WO2018168562A1 - Transducer array, photoacoustic probe, and photoacoustic measuring device - Google Patents

Abstract

Provided is a transducer array which both improves sensitivity and suppresses unnecessary responses. In a transducer array (20) provided with a plurality of transducer elements (21) capable of detecting ultrasound waves, the positions of the centers of gravity of the plurality of transducer elements (21) are arranged at random in a two-dimensional shape, and the plurality of transducer element (21) are disposed adjacent to one another without a gap.

Description

Transducer array, photoacoustic probe, and photoacoustic measuring device

The present invention relates to a transducer array including a plurality of transducer elements, and a photoacoustic probe and a photoacoustic measuring apparatus including the transducer array.

There is known a photoacoustic measuring apparatus that performs imaging (photoacoustic imaging) of an inside of an inspection target such as a living body using a photoacoustic effect. When performing this imaging, first, the photoacoustic measurement device irradiates a living body with light having a predetermined wavelength. Then, a substance contained in the living body absorbs light energy, and a photoacoustic wave, which is an elastic wave, is generated with the thermal expansion of the living tissue. And a photoacoustic measuring device detects this photoacoustic wave as an ultrasonic wave. Furthermore, photoacoustic imaging is performed by a photoacoustic measuring device creating a photoacoustic image based on the detected photoacoustic signal.

A transducer array (hereinafter sometimes referred to as “array”) configured by arranging a plurality of transducer elements (hereinafter sometimes referred to as “elements”) capable of detecting ultrasonic waves is a photoacoustic imaging. It is used for. By using the transducer array, the received beam can be deflected (steered) electronically. In particular, when the elements are arranged two-dimensionally, the inside of the inspection object can be three-dimensionally imaged by steering the reception beam over three dimensions.

In order to improve the sensitivity of the array, the solid aperture of the transducer array is increased and the elements are densely arranged. As a result, the S / N ratio can be improved, and as a result, deeper inspection can be performed. In order to further improve the sensitivity of the array, it is desirable that the electrical impedance of the element be equal to or less than the electrical impedance of the cable connected to the element and the input impedance of the preamplifier. In this case, it is necessary to increase the element size to some extent. However, when the element size is larger than λ / 2 with respect to the wavelength λ of the received ultrasonic wave, it is difficult to make the element interval smaller than λ / 2. Further, at this time, if the elements are arranged at equal intervals, a grating lobe is generated, thereby increasing an unnecessary response. In particular, when the reception beam is steered, it is greatly affected by the grating lobe.

An attempt has been made to arrange the elements at unequal intervals in order to suppress the occurrence of grating lobes. For example, Patent Document 1 discloses an array in which a plurality of elements are arranged at various radii at intervals along a logarithmic spiral.

Japanese Patent Laid-Open No. 10-93335

In the technique of Patent Document 1, since the elements are arranged in a desired manner, the area occupied by the elements with respect to the opening area of the transducer array, that is, the filling factor of the elements is reduced, so that the sensitivity of the transducer array is reduced. there were. In other words, in the conventional technique, when suppressing unwanted responses by suppressing the occurrence of grating lobes, the sensitivity of the transducer array decreases, making it difficult to achieve both improved sensitivity and suppression of unwanted responses. Met.

The present invention has been made in view of the background art, and an object of the present invention is to provide a transducer array that achieves both improvement in sensitivity and suppression of unnecessary response, and a photoacoustic probe and a photoacoustic measurement apparatus including the transducer array. The purpose is to provide. The present invention is not limited to this purpose, and is a function and effect derived from each configuration shown in the embodiment for carrying out the invention described later, and has another function and effect that cannot be obtained by conventional techniques. is there.

The present invention provides various specific embodiments shown below.
[1] A transducer array including a plurality of transducer elements capable of detecting ultrasonic waves, each of the plurality of transducer elements being randomly arranged in a two-dimensional manner, and the plurality of transducer elements Are arranged adjacent to each other without a gap.

[2] A transducer array including a plurality of transducer elements capable of detecting an ultrasonic wave, each of the plurality of transducer elements being randomly arranged in a two-dimensional manner, and when the received beam is not deflected The transducer array is characterized in that an unnecessary response level with respect to the main response is -30 dB or less.

[3] The transducer array according to [1] or [2], wherein the transducer elements are arranged in a partial spherical shape.
[4] The transducer element according to any one of [1] to [3], wherein the transducer element has a shape defined by Voronoi division with the center of a plurality of circles arranged adjacent to each other in a partial spherical shape. The transducer array described in 1.

[5] The transducer array according to any one of [1] to [4], wherein a filling factor indicating an area occupied by the transducer element with respect to an opening area of the transducer array is 90% or more.
[6] The transducer array according to any one of [1] to [5], wherein an area variation coefficient of the plurality of transducer elements is 50% or less.
[7] The transducer array according to any one of [1] to [6], wherein a variation coefficient of a distance between centroid positions of adjacent transducer elements is 25% or less.

[8] A transducer array according to any one of [1] to [7], and a light irradiation unit that irradiates a subject with light emitted from a light source, the transducer array being irradiated with the light. A photoacoustic probe which detects a photoacoustic wave generated in the subject and outputs a photoacoustic signal.

[9] A photoacoustic measurement device comprising: the photoacoustic probe according to [8]; and a signal processing unit that processes the photoacoustic signal to generate photoacoustic image data.

According to the present invention, it is possible to provide a transducer array that achieves both improvement in sensitivity and suppression of unnecessary response due to a grating lobe, and a photoacoustic probe and a photoacoustic measuring apparatus including the transducer array.

It is a block diagram which shows the structure of the photoacoustic measuring device of 1st embodiment. It is a fragmentary perspective view which shows the structure of the transducer array of 1st embodiment. It is a schematic diagram for demonstrating arrangement | positioning of the transducer element in 1st embodiment, (a) is a top view of a transducer array, (b) is a side view of a transducer array. It is a schematic diagram for demonstrating the filling factor of the transducer element in 1st embodiment. It is a schematic diagram for demonstrating the arrangement | positioning method of the transducer element in 1st embodiment, (a) is a figure which shows the case where eight circles are arrange | positioned, (b) is the case where twelve circles are arranged (C) is a figure which shows the case where 16 circles are arrange | positioned. It is a schematic diagram for demonstrating the arrangement method of the transducer element in 1st embodiment, (a) is a top view of a transducer array, (b) is a side view of the partial spherical surface in which a transducer array is provided. It is a schematic diagram for demonstrating the arrangement method of the transducer element in 1st embodiment, and is a top view of a transducer array. It is a histogram which shows the relationship between the element area of the transducer array of 1st embodiment, and the number of elements. It is a histogram which shows the relationship between the distance between adjacent elements of the transducer array of 1st embodiment, and the number of elements. It is a figure which shows a beam profile in case the focal displacement of the transducer array of 1st embodiment is 0 mm, (a) is a figure which shows a one-dimensional intensity distribution, (b) is a figure which shows a two-dimensional intensity distribution. is there. It is a figure which shows a beam profile in case the focal displacement of the transducer array of 1st embodiment is 1 mm, (a) is a figure which shows 1-dimensional intensity distribution, (b) is a figure which shows 2D intensity distribution. is there. It is a schematic diagram for demonstrating arrangement | positioning of the transducer element in the reference example 1, (a) is a top view of a transducer array, (b) is a side view of a transducer array. It is a figure which shows a beam profile in case the amount of focal movements of the transducer array of the reference example 1 is 0 mm, (a) is a figure which shows a one-dimensional intensity distribution, (b) is a figure which shows a two-dimensional intensity distribution. . It is a figure which shows the beam profile in case the amount of focal movements of the transducer array of the reference example 1 is 1 mm, (a) is a figure which shows a one-dimensional intensity distribution, (b) is a figure which shows a two-dimensional intensity distribution. . It is a figure which shows a beam profile in case the amount of focal movements of the transducer array of the reference example 2 is 0 mm, (a) is a figure which shows a one-dimensional intensity distribution, (b) is a figure which shows a two-dimensional intensity distribution. . It is a figure which shows the beam profile in case the amount of focal movements of the transducer array of the reference example 2 is 1 mm, (a) is a figure which shows a one-dimensional intensity distribution, (b) is a figure which shows a two-dimensional intensity distribution. . It is a graph which shows the relationship between a focal moving amount | distance and an unnecessary response level. It is a schematic diagram for demonstrating arrangement | positioning of the transducer element in 2nd embodiment, (a) is a top view of a transducer array, (b) is a side view of a transducer array. It is a histogram which shows the relationship between the element area of the transducer array of 2nd embodiment, and the number of elements. It is a histogram which shows the relationship between the distance between adjacent elements of the transducer array of 2nd embodiment, and the number of elements. It is a figure which shows a beam profile in case the focal displacement of the transducer array of 2nd embodiment is 0 mm, (a) is a figure which shows a one-dimensional intensity distribution, (b) is a figure which shows a two-dimensional intensity distribution. is there. It is a figure which shows the beam profile in case the focal displacement of the transducer array of 2nd embodiment is 1 mm, (a) is a figure which shows 1-dimensional intensity distribution, (b) is a figure which shows 2D intensity distribution. is there. It is a schematic diagram for demonstrating arrangement | positioning of the transducer element in a modification, and is a top view of a transducer array.

Hereinafter, a transducer array, a photoacoustic probe and a photoacoustic measurement apparatus including the transducer array according to an embodiment of the present invention will be described with reference to the drawings. The embodiment described below is merely an example, and there is no intention of excluding various modifications and technical applications that are not explicitly described in the following embodiment. Each configuration of the present embodiment can be implemented with various modifications without departing from the spirit thereof. Further, they can be selected as necessary, or can be appropriately combined.

In the following description, the dimensional ratios in the drawings are not limited to the illustrated ratios. Further, in this specification, when “˜” is used to express a numerical value or a physical property value before and after that, it is used as including the numerical value or physical property value before and after that. For example, the description of a numerical range of “1 to 100” includes both the upper limit value “1” and the lower limit value “100”, and represents “1 to 100”. The same applies to other numerical ranges.

[1. First embodiment]
The photoacoustic measurement device, photoacoustic probe, and transducer array according to the first embodiment will be described with reference to FIGS. Hereinafter, the first embodiment is also simply referred to as this embodiment. In the present embodiment, a case where the inspection target is a blood vessel of a living body will be described as an example.

[1-1. Constitution]
<Overall configuration>
As shown in FIG. 1, the photoacoustic measurement device 1 of the present embodiment includes a photoacoustic probe 2, a control unit 41, a preamplifier unit 42, an AD conversion unit 43, a beamform unit 44, a signal processing unit 45, a display unit 46, A mechanical scanning unit 47 and a position detection unit 48 are provided. The photoacoustic probe 2 includes a light irradiation unit 10 and a transducer array 20. Furthermore, the transducer array 20 includes a plurality of transducer elements 21 capable of detecting ultrasonic waves.

The control unit 41, the beamform unit 44, and the signal processing unit 45 are functional parts that are realized by executing a program through arithmetic processing by a CPU (Central Processing Unit) (not shown) included in the photoacoustic measurement apparatus 1. The CPU reads and executes programs stored in a data storage device that stores data and programs such as HDD (Hard Disk Drive), SSD (Solid State Device), RAM (Random Access Memory), and ROM (Read Only Memory). As a result, the control unit 41, the beamform unit 44, and the signal processing unit 45 function. The means for realizing the processing functions in the control unit 41, the beamform unit 44, and the signal processing unit 45 are not limited to programs, and may be realized by hardware mounted on the photoacoustic measurement apparatus 1. For example, the control unit 41, the beamform unit 44, and the signal processing unit 45 may be configured as a one-chip microcomputer incorporating a ROM, a RAM, a CPU, or the like, or a DSP (Digital Signal Processor), FPGA (Field It may be configured as an electronic circuit such as -Programmable (Gate Array) or ASIC (Application Specific Integrated Circuit).

The control unit 41 controls the light irradiation unit 10, the transducer array 20, the signal processing unit 45, and the mechanical scanning unit 47, and outputs a signal for synchronizing these operations. For example, the control unit 41 transmits an output timing signal for controlling the output timing of the irradiation light to the light irradiation unit 10 and transmits a detection timing signal for controlling the detection timing of the photoacoustic wave of the transducer array 20. As described above, the control unit 41 transmits a signal for controlling the operation timing of the light irradiation unit 10 and the transducer array 20 so that the photoacoustic probe 2 detects the photoacoustic signal in synchronization with the output of the irradiation light. Can do.

The preamplifier unit 42 is an amplifier that amplifies an input signal. The preamplifier section 42 is provided corresponding to a signal electrode 22 of the transducer array 20 described later (see FIG. 2). The preamplifier unit 42 amplifies the photoacoustic signal input from each signal electrode 22 and outputs the amplified signal to the AD conversion unit 43.

The AD converter 43 is an AD converter that converts an analog signal into a digital signal. The AD conversion unit 43 is provided corresponding to the signal electrode 22 and the preamplifier unit 42, respectively. The AD conversion unit 43 converts the amplified signal of the analog photoacoustic wave signal input from the preamplifier unit 42 into a digitized signal. The AD conversion unit 43 outputs the digitized signal to the beam form unit 44.

The beamform unit 44 is a delay process that gives a delay time corresponding to the positional relationship between the reception focus and each signal electrode 22 to each signal input from the plurality of AD conversion units 43 corresponding to the signal electrode 22. Then, a phasing addition process is performed together with an addition process for adding signals whose phases are matched by the delay process. The beamform unit 44 outputs the signal subjected to the phasing addition processing to the signal processing unit 45.

The signal processing unit 45 receives the signal input from the beamform unit 44 and generates photoacoustic image data. The signal processing unit 45 performs processes such as filter processing, logarithmic compression, and envelope detection on the input signal. And the signal processing part 45 performs a process required for image generation with respect to the signal which performed the above processes, and produces | generates photoacoustic image data. The signal processing unit 45 outputs the generated photoacoustic image data to the display unit 46.

The display unit 46 receives the photoacoustic image data input from the signal processing unit 45 and displays the photoacoustic image. The display unit 46 is a display such as a CRT (Cathode Ray Tube) or an LCD (Liquid Crystal Display). The display unit 46 may display a two-dimensional photoacoustic image or a three-dimensional photoacoustic image according to the processing in the signal processing unit 45.

The mechanical scanning unit 47 moves the photoacoustic probe 2 in a one-dimensional direction, a two-dimensional direction, or a three-dimensional direction, thereby changing the position of the subject, the light irradiation unit 10 and the transducer array 20. . As the mechanical scanning unit 47, for example, an automatic fine moving table that has a permanent magnet rotor induction motor and finely moves the photoacoustic probe 2 in three directions perpendicular to each other is used. The mechanical scanning unit 47 can mechanically scan the position where the transducer array 20 detects the photoacoustic wave. The operation of the mechanical scanning unit 47 is controlled by the control unit 41.

The position detection unit 48 detects the position of the photoacoustic probe 2. As the position detection unit 48, for example, a magnetic, infrared, ultrasonic, or optical position sensor is used. The position detection unit 48 can detect the amount of movement of the photoacoustic probe 2 and adjust the positional relationship between the subject and the photoacoustic probe 2. The position information of the photoacoustic probe 2 detected by the position detection unit 48 is output to the control unit 41.

The photoacoustic probe 2 has a cylindrical housing (not shown). The photoacoustic probe 2 has a cable connected to the control unit 41 and the preamplifier unit 42 on the upper surface of the housing. Furthermore, the photoacoustic probe 2 has an opening 30 in contact with the subject on the bottom surface of the housing (see FIG. 3). The light irradiation unit 10 and the transducer array 20 are provided in the opening 30. A photoacoustic wave is generated in the living body by irradiation of irradiation light emitted from the light source of the light irradiation unit 10, and the transducer array 20 detects this photoacoustic wave and outputs a photoacoustic signal. Then, the photoacoustic signal output from the photoacoustic probe 2 is input to the preamplifier unit 42.

The light irradiation unit 10 has one or more light sources (not shown) that emit light of a predetermined wavelength. As the light source, a light source that emits irradiation light to an object to be inspected and generates a photoacoustic wave by the irradiation light can be used. As such a light source, for example, a laser such as a solid laser, a gas laser, a semiconductor laser, or a chemical laser, a light emitting diode, or the like can be used. Among these, a laser is preferably used because it is excellent in directivity and convergence and can provide a high output. The light source is preferably a pulsed light source that outputs pulsed light having a pulse width of 1 to 100 nsec. The wavelength of the irradiation light emitted from the light source propagates to the substance in the subject to be measured, and a wavelength that can be absorbed according to the light absorption characteristics of the substance is selected. For example, when a blood vessel is imaged for hemoglobin in a living body, a wavelength belonging to the near infrared wavelength region is selected. In this case, the wavelength range is usually 600 to 1000 nm, preferably 700 to 850 nm.

The irradiation light output from the light source is guided to the opening 30 using a light guide means (not shown) such as an optical fiber, a light guide plate, a lens, and a mirror, and is irradiated on the subject. In the present embodiment, a case where the light irradiation unit 10 is provided integrally with the transducer array 20 will be described as an example. The light irradiation by the light irradiation unit 10 and the irradiation conditions are controlled by the control unit 41.

<Configuration of transducer array>
(Structure of transducer array and transducer element)
The structure of the transducer array 20 and the transducer element 21 will be described with reference to FIG. FIG. 2 shows a part of the common electrode 23 and the piezoelectric composite 24 provided in the opening 30. As shown in FIG. 2, the transducer array 20 is sandwiched between a plurality of signal electrodes 22a and 22b, a common electrode (ground electrode) 23, a signal electrode 22a and 22b, and a common electrode 23 provided on a substrate (not shown). The piezoelectric composite 24 is provided. FIG. 2 shows two transducer elements 21a and 21b. In the case where the transducer elements 21a and 21b are not distinguished from each other, a description may be given with the reference numeral “transducer element 21”. Further, when the signal electrodes 22a and 22b are not distinguished from each other, there may be a case where a symbol is given as “signal electrode 22”.

The piezoelectric composite 24 is arranged in a two-dimensional lattice shape with the height direction aligned, and the columnar piezoelectric bodies 25 having substantially the same height, and between the piezoelectric bodies 25 and around the piezoelectric bodies 25. And a polymer body 26 filled at substantially the same height. The piezoelectric body 25 is formed in a quadrangular prism shape with a square cross section, but the shape is not limited to this, and may be a polygonal column shape with a polygonal cross section or a cylindrical shape with a circular cross section. From the viewpoint of production efficiency, a quadrangular prism shape is preferable.

The signal electrode 22 and the common electrode 23 are provided to face each other with the piezoelectric composite 24 interposed therebetween. The signal electrode 22 and the common electrode 23 are provided to face one end and the other end in the longitudinal direction of the piezoelectric body 25 on a plane orthogonal to the direction in which the piezoelectric bodies 25 are continuous. The signal electrode 22 is electrically connected to the preamplifier section 42 by a signal line (not shown). The photoacoustic signal output from the signal electrode 22 is input to the preamplifier unit 42. The common electrode 23 is provided on a surface that receives photoacoustic waves. The common electrode 23 is grounded by a ground wire (not shown). The common electrode 23 is a ground electrode provided in common to the transducer elements 21.

The signal electrode 22 and the common electrode 23 are members in which a conductive metal or alloy is formed in a plate shape. Although it does not specifically limit as a metal used for the signal electrode 22 and the common electrode 23, Gold, silver, copper, platinum, aluminum, nickel etc. are mentioned. The method of forming the signal electrode 22 and the common electrode 23 on the piezoelectric composite 24 is not particularly limited, but can be formed by a method such as plating, sputtering, etching, vacuum deposition, or screen printing.

The piezoelectric composite 24 has a piezoelectric body 25 connected in one axial direction and a polymer body 26 connected in any of the three axial directions when the composite is viewed in three orthogonal directions. -3 type piezoelectric composite is used. The piezoelectric composite 24 is not limited to the 1-3 type, and for example, a 0-3 type, 3-0 type, 3-1 type, 3-2 type, 3-3 type piezoelectric composite may be used. Good. From the viewpoint of isolation by the surrounding polymer body 26 compensating for the deformation generated in the piezoelectric body 25 by receiving the photoacoustic wave, and from the viewpoint of flexibility for deforming the piezoelectric composite 24 into a partial spherical shape, 1- A type 3 piezoelectric composite is preferred. The ratio (length / width) between the length and width of the columnar piezoelectric body 25 is not particularly limited, but is usually 3 to 10, preferably 4 to 6.

The piezoelectric body 25 is formed by, for example, cutting a piezoelectric material into a lattice shape using a dicing machine or the like, and providing gaps at predetermined intervals between the columnar piezoelectric materials. As the piezoelectric material, a material exhibiting a piezoelectric effect that generates a voltage in response to pressure displacement caused by a photoacoustic wave applied from the outside is used. The piezoelectric material used for the piezoelectric body 25 is not particularly limited. For example, piezoelectric ceramics such as lead zirconate titanate (PZT), barium titanate, lead titanate, and lead niobate ceramics; lithium niobate; Examples thereof include single crystals such as zinc titanate niobate titanate (PZNT) and lead magnesium niobate titanate (PMNT); organic materials such as polyvinylidene fluoride (PVDF) and polyurea (PU). When an organic material is used as the piezoelectric material, it is not necessary to have a composite structure. Therefore, an integrated plate-like piezoelectric body made of an organic material of a piezoelectric material can be used instead of the piezoelectric composite 24.

The polymer body 26 is formed by filling a polymer material around the piezoelectric body 25 cut in a lattice shape. The polymer material used for the polymer body 26 is not particularly limited. For example, an organic synthetic resin such as an epoxy resin, a silicone resin, a polyester resin, a polyethylene resin, a polystyrene resin, a polyurethane resin, a polyamide resin, or a polycarbonate resin can be used. Molecule.

By providing the signal electrode 22 and the common electrode 23 with the piezoelectric composite 24 interposed therebetween, the signal electrode 22, the common electrode 23 opposed to the signal electrode 22, and the piezoelectric body 25 positioned between the signal electrode 22 and the common electrode 23. Thus, the transducer element 21 is configured. In other words, the transducer element 21 includes at least the signal electrode 22, the piezoelectric body 25, and the common electrode 23 in this order.

When the piezoelectric composite 24 is divided by the signal electrode 22, the piezoelectric bodies 25 arranged at positions corresponding to the signal electrode 22 are grouped so as to be included in each transducer element 21. In FIG. 2, 54 piezoelectric bodies 25 are grouped into 24 and 30 groups by two signal electrodes 22a and 22b, and are included in transducer elements 21a and 21b, respectively. By changing the size and shape of the signal electrode 22, the transducer element 21 can be formed in a desired size and shape. As described above, the transducer array 20 has a high degree of design freedom in the area occupied by the transducer elements 21 in the transducer array 20.

In FIG. 2, the case where the signal electrode 22 is rectangular has been described as an example. However, the shape of the signal electrode 22 is not limited to this, and for example, a polygon, a circle, an ellipse, a star, or a contour is used. It may be an irregular shape consisting of a curve. In the case of a polygon, the corner may be rounded. In FIG. 2, the signal electrodes 22 are arranged along the lattice-like arrangement of the piezoelectric bodies 25 so as to cover the individual piezoelectric bodies 25, but the correspondence relationship between the signal electrodes 22 and the piezoelectric bodies 25 is as follows. It is not limited to this. For example, the signal electrode 22 may be disposed obliquely with respect to the lattice-like arrangement of the piezoelectric bodies 25. Further, the signal electrode 22 may be arranged so that the piezoelectric body 25 is positioned on the boundary line of the end portion of the signal electrode 22 in a plan view with respect to the piezoelectric body 25. That is, the signal electrode 22 may be disposed so as to cover only a part of the piezoelectric body 25. However, when the signal electrode 22 is arranged so as to cover only a part of the piezoelectric body 25 and the piezoelectric body 25 is exposed to the outside of the signal electrode 22 from the boundary line of the signal electrode 22, The piezoelectric body 25 cannot contribute to detection of photoacoustic waves. For this reason, it is preferable to arrange the signal electrode 22 so that the boundary line of the signal electrode 22 passes between the adjacent piezoelectric bodies 25. Accordingly, the detection efficiency of the photoacoustic wave can be improved by arranging the signal electrode 22 so that the entire individual piezoelectric body 25 is covered with the signal electrode 22 in plan view. Further, the distance between the adjacent signal electrodes 22a and 22b preferably does not exceed the distance between the adjacent piezoelectric bodies 25, that is, the thickness of the polymer body 26 sandwiched between the piezoelectric bodies 25.

The number of transducer elements 21 provided in the transducer array 20 is usually 10 to 10,000, preferably 20 to 1,000, and more preferably 100 to 500. In the present embodiment, a case where the transducer array 20 includes 256 transducer elements 21 will be described as an example. As the number of transducer elements 21 increases, the resolution of the transducer array 20 tends to increase. On the other hand, as the number of transducer elements 21 increases, the number of circuits necessary for processing such as amplification and delay of the photoacoustic signal obtained by each transducer element 21 increases, and the load of calculation processing tends to increase. Moreover, when the number of connection lines from the transducer element 21 increases, the cable of the transducer element 21 becomes thick, and the handling is reduced.

A backing layer (not shown) is provided on the signal electrode 22 side of the transducer element 21. The backing layer is provided on the side opposite to the ultrasonic wave receiving direction of the transducer element 21 and suppresses noise by absorbing and attenuating the ultrasonic wave. Examples of the material used for the backing layer include epoxy resin, natural rubber, and synthetic rubber. Furthermore, the backing layer may contain powders such as titanium oxide, tungsten oxide, and ferrite.

An acoustic matching layer (not shown) is provided on the common electrode 23 side of the transducer element 21. The acoustic matching layer is provided on the ultrasonic wave receiving direction side of the transducer element 21 to match the acoustic impedance between the piezoelectric composite 24 and the inspection object and suppress reflection at these boundary surfaces. is there. The acoustic impedance of the acoustic matching layer is preferably set to the acoustic impedance between the piezoelectric composite 24 and the inspection object. Examples of the material used for the acoustic matching layer include polyethylene, polypropylene, polycarbonate, polydimide, polyethylene terephthalate, epoxy resin, and urethane resin. In order to improve the propagation efficiency of ultrasonic waves between the piezoelectric composite 24 and the living body, the acoustic matching layer may contain resin particles or metal particles.

(Placement of transducer elements)
The arrangement of the transducer elements 21 will be described with reference to FIGS.
FIG. 3A is a diagram showing an arrangement relationship between the light irradiation unit 10 and the transducer array 20 in the opening 30 on the side of the photoacoustic probe 2 in contact with the inspection object. FIG. 3A shows the transducer elements 21 arranged in a partial spherical shape projected on a plane. In FIG. 3A, the area occupied by the transducer element 21 is indicated by a white area. Moreover, the area | region which parts other than the transducer element 21 and the light irradiation part 10 occupy is shown by the black area | region. Further, the center of gravity position 27 of each transducer element 21 is indicated by a point. FIG. 3B is a diagram for explaining the structure of the transducer array 20 provided in a partial spherical shape.

3A shows a positional relationship between the transducer array 20 including a plurality of transducer elements 21 and the light irradiation unit 10 disposed at the center surrounded by the transducer elements 21. FIG. As shown in FIG. 3A, in the transducer array 20, the plurality of transducer elements 21 are randomly arranged at their center positions 27 in a two-dimensional manner. Further, the plurality of transducer elements 21 are arranged adjacent to each other without a gap. In this specification, the arrangement relationship and shape of the transducer elements 21 are determined by the arrangement relationship of the signal electrodes 22. That is, the arrangement relationship and shape of the transducer elements 21 refer to the arrangement relationship and shape of the signal electrodes 22.

In this specification, “random” means that the transducer elements 21 are irregularly arranged so as to suppress the generation of grating lobes. Furthermore, in the transducer array 20, the irregular arrangement of the transducer elements 21 that suppress the generation of grating lobes spreads in a two-dimensional manner. As a regularly arranged array in which grating lobes are generated, for example, a two-dimensional array in which elements are arranged in a lattice such as a square lattice, a rectangular lattice, a hexagonal lattice, an oblique lattice, or a parallel lattice. An array, a two-dimensional array in which elements arranged in a straight line at equal intervals or unequal intervals are arranged in parallel and at equal intervals, an element arranged in an annular shape at equal intervals or unequal intervals, and the ring diameters at equal intervals A two-dimensional array arranged concentrically instead of the above. Any transducer array 20 may be used as long as it suppresses the generation of grating lobes, and a regular arrangement of several transducer elements 21 may appear in a part of the transducer array 20.

In this specification, the barycentric position 27 of the transducer element 21 refers to the barycentric position of the signal electrode 22 of the transducer element 21. The position of the center of gravity of the signal electrode 22 is calculated as the centroid of the signal electrode 22 by regarding the density of the signal electrode 22 as being uniform. The calculation of the position of the center of gravity can be performed by a known method. For example, when the shape of the element 21 is a circle or an ellipse, the center thereof is calculated as the barycentric position. When the shape of the transducer element 21 is a triangle, the intersection of the three middle lines of each vertex is calculated as the barycentric position. When the shape of the transducer element 21 is a quadrangle, first, the element 21 is divided by a first diagonal line and divided into two triangles, and the barycentric position of each of the divided triangles is obtained. This procedure is also performed for a second diagonal line different from the first diagonal line, and the barycentric position of each of the divided triangles is obtained. The intersection of the line segment connecting the centroid positions of the two triangles divided by the first diagonal line and the line segment connecting the centroid positions of the two triangles divided by the second diagonal line is calculated as the centroid position. . When the shape of the transducer element 21 is a polygon, the element 21 is first divided into diagonal lines and divided into a plurality of triangles, and the barycentric position of each of the divided triangles is obtained. Next, a polygon that connects the obtained centroid positions of triangles is created, and the centroid position is calculated by repeating the procedure for obtaining the centroid position of the polygon. Further, when the shape of the element 21 is an indefinite shape whose contour is a curve, the shape of the element 21 can be approximated to a polygon inscribed in the contour, and the center of gravity of the polygon can be calculated.

In this specification, the term “adjacently arranged without a gap” does not mean an aspect in which the signal electrodes 22 of adjacent transducer elements 21 are in contact with each other, but are arranged so close that the signal electrodes 22 do not contact each other. Say what you are. As described above, the mode in which the signal electrodes 22 are arranged adjacent to each other with substantially no gap allows the photoacoustic signals from the transducer elements 21 to be extracted independently.

The transducer elements 21 are preferably arranged between adjacent transducer elements 21 so that the sides of the signal electrodes 22 face each other. Thereby, for example, the gap between the adjacent transducer elements 21 is reduced as compared with the case where the signal electrode 22 faces point-to-point and the case where the signal electrode 22 faces point-to-face, so that the transducer element 21 can be arranged. The shape of the transducer element 21 arranged in this way is preferably a polygon. The transducer array 20 is arranged so that the opening 30 is filled with the transducer elements 21.

Here, the reason why the plurality of transducer elements 21 are arranged adjacent to each other without a gap is that the inventors of the present invention generate a grating lobe when there is a gap between the randomly arranged transducer elements 21. This is because the unnecessary response at the time of non-deflection may be increased. That is, by arranging a plurality of randomly arranged transducer elements 21 adjacent to each other with no gap, it is possible to suppress an increase in unnecessary response when the received beam is not deflected.

Therefore, the arrangement of the transducer elements 21 can be defined from the relationship between the main response of the transducer array 20 and the unnecessary response. In this case, when the receiving beam is not deflected, the transducer array 20 preferably has an unnecessary response level with respect to the main response of −30 dB or less, more preferably −35 dB or less, and further preferably −40 dB or less. When the unnecessary response level is within the above range, the transducer elements 20 are arranged adjacent to each other without a gap so as to suppress the influence of unnecessary responses caused by the gap between the adjacent transducer elements 21. Can be provided.

The unnecessary response level is obtained from the beam profile of the transducer array 20. The beam profile indicates the intensity distribution of reception sensitivity with respect to the distance from the center of the array with respect to the reception beam formed by the transducer array 20. In the beam profile, a peak of reception sensitivity derived from the main lobe generated in the direction of the focus appears as a main response in a region near the array center. At this time, the intensity of the reception sensitivity that appears in a region outside the range including the peak derived from the main lobe is regarded as an unnecessary response. And the ratio of the strongest peak intensity in the intensity of the reception sensitivity derived from the unnecessary response to the peak intensity of the reception sensitivity of the main response with the strongest reception sensitivity is obtained, and the unnecessary response level ( dB) is calculated.

The point response characteristics in photoacoustic imaging are measured for a medium in which microspheres made of a material having a light absorption rate that cannot be ignored are embedded in a medium where light absorption can be ignored. A point response characteristic is measured by irradiating the microsphere with a light pulse and receiving and recording the generated photoacoustic wave with a transducer array. Furthermore, a beam profile is obtained by moving the microsphere relative to the transducer array and repeating the operations of irradiation with light pulses and reception of photoacoustic waves. At this time, when paying attention to the received beam profile, it is preferable to measure with the relative positional relationship between the light source and the microsphere being constant. The radius of the microsphere is preferably 1/2 or less of the focused ultrasonic wavelength. A similar beam profile can also be obtained by numerical simulation of ultrasonic propagation. When performing a numerical calculation simulation, the numerical value calculation is generally performed by regarding the transducer array as an aggregate of point receiving elements. The interval between the point receiving elements is preferably set to ½ or less of the focused ultrasonic wavelength. In order to satisfy this condition, when the transducer array is made of a piezoelectric composite, it is sufficient to replace each of the piezoelectric columns constituting the transducer with a point receiving element.

The transducer elements 21 may be spaced from each other as long as the effect of unnecessary response caused by the gap between the adjacent transducer elements 21 is suppressed. More specifically, the interval between adjacent transducer elements 21 is preferably 1 / 2λ or less, more preferably 1 / 3λ or less, further preferably, relative to the wavelength λ of the photoacoustic wave received by the transducer element 21. Is 1 / 6λ or less.

The arrangement relationship of the transducer elements 21 can also be indicated by a filling rate indicating the total area occupied by the transducer elements 21 with respect to the opening area of the transducer array 20. This filling rate is preferably 90% or more, more preferably 95% or more, still more preferably 98% or more, and particularly preferably 99% or more. When the filling rate is within the above range, the transducer array 20 in which the transducer elements 21 are arranged adjacent to each other without a gap is suppressed to such an extent that the influence of an unnecessary response caused by the gap between the adjacent transducer elements 21 is suppressed. Can be provided. In calculating the filling rate, the opening area of the transducer array 20 is the sum of the area occupied by the transducer elements 21 and the area of the portion sandwiched between adjacent transducer elements 21. That is, in the entire opening 30 shown in FIG. 4, the area of the portion where the light irradiation unit 10 is arranged and the region 102 indicated by the oblique lines outside the assembly composed of the plurality of transducer elements 21 are the transducer array 20. Not included in the opening area.

In the transducer array 20, the variation coefficient of the area of the transducer element 21 is preferably 50% or less, more preferably 30% or less, still more preferably 20% or less, and particularly preferably 10%. When the variation coefficient of the area of the transducer elements 21 is within the above range, the characteristics of the transducer elements 21 tend to be easily aligned. Thereby, control of the photoacoustic signal obtained from the transducer elements 21 included in the transducer array 20 is facilitated. The coefficient of variation (%) of the area of the transducer element 21 can be calculated by dividing the standard deviation of the area of the transducer element 21 by the average value of the transducer element 21 and multiplying by 100.

In the transducer array 20, the coefficient of variation of the distance between the gravity center positions 27 of the adjacent transducer elements 21 (hereinafter sometimes referred to as “distance between adjacent elements”) is preferably 25% or less, more preferably 10% or less. More preferably, it is 5% or less, particularly preferably 2% or less. When the variation coefficient of the distance between adjacent elements of the transducer element 21 is within the above range, the transducer elements 21 tend to be arranged at substantially equal distance intervals. As a result, the transducer elements 21 can be arranged in the entire transducer array 20 so as to reduce the bias, and a gap generated between the transducer elements 21 can be suppressed. The variation coefficient (%) of the distance between adjacent elements of the transducer element 21 is obtained by dividing the standard deviation of the distance between adjacent elements of the transducer element 21 by the average value of the distance between adjacent elements of the transducer element 21 and multiplying by 100. It can be calculated by

The distance between adjacent elements will be described with reference to FIG. In the case of the distance between adjacent elements of the element 21a, as shown in FIG. 3A, the distance between the gravity center positions 27 of the elements 21b, 21c, 21d, 21e, 21f, and 21g adjacent to the element 21a. . Here, illustrates the adjacent element distance L ₁ between the element 21a and the element 21f, the element 21a, device 21b, 21c, 21d, 21e, 21g regard to adjacent elements the distance between each of the elements 21a This is the distance between adjacent elements. The variation coefficient of the distance between adjacent elements of the adjacent transducer elements 21 described above indicates a variation coefficient of the distance between adjacent elements for all the transducer elements 21 included in the transducer array 20.

In measuring the filling factor, area, and distance between adjacent elements of the transducer element 21, it can be measured by actually measuring the size of the signal electrode 22 of the transducer element 21 included in the transducer array 20. At this time, it may be observed and measured using a magnifying glass or a microscope as necessary.

As shown in FIG. 3B, the transducer array 20 is provided with a partial spherical surface 31 in the opening 30 of the photoacoustic probe 2. The partial spherical surface 31 is a spherical crown which is a side surface portion of a spherical notch cut by a bottom surface of a cone having a vertex angle of 90 degrees and a generatrix length of 30 mm in a sphere having a radius of 30 mm and having a vertex angle of 90 degrees. It has the shape of The partial spherical surface 31 has a diameter of the opening 30 of 42.4 mm, and an F number representing a ratio of the focal length to the diameter is 0.8. The transducer element 21 is disposed on the concave portion on the partial spherical surface 31.

The transducer array 20 is formed so that the piezoelectric composite 24 forms a partial spherical surface 31. For example, the piezoelectric composite 24 formed into a partial spherical shape is heated by a plate-shaped piezoelectric composite 24 and sandwiched between a preliminarily heated spherical concave mold and a spherical convex shape, and is bent into a spherical shell shape. Can be obtained. Furthermore, the transducer element 21 is obtained by providing the signal electrode 22 and the common electrode 23 as well as the signal line and the ground line on the piezoelectric composite 24 formed into a partial spherical shape. The transducer element 21 is arranged in a partial spherical shape with the common electrode 23 facing the concave surface.

(Method for arranging transducer elements)
A method for arranging the transducer elements 21 will be described with reference to FIGS.
The transducer elements 21 are arranged by an adjacent circle arranging step of arranging a plurality of circles adjacent to each other in a partial spherical shape and a dividing step of dividing an area sandwiched between the plurality of circles arranged in the adjacent circle arranging step. be able to.

First, the adjacent circle placement process will be described. In the adjacent circle arrangement step, an additional circle is installed so as to be adjacent to the basic circle. Hereinafter, when the basic circle and the additional circle are not distinguished, they may be collectively referred to as a virtual circle. First, as shown in FIG. 5A, four basic circles 111 are installed near the array center 110 (step S1). The virtual circle is installed such that the outer circumference of the virtual circle is in contact with the surface of the partial spherical surface 31 described with reference to FIG. At this time, the center-to-center distance of each basic circle 111 is set to be less than twice the diameter of the basic circle. This is to prevent the additional circle 112 from being installed at a position overlapping the center 110 when the additional circle 112 described later is installed. The diameters of the basic circle 111 and the additional circle 112 and the additional circle described later are set to the same length. The diameters of these virtual circles correspond to the minimum distance between the gravity center positions 27 of the adjacent transducer elements 21 and can be appropriately set according to the desired performance of the transducer array 20. The array center 110 is a position corresponding to the center of the transducer array 20.

Next, as shown in FIG. 5 (a), an additional circle 112 is placed at a position where the distance from the array center 110 is the smallest, in contact with at least two of the basic circles 111 arranged in step S1. (Step S2). Here, four additional circles 112 are provided.

Further, as shown in FIG. 5 (b), eight virtual circles obtained by adding the four additional circles 112 installed in step S2 to the basic circle 111 installed in step S1 are used as the basic circle 113, and step S2 and Similarly, an additional circle 114 is set (step S3). Here, four additional circles 114 are provided.

Thereafter, additional circles will be set in the same manner. As an example, as shown in FIG. 5C, 12 virtual circles obtained by adding the four additional circles 114 installed in step S3 to the basic circle 113 are used as the basic circle 115, and the additional circle 116 is added in the same manner as in step S2. Is installed. Here, four additional circles 116 are provided.

In this way, by repeating the installation of additional circles, a large number of virtual circles can be adjacently arranged in a partial spherical shape. FIG. 6A shows that four additional circles 118 are installed in addition to the basic circle 117 installed around the array center 110. FIG. 6B shows a basic circle 117 and an additional circle 118 installed in a partial spherical surface 119 in a side view. The partial spherical surface 119 has the same crown shape as the partial spherical surface 31 described above. In this way, the installation of additional circles is repeated until a desired number of virtual circles are installed according to the design of the transducer array 20. As shown in FIG. 7, the virtual circle can be installed as long as the additional circle to be installed is located within the virtual opening 130 having the same shape and the same area as the opening 30. In the present embodiment, 256 virtual circles 121 are installed in the virtual opening 130. In FIG. 7, the area occupied by the virtual circle 121 is indicated by a white area. A region occupied by a portion other than the virtual circle 121 is indicated by a black region.

Next, the division process will be described. In the dividing step, the region sandwiched between the virtual circles 121 arranged in the adjacent circle arranging step is divided, and the region occupied by the virtual circle 121 is expanded to this divided region. The area between the virtual circles 121 is divided such that the area closest to the center of the virtual circle 121 adjacent to this area is incorporated in the virtual circle 121. At this time, the virtual circle 121 installed on the partial spherical surface is divided on the surface of the partial spherical virtual opening 130.

The division step can be performed by Voronoi division with the center of the plurality of virtual circles 121 arranged in the adjacent circle arrangement step as a generating point. Voronoi division means that when a plurality of points (hereinafter, sometimes referred to as “base points”) are arranged on a certain surface, any point on that surface belongs to the closest base point. This means dividing the surface. Specifically, the Voronoi division connects adjacent generating points with line segments, draws a vertical bisector between the generating points, and creates a Voronoi boundary connecting the vertical bisectors. Is done. By Voronoi division, a Voronoi diagram in which the surface of the virtual opening 130 is divided into polygonal Voronoi regions defined by Voronoi boundaries is obtained. Each Voronoi region has one virtual circle 121 center. Further, by Voronoi division, a region occupied by the virtual circle 121 is expanded with a Voronoi boundary that divides the region between the adjacent virtual circles 121 as a boundary line.

Thus, as shown in FIG. 3A, the transducer array 20 in which the transducer elements 21 are arranged is obtained. The shape of the signal electrode 22, that is, the shape of the transducer element 21 is determined by the Voronoi region delimited by the Voronoi boundary. As described above, it can be said that the transducer element 21 has a shape defined by Voronoi division with the center of a plurality of circles arranged adjacent to each other in a partial spherical shape.

Since the additional circle 112 is installed so as to be adjacent to at least two basic circles 111 on the partial spherical surface by the adjacent circle arrangement step, the virtual circle 121 is not disposed by fine packing such as hexagonal packing, Arranged with fluctuations. For this reason, the virtual circle 121 is arranged with some roughness. Furthermore, the virtual circle 121 is expanded by performing the dividing step in this state, so that the transducer elements 21 are not randomly arranged at the center positions 27 but are arranged randomly. The shape of the transducer element 21 is defined by Voronoi division, but is determined based on the center of the virtual circle 121 having the same diameter arranged adjacently. For this reason, as compared with the case where Voronoi division is performed using points arranged at random at random, the variation in the area of the transducer element 21 is small, and the variation in the distance between the gravity center positions 27 of the adjacent transducer elements 21 is small. . Compared to the case where Voronoi division is performed by randomly arranging generating points, and the one with less variation is extracted from the obtained Voronoi diagram, according to the arrangement method of this embodiment, the resources required for calculation are reduced. The transducer elements can be arranged in a short time by reducing.

[1-2. Operation and characteristics]
The photoacoustic measurement apparatus 1 is configured as described above, and irradiates the subject with irradiation light from the light irradiation unit 10. The transducer array 20 detects a photoacoustic wave emitted from the subject and outputs a photoacoustic signal. Then, the signal processing unit 45 processes the photoacoustic signal to generate photoacoustic image data, and the display unit 46 displays the photoacoustic image. At this time, the beamform unit 44 controls the delay time of the photoacoustic signals from the plurality of transducer elements 21 to electronically deflect (steer) the focal position of the received beam from the geometric focal position. Can do. Further, by moving the photoacoustic probe 2 by the mechanical scanning unit 47, it is possible to mechanically scan the irradiation position of the irradiation light and the detection position of the photoacoustic wave. At this time, the position detection unit 48 detects the position of the photoacoustic probe 2, thereby controlling the movement direction, movement amount, and movement speed of the mechanical scanning unit 47 via the control unit 41. In addition, by linking the operations of the light irradiation unit 10, the transducer array 20, the signal processing unit 45, and the mechanical scanning unit 47 by the control unit 41, irradiation of irradiation light and photoacoustic waves at a desired position and timing are performed. Detection. Thereby, in the photoacoustic measuring device 1, photoacoustic imaging can be performed combining the imaging by mechanical scanning and the imaging by an electronic focus. Alternatively, the mechanical scanning unit 47 may be omitted, and the photoacoustic probe 2 may be manually moved and its position detected by the position detection unit 48.

In the transducer array 20 of the present embodiment, the area distribution of the transducer elements 21 has the relationship shown in FIG. 8, and the distribution of the distance between adjacent elements has the relationship shown in FIG. The transducer array 20 has an average area of the transducer elements 21 of 0.942 mm ² , a standard deviation of 0.058 mm ² , and a variation coefficient of 6.2%. The transducer array 20 has an average distance between adjacent elements of the transducer element 21 of 2.47 mm, a standard deviation of 0.031 mm, and a variation coefficient of 1.3%. The filling rate of the transducer array 20 is 98%.

The beam profile of the transducer array 20 was estimated by numerical simulation. In this specification, the beam profile is defined on the XY plane so that the Z-axis passes through the center of the array in the XYZ 3-axis orthogonal coordinate system, and the direction of the received beam when not deflected coincides with the direction of the Z-axis. When the transducer array 20 is placed, the receiving sensitivity in the range of ± 3 mm square in the XY direction from the center of the array is shown.

10A and 10B show a case where the amount of movement of the focal position due to electronic deflection (hereinafter sometimes referred to as “focus movement amount”) is 0 mm, that is, the received beam is not deflected. The beam profile of the transducer array 20 is shown.

FIG. 10 (a) shows a one-dimensional intensity distribution from the Y-axis direction passing through the center of the array. In FIG. 10A, the horizontal axis represents the distance (mm) from the X-axis array center, and the vertical axis represents the intensity of reception sensitivity. As shown in FIG. 10A, a main lobe peak as a main response appears at a position of X = 0 mm. In FIG. 10A, the amplitude of the intensity of the reception sensitivity is represented by a relative value where the reception sensitivity of the main response is 1.

FIG. 10B shows a two-dimensional intensity distribution of reception sensitivity from the Z-axis direction. In FIG. 10B, the horizontal axis indicates the distance (mm) from the X-axis array center, the vertical axis indicates the distance (mm) from the Y-axis array center, and the intensity of reception sensitivity is the main response. The logarithm (dB) of the ratio of the main lobe peak to the reception sensitivity is shown.

Next, FIGS. 11A and 11B show a beam profile of the transducer array 20 when the amount of focal movement is 1 mm in the X-axis direction. FIG. 11A shows a one-dimensional intensity distribution as in FIG. Moreover, FIG.11 (b) has shown two-dimensional intensity distribution similarly to FIG.10 (b).

Furthermore, as reference example 1, there is a transducer array 220 in which fan-shaped transducer elements 221 are regularly arranged without gaps. The transducer array 220 has substantially the same opening area as the transducer array 20.

As shown in FIG. 12 (a), the transducer array 220 divides the ring portion excluding the center of the circle into nine rings, so that nine rings with different diameters are arranged on the outer circumference and inner circumference. Are arranged adjacent to each other. Furthermore, each of the rings is equally divided to form a fan-shaped element 221. There are 8, 16, 20, 24, 28, 32, 36, 44, and 48 elements 221 from the innermost ring to the outer ring, respectively, and 256 elements in the entire transducer array 220. 221. Further, in the transducer array 220, the ring width is set so that the areas of the elements 221 are the same. The transducer array 220 is provided with a partial spherical surface 231 as shown in FIG. Similar to the partial spherical surface 31, the partial spherical surface 231 has a spherical crown shape in a sphere having a radius of 30 mm. The transducer element 221 is arranged in a partial spherical shape on the concave surface portion on the partial spherical surface 231.

The beam profile of the transducer array 220 is shown in FIGS. 13 (a), 13 (b), 14 (a), and 14 (b). FIG. 13 (a) shows a one-dimensional intensity distribution with a focal shift amount of 0 mm, as in FIG. 10 (a). FIG. 13B shows a two-dimensional intensity distribution in the case where the focal point movement amount is 0 mm, as in FIG. Further, FIG. 14A shows a one-dimensional intensity distribution when the focal amount is 1 mm, as in FIG. FIG. 14B shows a two-dimensional intensity distribution when the focal amount is 1 mm, as in FIG. 11B.

Furthermore, as Reference Example 2, a transducer array 320 in which circular transducer elements 321 are arranged without gaps is given (see FIG. 7). The transducer array 320 has substantially the same opening area as the transducer array 20. In the transducer array 320, a virtual circle is arranged in the adjacent circle arranging step described with reference to FIG. 7, and the position and shape of the virtual circle are directly used as the position and shape of the signal electrode without performing the dividing step. is there. Thus, in the transducer array 320, the circular transducer elements 321 are randomly arranged in a partial spherical shape. The filling factor of the transducer array 320 is 83%.

The beam profile of the transducer array 320 is shown in FIGS. 15 (a), 15 (b), 16 (a), and 16 (b). FIG. 15A shows a one-dimensional intensity distribution in the case where the amount of focal movement is 0 mm, as in FIG. FIG. 15B shows a two-dimensional intensity distribution in the case where the focal point movement amount is 0 mm, as in FIG. FIG. 16A shows a one-dimensional intensity distribution in the case where the amount of focal movement is 1 mm, as in FIG. 11A. FIG. 16B shows a two-dimensional intensity distribution when the focal amount is 1 mm, as in FIG. 11B.

FIG. 17 shows the relationship between the focal shift amount and the unnecessary response level for the array 20 of the first embodiment, the array 220 of the reference example 1, the array 320 of the reference example 2, and the array 420 of the second embodiment described later. Is shown. In this case, the unnecessary response level was calculated by regarding the response in the region separated by 0.8 mm or more from the focal point as the unnecessary response.

From the comparison of the beam profiles of FIGS. 13A and 13B with FIGS. 15A and 15B, the array 320 is about 2 mm around the center of the array when the received beam is not deflected. It can be seen that an unnecessary response appears at the position of. From this, in the array 320 in which the circular elements 321 are randomly arranged, it is considered that unnecessary responses are increased due to the generation of grating lobes due to the gaps existing between the elements 321. On the other hand, as is apparent from the beam profiles of FIGS. 10A and 10B, in the array 20, since the elements 21 are arranged adjacent to each other without a gap, an unnecessary response at the time of non-deflection is observed. It can be seen that it is about the same as 220.

Next, from the comparison of the beam profiles of FIGS. 14 (a), 14 (b), 16 (a), and 16 (b), when the received beam is deflected, the array 220 is moved from the array center to the X axis. It can be seen that a large unnecessary response appears at a position near -0.8 mm in the direction. From this, it can be said that in the array 220 in which the fan-shaped elements 221 are arranged, unnecessary responses are increased due to the occurrence of grating lobes due to the regularity of the arrangement of the elements 221. On the other hand, in the array 320 in which the circular elements 321 are randomly arranged, an unnecessary response in the vicinity of −1 mm in the X-axis direction from the center of the array is suppressed as compared with the array 220. Similarly, as is apparent from the beam profiles of FIGS. 11A and 11B, in the array 20, an unnecessary response in the vicinity of −1 mm from the center of the array in the X-axis direction is suppressed. This is considered that the grating lobes are suppressed in the arrays 20 and 320 because the elements 21 and 321 are randomly arranged.

Furthermore, as shown in FIG. 17, in the array 220 of Reference Example 1, the unnecessary response level due to the grating lobe was greatly increased when the focal amount was deflected by 1 mm. On the other hand, in the array 320 of the reference example 2, although the unnecessary response at the time of deflection could be suppressed, the unnecessary response level was increased at the time of non-deflection when the focal point movement amount was 0 mm. On the other hand, the array 20 of the present embodiment has an unnecessary response level similar to that of the array 320 of Reference Example 2 when deflected, but has an unnecessary response level similar to that of the array 220 of Reference Example 1 when not deflected. ing. That is, the array 20 of the present embodiment suppresses unnecessary responses at the time of deflection that occur in an array having a regular array, and also suppresses unnecessary responses at the time of non-deflection that occur in an array having a gap between elements. . More specifically, the unnecessary response level at the time of non-deflection is 0.0269 (= −31.4 dB) in the array 20, 0.0589 (= −24.6 dB) in the array 320, and 0.0196 (in the array 220). = −34.2 dB).

The transducer array 20 has little unnecessary response when the received beam is not deflected, and can suitably perform photoacoustic imaging. Therefore, for example, when imaging in a wide range is required, imaging is performed by changing the position of the array 20 by moving the photoacoustic probe 2 by the mechanical scanning unit 47, and electronic deflection is performed in imaging in a narrow range. By doing so, photoacoustic imaging can be performed with high sensitivity. Such narrow range imaging is preferably in the range of 0 to 0.4 mm from the array center, more preferably in the range of 0 to 0.3 mm from the array center, and still more preferably in the range of 0 to 0.2 mm from the array center. It is.

[1-3. Action and effect]
Since the transducer array 20, the photoacoustic probe 2, and the photoacoustic measurement device 1 according to the present embodiment are configured as described above, the following operations and effects can be obtained.

[1] In the transducer array 20, the transducer elements 21 are arranged adjacent to each other without a gap, so that the opening 30 of the photoacoustic probe 2 is covered with the transducer elements 21. As a result, the photoacoustic wave generated from the subject is detected by the transducer element 21, thereby reducing the loss caused by receiving the photoacoustic wave at the portion of the opening 30 where the transducer element 21 is not provided. Can be improved. Further, by arranging the transducer elements 21 adjacent to each other without a gap, it is possible to suppress an unnecessary response at the time of non-deflection caused by a grating lobe generated when a gap is present between the elements. it can. Further, the transducer array 20 has an undesired response at the time of deflection caused by grating lobes caused when the elements are regularly arranged, because the gravity center positions 27 of the transducer elements 21 are randomly arranged two-dimensionally. Can be suppressed. That is, the transducer array 20 achieves both improvement in sensitivity by increasing the filling factor of the transducer elements 21 and suppression of unnecessary responses due to grating lobes.

[2] In the transducer array 20, the gravity center positions 27 of the transducer elements 21 are randomly arranged two-dimensionally. Furthermore, the transducer array 20 has an unnecessary response level with respect to the main response of −30 dB or less when the received beam is not deflected. Thereby, the transducer array 20 in which the transducer elements 21 are arranged adjacent to each other without a gap is obtained. Therefore, similarly to the above [1], the transducer array 20 can achieve both improvement in sensitivity by increasing the filling factor of the transducer elements 21 and suppression of unnecessary responses due to grating lobes.

[3] In the transducer array 20, the transducer elements 21 are arranged in a partial spherical shape. Thereby, the ultrasonic wave emitted from the vicinity of the geometric focus formed by the transducer element 21 can be efficiently detected. Moreover, the transducer array 20 can arrange | position the transducer element 21 to a partial spherical surface at random and without a gap | interval by the adjacent circle arrangement | positioning process and a division | segmentation process.

[4] The transducer array 20 has a shape in which the transducer elements 21 are defined by Voronoi division with the center of a plurality of circles arranged adjacent to each other in a partial spherical shape. When the transducer element 21 has such a shape, the transducer elements are randomly arranged in a spherical region, and variations in the area of the transducer element 21 and the distance between adjacent elements can be suppressed.

[2. Second embodiment]
A transducer array according to the second embodiment will be described with reference to FIGS. Hereinafter, the second embodiment is also simply referred to as this embodiment. The second embodiment is configured similarly except that the transducer array 20 is changed to the transducer array 420 in the photoacoustic measurement device 1 and the photoacoustic probe 2 according to the first embodiment. Therefore, description of the same components as those in the first embodiment will be omitted, and description will be made using the same symbols.

[2-1. Constitution]
<Configuration of transducer array>
(Structure of transducer array and transducer element)
As shown in FIG. 18A, the transducer array 420 includes a plurality of transducer elements 421 capable of detecting ultrasonic waves. The transducer element 421 has a layer structure similar to that of the transducer array 20 described with reference to FIG. 2, but the shape of the signal electrode 22 is different and the arrangement relationship of the elements 421 is also changed.

(Placement of transducer elements)
FIG. 18A is a diagram showing the positional relationship between the light irradiation unit 10 and the transducer array 420 in the opening 430 on the side in contact with the inspection object of the photoacoustic probe 2. FIG. 18A shows the transducer elements 421 arranged in a partial spherical shape projected on a plane. In FIG. 18A, the area occupied by the transducer element 421 is shown as a white area. Moreover, the area | region which parts other than the transducer element 421 and the light irradiation part 10 occupy is shown by the black area | region.

In the transducer array 420, as shown in FIG. 18A, a plurality of transducer elements 421 are randomly arranged in a two-dimensional manner with respect to the respective gravity center positions. Further, the transducer array 420 is provided with a partial spherical surface 431 as shown in FIG. Similar to the partial spherical surface 31, the partial spherical surface 431 has a spherical crown shape in a sphere having a radius of 30 mm. The transducer element 421 is disposed in a concave shape on the partial spherical surface 431 in a partial spherical shape. Further, the plurality of transducer elements 421 are arranged adjacent to each other without a gap. Further, the transducer elements 421 are arranged between the adjacent transducer elements 421 so that the sides of the signal electrodes 22 face each other. Further, the transducer element 421 has a polygonal shape. The transducer array 420 has a variation in the position of the center of gravity and the shape and area of the transducer element 421 compared to the transducer array 20.

The ratio of the maximum area of the transducer array 420 to the minimum area of the transducer elements 421 included in the transducer array 420 (hereinafter sometimes referred to as “maximum / minimum area ratio”) is preferably 15 or less, more preferably 10 or less. More preferably, it is 5 or less. If the maximum / minimum area ratio is more than the upper limit of the above range, an unnecessary response equivalent to or higher than that of the transducer array 220 may occur during deflection.

(Method for arranging transducer elements)
A method for arranging the transducer elements 421 will be described.
The placement of the transducer elements 421 is obtained by a virtual point placement step for placing random points on the partial sphere, a division step for performing Voronoi division using the points arranged in the virtual point placement step as a mother point, and Voronoi division. And an extraction process for extracting a desired Voronoi diagram from the Voronoi diagram.

First, in the virtual point arrangement step, a desired number of points (virtual points) are set at random positions in a virtual opening having the same shape and area as the opening 430. In this embodiment, 256 virtual points are arranged in a partial spherical shape.

Next, in the dividing step, a Voronoi diagram is obtained by dividing the surface of the virtual opening into polygonal Voronoi regions by using Voronoi division, using the virtual points arranged in the virtual point arranging step as mother points. At this time, the division is performed on the surface of the partially spherical virtual opening.

Further, the creation of a Voronoi diagram with the virtual point placement step and the division step as one set is repeated a plurality of times. As the number of Voronoi diagram creations is repeated, the maximum / minimum area ratio tends to be lower, and a desired Voronoi diagram with less unnecessary response tends to be obtained. Therefore, preferably 10 ⁴ times, more preferably 10 ⁶ times, Preferably 10 ⁸ times. In the present embodiment, it was conducted 10 ⁴ times the creation of Voronoi diagram.

Subsequently, in the extraction process, a Voronoi diagram having the smallest maximum / minimum area ratio is extracted from the Voronoi diagram obtained in the dividing step. The arrangement of the transducer elements 421 is determined by the Voronoi region of the extracted Voronoi diagram.

Thus, as shown in FIG. 18A, a transducer array 420 in which the transducer elements 421 are arranged is obtained. The shape of the signal electrode 22, that is, the transducer element 421 is determined by the Voronoi region delimited by the Voronoi boundary. As described above, it can be said that the transducer element 421 has a shape defined by Voronoi division using a plurality of randomly arranged points as mother points.

By performing a plurality of virtual point placement steps and division steps and further performing an extraction step, the placement, shape, and area of the transducer elements 421 can be determined based on randomly placed virtual points. Thereby, the transducer array 420 which shows the unnecessary response level comparable as the transducer array 20 of 1st embodiment can be obtained. In order to obtain a transducer element 421 having a maximum / minimum area ratio that is about the same as that of the transducer array 20, the number of Voronoi diagram generations is about 10 ²⁰ times.

[2-2. Operation and characteristics]
In the second embodiment, similar to the transducer array 20, the transducer array 420 detects a photoacoustic wave emitted from the subject and outputs a photoacoustic signal. Further, by controlling the delay amount of the photoacoustic signal from the plurality of transducer elements 421, the focal position of the received beam can be electronically deflected (steered).

In the transducer array 420, the area distribution of the transducer elements 421 is in the relationship shown in FIG. 19, and the distribution of the distance between adjacent elements is in the relationship shown in FIG. The transducer array 420 has an average area of the transducer elements 421 of 1.023 mm ² , a standard deviation of 0.478 mm ² , and a coefficient of variation of 46.7%. The transducer array 420 has an average distance between adjacent elements of the transducer element 421 of 1.963 mm, a standard deviation of 0.465 mm, and a variation coefficient of 23.7%. The maximum and minimum area ratio of the transducer array 220 is 10. The filling rate of the transducer array 220 is 99% or more.

The beam profile of the transducer array 420 was estimated by numerical simulation. The beam profile of the transducer array 420 is shown in FIGS. 21 (a), 21 (b), 22 (a), and 22 (b). FIG. 21 (a) shows a one-dimensional intensity distribution with a focal shift amount of 0 mm, as in FIG. 10 (a). FIG. 21B shows a two-dimensional intensity distribution when the focal amount is 0 mm, as in FIG. 10B. FIG. 22A shows a one-dimensional intensity distribution when the focal amount is 1 mm, as in FIG. 11A. FIG. 22B shows a two-dimensional intensity distribution when the focal amount is 1 mm, as in FIG. 11B.

As is apparent from the beam profiles of FIGS. 21A and 21B, in the array 420, the elements 21 are arranged adjacent to each other without a gap. It turns out that it is comparable.

Further, as is apparent from the beam profiles of FIGS. 22A and 22B, an unnecessary response in the vicinity of −0.8 mm from the center of the array in the X-axis direction is suppressed, which is about the same as the arrays 20 and 320. It has become. This is considered that the grating lobe is suppressed by the elements 421 being randomly arranged also in the array 420.

Furthermore, as shown in FIG. 17, the array 420 of the present embodiment has an unnecessary response level comparable to that of the array 320 of Reference Example 2 when deflected, but is comparable to the array 220 of Reference Example 1 when not deflected. Unnecessary response level. That is, the array 420 of the present embodiment suppresses unnecessary responses at the time of deflection that occur in a regularly arranged array, and also suppresses unnecessary responses at the time of non-deflection that occur in an array having a gap between elements. . The array 420 had an unnecessary response level of 0.0196 (= −34.2 dB) when the received beam was not deflected.

The transducer array 420 is configured as described above to achieve both improvement in sensitivity by increasing the filling ratio of the transducer elements 421 and suppression of unnecessary responses due to grating lobes. Furthermore, since the transducer array 420 exhibits the same unnecessary response level as the array 20 of the first embodiment, the positions of the center of gravity are randomly arranged in a two-dimensional manner and are arranged adjacent to each other without a gap. It has been confirmed that the effect of the present invention is achieved by a transducer array including the transducer elements.

[3. Others]
<Placement of transducer elements>
In the above embodiment, in the adjacent circle arrangement step, the four basic circles 111 are arranged at equal intervals and equidistant from the array center 110 with the array center 110 as the center. As described above, since the four basic circles 111 have four-time objectivity, the additional circles 112, 113, and 116 are arranged in a symmetrical positional relationship, and the virtual circle 121 also has four-time symmetry. However, the arrangement of the virtual circle is not limited to this. For example, by arranging the basic circles 111 in an unequal positional relationship, the virtual circles may be arranged so as not to have symmetry.

In the above embodiment, the case where four basic circles 111 are installed has been described. However, the number of basic circles 111 is not limited to four, and an arbitrary number of one or more can be installed. However, when the virtual circle is set so that the virtual circle and the array center do not overlap, it is preferable that the number of the basic circles 111 is three or more.

Further, in the above-described embodiment, the virtual circle is installed so that the peripheral portion of the array center 11 is opened so that the virtual circle does not overlap the array center 110. Since this is performed to provide the light irradiation unit 10 at the position of the array center 110, when the position of the light irradiation unit 10 is changed to a position other than the array center 110, the virtual position is set at the position of the array center 110. A circle may be set up. In this case, a virtual region may be installed by providing a predetermined region for providing the light irradiation unit 10 at an arbitrary position so that the region does not overlap with the virtual circle.

In the above embodiment, the case where circular virtual circles are installed adjacent to each other has been described as an example. The shape of the figure at the time of installation is not limited to a circle, and an ellipse or a polygon may be installed adjacent to each other. It is preferable to use a circular virtual circle from the viewpoint that calculation at the time of installation is easy and the distance between the center positions of adjacent figures after installation is uniform.

<Arrangement of light irradiation part>
In the above embodiment, the example in which the photoacoustic probe 2 has one light irradiation unit 10 in the opening 30 has been described. The light irradiation unit 10 may be provided integrally with the transducer array 20 in the photoacoustic probe 2 or may be provided separately from the transducer array 20. Moreover, the number of the light irradiation parts 10 is not limited to this, Two or more may be sufficient. As an example, FIG. 23 shows a photoacoustic probe 2 including five light irradiation units 510a to 510e and a transducer array 520 in which a plurality of transducer elements 521 are arranged. Here, one light irradiation unit 510a is provided at the center of the transducer array 520, and four light irradiation units 510b to 510e are provided at equal positions around the transducer array 520. Thus, when the photoacoustic probe 2 includes two or more light irradiation units 510, the light irradiation units 510 corresponding to the number of the light irradiation units 510 are provided in advance in the adjacent circle arrangement step and the virtual point arrangement step. And a virtual circle and a virtual point are not arranged in this region. In the dividing step, a Voronoi region is created by excluding a region where the light irradiation unit 510 is provided. Thereby, arrangement | positioning of the some light irradiation part 510 and the transducer element 521 can be performed.

<Shape of transducer array>
In the above-described embodiment, the example in which the transducer elements 21 are arranged in a partial spherical shape and the transducer array 20 is provided as the partial spherical surface 31 has been described. The transducer elements 21 may be arranged in a planar shape, and the transducer array 20 may be a two-dimensional planar array.

<Configuration of piezoelectric body and transducer array>
In the above-described embodiment, the example in which the transducer array 20 in which the transducer elements 21 are arranged is configured by dividing the piezoelectric body 25 included in the piezoelectric composite 24 by the signal electrode 22 has been described. However, the present invention is not limited to this, and the transducer array 20 may be configured by previously creating transducer elements each having a piezoelectric body and arranging the transducer elements. Further, the transducer array 20 may be configured by arranging the transducer elements 21 using cMUT (Capacitive Micromachined Ultrasonic Transducer).

<Inspection object>
In the above-described embodiment, a biological blood vessel has been described as an example of the inspection object. The inspection object is not limited to this, and may be a living organ, tissue, cell, or the like. Alternatively, metal, resin, rubber, wood, glass, ceramic, and the like may be targeted.

<Applicable target>
In the above embodiment, the example in which the photoacoustic imaging is performed by detecting the photoacoustic signal using the photoacoustic probe 2 including the light irradiation unit 10 and the transducer array 20 has been described. The application target of the transducer array 20 is not limited to this. For example, the transducer array 20 can be used for an ultrasonic transmitter that outputs ultrasonic waves from the transducer array 20. Further, it can be used in an ultrasonic diagnostic apparatus and an ultrasonic flaw detection test apparatus that transmit ultrasonic waves to an inspection object and detect a reflected wave reflected by the inspection object by the transducer array 20.

DESCRIPTION OF SYMBOLS 1 Photoacoustic measuring device 2 Photoacoustic probe 10 Light irradiation part 20 Transducer array 21 Transducer element 22 Signal electrode 23 Common electrode 24 Piezoelectric composite 25 Piezoelectric body 26 Polymer body 27 Center of gravity position 30 Opening part 41 Control part 42 Preamplifier part 43 AD conversion Unit 44 beam form unit 45 signal processing unit 46 display unit 47 mechanical scanning unit 48 position detection unit

Claims (9)

1. A transducer array comprising a plurality of transducer elements capable of detecting ultrasound,
   The transducer array, wherein the plurality of transducer elements are randomly arranged in a two-dimensional center of gravity, and the plurality of transducer elements are arranged adjacent to each other without a gap.
2. A transducer array comprising a plurality of transducer elements capable of detecting ultrasound,
   The plurality of transducer elements, each center of gravity position is randomly arranged two-dimensionally,
   A transducer array, wherein an unnecessary response level with respect to a main response is −30 dB or less when a reception beam is not deflected.
3. The transducer elements are arranged in a partial spherical shape,
   The transducer array according to claim 1 or 2.
4. The transducer element has a shape defined by Voronoi division with the center of a plurality of circles arranged adjacent to each other in a partial spherical shape,
   The transducer array according to any one of claims 1 to 3.
5. The filling factor indicating the area occupied by the transducer elements with respect to the opening area of the transducer array is 90% or more.
   The transducer array according to any one of claims 1 to 4.
6. The variation coefficient of the area of the plurality of transducer elements is 50% or less.
   The transducer array according to any one of claims 1 to 5.
7. The variation coefficient of the distance between the gravity center positions of the adjacent transducer elements is 25% or less.
   The transducer array according to any one of claims 1 to 6.
8. A transducer array according to any one of claims 1 to 7;
   A light irradiation unit that irradiates a subject with light emitted from a light source;
   The photoacoustic probe, wherein the transducer array detects a photoacoustic wave generated in the subject by the light irradiation and outputs a photoacoustic signal.
9. The photoacoustic probe according to claim 8,
   A photoacoustic measurement device comprising: a signal processing unit that processes the photoacoustic signal to generate photoacoustic image data.
   

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