranging from at least f / M to Nf, where M and N are integers greater than 1.

[0015] In some embodiments, the medium may include a nonlinear medium. In particular, in some embodiments, the medium may include biological tissue.

[0016] In some embodiments, a method of acousto-optic imaging includes transmitting one or more ultrasonic signals having one or more fundamental frequencies to a medium. send The method may include detecting at least one change in an optical response of one or more optical detectors, the change being generated upon receiving the ultrasonic echoes. The one or more signals may be incident on the medium, resulting in ultrasonic echoes capable of forming a visual representation of the medium. The method may further include detecting at least one change in an optical response of one or more optical detectors, the at least one change being generated upon receiving the ultrasonic echoes. Some of the received ultrasonic echoes may have a frequency that is a superharmonic frequency, an ultraharmonic frequency, a subharmonic frequency, or a linear combination of one or more fundamental frequencies. The method may also include generating an image of the medium based on the detected change in the optical response. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram illustrating an exemplary acousto-optic imaging system. [Figure 2]

[0018] FIG. 2 illustrates an exemplary spectral response of an optical sensor. [Figure 3A]

[0019] FIG. 2 illustrates an exemplary spectral response of a transducer. [Figure 3B]

[0020] FIG. 2 illustrates an exemplary spectral response of a transducer. [Figure 3C]

[0021] FIG. 2 illustrates an exemplary spectral response of an optical sensor. [Figure 4]

[0022] FIG. 1 illustrates an exemplary spectral response of an optical sensor in response to an ultrasonic signal. [Figure 5A]

[0023] 1A-1C are schematic diagrams illustrating exemplary geometries of optical microbubble / microsphere resonators. [Figure 5B]

[0024] 1A-1C are schematic diagrams illustrating exemplary geometries of optical microdisk resonators. [Figure 6A]

[0025] FIG. 1 illustrates an example spectral response of a set of optical sensors. [Figure 6B]

[0025] FIG. 1 illustrates an exemplary spectral response of a set of optical sensors. [Figure 6C]

[0025] FIG. 1 illustrates an exemplary spectral response of a set of optical sensors. DETAILED DESCRIPTION OF THE INVENTION

[0018]

[0026] Non-limiting examples of various aspects and variations of the present invention are described herein and illustrated in the accompanying drawings.

[0019]

[0027] As described herein, acousto-optic imaging systems based on optical sensors, such as piezoelectric or CMUT Transducer Traditional Transducer Using this high sensitivity and broadband response, acousto-optic imaging systems can simultaneously achieve high sensitivity and broadband response at levels not found in ultrasound systems that sense ultrasound echoes based on a conventional Transducer A wide range of acoustic frequencies can be detected to generate ultrasonic images of a medium with a greater penetration depth and / or greater spatial resolution than images generated by a conventional ultrasonic transducer.

[0020] <Harmonic Acousto-Optic Imaging System>

[0028] As shown in FIG. 1, an acousto-optic imaging system 101 includes one or more Transducer 110 and one or more optical sensors 120. Transducer 110 to generate an ultrasound signal 111 having a fundamental frequency f towards a medium for imaging, and / or send The medium may be a nonlinear medium, such as body tissue. The optical sensor 120 is configured to generate an optical response upon receiving ultrasound echoes 121 that reverberate in response to the interaction of the ultrasound signal 111 with the medium. In some variations, propagation of the ultrasound signal 111 through the medium may generate echoes at various frequencies, including the fundamental frequency f, and harmonically related frequencies, including one or more subharmonic frequencies, one or more ultraharmonic frequencies, one or more harmonic and / or superharmonic frequencies, etc. As described further below, the acousto-optic imaging system 101 may be configured to detect a wide range of frequencies, including these specialized harmonically related frequencies, which advantageously enables a wide variety of harmonically related imaging to be performed, including harmonic imaging, ultraharmonic imaging, superharmonic imaging, subharmonic imaging, etc., for a wide range of imaging modes and functionality. The use of one or more optical sensors in a single acousto-optic imaging system is also advantageous because it enables an imaging system with fewer ultrasound probes, thereby reducing the complexity and increasing the efficiency of the acousto-optic imaging system.

[0021] < Transducer >

[0029] To generate an ultrasonic signal and / or send In order to Transducer 110 is, for example, a piezoelectric Transducer , lead zirconate titanate (PZT) Transducer , Polymer Thick Film (PTF) Transducer , polyvinylidene fluoride (PVDF) Transducer , capacitive micro-ultrasound Transducer (CMUT), Piezoelectric Micro-Ultrasonics Transducer (PMUT), photoacoustics Transducer, 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 / 3 )-PbTiO3(PIN-PMN-PT) Transducer and / or for generating an ultrasonic signal and / or send Further, in some variations, the present invention may include any suitable components for: Transducer 110 may be configured to detect ultrasound echoes at specific restricted frequencies for use in generating images (eg, in combination with signals from optical sensor 120).

[0022] <Optical sensor>

[0030] The optical sensors 120 may be suitable for high-sensitivity, high-bandwidth applications, including high-sensitivity acousto-optic imaging systems. In some cases, for example, each optical sensor 120 may include a closed loop of transparent medium that allows any allowed optical frequencies to propagate continuously within the closed loop and store the optical energy of the allowed optical frequencies within the closed loop. For example, the optical sensor 120 allows whispering gallery modes (WGMs) to propagate along the concave surface of the optical sensor 120 and circulate around the sensor, corresponding to the allowed frequencies. Each mode from the WGMs corresponds to the propagation of an optical frequency from the allowed optical frequencies. The aforementioned WGM resonators may appear in the form of, for example, spheres, disks, rings, bubbles, cylinders, and / or annuli. They may be made of optically transparent materials with low loss at the wavelengths of light propagating within the resonator, such as silica and silicon in the infrared spectral window or chalcogenides in the mid-infrared window.

[0023]

[0031] The optical sensors 120 advantageously have high sensitivity and wide bandwidth due at least in part to having a high quality factor, in that the allowed light frequencies can remain for long periods within the closed loop of each optical sensor 120. The allowed light frequencies of the optical sensors 120 may be based at least in part on the geometric parameters of the optical sensors 120, the refractive index of the transparent medium, and the refractive index of the environment surrounding the optical sensors 120. The quality factors described herein are determined by the losses experienced by light propagating within the resonators, which may be caused by material absorption, material and structural inhomogeneities, radiative dissipation, light scattering, and coupling rates to external waveguides.

[0024]

[0032] Each optical sensor 120 receives light and send and can be coupled to the outside world to be actually useful (e.g., for ultrasound imaging in an acousto-optic imaging system or other sensing applications). An acousto-optic imaging system based on optical sensor 120 can directly detect ultrasound waves via the photoelastic effect and / or physical deformation of the sensor in response to ultrasound (e.g., ultrasound echoes). For example, in the presence of ultrasound (or any pressure wave), WGM traveling through the resonator experiences a spectral shift caused by changes in the refractive index and the shape of the resonator. The spectral change is due to the optical domain and the optical response between the optical sensor 120 and the sensor. send The intensity can be easily monitored and analyzed. Additional spatial and other information can be further derived by monitoring and analyzing the optical sensor 120.

[0025] <Example of optical sensor>

[0033] As mentioned above, optical sensors have high quality factors and broadband spectral responses, as well as various other beneficial characteristics, that make them advantageous for use in applications such as ultrasound sensing and / or ultrasound imaging. Optical sensors may include, for example, optical resonators (e.g., WGM optical resonators), microbubble resonators, fiber-based resonators, integrated optical resonators, microdisk resonators, etc.

[0026]

[0034] As shown in FIG. 5A, at least one optical sensor can be a whispering gallery mode (WGM) optical resonator, such as an optical microbubble resonator. The optical microbubble resonator can be made of an optically transparent material, such as glass, transparent polymer, silicon nitride, titanium dioxide, or any other material that is suitably optically transparent at the operating wavelength of the optical microbubble resonator. The optical microbubble resonator includes an outer microbubble surface of radius (R) and an inner microbubble surface of radius (r), thereby defining an equivalent resonator wall thickness (Rr). The set of resonant frequencies (resulting from the propagation of a set of WGMs) of the optical microbubble resonator can have a high quality factor suitable for a highly sensitive acousto-optic sensing probe. In general, the sensitivity of a WGM optical resonator can be improved by increasing the quality factor of the WGM optical resonator. In particular, in such an embodiment, the sensitivity can be controlled by the wall thickness (Rr) of the optical microbubble resonator. When used as an ultrasound detector, the optical microbubble resonator can have a low-noise equivalent pressure and a wide operating bandwidth, as described in further detail herein.

[0027]

[0035] In some embodiments, the optical sensor may include a sensing node formed at a cross section of the optical fiber and the optical waveguide when light propagating in the optical waveguide couples into the optical fiber and propagates around the optical fiber. In some variations, the optical sensor may include an integrated optical resonator. For example, in some variations, the optical sensor may be similar to any of the WGM optical resonators described in PCT Application Nos. PCT / US2020 / 064094 and PCT Application Nos. PCT / US2021 / 022412, each of which is incorporated herein in its entirety.

[0028]

[0036] The space within and / or around the optical sensor can be filled with a polymer structure, such as an ultrasonic enhancement material. For example, the optical sensor can be filled with polyvinylidene fluoride, parylene, polystyrene, or the like. The ultrasonic enhancement material can increase the sensitivity of the optical sensor. For example, the ultrasonic enhancement material can have a relatively high elasto-plastic optical coefficient such that, in response to the optical sensor receiving a set of ultrasonic echoes, the refractive index of the ultrasonic enhancement material changes more than the refractive index of the material of the optical sensor (e.g., upon receiving mechanical stress or strain induced by the set of ultrasonic echoes). The effective refractive index of the polymer structure can be lower than the effective refractive index of the optical sensor.

[0029]

[0037] As shown in FIG. 5B, the optical sensor can be a microdisk resonator. The microdisk resonator can be made of optically transparent and / or optically opaque materials, such as glass, transparent polymers, silicon nitride, titanium dioxide, silicon, or any other material suitable for propagating light in, on, and / or around the microdisk resonator. In some variations, the microdisk resonator can be made of a combination of optically transparent and optically opaque materials. The set of resonant frequencies (resulting from the propagation of a set of WGMs) of the microdisk resonator can have a high quality factor suitable for a highly sensitive acousto-optic sensing probe.

[0030]

[0038] In some variations, sensing of an ultrasonic signal by such an optical sensor (e.g., a WGM optical resonator) occurs because ultrasonic pressure on the optical sensor can cause a change in the refractive index of the material included in the optical sensor. The thickness of the WGM modes propagating in, on, and / or around the optical sensor and the mode distribution in, on, and / or around the optical sensor can be considered a spatial window for ultrasonic sensing. The convolution of the ultrasonic signal and the spatial window can result in a change in the optical response of the optical sensor.

[0031]

[0039] 6A-6C are exemplary spectral responses of a set of optical sensors (e.g., WGM optical resonators). The top plot of each of FIGS. 6A-6C shows a generally rectangular spatial window corresponding to the physical dimensions / distribution of the optical WGM resonant modes. In some cases, the spectral response in the frequency domain of the incoming ultrasound echo may be convolved with the rectangular spatial window. Convolution of the spectral response with the rectangular spatial window results in a sinc function, as shown in the bottom plot of each of FIGS. 6A-6C. The sinc function is the Fourier transform (i.e., a rectangular function) of each rectangular spatial window. Different lengths of each rectangular spatial window result in different spectral responses in the frequency domain, as shown in the bottom of each of FIGS. 6A-6C. In some variations, the bandwidth of a set of optical sensors (or any sensor, for that matter) may be defined as the frequency range over which the amplitude of the spectral response is above a certain threshold (e.g., 0.5). A comparison of Figures 6A to 6C shows that a wider bandwidth (broadband response) can be achieved by narrowing the rectangular spatial window of the WGM optical resonator. In contrast, a comparison of Figures 6A to 6C shows that a narrower bandwidth can be achieved by widening the rectangular spatial window of the WGM optical resonator. As shown in Figure 6B, for narrow WGM optical resonator structures, the spatial distribution of the WGM resonant modes can be constrained by the geometry of the WGM optical resonator. As shown in Figure 6A, for larger WGM optical resonator structures, the spatial distribution of the WGM resonant modes is less constrained by the geometry of the WGM optical resonator and can potentially change significantly. Different orders of WGM resonant modes can have different thicknesses or distributions within the structure.

[0032]

[0040] In some variations, other spatial windows (e.g., Gaussian windows, Hamming windows, Kaiser windows, concave functions, etc.) may be convolved with the spectral response of the incoming ultrasonic echoes in the frequency domain. For example, in some cases, a Kaiser window may be convolved with the spectral response of the incoming ultrasonic echoes in the frequency domain. The Kaiser window includes a first parameter M and a second parameter b. The first parameter M determines the width, and the second parameter b controls the shape. In some cases, when the second parameter b = 0, the Kaiser window may represent a rectangular window. In some cases, when the second parameter b = 4.86, the Kaiser window may represent a Hamming window. However, it should be understood that the aforementioned spectral responses are merely examples, and that in other variations, the set of one or more optical sensors may have any suitable spectral response.

[0033]

[0041] The bandwidth of an optical sensor can be adjusted by selecting optical modes propagating within the optical sensor with different spatial distributions. For example, a fundamental mode that is mostly confined within the equatorial plane of the optical sensor may provide a broadband response. In contrast, higher-order modes with larger spatial distributions may have narrowband responses. The broadband response of an optical sensor may be achieved when an acousto-optic imaging system selects optical modes with fundamental frequency f, subharmonic frequencies (e.g., f / 2), and / or superharmonic frequencies (e.g., 2f). send In some cases, higher order modes with narrowband responses may be used to monitor ultrasound echoes with the same or similar frequencies as the ultrasound signal being transmitted, providing additional spectral sensitivity. send do TransducerThe optical sensor focuses on signals within a specific band of interest within the fundamental frequency f of the optical sensor. In some variations, the ultrasonic bandwidth of the optical sensor can be adjusted by controlling the geometry of the optical sensor. In some embodiments, stronger confinement of light (i.e., the optical mode) within the optical sensor and along the direction of propagation of the ultrasonic echo can result in a wider bandwidth spectral response within the optical sensor. For example, a microdisk resonator with tighter spatial confinement to the bright field along the direction of propagation of the ultrasonic echo perpendicular to the microdisk resonator can provide a wider bandwidth than an optical microbubble resonator.

[0034] <Computing Device>

[0042] In some variations, the acousto-optic imaging system 101 may include a computing device 150 for processing and generating an image based on one or more optical responses of the optical sensors 120. In some embodiments, each optical sensor is coupled to one or more optical waveguides configured to propagate the one or more optical responses to one or more optical detectors. In some embodiments, the one or more detectors convert the one or more optical responses into electrical signals, which are then transmitted to the computing device 150. In some cases, one or more optical detectors may be included in the acousto-optic imaging system 101.

[0035]

[0043] In some embodiments, computing device 150 may include a memory, a communication interface, and a processor (not shown). The communication interface may communicate with various internal components of computing device 150 (e.g., memory, processor) or external components of computing device 150 (e.g., TransducerThe optical sensor 120 may transmit / receive data to / from the optical detector 110. The communication interface may receive electrical signals from the one or more optical detectors and transmit them to a memory and / or a processor. The memory may store data based on the electrical signals. The processor may include a hardware-based integrated circuit (IC) or any other suitable processing device configured to implement and / or execute a set of instructions or code, for example, to generate an image based on one or more optical responses.

[0036]

[0044] In some embodiments, the computing device 150 processes and generates an image based on changes in one or more optical responses of the optical sensor 120. Each optical response includes at least one spectral resonant feature that can be characterized / described by a full width at half maximum (FWHM) and / or a quality factor (Q factor) of the spectral resonant feature. The change can be a change in the amplitude of the one or more optical responses or a change in the resonant frequency of the one or more optical responses. Because the change can indicate the magnitude of each ultrasonic echo, the computing device 150 can calculate the magnitude of that ultrasonic echo at the location of the optical sensor 120 based on the change. Additionally or alternatively, the change can be due to a change in the effective refractive index of the optical sensor 120 due to a photoelastic effect on the optical sensor 120 upon receiving the ultrasonic echo. As a result of the change in the effective refractive index, the resonant frequency changes by a spectral shift. The optical sensor 120 is highly sensitive to the ultrasonic echo in the sense that the FWHM of at least one spectral feature is smaller than the spectral shift. Computing device 150 may further associate the magnitude of each ultrasound echo with a location of optical sensor 120. By repeating the above process in various manners (e.g., raster scanning, parallel processing, etc.), computing device 150 may map a set of mapped magnitudes to a set of locations to generate an image.

[0037] <Operation>

[0045] As previously mentioned, the acousto-optic imaging system 101 may be configured to perform ultrasound imaging across a wide range of frequencies. Transducer 110 (e.g., piezoelectric Transducer ) can be used to generate an ultrasonic signal (e.g., an ultrasonic pulse, an ultrasonic sine wave, etc.) having at least one fundamental frequency f. Transducer The optical sensor 120 may be used to detect ultrasound echoes corresponding to ultrasound signals at frequencies less than, equal to, and / or greater than the fundamental frequency f (e.g., WGM optical resonators with improved sensitivity and expanded bandwidth relative to 110). Thus, the incorporation of optical sensor 120 may enable the acousto-optic probes described herein to detect and generate images from harmonically related modes of the fundamental frequency f (e.g., including subharmonic and / or ultraharmonic and / or superharmonic and / or difference frequencies), as described further below. By enabling detection and image generation from such harmonically related frequencies, optical sensor 120 may significantly increase the resolution and contrast of medical ultrasound imaging achieved by acousto-optic imaging system 101.

[0038] <Basic Imaging>

[0046] In some variations, the acousto-optic imaging system 101 includes a corresponding send At least fundamental imaging (FI) can be performed, which is a form of ultrasound imaging based on reflected echoes having the same frequency as the fundamental frequency f of the ultrasound signal. send The fundamental frequency f of an ultrasound signal is often selected using a trade-off between penetration depth and spatial resolution. For example, for deep tissue imaging, the fundamental frequency f of the ultrasound probe may be determined so that the ultrasound signal can penetrate deeper into the tissue, but the resulting image will have lower spatial resolution. In another example for high-resolution imaging, the fundamental frequency f of the ultrasound probe may be determined so that sendThe wavelength of the ultrasound signal can be determined so that it can resolve detailed spatial features within tissue, but only at shallow tissue depths. send Fundamental imaging may have limited applications because frequency sacrifices either penetration depth or spatial resolution, but unlike conventional systems, the acousto-optic imaging system 101 can be readily configured to detect other specialized frequencies, additionally or alternatively, to improve both the penetration depth and spatial resolution of ultrasound imaging compared to fundamental imaging.

[0039] Harmonic, Superharmonic, and Ultraharmonic Imaging

[0047] In some variations, the acousto-optic imaging system 101 may perform tissue harmonic imaging (THI) as an alternative to or in addition to fundamental imaging. THI involves detection and imaging based on a frequency equal to 2f (the second harmonic frequency). Compared to fundamental frequency-based fundamental imaging (FI), THI produces fewer artifacts in the resulting image because harmonic waves occur primarily within the main beam rather than in side lobes, and thus harmonic images are less sensitive to clutter and off-axis scattering events. Additionally, because the harmonic field gradually increases (i.e., the generated harmonic wave energy increases with increasing depth), the effects of reverberation and near-field noise in images generated by THI may be reduced.

[0040]

[0048] In some variations, the acousto-optic imaging system 101 performs superharmonic imaging (SHI) as an alternative or addition to fundamental imaging and / or THI. SHI involves detecting at least Qf superharmonic frequencies, where Q is an integer greater than or equal to 3. Advantages of harmonic imaging include improved ultrasound imaging resolution, better signal-to-noise ratio (SNR), reduced speckle noise, and / or increased penetration depth.

[0041]

[0049] In some variations, the acousto-optic imaging system 101 may perform ultraharmonic imaging (UHI) as an alternative or in addition to fundamental imaging, THI, and / or SHI. UHI involves detecting ultraharmonic frequencies of at least Pf, where P is a non-integer number greater than 1 (e.g., a non-integer rational number greater than 1). Advantages of ultraharmonic imaging include improved ultrasound imaging resolution, better signal-to-noise ratio (SNR), reduced speckle noise, and / or increased penetration depth.

[0042]

[0050] Conventional ultrasound systems use conventional Transducer However, conventional methods do not benefit from the advantages of THI, SHI, and / or UHI due to their inherent limitations in bandwidth and sensitivity. Transducer The bandwidth limitation reduces (eliminates) the detection of higher frequencies. Furthermore, the sensitivity limitation reduces the energy intensity of ultrasonic echoes at higher harmonic frequencies, which is a problem in conventional ultrasonic transducers. Transducer In contrast, the acousto-optic imaging system 101 with the optical sensor 120 requires at least one optical sensor to perform all of the THI, SHI, and UHI without the drawbacks of conventional systems. Transducer 110 has an expanded bandwidth and improved sensitivity.

[0043] <Subharmonic Imaging>

[0051] In some variations, the acousto-optic imaging system 101 may perform subharmonic imaging as an alternative or addition to fundamental imaging, THI, and / or SHI. Subharmonic imaging employs a subharmonic frequency f / Q, where Q is an integer and f is the fundamental frequency. The use of subharmonic frequencies provides better positional resolution. Additionally, subharmonic imaging may provide improved blood-to-tissue contrast to clearly reveal vascular information from surrounding tissue, which is difficult to achieve with conventional ultrasound imaging systems. At least one Transducer With an expanded bandwidth and increased sensitivity relative to 110, the acousto-optic imaging system 101 with optical sensor 120 can collect / receive sufficient information from ultrasound echoes at subharmonic (lower) frequencies.

[0044] <Subtractive Tissue Harmonic Imaging>

[0052] In some variations, the acousto-optic imaging system 101 can perform differential tissue harmonic imaging (DTHI) as an alternative or in addition to fundamental imaging, THI, SHI, UHI, and / or subharmonic imaging. The acousto-optic imaging system 101 can perform differential tissue harmonic imaging (DTHI) at multiple fundamental frequencies f1, f2,...f n For example, k1f1+k2f2+k n f n One or more ultrasound images may be generated based on an arithmetic relationship between multiple fundamental frequencies, such as k1, k2, . . . k n is an integer. The use of DTHI frequencies can provide a variety of new and unexplored imaging modes, which can range from frequencies lower than subharmonic frequencies to frequencies higher than those used in SHI. Such a wideband frequency response is difficult to achieve with conventional ultrasound imaging systems. Therefore, the use of acousto-optic imaging system 101 with optical sensor 120 can provide imaging DTHI frequencies with various advantages, including higher resolution, better penetration, and fewer artifacts than potential FI, THI, SHI, UHI, and / or subharmonic imaging.

[0045]

[0053] In some embodiments, one or more Transducer 110 generates and / or transmits a set of ultrasound signals 111 including a first fundamental frequency f1 and a second fundamental frequency f2 (as shown in FIG. 3A) to a medium for imaging. send One or more Transducer110 may only detect a narrow bandwidth of harmonic frequencies relative to the first fundamental frequency and / or the second harmonic frequency (f2-f1 and 2f1 as shown in FIG. 3B), and therefore may not be able to detect useful imaging information from other DTHI-related frequencies (e.g., f2+f1 and 2f2). However, as shown in FIG. 3C, one or more optical sensors 120 may have a bandwidth that more broadly detects a selection of one or more linear combinations mf1+nf2, where m and n are integers and therefore mf1+nf2 is a positive number (as shown in FIG. 3C). Thus, the otherwise conventional Transducer Using the optical sensor 120 to detect frequencies (e.g., f2+f1 and 2f2) that cannot be detected by |f2+f1|, can significantly enhance ultrasound imaging capabilities. In other words, the sum and absolute difference of the first and second fundamental frequencies (|f2+f1| and |f2-f1|, respectively) are detectable for enhanced ultrasound imaging using the acousto-optic imaging system 101.

[0046]

[0054] For example, the first fundamental frequency f1 can be 2 MHz, the second fundamental frequency f2 can be 5 MHz, and m and n can be positive and negative integers 6 and −1. As a result, the linear combination of mf1+nf2 is 7 MHz, which is within the bandwidth of and can be detected by at least one optical sensor 120.

[0047]

[0055] For example, the first fundamental frequency f1 may be 3 MHz, the second fundamental frequency f2 may be 2.5 MHz, and m and n may both be positive integers 1 and 5. As a result, the linear combination of mf1+nf2 is 15.5 MHz, which is within the bandwidth of and will be detected by at least one optical sensor 120.

[0048]

[0056] It should be appreciated that any one of the first fundamental frequency f1 and the second fundamental frequency f2 may additionally or alternatively form the basis for fundamental imaging, harmonic imaging, superharmonic imaging, ultraharmonic imaging, and / or subharmonic imaging. For example, one or more optical sensors 120 may detect a selection of the first fundamental frequency f1 or all of its harmonically related frequencies, including f1 / Q, f1 / 2, f1, 2f1, and / or Rf1, where Q and R are positive numbers, including integers greater than 1. Additionally or alternatively, one or more optical sensors 120 may detect a selection of the second fundamental frequency f2 or all of its harmonically related frequencies, including f2 / S, f2 / 2, f2, 2f2, and / or Tf2, where S and T are positive numbers, including integers greater than 1.

[0049]

[0057] In some variations, Transducer 110 generates an ultrasonic signal 111 in a medium for acousto-optic imaging / send However, to detect acoustic echoes, Transducer In some variations, only the optical sensor 120 (rather than both 110 and optical sensor 120) may be used. The optical sensor 120 may have a bandwidth wide enough to detect select or all frequencies of the ultrasound echo 121, including f / Q, f / 2, f, 2f, 3f, 4f, 5f, and / or Rf, where Q and R are positive numbers including integers greater than 1 (as shown in FIG. 2). Thus, the optical sensor 120 can be used simultaneously for frequencies including subharmonic imaging, fundamental imaging (FI), tissue harmonic imaging (THI), superharmonic imaging (SHI), ultraharmonic imaging (UHI), and subharmonic modes. However, in some variations, TransducerSome or all of 110 may additionally be used to detect several frequencies. A subset of subharmonic imaging, FI, THI, SHI, and UHI modes may be selected depending on the clinical application. In some cases, the acousto-optic imaging system may simultaneously use only FI and THI for a first type of imaging, and subharmonic and SHI modes for a second type of imaging. Similarly, the acousto-optic imaging system may be used in only one of subharmonic imaging, fundamental imaging (FI), tissue harmonic imaging (THI), superharmonic imaging (SHI), or ultraharmonic imaging (UHI) modes at any given time depending on the clinical application.

[0050]

[0058] FIG. 4 shows an example spectral response of an optical sensor to an ultrasonic signal. The acousto-optic imaging system includes at least one optical sensor that is spectrally sensitive and has a broadband response. Transducer and at least one optical sensor (e.g., a whispering gallery mode (WGM) resonator). Transducer is the ultrasonic signal send The at least one optical sensor may be configured to receive ultrasonic echoes in response to the ultrasonic signals, the ultrasonic signals having a set intensity and a fundamental frequency f i (e.g., a first fundamental frequency f1, a second fundamental frequency f i The optical sensor may receive ultrasonic echoes at ultrasonic echo frequencies including a set of fundamental frequencies, a set of sub-harmonic frequencies of the set of fundamental frequencies, a set of super-harmonic frequencies of the set of fundamental frequencies, a set of ultra-harmonic frequencies of the set of fundamental frequencies, and / or a set of differential harmonics of the set of fundamental frequencies.

[0051]

[0059] In some embodiments, ultrasound contrast agents (e.g., gas microbubbles) can be introduced / injected into blood vessels to increase signal reflection and / or enhance contrast in ultrasound imaging. When insonified at a fundamental frequency, f, ultrasound contrast agents can also help better reflect incoming ultrasound signals and better generate nonlinear oscillations at harmonic and subharmonic frequencies. In some cases, tissue can also generate nonlinear oscillations at harmonic frequencies, but the ability to generate signals at subharmonic frequencies (e.g., f / 2) can be limited to ultrasound contrast agents. Because tissue does not generate subharmonic responses, subharmonic imaging has been used as a method to separate signals from ultrasound contrast agents while suppressing signals from surrounding tissues. However, signal suppression of surrounding tissues can reduce the sonographer's ability to see anatomical and tissue landmarks. Therefore, signal suppression is generally known to limit the use of subharmonic imaging as a primary imaging mode. The acousto-optic imaging system 101, using a wide bandwidth and high sensitivity sensor, can advantageously enable the use of subharmonic imaging in addition to the other imaging modalities described herein.

[0052]

[0060] Therefore, the optical sensor 120 detects ultrasonic waves. Transducer 110 or to detect ultrasonic frequencies in an ultrasound imaging system. Transducer110. One or more optical sensors 120 may have a bandwidth wide enough to detect all frequencies (f / M, . . . , f / 2, f, 2f, 3f, 4f, 5f, . . . , Nf), where M and N are positive numbers including integers greater than 1. Some or all of these frequencies may be used for ultrasound imaging. For example, one or more optical sensors 120 may be used simultaneously for subharmonic imaging, fundamental imaging, tissue harmonic imaging, ultraharmonic imaging, and / or superharmonic imaging for multiple dynamic imaging modes. Furthermore, one or more optical sensors 120 may be used for differential tissue harmonic imaging. Transducer This may overcome the bandwidth limitations of 110, thus enabling new imaging modes based on the combination of multiple fundamental frequencies (e.g., detection of additional f2+f1 and 2f2 frequencies, where f2+f1 are two different fundamental frequencies).

[0053]

[0061] In other words, by leveraging the broadband response of the optical sensor 120, the acousto-optic imaging system may enable imaging modes involving fundamental, subharmonic, superharmonic, ultraharmonic, and / or difference frequencies, including new superharmonic and difference-related frequencies, previously unattainable with conventional ultrasound imaging systems. Accordingly, the acousto-optic imaging systems described herein may overcome the bandwidth and sensitivity limitations of conventional acoustic imaging systems (e.g., medical ultrasound imaging systems).

[0054]

[0062] The foregoing description, for purposes of explanation, used specific terminology to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that specific details are not required to practice the present invention. Thus, the foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously, many modifications and variations are possible in light of the above teachings. The embodiments were chosen and described in order to explain the principles of the invention and its practical application, so that those skilled in the art will be able to utilize the invention and its various embodiments with various modifications as suited to the particular use contemplated. It is intended that the following claims and their equivalents define the scope of the invention.

Claims

1. at least one transducer configured to transmit an ultrasonic signal having a fundamental frequency f; at least one optical sensor configured to generate one or more optical responses upon receiving harmonic or subharmonic ultrasonic echoes corresponding to the transmitted ultrasonic signal; Equipped with the at least one optical sensor has a bandwidth ranging from at least f / M to Nf; An acousto-optic imaging system, wherein M and N are integers greater than one.

2. the at least one optical sensor is configured to generate at least a portion of the one or more optical responses upon receiving an ultrasonic echo having a superharmonic frequency of at least Qf; The system of claim 1 , wherein Q is an integer greater than or equal to 3.

3. 2. The system of claim 1, wherein the at least one optical sensor is configured to generate at least a portion of the one or more optical responses upon receiving ultrasonic echoes having a frequency of 2f or f.

4. the at least one optical sensor is configured to generate at least a portion of the one or more optical responses upon receiving ultrasonic echoes having an ultraharmonic frequency of at least Pf; The system of claim 1 , wherein P is a non-integer greater than one.

5. the at least one optical sensor is configured to generate at least a portion of the one or more optical responses upon receiving ultrasonic echoes having an ultraharmonic frequency of at least Pf; 5. The system of claim 4, wherein P is a non-integer rational number greater than one.

6. the at least one optical sensor is configured to generate at least a portion of the one or more optical responses upon receiving ultrasonic echoes having subharmonic frequencies of f / R; The system of claim 1 , wherein R is a number greater than one.

7. The fundamental frequency f is a first fundamental frequency f １ and the at least one transducer has a second fundamental frequency f ２ The system of claim 1 , configured to generate a second ultrasonic signal having:

8. The at least one optical sensor may include one or more linear combinations nf １ +mf ２ and configured to generate at least a portion of the one or more optical responses upon receiving an ultrasonic echo corresponding to a frequency of n and m are nf １ +mf ２ 8. The system of claim 7, wherein is an integer such that is a positive number.

9. The system of claim 8 , wherein n and m are positive integers.

10. The system of claim 1 , further comprising a computer-readable medium storing instructions for generating an image based on the one or more optical responses of the at least one optical sensor.

11. The system of claim 1 , further comprising a computer-readable medium storing instructions for generating an image based on a change in the one or more optical responses of the at least one optical sensor.

12. The computer-readable medium comprises: calculating a magnitude of each ultrasonic echo at the at least one optical sensor based on the variation; and converting the magnitude of each ultrasound echo into a pixel value for display; The system of claim 11 , further storing instructions to:

13. the change represents a spectral shift; The system of claim 11 , wherein each optical response includes at least one spectral resonance feature with a full width at half maximum (FWHM) smaller than the spectral shift.

14. 10. The system of claim 1, wherein the at least one transducer comprises at least one of a piezoelectric transducer, a capacitive micro-ultrasound transducer (CMUT), a polymer thick film (PTF) transducer, an optoacoustic transducer, and a piezoelectric micro-ultrasound transducer (PMUT).

15. The system of claim 1 , wherein the at least one optical sensor is coupled to one or more optical waveguides configured to propagate the one or more optical responses to one or more optical detectors.

16. The system of claim 1 , wherein the at least one optical sensor comprises a closed loop of material that is optically transparent to the one or more optical responses.

17. 10. The system of claim 1, wherein the at least one optical sensor is configured to have an effective refractive index and wall thickness that allows propagation of a set of whispering gallery modes (WGMs) in the at least one optical sensor.

18. 20. The system of claim 17, wherein the at least one optical sensor is embedded in a polymer structure with an effective refractive index lower than the effective refractive index of the at least one optical sensor.

19. 20. The system of claim 17, wherein the effective refractive index of the at least one optical sensor changes due to a photoelastic effect of the at least one optical sensor upon receiving the harmonic or subharmonic ultrasonic echoes.

20. transmitting an ultrasonic signal into a medium via at least one transducer having a fundamental frequency f; generating one or more optical responses via at least one optical sensor upon receiving harmonic or subharmonic ultrasonic echoes corresponding to the transmitted ultrasonic signals; the at least one optical sensor has a bandwidth ranging from at least f / M to Nf; A method for acousto-optic imaging, wherein M and N are integers greater than one.

21. the at least one optical sensor is configured to generate at least a portion of the one or more optical responses upon receiving an ultrasonic echo having a superharmonic frequency of at least Qf; 21. The method of claim 20, wherein Q is an integer of 3 or greater.

22. 21. The method of claim 20, wherein the at least one optical sensor is configured to generate at least a portion of the one or more optical responses upon receiving ultrasonic echoes having a frequency of 2f or f.

23. the at least one optical sensor is configured to generate at least a portion of the one or more optical responses upon receiving ultrasonic echoes having an ultraharmonic frequency of at least Pf; 21. The method of claim 20, wherein P is a non-integer greater than 1.

24. the at least one optical sensor is configured to generate at least a portion of the one or more optical responses upon receiving ultrasonic echoes having an ultraharmonic frequency of at least Pf; 24. The method of claim 23, wherein P is a non-integer rational number greater than 1.

25. the at least one optical sensor is configured to generate at least a portion of the one or more optical responses upon receiving ultrasonic echoes having subharmonic frequencies of f / R; 21. The method of claim 20, wherein R is an integer of 2 or greater.

26. The fundamental frequency f is a first fundamental frequency f １ and the at least one transducer has a second fundamental frequency f ２ 21. The method of claim 20, further comprising generating a second ultrasonic signal having:

27. The at least one optical sensor may include one or more linear combinations nf １ +mf ２ and configured to generate at least a portion of the one or more optical responses upon receiving an ultrasonic echo corresponding to a frequency of n and m are nf １ +mf ２ 27. The method of claim 26, wherein is an integer such that is a positive number.

28. 28. The method of claim 27, wherein n and m are positive integers.

29. generating, via a computer-readable medium, an image based on the one or more optical responses of the at least one optical sensor; 21. The method of claim 20, further comprising:

30. generating, via a computer-readable medium, an image based on changes in the one or more optical responses of the at least one optical sensor; 21. The method of claim 20, further comprising:

31. calculating, via a computer-readable medium, a magnitude of each ultrasonic echo at the at least one optical sensor based on the variation; and converting, via a computer readable medium, the magnitude of each ultrasound echo into a pixel value for display; 31. The method of claim 30, further comprising:

32. 31. The method of claim 30, wherein the change indicates a spectral shift, and each optical response includes at least one spectral resonance feature with a full width at half maximum (FWHM) that is less than the spectral shift.

33. 21. The method of claim 20, wherein the at least one transducer comprises at least one of a piezoelectric transducer, a capacitive micro-ultrasound transducer (CMUT), a polymer thick film (PTF) transducer, an optoacoustic transducer, and a piezoelectric micro-ultrasound transducer (PMUT).

34. 21. The method of claim 20, wherein the at least one optical sensor is coupled to one or more optical waveguides configured to propagate the one or more optical responses to one or more optical detectors.

35. 21. The method of claim 20, wherein the at least one optical sensor comprises a closed loop of material that is optically transparent to the one or more optical responses.

36. 21. The method of claim 20, wherein the at least one optical sensor is configured to have an effective refractive index and wall thickness that allows propagation of a set of whispering gallery modes (WGMs) in the at least one optical sensor.

37. 37. The method of claim 36, wherein the at least one optical sensor is embedded in a polymer structure with an effective refractive index lower than the effective refractive index of the at least one optical sensor.

38. 37. The method of claim 36, wherein the effective refractive index of the at least one optical sensor changes due to a photoelastic effect upon receiving the harmonic or subharmonic ultrasonic echoes.

39. The method of claim 20 , wherein the medium is a nonlinear medium.

40. 21. The method of claim 20, wherein the medium is biological tissue.

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