Patent Application
20170067994
Field of the Invention
The claimed disclosure relates to a transducer array that measures an acoustic wave and, in particular, relates to a transducer array that measures an acoustic wave that is generated by a photoacoustic effect.
Description of the Related Art
A photoacoustic tomography (PAT) diagnostic apparatus utilizing the photoacoustic effect is known. In such an apparatus, an object is irradiated by an illumination light (near-infrared light) from an Nd:YAG laser pulse light source, and during the irradiation, an acoustic wave generated inside the object by the photoacoustic effect is received by a two-dimensional or a three-dimensional array transducer (transducer array) to generate and display an image.
PCT Japanese Translation Patent Publication No. 2001-507952 discloses a photoacoustic measurement apparatus provided with a transducer array in which a plurality of transducers are arranged in a supporting structure having a curved surface shape in order to increase accuracy in the separation and synthesis of acoustic wave signals propagated from the subject through each propagation path. Furthermore, the transducer disclosed in PCT Japanese Translation Patent Publication No. 2001-507952 is a piezoelectric transducer including a round receiving surface.
Owing to micro-electric-mechanical system technology, a transducer formed of a capacitive micromachined ultrasonic transducer (a CMUT) that has high density, high sensitivity, and wide reception band properties is known. The micro-electric-mechanical system technology is also referred to as Micro Electro Mechanical systems (MEMS) technology, and hereafter, in the present specification, the technology will be referred to as MEMS.
Since the CMUT element is formed through a semiconductor process, the CMUT element is cut out from a semiconductor wafer 18 using a dicing cut technique that is capable of cutting the semiconductor wafer 18 into a predetermined shape and size. Accordingly, in order to increase the yield of the semiconductor wafer, the outer edge shape of the CMUT element is not circular as in PCT Japanese Translation Patent Publication No. 2001-507952, but has a parallelogram shape including a square shape.
When mounting such transducers having a parallelogram-shaped receiving surface on a transducer array, in an arrangement in which one of the vertexes that define a receiving surface and one of the vertexes that define an adjacent receiving surface are proximate to each other, the mount density of the transducers decreases and the resolution of the image becomes disadvantageously limited. Furthermore, in an arrangement in which one of the vertexes defining the receiving surface and a side that defines the adjacent receiving surface are proximate to each other, the effective reception regions overlaps each other and crosstalk is disadvantageously generated, disadvantageously restricting the resolution of the image. Furthermore, in such a mode, when an area of a receiving surface of a single transducer is reduced in order to secure a mount density of the receiving surface, consequently, the effective reception region becomes limited and the receiving sensitivity of the transducer array decreases, making it disadvantageously difficult to obtain information of a deep portion inside the subject.
A transducer array of the claimed disclosure is a transducer array including a plurality of transducers each of which is configured to receive an acoustic wave and to transduce the received acoustic wave into an electric signal, and a support member supporting the plurality of transducers, and having an inner surface which is defined by a quadric surface of revolution that is formed according to an imaginary quadratic curve rotating about an imaginary rotation axis. Each transducer includes a receiving surface having a substantially parallelogram shape defined by four vertexes, the receiving surface being connected to the support member so as to be oriented towards the inner surface of the support, and a transducing element configured to transduce an acoustic wave, received by the transducer via the receiving surface, into an electric signal. The receiving surface is arranged in the transducer array such that any one of the four vertexes is closer to the imaginary rotation axis than the other three vertexes.
Furthermore, the transducer array of the claimed disclosure is a transducer array including a plurality of transducers, and a bowl-like support member to support the plurality of transducers. Each transducer includes a substantially parallelogram-shaped receiving surface that receives an acoustic wave, and the plurality of transducers are supported by the support member such that a plurality of the receiving surfaces included in a predetermined area of the support member are arranged on a grid formed by points of intersection between a plurality of imaginary right-handed spirals (CW) and a plurality of imaginary left-handed spirals (CCW) which cross one another and extend along an inner surface of the support member from a side on which a center of the inner surface of the support member is positioned.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
The transducer array 32 sends an acoustic wave to the object 20, and the acoustic wave reflected by the object 20 is received by the transducer array 32. Alternatively, the transducer array 32 receives, as an acoustic wave, a pressure elastic wave that is created as a result of a local and short time change, such as swelling or contraction, of the object 20 caused by the object 20 being irradiated with a pulsed light from a light irradiation unit (light irradiation member) 31 described later.
In the transducer array 32, receiving surfaces 10 included in transducers 321 are disposed so as to be oriented towards the object 20. The receiving surfaces 10 are connected to a vessel 36 and a support member 322 such that the receiving surfaces 10 are oriented towards the inside of the vessel 36; accordingly, the transducers 321 are capable of efficiently acquiring the acoustic wave propagating from the object 20.
A matching liquid 35 is filled and stored in the vessel 36 between the transducer array 32 and the holding member 11. The transducer array 32 is connected to the vessel 36 filled with the matching liquid 35. Furthermore, it can be said that the transducer array 32 constitutes a portion of the vessel 36 in which the matching liquid 35 is filled. The vessel 36 includes an opening portion 16 that is acoustically opened at a position that overlaps the insertion opening 12 so that the object 20 can be in acoustic contact with the matching liquid 35 stored in the vessel 36. The transducer array 32 is connected to the vessel 36 on a side that faces the opening portion 16.
Water, an acoustic impedance of which is closer to the acoustic impedance of the tissue of the subject than the acoustic impedance of air, is used in the matching liquid 35. Other than water, gel or the like may be used as the matching liquid 35.
The transducer array 32 includes a camera 33 for observing the state in which the object 20 is held by the holding member 11, the transducers 321, and a vessel scanning unit 34 that moves the vessel 36 in two dimensions along a horizontal plane (an XY plane).
The vessel scanning unit 34 moves the vessel 36 relative to the insertion opening 12 to perform two-dimensional scanning of an effective reception region of the transducer array 32 along a horizontal plane such that the object 20 and the effective reception region overlap each other. It can be said that in the present exemplary embodiment, in a state in which the light irradiation area (not shown) irradiated by light from the light irradiation unit 31 is overlapped with the object 20, the light irradiation area is capable of performing two-dimensional scanning along the horizontal plane.
Note that an XY vessel scanning unit, which is a combination of a linear guide, a feed screw mechanism, and a motor, and the like (all not shown), is also included in the vessel scanning unit 34 of the claimed disclosure.
A signal processing unit 4 performs an AD conversion and performs signal processing on digital data (acoustic data). An image generation unit 6 generates a two-dimensional or three-dimensional acoustic image using the acoustic data. The display unit 7 displays the generated acoustic image and the image acquired with the camera 33. A control unit 2 integrally controls at least the XY vessel scanning unit, the light source 5 and the signal processing unit 4.
The holding member 11 has a maintaining function that holds the shape of the object 20 to a predetermined shape during measurement, and has an acoustic impedance that does not hinder the propagation of the acoustic wave reaching the transducer array 32 from the object 20. While the holding member 11 is selected according to the form of the object 20, when the object 20 is a breast, a bowl-like curved surface support is used. Regarding the holding member 11, a plurality of replaceable supports that have sizes and curvatures according to the sizes and shapes of the objects are prepared, or an elastomer and the like that has flexibility is applied.
Note that in order to facilitate transmission of the acoustic wave, a thickness as thin as 0.05 mm to 1.0 mm is applied to the holding member 11. Furthermore, in the present exemplary embodiment, the holding member 11 is a light transmitting member that transmits pulsed light irradiated from the light irradiation unit 31. In a case of an acoustic wave measurement apparatus (not shown) in which the light irradiation unit 31, a light guiding member 51, and a light source 5 are removed from the present exemplary embodiment, the light transmitting property of the holding member 11 is not necessarily required.
Since the holding member 11 maintains the photographing position, the holding member 11 is, desirably, configured of a member that has strength that can endure the load of the object 20, and polyethylene terephthalate (PET), for example, is applied.
The light source 5 generates a photoacoustic wave inside the object 20 by having the object 20 be irradiated by pulsed light. When the object 20 is a tissue, the light source 5 emits a light with a specific wavelength that is absorbed by a specific component among the components constituting the object 20. The light source 5 may be provided together with the transducer array 32 in an integrated manner; however, as in the present exemplary embodiment, the light source 5 may be separated from the transducer array 32 through the light guiding member 51 and may be optically connected.
The light source 5 is desirably a pulse light source that is capable of generating, as an irradiation light, a pulsed light that has a pulse width of a few nanoseconds to a few hundred micro seconds; however, with an intention to generate a photoacoustic wave in an efficient manner, the present exemplary embodiment is configured so that a pulse width between 10 to 100 nanosecond can be adjusted.
Since a high output can be obtained, laser is desirable for the light source 5; however, a light emitting diode or the like may be used instead of the laser. As for the laser, various lasers such as a solid-state laser, a gas laser, a fiber laser, a dye laser, and a semiconductor laser can be used. The irradiation timing, the waveform, and the intensity are controlled with a light source controller (not shown). In the claimed disclosure, the wavelength of the light source that is used is desirably an infrared wavelength in which the light propagates to the inside of the object 20. A center wavelength of light emitted of the light source 5 in the present exemplary embodiment is 500 nm or larger to 1200 nm or smaller, that is, the light is a near-infrared light.
Light that has been emitted from the light source 5 is guided to the object 20 while being processed into a desired light distribution shape with the light guiding member 51. The light guiding member 51 includes an articulating arm in which optical fiber and a lens-barrel with a mirror are built therein.
The light guiding member 51 includes, other than the above, a mirror that reflects light, a lens that collects, magnifies, and changes the shape of light, and a diffusing plate that diffuses light, for example.
As illustrated in
Note that since the transducer array 32 of the present exemplary embodiment is, as illustrated in
The claimed disclosure is an array of a plurality of receiving surfaces in the transducer array in which the shape of the inner surface is defined by a quadric surface of revolution, which will be described later.
The transducers 321 each detect an acoustic wave and transduce the acoustic wave into an electric signal that is an analog signal. Any element (or transducing element) that is capable of detecting an acoustic wave, such as a transducing element utilizing a piezoelectric phenomenon, a transducing element utilizing optical resonance, or a transducing element utilizing change in capacity, may be used.
In the present exemplary embodiment, by disposing the plurality of transducers 321 in the support member 322 with a gap between each other, the transducer array 32 including a multidimensional array of transducers is formed. Using such a multidimensional array of elements enables simultaneous detection of acoustic waves at a plurality of locations, and the detection time can be shortened.
As one of the transducers, a capacitive micromachined ultrasonic transducer is being developed that is fabricated using a micromachining process. A capacitive micromachined ultrasonic transducer includes a cell including a supported vibrating membrane having a gap between a lower electrode, and an upper electrode that is disposed on a surface of the vibrating membrane. Such a capacitive micromachined ultrasonic transducer is referred to as a capacitive micromachined ultrasonic transducer (CMUT). A CMUT is capable of forming a receiving surface including a few ten to a few thousand capacitive cells in a few square millimeters and employs a light-weight vibrating membrane; accordingly, a CMUT is capable of securing a wide receiving band.
CMUT elements are formed from a semiconductor wafer 18 using a dicing cut technique such that an aggregate area of each vibrating membrane (membrane) is cut into a unit cell. The unit cell becomes a minimum unit of a channel reading out an electric signal based on an acoustic wave signal received by the transducer 321. In performing the dicing cut technique, cutting in a parallel manner is repeated at predetermined spatial intervals to cut out the required device areas. The CMUT elements including the cut out receiving surfaces 10 can be made to have a predetermined uniform shape and size.
Accordingly, as illustrated in
Note that as illustrated in
In the receiving surface 10 illustrated in
Meanwhile, the receiving surface 10 illustrated in
Furthermore, the receiving surface 10 illustrated in
Furthermore, the receiving surface 10 illustrated in
As described above, not only a geometrically perfect square illustrated in
Note that the transducer that can be applied to the transducer array of the claimed disclosure includes, other than CMUT, a piezoelectric acoustic wave transducer (a piezoelectric ultrasonic transducer).
Referring to
The plurality of transducers 321 are connected to the support member 322 so that the receiving surfaces of the transducers 321 are oriented towards the inner side of the bowl-like bent surface. From the aspect of symmetry, the bent surface is desirably a quadric surface of revolution. Generally, a quadric surface of revolution includes, other than a sphere, a hemisphere, an ellipsoid, a paraboloid of revolution, and a hyperboloid of revolution, a cone, a column, a parabola pillar, a hyperbolic pillar, an elliptic cylinder, a sinusoidal column, and a parabola pillar. On the other hand, the quadric surface of revolution of the claimed disclosure includes a sphere, a hemisphere, an ellipsoid, a paraboloid of revolution, and a hyperboloid of revolution.
In other words, the quadric surface of revolution of the claimed disclosure is a mode that satisfies an “undevelopable surface requirement” and an “isocenter requirement”.
The undevelopable surface requirement is a requirement in which a collimated problem occurs between adjacent receiving surfaces when receiving surfaces each having a parallelogram shape are arranged. The undevelopable surface requirement corresponds to the problem to be solved by the claimed disclosure. Note that a developable surface refers to a bent surface that is formed only by deformation without having to swell or contract a development view depicted on a flat surface, and the undevelopable surface refers to a bent surface that is not formed without having to partially swell or contract a development view depicted on a flat surface.
Furthermore, the “isocenter requirement” is a condition for forming a high-sensitivity region formed when effective reception regions of a transducer array formed of a plurality of transducers overlap each other at a specific single point. The isocenter requirement is a requirement that corresponds to the precondition of the claimed disclosure. Such a specific single point is referred to as an isocenter and when the inner surface of the transducer array is a hemisphere, the center of curvature of the hemisphere coincides with the isocenter. The quadric surfaces of revolution illustrated in
As illustrated in
Note that in
Without loss of generality, it can be understood that the effective reception regions of the receiving surfaces 10 of the transducers 321 are around the normal lines Ni, Ni+1 in the drawing. As illustrated in
Note that the support member 322 includes the opening portion 16 in a direction in which the object 20 is disposed. Furthermore, the support member 322 includes a support apex v1 on the side that is most far away from the opening portion 16. Furthermore, the support member 322 includes the plurality of openings 40, and the receiving surfaces 10 are each substantially parallel to a corresponding tangent plane 15 of the quadric surface of revolution intersecting the opening 40. In the present exemplary embodiment, the angle formed between each receiving surface 10 and the corresponding tangent plane 15 is within a ±3 degrees range.
As illustrated in
Note that as illustrated in
The arrangement of the receiving surfaces on the quadric surface of revolution, which is a feature of the claimed disclosure will be described next with reference to
Referring to
In order to understand the arrangement of the receiving surfaces 10 on the quadric surface of revolution, one of the receiving surface, on which focus will be given, will be considered as a representative example. Such generalization may be applied to almost all of the portions in the arrangement of the receiving surface except for a singular point, such as a peripheral portion in the arrangement of the receiving surface.
The receiving surfaces 10 illustrated in
In the present exemplary embodiment, as illustrated in
By disposing the receiving surface in the above manner, the receiving surface 10 is disposed so as to be surrounded by the four adjacent receiving surfaces that are adjacent to the receiving surface 10 while being spaced apart at a distance that is smaller than the fifth distance among the distances between the other receiving surfaces. By shortening the distance between the adjacent receiving surface and the receiving surface 10, on which focus is given, the mount density of the transducers 321 can be increased and crosstalk between the effective reception regions of the adjacent transducers 321 can be suppressed.
Furthermore, by disposing the substantially square shaped receiving surfaces 10 in the above parallel arranged manner, the receiving surfaces 10 are capable of forming a spiral array on the quadric surface of revolution at the corresponding positions of the openings 40 such that crosstalk between the effective reception regions of the adjacent transducers 321 can be suppressed and the mount density of the transducers 321 in the transducer array 32 can be increased.
In an overhead view of
The spiral arrangement of the receiving surfaces 10 is formed by a plurality of points of intersection between two types of spiral arrays that extend along the inner surface of the support member 322 from the support apex v1 side towards the opening portion of the support member 322 (in
As illustrated in
Note that the imaginary quadratic curve 41R coincides with an imaginary quadratic curve that is defined by intersections between an imaginary plane 47 including the imaginary rotation axis 46 and the support member 322, and in the present exemplary embodiment, is a quadrant. Furthermore, it may be said that the imaginary quadratic curve 41R illustrated in
As described above, by arranging a plurality of receiving surfaces 10, which have a substantially parallelogram shape on a plane, on the support member 322 including the inner surface formed of the quadric surface of revolution 45, it is possible to achieve high density mounting of the transducers 321 on the support member 322.
The present exemplary embodiment may be a mode described in the following manner.
The transducer array 32 includes the bowl-like support member 322 for supporting the plurality of transducers 321, in which the transducers 321 each include the receiving surfaces 10 that have a substantially parallelogram shape and that receives an acoustic wave.
Furthermore, the plurality of receiving surfaces 10 included in a predetermined area of the support member 322 are arranged on a grid formed by points of intersection between a plurality of imaginary right-handed spirals CW (clock wise) and a plurality of imaginary left-handed spirals CCW (counter clock wise), which cross the imaginary right-handed spirals CW, that extend along the inner surface from the side on which the support apex v1 of the bowl-like inner surface of the support member 322.
Note that the predetermined area described above is an optional area in which the receiving surfaces 10 are arranged in at least two directions that are not parallel to each other and, for example, includes a rectangular area depicted by a broken line in
Accordingly, the predetermined area described above is an area including at least four receiving surfaces 10 that are adjacent to each other in at least two array directions.
Note that as for a non-bowl-like support that is not the target of the claimed disclosure, there are non-quadric surfaces, such as a column and elliptic cylinder. For example, in a columnar support in which the inner surface is defined with a column, when receiving surfaces with a substantially parallelogram shape are arranged, there is no constraint in the geometries of the vertexes and the imaginary rotation axis such that a mode in which the receiving surfaces are mounted in a close-packed manner can be achieved without any spiral array.
A trajectory of a transducer array in an ultrasonic wave measurement apparatus according to the second exemplary embodiment will be described with reference to
x=r(t)cos φ
y=r(t)sin φ (1)
Note that r(t) is a coordinate (moving radius) in the radial direction, and φ is an angle formed by the X axis and a line extending from the point of coordinate origin towards point P. In the present exemplary embodiment, the transducer array is moved so that the coordinate of the transducer array on the moving trajectory in the radial direction, that is, r(t), changes so as to either increase or decrease. Furthermore, it is desirable that the vessel scanning unit moves the transducer array so that the velocity of the moving trajectory in a tangential direction is constant.
Typically, the detection timing of the photoacoustic wave is determined by the repetition frequency of the pulsed light emitted from the light source. For example, when a light source having a repetition frequency of 10 Hz is used, the photoacoustic wave can be generated once in 0.1 seconds. Accordingly, when the velocity in the tangential direction is uniform, and when it is assumed that detection of the photoacoustic wave is performed each 0.1 seconds, it will be possible to uniformly sample the space.
Furthermore, considering the acceleration towards the point of origin, it is desirable that the vessel scanning unit moves the transducer array from the outside of the moving plane. In other words, when the acceleration is large at the initial stage, shaking of the entire apparatus becomes large, and there are cases in which the shaking affects the measurement. Accordingly, shaking of the vessel can be reduced by starting to move from the outer periphery where the acceleration towards the point of origin is small towards the inner periphery.
Furthermore, it is desirable that the vessel scanning unit performs continuous motion in which motion is performed continuously rather than using a step and repeat method in which moving and stopping is repeated. With the above, the period of time in which the vessel is scanned can be shortened. Furthermore, since the change in acceleration during the motion is small, surface waviness of the matching liquid stored in the vessel can be reduced.
The claimed disclosure is capable of providing a transducer array that acquires an acoustic wave image that achieves both resolution and sensitivity when applied in measuring an acoustic wave. Furthermore, the claimed disclosure is capable of providing an acoustic wave measurement apparatus that exerts excellent quality in taking images.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. For example, the present invention can be adapted for a hand-held type probe (not shown), a photo-acoustic wave detection system for a various parts of the human body.
This application claims the benefit of Japanese Patent Application No. 2015-175022, filed Sep. 4, 2015 and No. 2016-125590, filed Jun. 24, 2016, which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-175022 | Sep 2015 | JP | national |
| 2016-125590 | Jun 2016 | JP | national |
