Mixed Ultrasonic Transducer Array

Abstract

Providing a mixed ultrasonic transducer array The present disclosure relates generally to the field of ultrasound, and more particularly to methods and devices for enabling ultrasound transduction using a mixed array including an array of optical sensors and other transducers. The ultrasound device may include an ultrasound transducer array including one or more array elements of a first type and one or more array elements of a second type different from the first type. The first type may include a transducer configured to transmit acoustic waves. The second type may include an optical sensor. The first and second types of array elements are configured to detect acoustic echoes corresponding to the transmitted acoustic waves.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Patent Application No. 63 / 029,044, filed May 22, 2020, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates generally to the field of ultrasound, and more particularly to methods and devices that enable ultrasound transduction using mixed arrays, including arrays of optical sensors and other transducers. [Background technology]

[0003] Ultrasound transducers are used in a variety of industries, including medical imaging and diagnostics, due to their many advantages. For example, ultrasound transduction utilizes ultrasound signals that have significant penetration depth. Furthermore, ultrasound imaging is known to be an advantageous non-invasive form of imaging because it is based on non-ionizing radiation.

[0004] Various known ultrasound transducers used in ultrasound imaging have many drawbacks. For example, some ultrasound transducers are made from piezoelectric materials such as lead zirconate titanate (PZT). However, the 6 dB bandwidth of PZT materials is generally limited to approximately 70%. While certain composite PZT materials have shown slight increases in bandwidth, they still only achieve a maximum bandwidth of approximately 80%. As another example, single-crystal materials are increasingly being used to improve the performance of ultrasound 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 micromachined ultrasound transducer (CMUT) probes that can extend bandwidth. However, CMUT probes lack sensitivity or reliability. CMUT probes also have several operational limitations. For example, CMUT probes are nonlinear transducers and therefore generally unsuitable for harmonic imaging. Furthermore, CMUT probes require additional bias voltages for proper operation. Therefore, new and improved devices and methods for ultrasound transduction are needed. Summary of the Invention [Means for solving the problem]

[0005] Generally, in some embodiments, an apparatus for imaging a target may include an ultrasonic transducer array including one or more array elements of a first type and one or more array elements of a second type different from the first type. The first type may be a transducer (e.g., a piezoelectric transducer or a capacitive micromachined ultrasonic transducer (CMUT)) configured to transmit acoustic waves, and the second type may be an optical sensor (e.g., an optical resonator, an interference-based optical sensor such as an optical interferometer, etc.). The first and second types of array elements are configured to detect acoustic echoes corresponding to the transmitted acoustic waves.

[0006] In some variations, the ultrasound transducer array may include one or more rows in the elevation dimension. The ultrasound transducer array may include, for example, odd numbered rows or even numbered rows.

[0007] In some variations, the one or more array elements of the first type and the one or more array elements of the second type are in alternating rows. In some configurations, at least some of the array elements of the first type may be in a center row. In some configurations, at least some of the array elements of the second type may be in a center row.

[0008] The array elements may be arranged in an array with various suitable spacings from one another. For example, in some variations, at least one row has a pitch (e.g., in the row) greater than half the wavelength of the center frequency of the transducer. In some variations, at least one row may have a pitch (e.g., in the row) less than half the wavelength of the center frequency of the transducer. In some variations, the array may include rows with equal pitches in the lateral dimensions. Alternatively, in some variations, the ultrasound transducer array may include at least one row with a first pitch in the lateral dimension and at least one row with a second pitch in the lateral dimension that is different from the first pitch. For example, in some variations, the ultrasound transducer array may include an inner row with a first pitch and a row adjacent to the inner row with a second pitch, the second pitch being greater than the first pitch. In some variations, an inner row having a first pitch may include one or more array elements of a first type, and a row adjacent to the inner row having a second pitch may include one or more array elements of a second type.

[0009] Furthermore, in some variations, the ultrasonic transducer array may include at least one row having a variable pitch in a lateral dimension, such that the pitch varies within the row. For example, the at least one row having a variable pitch may include a central region having a first pitch and lateral regions adjacent to the central region having a second pitch greater than the first pitch. In some variations, the ultrasonic transducer array may include a first row having a first variable pitch pattern in the lateral dimension and a second row having a second variable pitch pattern in the lateral dimension, where the second variable pitch pattern may be different from the first variable pitch pattern. For example, in some variations, the ultrasonic transducer array may include an inner row having a first variable pitch pattern including one or more array elements of a first type and a row adjacent to the inner row having a second variable pitch pattern including one or more array elements of a second type.

[0010] The first and second types of array elements may be arranged in different rows of the ultrasonic transducer array. For example, in some variations, the ultrasonic transducer array may include at least one row including at least one array element of the first type and at least one array element of the second type. The at least one row including at least one array element of the first type and at least one array element of the second type may be a center row. In some variations, the center row has a single array element of the second type. The single array element of the second type may include an optical sensor approximately equal to or smaller than the wavelength of the transmitted acoustic wave.

[0011] In some variations, the first and second types of array elements may be arranged in the same row of the ultrasound transducer array. For example, in some variations, the ultrasound transducer array may include a central row including a set of array elements of the first type and a set of array elements of the second type. The second type of array elements may be sized, for example, approximately equal to or smaller than the wavelength of the transmitted acoustic waves. In some variations, the ultrasound transducer array may include two or more rows, each including at least one array element of the first type and at least one array element of the second type. The second type of array elements may be spatially distributed in a regular pattern. The second type of array elements may be spatially distributed in an irregular pattern. In some variations, the ultrasound transducer array may include at least 31 rows, and at least some of the 31 rows may include at least one array element of the first type and at least one array element of the second type. In some variations, the ultrasound transducer array may include a single row, the single row including at least one array element of a first type and at least one array element of a second type.

[0012] In some variations, the ultrasound transducer array may include a set of subapertures. The set of subapertures may include a first subaperture and a second subaperture, where the first subaperture includes a greater number of rows than the second subaperture. In some variations, the first subaperture may be a central subaperture, and the second subaperture may be adjacent to the central subaperture. In some variations, at least one subaperture may include at least one array element of a first type and / or at least one array element of a second type.

[0013] In some variations, the ultrasound transducer array may include a first set of array elements of a first type and a second set of elements of a second type, where the first set of array elements and the second set of array elements are each in a sparse array configuration, and the spatial distribution of the first set of array elements may be different from the spatial distribution of the second set of array elements.

[0014] The ultrasound transducer array may be on a substrate or other suitable surface. In some variations, the ultrasound transducer array may be on a planar surface. In some variations, the ultrasound transducer array may be on a curved surface. The curved surface may be a parabola, hyperbola, or ellipse.

[0015] In some variations, the ultrasound transducer array may include at least one annular array element. The ultrasound array may include a second type of circular array element concentric with the at least one annular array element. In some variations, the at least one annular array element may be of the first type.

[0016] The ultrasound transducer array can be a one-dimensional (1D) array, a one-and-a-half-dimensional (1.25D) array, a one-and-a-half-dimensional (1.5D) array, a one-and-a-half-dimensional (1.75D) array, or a two-dimensional (2D) array.

[0017] In some variations, one or more of the array elements is an optical sensor embedded in the 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 transmit the set of optical signals in response to acoustic echoes. The present invention provides, for example, the following. (Item 1) 1. An apparatus for imaging a target, comprising: 1. An ultrasound transducer array, comprising: one or more array elements of a first type, said first type transmitting acoustic waves; one or more array elements of a first type being transducers configured to an ultrasonic transducer array comprising one or more array elements of a second type different from the first type, the second type being an optical sensor; The apparatus, wherein the array elements of the first and second types are configured to detect acoustic echoes corresponding to the transmitted acoustic waves. (Item 2) Item 10. The apparatus of item 1, wherein the ultrasound transducer array includes one or more rows in the elevation dimension. (Item 3) Item 3. The apparatus of item 2, wherein the ultrasound transducer array includes an odd number of rows. (Item 4) Item 3. The apparatus of item 2, wherein the ultrasound transducer array includes an even number of rows. (Item 5) Item 3. The apparatus of item 2, wherein the one or more array elements of the first type and the one or more array elements of the second type are in alternating rows. (Item 6) Item 6. The apparatus of item 5, wherein at least some of the array elements of the first type form a central row. (Item 7) Item 6. The apparatus of item 5, wherein at least some of the array elements of the second type form a central row. (Item 8) Item 3. The device of item 2, wherein the ultrasonic transducer array includes at least one row having a pitch greater than half the wavelength of the center frequency of the transducer. (Item 9) Item 3. The device of item 2, wherein the ultrasonic transducer array includes at least one row having a pitch that is less than or equal to half the wavelength of the center frequency of the transducer. (Item 10) Item 3. The device of item 2, wherein the rows have equal pitch in the lateral dimension. (Item 11) Item 3. The apparatus of item 2, wherein the ultrasound transducer array includes at least one row having a first pitch in a lateral dimension and at least one row having a second pitch in the lateral dimension that is different from the first pitch. (Item 12) Item 12. The apparatus of item 11, wherein the ultrasound transducer array includes an inner row having the first pitch and a row adjacent to the inner row having the second pitch, the second pitch being greater than the first pitch. (Item 13) Item 13. The apparatus of item 12, wherein the inner row includes one or more array elements of the first type, and the row adjacent to the inner row includes one or more array elements of the second type. (Item 14) Item 3. The device of item 2, wherein the ultrasound array includes at least one row having a variable pitch in a lateral dimension. (Item 15) Item 15. The device of item 14, wherein the at least one row having a variable pitch includes a central region having a first pitch and lateral regions adjacent the central region having a second pitch greater than the first pitch. (Item 16) Item 16. The apparatus of item 15, wherein the ultrasonic transducer array includes a first row having a first variable pitch pattern in a lateral dimension and a second row having a second variable pitch pattern in the lateral dimension, the second variable pitch pattern being different from the first variable pitch pattern. (Item 17) Item 17. The apparatus of item 16, wherein the ultrasound transducer array includes an inner row including one or more array elements of the first type and a row adjacent to the inner row including one or more array elements of the second type. (Item 18) Item 3. The device of item 2, wherein the ultrasound transducer array includes at least one row including at least one array element of the first type and at least one array element of the second type. (Item 19) Item 19. The apparatus of item 18, wherein the at least one row including at least one array element of the first type and at least one array element of the second type is a central row. (Item 20) 20. The apparatus of claim 19, wherein the central row has a single array element of the second type. (Item 21) 21. The apparatus of claim 20, wherein the single array element of the second type is an optical sensor approximately equal to or smaller than the wavelength of the transmitted acoustic wave. (Item 22) 20. The apparatus of claim 19, wherein the central row includes a plurality of array elements of the first type and a plurality of array elements of the second type. (Item 23) Item 23. The apparatus of item 22, wherein the array elements of the second type are approximately equal to or smaller than the wavelength of the transmitted acoustic wave. (Item 24) Item 19. The apparatus of item 18, wherein the ultrasound transducer array includes two or more rows, each of the two or more rows including at least one array element of the first type and at least one array element of the second type. (Item 25) 25. The apparatus of claim 24, wherein the array elements of the second type are spatially distributed in a regular pattern. (Item 26) 25. The apparatus of claim 24, wherein the array elements of the second type are spatially distributed in an irregular pattern. (Item 27) Item 25. The apparatus of item 24, wherein the ultrasound transducer array includes at least 31 rows, and at least some of the 31 rows include at least one array element of the first type and at least one array element of the second type. (Item 28) Item 19. The apparatus of item 18, wherein the ultrasound transducer array includes a single row, the single row including at least one array element of the first type and at least one array element of the second type. (Item 29) Item 10. The device of item 1, wherein the ultrasound transducer array includes a plurality of sub-apertures. (Item 30) Item 30. The apparatus of item 29, wherein the plurality of subapertures includes a first subaperture and a second subaperture, the first subaperture including a greater number of rows than the second subaperture. (Item 31) Item 31. The apparatus of item 30, wherein the first subaperture is a central subaperture and the second subaperture is adjacent to the central subaperture. (Item 32) 30. The apparatus of claim 29, wherein each sub-aperture includes at least one array element of the first type. (Item 33) Item 33. The apparatus of item 32, wherein each sub-aperture further comprises at least one array element of the second type. (Item 34) Item 10. The apparatus of item 1, wherein the ultrasound transducer array includes a first plurality of array elements of the first type and a second plurality of elements of the second type, and the first plurality of array elements and the second plurality of array elements are each in a sparse array configuration. (Item 35) Item 35. The apparatus of item 34, wherein the spatial distribution of the first plurality of array elements is different from the spatial distribution of the second plurality of array elements. (Item 36) Item 10. The device of item 1, wherein the ultrasound transducer array is on a plane. (Item 37) Item 10. The device of item 1, wherein the ultrasound transducer array is on a curved surface. (Item 38) Item 38. The apparatus of item 37, wherein the curved surface comprises a quadratic curve. (Item 39) Item 39. The apparatus of item 38, wherein the quadratic curve is a parabola, hyperbola, or elliptic curve. (Item 40) Item 38. The apparatus of item 37, wherein the curved surface comprises a circular curve. (Item 41) Item 10. The device of item 1, wherein the ultrasound transducer array includes at least one annular array element. (Item 42) Item 42. The apparatus of item 41, wherein the ultrasound array includes the second type of circular array element concentric with the at least one annular array element. (Item 43) Item 42. The apparatus of item 41, wherein the at least one annular array element is of the first type. (Item 44) Item 1, wherein at least a portion of the array elements of the first type include at least one piezoelectric transducer, single crystal material transducer, piezoelectric micromachined ultrasonic transducer (PMUT), or capacitive micromachined ultrasonic transducer (CMUT). (Item 45) Item 10. The device of item 1, wherein the ultrasound transducer array is a one-dimensional (1D) array. (Item 46) The ultrasonic transducer array is a 1.25 dimensional (1.25D) array. The apparatus described in item 1. (Item 47) Item 10. The device of item 1, wherein the ultrasound transducer array is a 1.5 dimensional (1.5D) array. (Item 48) Item 10. The device of item 1, wherein the ultrasound transducer array is a 1.75 dimensional (1.75D) array. (Item 49) Item 10. The device of item 1, wherein the ultrasound transducer array is a two-dimensional (2D) array. (Item 50) Item 10. The device of item 1, wherein the one or more array elements are optical sensors embedded in a polymer structure. (Item 51) Item 1 , the apparatus of item 1, wherein the optical sensor is optically coupled to an optical fiber to transmit a set of optical signals to a photodetector. (Item 52) Item 52. The apparatus of item 51, wherein the optical sensor is configured to transmit the set of optical signals in response to the acoustic echoes. (Item 53) Item 10. The apparatus of item 1, wherein the optical sensor is an interference-based optical sensor. (Item 54) Item 54. The apparatus of item 53, wherein the optical sensor comprises an optical resonator or an optical interferometer. (Item 55) Item 55. The apparatus of item 54, wherein the optical sensor comprises an optical resonator that is a whispering gallery mode (WGM) optical resonator, a microbubble optical resonator, a microsphere resonator, a microtoroid resonator, a microring resonator, or a microdisk optical resonator. (Item 56) 1. A method of ultrasonic transduction comprising: transmitting acoustic waves using an ultrasonic probe, the ultrasonic probe comprising an ultrasonic transducer array having one or more array elements of a first type and one or more array elements of a second type different from the first type; receiving acoustic echoes in response to the acoustic waves using the one or more array elements of the first type and the one or more array elements of the second type; The method wherein the one or more array elements of the second type are optical sensors. (Item 57) Item 57. The method of item 56, wherein the ultrasound transducer array includes one or more rows in the elevation dimension. (Item 58) Item 58. The method of item 57, wherein the ultrasound transducer array includes an odd number of rows. (Item 59) Item 58. The method of item 57, wherein the ultrasound transducer array includes an even number of rows. (Item 60) Item 58. The method of item 57, wherein the one or more array elements of the first type and the one or more array elements of the second type are in alternating rows. (Item 61) Item 61. The method of item 60, wherein at least some of the array elements of the first type form a central row. (Item 62) Item 61. The method of item 60, wherein at least some of the array elements of the second type form a central row. (Item 63) Item 58. The method of item 57, wherein the ultrasound transducer array includes at least one row having a pitch less than half the wavelength of the center frequency of the transducer. (Item 64) Item 58. The method of item 57, wherein the ultrasound transducer array includes at least one row having a pitch equal to or less than half the wavelength of the center frequency of the transducer. (Item 65) Item 58. The method of item 57, wherein the rows have equal pitch in the lateral dimension. (Item 66) Item 58. The method of item 57, wherein the ultrasound transducer array includes at least one row having a first pitch in a lateral dimension and at least one row having a second pitch in the lateral dimension that is different from the first pitch. (Item 67) Item 67. The method of item 66, wherein the ultrasound transducer array includes an inner row having the first pitch and a row adjacent to the inner row having the second pitch, the second pitch being greater than the first pitch. (Item 68) Item 68. The method of item 67, wherein the inner row includes one or more array elements of the first type, and the row adjacent to the inner row includes one or more array elements of the second type. (Item 69) Item 58. The method of item 57, wherein the ultrasound array includes at least one row having a variable pitch in a lateral dimension. (Item 70) Item 70. The method of item 69, wherein the at least one row having a variable pitch includes a central region having a first pitch and lateral regions adjacent the central region having a second pitch greater than the first pitch. (Item 71) Item 71. The method of item 70, wherein the ultrasonic transducer array includes a first row having a first variable pitch pattern in a lateral dimension and a second row having a second variable pitch pattern in the lateral dimension, the second variable pitch pattern being different from the first variable pitch pattern. (Item 72) Item 72. The method of item 71, wherein the ultrasound transducer array includes an inner row including one or more array elements of the first type and a row adjacent to the inner row including one or more array elements of the second type. (Item 73) Item 58. The method of item 57, wherein the ultrasound transducer array includes at least one row including at least one array element of the first type and at least one array element of the second type. (Item 74) Item 74. The method of item 73, wherein the at least one row containing at least one array element of the first type and at least one array element of the second type is a central row. (Item 75) Item 74. The method of item 73, wherein the center row has a single array element of the second type. (Item 76) Item 74. The method of item 73, wherein the single array element of the second type is an optical sensor approximately equal to or smaller than the wavelength of the transmitted acoustic wave. (Item 77) Item 75. The method of item 74, wherein the center row includes a plurality of array elements of the first type and a plurality of array elements of the second type. (Item 78) Item 78. The method of item 77, wherein the array elements of the second type are approximately equal to or smaller than the wavelength of the transmitted acoustic wave. (Item 79) Item 74. The method of item 73, wherein the ultrasound transducer array includes two or more rows, each of the two or more rows including at least one array element of the first type and at least one array element of the second type. (Item 80) Item 72. The method of item 71, wherein the array elements of the second type are spatially distributed in a regular pattern. (Item 81) Item 72. The method of item 71, wherein the array elements of the second type are spatially distributed in an irregular pattern. (Item 82) Item 72. The method of item 71, wherein the ultrasound transducer array includes at least 31 rows, and at least some of the 31 rows include at least one array element of the first type and at least one array element of the second type. (Item 83) Item 57. The method of item 56, wherein the ultrasound transducer array includes a single row, the single row including at least one array element of the first type and at least one array element of the second type. (Item 84) Item 57. The method of item 56, wherein the ultrasound transducer array includes a plurality of sub-apertures. (Item 85) Item 85. The method of item 84, wherein the plurality of subapertures includes a first subaperture and a second subaperture, the first subaperture including a greater number of rows than the second subaperture. (Item 86) Item 86. The method of item 85, wherein the first subaperture is a central subaperture and the second subaperture is adjacent to the central subaperture. (Item 87) Item 85. The method of item 84, wherein each sub-aperture includes at least one array element of the first type. (Item 88) Item 88. The method of item 87, wherein each sub-aperture further comprises at least one array element of the second type. (Item 89) Item 57. The method of item 56, wherein the ultrasound transducer array includes a first plurality of array elements of the first type and a second plurality of elements of the second type, the first plurality of array elements and the second plurality of array elements each in a sparse array configuration. (Item 90) Item 90. The method of item 89, wherein the spatial distribution of the first plurality of array elements is different from the spatial distribution of the second plurality of array elements. (Item 91) Item 57. The method of item 56, wherein the ultrasound transducer array is on a plane. (Item 92) Item 57. The method of item 56, wherein the ultrasound transducer array is on a curved surface. (Item 93) Item 93. The method of item 92, wherein the curved surface comprises a quadratic curve. (Item 94) Item 94. The method according to item 93, wherein the quadratic curve is a parabola, a hyperbola, or an elliptic curve. (Item 95) Item 93. The method of item 92, wherein the curved surface comprises a circular curve. (Item 96) Item 57. The method of item 56, wherein the ultrasound transducer array includes at least one annular array element. (Item 97) Item 97. The method of item 96, wherein the ultrasound array includes a second type of circular array element concentric with the at least one annular array element. (Item 98) Item 98. The method of item 97, wherein the at least one annular array element is of the first type. (Item 99) Item 57. The method of item 56, wherein at least some of the array elements of the first type comprise at least one piezoelectric transducer, single crystal material transducer, piezoelectric micromachined ultrasonic transducer (PMUT), or capacitive micromachined ultrasonic transducer (CMUT). (Item 100) Item 57. The method of item 56, wherein the ultrasound transducer array is a one-dimensional (1D) array. (Item 101) Item 57. The method of item 56, wherein the ultrasound transducer array is a 1.25 dimensional (1.25D) array. (Item 102) Item 57. The method of item 56, wherein the ultrasound transducer array is a 1.5 dimensional (1.5D) array. (Item 103) Item 57. The method of item 56, wherein the ultrasound transducer array is a 1.75 dimensional (1.75D) array. (Item 104) Item 57. The method of item 56, wherein the ultrasound transducer array is a two-dimensional (2D) array. (Item 105) Item 57. The method of item 56, wherein the one or more array elements of the second type are optical sensors embedded in a polymer structure. (Item 106) Item 57. The method of item 56, wherein the optical sensor is optically coupled to an optical fiber for transmitting a set of optical signals to a photodetector. (Item 107) Item 107. The method of item 106, wherein the optical sensor is configured to transmit the set of optical signals in response to the acoustic echoes. (Item 108) Item 57. The method of item 56, wherein the optical sensor is an interference-based optical sensor. (Item 109) Item 109. The method of item 108, wherein the optical sensor includes at least one of an optical resonator and an optical interferometer. (Item 110) Item 110. The method of item 109, wherein the optical sensor comprises an optical resonator that is a whispering gallery mode (WGM) optical resonator, a microbubble optical resonator, a microsphere resonator, a microtoroid resonator, a microring resonator, or a microdisk optical resonator. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a block diagram of an exemplary ultrasound imaging system having a mixed ultrasound transducer array. [Figure 2] FIG. 1 is a schematic diagram of an exemplary mixed ultrasound transducer array. [Figure 3] FIG. 1 is a schematic diagram of an exemplary mixed ultrasound transducer array. [Figure 4] FIG. 1 is a schematic diagram of an exemplary mixed ultrasound transducer array. [Figure 5] FIG. 1 is a schematic diagram of an exemplary mixed ultrasound transducer array. [Figure 6] FIG. 1 is a schematic diagram of an exemplary mixed ultrasound transducer array. [Figure 7] FIG. 1 is a schematic diagram of an exemplary mixed ultrasound transducer array. [Figure 8] FIG. 1 is a schematic diagram of an exemplary mixed ultrasound transducer array. [Figure 9] FIG. 1 is a schematic diagram of an exemplary mixed ultrasound transducer array. [Figure 10] FIG. 1 is a schematic diagram of an exemplary mixed ultrasound transducer array. [Figure 11] FIG. 1 is a schematic diagram of an exemplary 1D mixed ultrasound transducer array. [Figure 12] FIG. 1 is a schematic diagram of an exemplary 2D mixed ultrasound transducer array. [Figure 13] FIG. 1 is a schematic diagram of an exemplary 2D mixed ultrasound transducer array. [Figure 14] FIG. 1 is a schematic diagram of an exemplary annular mixing ultrasonic transducer array. [Figure 15]FIG. 1 is a schematic diagram of an exemplary mixed ultrasound transducer array. [Figure 16] 1 illustrates an elevation beam pattern of an exemplary 1D mixed ultrasound transducer array. [Figure 17] 1 illustrates elevation beam patterns for an exemplary 1D and 1.5D mixed ultrasound transducer array. [Figure 18] FIG. 1 illustrates an exemplary beam pattern. DETAILED DESCRIPTION OF THE INVENTION

[0019] Non-limiting examples of various aspects and variations of the present invention are described herein and illustrated in the accompanying drawings.

[0020] Described herein is an ultrasound probe having a mixed ultrasound transducer array including multiple different types of array elements. The mixed array described herein includes one or more array elements of a first type and one or more array elements of a second type (e.g., optical sensor, interference-based optical sensor, optical resonator, optical interferometer, etc.) different from the first type. For example, an optical sensor, such as a WGM optical resonator, may have high sensitivity and wide bandwidth in receiving ultrasound signals compared to other types of ultrasound sensors. One or more array elements (e.g., transducers) of the first type may be used to form a first image. In parallel, one or more array elements (e.g., optical sensors) of the second type may be used to detect acoustic echoes that can be used to form a second image. The second image generated by the high-sensitivity, wide-bandwidth optical sensor may be used independently or combined with the first image to form a further improved image. Due to the high sensitivity and wide bandwidth of the optical sensor, the image generated by the optical sensor may have improved spatial resolution, improved penetration depth, improved signal-to-noise ratio (SNR), improved tissue harmonic imaging, and / or improved Doppler sensitivity.

[0021] The optical sensors described herein may include interference-based optical sensors such as optical resonators, optical interferometers, etc. The optical resonators may include, for example, whispering galley mode (WGM) optical resonators, microbubble optical resonators, microsphere resonators, microtoroid resonators, microring resonators, microdisk optical resonators, and / or the like.

[0022] An optical resonator may include a closed loop of a transparent medium that allows light of some allowed frequencies to propagate continuously within the closed loop and may allow light energy of the allowed frequencies to accumulate within the closed loop. For example, the optical resonator may allow propagation of whispering gallery modes (WGMs) that travel along the concave surface of the optical resonator and correspond to the allowed frequencies to circulate around the resonator. Each mode from the WGMs corresponds to the propagation of light of a frequency from the allowed frequencies of light. The allowed frequencies of light and the Q-factor of the optical resonator 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.

[0023] The optical interferometer may include a Mach-Zehnder interferometer, a Michelson interferometer, a Fabry-Perot interferometer, a Sagnac interferometer, and / or the like. For example, a Mach-Zehnder interferometer may include two nearly identical optical paths (e.g., fiber, on-chip silicon waveguides, etc.) that are acoustically tuned (e.g., by acoustic wave-induced physical motion, acoustic wave-induced refractive index modulation, etc.) to produce a distribution of optical power at the output of the Mach-Zehnder interferometer, and thus detect the presence or magnitude of the acoustic wave.

[0024] As further described herein, optical sensors can be coupled to the external world to receive and transmit light, and can be practically useful (e.g., for ultrasound imaging or other transduction applications in acousto-optical systems). Acousto-optical systems based on optical sensors can directly measure ultrasound waves via the photoelastic effect and / or physical deformation of the resonator in response to ultrasound waves (e.g., ultrasound echoes). For example, in the presence of ultrasound (or any pressure), WGMs moving through an optical resonator can undergo a spectral shift caused by changes in the refractive index and shape of the optical resonator. The spectral changes can be easily monitored and analyzed in spectral regions and in the optical transmission intensity to and from the optical resonator. Furthermore, additional spatial and other information can be derived by monitoring and analyzing the shifting WGMs between multiple optical resonators. An exemplary mixed ultrasound array is described herein.

[0025] Mixed array dimensions A mixed ultrasound transducer array as described herein may have a variety of dimensions. For example, a mixed array may be configured for operation in a one-dimensional (1D) configuration, a 1.25-dimensional (1.25D) array configuration, a 1.5-dimensional (1.5D) array configuration, a 1.75-dimensional (1.75D) array configuration, or, as described in more detail below, a two-dimensional (2D) array configuration. In general, the size of an ultrasound transducer array relates to the range of elevation beamwidths (or elevation beam slice thicknesses) achievable when imaging with the ultrasound transducer array, as well as the degree of control the system provides over the elevation beam aperture size, focus, and / or steering across the imaging field of view (e.g., across the imaging depth) of the transducer array. A 1D array has only one row of elements in the elevation dimension and a fixed elevation aperture size. A 1.25D array has multiple rows of elements in the elevation dimension, a variable elevation aperture size, but a fixed elevation focus via an acoustic lens. A 1.5D array has multiple rows of elements in the elevation dimension, a variable elevation aperture size, and a variable elevation focus with electronic delay control. A 1.75D array is a 1.5D array with additional elevation beam steering capability. A 2D array has a large number of elements in both the lateral and elevation dimensions to meet minimum pitch requirements for large beam steering angles.

[0026] FIG. 18 shows a schematic diagram of an exemplary beam pattern from an ultrasound probe. Having an appropriate beam width can be important in medical imaging. For example, if a lesion, such as cancerous tissue, is larger than the elevation beam width, it can be detected (a "visible lesion"). Alternatively, if the lesion is smaller than the elevation beam width, the lesion may not be detected (an "invisible region"). This is because lesions generally have hypoechoic properties compared to the surrounding tissue and appear as darker regions in the image. If the elevation beam is wider than the lesion, echo signals generated from tissue surrounding the lesion within the beam width may fill in the dark lesion, making it invisible or difficult to see. Therefore, the ability to control one or more parameters of the elevation beam (e.g., elevation aperture size, elevation focus, etc.) can provide greater control of ultrasound imaging and / or result in better image quality in certain situations.

[0027] A 1D array has only one row of elements in the elevation dimension and a fixed elevation aperture size. In other words, a 1D array has multiple array elements arranged in only one row extending in one dimension (i.e., the lateral dimension). For example, as shown in FIG. 11, the array elements of a 1D array may be arranged in a single row that is linear only along the lateral dimension but not in the elevation dimension. In some variations of linear arrays, the spacing between two adjacent elements may be equal to approximately one wavelength of the transmitted acoustic wave. In some variations of phased arrays, the spacing between two adjacent elements may be approximately half the wavelength of the transmitted acoustic wave. A single row of array elements in a transducer array means there is no range in the elevation dimension. Therefore, a 1D array has both a fixed elevation aperture size and a fixed elevation focus, and the thickness of a thin slice in the elevation dimension cannot be maintained throughout the entire imaging depth. In addition to this slice thickness limitation, 1D arrays have an elevation aperture that is a compromise between near-field and far-field performance.

[0028] Figure 16 provides a comparison between a linear 1D array with a 3 mm elevation aperture and a linear 1D array with a 6 mm elevation aperture. Specifically, Figure 16 shows the beam patterns (top row) and normalized beam patterns (middle row) of the two 1D arrays with varying image depths. Figure 16 also shows a plot (bottom row) representing 6 dB and 20 dB elevation beamwidths for image depths ranging from approximately 10 mm to approximately 80 mm. As shown in Figure 16, the elevation beamwidth of the 3 mm aperture array generally increases linearly with image depth for both the 6 dB and 20 dB elevation beams. However, the elevation beamwidth of the 6 mm aperture array decreases from 10 mm to approximately 22 mm, remains flat up to 31 mm, and then begins to increase linearly with depth. Therefore, while the 1D configuration may have some limitations in imaging, it may nevertheless be useful in certain applications (e.g., certain imaging depths).

[0029] A 1.25D array has multiple rows of elements in the elevation dimension and a variable elevation aperture size, but has a fixed elevation focus via an acoustic lens. The variable elevation aperture size can be controlled, for example, electronically. Varying the elevation aperture size provides some control over the narrowing of the elevation beam width, meaning the ultrasound system can achieve a more appropriate overall elevation beam slice thickness. Adding rows to the array in the elevation dimension can further narrow the elevation beam width. However, because a 1.25D array has a fixed elevation focus while having a variable elevation aperture size, it is not possible to control the beam width across the entire imaging field of view (e.g., imaging depth).

[0030] A 1.5D array has multiple rows of elements in the elevation dimension, a variable elevation aperture size, and a variable elevation focus via electronic delay control. The variable elevation aperture size and one or more variable elevation focuses can be controlled, for example, electronically. For example, FIG. 15 shows an exemplary 1.5D mixed array having at least two elements (e.g., two rows) in the elevation dimension. In some variations, the mixed array may include an odd number of rows to allow symmetry across a single central row in the mixed array. In some variations, the mixed array may include an even number of rows. The mixed array has one or more array elements of a first type (e.g., PZT transducers) and one or more array elements of a second type (e.g., optical resonators, optical interferometers, etc.), as described above. The 1.5D array shown in FIG. 15 includes three rows for illustrative purposes, but it should be understood that the array may include any suitable number of rows. These three rows are positioned adjacent to one another in the elevation dimension. That is, one inner (center) row with one or more array elements of a first type and two outer rows with one or more array elements of a second type. The spacing between these elements in the elevation dimension can be greater than one wavelength of the transmitted acoustic wave. In some variations, the 1.5D array can include a linear array, and the inner row and two outer rows can each have enough elements to meet the minimum pitch requirement of one wavelength of the transmitted acoustic wave. Alternatively, in some variations, the 1.5D array can be a phased array, and the inner row and two outer rows can each have a pitch of half the wavelength of the transmitted acoustic wave. The inner row and the two outer rows can have the same pitch or different pitches. For example, the inner row can include 128 transducer elements, and the two outer rows can include 32 transducer elements.

[0031] As described above, both the elevation aperture size and elevation focus of the 1.5D array can be controlled. In some variations, the number of array elements can be greater than the number of channels in the imaging system, so in these variations, the system can include one or more analog switches (e.g., high-voltage switches) to select the desired sub-aperture of the 1.5D array. Because both the elevation aperture size and elevation focus can be selectively adjusted, the 1.5D array can be controlled to selectively achieve a narrower elevation beamwidth across the imaging field of view, allowing the ultrasound probe to image smaller lesions in addition to larger lesions at various imaging depths.

[0032] Figure 17 shows a comparison of the elevation beam patterns of exemplary 1D and 1.5D mixed arrays. The top two images in Figure 17 show the beam patterns of a linear 1D array with a 3 mm elevation aperture and a linear 1D array with a 6 mm elevation aperture, as described above with respect to Figure 16. The top two images in Figure 17 are similar to those shown in Figure 16, except that Figure 17 also shows the very near-field beam patterns (0 to 10 mm) to show a more complete beam pattern profile from 0 to 80 mm image depth. For the linear 1D array with a 3 mm elevation aperture (top row), the elevation beam width is narrow in the near field from 0 mm to approximately 20 mm, but the elevation beam width becomes wider in the far field beyond approximately 20 mm. For the linear 1D array with a 6 mm elevation aperture (middle row), the elevation beam width is narrow from approximately 20 mm to approximately 40 mm, but the elevation beam width becomes wider beyond approximately 20 mm. However, a 1.5D array (bottom row) with variable elevation aperture size and elevation focus provides a narrower elevation beamwidth over a wider imaging depth range than an individual 1D array, i.e., at least over a very close field of view from about 0 mm to about 40 mm. In other words, the 1.5D array can achieve a better overall elevation beamwidth across the entire imaging field of view. Adding elements to the array in the elevation dimension can further narrow the elevation beamwidth.

[0033] Therefore, 1.5D arrays can have many advantages over 1D arrays. First, 1.5D arrays can have thinner elevation beam slices, which can be useful for resolving small structures such as small blood vessels and cysts. Second, 1.5D arrays can have better, more uniform image quality across the near-field and far-field ranges. Finally, 1.5D arrays can have better fine resolution than 1D arrays without sacrificing penetration and sensitivity.

[0034] A 1.75D array is a 1.5D array but with the additional capability of elevation beam steering. In other words, a 1.75D array is similar to a 1.5D array in that it includes multiple rows in the elevation dimension, a variable elevation aperture size, and a variable elevation focus. However, a 1.75D array may be electronically controllable, allowing for some degree of freedom in beam steering (e.g., up to about 5 degrees in at least one direction, up to about 10 degrees in at least one direction, up to about 15 degrees in at least one direction, or up to about 20 degrees in at least one direction). Like a 1.5D array, a system incorporating a 1.75D array may include one or more analog switches to select a desired sub-aperture of the array.

[0035] Finally, 2D arrays have a large number of elements in both the lateral and elevation dimensions to meet minimum pitch requirements for large beam steering angles. For example, a 2D array may include multiple array elements arranged in both the lateral and elevation dimensions and be electronically controllable to enable a variable elevation aperture, variable elevation focus, and a full suite of beam steering controls. Similar to 1.5D arrays, systems incorporating 2D arrays may include one or more analog switches to select the desired sub-aperture of the array.

[0036] Ultrasound imaging system with a mixed ultrasound transducer array FIG. 1 is a block diagram of an exemplary ultrasound imaging system 100 with a mixed array (also referred to herein as a “mixed ultrasound transducer array”). The ultrasound imaging system includes a probe 125, an imaging system 150, and a display 160. The probe 125 can be connected (without intervening components) or coupled (with or without intervening components) to the imaging system 150. The probe 125 can receive and / or transmit a set of signals (e.g., electrical signals, acoustic signals, optical signals, etc.) from / to the imaging system 150. The imaging system 150 can be connected (without intervening components) or coupled (with or without intervening components) to the display 160. The imaging system 150 can receive and / or transmit a set of signals (e.g., electrical signals, electromagnetic signals, etc.) from / to the display 160.

[0037] The probe 125 includes a mixing array 110, a multiplexer 120, and an optical cable 130. The mixing array 110 includes one or more array elements of a first type (e.g., piezoelectric transducers) capable of transmitting acoustic waves and one or more array elements of a second type (e.g., WGM optical resonators) with broadband response and high sensitivity. The mixing array 110 includes an array of transducer elements and can be configured to operate in a one-dimensional (1D) configuration, a one-and-a-half-dimensional (1.25D) array configuration, a one-and-a-half-dimensional (1.5D) array configuration, a one-and-a-half-dimensional (1.75D) array configuration, or a two-dimensional (2D) array configuration, as described further below. One or more array elements of the first type in the mixing array 110 can be operably coupled to the multiplexer 120. One or more array elements of the second type in the mixing array 110 can be operably coupled to the optical cable 130.

[0038] In some variations, the probe 125 can be configured to repeatedly scan across the field of view by using a phased array of the mixed array 110. In doing so, a line-by-line image is generated using one or more array elements of a first type and / or one or more array elements of a second type. A high-resolution image can then be generated using known synthetic aperture (SA) algorithms. Additionally or alternatively, in some variations, the probe 125 can be configured to use different patterns of acoustic excitation, such as, for example, transmitting acoustic waves using a first group of transducer elements while receiving ultrasound echoes corresponding to the acoustic waves using a second group of transducer elements or all of the transducers.

[0039] The mixed array 110 may include a large number of elements (e.g., 10, 100, 200, 1000, 2000, 10,000, and / or the like). In some variations, the array may be arranged in a rectangular configuration and may include N×M elements, where N is the number of rows and M is the number of columns. The mixed array may include 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 a transducer configured to transmit ultrasound and the second type may be an optical sensor (e.g., an optical resonator, an optical interferometer, etc.). The one or more array elements of the first type and the one or more array elements of the second type may be collectively arranged in a rectangular arrangement, a curved arrangement, a circular arrangement, or a sparse array arrangement. Various example configurations of array elements in the mixed array 110 are described in further detail below.

[0040] The transducers in the mixed array 110 may be, for example, lead zirconate titanate (PZT) transducers, polymer thick film (PTF) transducers, polyvinylidene fluoride (PVDF) transducers, capacitive micromachined ultrasonic transducers (CMUT), piezoelectric micromachined ultrasonic transducers (PMUT), photoacoustic sensors, single crystal materials (e.g., LiNbO3 (LN)), Pb(Mg 1 / 3 Nb2 / 3 )-PbTiO3(PMN-PT), and Pb(In 1 / 2 Nb 1 / 2 )-Pb(Mg 1 / 3 Nb 2 / 3 The transducers may include transducers based on PbTiO3 (PIN-PMN-PT)-PbTiO3 (PIN-PMN-PT) and / or any transducer suitable for acoustic transduction.

[0041] The optical sensor can be, for example, a microbubble resonator, a fiber-based resonator, an integrated photonic resonator, a microdisk resonator, a Fabry-Perot interferometer, and / or the like. For example, in some implementations, the optical sensor can include an optical microbubble resonator. The optical microbubble resonator can be made of an optically transparent material, such as glass, a 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 having a radius (R) and an inner microbubble surface having a radius (r), thereby defining a resonator wall thickness equal to (Rr). The set of resonant frequencies of the optical microbubble resonator (due to the propagation of a set of WGMs) can have a high Q factor suitable for a highly sensitive transduction probe. In general, the sensitivity of an optical resonator can be improved by increasing the Q factor of the optical resonator. In particular, in such implementations, 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. In some implementations, the optical sensor can include a sensing node formed at a cross section of the optical fiber and optical waveguide when light propagating in the optical waveguide couples into and propagates around the optical fiber. In some variations, the optical sensor can include an integrated photonic optical resonator. For example, in some variations, the optical sensor can be similar to any of the optical resonators described in U.S. Patent Application Nos. 62 / 945,538 and 63 / 001,738, each of which is incorporated herein in its entirety.

[0042] The space inside and / or around the optical sensor may be filled with an ultrasound-enhancing material, such as, for example, polyvinylidene fluoride, parylene, polystyrene, and / or the like. The ultrasound-enhancing material may increase the sensitivity of the optical sensor. For example, the ultrasound-enhancing material may have a relatively high elastic-optic coefficient, such that in response to the optical sensor receiving a train of ultrasound echoes, the refractive index of the ultrasound-enhancing material changes more than the refractive index of the material of the optical sensor (e.g., when subjected to mechanical stress or strain induced by the train of ultrasound echoes). Camera

[0043] The optical cable 130 may include a dedicated optical path for transmitting and / or receiving optical signals to and from the optical sensor. The optical cable 130 may include a fiber optic cable or a coaxial cable. The choice of optical cable 130 may depend on the type of optical signal. The array of optical sensors in the mixed array 110 may be linearly arranged on the substrate. The array of optical sensors may be equidistant from one another. Additionally or alternatively, at least some of the optical sensors in the array may be separated by different distances. In some configurations, the array of optical sensors may all be optically coupled to a single optical waveguide. Thus, signals from multiple optical sensors may be combined into and transmitted by a single optical waveguide. In some configurations, the array of optical sensors may be optically coupled to an array of optical waveguides. Thus, optical signals from the array of optical sensors may be coupled into multiple optical waveguides in the optical cable 130 and thereby transmitted to the imaging system 150.

[0044] The multiplexer 120 may include analog switches. The analog switches may include multiple high-voltage analog switches. Each analog switch may be connected to an individual system channel. As a result, the multiplexer 120 may selectively connect individual system channels from the set of system channels of the imaging system 150 to the transducers of the mixed array 110. Thus, electrical signals from one or more array elements of the first type may be coupled to multiple optical waveguides within the optical cable 130 and thereby transmitted to the imaging system 150.

[0045] The imaging system 150 may include a front-end system 151 and a back-end system 153. Generally, the front-end system 151 may include at least two components, including a transmit beamformer and a receive beamformer. The transmit beamformer and the receive beamformer may include multiple transmit and receive channels, which are connected (e.g., via a set of electrical wires, via a set of optical waveguides, and / or the like) to one or more array elements of a first type and / or one or more array elements of a second type. For example, the transmit beamformer may include 128 transmit channels connected to the multiplexer 120, and the receive beamformer may include 256 receive channels connected to the optical cable 130 and / or the multiplexer 120. The front-end system may further include a set of photodetectors for converting optical signals to electrical signals. The back-end system 153 may include a processor that processes signals received from the mixing array 110 to generate an image, a memory operably coupled to the processor that stores the image, and a communication interface that presents the image to a user (e.g., via a graphical user interface).

[0046] The display 160 may be operatively coupled to the back-end system 153 of the imaging system 150 to display a set of images generated by the imaging system 150. In some variations, the display 160 may include an interactive user interface (e.g., a touch screen) and may be configured to send a set of commands (e.g., pause, resume, and / or the like) to the imaging system 150. In some variations, the ultrasound imaging system 100 may further include a set of auxiliary devices (not shown) used to input information into or output information from the ultrasound imaging system 100. The set of auxiliary devices may include, for example, a keyboard, a mouse, a monitor, a webcam, a microphone, a touch screen, a printer, a scanner, a virtual reality (VR) head-mounted display, a joystick, a biometric reader, and / or the like (not shown).

[0047] Exemplary Configurations of Mixed Arrays Various exemplary configurations of array elements in a mixed ultrasonic transducer array are described below. As mentioned above, a mixed ultrasonic transducer array may generally include one or more array elements of a first type and one or more array elements of a second type, where the one or more array elements of the first type may include a set of transducers (e.g., piezoelectric transducers, single crystal material transducers, piezoelectric micromachined ultrasonic transducers (PMUTs), or capacitive micromachined ultrasonic transducers (CMUTs)), and the one or more array elements of the second type may include a set of optical sensors.

[0048] In some variations, the ultrasound transducer array may include one or more rows in the elevation dimension. For example, the array elements may be collectively arranged in a rectangular array including multiple rows and multiple columns. In some variations, as shown in FIG. 2, the mixed array may include three rows of elements in the elevation dimension. The three rows include an inner row and two outer rows. The two outer rows may be made of a second type 114 (e.g., optical sensors). The second type 114 may include, for example, a set of microbubble resonators, a set of fiber-based resonators, a set of integrated photonic resonators, a set of microdisk resonators, a set of optical interferometers, and / or the like. The inner rows may be made of a first type 112 (also referred to herein as "transducers"). The first type 112 may include, for example, lead zirconate titanate (PZT) transducers, polymer thick film (PTF) transducers, capacitive micromachined ultrasonic transducers (CMUT), and / or any transducer suitable for acoustic transduction.

[0049] The two outer rows may include an equal number of elements positioned parallel to corresponding columns, with each pair of elements 114 positioned in the same column in the two outer rows optionally connected (e.g., electrically connected or electromagnetically coupled) to form a single combined outer element for a 1.25 dimensional (1.25D) or 1.5 dimensional (1.5D) array configuration.

[0050] While FIG. 2 shows a transducer array with three rows, in some variations, the number of rows can be any odd number, such as 3, 5, ..., 2n+1, where n is an integer. In some variations, the first-type array elements 112 can be located in the center row of a set of odd-numbered rows. For example, a 1.5D array configuration can include five rows, with a row of PZT transducers in the center row, two rows of optical sensors adjacent to the center row, and two rows of PZT transducers in the outermost rows adjacent to the rows of optical sensors. In some variations, including transducers in the center row can be advantageous. For example, because the center row includes first-type transducer elements 112 that can both transmit and receive ultrasound, the elevation beam profile does not have a "dip" in the middle for both the transmit and receive modes of the transducer. This dip in the elevation beam profile can degrade image quality and introduce image artifacts. Therefore, placing the first type of transducer elements 112 in the center row (e.g., as shown in FIG. 2) may advantageously help avoid such degradation in image quality and image artifacts. However, in some variations, such as shown in FIG. 6, the mixed transducer array may include optical sensors in the center row.

[0051] In some variations, one or more array elements 112 of a first type (e.g., transducers) and one or more array elements 114 of a second type (e.g., optical sensors) may be in alternating rows. For example, FIG. 2 shows an exemplary variation in which the array elements 112 of a first type are interleaved with the array elements 114 of a second type, with the first type 112 in the center row. As another example, FIG. 6 shows an exemplary variation in which the array elements 112 of a first type are interleaved with the array elements 114 of a second type, i.e., the second type, in the center row.

[0052] In some variations, the spacing (pitch) between adjacent array elements may be selected for a particular performance parameter. The pitch may be defined as the distance between the center of a transducer element and the center of an adjacent transducer element. In some variations, the pitch may measure greater than half a wavelength of the operating frequency of the acoustic wave (e.g., transmitted by a piezoelectric transducer), such as when the array is in phased array operation. In some variations, the pitch may measure greater than a full wavelength of the operating frequency of the acoustic wave, such as when the array is in linear array operation. In some variations, the pitch may measure less than half a wavelength of the operating frequency of the acoustic wave, or less than a full wavelength of the operating frequency of the acoustic wave.

[0053] In some variations, all rows in the mixed array may have the same pitch in the lateral dimension (e.g., as shown in FIG. 2). However, in some variations, at least some of the rows in the mixed array may have different pitches in the lateral dimension. In other words, some rows have a first pitch and other rows have a second pitch, which is smaller or larger than the first pitch.

[0054] For example, as shown in FIG. 3 , the mixed array 110 may include an inner (center) row having a first uniform pitch and two outer rows having a second uniform pitch different from the first uniform pitch. In some variations, the second uniform pitch may be larger (i.e., further apart) than the first uniform pitch. The two outer rows may include optical sensors 114. The inner row may include a first type 112 of transducers, such as PZT transducers, CMUT transducers, and / or the like. In some variations, one of the two outer rows may have the second uniform pitch, and the other of the two outer rows may have a third uniform pitch different from both the first and second pitches. In some variations, the mixed array may include a set of rows including any odd number of rows, such as 3, 5, ..., 2n+1 rows (n is an integer). In such variations, each row from the set of rows may have a unique pitch that is different from the pitch of any other row, hi some implementations, the set of rows may have an ascending pitch that starts with the central row having the smallest pitch of the set and gradually increases toward the outer rows having the largest pitch of the set.

[0055] In ultrasound imaging, the transducer pitch is generally selected based on the operating frequency. More specifically, the transducer pitch may be inversely proportional to the operating frequency (e.g., proportional to the operating wavelength corresponding to the operating frequency) to avoid grating lobes. When imaging superficial tissue, a small elevation aperture and a high frequency are often used. On the other hand, a large elevation aperture and a low frequency may be advantageous for imaging deep tissue.

[0056] Because of the different pitches between the rows, the mixed array shown and described with respect to Figure 3 can advantageously perform both superficial and deep tissue imaging. In this variation, the central rows with smaller pitch can be used to produce high resolution images of superficial tissue using a high operating frequency. For imaging deep tissue, all rows (including those with larger pitch) can be used to produce high transmission images using a low operating frequency.

[0057] Another advantage of using a larger pitch is the option to reduce the total number of transducer elements in the imaging system 150. The larger the pitch, the fewer transducer elements per area and the lower the areal density of the cables (e.g., optical cables 130, coaxial cables, etc.) of the probe 125 that connect the mixed array 110 of the probe 125 to the front end 151 of the imaging system 150. Thus, the reduced number of transducer elements shown and disclosed in this embodiment includes several advantages, including a reduced number of cables (i.e., thinner cable bundles), a lighter weight for the probe 125, and reduced manufacturing and operating costs.

[0058] Additionally or alternatively, in some variations, the distance (pitch) between transducer array elements in a particular row may be the same or may vary along the length of the row. Using such a variable pitch may generally be beneficial, as described above with respect to FIG. 3, since it allows imaging of both superficial and deep tissue. FIG. 4 is a schematic illustration of an exemplary mixed array having at least one row with a variable pitch in the lateral dimension. For example, in some variations, a row with a variable pitch may include a central region with a first pitch and one or more lateral regions adjacent to the central region with a second pitch that is different (e.g., smaller or larger) than the first pitch. While only three groups of pitch (left, center, and right) in each row are shown in FIG. 4, in some variations, two or more groups of pitch may be used as well. In some variations, the center row and the two outer rows may each have a variable pitch (instead of the uniform pitch disclosed with respect to FIG. 2 or FIG. 3), as shown in FIG. 4. For example, an ultrasonic transducer array may include a first row having a first variable pitch pattern in the lateral dimension and a second row having a second variable pitch pattern in the lateral dimension, the second variable pitch pattern being different from the first variable pitch pattern. Additionally or alternatively, two or more rows in a mixed array may each include the same or similar variable pitch pattern along their length in the lateral dimension.

[0059] In some variations, 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 set of subgroups or subapertures of the mixed array 110. For example, in some variations, the mixed array 110 may be divided into a set of subapertures, each having a set of one or more rows. Each subaperture may include a set of transducer elements from one or more array elements of the first type and / or one or more array elements of the second type. In some variations, the mixed array may be configured as a 1.5-dimensional (1.5D) array including three rows (e.g., three rows of elements as shown in FIG. 7). In some variations, only the central transducer element of the set of transducer elements in the subaperture positioned at the center of the mixed array is the optical sensor 114. In such variations, the remainder of the transducer element is made of a different type of transducer 112, which may include, for example, a lead zirconate titanate (PZT) transducer, a polymer thick film (PTF) transducer, a CMUT transducer, and / or any transducer suitable for acoustic transduction. In some implementations, the size of the optical sensor is small (e.g., comparable to or smaller than the operating wavelength of the acoustic wave and / or acoustic echo).

[0060] Each subaperture may include a different number of rows than one or more other rows in the set of rows. Each row may include a uniform pitch or a variable pitch. For example, the mixed array 110 may include five subapertures having one row, three rows, five rows, three rows, and one row, consecutively from the leftmost aperture to the rightmost aperture of the five subapertures.

[0061] For example, FIG. 5 is a schematic illustration of an exemplary mixing array 110 having subapertures. The mixing array 110 shown in FIG. 5 can be divided into three subapertures, including a left subaperture, a center subaperture, and a right subaperture. While both the left and right subapertures 110 may have only one row, shown as having a uniform pitch, it should be understood that in some variations, these subapertures may include rows with a variable pitch. However, the center subaperture may have multiple rows, such as an inner row 118 and two outer rows 116. The inner row 118 may have a specific pitch, and the two outer rows 116 may have a different pitch than the inner rows. Any of these pitches of the center subaperture may be uniform or variable. The two outer rows 116 may include optical sensors. All other rows, including the inner rows of the center, left, and right subapertures, may include other transducers, such as, for example, PZT transducers, CMUT transducers, etc.

[0062] Figure 6 is a schematic illustration of an exemplary mixed array similar to the mixed array of Figure 2, except that only the relative positions of the first type array elements 112 and the second type array elements 114 are swapped. Similarly, in the mixed array of Figure 3, the mixed array of Figure 4, and the mixed array of Figure 5, and / or any other mixed array shown and described herein, the relative positions of the first type array elements 112 and the second type array elements 114 may be swapped.

[0063] FIG. 7 is a schematic illustration of an exemplary mixed array. The mixed array may include one or more array elements of a first type including a set of transducers and one or more array elements of a second type including a set of optical sensors. The mixed array 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. For example, as shown in FIG. 7, the mixed array may include a center row including at least one array element of the first type and at least one array element of the second type. For example, the center row may have a single array element of the second type, while the other rows may have only array elements of the first type. The single array element of the second type may be an optical sensor approximately equal to or smaller than the wavelength of the transmitted acoustic wave. In some variations, the use of an optical sensor can minimize the complexity of probe fabrication while taking advantage of the ultra-high sensitivity of optical sensors (e.g., the ultra-high sensitivity of WGM optical resonators) for improved image quality.

[0064] FIG. 8 is a schematic illustration of an exemplary mixed array 110. The mixed array may include two or more rows, including a center row. The center row may include a plurality of elements 112 of a first type and a plurality of array elements 114 of a second type. The array elements of the second type may be approximately equal to or smaller than the wavelength of the transmitted acoustic wave. At least one transducer element in the inner rows is an optical sensor 114, and the remaining elements are array elements of the first type 112, which may include, for example, PZT and / or CMUT transducers. Similar to the mixed array 110 of FIG. 7, in some implementations, the size of the optical sensor in the mixed array 110 of FIG. 8 may be comparable to or smaller than the operating wavelength of the acoustic wave and / or acoustic echo. In some implementations, the size of the optical sensor may be larger than the operating wavelength of the acoustic wave and / or acoustic echo.

[0065] FIG. 9 is a schematic illustration of an exemplary mixed array. The ultrasound transducer array may include two or more rows. Each of the two or more rows may have at least one array element of a first type and at least one array element of a second type. The array elements of the second type may be spatially distributed in a regular pattern or an irregular pattern (e.g., random pattern). A set of elements in the inner row and the two outer rows may include optical sensors 114, and the remaining elements include the first type 112, e.g., PZT transducers and / or CMUT transducers. In some configurations, the spatial distribution of the positions of the optical sensors 114 may be random. In some configurations, the spatial distribution of the positions of the optical sensors 114 may follow a placement pattern (e.g., the same, one sensor element shifted to the right, two sensor elements shifted down). The size of the optical sensors may be smaller than or the same as the size of the first type 112.

[0066] The mixed array variations described in Figures 7-9 may entail multiple advantages. For example, each row of these mixed arrays, having both array elements of both types, can both transmit acoustic waves (e.g., ultrasound) and detect acoustic echoes (e.g., ultrasound echoes) to some extent, thereby enabling more distributed imaging capabilities. Furthermore, distributed optical sensors can increase the overall distributed sensitivity of the mixed array to acoustic echoes. Furthermore, these mixed array variations may generate two independent images, generated by one or more array elements of a first type and one or more array elements of a second type, and an imaging system (such as imaging system 150 shown and described with respect to Figure 1) can then combine the two independent images to form a single combined image that is improved compared to each of the two independent images.

[0067] While the mixed arrays shown in Figures 2-9 are generally depicted on planar substrates or surfaces, it should be understood that the mixed array can be disposed on any other suitable surface (e.g., curved surfaces). For example, Figure 10 is a schematic illustration of an exemplary mixed array 110 on a curved substrate. The mixed array 110 can include one or more array elements of a first type including a set of transducers and one or more array elements of a second type including a set of optical sensors on a curved surface, such as a curved panel. The curved surface can include a circular curve, a quadratic curve (e.g., a parabolic curve, a hyperbolic curve, an elliptic curve, etc.), and / or any curve profile suitable for ultrasound imaging. The curvature of the panel can be the direction of the field of view of the mixed array 110. In some configurations, the curvature is a concave curvature. In some configurations, the curvature is a convex curvature. The mixed array can include three rows of elements in the elevation dimension, as shown in Figure 10. The three rows can include an inner row and two outer rows. In some variations, the two outer rows may include second-type array elements 114 (e.g., optical sensors), and the inner row may include first-type array elements 112 (e.g., PZT transducers, CMUT transducers, and / or the like). In some variations, the mixed array may include any odd number of rows, such as 3, 5, ..., 2n+1 rows, where n is an integer. In such variations, the inner row of the mixed array may include first-type array elements 112, and then the remaining rows may alternate between second-type array elements 114 and first-type array elements 112.

[0068] The positioning of the transducer elements in the mixed array of Figure 10 is similar to the positioning of the transducer elements in the mixed array of Figure 2, except that the mixed array of Figure 10 is mounted on a curved panel. The positioning of the mixed array of Figure 10 can be achieved by multiplying the position matrix of the mixed array of Figure 2 by a transformation matrix corresponding to the curvature of the mixed array of Figure 10. The relative positions of the transducer elements in any of the mixed arrays of Figures 2-13 can be transformed for mounting on a curved panel.

[0069] 11 is a schematic illustration of an exemplary 1D mixed array 110 including a single row including multiple array elements or transducer elements. The multiple array elements may include at least one array element 112 of a first type (e.g., a PZT transducer, a CMUT transducer, and / or the like) and at least one array element 114 of a second type (i.e., an optical sensor). 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 placement pattern. Compared to conventional 1D arrays containing only one type of transducer, mixed arrays (containing a set of optical sensors, as shown in FIG. 11 ) may have improved performance in sensing bandwidth and / or sensitivity due to the addition of optical sensors such as optical resonators (e.g., WGM optical resonators, microbubble optical resonators, microsphere resonators, microtoroid resonators, microring resonators, or microdisk optical resonators, and / or the like).

[0070] 2-11 show transducer arrays having an odd number of rows, such as 1, 3, 5, ..., 2n+1 (where n is an integer), in some variations, the transducer array may have an even number of rows, such as 2, 4, 6, ..., 2n. For example, in some variations, the mixed array 110 may have two rows of a first type of array elements 112 (CMUT transducers, PMUT transducers, and / or the like) and two rows of a second type of elements 114 (e.g., optical resonators, optical interferometers, and / or the like).

[0071] FIG. 12 is a schematic illustration of an exemplary 2D mixed array 110 that may include N×M transducer elements arranged in a rectangular configuration, where N is the number of rows and M is the number of columns, both integers. In some implementations, the number of rows and / or columns may be greater than 31 rows and / or 31 columns. For example, the 2D mixed array may include 64×96=6,144 transducer elements. The mixed array may include one or more array elements of a first type and one or more array elements of a second type. The one or more array elements of the first type may include a set of transducers, and the one or more array elements of the second type may include a set of optical sensors. The one or more array elements of the first type and the one or more array elements of the second type may be collectively positioned in a rectangular arrangement. In some configurations, the spatial distribution of the first type 112 and the second type 114 may be random. In some configurations, the spatial distribution of the first type 112 and the second type 114 may follow a layout pattern. Compared to conventional 2D arrays containing only one type of transducer, mixed arrays (containing a set of optical sensors, as shown in FIG. 12) may demonstrate improved performance in detection bandwidth and / or sensitivity due to the addition of optical sensors.

[0072] FIG. 13 is a schematic illustration of an exemplary 2D mixed array 110 in a sparse array configuration. Arranging the mixed array 110 in a sparse array configuration instead of a fully sampled arrangement (such as the arrangement shown and described with respect to FIG. 12 ) can reduce the total number of transducer elements used to fabricate the mixed array. For example, a sparse 2D array of the same size as a fully sampled 2D array (as shown and described with respect to FIG. 12 ) can include only 1,000 transducer elements, compared to the 64 × 96 = 6,144 transducer elements of the fully sampled mixed array of FIG. 12 . The mixed array can include one or more array elements of a first type and one or more array elements of a second type. The one or more array elements of the first type can include a set of transducers, and the one or more array elements of the second type can include a set of optical sensors. The one or more array elements of the first type and the one or more array elements of the second type can be collectively positioned in a sparse array configuration. In some configurations, the spatial distribution of the first type array elements 112 and the second type array elements 114 may be random. In some configurations, the spatial distribution of the first type 112 and the second type 114 array elements may follow a statistical distribution (e.g., a normal distribution, a Gaussian distribution, and / or the like). Using a sparse spatial distribution of the first type 112 and the second type 114 array elements may reduce / prevent the generation of grating lobes in images generated by the mixed array. 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 random spatial distribution, and the positions of a second set of PZT transducers in the mixed array 110 may have a normal distribution.

[0073] While the mixing arrays described above with respect to Figures 2-13 have been primarily described with respect to rectangular arrangements having one or more rows, it should be understood that other array shapes can be similarly mixed with multiple types of array elements 112 and 114. For example, Figure 14 is a schematic illustration of an exemplary annular mixing array 110. Annular arrays generally can produce improved acoustic (e.g., ultrasound) beam patterns in three-dimensional space due to their symmetrical shape. Because image quality is highly correlated with acoustic beam patterns, improved acoustic (e.g., ultrasound) beam patterns can result in improved image quality in acoustic imaging systems (e.g., medical ultrasound imaging systems).

[0074] Similar to the arrays described above, the annular mixing array may include one or more array elements 112 of a first type and one or more array elements 114 of a second type. The one or more array elements of the first type may include a set of transducers, and the one or more array elements of the second type may include a set of optical sensors. The mixing array may include at least one circular array element and at least one annular array element concentrically arranged around the circular array element. For example, as shown in FIG. 14 , the mixing array may include at least one circular optical sensor 114 (e.g., a ring resonator) at the center of the mixing array and a set of annular transducers 112 (e.g., PZT transducers and / or CMUT transducers, etc.) arranged concentrically around the circular optical sensor in order of increasing diameter. 14 includes three annular array elements around a circular array element, it should be understood that the mixed array may include any suitable number of annular array elements, such as two, three, four, five, or more than five annular or ring-shaped elements. Furthermore, in some variations, the one or more array elements of the first type and the one or more array elements of the second type may both be annular elements collectively arranged in a concentric configuration.

[0075] The foregoing description, for purposes of explanation, used specific nomenclature 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 in order 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, thereby enabling those skilled in the art to utilize the present invention and 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. An apparatus for imaging a target, wherein the apparatus comprises an ultrasonic transducer array, The ultrasonic transducer array is A plurality of array elements of a first type, wherein the first type is a transducer configured to transmit acoustic waves, A plurality of array elements of a second type, which is different from the first type, wherein the second type is an optical sensor, and Equipped with, The ultrasonic transducer array comprises at least a first row having a first pitch in the lateral dimension and at least a second row having a second pitch different from the first pitch in the lateral dimension.

2. The apparatus according to claim 1, wherein the first and second types of array elements are configured to detect acoustic echoes corresponding to the acoustic waves.

3. The apparatus according to claim 1, wherein the first pitch is less than or equal to half the wavelength of the center frequency associated with the acoustic wave, and the second pitch is greater than half the wavelength.

4. The apparatus according to claim 1, wherein the ultrasonic transducer array includes an inner row and a row adjacent to the inner row, the inner row having the first pitch and the adjacent row having the second pitch which is greater than the first pitch.

5. The apparatus according to claim 4, wherein the inner row comprises a plurality of array elements of the first type, and the row adjacent to the inner row comprises a plurality of array elements of the second type.

6. The apparatus according to claim 1, wherein at least one row has a variable pitch in the lateral dimension.

7. The apparatus according to claim 6, wherein the row having a variable pitch includes a central region having a first pitch and a lateral region adjacent to the central region having a second pitch greater than the first pitch.

8. The apparatus according to claim 6, wherein the ultrasonic transducer array includes a first row having a first variable pitch pattern and a second row having a second variable pitch pattern different from the first variable pitch pattern.

9. The apparatus according to claim 8, wherein the first row comprises a plurality of array elements of the first type, and the second row comprises a plurality of array elements of the second type.

10. The apparatus according to claim 1, wherein the ultrasonic transducer array comprises a first set of array elements of the first type and a second set of array elements of the second type, wherein the first set and the second set are arranged in a sparse array configuration, and the spatial distribution of the first set is different from the spatial distribution of the second set.

11. The apparatus according to claim 10, wherein the spatial distribution of the second set is selected from regular patterns and irregular patterns.

12. The apparatus according to claim 1, wherein the ultrasonic transducer array comprises a plurality of sub-apertures, and a multiplexer selectively couples at least a subset of the plurality of array elements of the first type into a set of system channels in order to select sub-apertures for transmission or reception.

13. The apparatus according to claim 12, wherein the first sub-aperture includes more rows than the second sub-aperture.

14. The apparatus according to claim 13, wherein the first sub-aperture is a central sub-aperture, and the second sub-aperture is adjacent to the central sub-aperture.

15. The apparatus according to claim 1, wherein the optical sensor is an interference-based optical sensor including an optical resonator or an optical interferometer.

16. An apparatus for imaging a target, wherein the apparatus comprises an ultrasonic transducer array, The ultrasonic transducer array is A plurality of array elements of a first type, wherein the first type is a transducer, A second type of multiple array elements, wherein the second type is an optical sensor, and Equipped with, The ultrasonic transducer array is arranged on a curved surface in the apparatus.

17. The apparatus according to claim 16, wherein the curved surface includes a parabola, a hyperbola, or an elliptic curve.

18. The apparatus according to claim 16, wherein the ultrasonic transducer array includes at least one annular array element.

19. The apparatus according to claim 18, wherein the ultrasonic transducer array includes the second type of circular array element which is concentric with at least one annular array element.

20. The apparatus according to claim 19, wherein the at least one annular array element is arranged around the circular array element.

21. The apparatus according to claim 18, wherein the at least one annular array element is of the first type.

22. A method for ultrasonic conversion, The method involves transmitting acoustic waves using an ultrasonic probe, wherein the ultrasonic probe comprises an ultrasonic transducer array including a plurality of array elements of a first type and a plurality of array elements of a second type different from the first type, the second type being an optical sensor. Using the plurality of array elements of the first type and the plurality of array elements of the second type, to receive an acoustic echo corresponding to the acoustic wave. Includes, The method wherein the ultrasonic transducer array includes at least a first row having a first pitch in the lateral dimension and at least a second row having a second pitch different from the first pitch in the lateral dimension.

23. The method according to claim 22, wherein the first pitch is less than or equal to half the wavelength of the center frequency associated with the acoustic wave, and the second pitch is greater than half the wavelength.

24. The method according to claim 22, wherein at least one row has a variable pitch in the lateral dimension.

25. The method according to claim 24, wherein the row having a variable pitch includes a central region having a first pitch and a lateral region having a second pitch greater than the first pitch.

26. The method according to claim 22, wherein the ultrasonic transducer array comprises a first set of array elements of the first type and a second set of array elements of the second type, the first set and the second set each having a sparse array configuration and different spatial distributions.

27. ​​The method according to claim 22, further comprising selecting a sub-aperture of the ultrasonic transducer array by switching a subset of the plurality of array elements of the first type to a set of system channels via a multiplexer.

28. A method for ultrasonic conversion, The method of transmitting acoustic waves using an ultrasonic probe, wherein the ultrasonic probe comprises an ultrasonic transducer array arranged on a curved surface, and the ultrasonic transducer array includes a first type of array element comprising transducers and a second type of array element comprising optical sensors. Using the first type of array element and the second type of array element, to receive an acoustic echo corresponding to the acoustic wave. Methods that include...

29. The method according to claim 28, wherein the ultrasonic transducer array comprises at least one annular array element and the second type of circular array element concentric with the at least one annular array element.

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