JP5495882B2 - measuring device - Google Patents

Description

  The present invention relates to a measurement apparatus that receives an acoustic wave generated from a subject irradiated with light.

  2. Description of the Related Art Conventionally, a measuring apparatus (image diagnostic apparatus) that irradiates a living body with pulsed laser light and receives an acoustic wave generated from the inside of the living body to image the form and function of the internal tissue is often used in the medical field. In such a measuring apparatus, an acoustic wave generated from the inside of a living body is converted into an electric signal by a probe in which an electroacoustic transducer is integrated. Thereafter, signal processing is performed on the electrical signal to obtain a diagnostic image expressing the form and function inside the living body.

  Japanese Patent Application Laid-Open No. 2004-133867 discloses an ultrasonic diagnostic apparatus having a mechanism for mechanically scanning a probe to acquire a wide range of acoustic waves. In the ultrasonic diagnostic apparatus of Patent Document 1, a probe is provided with a motor, and ultrasonic waves are transmitted and received while performing mechanical scanning.

  In general, an electric signal acquired from a probe is mixed with noise propagating to an electric circuit, a cable, or the like in addition to a signal caused by an acoustic wave generated from the inside of a living body. In particular, when a probe is provided with a motor, a lot of noise tends to be generated from the motor and peripheral circuits. In order to obtain a good quality diagnostic image, it is necessary to reduce the influence of this noise on the image. For example, in the case of a stepping motor, noise is likely to occur when the drive coil is energized by input of a control signal or switching.

  Patent Document 2 describes a noise reduction method in a system having a plurality of motors and sensors. In Patent Document 2, the operating states of a plurality of motors and the degree of noise exerted on the sensors are stored in advance, and some evaluation values indicating the degree of noise of each motor exceed a predetermined allowable amount. This is reflected in motor operation control and sensor noise removal processing.

JP 2004-195088 A Japanese Patent Laid-Open No. 10-243681

  However, in the measuring apparatus described in Patent Document 1, noise from a mechanical scanning motor is generated while a weak electric signal due to an acoustic wave from inside the living body is received. This noise propagates from the probe to the cable that transmits the electrical signal and the receiving circuit, and there is a possibility that the image quality of the diagnostic image is deteriorated due to the noise mixed in the signal.

  In the noise reduction method described in Patent Document 2, a part of the plurality of motors is stopped within a range in which the evaluation value does not exceed a predetermined allowable amount. However, when the degree of noise exerted on the sensor of each motor is large and the allowable amount is small, the noise may exceed the allowable amount unless all the motors are always stopped. Therefore, it has been difficult to apply to a measuring apparatus that needs to receive a very weak signal from a living body.

  The present invention has been made in view of the above circumstances, and an object thereof is to reduce the influence of noise from a motor on image quality in an apparatus for measuring an acoustic wave generated from a subject irradiated with light. It is to provide a technique for doing this.

In order to solve the above problems, the present invention adopts the following configuration.
That is, a probe that receives an acoustic wave generated from a subject that has absorbed light emitted from a light source and converts it into an electrical signal, a drive unit that moves the probe to perform scanning, and the drive unit Control means for outputting a control signal for controlling the operation of the driving means, and the control means stops at least a part of the operation of the driving means during a period in which the probe receives an acoustic wave. In the measuring apparatus, the control unit stops at least a part of the operation of the driving unit based on an elapsed time from light irradiation.
The present invention also employs the following configuration.
That is, a probe that receives an acoustic wave generated from a subject that has absorbed light emitted from a light source and converts it into an electrical signal, a drive unit that moves the probe to perform scanning, and the drive unit Control means for outputting a control signal for controlling the operation of the driving means, and the control means stops at least a part of the operation of the driving means during a period in which the probe receives an acoustic wave. The operation of the driving means includes an operation in which the driving means holds the position of the probe, and the control means is operable during a period in which the probe receives an acoustic wave. The measuring device is characterized in that holding of the probe by the driving means is stopped.

  ADVANTAGE OF THE INVENTION According to this invention, the influence which the noise from a motor has on an image quality can be reduced in the measuring apparatus of the acoustic wave generated from the subject irradiated with light.

1 is a block diagram illustrating a configuration of a measurement apparatus according to Embodiment 1. FIG. 2 is a flowchart of the entire processing in the first embodiment. FIG. 3 is an internal configuration diagram of a control unit and a driving unit in the first embodiment. 3 is a flowchart of measurement processing in the first embodiment. 4 is a timing chart in the first embodiment. FIG. 3 is a diagram illustrating a structure in the vicinity of a measurement target in Example 1. 7 is a flowchart of measurement processing in the second embodiment. 9 is a timing chart in the second embodiment. 9 is a timing chart according to the third embodiment. The figure which shows the relationship between the time of a probe in Example 1, and a position. The figure which shows the relationship between the time of a probe in Example 2, and a position. FIG. 3 is a diagram illustrating an example of an electrical signal from a probe according to the first embodiment.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings.

<Example 1>
FIG. 1 is a block diagram showing a first embodiment of a measuring apparatus (image diagnostic apparatus) 101 according to the present invention. In FIG. 1, a measurement target (subject) 102 is a target for measuring a biological signal, and is, for example, a part of a subject's body such as a breast. The light source 103 is a pulse laser light source for generating an acoustic wave from the measurement object 102, the probe 104 is a transducer that converts the acoustic wave generated from the measurement object into an electric signal, and the driving means 105 mechanically moves the probe 104. A motor for two-dimensional scanning. The control means 106 is a controller that transmits control signals to the light source 103 and the driving means 105 and executes a biological signal reception sequence. The control means is configured by a circuit such as a microprocessor or FPGA and software, for example. The signal acquisition means 107 is an electric circuit for receiving an electric signal from the probe 104, converting it into data used for imaging, and outputting it to the outside, and is composed of an amplifier circuit, an A / D conversion circuit, and the like. .

FIG. 6 shows an enlarged view of the structure near the measurement object 102. The plate-like members 601 and 602 fix the measurement object 102. In this embodiment, the plate-like members 601 and 602 are parallel flat plates, and are fixed with the measurement object 102 interposed therebetween. The light projecting unit 603 irradiates the measurement target 102 with pulsed laser light 606. The optical path 604 guides the pulse laser beam from the light source 103 to the light projecting unit 603. A cable 605 connects the probe 104 and the signal acquisition unit 107. The light absorption portion 607 is a portion that is inside the measurement object 102 and has a large light absorption. When the light absorption site 607 is irradiated with the pulse laser beam 606, energy is absorbed and an acoustic wave 608 is generated. The probe 104 converts the acoustic wave 608 into an electric signal, and transmits it to the signal acquisition means 107 via the cable 605. This electric signal is called a photoacoustic signal. Further, the probe 104 and the light projecting unit 603 move so as to cover the measurement range of the measurement object 102 in a two-dimensional manner by scanning in the XY direction in the drawing under the control of the driving unit 105 (not shown).

FIG. 2 shows a flowchart of the entire processing of this embodiment executed by the control means 106.
In step S201, the control means checks whether or not measurement preparation is ready. If the measurement object 102 is fixed at a predetermined measurement position, it is determined that the measurement is ready, and the process proceeds to step S203. If the measurement is not ready, the process proceeds to step S202 and waits for a certain time. After that, the process returns to step S201.
In step S203, the control means reads the measurement conditions specified by the user. Measurement conditions include the number of light emission times and the movement range of the probe.
In step S204, measurement processing of the measurement object 102 is performed. Specifically, the control unit moves the probe 104 and the light projecting unit 603 to cause the light source 103 to emit light and cause the probe to receive an acoustic wave. Then, the signal acquisition means 107 is made to acquire a photoacoustic signal. Details of the measurement process will be described later.

In step S205, the signal acquisition unit 107 outputs measurement data after performing signal processing such as A / D conversion to the outside. The data output to the outside can be used for imaging (generation of image data) in an information processing apparatus such as a PC.
In step S206, the control unit determines whether or not the output of the data of the entire measurement range of the measurement object 102 has been completed. If completed, the process proceeds to step S207.
In step S207, the control unit returns the probe 104 and the light projecting unit 603 to the initial positions, outputs a message to the outside, and ends the process. If not completed, the process proceeds to step S204 to perform the next measurement process.

  FIG. 3 shows the detailed structure of the control means 106 and the drive means 105. The microprocessor (CPU) 301 transmits a command to the FPGA 302 according to the control sequence. The FPGA 302 outputs a control signal for controlling the driving unit 105 and the light source 103 in accordance with a control command from the microprocessor 301. Control signals for controlling the operation of the driving means 106 include a right rotation instruction signal 306, a left rotation instruction signal 307, and an excitation signal 308. The light emission instruction signal 309 is a control signal output to the light source 103 (not shown). These control signals are digital signals. In this embodiment, the H level is 5V and the L level is 0V.

  The motor driver circuit 303 supplies a current to the drive coil 304 in the drive unit 105 based on the control signals 306, 307, and 308. When a current flows through the drive coil 304, the rotor shaft 305 rotates. The rotor shaft 305 is connected to the probe 104 and the light projecting unit 603 by mechanical transmission means such as a gear and a belt. When the rotor shaft 305 rotates, the probe 104 and the light projecting unit 603 are connected to the measurement object 102. Move relative to it.

  When one pulse signal is input to the right rotation instruction signal 306, the rotor shaft 305 rotates right by one step. On the other hand, when one pulse signal is input to the left rotation instruction signal 307, the rotor shaft 305 rotates counterclockwise by one step. When the voltage level of the excitation signal 308 becomes H level, even if an electric current flows through the coil 304 and an external force is applied to the rotor shaft 305, the rotor shaft does not rotate. On the other hand, when the voltage level of the excitation signal 308 becomes L, the current of the coil 304 is stopped, and when an external force is applied to the rotor shaft 305, the rotor shaft rotates. When one pulse signal is input to the light emission instruction signal 309, the pulse laser beam is emitted from the light source 103 once.

In FIG. 3, only the control signal of one motor is shown for simplicity, but there are four motors for two-dimensional scanning of the probe 104 and the light projecting unit 603 in the XY direction.

Details of the timing of the measurement process in step S204 will be described with reference to FIGS. FIG. 4 is a flowchart describing details of the measurement process. FIG. 5 is a timing chart showing the timing of the control signal and the photoacoustic signal. The timing chart shows how the right rotation instruction signal 306, the left rotation instruction signal 307, the excitation signal 308, the light emission instruction signal 309, and the photoacoustic signal received by the signal acquisition unit change as time advances. It is shown.
In the initial state, as in the left end portion of FIG. 5, the voltage level of any control signal is L level. The photoacoustic signal is assumed to have a waveform in which a noise component 501 having substantially the same amplitude is superimposed in addition to the component 502 due to the acoustic wave generated from the measurement target.

In step S401, the control unit outputs a control signal to the driving unit 105, rotates the motor, and moves the probe 104 and the light projecting unit 603 to the measurement point. In this embodiment, the microprocessor 301 transmits a command to the FPGA 302 to set the voltage level of the excitation signal 308 to the H level and output the pulse signal to the right rotation instruction signal 306 as many times as necessary. If it moves to a measurement point, it will progress to step S402.
In step S <b> 402, the control unit determines whether it is a timing at which the light source 103 can emit light. The light source 103 outputs pulsed laser light at a frequency of 10 Hz. Therefore, in step S402, if 100 ms has elapsed since the last light emission, it is determined that light can be emitted, and the process proceeds to step S404. On the other hand, if the time of 100 ms has not elapsed since the last light emission, it is determined that the light cannot be emitted yet, and the process proceeds to step S403. In step S403, the process waits for a certain period and returns to step S402.

Step S404 corresponds to time 503. Here, the control means sets the voltage level of the excitation signal 308 to L level and stops energization of the drive coil 304. As a result, the holding power of the probe 104 and the light projecting unit 603 is lost, but the noise component 501 generated from the motor driver circuit 303 and the driving unit 105 is reduced.
Step S405 corresponds to time 504. Here, the control means outputs a pulse signal to the light emission instruction signal 309 and causes the light source 103 to emit pulsed laser light. The pulse laser beam is irradiated onto the measurement object 102, and an acoustic wave 608 is generated from the light absorption portion 607.
In step S <b> 406, the probe 104 receives the acoustic wave 608 and converts it into a photoacoustic signal 502. The signal acquisition unit 107 performs A / D conversion on the photoacoustic signal 502 input between time 505 and time 506 and performs signal processing. In this signal processing, the photoacoustic signals from the electroacoustic elements corresponding to the same position of the measurement object 102 of the probe 104 are added and averaged. The S / N ratio is improved by averaging a plurality of photoacoustic signals.

Step S407 corresponds to time 507. Here, the control means sets the voltage level of the excitation signal 308 to the H level and resumes energization of the drive coil. As a result, the holding force of the probe 104 is recovered, but the noise component 501 generated from the motor driver 303 and the driving means 105 increases.
In step S408, the control unit determines whether or not the measurement for the number of repetitions read in step S203 has been completed. If not completed, the process returns to step S402, and the pulse laser beam irradiation and signal reception are performed again. If it has been completed, the measurement process is terminated. Note that the time chart of FIG. 5 shows a case where the number of repetitions is 3, and reception of photoacoustic signals is started at times 505, 508, and 509.

The time from irradiation of light to the start of reception of the photoacoustic signal 502 is between time 504 and time 505. If the sound velocity in the plate-like member 601 is V601 and the thickness of the plate-like member 601 is D601, the following is given. It is represented by Formula 1.
Time 505-Time 504 = D601 / V601 (Formula 1)

The time for receiving the photoacoustic signal 502 is between time 506 and time 505, and is expressed by the following formula 2 where the sound velocity in the measurement object 102 is V102 and the thickness of the measurement object 102 is D102.
Time 506-Time 505 = D102 / V102 (Formula 2)
That is, the reception period of the photoacoustic signal (same as the period in which the probe receives the acoustic wave) is the light emission time of the light source (same as the light irradiation time to the subject), the thickness of the measurement object, and the measurement object. If the speed of sound is known, it can be obtained. Therefore, the control unit can stop or restart at least a part of the operation of the driving unit based on the elapsed time from the light irradiation.

When the excitation signal is set to the L level at time 503, the holding power of the probe 104 and the light projecting unit 603 is lost. Let Toff be the time from when the holding force is lost until the probe 104 and the light projecting unit 603 move beyond the allowable amount. Then, if the time between time 507 and time 503 is calculated so as to satisfy the following three relations of expression 3 to expression 5, even if the excitation signal is at the L level, the probe and the light projecting unit are allowed to move. Can be within the range. If the excitation signal is measured at the L level in this way, the noise component 501 can be reduced only while the photoacoustic signal 502 is received, and the image quality of the diagnostic image can be improved.
Time 503 <Time 505 (Formula 3)
Time 506 <Time 507 (Formula 4)
Time 507−Time 503 <Toff (Formula 5)

Further, there may be a case where D102 is large and the reception period of the photoacoustic signal is long, and the excitation signal cannot be set to the L level throughout the reception period. In such a case, it is only necessary to set the depth of the light absorption part 607 where the image quality of the diagnostic image is to be enhanced, and to set the excitation signal to the L level only during the period of receiving the acoustic wave from that depth.
For example, in FIG. 6, since the pulse laser beam 606 is difficult to reach in the vicinity of the plate-like member 601, the intensity of the acoustic wave 608 is weakened and the intensity of the photoacoustic signal 502 is weakened. Since this portion of the photoacoustic signal 502 is easily buried in the noise component 501, it is conceivable that the excitation signal is preferentially set to the L level in the vicinity of the plate-like member 601, that is, in the vicinity of time 505.

  FIG. 10 shows the relationship between the position of the probe 104 and the light projecting unit 603 and time in the present embodiment. Here, photoacoustic signals are received at three points 1001, 1002, and 1003. In the first measurement process, the probe 104 and the light projecting unit 603 are moved to the position 1001, and the photoacoustic signal is received three times at times 505, 508, and 509. That is, three measurements are performed at the same measurement point. During the measurement process, the probe 104 and the light projecting unit 603 are stopped. In the second measurement process, the probe 104 and the light projecting unit 603 are moved to the position 1002, and the photoacoustic signal is received three times as in the first time. In the third measurement process, the probe 104 and the light projecting unit 603 are moved to the position 1003, and the photoacoustic signal is similarly received. However, in this embodiment, the number of acoustic wave receptions at the same measurement point may be appropriately selected according to the S / N ratio to be obtained.

FIG. 12A shows an example of an electric signal waveform obtained from the probe 104 when the motor is energized. The vertical axis is the output value from the A / D converter of the signal acquisition means 107, and the unit is digit. The horizontal axis is time and the unit is microseconds. A signal near the time of 40 microseconds is a photoacoustic signal, and its absolute value is about 100 to 200. On the other hand, when the motor is energized, a noise signal due to the motor is generated from the time around 20 microseconds, and the absolute value is about 50. Therefore, the S / N ratio of the photoacoustic signal is about 2 to 4.

FIG. 12B shows an example of an electric signal waveform obtained from the probe 104 when the motor energization is stopped. There is no significant noise signal and the absolute value is at most about 1 to 2. Therefore, the S / N ratio of the photoacoustic signal is increased from about 50 to about 100.

  In this embodiment, a method for generating one motor control signal has been described. However, the present invention is not limited to the number of motors. That is, even when there are a plurality of motors, the control signal can be generated at the same timing, and the image quality of the diagnostic image can be improved.

  In this embodiment, a stepping motor is used as an example of a motor. However, the type of motor is not limited to this. For example, even in a device driven using another motor such as a DC motor, the image quality of a diagnostic image can be improved by controlling the energization of the drive coil at the same timing.

  Further, in this embodiment, the case where there are three cases of the right rotation instruction signal, the left rotation instruction signal, and the excitation signal as the motor driver control signal has been described as an example. The type and number of signals are not limited to these.

  In this embodiment, the signal processing is performed inside the apparatus, and then the data is output to the outside and imaged. However, the imaging unit and the display for displaying the image are further provided inside, and the light is output. The sound signal data may be displayed as an image.

  As described above, according to this embodiment, noise can be reduced by stopping energization of the drive coil while receiving the photoacoustic signal. Noise can also be reduced by stopping the output of a pulse signal such as a right turn instruction signal. Thereby, it becomes possible to improve the S / N ratio of diagnostic data.

<Example 2>
Next, Example 2 will be described. The difference between the second embodiment and the first embodiment is that the probe 104 and the light projecting unit 603 are moved between a plurality of times of pulse laser emission. The block diagram of FIG. 1, the flowchart of FIG. 2, the configuration of the control means 106 and the drive means 105 of FIG. 3, and the structure in the vicinity of the measurement target of FIG.

Details of the measurement process will be described with reference to FIGS. FIG. 7 is a flowchart describing details of the measurement process.
The processing from step S701 to step S703 is the same as the processing from step S401 to step S403 in FIG.
In step S <b> 704, the microprocessor 301 transmits a command to the FPGA 302 and interrupts the pulse signal output of the right rotation instruction signal 306.

The processing from step S705 to step S708 is the same as the processing from step S404 to step S407 in FIG. That is, in step S705, the motor drive is stopped corresponding to time 503, and in step S706, light is emitted from the light source corresponding to time 504. In step S707, the acoustic wave is received, and in step S708, the motor driving is resumed corresponding to time 507. Through these steps S705 to S708, a signal having no noise component is acquired.
In step S709, the microprocessor 301 transmits a command to the FPGA 302, restarts the pulse signal output of the right rotation instruction signal 306, and moves the probe 104 to the next measurement position.
The process of step S710 is the same as the process of step S408 of FIG. 4, and the process ends if the measurement of the number of repetitions has been completed.

FIG. 8 is a timing chart showing the timing of the control signal and the photoacoustic signal. A difference from the first embodiment is that a pulse signal is supplied to the right rotation instruction signal 306 after the energization of the coil is resumed at the time 507 in step S708 and until the energization of the coil is stopped in step S704 at the next repetition. Is a point to output. By this right rotation instruction signal, the probe 104 and the light projecting unit 603 are moved between time 507 and time 801 in FIG. In this case, addition averaging is performed in consideration of the moving distance during signal processing.

  FIG. 11 shows the relationship between the position of the probe 104 and the light projecting unit 603 and the time in this embodiment. Photoacoustic signals are received at three points 1001, 1002, and 1003. In the first measurement process, the probe 104 and the light projecting unit 603 are moved to the position 1001, and the photoacoustic signal is received three times at times 505, 508, and 509. During the measurement process, the probe 104 and the light projecting unit 603 are continuously moved to 1002 and 1003.

  Also in the present embodiment, the excitation signal is set to the L level during the reception of the photoacoustic signal as in the first embodiment, and the influence of the noise component 501 on the diagnostic image can be reduced. Noise can also be reduced by stopping the output of a pulse signal such as a right turn instruction signal. This improves the S / N ratio of the signal. Furthermore, in the present embodiment, the entire measuring object 102 can be measured in a shorter time than in the first embodiment by driving the probe between a plurality of laser emission.

<Example 3>
Next, Example 3 will be described. The difference of the present embodiment from the second embodiment is that the energization of the drive coil is maintained and the holding force of the probe 104 and the light projecting unit 603 is maintained during the reception of the photoacoustic signal. The block diagram of FIG. 1, the flowchart of FIG. 2, the configuration of the control means 106 and the drive means 105 of FIG. 3, and the structure in the vicinity of the measurement target of FIG. The relationship between the position of the probe 104 and the light projecting unit 603 and the time is the same as that in the second embodiment.

  The flow of the measurement process of the present embodiment is basically the same as the flowchart of the second embodiment shown in FIG. However, the difference between the measurement process of the present embodiment and the second embodiment is that nothing is performed in steps S705 and S708, and the energization of the coil is maintained.

  FIG. 9 is a timing chart showing the timing of the control signal and the photoacoustic signal. This timing chart is different from the timing chart of the second embodiment shown in FIG. 8 in that the excitation signal 308 remains at the H level even while the photoacoustic signal is received. That is, the excitation signal 308 remains at the H level between time 503 and time 507 in FIG. 9, and the drive coil is energized. Note that the pulse output to the right rotation instruction signal 306 and the left rotation instruction signal 307 is stopped while the photoacoustic signal is received, as in the second embodiment.

  In the present embodiment, a steady current flows through the drive coil during reception of the photoacoustic signal, but the current output is not switched because the pulse output to the right rotation instruction signal 306 and the left rotation instruction signal 307 is stopped. . Therefore, although the influence of noise due to steady current cannot be reduced, it is possible to reduce the influence of noise due to switching on the diagnostic image. Even when the reception period of the photoacoustic signal is long and the influence due to the decrease in holding power when the energization of the drive coil is stopped cannot be ignored, the influence of noise caused by switching on the diagnostic image can be reduced. Thereby, the S / N ratio of diagnostic data can be improved.

  In this embodiment, the case of three signals of the right rotation instruction signal, the left rotation instruction signal, and the excitation signal has been described as an example of the motor driver control signal. However, if there is a means for stopping the switching, the control of the present invention is possible. The type and number of signals are not limited to this.

Moreover, although the present Example demonstrated using the example which stops switching of a drive coil, the place of a switching source is not limited to a drive coil. For example, when there is a switching source such as a clock generation circuit to the PWM control circuit in the motor driver, switching of these circuits may be stopped during reception of the photoacoustic signal.

  104: probe, 105: drive means, 106: control means, 107: signal acquisition means

Claims (4)

A probe that receives an acoustic wave generated from a subject that has absorbed light emitted from a light source and converts it into an electrical signal;
Driving means for moving the probe to perform scanning;
Control means for outputting a control signal for controlling the operation of the driving means,
The control means stops at least a part of the operation of the driving means during a period in which the probe receives an acoustic wave .
The measurement apparatus characterized in that the control means stops at least a part of the operation of the drive means based on an elapsed time from light irradiation . A probe that receives an acoustic wave generated from a subject that has absorbed light emitted from a light source and converts it into an electrical signal;
Driving means for moving the probe to perform scanning;
Control means for outputting a control signal for controlling the operation of the driving means,
The control means stops at least a part of the operation of the driving means during a period in which the probe receives an acoustic wave.
The operation of the driving means includes an operation in which the driving means holds the position of the probe,
The control means stops holding the probe by the driving means during a period in which the probe receives an acoustic wave.
A measuring device. The probe repeats reception of acoustic waves after a predetermined time,
3. The measuring apparatus according to claim 1, wherein the driving unit moves the probe so as to receive an acoustic wave a plurality of times at the same measurement point during scanning of the probe. 4. . At least a part of the operation of the drive means is an operation based on energization of the drive coil included in the drive means or switching of the current of the drive coil,
The probe repeats reception of acoustic waves after a predetermined time,
It said drive means, in the scanning of the probe, the measuring device according to claim 1 or 2, characterized in that moving the probe continuously.

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