JP2019097669A - Signal processing device and signal processing method - Google Patents

Abstract

To execute accurate signal restoration.SOLUTION: A signal processing device includes a reverse filter calculation unit 533 for calculating a reverse filter based on a reception characteristic function of a detection signal detected by an acoustic element, and a signal restoration unit 534 for convolving a result of Fourier transformation for the detection signal and a result of Fourier transformation for the reverse filter, and executing reverse Fourier transformation for a result of the convolution. The reception characteristic function is based on a direction of a detection signal source with respect to a detection unit, and has wide-band frequency characteristics. The reverse filter calculation unit 533 sets a reverse filter so that an arbitrary frequency component has a value larger than 0 in the reverse filter.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a signal processing apparatus that processes a detection signal detected by a detection unit and a technique of a signal processing method.

In the treatment of stenosis and the like of the blood vessels, general imaging of the blood vessels by fluoroscopy is performed to identify a lesion. However, there is a problem that it is not preferable because exposure occurs. As a method of solving such a subject, intravascular catheter imaging using light or an ultrasonic wave is performed. In intravascular catheter imaging, patient burden can be reduced and local imaging can be performed.
In addition, catheter treatment for treating stenosis of blood vessels tends to increase as the procedure is less burdensome on patients than open surgery.

  As a technique for such an intravascular catheter imaging, Patent Document 1 states that “an optical fiber for transmitting light between the tip side and the rear side of the probe has a condenser lens at the tip side, and The optical fiber in the vicinity has a piezoelectric element or an electrostrictive element giving an angle with respect to an axial line, an optical path conversion means is disposed on the same line at the tip of the condensing lens, and light rays emitted from the condensing lens A light beam can be emitted in three dimensions by changing the radiation angle by the optical path conversion means, and radiation can be made three-dimensional scanning "(see abstract).

When performing surgery in a very small area such as catheter treatment, it is required to have both (1) visibility and (2) operability.
In particular, in the case of a case such as chronic total occlusion (CTO), it is required to image a lesion image in real time and accurately perform device treatment at a place designated by the operator (doctor).
The visibility in front of the catheter becomes important when narrowing of a blood vessel such as CTO occurs.

  Therefore, research has been conducted on photoacoustic catheters that perform three-dimensional forward field imaging by controlling the irradiation direction of the laser with a small actuator (fiber scan).

  There is a technology described in Patent Document 2 as a technology for preventing a reduction in resolution of an image due to the propagation speed of light. In Patent Document 2, “Set an attention area in a part of the subject, adjust the phase of each detection signal based on the distance from each detection element to the attention area, and the assumed speed, and adjust the phase Calculating the variation in strength of the detected signals, for a plurality of assumed speeds, and determining, among the plurality of assumed speeds, the speed at which the variation in strength is the smallest as the propagation speed An image generation apparatus, an image generation method, and a program characterized by having means are disclosed (see abstract).

International Publication No. 2016/063406 JP, 2011-120765, A

However, in photoacoustic imaging, the reception sensitivity of the acoustic element changes depending on the angle of laser irradiation. That is, the incident angle of the sound wave to the acoustic element is inclined depending on the angle of the laser irradiation. As a result, there is a problem that unevenness of the image resulting from this inclination occurs.
However, the techniques described in Patent Document 1 and Patent Document 2 do not take into account the change in the reception sensitivity of the acoustic element caused by the angle of laser irradiation.

  The present invention has been made in view of such a background, and the object of the present invention is to perform signal restoration with high accuracy.

In order to solve the problems described above, according to the present invention, an inverse filter calculation unit that calculates an inverse filter based on a reception characteristic function of a detection signal that is detected and generated by a detection unit that detects an incoming signal; The signal processing apparatus further includes: a signal restoration unit configured to convolute a result of Fourier transform and a result of Fourier transform of the inverse filter and further inverse Fourier transform the result of the convolution; the reception characteristic function is a detection surface of the detection unit And based on the inclination of the incoming signal with respect to and having a wide-band frequency characteristic, and the inverse filter calculation unit is configured such that any frequency component in the inverse filter has a value larger than 0, The inverse filter is set.
Other solutions will be described as appropriate in the embodiment.

  According to the present invention, highly accurate signal restoration can be performed.

It is a figure which shows the structure of the front-end | tip part of the catheter 1 used in 1st Embodiment. FIG. 3 is a schematic view showing a light emission mechanism at the tip of the catheter 1; It is a functional block diagram showing composition of photoacoustic catheter system C concerning a 1st embodiment. It is a functional block diagram which shows the detailed structure of the image structure part 53 used by this embodiment. It is a figure which shows the hardware block diagram of the address management apparatus 4 used by this embodiment. It is a figure which shows the hardware block diagram of the imaging process apparatus 5 used by this embodiment. It is a flowchart which shows the process sequence of the photoacoustic catheter system C performed in 1st Embodiment. It is a flowchart which shows the detailed process sequence of the laser emission process for imaging (step S2 of FIG. 7) performed in 1st Embodiment. FIG. 6 is a diagram showing an example of a waveform of a drive voltage applied to a drive unit 19; It is the figure which looked at the drive part 19 (drive device 14) from the front (catheter catheter 1 axial direction). It is a figure which shows the voltage waveform applied to the drive part 19, and the laser emission timing for imaging. It is a figure which shows the injection | emission locus | trajectory of laser R1 for imaging by the applied voltage shown in FIG. It is the figure which expanded the origin vicinity of FIG. It is a flowchart which shows the detailed process sequence of the address correction process (step S5 of FIG. 7) performed in 1st Embodiment. It is a schematic diagram which shows the injection | emission position in a normal state (state without distortion). It is a schematic diagram which shows the injection | emission position which has produced distortion. It is a flowchart which shows the detailed process sequence of the angle correction | amendment processing (step S6 of FIG. 7) performed in 1st Embodiment. It is a figure which shows the arrival direction of a sound wave. It is a figure showing horizontal angle alpha among arrival directions. It is a figure which shows the elevation angle (beta) among arrival directions. It is a figure which shows the case where a sound wave has arrived from just above the acoustic element 11 (a tilt angle of 0 °). It is a figure (the 1) which shows the example to which the sound wave has arrived by 90 degrees of horizontal angles, and raising angle (beta) with respect to the acoustic element 11. FIG. It is a figure (the 2) which shows the example to which the sound wave has arrived at 90 degrees of horizontal angles, and angle of elevation beta to sound element 11. It is a figure (the 3) which shows the example to which the sound wave has arrived by 90 degrees of horizontal angles, and rotation angle | corner (beta) with respect to the acoustic element 11. FIG. FIG. 7 is a diagram showing an example of a time change of a detection signal detected by the acoustic element 11 when a sound wave is incident on the acoustic element 11. It is a figure which shows the principle of a receiving characteristic function. It is a figure which shows the time change of detection intensity. It is a figure which shows an example of a receiving characteristic function. It is a figure which Fourier-transforms the receiving characteristic function H, and also shows an example which showed the absolute value of the amplitude of each frequency. It is a figure which shows the behavior of the real part at the time of Fourier-transforming receiving characteristic function H. FIG. It is a figure which shows the behavior of the imaginary part at the time of Fourier-transforming receiving characteristic function H. FIG. It is a figure which shows only the envelope 421. FIG. It is a figure (the 1) showing the arrival direction (horizontal angle) of the sound wave used for simulation. It is a figure (the 2) showing the arrival direction (turning angle) of the sound wave used for simulation. It is a figure which shows a simulation result when a sound wave arrives from the direction of horizontal angle 0 degree and elevation angle 10 degrees. It is a figure (the 1) showing the arrival direction (horizontal angle) of the sound wave used for simulation. It is a figure (the 2) showing the arrival direction (turning angle) of the sound wave used for simulation. It is a figure which shows a simulation result when a sound wave arrives from the direction of 45 degrees of horizontal angles, and 10 degrees of elevation angles. It is a flowchart which shows the detailed process sequence of the image processing (step S7 of FIG. 7) performed in 1st Embodiment. It is a figure which shows the distance of the acoustic element 11 and the target object with which laser R1 for imaging was irradiated. It is a figure which shows the time change of the signal strength detected by the acoustic element part 18 shown in FIG. It is a figure which shows the modification of the imaging processing apparatus 5a used by this embodiment. It is a figure which shows the example of the receiving characteristic function table used by this embodiment.

  Next, modes for carrying out the present invention (referred to as “embodiments”) will be described in detail with reference to the drawings as appropriate.

First Embodiment
[Structure of catheter 1]
FIG. 1 is a view showing the configuration of the distal end portion of the catheter 1 used in the first embodiment. FIG. 2 is a schematic view showing a light emission mechanism at the distal end portion of the catheter 1. In the present application, the emission of the imaging laser R1 from the optical fiber 13 is referred to as “emission”, and the emission of the imaging laser R1 emitted to the observation target is referred to as “irradiation”.
As shown in FIG. 1, in the photoacoustic catheter 1 (hereinafter simply referred to as the catheter 1), a plurality of acoustic elements (detection units) 11 are arranged in a ring at the tip of the catheter 1 itself. Here, the acoustic element 11 is formed of a piezoelectric element or the like manufactured by MEMS (Micro Electro Mechanical Systems) technology. The acoustic element 11 may be a single element or, as shown in FIG. 1, may be an array type in which a plurality of elements are mounted. By setting the acoustic element 11 to an array type in which a plurality of elements are mounted, it is possible to perform delay and sum. Therefore, since it is possible to enhance the detection signal by Delay and Sum, it is possible to sharpen the catheter imaging image.

The imaging laser R1 emitted from the optical fiber 13 passes through the hollow portion 12 formed inside the acoustic element 11 disposed in a ring shape.
When the imaging laser R1 emitted from the optical fiber 13 provided inside the catheter 1 passes through the hollow portion 12 and is irradiated to the observation target which is a living body, the observation target emits heat, and as a result, The observation target expands in volume. The acoustic element 11 detects a sound wave generated as a result of this volume expansion. That is, the acoustic element 11 receives the sound wave generated by the irradiated imaging laser R1.

Next, the light emission mechanism in the catheter 1 used in the first embodiment will be described with reference to FIGS. 1 and 2.
In the catheter 1, the imaging laser R 1 is transmitted from the imaging laser generator 2 by the optical fiber 13.
As shown in FIGS. 1 and 2, it is preferable that the drive device 14 use a piezoelectric element such as, for example, a cylindrical four-pole PZT element (hereinafter simply referred to as a PZT element). As shown in FIG. 2, the PZT element is bent in the direction by applying a potential difference between the opposing electrodes in the PZT element via the conducting wire D. The tip of the optical fiber 13 passed through the PZT element can be rotated as shown in FIG. 2 by setting the voltage applied to the two opposing pairs of electrodes as a sine wave and shifting the phase by π / 2.

The radius of gyration (radius of gyration shown in FIG. 2) of the optical fiber 13 is controlled by the amplitude of the sinusoidal voltage applied to the PZT element.
Therefore, by changing the amplitude of the voltage applied to the PZT element, the imaging laser R1 emitted from the catheter 1 draws a spiral trajectory 101 shown in FIG. At this time, the rotational frequency of the imaging laser R1 is 8 kHz, for example.
In this manner, the driving device 14 drives the imaging laser R1 to emit in the predetermined direction with respect to the traveling direction of the catheter 1.

  As described above, when the tip of the catheter 1 is rotated, the imaging laser R1 is rotated and emitted, which is referred to as a fiber scan.

  The imaging laser R1 emitted from the tip of the optical fiber 13 diverges into the optical fiber 13 at an inherent angle. Therefore, as shown in FIG. 1 and FIG. 2, a lens 16 for condensing light onto the observation target is provided in front of the tip of the optical fiber 13.

  Also, as shown in FIGS. 1 and 2, these elements are covered with a cover 15 responsible for the mechanical properties of the catheter 1.

  Although not shown in FIG. 1, the catheter 1 may be provided with a guide wire and a flushing mechanism. Flushing is to wash blood and the like with water. In addition, the provision of the guide wire enables treatment using not only the imaging laser R1 but also a guide wire according to the situation. Furthermore, it is possible to provide a tubular structure (not shown) for injecting a transparent liquid for temporarily removing blood into the inside of the catheter 1. In this way, blood in the blood vessel can be temporarily removed, and a good catheter imaging image can be obtained.

[System block diagram]
FIG. 3 is a functional block diagram showing the configuration of the photoacoustic catheter system C according to the first embodiment.
The photoacoustic catheter system C includes a catheter 1 and a laser generator 2 for imaging. Further, the photoacoustic catheter system C includes an address management device 4, an imaging processing device 5, and an interface device 6.

The imaging laser generator 2 generates an imaging laser R1, which is a low-power pulsed laser for imaging.
The imaging laser R1 travels in the optical fiber 13. In addition, in FIG. 3, the broken line arrow has shown laser R1 for imaging (refer FIG. 1, FIG. 2).

The catheter 1 includes an optical element unit 17, a drive unit 19, and an acoustic element unit (detection unit) 18.
The optical element unit 17 is the tip of the optical fiber 13 or the lens 16, and the imaging laser R1 is emitted.
The drive unit 19 is the drive device 14 in FIG. 1 and FIG. 2 and has already been described in FIG. 1 and FIG. Moreover, since the acoustic element part 18 is the acoustic element 11 of FIG.1 and FIG.2, description here is abbreviate | omitted.

The address management device 4 manages, as an address, the timing at which the imaging laser R1 is emitted. The address indicates the position (emission position) where the imaging laser R1 is emitted, and is represented by, for example, coordinates.
The address management device 4 includes a timing latch unit 41, a timing control unit 42, a drive waveform setting unit 43, and a drive control unit 44.
The timing latch unit 41 records the emission timing of the imaging laser R <b> 1 based on the information from the imaging laser generator 2.

The timing control unit 42 calculates an address at which the imaging laser R1 is emitted, based on the injection timing recorded by the timing latch unit 41 and the drive voltage waveform set by the drive waveform setting unit 43. Further, the timing control unit 42 corrects the calculated address based on the calibration information 8 or the like input in advance by manual input or the like. By this, the timing control unit 42 generates a correction address. The processing performed by the timing control unit 42 will be described later.
The drive waveform setting unit 43 sets a drive voltage waveform.
The drive control unit 44 applies a drive voltage to the drive unit 19 in accordance with the drive voltage waveform set by the drive waveform setting unit 43.

The imaging processing device 5 reconstructs a catheter imaging image based on the detection signal transmitted from the acoustic element unit 18, the correction address, and the like.
The imaging processing device 5 includes a signal receiving unit 51, an information storage unit (storage unit) 52, and an image configuration unit (image generation unit) 53.
The signal receiving unit 51 receives the detection signal transmitted from the acoustic element unit 18.
The information storage unit 52 stores the detection signal received by the signal receiving unit 51, the address of the laser emission timing for imaging sent from the timing control unit 42, the correction address calculated by the timing control unit 42, and the like.
The image construction unit 53 reconstructs a catheter imaging image based on the information and the like stored in the information storage unit 52. In the present embodiment, the detection signal received by the signal receiving unit 51, the address of the laser emission timing for imaging sent from the timing control unit 42, the correction address, and the like are temporarily stored in the information storage unit 52. Thereafter, the image construction unit 53 reads out these pieces of information. However, the detection signal received by the signal reception unit 51, the address of the laser emission timing for imaging sent from the timing control unit 42, the correction address, etc. are directly input to the image configuration unit 53 without being stored in the information storage unit 52. May be Further, the image configuration unit 53 stores the reconstructed catheter captured image in the information storage unit 52.

The interface device 6 performs input and output.
The interface device 6 has a display unit 61.
The display unit 61 displays a catheter-captured image reconstructed by the image configuration unit 53.

  The address management device 4, the imaging processing device 5 and the interface device 6 constitute an image generation system (signal processing device) Z.

(Image configuration unit 53)
FIG. 4 is a functional block diagram showing a detailed configuration of the image configuration unit 53 used in the present embodiment.
The image configuration unit 53 includes an angle correction processing unit (intensity processing unit) 530.
The angle correction processing unit 530 includes an arrival direction identification unit 531, a reception characteristic function calculation unit 532, an inverse filter calculation unit 533, and a signal restoration unit 534. The details of the process performed by the angle correction processing unit 530 will be described later.
The arrival direction identification unit 531 identifies from which direction the acoustic wave generated by the irradiation of the imaging laser R1 has arrived.
The reception characteristic function calculation unit 532 calculates a reception characteristic function based on the arrival direction of the sound wave identified by the arrival direction identification unit 531.
The inverse filter calculation unit 533 calculates an inverse filter based on the calculated reception characteristic function.
The signal restoration unit 534 restores the received detection signal using the calculated inverse filter.

(Hardware configuration of address management device 4)
FIG. 5 is a diagram showing a hardware configuration of the address management device 4 used in the present embodiment.
The address management device 4 includes an FPGA (Field-Programmable Gate Array) 4A, an input device 4B, an output device 4C, and a voltage output device 4D.
The program executed by the FPGA 4A embodies the timing latch unit 41, the timing control unit 42, the drive waveform setting unit 43, and the like of FIG.
In the input device 4B, information on the emission timing of the imaging laser R1 is input from the imaging laser generation device 2, and calibration information 8 is input.
The output device 4C outputs the result of the process performed by the timing control unit 42 to the imaging processor 5.
The voltage output device 4D is the drive control unit 44 of FIG. 3 and applies the drive voltage to the drive unit 19 in accordance with the drive voltage waveform set by the drive waveform setting unit 43.

(Hardware configuration of the imaging processor 5)
FIG. 6 is a diagram showing a hardware configuration of the imaging processing apparatus 5 used in the present embodiment.
The imaging processing device 5 includes a CPU (Central Processing Unit) 5A, a memory 5B, a storage device (storage unit) 5C such as a HD (Hard Disk), an input device 5D, and an output device 5E.
Here, the program stored in the storage device 5C is loaded into the memory 5B. Then, the loaded program is executed by the CPU 5A, whereby the image configuration unit 53 shown in FIG. 4 and the units 530 to 530 that configure the image configuration unit 53 are embodied.
The storage device 5C corresponds to the information storage unit 52 of FIG. Further, the input device 5D corresponds to the signal receiving unit 51.

[flowchart]
(Overall processing)
FIG. 7 is a flow chart showing the processing procedure of the photoacoustic catheter system C performed in the first embodiment. The process shown by the broken line in FIG. 7 is a process other than the photoacoustic catheter system C. In each of the subsequent flowcharts, FIG. 3 is referred to as appropriate.
First, the operator activates each part of the photoacoustic catheter system C via the interface device 6 (S1).
Next, an imaging laser emission process is performed in which the imaging laser R1 is emitted (S2). Details of the imaging laser emission process will be described later.
The imaging laser R1 emitted is emitted to the object. The object thermally expands instantaneously by absorbing the imaging laser R1, and a sound wave is generated (S3).

Then, the acoustic element unit 18 detects the sound wave that has arrived from the target (S4). When a sound wave is received, the acoustic element unit 18 generates a voltage having a magnitude corresponding to the detected sound wave. The generated voltage is converted into a digital signal of a predetermined size by a signal receiving unit 51 equipped with an amplifier and an ADC (Analogue-Digital Converter) not shown. The converted digital signal is stored in the information storage unit 52.
When the acoustic element unit 18 is arrayed using a plurality of channels, data may be stored for each channel.

When the acoustic element unit 18 receives a sound wave, it transmits a voltage signal (detection signal) at a voltage corresponding to the intensity of the sound wave (density of air). The transmitted detection signal is received by the imaging processor 5.
Thereafter, the address management device 4 performs an address correction process (S5). Details of the address correction process will be described later.
Next, the imaging processing device 5 performs angle correction processing using the result of the address correction processing (correction address) (S6). Details of the angle correction process will be described later.
Then, the imaging processing device 5 performs image processing using the result of the angle correction processing (S7). Details of the image processing will be described later.
Then, as a result of the image processing, the catheter imaging image to be output is displayed on the display unit 61 (S8).

(Laser emission processing for imaging)
FIG. 8 is a flowchart showing a detailed processing procedure of the imaging laser emission process (step S2 in FIG. 7) performed in the first embodiment.
The drive waveform setting unit 43 sets a drive voltage waveform according to the angular velocity of the rotation of the optical fiber 13 (S201).
Then, the drive control unit 44 generates the drive voltage set in step S201 (S202).
Subsequently, the drive control unit 44 applies the generated drive voltage to the drive unit 19 (S203). As a result, the rotation of the optical fiber 13 by the drive unit 19 is started.

Thereafter, the timing latch unit 41 records the emission timing of the imaging laser R1 (S204). Specifically, the emission timing is the emission time of the imaging laser R1 or the like.
As the emission timing, the emission time of the imaging laser R1 may be stored using a photo detector, or the output time of the synchronization signal output when the imaging laser R1 is output may be stored.
The timing control unit 42 calculates, as an address, information regarding the emission timing of the imaging laser R1. Then, the timing control unit 42 stores information on the emission timing of the imaging laser R1 as an address in the information storage unit 52 (S205). The timing control unit 42 calculates an address based on the drive voltage waveform set by the drive waveform setting unit 43 and the emission timing.

FIG. 9 is a diagram showing an example of the waveform of the drive voltage applied to the drive unit 19. FIG. 10 is a view of the drive unit 19 (drive device 14) viewed from the front (catheter 1 axis direction).
As shown in FIG. 10, in the drive unit 19, the conductors D1 to D4 (D) are connected to each other by π / 2.
Here, the waveform V1 in FIG. 9 is a drive voltage waveform applied to the conductor D1 and the conductor D3 in FIG. A waveform V2 in FIG. 10 is a drive voltage waveform applied to the conductor D2 and the conductor D4 in FIG. Here, the waveform V1 and the waveform V2 are out of phase with each other by π / 2.
By applying the voltages of such waveforms V1 and V2 to the drive unit 19, the tip of the optical fiber 13 draws a spiral trajectory 101 as shown in FIG.
Here, ΔTL in FIG. 9 is a spiral trajectory 101 (see FIG. 2), and is a cycle until the tip of the optical fiber 13 spreads the radius of the trajectory 101 from the center and returns to the center.

(Address calculation)
Next, the address calculation will be described with reference to FIGS.
FIG. 11 is a diagram showing a voltage waveform applied to the drive unit 19 and an imaging laser emission timing. The waveform V11 in FIG. 11 is an enlarged view of the vicinity of time 0 of the waveform V1 in FIG. Similarly, the waveform V12 is an enlarged view of the vicinity of the time of the waveform V2 in FIG. Furthermore, the timing P1 indicates the emission timing of the imaging laser R1.
Here, the period of the voltage waveform is ΔTF. Then, the time from time 0 to the first imaging laser emission timing t1 is taken as δt L1. Further, the time from the time ΔTF to the second imaging laser emission timing t2 is set as δtL2. Further, the time from time 2ΔTF to the third imaging laser emission timing t3 is set as δtL3.

FIG. 12 is a view showing an emission locus of the imaging laser R1 by the applied voltage shown in FIG. 11, and FIG. 13 is an enlarged view of the vicinity of the origin in FIG.
Here, the code | symbol 201 of FIG. 13 has shown the position of the laser R1 for imaging initially inject | emitted from the injection start of laser R1 for imaging. That is, the reference numeral 201 indicates the emission position (address) of the imaging laser R1 emitted at the timing of the reference symbol t1 in the timing P1 of FIG. As shown in FIGS. 12 and 13, when the x axis and the y axis are set with respect to the injection locus, an angle φ1 between the reference numeral 201 and the x axis is expressed by the following equation (1).

  φ1 = 2π · δt L1 / ΔTF (1)

  That is, the image configuration unit 53 determines that the position imaged by the imaging laser R1 emitted at the imaging laser emission timing t1 in FIG. 11 is the position of the code 201 whose angle with the x axis is φ1.

  Similarly, angles φ2 and φ3 formed by the emission positions 202 and 203 of the imaging laser R1 emitted at the timings t2 and t3 in FIG. 11 with the x-axis become the following expressions (2) and (3).

φ 2 = 2π · δt L 2 / ΔTF (2)
φ 3 = 2π · δt L 3 / ΔTF (3)

  Thus, the address is calculated by the image configuration unit 53 calculating to which emission position (address) each imaging laser emission timing shown at timing P1 in FIG. 11 corresponds.

(Address correction process)
FIG. 14 is a flowchart showing a detailed processing procedure of the address correction process (step S5 of FIG. 7) performed in the first embodiment.
First, the timing control unit 42 acquires the calibration information 8 (S501). The calibration information 8 is information for calibrating the distortion of the image (information regarding distortion of the emission position of the imaging laser R1). The calibration information 8 is information previously input via the interface device 6. Specifically, it is information on the deviation of the rotation of the optical fiber 13 acquired at the time of test operation of the photoacoustic catheter system C.
The calibration information 8 may be stored in an EEPROM (Electrically Erasable Programmable Read-Only Memory), a server, a Universal Serial Bus (USB) memory, or the like. Further, as a method of acquiring the calibration information 8, for example, the following method is used. First, a calibration kit attached with calibration points (scales) is attached to the tip of the catheter 1. And the catheter captured image produced | generated by performing the process of FIG.7 S2-S4 is acquired. Then, the calibration information 8 may be created based on the deviation of the calibration point shown in the acquired catheter imaging image.

  Then, the timing control unit 42 calculates the imaging laser emission position (correction address) corrected based on the calibration information 8 and the address (S502).

(Calibration information 8)
Next, the calibration information 8 will be described with reference to FIGS. 15 and 16.
FIG. 15 is a schematic view showing an injection position in a normal state (state without distortion). The emission position of such an imaging laser R1 is an address.
As shown in FIG. 15, it is assumed that the ideal injection position (address) is a circle of radius A. As shown in FIG. 2, the injection position is originally in a spiral shape (helical shape), but here, in order to simplify the description, it is circular.
The arbitrary injection position (xt, yt) shown in FIG. 15 is expressed by the following equation (11). Here, ω = dθ / dt.

FIG. 16 is a schematic view showing an injection position where distortion occurs in the injection position.
As shown in FIG. 16, it is assumed that the measured injection position has a phase shift φ and an angular distortion B (θ) with respect to the injection position shown in FIG. Here, AB (θ) shown in FIG. 16 is obtained by multiplying A by B (θ). φ is derived from the signal delay of the imaging laser R1. Further, B (θ) is derived from the deviation of the voltage waveform applied to the drive unit 19. In addition, (phi) and B ((theta)) are measured previously as mentioned above. A restriction is imposed that AB (θ) becomes A when taking a circumferential average (or integration). At this time, the injection position (address) (xm (θ), ym (θ)) is expressed by the following equation (12). This address is the address calculated by the timing control unit 42.

  Equation (12) is transformed into equation (13) and equation (14).

The part of the inverse matrix in equation (14) is the calibration information 8. In addition, in order to specify the calibration information 8, it is necessary to perform calculation at a plurality of points.
By doing this, it is possible to correct the signal delay of the imaging laser R1. Furthermore, when a catheter imaging image is displayed on the display unit 61 with the injection position (xm (θ), ym (θ)) (that is, the irradiation position) as shown in FIG. 16, the distorted shape is displayed. It becomes difficult for the person to see. Therefore, by using the calibration information 8 shown in Expression (14), it is possible to perform display in a shape that matches the shape of the display unit 61. That is, the irradiation position of the imaging laser R1 can be calibrated. In addition, when the calibration information 8 shown in the equation (14) is used, a deviation occurs between the actual injection position (that is, the irradiation position) and the image position of the catheter captured image displayed on the display unit 61. In general, B (θ) is small, which causes no problem. Note that, in FIG. 16, B (θ) is shown largely for the sake of clarity.

(Angle correction process)
FIG. 17 is a flowchart showing a detailed processing procedure of the angle correction process (step S6 in FIG. 7) performed in the first embodiment. Refer to FIG. 3 and FIG. 4 as appropriate.
First, the arrival direction identification unit 531 identifies the arrival direction of the sound wave based on the time when the sound element unit 18 detects the sound wave and the address related to the emission timing sent from the timing control unit 42 (S601). The direction of arrival of sound waves will be described later.
Next, the reception characteristic function calculation unit 532 calculates a reception characteristic function based on the arrival direction of the sound wave specified in step S601 and the shape of the acoustic element unit 18 (S602). The reception characteristic function will be described later.
Then, the inverse filter calculation unit 533 calculates an inverse filter based on the reception characteristic function (S603). The inverse filter will be described later.
Next, the signal restoration unit 534 restores the detection signal based on the calculated inverse filter and the detection signal (S604). The restoration of the detection signal will be described later.

(About the direction of arrival)
FIG. 18A is a diagram showing the arrival direction of a sound wave.
It is assumed that the imaging laser R1 is emitted in the direction shown in FIG. 18A. Then, it is assumed that the object F1 exists in the traveling direction of the imaging laser R1.
The sound wave emitted from the object F <b> 1 by the irradiation of the imaging laser R <b> 1 reaches the acoustic element 11 (acoustic element unit 18) through the path 301. FIG. 15A shows a side view of the acoustic element 11. The actual acoustic element 11 has a shape as shown in FIG. However, in order to simplify the description, in the following description, it is assumed that the acoustic element 11 has a simple shape as shown in FIGS. 18B and 18C. This is because the principle of the present embodiment is the same whether the shape is as shown in FIG. 1 or the shape as shown in FIGS. 18B and 18C.
The path 301 through which the sound wave passes is inclined at γ with respect to a line 302 perpendicular to the acoustic element 11.

FIG. 18B is a diagram showing the horizontal angle α in the arrival direction.
FIG. 18B shows the acoustic element 11 (acoustic element unit 18) as viewed from above.
In such a case, it is assumed that the object F1 is in the position as shown in FIG. 18B. The sound wave emitted from the object F1 reaches the acoustic element 11 through the path 311.
This path 311 is at an angle α with respect to the axial line 312 of the acoustic element 11. Such an angle α is referred to as a horizontal angle α. Here, 0 ° ≦ horizontal angle α <360 °.
The arrival direction of the sound wave can be easily estimated from the emission position (address) of the imaging laser R1 described with reference to FIGS.

FIG. 18C is a view showing a tilt angle β in the arrival direction.
FIG. 18C shows a side view of the acoustic element 11 (acoustic element unit 18).
In such a case, it is assumed that the object F1 is in the position as shown in FIG. 18C. The sound wave emitted from the object F1 reaches the acoustic element 11 through the path 321.
This path 321 is located at an angle β with respect to the normal 322 of the acoustic element 11. Such an angle β is referred to as a tilt angle β.

  The arrival direction of the sound wave is represented by the horizontal angle α and the swing angle β shown in FIGS. 18B and 18C.

(Influence by deviation of arrival direction)
Next, the influence of the deviation of the arrival direction of the sound wave will be described with reference to FIGS. 19A to 19D. In FIGS. 19A to 19D, it is assumed that sound waves such as sine waves have arrived.
19A to 19D show lateral views of the acoustic element 11 (acoustic element unit 18). And in Drawing 19A-Drawing 19D, a solid line shows a peak of a sound wave, and a dashed line shows a valley of a sound wave. Note that since the sound wave is a compression wave, the peak of the sound wave indicates a portion where air is dense, and the valley indicates a portion where air is sparse. Further, in FIGS. 19A to 19D, arrows indicate the traveling direction of the sound wave.
In the following figures, the detection surface of the acoustic element 11 is the upper surface of the acoustic element 11.

FIG. 19A is a view showing a case where a sound wave arrives from directly above the acoustic element 11 (a tilt angle of 0 °).
As shown in FIG. 19A, when the sound wave arrives from directly above the acoustic element 11, only the peaks and valleys of the sound wave reach the acoustic element 11, so that highly accurate detection is possible.

19B to FIG. 19D are diagrams showing an example in which a sound wave arrives at the horizontal angle 90 ° and the pivot angle β with respect to the acoustic element 11.
It is assumed that the time advances in the order of FIG. 19B → FIG. 19C → FIG. 19D.
At the time shown in FIG. 19B, the sound wave valleys 331 and the sound wave peaks 332 are simultaneously detected by the acoustic element 11.
Then, at the time shown in FIG. 19C, the valley 333 of the next sound wave reaches the acoustic element 11 as the valley 331 of the sound wave and the mountain 332 of the sound wave travel in the traveling direction. That is, in FIG. 19C, sound wave valleys 331 and 333 and mountains 332 are detected at that time.

Next, at the time shown in FIG. 19D, the valleys 331 of the sound waves shown in FIGS. 19B and 19C are passing away, and instead, a new sound wave peak 334 reaches the acoustic element 11.
That is, in FIG. 19D, the peaks 332 and 334 and the valley 333 of the sound wave are simultaneously detected.
As described above, when the arrival direction of the sound wave deviates, the peak and the valley of the sound wave are simultaneously detected by the acoustic element 11.

FIG. 20 is a view showing an example of a time change of a detection signal detected by the acoustic element 11 when a sound wave is incident on the acoustic element 11.
In FIG. 20, reference numeral 401 denotes a time change of the detection signal when the horizontal angle is 0 ° and the swing angle is 0 °. That is, reference numeral 401 indicates time change of the detection signal when the sound wave arrives from the direction shown in FIG. 19A. By the way, the incident sound wave is a sound wave which shows time change as shown in a code 401.
In addition, reference numeral 402 indicates the time change of the detection signal when the horizontal angle is 0 ° and the swing angle is 15 °. That is, reference numeral 402 indicates time change of the detection signal when the sound wave arrives from the direction as shown in FIGS. 19B to 19D.

As shown in FIG. 20, when the horizontal angle is 0 ° and the swing angle is 0 °, clear detection (detection signal 401) is possible.
On the other hand, the detection signal (detection signal 402) when the horizontal angle is 0 ° and the swing angle is 15 ° is in a state of being totally broken. This is because, as described with reference to FIGS. 19B to 19D, when an angle is made in the direction of arrival of the sound wave, the peak and the valley of the sound wave are simultaneously detected, and the signal strength is canceled.
In the present embodiment, it is an object of the present invention to restore the detection signal 402 which is dulled so as to be close to the detection signal 401 by forming an angle in the direction of arrival of such sound waves.

(Reception characteristic function)
Next, the reception characteristic function will be described with reference to FIGS. 21A and 21B.
FIG. 21A shows the acoustic element 11 (acoustic element unit 18) as viewed from above.
The direction of arrow 412 is the direction of the horizontal angle 0 °. On the other hand, it is assumed that the sound wave arrives from the direction of the arrow 411 in which the horizontal angle and the elevation angle are a predetermined angle.
Here, a solid line, a broken line, and an alternate long and short dash line drawn on the acoustic element 11 indicate portions where peaks (or valleys) in the arriving sound wave overlap the acoustic element 11. The lengths of a solid line, a broken line, and an alternate long and short dash line drawn on the acoustic element 11 are detected intensities when the acoustic element 11 detects a peak of the sound wave.

The time change of the detection intensity detected by the broken line, the solid line, and the alternate long and short dash line drawn on the acoustic element 11 of FIG. 21A is shown in FIG. 21B.
The time change is proportional to the lengths of the broken line, solid line, and dashed dotted line drawn on the acoustic element 11 of FIG. 21A. Therefore, the vertical axis in FIG. 21B may be the length of a broken line, a solid line, or an alternate long and short dash line drawn on the acoustic element 11.

First, as indicated by reference numeral 431 in FIG. 21B, the detection intensity increases. This corresponds to the broken line portion drawn on the acoustic element 11 of FIG. 21A.
Next, as indicated by reference numeral 432, the detected intensity becomes constant. This corresponds to the solid line portion drawn on the acoustic element 11 of FIG. 21A. That is, it originates in the solid line drawn on the acoustic element 11 of FIG. 21A having a fixed length.
Then, as indicated by reference numeral 432, the detected intensity decreases. This corresponds to the dashed-dotted line portion drawn on the acoustic element 11 of FIG. 21A.

The temporal change in detection intensity shown in FIG. 21B is a reception characteristic function.
The detection strength actually detected is a convolution of the detection signal s (t) and the reception characteristic function.
As shown in FIG. 21B, the reception characteristic function has a rectangular or trapezoidal shape.

Here, the reception characteristic function as shown in FIG. FIG. 22B Fourier-transforms the reception characteristic function H shown in FIG. 22A and further shows the absolute value of the amplitude of each frequency.
The reception characteristic function shown in FIG. 22A is, for example, a reception characteristic function when a sound wave arrives at a horizontal angle of 0 °, 90 °, or 270 °, and an elevation angle of 90 °. However, by replacing the reception characteristic function shown in FIG. 22A with the reception characteristic function shown in FIG. 21, it is possible to apply to sound waves coming from any horizontal angle or direction of the elevation angle.

  When Fourier transform is performed on the reception characteristic function shown in FIG. 22A, it can be seen that it has wide band frequency characteristics as shown in FIG. 22B. The same applies to the Fourier transform of the reception characteristic function as shown in FIG. 21B. That is, the reception characteristic function having a rectangular or trapezoidal shape has wide band frequency characteristics. Here, the wide band is a band of about 80 MHz.

At this time, by making the inverse filter 1 / H (ω), it is theoretically possible to restore the original detection signal S0 (t). Here, ω indicates a frequency.
However, H (ω) has the value 0 in some places, as shown in FIG. 22B. Therefore, in such a place, so-called zero division occurs and the inverse filter diverges.
In the present embodiment, an inverse filter that does not generate such zero division is proposed.

(Winner filter M)
First, there is a Wiener filter M as an inverse filter which does not generate such a zero division.
The Wiener filter M is an inverse filter represented by the following equation (21).

M = H ^* / (| H | ² + Γ) (21)

Then, the signal restoration unit 534 calculates the following Expression (22) using the inverse filter (Winner filter M) of Expression (21), to obtain the detected signal (restoration signal) S0. However, H in Formula (21) is H (ω). Also, H ^* is a complex conjugate of H. Here, Γ is a constant for preventing the denominator of equation (21) from being divided by zero.
By using the Wiener filter M, zero division can be avoided, and divergence of the restored signal can be prevented.

S0 = FT- ¹ [FT [S] * FT [M]] ... (22)

Here, S represents a detection signal, S 0 represents a restored signal, FT [•] represents a Fourier transform, FT ⁻¹ [•] represents an inverse Fourier transform, and * represents convolution.

  In the inverse filter (Winner filter M) as shown in Expression (21), zero division can be prevented and divergence of the inverse filter can be prevented by arranging a predetermined constant Γ in the denominator.

(Proposed reverse filter M1)
Next, an inverse filter (referred to as a proposed inverse filter M1) devised by the inventor will be described with reference to FIGS. 23A to 23C.
FIG. 23A is a diagram showing the behavior of the real part when the reception characteristic function H of FIG. 22A is Fourier transformed. FIG. 23B is a diagram showing the behavior of an imaginary part when Fourier transforming the reception characteristic function H of FIG. 22A.
When FIG. 23A and FIG. 23B are compared, the value of the real part is larger than that of the imaginary part. That is, it can be seen that the real part is more influential than the imaginary part.
Here, consider an envelope 421 of an imaginary part as shown in FIG. 23B.
FIG. 23C is a diagram showing only the envelope 421 of FIG. 23B.

  Using such an envelope of the imaginary part, the reception characteristic function calculation unit 532 calculates the reception characteristic function H1 shown in the following equation (23).

  H1 = Re {H} + i Env (Im {H}) (23)

Here, Re {H} indicates the real part of H (FIG. 23A), and Im {H} indicates the imaginary part of H (FIG. 23B). Also, Env (Im {H}) indicates the envelope 421 of the imaginary part of H (see FIGS. 23B and 23C). However, H in Formula (23) is H ((omega)).
Next, the inverse filter calculation unit 533 calculates a proposed inverse filter M1 shown in the following equation (24) using H1 of the equation (23).

M1 = H1 ^* / | H1 | ² (24)

  Then, the signal restoration unit 534 calculates the restoration signal S0 using the following equation (25).

S0 = FT- ¹ [FT [S] * FT [M1]] (25)

As shown in FIG. 23C, the envelope 421 of the imaginary part of H has a value of 0 at 60 MHz, but the inverse filter calculation unit 533 may stop the calculation before 60 MHz.
The reception characteristic function H1 is different in form from the reception characteristic function H. However, as described in FIGS. 23A and 23B, the real part has a greater influence on the shape of the reception characteristic function than the imaginary part, so the change in the shape of the reception characteristic function H1 is small.
According to the proposed inverse filter M1, the arbitraryness of the constant 恣 of the Wiener filter M shown in the equation (21) can be eliminated.

(simulation result)
Next, simulations of restoration using the winner filter M and the proposed inverse filter M1 are shown in FIGS. 24A to 25C.
FIG. 24C is a diagram showing a simulation result when a sound wave arrives from the direction shown in FIGS. 24A and 24B.
Here, FIG. 24A is a top view of the acoustic element 11 (acoustic element unit 18), and FIG. 24B is a side view of the acoustic element 11 (acoustic element unit 18). Here, the sound wave incident on the acoustic element 11 is a sound wave having a time change as indicated by reference numeral 401 in FIG.
As shown in FIGS. 24A and 25B, a simulation result in the case where a sound wave arrives from the direction of the horizontal angle 0 ° and the elevation angle 10 ° is shown in FIG. 24C.
In FIG. 24C, reference numeral 601 denotes a detection signal in the case where a sound wave arrives from the direction of a tilt angle of 0 °. That is, reference numeral 601 indicates a detection signal when a sound wave arrives from directly above the detection surface (upper surface of the acoustic element 11). In addition, a detection signal shall show the time change of a detection signal hereafter.
Reference numeral 602 denotes a detection signal when the sound wave arrives from the direction of the horizontal angle 0 ° and the elevation angle 10 °.
Reference numeral 603 denotes a result (restored signal) obtained by performing signal restoration using the Wiener filter M on the detection signal indicated by reference numeral 602.
Further, reference numeral 604 denotes a result (restoration signal) obtained by performing signal restoration using the proposed inverse filter M1 on the detection signal of the reference numeral 602.

As the code 603 and the code 604 are closer to the code 601, the degree of restoration is better.
Here, comparing the code 603 with the code 604, the Wiener filter M has a better restoration degree than the proposed inverse filter M1 in the vicinity of the positive and negative peaks.
However, in the portion other than the peak, the proposed inverse filter M1 has a better restoration degree than the winner filter M.
When the SN ratio was compared over the entire time window shown in FIG. 24C, the SN ratio of the proposed reverse filter M1 was improved 1.9 times that of the winner filter M.

FIG. 25C is a diagram showing a simulation result when a sound wave arrives from the direction shown in FIGS. 25A and 25B. Here, the sound wave incident on the acoustic element 11 is a sound wave having a time change as indicated by reference numeral 401 in FIG.
Here, FIG. 25A is a top view of the acoustic element 11 (acoustic element unit 18), and FIG. 25B is a side view of the acoustic element 11 (acoustic element unit 18).
As shown in FIG. 25A and FIG. 25B, FIG. 25C shows a simulation result in the case where a sound wave arrives from the direction of the horizontal angle 45 ° and the elevation angle 10 °.
In FIG. 25C, reference numeral 611 denotes a detection signal when a sound wave arrives from the direction of a tilt angle of 0 °. That is, reference numeral 611 indicates a detection signal when a sound wave arrives from directly above the detection surface (upper surface of the acoustic element 11).
Reference numeral 612 denotes a detection signal when the sound wave arrives from the direction of 45 ° in the horizontal angle and 10 ° in the elevation angle.
Reference numeral 613 denotes a result (restoration signal) obtained by performing signal restoration using the Wiener filter M on the detection signal of reference numeral 612.
Further, reference numeral 614 denotes a result (restored signal) obtained by performing restoration of a signal using the proposed inverse filter M1 on the detection signal indicated by reference numeral 612.
Here, comparing the code 613 with the code 614, as in FIG. 24C, the Wiener filter M has a better restoration degree than the proposed inverse filter M1 near positive and negative peaks.
However, as in FIG. 24C, in the portion other than the peak, the proposed inverse filter M1 has a better restoration degree than the winner filter M.
When the SN ratio was compared over the time window shown in FIG. 25C, the proposed inverse filter M1 was improved by 1.5 times and the SN ratio was improved compared to the winner filter M.

According to the present embodiment, it is possible to restore a detection signal derived from a sound wave that has arrived in an oblique direction with respect to the acoustic element 11. As a result, highly accurate images can be reconstructed.
The technique described in Patent Document 1 aims to suppress the variation in the propagation speed of the acoustic wave propagating in the object. Therefore, although different from the purpose of the present embodiment, in the technology described in Patent Document 1, image reconstruction is performed by narrowing down to one representative frequency such as the center frequency. Therefore, when the technique described in Patent Document 1 is applied to the correction of the direction of arrival of the sound wave with respect to the acoustic element 11 as in the present embodiment, the loss of image information occurs.
On the other hand, in the present embodiment, the wide band frequency components (in other words, all frequency components) are corrected at one time. Therefore, in the present embodiment, the image information is not lost. Therefore, in the present embodiment, it is possible to generate an image with high accuracy.

  Further, by applying the angle correction processing according to the present embodiment to the photoacoustic catheter 1, it is possible to reconstruct a catheter image with high accuracy. In particular, by applying to the catheter 1 which performs a fiber scan, it is possible to correct the inclination of the sound wave to the acoustic element 11 due to the rotation and emission of the imaging laser R1.

(Image processing)
FIG. 26 is a flowchart showing a detailed processing procedure of the image processing (step S7 of FIG. 7) performed in the first embodiment.
The image construction unit 53 converts the detection signal stored in the information storage unit 52 into an image signal (S701). The conversion into an image signal may be any of Hilbert transform, quadrature detection, back projection, and absolute value calculation.

  Next, based on the correction address and the like calculated by the timing control unit 42, the image configuration unit 53 calculates the distance and direction from the object irradiated with the imaging laser R1 to the acoustic element unit 18 (S702). The direction (arrival direction) calculated in the angle correction process may be used as the direction at this time.

Next, the image configuration unit 53 generates a catheter imaging image based on the image signal and the emission position (correction address) of the corrected imaging laser R1 stored in the information storage unit 52 (S703). The image may be 1D (Dimension), 2D, or 3D.
By generating a catheter imaging image based on the correction address, the photoacoustic catheter system C calibrates the catheter imaging image captured by the imaging laser R1 according to the calibration information 8.
The image configuration unit 53 stores the generated catheter imaging image in the information storage unit 52.

Here, with reference to FIGS. 27 and 28, a method of calculating the distance and direction from the object to the acoustic element 11 (acoustic element unit 18) will be described.
It is assumed that the imaging laser R1 is emitted in the direction shown in FIG. Then, consider the case where the object F1 and the object F2 exist in the traveling direction of the imaging laser R1.
Since the imaging laser R1 travels at the speed of light, it can be considered that the time to reach the object F1 after the imaging laser R1 is emitted and the time to reach the object F2 are the same. That is, it can be considered that the time for reaching the object F1 after the emission of the imaging laser R1 and the time for reaching the object F2 are both zero.
Accordingly, the distance L1 to the object F1 and the distance L2 to the object F2 can be expressed by the following equation.

L1 = Vs × T1
L2 = Vs × T2

  Here, Vs is the speed of sound. T1 is the time from when the imaging laser R1 is emitted to when the acoustic element 11 detects a sound wave. Similarly, T2 is a time from when the imaging laser R1 is emitted to when the acoustic element 11 detects a sound wave.

FIG. 28 is a diagram showing a time change of signal intensity detected by the acoustic element 11 shown in FIG.
In FIG. 28, the horizontal axis indicates time, and the vertical axis is signal intensity (sound intensity). Further, in FIG. 28, time 0 is the emission time of the imaging laser R1.
Time T1 and time T2 are times when the sound waves emitted from the objects F1 and F2 in FIG. 27 reach the acoustic element 11, respectively.
That is, the signal strength I1 at time T1 is information of the object F1 (see FIG. 27) at the distance L1 of FIG. Similarly, the signal strength I2 at time T2 is information of the object F2 (see FIG. 27) at the distance L2 in FIG.
The direction in which the detected object F1 or the object F2 is present with respect to the acoustic element 11 can be easily calculated from the emission direction (that is, the address) of the imaging laser R1.
Thus, image data is reconstructed.
In addition, when multiple acoustic elements 11 are arrange | positioned, as mentioned above, the image structure part 53 may reinforce a detection signal by performing Delay and Sum.

  After the image processing is performed, the operator emits a treatment laser (not shown) while referring to the generated image.

(Angle gain correction lever 701)
FIG. 29 is a view showing a modified example of the imaging processing device 5a used in the present embodiment.
The imaging processing device 5a in FIG. 29 includes the interface device 6 in FIG.
The imaging processing device 5a is provided with a plurality of angle gain correction levers (operation units) 701.
The angle gain correction lever 701 corresponds to the elevation angle shown in FIG. 18C. For example, the angle gain correction lever 701a corresponds to an elevation angle of 10 °, the angle gain correction lever 701b corresponds to an elevation angle of 20 °, and so on.

Then, when the angle gain correction lever 701 is operated, the angle correction processing unit 530 amplifies the signal strength of the restoration signal that has arrived from the direction corresponding to the elevation angle.
For example, when the angle gain correction lever 701a corresponding to the elevation angle of 10 ° is moved in the amplification direction, the angle correction processing unit 530 determines the signal strength of all restored signals determined to have received sound waves from the direction of the elevation angle of 10 °. To amplify. Conversely, when the angle gain correction lever 701a corresponding to the elevation angle of 10 ° is moved in the decreasing direction, the angle correction processing unit 530 determines that all the restored signals determined to have arrived as sound waves from the direction of the elevation angle of 10 °. Decrease the strength.

As shown in FIG. 24C and FIG. 25C, the restored signal does not match the signal to be originally detected. Therefore, by adjusting the signal strength of the restoration signal by the angle gain correction lever 701, the restoration signal can be made closer to a signal that should be originally detected.
By doing this, the accuracy of signal restoration can be improved.

(Receive characteristic function table)
FIG. 30 is a diagram showing an example of the reception characteristic function table 710 used in the present embodiment.
In the present embodiment, the reception characteristic function calculation unit 532 calculates the reception characteristic function each time. However, the present invention is not limited to this, and as shown in FIG. 30, the reception characteristic function corresponding to each arrival direction may be stored in advance in the information storage unit 52 (see FIG. 3) as the reception characteristic function table 710.
In the example of FIG. 30, the reception characteristic function of the top stage is 90 ° horizontal angle, 90 ° elevation angle, the second from the top is 80 ° horizontal angle, 90 ° elevation angle, 45 ° horizontal angle at the bottom stage, 90 ° elevation angle It is.
In the reception characteristic function table 710, as shown in FIG. 30, reception characteristic functions are stored for each horizontal angle and elevation angle.
By doing this, the calculation process of the reception characteristic function can be omitted, and the calculation load can be reduced.
Each reception characteristic function in reception specific function table 710 shown in FIG. 30 may be measured beforehand by an experiment or the like.

  The present invention is not limited to the embodiments described above, but includes various modifications. For example, the above-described embodiments are described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. Also, part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Moreover, it is possible to add, delete, and replace other configurations for part of the configurations of the respective embodiments.

In addition, the above-described configurations, functions, units 41 to 44, 51, 53, 530 to 534, information storage unit 52, etc. are realized by hardware, for example, by designing part or all of them with an integrated circuit. You may Further, as shown in FIGS. 5 and 6, even if each of the configurations, functions, etc. described above is realized by software by the processor such as the FPGA 4A or the CPU 5A interpreting and executing a program for realizing the respective functions. Good. In addition to storing information such as programs, tables, and files that realize each function in a hard disk (HD), a memory, a recording device such as a solid state drive (SSD), or an integrated circuit (IC) card It can be stored in a recording medium such as an SD (Secure Digital) card, a DVD (Digital Versatile Disc), or the like.
Further, in each embodiment, the control lines and the information lines indicate what is considered necessary for the description, and not all the control lines and the information lines in the product are necessarily shown. In practice, almost all configurations can be considered to be connected to each other.

1 Catheter (photoacoustic catheter)
5C storage unit (storage unit)
11 Acoustic device (detection unit)
13 optical fiber 18 acoustic element unit (detection unit)
52 Information storage unit (storage unit)
53 Image configuration unit (image generation unit)
530 Angle correction processing unit (intensity processing unit)
533 Inverse filter calculation unit 534 Signal restoration unit 701, 701a, 701b Angle gain correction lever (operation unit)
710 Reception Characteristic Function Table Z Image Generation System (Signal Processing Device)

Claims (11)

An inverse filter calculation unit that calculates an inverse filter based on a reception characteristic function of a detection signal that is detected and generated by a detection unit that detects an incoming signal;
A signal restoration unit which convolves the result of the Fourier transform of the detection signal and the result of the Fourier transform of the inverse filter, and further inverse Fourier transforms the result of the convolution;
Have
The reception characteristic function is based on the inclination of the incoming signal with respect to the detection surface of the detection unit, and has wide-band frequency characteristics.
The inverse filter calculation unit
In the inverse filter, the inverse filter is set such that an arbitrary frequency component has a value larger than 0. The inverse filter calculation unit
Assuming that the reception characteristic function is H, a reception characteristic function H1 shown in the following equation (1) is calculated as a new reception characteristic function,
The signal processing apparatus according to claim 1, wherein an inverse filter M represented by the following equation (2) is calculated based on the newly calculated reception characteristic function H1.
H1 = Re {H} + iEnv (Im {H}) (1)
M = H1 ^* / | H1 | ² (2)
Here, Re {H} indicates the real part of H, Im {H} indicates the imaginary part of H, Env (Im {H}) indicates the envelope of the imaginary part of H, and H1 ^* indicates The complex conjugate of H1 is shown. The inverse filter calculation unit
The signal processing apparatus according to claim 1, wherein a Wiener filter represented by the following equation (3) is used as the inverse filter, where H is the reception characteristic function.
M = H ^* / (| H | ² + Γ) (3)
Here, H ^* is a complex conjugate of H, and Γ is a predetermined constant. The detection unit is provided in a photoacoustic catheter.
The signal processing apparatus according to claim 1, wherein the incoming signal is a detection of a sound wave emitted from an irradiation target of a laser emitted from an optical fiber of the photoacoustic catheter. The signal processing apparatus according to claim 4, wherein the tip of the optical fiber emits the laser while rotating. The signal processing apparatus according to claim 4, further comprising: an image generation unit configured to generate an image based on the signal output from the signal restoration unit. The signal processing apparatus according to claim 1, wherein the reception characteristic function corresponding to each angle at which the detection signal arrives to the detection unit is stored in a storage unit. An operation unit corresponding to each angle at which the detection signal arrives at the detection unit;
An intensity processing unit that increases or decreases the signal intensity of the detection signal;
Have
When the operation unit corresponding to a predetermined angle is operated, the intensity processing unit increases or decreases the intensity of the detection signal determined to have arrived from the angle corresponding to the operated operation unit. The signal processing apparatus according to claim 1. A signal processing apparatus that processes a detection signal that is detected and generated by a detection unit that detects an incoming signal,
A first step of calculating an inverse filter based on a reception characteristic function of the detection signal;
A signal restoration unit which convolves the result of the Fourier transform of the detection signal and the result of the Fourier transform of the inverse filter, and further inverse Fourier transforms the result of the convolution;
Have
The reception characteristic function is based on the inclination of the incoming signal with respect to the detection surface of the detection unit, and has wide-band frequency characteristics.
The signal processing device
In the inverse filter, the inverse filter is set such that any frequency component has a value larger than 0. The signal processing device
Assuming that the reception characteristic function is H, a reception characteristic function H1 shown in the following equation (1) is calculated as a new reception characteristic function,
The signal processing method according to claim 9, wherein an inverse filter M represented by the following equation (2) is calculated based on the newly calculated reception characteristic function H1.
H1 = Re {H} + iEnv (Im {H}) (1)
M = H1 ^* / | H1 | ² (2)
Here, Re {H} indicates the real part of H, Im {H} indicates the imaginary part of H, Env (Im {H}) indicates the envelope of the imaginary part of H, and H1 ^* indicates The complex conjugate of H1 is shown. The signal processing device
10. The signal processing method according to claim 9, wherein a Wiener filter represented by the following equation (3) is used as the inverse filter, where H is the reception characteristic function.
M = H ^* / (| H | ² + Γ) (3)
Here, H ^* is a complex conjugate of H, and Γ is a predetermined constant.

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