JP6686066B2 - Photoacoustic device - Google Patents

Description

  The present invention relates to a photoacoustic apparatus that irradiates a subject with light and receives a photoacoustic wave generated.

  BACKGROUND ART Research on an optical imaging device that irradiates a living body with light from a light source such as a laser and images information in the living body obtained based on the incident light is being actively pursued in the medical field. As one of the optical imaging techniques, there is Photo Acoustic Tomography (PAT: Photoacoustic Tomography). In photoacoustic tomography, pulsed light generated from a light source is applied to a living body, and an acoustic wave generated from living tissue that has absorbed the energy of the pulsed light propagated and diffused in the living body is detected (Patent Document 1). That is, by utilizing the difference in absorption rate of light energy between a test site such as a tumor and other tissues, elastic waves generated when the test site absorbs the irradiated light energy and instantaneously expands. That is, the photoacoustic wave is received by the transducer. By analyzing the detection signal, the optical characteristic distribution in the living body, particularly the light energy absorption density distribution, can be obtained. These pieces of information can also be used for quantitative measurement of a specific substance in the subject, for example, glucose or hemoglobin contained in blood. As a result, it can be used for identifying the location of a malignant tumor accompanied by proliferation of new blood vessels.

  Further, Non-Patent Document 1 discloses an application example as a photoacoustic microscope. According to Non-Patent Document 1, ultrasonic waves generated by irradiating a subject with pulsed light are received by a transducer and imaged. Further, the spectral characteristics of the subject are imaged by changing the wavelength of the pulsed light.

US Pat. No. 5,840,023

IEEE Journal of Selected Topics in Quantum Electronics, Vol. 14, No. 1,171-179 (2008)

  The PAT can obtain local light absorption information by measuring an acoustic wave generated by being absorbed at a local test site. The initial sound pressure P of the acoustic wave generated at the test site is expressed by the following equation (1) using the distance r from the light irradiation point to the test site.

P (d) = Γμ _a (r) Φ (r) (1)
here,
Γ: Grueneisen coefficient (heat-acoustic conversion efficiency)
μ _a (r): Absorption coefficient at position at distance r Φ (r): Light intensity at position at distance r The Grueneisen coefficient Γ, which is the elastic characteristic value, is the product of the square of the thermal expansion coefficient β and the sound velocity c divided by the constant pressure specific heat Cp. It is known that Γ takes a substantially constant value if the biological tissue is determined. Therefore, by measuring the change in the sound pressure P, which is the magnitude of the acoustic wave, in a time-division manner, the product of μ _a and Φ, that is, The light energy absorption density distribution H can be obtained. Then, μ _a (r) can be obtained by dividing the light intensity Φ (r) from H.

Here, it is known that the pulse laser used for generating a photoacoustic wave cannot always generate a constant amount of pulsed light due to its principle, and has a certain time-dependent output fluctuation. Specifically, the fluctuation of the light amount may reach 10% or more. When the amount of generated pulsed light fluctuates, the amount of light Φ (r) in a local region inside the subject also fluctuates. As described above, since the light amount Φ and the intensity P of the photoacoustic wave are in a proportional relationship, the photoacoustic wave also undergoes the same variation for each laser pulse. Therefore, when such a fluctuation is left as it is and the light energy absorption density H distribution or the absorption coefficient μ _a distribution is imaged, intensity unevenness also occurs on the screen after the reconstruction, and the quantitativeness of the measurement is quantified. Will be lost.

  However, in the above-mentioned Patent Document 1, there is no description regarding the temporal change in output from the light source. Although Non-Patent Document 1 describes that the light amount is corrected using a sensor for measuring the pulse light amount, the measurement, usage, and correction target are not clearly described. In particular, Non-Patent Document 1 is premised on the use as a photoacoustic microscope, and thus the optical attenuation in the depth direction, which is important when measuring a thick object, is not clearly described.

  The present invention has been made on the basis of such background art and recognition of the problems. An object of the present invention is to provide a photoacoustic apparatus capable of reducing adverse effects on an image caused by the change in the output light amount of a light source with time.

Engaging Ru processing apparatus according to the present invention, light is a detection signal obtained by detecting an acoustic wave generated by irradiating the object, based rather on the detection signal corresponding to a plurality of times of light irradiation An image reconstruction data acquisition unit that acquires image reconstruction data inside the subject, a light amount of irradiation light for each light irradiation applied to the subject , and an in- plane surface of the irradiation surface of the light stored in advance . based on the intensity distribution obtains the light intensity distribution inside the subject, and a correction processing unit for correcting said image reconstruction data based on the image reconstruction data in the light intensity distribution inside the subject Prepare
A processing device according to another aspect of the present invention is a processing device for acquiring information inside a subject as voxel data, which is obtained by receiving an acoustic wave generated by irradiation of light to the subject, A signal acquisition unit that acquires a signal corresponding to a single irradiation of light, a sensor unit that acquires information about the light amount variation of the light that is irradiated to the subject multiple times, and an irradiation surface of irradiation light that is irradiated to the subject at one time. A memory unit that stores intensity distribution information in the inside, and the signal acquired by the signal acquisition unit, information about the light amount variation acquired by the sensor unit, and the intensity prestored in the memory unit. Using the distribution information, a correction process for reducing the influence of the variation of the light amount for each irradiation of the irradiation light irradiated on the object a plurality of times on the voxel data corresponding to the information inside the object is performed. Cormorant correction processing unit, equipped with a.
Furthermore, another processing method according to the present invention is a processing method for acquiring information on the inside of a subject as voxel data, and light irradiation in which an acoustic wave is generated from the subject by irradiation with light. Performing a plurality of times to obtain a signal obtained by receiving the acoustic wave generated by the light irradiation,
A step of acquiring information regarding a light amount variation of light irradiated to the subject a plurality of times, and the signal, information regarding the light amount variation, and an irradiation surface of irradiation light that is previously obtained and is applied to the subject at a time. Using the intensity distribution information in the inside, a correction process is performed to reduce the influence of the fluctuation of the light amount for each irradiation of the irradiation light irradiated on the object a plurality of times on the voxel data corresponding to the information inside the object. Have steps.

  According to the present invention, the photoacoustic apparatus is provided with the light amount measuring device, and the intensity of the photoacoustic signal is corrected in consideration of the change with time of the measured output light amount. Therefore, even if the output of the light source changes with time. Thus, it is possible to provide a photoacoustic device that has less adverse effects on images.

1 is a diagram schematically showing a configuration of a photoacoustic apparatus according to Embodiment 1 of the present invention. It is a figure for demonstrating the output fluctuation of a laser pulse. FIG. 6 is a flow chart for explaining an example of determining the correction amount of the intensity of the detection signal in the first embodiment of the present invention. It is a figure for demonstrating arrangement | positioning of the photosensor of this invention. It is the figure which showed typically the structure of the photoacoustic apparatus by Embodiment 2 of this invention. FIG. 9 is a flowchart for explaining an example of determining a correction amount of detection signal intensity in the second embodiment of the present invention. It is the figure which showed typically the structure of the photoacoustic apparatus by Embodiment 3 of this invention.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. In principle, the same constituent elements will be given the same reference numerals, and the description thereof will be omitted.

(Embodiment 1: Photoacoustic apparatus)
First, the configuration of the photoacoustic apparatus according to the present embodiment will be described with reference to FIG.
The photoacoustic apparatus of this embodiment is a photoacoustic imaging apparatus that images information inside a subject. When the subject is a living body, the photoacoustic apparatus enables imaging of biological information for the purpose of diagnosing malignant tumors, vascular diseases, etc., and observing the progress of chemotherapy. The "information inside the subject" in the present invention is information on the source distribution of acoustic waves generated by light irradiation, information on the initial sound pressure distribution in the living body, and information on the light energy absorption density distribution derived from it. The information is, for example, the information on the concentration distribution of the substances forming the biological tissue obtained from the information. For example, the substance concentration distribution is oxygen saturation or the like.

  The photoacoustic apparatus of this embodiment has a pulse laser 2a, a detector 5, and a photosensor 8a as a basic hardware configuration. The pulse laser 2a is a light source for irradiating a subject with pulsed light.

  The subject 3 such as a living body is fixed to the plates 4a and 4b for compressing and fixing it from both sides, if necessary. The light from the light source is guided to the surface of the plate 4b by an optical system (not shown) such as a lens, a mirror, and an optical fiber, and is irradiated on the subject. When a part of the energy of the light propagating inside the subject 3 is absorbed by a light absorber such as a blood vessel, an acoustic wave (typically an ultrasonic wave) is generated from the light absorber due to thermal expansion. This is sometimes called "photoacoustic wave". That is, the absorption of the pulsed light raises the temperature of the light absorber, and the temperature rise causes volume expansion to generate an acoustic wave. The time width of the light pulse at this time is preferably such that the heat / stress confinement conditions are satisfied in order to efficiently confine the absorbed energy in the light absorber. It is typically about 1 nanosecond to 0.2 seconds.

  The detector 5 for detecting an acoustic wave detects the acoustic wave generated in the subject and converts it into an electric signal which is an analog signal. The detection signal acquired from this detector is also called a "photoacoustic signal."

  The signal processing unit 15 for processing the photoacoustic signal and acquiring the information inside the subject includes a reception amplifier 6, an A / D converter 7, a signal correction unit 11, and an image reconstruction processing unit in the present embodiment. 12 and an optical attenuation correction unit 16. The photoacoustic signal obtained from the detector 5 is amplified by the reception amplifier 6 and converted into a photoacoustic signal as a digital signal by the A / D converter 7. The signal correction unit 11 is one of the characteristic configurations of this embodiment, and corrects the intensity of this digital signal. Then, after the image reconstruction processing unit 12 performs arithmetic processing on the three-dimensional information, the optical attenuation correction unit 16 performs correction on the obtained voxel data in consideration of the optical attenuation in the subject. Then, a photoacoustic image of the subject is displayed on the image display unit 13 as needed. Further, all elements are controlled by the system control unit 1. Here, the “photoacoustic image” is an image in which the obtained information on the inside of the subject is shown by coordinates in a three-dimensional space and the information is converted into luminance information and displayed.

  Here, a characteristic part of the present embodiment will be briefly described. The output light quantity of the laser 2a is measured by a photo sensor 8a which is a light quantity measuring device. When the output light amount of the laser 2a varies with time, this variation is also measured by the photo sensor 8a. Then, the signal correction unit 11 corrects the intensity of the photoacoustic signal so as to suppress the intensity fluctuation of the photoacoustic signal based on the change over time of the output light amount. That is, it is possible to reduce the intensity fluctuation of the photoacoustic signal due to the temporal change (time fluctuation) of the output light amount.

(Variation of light source and light output from light source)
The laser light generated by the pulse laser 2a changes for each pulse. FIG. 2 shows an example of the light quantity fluctuation. The figure shows the change over time in the measured output when 10 Hz pulsed light is generated for 60 seconds at about 5 W (500 mJ) with a YAG laser. From the figure, it can be confirmed that the output light quantity fluctuates by about 10%.

  When the subject is a living body, the light source irradiates with light of a specific wavelength that is absorbed by a specific component among the constituents of the living body. As the light source, a pulsed light source capable of generating pulsed light on the order of 1 nanosecond to 0.2 nanosecond is preferable. A laser is preferable as the light source, but a light emitting diode or the like can be used instead of the laser. As the laser, various lasers such as a solid laser, a gas laser, a dye laser, and a semiconductor laser can be used.

  It is assumed that the fluctuation of the output light quantity of the laser as shown in FIG. 2 is mainly due to the fluctuation of the light quantity of the flash lamp which is the laser excitation light source. Therefore, when the flash lamp itself or the laser including the flash lamp is used as the light source of the present invention, the effect of the present invention can be further obtained. However, needless to say, the light source of the present invention is not limited to these, and the present invention can be used as long as it is a light source capable of causing fluctuation in light amount even if it is a semiconductor laser or a light emitting diode that does not include a flash lamp.

  In this embodiment, a single light source is shown, but a plurality of light sources may be used. In the case of a plurality of light sources, a plurality of light sources that oscillate the same wavelength may be used in order to increase the irradiation intensity of the light that irradiates the living body. A plurality of light sources may be used. It should be noted that if a dye capable of converting an oscillating wavelength or OPO (Optical Parametric Oscillators) can be used as the light source, it is possible to measure the difference in the optical characteristic value distribution depending on the wavelength. The wavelength to be used is selected from the wavelength band of 700 nm to 1100 nm, which is less absorbed in the living body. However, in the case of obtaining the optical characteristic value distribution of the living tissue relatively near the surface of the living body, a wavelength band having a wider range than the above wavelength band, for example, 400 nm to 1600 nm is selected and used.

  The light emitted from the light source can be propagated using an optical waveguide or the like, if necessary. Although not shown in FIG. 1, an optical fiber is preferable as the optical waveguide. When using an optical fiber, it is possible to guide the light to the surface of the living body by using multiple optical fibers for each light source, or to guide the light from multiple light sources to one optical fiber. Alternatively, all the light may be guided to the living body by using only one optical fiber. Further, the light may be guided mainly by an optical component such as a mirror that reflects the light or a lens that condenses or enlarges the light or changes the shape. Any of such optical components may be used as long as the light emitted from the light source irradiates the light irradiation region on the surface of the subject in a desired shape.

(Detection signal correction 1)
Hereinafter, the correction of the detection signal in this embodiment will be described in detail.
As shown in FIG. 1, when the subject is fixed on a flat plate and the light irradiation region by the laser 2a is two-dimensionally set on the subject surface, the light irradiation region is sufficiently larger than the imaging range. Explain to the model. Let Φ ₀ be the amount of pulsed light with which the surface of the subject is irradiated. Inside the object, light attenuates exponentially as it moves away from the surface due to absorption and scattering. That is,
Φ (r) = Φ ₀ · exp (−μ _eff · r) ... Can be expressed as equation (2). μ _eff is the average equivalent attenuation coefficient of the subject. From equation (2) and equation (1),
P (r) = Γ μ _a (d) Φ ₀ · exp (−μ _eff · r) (3) In the present invention, it is a problem that Φ ₀ varies from pulse to pulse. For example, the output light amount [Phi ₀₁ of a pulse 1, when the output light amount [Phi ₀₂ of another pulse 2 was 0.9Fai _01, the sound pressure of the photoacoustic wave by pulses _{2 P 2 (r) = 0} . 9P ₁ (r).

Then, the luminance signal differs between the image (μ _a distribution) created from the pulse 1 and the image created from the pulse 2, corresponding to the sound pressure, and the reproducibility of the image cannot be obtained. . As described above, when the same place is measured a plurality of times, the reproducibility of the image is deteriorated, which may cause misrecognition of information in the subject. Further, when the measurement is performed while scanning the laser and the detector along the surface of the subject, one image is created from the sound pressures corresponding to the plurality of pulses. In this case, the above-mentioned fluctuation of the light amount causes uneven brightness in the image, which also causes misidentification of information in the subject.

Therefore, in this embodiment, the photosensor 8a measures the output light amount Φ _0n of each pulse. Then, the intensity of the detection signal by each photoacoustic wave is corrected so that it can be considered that the sound pressure P _n (r) is always obtained with the reference light amount such as the constant initial light amount Φ ₀ . In the above example, when P ₁ (r) is used as a reference, the detection signal is corrected assuming that the intensity obtained by multiplying P ₂ (r) by 1 / 0.9 is obtained. With this configuration, even if the output of the light source varies with time, it is possible to reduce the influence and obtain information regarding the position and sound pressure of the sound source inside the subject.

The reciprocal of the ratio of the output light amount Φ ₀₁ of the pulse 1 to the output light amount Φ ₀₂ of another pulse 2, that is, Φ ₀₁ / Φ ₀₂ is referred to as “correction coefficient” in this specification. Further, although the above detection signal can be corrected for both an analog signal and a digital signal, in the present embodiment, the amount converted into a digital signal by the A / D converter 7 is corrected. There is. Since the digital signal outputs the value of the sound pressure P (r) for each sampling frequency from the A / D converter 7, the correction coefficient of the pulse is applied to the digital signal indicating P (r) corresponding to a certain pulse. Correction is performed by performing a multiplication process.

  The details will be described below. In this embodiment, the pulse light amount of the laser 2a is detected by the photo sensor 8a for each pulse, and then stored in the light amount memory 9a. From the viewpoint of the reliability of signal processing, it is preferable to have a memory that stores the output light amount in this way. The correction amount determination unit 10 reads the data regarding the change with time of the output light amount stored in the memory 9a and determines the correction amount (correction coefficient) for each detection signal. The signal correction unit 11 corrects the intensity of each detection signal according to the determined correction amount.

  FIG. 3 shows a processing flow of the correction amount calculation. The correction amount determination unit 10 reads the data from the light amount memory 9a (S301). A correction coefficient corresponding to each pulse is calculated based on the light amount of the pulse obtained by the light amount memory 9a (S302). The correction coefficient uses a light amount measured in advance as a reference value. Here, in this specification, a correction coefficient set for each of a plurality of pulses is referred to as a “correction amount table”. Then, the correction amount table is transferred to the signal correction unit 11 (S304), and is calculated for the obtained photoacoustic signal. That is, the correction coefficient is multiplied to the digital signal of the sound pressure P (d) acquired for each sampling frequency.

(Image reconstruction and optical attenuation correction)
The image reconstruction processing unit 12 performs image reconstruction on the digital signal corrected as described above. PAT and image reconstruction, and to derive the sound pressure received by the detector P _{d (r d, t)} distribution P ₀ of the initial sound pressure when generated in the subject from _(r), Mathematics It is called the inverse problem. The Universal Back Projection (UBP) method, which is typically used in the image reconstruction method of PAT, is described in PHYSICAL REVIEW E71,016670 (2005) and REVIEW OF SCIENTIFIC INSTRUMENTS, 77,042201 (2006).

Up to this point, the initial sound pressure distribution or the product of μ _a and Φ, that is, the light energy absorption density distribution H can be obtained as the information inside the subject. If Φ is constant and H is divided by Φ, the absorption coefficient μ _a (r) distribution in the subject can be obtained. However, the amount of light that illuminates a local region within the subject exponentially attenuates as described above, so if there are two tissues having the same absorption coefficient, they will be generated from a tissue that is farther from the subject surface. The acoustic pressure of the acoustic wave is less than that from nearby tissue. Therefore, in order to obtain an accurate absorption coefficient distribution, it is preferable to correct the influence of such light attenuation. This correction is called "light attenuation correction" in this specification.

  Specifically, the light attenuation correction unit 16 performs a process of dividing the light amount at the position of the corresponding voxel with respect to each voxel data indicating the light energy absorption density distribution H output from the image reconstruction processing unit 12. To do. The light quantity at the position of the corresponding voxel can be calculated from the above equation (2).

  With such a configuration, an accurate absorption coefficient distribution in the subject can be imaged in consideration of the influence of light attenuation.

(Aspect of signal correction 1)
Note that, in the present embodiment, an example in which the correction for the fluctuation of the light amount for each pulse is performed on the data before being subjected to the image reconstruction processing after being converted into a digital signal by the A / D converter 7 has been shown. It is not limited to this. This correction can also be performed on voxel data after image reconstruction. That is, even if the correction calculation is performed by inputting the correction coefficient calculated by the correction amount determination unit 10 to the optical attenuation correction unit 16, the photoacoustic signal can be similarly corrected. Further, the analog data before A / D conversion can be corrected. In this case, a method of controlling the gain of the reception amplifier 6 by the output of the correction amount determination unit 10 can be used. That is, the “detection signal” in this specification includes both an analog signal, a digital signal after A / D conversion, and luminance data after image reconstruction of this digital signal.

  Further, if the light quantity distribution in the subject when a certain light is irradiated can be set, the photoacoustic signal is similarly generated when the light is incident from both sides of the plate 4 or when the light is irradiated from multiple directions. Can be corrected.

  Further, in the above-described embodiment, the photoacoustic signal is acquired while the transducer 5 and the laser 2a are fixed. However, even when the photoacoustic signal is acquired while scanning the transducer 5 and the laser 2a, each scanning is performed. Similar correction of the photoacoustic signal is possible by acquiring the light quantity measurement data at the position.

  Further, the laser pulse 2a used is a laser beam having a certain thickness, but if there is spatial unevenness in the intensity of the cross section, it is corrected in the three-dimensional space after considering the light quantity distribution. A similar photoacoustic signal can be corrected by calculating the light quantity.

(Detailed description of each component)
The detector (probe) 5 detects an acoustic wave such as a sound wave or an ultrasonic wave and converts it into an electric signal. Any acoustic wave detector may be used as long as it can detect an acoustic wave signal, such as a transducer using a piezoelectric phenomenon, a transducer using optical resonance, a transducer using a change in capacitance. The detector 5 of this embodiment is preferably an array type having a plurality of transducer elements. By using such two-dimensionally arranged transducer elements, acoustic waves can be detected at a plurality of places at the same time. As a result, the detection time can be shortened and the influence of vibration of the subject can be reduced. Further, it is desirable to use an acoustic impedance matching agent such as gel or water for suppressing reflection of sound waves between the detector 5, the plate 4b, and the subject 3.

  As the light quantity measuring device, a photo sensor represented by a photodiode or a pyroelectric sensor is representative, but when a one-dimensional or two-dimensional photo sensor array is required, a CCD image sensor, a CMOS image sensor, The same effect can be obtained by using a light-dependent resistor (LDR) or the like.

  A preferred arrangement of the photo sensor 8a as the light quantity measuring device will be described with reference to FIG. Reference numeral 18 is a reflection mirror, and 19 is a laser.

  FIG. 4A shows a case where leak light of the reflection mirror is detected in the middle of the optical system before reaching the plate 4b. Thus, by disposing the photo sensor 8a behind the reflection mirror, a part of the light from the light source can be detected. If the ratio of leaked light is known, it is possible to calculate the light amount fluctuation of the light source.

  FIG. 4B shows a case where a part of the light reflected from the plate 4b is detected. Thus, it is also preferable to dispose the photo sensor 8a near the plate 4b.

  FIG. 4C shows a case in which light is also detected in part of the light that has propagated inside the plate 4b. In this way, the photo sensor 8a can be provided at the end of the plate 4b. In particular, when light is obliquely incident on the plate, such a propagating light inside the plate increases, which is a preferable mode.

  As the memory, a memory on a PC or a control board can be considered, but the same effect can be obtained by using a memory attached to the photo sensor unit or a hard disk if the speed is equal to or higher than the laser pulse period.

(Example 1)
Hereinafter, in the first embodiment, a case where the photoacoustic apparatus according to the present invention is used for a breast examination will be specifically described. In the breast examination in the present embodiment, it is assumed that breast compression similar to X-ray mammography generally used is performed. In other words, it is sufficient for the breast to be able to acquire a photoacoustic signal up to a depth of 4 cm, which is the average breast compression thickness.

  In this example, a Q-switched YAG laser having a wavelength of 1064 nm, 10-hertz driving, a pulse width of 5 nanoseconds, and an output per pulse of 1.6 J was used as a light source. Since the JIS stipulates that the laser light intensity that can be applied to the human body under these conditions is 100 mJ / cm 2 or less, the illumination optical system was designed to spread the emitted laser light to 4 cm square.

  As a result, when the breast was pressed and light was emitted from both sides, the range in which the photoacoustic signal was generated was 4 cm in depth and 4 cm in width. Moreover, in order to acquire the photoacoustic signal within this range, one side of the ultrasonic transducer was set to 4 cm. Further, the element pitch was 2 mm, and a two-dimensional probe having 400 elements was constructed. The frequency used was 1 MHz. As the photo sensor, a S5973 PIN photodiode manufactured by Hamamatsu Photonics KK was used.

  When acquiring a photoacoustic signal under the above conditions, the irradiation light quantity at the time of laser irradiation is always stored in the light quantity memory. The correction coefficient corresponding to each pulse is calculated with 1 being the maximum value of the measured light amount fluctuation. The detection signal was corrected according to the correction method described in the configuration of FIG. Image reconstruction was performed and the generated photoacoustic image was accumulated as volume data and displayed on the screen.

  By using this method, it is possible to improve the intensity unevenness of the photoacoustic image, but the reproducibility of the photoacoustic signal itself based on electrical noise is about 2 to 3%, and the unevenness of the distribution of irradiation light is about 2%. Therefore, the same image unevenness remains. However, by using this method, it has become possible to improve the image unevenness which was conventionally about 8 to 10% to about 3 to 4%.

  The distribution of irradiation light can be measured by disposing a CCD or the like separately in the optical path, and the reproducibility of photoacoustic signals can be measured by operating this system without laser irradiation. Can be done. The image unevenness is defined as 3 times the standard deviation of the brightness value change in the same pixel when the image is acquired multiple times.

  In the present embodiment, the case where the photoacoustic apparatus is used for the breast examination was specifically described, but the same effect can be obtained by performing the same processing for the measurement of the other parts of the human body and the subject other than the human body. It is possible to obtain

(Embodiment 2)
In the first embodiment, the laser light is emitted from only one side, but in the present embodiment, a correction method when the laser light is emitted from both sides of the plate 4 will be described. FIG. 5 shows an example of a photoacoustic apparatus for explaining the present embodiment. The irradiation of the laser pulse and the acquisition of the light intensity data and the photoacoustic signal are the same as in the first embodiment. The difference from the first embodiment is that laser light is emitted from both sides of the lasers 2a and 2b, and the outputs of the lasers 2a and 2b are detected by the two photosensors 8a and 8b. The detected light amount is stored in the light amount memories 9a and 9b and is transferred to the correction amount determination units 10a and 10b. Then, two correction coefficients are calculated using the same method as in the first embodiment, and the correction coefficients are transferred to the signal correction unit 11.

  The operations of the correction amount determination units 10a and 10b and the signal correction unit 16 will be described in detail with reference to FIG. A correction coefficient of the light amount from each laser obtained by the light amount memories 9a and 9b (S601) is calculated with the maximum value of each light amount fluctuation measured in advance being 1 (S602). Then, the normalized light intensity and the coefficient are used to calculate the relative attenuation in the depth direction, and two correction amount tables are created from the two light intensity data (S603). These correction amount tables in the depth direction are subjected to addition processing for the same depth to generate one combined correction amount table (S604).

That is, the sound pressure due to the light emitted from one side of the plate 4 is the same as the above-mentioned formula (3): P (r) = Γμ _a (r) Φ _0A · exp (−μ _eff · r) In the case of (3), the sound pressure due to the light emitted from the other side is expressed by the following equation.
P (r) = Γ μ _a (r) Φ _0B · exp (−μ _eff · (D−r)) (4)

Here, D is the distance between the compression plates 4a and 4b. Further, Φ _0A is the initial light amount of the pulsed light emitted by the laser 2a among the pulsed light that generated the acoustic wave, after being multiplied by the correction coefficient of the light amount fluctuation. Φ _0B is the initial light amount of the pulsed light emitted by the laser 2b among the pulsed lights that generated the acoustic wave, after being multiplied by the correction coefficient of the light amount fluctuation. One correction amount table is obtained by converting the light amount and the light attenuation amount in the above formula into numerical values with respect to the sampling frequency and adding them, and is represented by the following formula.
C (r) = 1 / (Φ _0A · (exp (−μ _eff · r) + Φ _0B exp (−μ _eff · (D−r)))) Equation (5)

Here, C (r) is each value in the correction amount table, and Φ _0A , Φ _0B , r, D, and μ _eff are known and can be obtained. Then, the combined correction amount table C (d) is multiplied by the obtained image reconstruction data (S605). At this time, the correction amount table is a function in the depth direction (straight distance from the surface of the subject), whereas the image reconstruction data is three-dimensional data, but multiplication processing is performed only in the depth direction. The same process is performed in all the spreading directions (in-plane direction of the surface of the subject). Then, the photoacoustic image is accumulated as volume data and displayed on the screen. This method is a method of collectively performing a correction that considers a light amount variation from a light source and a correction that considers light attenuation in the depth direction on digital data after image reconstruction. The detection signal in this case may be a sound pressure signal converted into a luminance signal.

  By using this embodiment, it is possible to improve image unevenness as in the first embodiment even when light irradiation is performed from both sides of the plate 4.

(Embodiment 3)
In the first and second embodiments, the intensity of the photoacoustic signal is corrected assuming that the surface of the subject is irradiated with a constant light amount Φ ₀ irrespective of the location, but in the third embodiment, the laser irradiation surface (the surface of the subject) is corrected. The correction method when the initial light amount has an intensity distribution will be described.

  FIG. 7 shows an example of a photoacoustic apparatus for explaining the present embodiment. The laser pulse irradiation, the light amount data, and the photoacoustic signal acquisition are the same as those in the second embodiment. The laser that irradiates the subject 3 is expanded and illuminated in the same 4 cm square as the transducer 5, but there is an intensity distribution in the plane. This is especially seen when using multimode lasers. The in-plane intensity distribution is measured and stored in advance in the light amount distribution memories 14a and 14b, respectively.

The correction amount corrected here reflects the light intensity distribution. In other words, the correction amount is a function of the light intensity distribution, the Grueneisen coefficient, the absorption coefficient, the initial light amount multiplied by the correction coefficient, and the attenuation coefficient, but the light intensity distribution cannot be analytically solved, so a light propagation simulation is performed. Calculated by The light quantity distribution in the three-dimensional direction is obtained by calculation. Explaining using an equation, equation (3) is: P (r) = Γμ _a (d) Φ ₀ (x, y, r, t) .Exp (-. _Mu.eff.r ) ... Equation (6)
And the light quantity Φ ₀ (x, y, r, t) is a function of the spatial (x, y, r) distribution and each pulse oscillated at each time t. This light quantity Φ ₀ is calculated by simulation, and after multiplying each coefficient, the reciprocal is taken to calculate the correction coefficient at each place in the three-dimensional space.

  The correction amount calculation according to the present embodiment is excellent in that the signal correction can be performed in consideration of the spatial irradiation light amount distribution on the surface of the subject in addition to the temporal light amount variation. The reproducibility of the photoacoustic signal is similar to that of the first embodiment. When the photoacoustic image was acquired and corrected in consideration of these factors, the intensity unevenness of the photoacoustic image, which was 8 to 10% without the correction of the light amount fluctuation and the light amount distribution, is about 3%, that is, the photoacoustic image. The signal reproducibility was improved to the same extent.

(Embodiment 4)
In the first to third embodiments, the photoacoustic signal is acquired while the transducer 5 and the laser 2a are fixed, but in the present embodiment, a case where the photoacoustic signal is acquired while scanning these along the plate will be described. .

  The system configuration is as shown in FIG. 4, but in the present embodiment, it has a movable mechanism for scanning the lasers 2a and 2b and the transducer 5 with respect to the subject. It should be noted that it suffices that the incident portion from the light source to the subject be scanned, and it is not always necessary to scan the laser itself. In this case, it becomes necessary to correct the light amount fluctuation during scanning, which is not considered in the first to third embodiments.

  Considering that the breast is scanned using the above light source and ultrasonic transducer, the scanning area is 20 cm × 20 cm, and the stripe width is 4 cm. Therefore, the stripe of 4 cm × 20 cm is formed five times. In addition, the scanning of the transducer is a so-called step-and-repeat method, that is, a method of repeating the movement and stop of the transducer and irradiating the laser when the transducer is stopped is adopted, and the photoacoustic signal is acquired. On the other hand, upon laser irradiation, the irradiation light amount is always stored in the light amount memory.

  The standardization of the light quantity, the calculation process, and the correction of the photoacoustic signal are the same as those in the second embodiment, but the corrected photoacoustic signal is temporarily stored in the memory until the end of scanning. Then, after all scanning is completed, image reconstruction is performed using the corrected photoacoustic signal, and the generated photoacoustic image is accumulated as volume data and displayed on the screen.

  Although it is possible to improve the intensity unevenness of the photoacoustic image by using this method, the reproducibility of the photoacoustic signal itself is about 2 to 3%, while the averaging effect of the photoacoustic signal by scanning is S. There is an effect of increasing / N by 4 to 5 times. Considering these influences, it becomes possible to improve the image unevenness, which was about 8 to 10% without the conventional scanning and light amount correction, to 1% or less.

(Embodiment 5)
The present invention is also realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or device via a network or various storage media, and the computer (or CPU, MPU, etc.) of the system or device reads the program. This is the process to be executed.

1 system control unit 2a, 2b laser 3 subject 4a, 4b plate 5 detector 6 receiving amplifier 7 analog-digital converter 8a, 8b photosensor 9a, 9b light amount memory 10 correction amount calculation unit 11 signal correction unit 12 image reconstruction processing unit 15 signal processing unit 16 optical attenuation correction unit

Claims (14)

Light a detection signal obtained by detecting an acoustic wave generated by irradiating the object, multiple image reconstruction data inside the subject rather based on the detection signal corresponding to the light irradiation An image reconstruction data acquisition unit that acquires
The light intensity of the irradiation light for each light irradiation applied to the subject is acquired, and the light intensity distribution inside the subject is acquired based on the in- plane intensity distribution on the irradiation surface of the light stored in advance , and the subject processor, comprising a correction processing unit for correcting said image reconstruction data based on the light intensity distribution of the inside. The correction processing unit acquires the light intensity distribution inside the subject based on the attenuation of the light with which the subject is irradiated in the depth direction of the subject. The processing device described. The image reconstruction data acquisition unit further includes an A / D converter that converts the detection signal that is an analog signal into a digital signal, and the image reconstruction data acquisition unit acquires the image reconstruction data based on the digital signal. The processing device according to claim 1 or 2 . The image reconstruction data acquisition unit acquires the image reconstruction data by converting the detection signal into an initial sound pressure distribution or a light energy absorption density distribution inside the subject. processing apparatus according to any one of 3. A processing device for acquiring information inside a subject as voxel data,
A signal acquisition unit that acquires a signal corresponding to a plurality of times of light irradiation, which is obtained by receiving an acoustic wave generated by irradiation of light on a subject,
A sensor unit for acquiring information about the light amount variation of the light irradiated to the subject multiple times,
A memory unit that stores intensity distribution information of irradiation light that is irradiated to the subject at one time, and
Using the signal acquired by the signal acquisition unit, the information regarding the light amount variation acquired by the sensor unit, and the intensity distribution information stored in advance in the memory unit, the subject is irradiated multiple times. A processing device, comprising: a correction processing unit that performs a correction process for reducing the influence of a variation in the light amount for each irradiation of the irradiation light on voxel data corresponding to the information inside the subject. The processing apparatus according to claim 5, wherein the correction processing unit performs correction in consideration of an influence of light attenuation in the depth direction of the subject, which is applied to the light with which the subject is irradiated. 7. The processing device according to claim 5, wherein the correction processing unit performs the correction processing on an analog signal before converting the signal into a digital signal, using information about the light amount variation. The processing device according to claim 5, wherein the correction processing unit performs a process of correcting the digital signal by using the information about the light amount variation after converting the signal into a digital signal. The correction processing unit corrects voxel data obtained by performing image reconstruction processing after converting the signal into a digital signal, using the information related to the light amount variation. The processing device according to 5 or 6. A processing method for acquiring information inside a subject as voxel data,
A step of performing light irradiation in which an acoustic wave is generated from the object by irradiating the object with light a plurality of times, and acquiring a signal obtained by receiving the acoustic wave generated by the light irradiation,
A step of acquiring information regarding a light amount variation of light irradiated to the subject a plurality of times; and
Using the signal, the information about the light amount variation, and the intensity distribution information in the irradiation plane of the irradiation light that is previously irradiated to the object that is previously acquired, the irradiation light that is irradiated to the object multiple times. A processing method comprising a step of performing a correction process for reducing an influence of a variation in light amount for each irradiation on voxel data corresponding to the information inside the subject. 11. The process according to claim 10, wherein the step of performing the correction processing is a step of performing a correction in consideration of an influence of light attenuation in the depth direction of the subject with respect to the light emitted to the subject. Method. The processing method according to claim 10 or 11, wherein in the step of performing the correction process, the correction process is performed on the analog signal before the signal is converted into a digital signal, using information about the light amount variation. 12. The process according to claim 10, wherein the step of performing the correction process includes a process of correcting the digital signal by using the information regarding the light amount variation after converting the signal into a digital signal. Method. The step of performing the correction processing is characterized in that the voxel data obtained by performing the image reconstruction processing after converting the signal into a digital signal is corrected using the information relating to the light amount variation. The processing method according to claim 10.

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