JP2017094169A - Subject information acquisition device and subject information acquisition method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a subject information acquisition device and a subject information acquisition method which can accurately acquire an optical characteristic value in photoacoustic imaging.SOLUTION: A subject information acquisition device has signal processing means 40 comprising: a setting unit 41 for setting a predetermined sensitivity area corresponding to each of a plurality of acoustic wave detection elements e1, e2, e3 on the basis of sensitivity distributions of the plurality of acoustic wave detection elements; an initial sound pressure acquisition unit 42 for acquiring an initial sound pressure in an area of interest without using a detection signal corresponding to the area of interest, which is acquired by the acoustic wave detection element not including the area of interest in the predetermined sensitivity area; a light volume value acquisition unit 43 for acquiring an integrated light volume value in the area of interest on the basis of the detection signal used by the initial sound pressure acquisition unit; and an optical characteristic value acquisition unit 44 for acquiring an optical characteristic value in the area 33 of interest using the initial sound pressure acquired by the initial sound pressure acquisition unit and the integrated light volume value acquired by the light volume value acquisition unit.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a subject information acquisition apparatus and a subject information acquisition method for acquiring subject information by detecting a photoacoustic wave generated by irradiating a subject with light.

  Research on an optical imaging apparatus that obtains information in a subject by propagating light irradiated on the subject from a light source such as a laser is actively advanced mainly in the medical field. One such optical imaging technique is photoacoustic imaging (PAI). Photoacoustic imaging refers to detecting and detecting photoacoustic waves generated by irradiating a subject (living body) with pulsed light generated from a light source and absorbing and propagating light within the subject. This is a technique for visualizing information related to optical characteristics in a subject by analyzing acoustic waves. Thereby, an optical characteristic value distribution in the subject, in particular, an absorption coefficient distribution, an oxygen saturation distribution, and the like can be obtained.

  In photoacoustic imaging, the initial sound pressure P0 of the photoacoustic wave generated from the region of interest in the subject can be expressed by the following equation.

  Here, Γ is the Gruneisen coefficient, which is the product of the square of the volume expansion coefficient β and the speed of sound c divided by the constant pressure specific heat CP. It is known that Γ takes a substantially constant value when the subject is determined. Μa is an absorption coefficient of the region of interest, and Φ is an integrated light amount value in the region of interest.

  Patent Document 1 describes a technique for detecting a temporal change in the sound pressure P of a photoacoustic wave propagating through a subject with an acoustic wave detector and calculating an initial sound pressure distribution in the subject from the detection result. Has been. According to Patent Document 1, the product of μa and Φ, that is, the light energy absorption density can be obtained by dividing the calculated initial sound pressure by the Gruneisen coefficient Γ. Then, as shown by the equation (1), in order to obtain the absorption coefficient μa from the initial sound pressure P0, it is necessary to divide the light energy absorption density by the light quantity Φ.

JP 2010-88627 A JP 2006-51355 A

  However, in the photoacoustic imaging described in Patent Document 1, it has been desired to obtain optical characteristic values with higher accuracy.

  Therefore, an object of the present invention is to provide a subject information acquisition apparatus and a subject information acquisition method capable of acquiring an optical characteristic value with higher accuracy in photoacoustic imaging.

  In view of the above problems, a subject information acquisition apparatus according to the present invention detects a photoacoustic wave generated by irradiating a subject with light from the light source and outputs a plurality of detection signals. A detector and signal processing means for acquiring optical characteristic values in the region of interest based on the plurality of detection signals. The signal processing means selects a part of the plurality of detection signals and selects a part thereof And the optical characteristic value in the region of interest are acquired using the detection signal of the above and the light amount value in the region of interest corresponding to a part of the detection signals.

  ADVANTAGE OF THE INVENTION According to this invention, the subject information acquisition apparatus and subject information acquisition method which can acquire an optical characteristic value more accurately can be provided.

It is a schematic diagram of the subject information acquiring apparatus according to the first embodiment. It is a flowchart figure of the subject information acquisition method concerning a 1st embodiment. It is a schematic diagram of the subject information acquiring apparatus according to the second embodiment. It is a schematic diagram of the subject information acquiring apparatus according to the second embodiment. It is a schematic diagram of the subject information acquiring apparatus according to the second embodiment. It is a schematic diagram of the subject information acquiring apparatus according to the fourth embodiment. It is a schematic diagram of the subject information acquiring apparatus according to the fourth embodiment. It is a schematic diagram of the subject information acquiring apparatus according to the fourth embodiment. It is a schematic diagram of another subject information acquisition apparatus which concerns on 4th Embodiment. It is a schematic diagram of another subject information acquisition apparatus which concerns on 4th Embodiment. It is a schematic diagram of another subject information acquisition apparatus which concerns on 4th Embodiment.

  In photoacoustic imaging, a detection signal acquired by detecting a photoacoustic wave includes background noise. Therefore, in photoacoustic imaging, it is desirable to acquire the initial sound pressure in the region of interest without using a detection signal with low S / N including background noise. For example, in Patent Document 2, although ultrasound imaging is used, if the angle formed between the region of interest and the acoustic wave detection element is equal to or smaller than a predetermined value (the region of interest is in a predetermined sensitivity region corresponding to the acoustic wave detection element). If not, it is described that the acoustic wave detection element prevents the reception of acoustic waves from the region of interest. By performing such a method, an ultrasonic image is acquired without using a detection signal having a low S / N.

  Therefore, the present inventor applied the technique described in Patent Document 2 to photoacoustic imaging. Specifically, reconstruction was performed by using a detection signal acquired by an acoustic wave detection element that does not include a region of interest in a predetermined sensitivity region by simulation, and an initial sound pressure in the region of interest was acquired. Since the initial sound pressure obtained in this manner is an initial sound pressure reconstructed without using a detection signal having a low S / N, an error due to noise is small. And this inventor calculated | required the absorption coefficient in the region of interest by the method of patent document 1 using this initial sound pressure. However, the absorption coefficient value calculated by the above method is different from the absorption coefficient value set by the simulation.

  Therefore, in view of the above problems, as a result of intensive studies by the inventor, when acquiring the initial sound pressure, the detection signal to be used is selected based on the sensitivity of the acoustic wave detection element. It was found that the cause was that the sensitivity of the acoustic wave detection element was not taken into account when acquiring the.

  Therefore, the present inventor obtains the integrated light amount value based on the sensitivity of the acoustic wave detection element in addition to selecting the detection signal used based on the sensitivity of the acoustic wave detection element when acquiring the absorption coefficient. Thus, it has been found that an absorption coefficient as an optical characteristic value can be obtained with high accuracy.

  Hereinafter, embodiments according to the present invention by simulation will be described.

(First embodiment)
FIG. 1 is a schematic diagram of a subject information acquisition apparatus according to this embodiment. The pulsed light emitted from the light source 10 is guided to the optical system 11 and irradiated onto the subject 30 as the irradiation light 12. The photoacoustic wave 32 generated from the light absorber 31 in the subject 30 is detected by the acoustic wave detector 20 including the acoustic wave detection elements e1, e2, and e3. The plurality of detection signals acquired by the acoustic wave detector 20 are amplified and digitally converted by the signal collector 47 and stored in the memory of the signal processing device 40. Then, the initial sound pressure acquisition module 42 as the initial sound pressure acquisition unit provided in the signal processing device 40 as the signal processing means reconstructs an image using a plurality of detection signals, and thereby interests in the subject 30. The initial sound pressure in the area 33 is acquired. Further, the light quantity value acquisition module 43 as a light quantity value acquisition unit provided in the signal processing device 40 acquires the integrated light quantity value in the region of interest 33. Then, the optical characteristic value acquisition module 44 as an optical characteristic value acquisition unit provided in the signal processing device 40 acquires the optical characteristic value in the region of interest 33 using the initial sound pressure and the light amount value in the region of interest 33. And the acquired optical characteristic value is displayed on the display apparatus 50 as a display means.

  Here, the region of interest refers to a voxel that is the minimum unit of the region reconstructed by the initial sound pressure acquisition module 42. The initial sound pressure acquisition module 42 can acquire the initial sound pressure distribution of the entire subject by setting the region of interest over the entire region of the subject 30. Similarly, the light amount value acquisition module 43 and the optical characteristic value acquisition module 44 can acquire the integrated light amount value distribution and the absorption coefficient distribution of the entire subject by setting the region of interest over the entire region of the subject. it can.

  Here, detection signals corresponding to the region of interest 33 acquired by each of the acoustic wave detection elements e1, e2, and e3 shown in FIG. 1 are Pd1 (rT), Pd2 (rT), and Pd3 (rT). In addition, the conversion efficiency of the photoacoustic wave entering from the front of the acoustic wave detecting element to the detection signal of the photoacoustic wave entering at an angle of θ from the front of the acoustic wave detecting element is A (θ). And When the angles formed by the respective acoustic wave detection elements with respect to the region of interest 33 are θ1, θ2, and θ3, the conversion efficiencies due to the directivities of the respective acoustic wave detection elements are A (θ1), A (θ2), It can be expressed as A (θ3). Further, the light quantity values Φ1 (rT), Φ2 (rT), and Φ3 (rT) in the region of interest 33 corresponding to the detection signals Pd1 (rT), Pd2 (rT), and Pd3 (rT), respectively. Here, in the present embodiment, the region of interest 33 is set at the position rT of the light absorber 31.

  Here, the distance from the acoustic wave detection element to the region of interest 33 is r, the propagation speed of the photoacoustic wave in the subject is c, and the time when the subject 30 is irradiated with the irradiation light 12 is t = 0. In this case, the detection signal corresponding to the region of interest indicates the detection signal acquired by the acoustic wave detection element at the time t = r / c. The light amount value in the region of interest 33 corresponding to the detection signal corresponding to the region of interest refers to the light amount value in the region of interest 33 of the irradiation light 12 irradiated at the time t = 0.

(Example of simulation without using some detection signals)
Hereinafter, an example of a simulation for acquiring an absorption coefficient from an initial sound pressure acquired without using some detection signals based on the sensitivity of an acoustic wave detection element will be described with reference to FIG. In this simulation, the absorption coefficient of the light absorber 31 was set to μa = 0.088 / mm.

  First, the initial sound pressure acquisition module 42 detects detection signals Pd1 (rT), Pd2 (rT), Pd3 (rT) and conversion efficiencies A (θ1), A (θ2), A ( θ3) is used to obtain the initial sound pressure P0 (rT) in the region of interest 33.

  Here, the detection signal obtained by the simulation and the conversion efficiency set by the simulation are as follows.

Pd1 (rT) = 132Pa
Pd2 (rT) = 231 Pa
Pd3 (rT) = 198Pa
A (θ1) = 0.4
A (θ2) = 0.7
A (θ3) = 0.6
Then, using these parameters, the initial sound pressure calculated from Equation (2) is P0 (rT) = 990.

  In FIG. 1, a region (predetermined sensitivity region) where the conversion efficiency of the acoustic wave detecting element is larger than a predetermined value is indicated by a dotted triangular region. Here, the conversion efficiency A (θ) = 0.5 is set as a predetermined value.

  Here, in the present embodiment, the region of interest 33 is not included in the triangular region (predetermined sensitivity region) corresponding to the acoustic wave detection element e1. Therefore, the initial sound pressure acquisition module 42 does not use the detection signal Pd1 (rT) corresponding to the region of interest 33 acquired by the acoustic wave detection element e1, and the initial sound pressure P0 in the region of interest 33 expressed by the equation (3). '(RT) is acquired.

  Then, using the above-described parameters, the initial sound pressure in the region of interest 33 calculated from Expression (3) is P0 ′ (rT) = 660.

  Next, the light amount value acquisition module 43 acquires the integrated light amount value in the subject using the light propagation Monte Carlo method, the transport equation, the light diffusion equation, or the like from the background optical coefficient of the subject.

  For example, the light quantity value acquisition module 43 includes the light quantity values Φ1 (rT), Φ2 (rT), and Φ3 (rT) in the region of interest 33 corresponding to the detection signals Pd1 (rT), Pd2 (rT), and Pd3 (rT). Is calculated.

  And the light quantity value acquisition module 43 acquires integrated light quantity value (PHI) (rT) in the region of interest 33 shown by Formula (4) using these.

  Here, the light quantity value in the region of interest obtained by the simulation was as follows.

Φ1 (rT) = 3750 mJ / m2
Φ2 (rT) = 3750 mJ / m2
Φ3 (rT) = 3750 mJ / m2
Then, using these parameters, when the integrated light quantity value in the region of interest is calculated from Equation (4), Φ (rT) = 112250 mJ / m 2.

  Next, the optical characteristic value acquisition module 44 obtains the initial sound pressure P0 ′ (rT) in the region of interest 33 shown in Expression (3) and the integrated light amount value Φ (rT) in the region of interest 33 shown in Expression (4). The absorption coefficient μa (rT) in the region of interest 33 shown in Expression (5) is acquired.

  Here, the Gruneisen coefficient Γ = 1.

  Here, the absorption coefficient in the region of interest 33 set at the position rT of the light absorber, which is calculated from the equation (5) using the parameters described above, is μa = 0.059 / mm. On the other hand, the absorption coefficient of the light absorber 31 set in the simulation is μa = 0.088 / mm. From this, it can be seen that the absorption coefficient obtained from the equation (5) is smaller than the set value. That is, when acquiring an absorption coefficient using the initial sound pressure acquired by the said method, the further device is required for acquisition of an integrated light quantity value.

(Example of simulation without using some detection signals and some light intensity values)
Therefore, the subject information acquisition method according to the present embodiment found by the present inventor will be described below with reference to the flowchart of FIG. The following numbers correspond to the process numbers shown in FIG.

  (S100: a step of setting a predetermined sensitivity region based on the sensitivity distribution of the acoustic wave detection elements) In this step, each of the plurality of acoustic wave detection elements is handled based on the sensitivity distribution of the plurality of acoustic wave detection elements. A predetermined sensitivity area is set. A table of predetermined sensitivity regions corresponding to each acoustic wave detection element is stored in the memory of the signal processing device 40.

  Here, the setting module 41 as a setting unit provided in the signal processing device 40 may set a region where the sensitivity of the acoustic wave detection element is larger than a predetermined value as the predetermined sensitivity region. The predetermined value may be automatically set by the setting module 41 based on the system noise. The predetermined value may be displayed on the display device 50 as a sensitivity of the acoustic wave detection element as a histogram, and the operator may select the predetermined value based on the histogram. At this time, the predetermined value is preferably selected in consideration of system noise.

  Here, the sensitivity of the acoustic wave detection element is determined by, for example, the conversion efficiency of the acoustic wave detection element, the attenuation rate indicating attenuation due to diffusion or scattering of the photoacoustic wave from the region of interest to the acoustic wave detection element, and the like. . The conversion efficiency is determined by the angle at which the photoacoustic wave is incident on the acoustic wave detection element. The attenuation rate is determined by the distance between the region of interest and the acoustic wave detection element.

  For example, in the case of the simulation example shown above, the setting module 41 sets the conversion efficiency A (θ) = 0.5 as a predetermined value. For each of the acoustic wave detection elements e1, e2, and e3, a region where the conversion efficiency A (θ) is greater than 0.5 is indicated by a triangular region. As a result, the region of interest 33 was not included in the region (predetermined sensitivity region) in which the conversion efficiency A (θ) of the acoustic wave detection element e1 is greater than 0.5.

  In addition, a predetermined sensitivity region can be set based on an arbitrary region selected from the sensitivity distribution image of the acoustic wave detection element.

  For example, first, the image data of the sensitivity distribution of the acoustic wave detection element stored in the memory of the signal processing device 40 is displayed on the display device 50. Then, the worker selects an arbitrary region from the displayed sensitivity distribution image using the PC input device. Then, the setting module 41 can set the selected arbitrary region as a predetermined sensitivity region. At this time, for example, while displaying an image of the sensitivity distribution, an arbitrary region can be selected by connecting from the start point to the end point by the recognition by the mouse or the recognition method by the sensor on the touch panel.

  The setting module 41 may be set as a predetermined sensitivity region based on the sensitivity distribution of the selected arbitrary region. For example, a predetermined sensitivity region can be set with the smallest sensitivity as a reference.

  Further, a predetermined sensitivity region may be set individually for each acoustic wave detection element, or a predetermined sensitivity region is set for one acoustic wave detection element, and the same sensitivity region as the predetermined sensitivity region is set. May be set for other acoustic wave detection elements.

(S200: A step of acquiring the initial sound pressure in the region of interest without using the detection signal acquired by the acoustic wave detection element whose region of interest is not included in the predetermined sensitivity region)
In this step, for the acoustic wave detection element in which the region of interest is not included in the predetermined sensitivity region set in S100, the detection signal corresponding to the region of interest acquired by the acoustic wave detection element is not used, and the initial value in the region of interest. Get sound pressure. Then, the initial sound pressure data is stored in the memory of the signal processing device 40.

  For example, in the case of the simulation example shown above, the region of interest 33 is not included in the predetermined sensitivity region corresponding to the acoustic wave detection element e1. Therefore, the initial sound pressure acquisition module 42 uses the detection signal Pd1 (rT) corresponding to the region of interest acquired by the acoustic wave detection element e1 among the detection signals Pd1 (rT), Pd2 (rT), and Pd3 (rT). Without performing the image reconstruction, the initial sound pressure P0 ′ (rT) represented by the equation (4) is acquired.

  At this time, the image reconstruction algorithm performed by the initial sound pressure acquisition module 42 includes, for example, back projection in the time domain or Fourier domain normally used in the tomography technique.

  In the present invention, if a predetermined sensitivity region is included in a part of the region of interest, it can be assumed that the region of interest is included in the predetermined sensitivity region.

  In the present invention, not using a detection signal is a concept including not using a detection signal at all and acquiring substantially no detection signal when acquiring an initial sound pressure.

(S300: Step of acquiring the integrated light amount value in the region of interest without using the light amount value corresponding to the detection signal not used when acquiring the initial sound pressure)
In this step, the integrated light amount value in the region of interest is acquired without using the light amount value in the region of interest corresponding to the detection signal not used in S200. Then, the integrated light quantity value data is stored in the memory of the signal processing device 40.

  For example, the light quantity value acquisition module 43 in the region of interest corresponding to the detection signal Pd1 (rT) that is not used by the initial sound pressure acquisition module 42 among the light quantity values Φ1 (rT), Φ2 (rT), and Φ3 (rT). Without using the light quantity value Φ1 (rT), the integrated light quantity value Φ ′ (rT) in the region of interest represented by Expression (6) is acquired.

  That is, the light amount acquisition module 43 acquires the integrated light amount value in the region of interest using the light amount value in the region of interest corresponding to the detection signal used when the initial sound pressure acquisition module 42 calculates the initial sound pressure. ing.

  Here, the integrated light amount value in the region of interest 33 obtained from Expression (6) using the parameters described above is Φ ′ (rT) = 7500 mJ / m 2.

  In the present invention, not using a light amount value is a concept including not using a light amount value at all and acquiring substantially no light amount value when acquiring an integrated light amount value.

  In this embodiment, since the irradiation condition of the irradiation light 12 is constant, the amount of light irradiated to the region of interest 33 is constant. Therefore, the light quantity values corresponding to the plurality of detection signals acquired by the plurality of acoustic wave detection elements are also constant. In such a case, the light amount acquisition module 43 calculates a value obtained by multiplying the number of detection signals used when the initial sound pressure acquisition module 42 acquires the initial sound pressure by the amount of light reaching the region of interest 33. You may acquire as an integrated light quantity value in 33. In the present invention, the integrated light quantity value acquired in this way is also handled as an integrated light quantity value acquired without using the light quantity value.

(S400: Step of obtaining an optical characteristic value in the region of interest using the initial sound pressure and the integrated light amount value in the region of interest)
In this step, an absorption coefficient as an optical characteristic value in the region of interest is acquired using the initial sound pressure in the region of interest acquired in S200 and the integrated light amount value in the region of interest acquired in S300.

  For example, in the case of the simulation example shown above, the optical characteristic value acquisition module 44 uses the initial sound pressure P0 ′ (rT) shown in Expression (3) and the integrated light amount value Φ ′ (rT) shown in Expression (6). And are applied to the equation (1). Then, the absorption coefficient μa (rT) in the region of interest 33 represented by Expression (7) is acquired. Here, the Gruneisen coefficient Γ = 1.

  For example, the absorption coefficient in the region of interest 33 obtained from Expression (7) using the parameters described above is μa = 0.088 / mm. On the other hand, the absorption coefficient in the region of interest 33 obtained from the equation (5) was μa = 0.059 / mm. The absorption coefficient of the light absorber 31 set in the simulation is μa = 0.088 / mm. That is, according to Equation (7), the absorption coefficient can be obtained with higher accuracy than Equation (5).

  As described above, for an acoustic wave detection element that is not included in the region of interest in the predetermined sensitivity region, the detection signal corresponding to the region of interest acquired by the acoustic wave detection element and the light amount value in the region of interest corresponding to the detection signal By not using the above, it is possible to obtain an absorption coefficient having a high quantitative property with less error due to noise.

  In addition, you may acquire the absorption coefficient for every wavelength by performing the above process in several wavelengths. Then, using these absorption coefficients, oxygen saturation as an optical characteristic value may be acquired.

  Moreover, you may make the signal processing apparatus 40 as a computer perform the program containing the above process.

(Second Embodiment)
3A to 3C are schematic views of the subject information acquiring apparatus according to the present embodiment.

  The subject information acquisition apparatus according to the present embodiment includes an acoustic wave detector 20 including one acoustic wave detection element. Further, a detector scanning mechanism 21 for relatively moving the subject 30 and the acoustic wave detector 20 is provided. In the present embodiment, the detector scanning mechanism 21 is capable of detecting photoacoustic waves at a plurality of positions by scanning the acoustic wave detector 20 having one acoustic wave detection element in the right direction on the paper surface. Here, the acoustic wave detection elements at the respective positions shown in FIGS. 3A, 3B, and 3C are denoted by e1, e2, and e3. A region indicated by a triangle indicates a predetermined sensitivity region corresponding to the acoustic wave detection element.

  In the present invention, the plurality of acoustic wave detection elements means that the acoustic wave detection elements can detect photoacoustic waves at a plurality of positions. That is, as in the present embodiment, an acoustic wave detection element that can detect photoacoustic waves at a plurality of positions by scanning the acoustic wave detector 20 is also a plurality of acoustic wave detection elements.

  In addition, the subject information acquisition apparatus according to the present embodiment is provided with an optical scanning mechanism 13 that scans the optical system 11 in order to scan the irradiation light 12. In this embodiment, the acoustic wave detector 20 and the irradiation light 12 are scanned synchronously. In this way, by scanning the acoustic wave detector 20 and the irradiation light 12 in synchronization, the irradiation light 12 is always irradiated to a predetermined sensitivity region (triangular region) corresponding to the acoustic wave detection element. A detection signal with a high S / N can always be obtained.

  Also in the subject information acquiring apparatus according to the present embodiment, the region of interest 33 is not included in the predetermined sensitivity region corresponding to the acoustic wave detection element e1 as in the first embodiment. Therefore, the initial sound pressure acquisition module 42 acquires the initial sound pressure in the region of interest 33 without using the detection signal corresponding to the region of interest 33 acquired by the acoustic wave detection element e1. Then, the light amount value acquisition module 43 acquires the integrated light amount value in the region of interest 33 without using the light amount value in the region of interest 33 corresponding to the detection signal not used when acquiring the initial sound pressure. Then, the optical characteristic value acquisition module 44 acquires the absorption coefficient in the region of interest 33 represented by Expression (7) using the initial sound pressure and the integrated light quantity value. By acquiring the absorption coefficient in this way, the absorption coefficient can be acquired with high accuracy also in the present embodiment.

(Third embodiment)
In the first embodiment and the second embodiment, for an acoustic wave detection element in which the region of interest is not included in the predetermined sensitivity region, a detection signal corresponding to the region of interest acquired by the acoustic wave detection element, and the The value in the region of interest corresponding to the detection signal is a concept that includes completely the same value and a value that is substantially the same when acquiring the absorption coefficient.

  Hereinafter, a subject information acquisition method according to the present embodiment will be described using the subject information acquisition apparatus shown in FIG.

  In the present embodiment, the initial sound pressure acquisition module 42 applies the first reduction coefficient to the detection signal corresponding to the region of interest 33 acquired by the acoustic wave detection element e1 that does not include the region of interest 33 in the predetermined sensitivity region. Multiply. The initial sound pressure acquisition module 42 acquires the initial sound pressure in the region of interest 33 using the detection signal multiplied by the first reduction coefficient.

  As described above, for an acoustic wave detection element that does not include the region of interest in the predetermined sensitivity region, the detection signal corresponding to the region of interest acquired by the acoustic wave detection element is multiplied by the first reduction coefficient to obtain S / The initial sound pressure can be acquired by reducing the detection signal having a low N. Therefore, it is possible to acquire an initial sound pressure with little error due to noise.

  Next, the light quantity value acquisition module 43 multiplies the light quantity value in the region of interest 33 corresponding to the detection signal multiplied by the first reduction coefficient by the second reduction coefficient. And the light quantity value acquisition module 43 acquires the integrated light quantity value in the region of interest 33 using the light quantity value multiplied by the second reduction coefficient.

  Then, the optical characteristic value acquisition module 44 acquires an absorption coefficient in the region of interest 33 using the initial sound pressure acquired by the initial sound pressure acquisition module 42 and the integrated light amount value acquired by the light amount value acquisition module 43.

  In this way, in addition to multiplying the detection signal by the first reduction coefficient, the light absorption value can also be obtained with high accuracy by multiplying the light amount value corresponding to the detection signal by the second reduction coefficient.

  The first reduction coefficient and the second reduction coefficient are values smaller than 1. Further, another reduction coefficient may be set depending on the region of interest. The first reduction coefficient and the second reduction coefficient are preferably the same value. Here, the same value is a concept that includes a completely same value and a value that is substantially the same when acquiring the absorption coefficient.

(Fourth embodiment)
The present invention is also applicable to the subject information acquisition apparatus shown in FIGS. 4A to 4C and the subject information acquisition apparatus shown in FIGS. 5A to 5C. 4A to 4C, the detector scanning mechanism 21 rotates and scans the acoustic wave detector 20 around the subject 30 so that photoacoustic waves can be detected at a plurality of positions. Further, in order to achieve acoustic impedance matching between the subject 30 and the acoustic wave detector 20, the subject 30 is immersed in water 80 filled in a water tank 81. Further, a subject scanning mechanism 34 that scans the subject 30 is provided. By adopting such a configuration, it is possible to measure even at a site where the shape cannot be defined by a holding plate or the like. In addition, since the detection elements can be installed in many directions with respect to the subject, it is possible to acquire data with a large amount of information.

  In the subject information acquisition apparatus shown in FIGS. 4A to 4C, the subject scanning mechanism 34 scans the subject in the downward direction on the paper from the state of FIG. Then, when the detector scanning mechanism 21 scans the acoustic wave detector 20 from the state of FIG. 4B, the state of FIG. 4C is obtained. Here, let the acoustic wave detection elements in the respective states of FIGS. 4A, 4B, and 4C be e1, e2, and e3. Moreover, the triangular area | region shown with the dotted line shows the predetermined | prescribed sensitivity area | region corresponding to an acoustic wave detection element.

  5A to 5C is provided with the acoustic wave detector 20 and the optical system 11 housed in one housing 70. The housing 70 also includes a handheld mechanism 71 that allows the operator to grip the handheld mechanism 71 and scan the housing 70. By scanning the housing 70 in this manner, the acoustic wave detection element can detect photoacoustic waves at a plurality of positions. 5A to 5C, the operator grasps the handheld mechanism 71 and scans the housing 70 in the right direction on the paper surface, so that the acoustic wave detecting element detects the photoacoustic wave. Here, let the acoustic wave detection elements in the respective states of FIGS. 5A, 5B, and 5C be e1, e2, and e3. Moreover, the triangular area | region shown with the dotted line shows the predetermined | prescribed sensitivity area | region corresponding to an acoustic wave detection element.

  However, unlike the other embodiments, this embodiment does not mechanically scan the acoustic wave detector 20, but the operator grips the handheld mechanism 71 and freely scans the housing 70. Therefore, the positional relationship between the acoustic wave detector 20 and the region of interest 33 when the photoacoustic wave 32 is detected cannot be grasped. However, in order to extract the detection signal corresponding to the region of interest from the detection signal acquired by the acoustic wave detector 20, it is necessary to grasp the positional relationship between the acoustic wave detector 20 and the region of interest 33. Therefore, in the present embodiment, it is preferable that the housing 70 includes the position detector 72 for detecting the position of the housing 70, that is, the position of the acoustic wave detector 20 and the optical system 11 housed in the housing 70. .

  4A to 4C and FIGS. 5A to 5C, the region of interest 33 is not included in the predetermined sensitivity region corresponding to the acoustic wave detection element e1. Therefore, the signal processing device 40 uses the subject information acquisition method described in the first and second embodiments and the subject information acquisition method described in the third embodiment to calculate the absorption coefficient of the region of interest 33. Can be acquired. By acquiring the absorption coefficient in this way, the absorption coefficient can be acquired with high accuracy also in the present embodiment.

  The main configuration will be described below.

(Light source 10)
The light source 10 includes a light source capable of generating pulsed light of 5 to 50 nanoseconds. Although a laser capable of obtaining a large output is preferable as the light source, 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. Ideally, an Nd: YAG-excited Ti: Sa laser or an alexandrite laser that has a strong output and can continuously change the wavelength is preferable. A plurality of single wavelength lasers having different wavelengths may be held.

(Optical system 11)
The pulsed light emitted from the light source 10 is typically guided to the subject while being processed into a desired light distribution shape by an optical component such as a lens or a mirror, but propagates using an optical waveguide such as an optical fiber. It is also possible to make it. The optical system 11 is, for example, a mirror that reflects light, a lens that collects or enlarges light, or changes its shape, or a diffusion plate that diffuses light. As such an optical component, any optical component may be used as long as pulse light emitted from a light source is irradiated in a desired shape on the subject. Note that it is preferable to spread light over a certain area rather than condensing with a lens from the viewpoint of extending the safety to the subject and the diagnostic area. Note that an optical scanning mechanism may be provided in the optical system 11 in order to scan the irradiation light.

(Acoustic wave detector 20)
The acoustic wave detector 20, which is a detector that detects photoacoustic waves generated on the subject surface and inside the subject by light, detects the acoustic waves and converts them into electrical signals that are analog signals. Hereinafter, it may be simply referred to as a probe or a transducer. 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, or a transducer using a change in capacitance.

  The acoustic wave detector 20 includes a plurality of acoustic wave detection elements. By arranging the plurality of acoustic wave detection elements in a one-dimensional or two-dimensional array in an array, photoacoustic waves can be detected at a plurality of positions. By using such a multidimensional array element, acoustic waves can be detected at a plurality of positions simultaneously, so that the detection time can be shortened and the influence of vibration of the subject can be reduced.

  Note that the acoustic wave detector 20 may be configured to be mechanically scanable by the detector scanning mechanism 21 in order to enable detection of photoacoustic waves at a plurality of positions. In addition, a handheld mechanism that can be gripped by an operator and freely scanned by the acoustic wave detector 20 can be provided.

(Signal collector 47)
It is preferable to have a signal collector 47 that amplifies the electrical signal obtained from the acoustic wave detector 20 and converts the electrical signal from an analog signal to a digital signal. The signal collector 47 is typically composed of an amplifier, an A / D converter, an FPGA (Field Programmable Gate Array) chip, and the like. When there are a plurality of detection signals obtained from the acoustic wave detector, it is desirable that a plurality of signals can be processed simultaneously. Thereby, the time until the image is formed can be shortened. In the present specification, the “detection signal” is a concept including an analog signal output from the acoustic wave detector 20 and a digital signal AD-converted by the signal collector 47.

(Signal processing device 40)
The signal processing device 40 acquires an optical characteristic value inside the subject by performing image reconstruction or the like. As the signal processing device 40, a workstation or the like is typically used, and image reconstruction processing or the like is performed by software programmed in advance. For example, software used in the workstation includes a setting module 41, an initial sound pressure acquisition module 42, a light amount acquisition module 43, an optical characteristic value acquisition module 44, and the like.

  Each module may be provided as separate hardware. In this case, the respective hardware may be collectively used as the signal processing device 40.

  In some cases, the signal collector 47 and the signal processing device 40 may be integrated. In this case, the optical characteristic value of the subject can be generated not by software processing as performed at the workstation but by hardware processing.

  The present invention is not limited to the above-described embodiment, and various changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, in order to make the scope of the present invention public, the following claims are attached.

DESCRIPTION OF SYMBOLS 20 Acoustic wave detector 30 Subject 40 Signal processing apparatus 41 Setting module 42 Initial sound pressure acquisition module 43 Light quantity value acquisition module 44 Optical characteristic value acquisition module

A processing apparatus according to the present invention is a processing apparatus that acquires optical characteristic values in a region of interest based on a plurality of detection signals obtained by detecting photoacoustic waves generated by irradiating a subject with light. A correction signal is acquired by correcting the plurality of detection signals based on a first weighting factor, and a light amount value in the region of interest corresponding to the plurality of detection signals is corrected based on a second weighting factor. Thus, a corrected light amount value in the region of interest corresponding to the plurality of detection signals is acquired, and the optical characteristic value is acquired based on the correction signal and the corrected light amount value.

Claims (19)

A light source;
An acoustic wave detector that detects a photoacoustic wave generated by irradiating the subject with light from the light source and outputs a plurality of detection signals;
Signal processing means for obtaining an optical characteristic value in a region of interest based on the plurality of detection signals,
The signal processing means includes
Selecting a detection signal that is part of the plurality of detection signals;
The subject information acquisition apparatus, wherein the optical characteristic value in the region of interest is acquired using the partial detection signal and a light amount value in the region of interest corresponding to the partial detection signal. The object information acquiring apparatus according to claim 1, wherein the acoustic wave detector detects photoacoustic waves at a plurality of different positions and outputs the plurality of detection signals. The light source emits light at a plurality of different timings,
The object information acquisition according to claim 1, wherein the acoustic wave detector detects a photoacoustic wave generated by the light irradiation at the plurality of timings and outputs the plurality of detection signals. apparatus. A detector scanning mechanism for moving the acoustic wave detector relative to the subject;
The object information acquiring apparatus according to claim 3, wherein the detector scanning mechanism moves the acoustic wave detector so that positions of the acoustic wave detector are different at the plurality of timings. An optical system for guiding light from the light source to the subject;
An optical system scanning mechanism that moves the optical system relative to the subject, and the optical system scanning mechanism is configured so that the positions of the optical systems are different at the plurality of timings. 5. The subject information acquiring apparatus according to claim 3, wherein the system is moved. The object information acquiring apparatus according to claim 1, wherein the acoustic wave detector includes a plurality of acoustic wave detection elements. The signal processing means includes
Integrating the light amount values in the region of interest corresponding to the part of the detection signals to obtain the integrated light amount value in the region of interest;
7. The object according to claim 1, wherein the optical characteristic value in the region of interest is acquired using the partial detection signal and an integrated light amount value in the region of interest. Sample information acquisition device. The signal processing means includes
Using the partial detection signal to obtain an initial sound pressure in the region of interest;
The object information acquiring apparatus according to claim 7, wherein the optical characteristic value in the region of interest is acquired using the initial sound pressure and the integrated light amount value in the region of interest. 9. The signal acquisition unit according to claim 1, wherein the signal acquisition unit selects the part of the detection signals from the plurality of detection signals based on a sensitivity distribution of the acoustic wave detector. Subject information acquisition apparatus. The signal acquisition means includes
At each of the plurality of timings, a detection signal detected by the acoustic wave detector when the sensitivity of the acoustic wave detector in the region of interest is equal to or higher than a predetermined value is selected, and the selected detection signal is The object information acquiring apparatus according to claim 3, wherein the object information acquiring apparatus is a detection signal. The signal acquisition means includes
In each of the plurality of acoustic wave detection elements, a detection signal detected by the acoustic wave detection element when the sensitivity of the acoustic wave detection element in the region of interest is a predetermined value or more is selected, and the selected detection signal is The object information acquisition apparatus according to claim 6, wherein the detection signals are the partial detection signals. The sensitivity of the acoustic wave detector is based on at least one of the conversion efficiency of the acoustic wave detector from a photoacoustic wave to a detection signal and the attenuation of the photoacoustic wave from the region of interest to the acoustic wave detector. The object information acquiring apparatus according to claim 9, wherein the object information acquiring apparatus is determined as follows. The object information acquiring apparatus according to any one of claims 1 to 12, wherein the signal processing unit acquires an absorption coefficient in the region of interest as the optical characteristic value in the region of interest. The signal processing means includes
Correcting the part of the detection signals based on a weighting factor to obtain a correction signal;
Correcting the light amount value in the region of interest corresponding to the partial detection signal based on the weighting factor to obtain a corrected light amount value in the region of interest corresponding to the partial detection signal;
The object information acquisition apparatus according to claim 1, wherein the optical characteristic value in the region of interest is acquired using the correction signal and the correction light amount value in the region of interest. . A light source that emits light at a plurality of different timings;
An acoustic wave detector that detects a photoacoustic wave generated by irradiating the subject with light at the plurality of timings and outputs a plurality of detection signals; and
Signal processing means for obtaining an optical characteristic value in a region of interest based on the plurality of detection signals,
The signal processing means includes
Selecting at least some detection signals of the plurality of detection signals;
Subject information acquisition characterized in that the optical characteristic value in the region of interest is acquired using the at least part of the detection signal and a light amount value in the region of interest corresponding to the at least part of the detection signal. apparatus. A detector scanning mechanism for moving the acoustic wave detector relative to the subject;
The object information acquiring apparatus according to claim 15, wherein the detector scanning mechanism moves the acoustic wave detector so that the positions of the acoustic wave detectors are different at the plurality of timings. An optical system for guiding light from the light source to the subject;
An optical system scanning mechanism that moves the optical system relative to the subject, and the optical system scanning mechanism is configured so that the positions of the optical systems are different at the plurality of timings. The subject information acquiring apparatus according to claim 15 or 16, wherein the system is moved. A signal processing method for obtaining optical characteristic values in a region of interest based on a plurality of detection signals obtained by detecting photoacoustic waves generated by irradiating a subject with light,
Selecting a detection signal of a part of the plurality of detection signals;
Obtaining the optical characteristic value in the region of interest using the partial detection signal and a light amount value in the region of interest corresponding to the partial detection signal. Processing method.   A program causing a computer to execute the signal processing method according to claim 18.

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