JP2019136520A - Processing device, photoacoustic image display method, and program - Google Patents

Abstract

To provide a subject information obtaining device for obtaining a photoacoustic imaging image having high contrast between a region of interest and a region other than the region of interest in photoacoustic imaging, and to provide a signal processing device.SOLUTION: The subject information obtaining device includes signal processing means which obtains weighted optical characteristic value distribution about a subject on the basis of feature information about the subject obtained by elastography measurement or B-mode image measurement using an elastic wave signal obtained by transmission and reception of elastic waves to and from the subject.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a subject information acquisition apparatus and a subject information acquisition method for acquiring an optical characteristic value using a photoacoustic wave generated by irradiating a subject with light.

  Research on an optical imaging apparatus that irradiates light to a living body from a light source such as a laser and images in vivo information obtained based on incident light has been advanced in the medical field. As one of the optical imaging techniques, there is Photo Acoustic Imaging (PAI: photoacoustic imaging). In photoacoustic imaging, a living body is irradiated with pulsed light generated from a light source, and photoacoustic waves (typically ultrasonic waves) generated from living tissue that absorbs the energy of pulsed light that has propagated and diffused in the living body are received. The optical characteristic value distribution in the living body is imaged based on the detection signal.

  In other words, photoacoustic imaging uses the difference in the absorption rate of light energy between a test site such as a tumor and other tissues, and when the test site absorbs irradiated light energy and expands instantaneously. The photoacoustic waves (typically ultrasonic waves) generated in the above are received by a probe (also referred to as a transducer or an acoustic wave detector). By analyzing this detection signal, an optical characteristic value distribution can be obtained. Here, the optical characteristic value distribution includes an initial sound pressure distribution, a light absorption energy density distribution, a light absorption coefficient distribution, and the like.

  These pieces of information can also be used for quantitative measurement of specific substances in the subject (for example, the concentration of hemoglobin contained in blood or the oxygen saturation level of blood) by measuring with light of various wavelengths.

  There are various image reconstruction methods for forming an image based on a detection signal from a probe. In general, analyzing an initial sound pressure distribution of a photoacoustic wave based on a detection signal obtained from a probe is called an inverse problem analysis. In photoacoustic imaging, the inverse problem has been shown to have a unique solution by solving the photoacoustic wave equation in an ideal environment. As an example, an analytical solution of Universal Back Projection (hereinafter referred to as UBP) showing the analysis result in time space is as follows.

In this way, in UBP, by performing solid angle correction (correction by the measurement system) and integrating the detection signal p (r ₀ , t) obtained by the probe and the detection signal time-differentiated, An initial sound pressure distribution p ₀ (r) can be obtained (see Non-Patent Document 1).

PHYSICAL REVIEW E 71,016706 (2005) Journal of Medical Ultrasonics Volume 29, Number 3, 119-128, DOI: 10.1007 / BF02481234

  However, the conventional techniques have the following problems.

  Since the solution of the photoacoustic wave equation is solved under ideal conditions, it includes conditions that cannot be actually realized. For example, in the case of the above-described UBP, a solution can be obtained even in an environment where acoustic wave detection elements are arranged on a plane, but an ideal solution can be obtained when the arrangement is arranged without limitation. However, in practice, there is a limit to the number of acoustic wave detection elements arranged, and only information on a region corresponding to the number of acoustic wave detection elements arranged can be acquired. As a result, artifacts were generated in the reconstructed image. When such an artifact occurs at the boundary between the region of interest and the region other than the region of interest in the photoacoustic imaging image, the contrast between the region of interest of the photoacoustic imaging image and the region other than the region of interest is reduced.

  In addition, when a noise image due to system noise or the like is generated at the boundary between the region of interest and the region other than the region of interest in the photoacoustic imaging image, the contrast ratio between the region of interest and the region other than the region of interest decreases. .

  Therefore, the present invention has an object to provide a subject information acquisition apparatus and a subject information acquisition method for acquiring a photoacoustic imaging image having high contrast between a region of interest and a region other than the region of interest in photoacoustic imaging. .

A processing apparatus according to a first aspect of the present invention is a processing apparatus that causes a display means to display a photoacoustic image obtained based on a photoacoustic wave generated by irradiating a subject with light,
Display control means for displaying on the display means an ultrasonic image obtained on the basis of an ultrasonic echo transmitted to the subject, and a region of interest in the ultrasonic image determined based on an operator's instruction. Acquisition means for acquiring information indicating, wherein the display control means corresponds to the region other than the region of interest corresponding to the photoacoustic image corresponding to the region of interest based on the information indicating the region of interest. It is characterized by displaying a higher contrast ratio than photoacoustic images,
Further, a second photoacoustic image display method of the present invention is a photoacoustic image display method obtained based on a photoacoustic wave generated by irradiating a subject with light. An ultrasonic image obtained based on an echo of the transmitted ultrasonic wave is displayed, information indicating a region of interest in the ultrasonic image determined based on an instruction of an operator is obtained, and the region of interest is indicated Based on the information, the photoacoustic image corresponding to the region of interest is displayed with a higher contrast ratio than the photoacoustic image corresponding to a region other than the region of interest.

  According to the present invention, in photoacoustic imaging, it is possible to provide an object information acquisition apparatus and an object location method acquisition method that acquire a photoacoustic imaging image having a high contrast between a region of interest and a region other than the region of interest.

It is a schematic diagram of the subject information acquiring apparatus according to the present embodiment. It is a figure which shows the flow of the subject information acquisition method which concerns on this embodiment. It is a figure which shows the signal processing which the signal processing apparatus which concerns on this embodiment performs. It is a figure which shows the distortion distribution by the initial sound pressure distribution and the elastography measurement which the subject information acquisition apparatus concerning a present Example acquires.

  In order to improve the contrast of a photoacoustic imaging image, the present invention provides a weighted optical characteristic value distribution in a subject based on feature information of the subject obtained from an elastic wave signal obtained by transmitting and receiving elastic waves. get. Here, the elastic wave refers to an elastic wave (typically an ultrasonic wave) transmitted from the probe. A photoacoustic wave refers to an elastic wave (typically an ultrasonic wave) generated from a light absorber by irradiating light. The feature information of the subject is information obtained by transmitting / receiving elastic waves to / from the subject, such as acoustic impedance, strain amount, and elastic modulus.

  The above-described elastic wave signal is acquired by reflecting the transmitted elastic wave from the local region using the high degree of straightness of the elastic wave in the subject. Information can be acquired. Therefore, the feature information of the subject acquired based on the elastic wave signal acquired in this way can also be acquired as local region information. Therefore, the resolution of the feature information image of the subject based on the elastic wave signal is higher than the resolution of the photoacoustic imaging image in which incident light is diffused.

  The feature information of the subject is information indicating characteristic parameters (for example, strain) of an observation target (for example, tumor) that cannot be grasped from the optical characteristic value distribution obtained by photoacoustic imaging.

  For this reason, the region of interest and the region other than the region of interest are weighted by weighting the optical characteristic value distribution in the subject based on the feature information of the subject having high resolution and indicating the characteristic parameter of the observation target as described above. A photoacoustic imaging image with a high contrast can be obtained.

  Hereinafter, the subject information acquisition apparatus according to the present embodiment will be described with reference to FIG. FIG. 1 schematically shows a subject information acquisition apparatus according to this embodiment. The subject information acquisition apparatus shown in FIG. 1 includes a light source 110, an optical system 120, a probe 130, a control device 140, a signal processing device 150 as signal processing means, and a display device 160 as display means.

  The probe 130 according to the present embodiment functions as an elastic wave transmitter that transmits elastic waves to the subject 100 and functions as an elastic wave receiver that receives elastic waves and photoacoustic waves that have propagated through the subject 100. Is provided.

  Each configuration will be described below.

(Subject 100 and light absorber 101)
These do not constitute a part of the subject information acquisition apparatus of the present invention, but will be described below. The subject information acquisition apparatus of the present invention is mainly intended for the diagnosis of human or animal malignant tumors, vascular diseases, etc., and the follow-up of chemical treatment. Accordingly, the subject is assumed to be a living body, specifically, a diagnosis target site such as the breast, neck, abdomen, and transrectum of a human body or an animal.

  Further, the light absorber inside the subject shows a relatively high absorption coefficient inside the subject. For example, if the human body is a measurement target, oxyhemoglobin or deoxyhemoglobin or a blood vessel containing many of them or Malignant tumors containing many new blood vessels are targeted for light absorbers. Other examples include carotid artery plaque.

(Light source 110)
The light source 110 is preferably a pulse light source capable of generating pulsed light on the order of several nanoseconds to several microseconds. Specifically, a pulse width of about 10 nanoseconds is used to efficiently generate photoacoustic waves. 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. As the wavelength of the light source used, it is desirable to use a wavelength at which light propagates to the inside of the subject. Specifically, when the subject is a living body, the thickness is 500 nm or more and 1200 nm or less.

(Optical system 120)
The light emitted from the light source is typically guided to the subject while being processed into a desired light distribution shape by optical components such as lenses and mirrors, but is propagated using an optical waveguide such as an optical fiber. Is also possible. The optical system 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 the light emitted from the light source is irradiated on the subject in a desired shape. Note that it is preferable to spread light over a certain area rather than condensing with a lens from the viewpoint of expanding the safety to the living body and the diagnostic area.

(Probe 130)
The probe 130 detects an acoustic wave and converts it into an electrical signal that is an analog signal. Any detector may be used as long as it can detect an acoustic wave signal, such as a piezoelectric phenomenon, light resonance, change in capacitance, and the like.

  Note that a probe having a function as an elastic wave transmitter and a probe having a function as an elastic wave receiver may be prepared. However, in consideration of signal detection and space saving in the same region, the probe 130 preferably has both a function as an elastic wave transmitter and a function as an elastic wave receiver.

  The probe 130 preferably includes a plurality of acoustic wave detection elements arranged on the array.

(Control device 140)
The subject information acquisition apparatus according to the present embodiment preferably includes a control device that generates a transmission signal having a delay time and an amplitude corresponding to the position of interest and the direction of interest. This transmission signal is converted into an elastic wave by the probe 130, and the elastic wave is transmitted into the subject.

  In addition, it is preferable that the subject information acquisition apparatus of the present embodiment includes a control device 140 that amplifies the electrical signal obtained from the probe 130 and converts the electrical signal from an analog signal to a digital signal.

  In addition, when the probe 130 transmits and receives elastic waves from a plurality of acoustic wave detection elements and acquires a plurality of electrical signals, the control device 140 has a plurality of signals depending on the direction and position where the acoustic waves are transmitted. It is preferable to perform a delay process on the electrical signal.

  The control device 140 typically includes an amplifier, an A / D converter, an FPGA (Field Programmable Gate Array) chip, and the like.

(Signal processing device 150)
As the signal processing device 150, a workstation or the like is typically used, and signal processing such as weighting processing and image reconstruction processing is performed by software programmed in advance. For example, software used in the workstation includes a weighting module 151 that performs weighting processing which is characteristic signal processing of the present invention. Other software includes modules such as an image reconstruction module 152, a feature information acquisition module 153, and a region setting module 154 for setting a region of interest.

  Each module may be provided as separate hardware. Also in this case, the respective modules can be collectively used as the signal processing device 150.

  In photoacoustic imaging, an optical characteristic distribution image in a living body can be formed without image reconstruction by using a focused probe. In such a case, it is not necessary to perform signal processing using an image reconstruction algorithm.

  In some cases, the control device 140 and the signal processing device 150 may be integrated. In this case, the optical characteristic value distribution of the subject can be generated not by software processing such as that performed at a workstation but by hardware processing.

(Display device 160)
The display device 160 is a device that displays the optical characteristic value distribution output from the signal processing device 150. Typically, a liquid crystal display or the like is used. In addition, you may provide separately from the subject information acquisition apparatus of this invention.

  Next, a preferred embodiment of a subject information acquisition method using the subject information acquisition apparatus shown in FIG. 1 will be described.

  The subject information acquisition method according to this embodiment will be described with reference to FIG.

(S100: Step of acquiring elastic wave signal)
In this step, an elastic wave signal is acquired by transmitting / receiving an elastic wave to / from the subject.

  First, in order to perform flow velocity measurement, elastography measurement, B-mode image measurement, etc. for acquiring characteristic information of the subject, an elastic wave 102a is transmitted from the probe 130 to the subject 100. Here, the control device 140 transmits a transmission signal having a delay time and an amplitude generated to each of the acoustic wave detection elements of the probe 130 according to the position of the region of interest, and converts it into an elastic wave 102a.

  Within the subject, the transmitted elastic wave 102a is reflected, and an echo elastic wave 102b is generated. The probe 130 receives the echo elastic wave 102b and outputs a detection signal.

  Then, the control device 140 performs processing such as amplification and A / D conversion on the detection signal, and stores the signal data in a memory inside the control device 140. Here, in the present invention, the elastic wave signal is a concept including both a detection signal output from the probe 130 and a signal processed by the control device 140.

(S200: Step of acquiring feature information of subject based on elastic wave signal)
In this step, the feature information acquisition module 153 acquires the feature information of the subject acquired from the elastic wave signal obtained in S100. Then, the acquired feature information table is stored in the memory inside the signal processing device 150.

  Here, the feature information acquired from the elastic wave signal may be any information as long as the operator can grasp the shape of the object to be observed by photoacoustic imaging. For example, the characteristic information includes acoustic impedance, strain amount, and elastic modulus. In addition, the feature information may be appropriately selected according to the site or substance to be observed by the photoacoustic wave signal.

  For example, when identifying a tumor site (neovascular region) and a normal site, it is preferable to acquire a strain value, an elastic modulus, and the like as feature information from the elastic wave signal acquired in S100. In addition, when acquiring a strain value and an elasticity modulus, as described in the nonpatent literature 2, you may perform the elastography measurement using an elastic wave signal. By the way, typically, a region having a high elastic modulus (hard region) is a region having a high suspicion of malignant tumor, and a region having a low elastic modulus (soft region) is a region having a low suspicion of malignant tumor. The distribution of optical characteristic values calculated from photoacoustic waves is approximately the same as the distribution of hemoglobin, indicating the distribution of tumor regions where blood vessels and blood vessel clusters can be seen. This is an effective means for extracting the location.

  In addition, for example, when determining the boundary of a living tissue, it is preferable to acquire acoustic characteristics such as acoustic impedance as characteristic information from the elastic wave signal acquired in S100. In addition, when acquiring an acoustic characteristic, you may perform the B mode image measurement using an elastic wave signal. By the way, the inside of the cyst, which is a suspected tumor, forms an echoless image. Therefore, it is effective to make such a region an observation target in extracting a tumor.

(S300: Step of setting the region of interest from the feature information of the subject)
In this step, the region setting means sets a region of interest that is a region including the light absorber from the feature information of the subject acquired in S200. Then, the table of the set region of interest is stored in the memory inside the signal processing device 150.

  Here, as a method of setting a region of interest, a method in which the region setting module 154 as a region setting unit provided in the signal processing device 150 sets using an arbitrary numerical range, or a PC input as a region setting unit. There is a method of setting by an operator using a device.

  First, a method in which the region setting module 154 sets a region within an arbitrary numerical value range as a region of interest will be described with reference to FIG.

  FIG. 3A is a diagram when the subject 100 shown in FIG. 1 is viewed from the front. FIG. 3B shows the feature information 310 at the position of the dotted line (a-a ′) shown in FIG. Here, the vertical axis of FIG. 3B indicates the value of the feature information, and the horizontal axis indicates the distance from the probe 130. As shown in FIG. 3B, the value of the feature information in the region where the light absorber 101 exists (the region where the distance from the probe 130 is r to r + R) is higher than the other regions. Yes.

  For example, in this process, first, the region setting module 154 sets a threshold value 311 as shown in FIG. Then, the region setting module 154 sets, as a region of interest, a region in which the feature information 310 is equal to or greater than the threshold value 311 (a region within the numerical range). On the other hand, the region setting module 154 sets regions (regions outside the numerical range) in which the feature information 310 is smaller than the threshold value 311 as regions 313 and 314 other than the region of interest.

  That is, the region setting module 154 sets a region where the feature information acquired in S200 is within an arbitrary numerical range as a region of interest, and sets a region outside the arbitrary numerical range as a region other than the region of interest.

  As described above, when the characteristic information is high in the region where the light absorber 101 exists (for example, when the observation target is a tumor having a high elastic modulus measured by elastography measurement), the threshold value is 311 or more. By setting this region as the region of interest, the region including the light absorber 101 can be set as the region of interest.

  On the other hand, when the value of the characteristic information in the region where the light absorber 101 exists is small (for example, when the observation target is a tumor with a low strain measured by elastography measurement), the threshold value or less is set. It can be within a numerical range.

  As a method for setting the numerical range, the region setting module 154 uses a method for obtaining a threshold value for determining a numerical range in which the degree of separation is maximized by a discriminant analysis method. The range can be set automatically. Further, the threshold value that defines the numerical range may be determined based on the signal strength of the system noise. Alternatively, the operator may arbitrarily specify a numerical range from the histogram shape of the obtained feature information. Further, the numerical range to be specified is not limited to one, and a plurality of numerical ranges may be set.

  Next, a method will be described in which an operator sets an arbitrary region as a region of interest from an image of feature information using an input device of a PC as a region setting unit.

  First, an image of feature information is displayed on a monitor which is the display device 160. Next, the operator arbitrarily sets a region to be highlighted from the displayed image of the feature information as a region of interest. At this time, the region setting method may be to set the region connected 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 as the region of interest while displaying the image of the feature information.

  The region setting means may set an arbitrary region as a region of interest from the set region of interest after setting a region within an arbitrary numerical value range as the region of interest.

(S400: Step of acquiring a photoacoustic wave signal)
In this step, a photoacoustic wave signal is acquired by receiving a photoacoustic wave generated by irradiating the subject with light.

  The subject 100 is irradiated with pulsed light 121 emitted from the light source 110 via the optical system 120. Then, the irradiated pulsed light 121 is absorbed by the light absorber 101, and the light absorber 101 is instantaneously expanded, whereby the photoacoustic wave 103 is generated. Then, the probe 130 receives the photoacoustic wave 103 and outputs a detection signal. The detection signal output from the probe 130 is subjected to processing such as amplification and A / D conversion by the control device 140 and is stored as detection signal data in a memory inside the control device 140. Here, in the present invention, the photoacoustic wave signal is a concept including both the detection signal output from the probe 130 and the signal processed by the control device 140.

(S500: a step of weighting the photoacoustic wave signal based on the feature information and the region of interest)
In this step, the weighting module 151 in the signal processing device 150 weights the photoacoustic wave signal acquired in S400 based on the feature information acquired in S200 and the region of interest set in S300. Then, the weighted photoacoustic wave signal is stored in a memory inside the signal processing device 150.

  Hereinafter, a signal processing method performed by the weighting module 151 will be described with reference to FIG.

  FIG. 3C shows the photoacoustic wave signal 320 before the weighting module 151 performs the weighting process. On the other hand, FIG. 3D shows the photoacoustic wave signal 330 after the weighting module 151 performs the weighting process. Here, the vertical axis of FIGS. 3C and 3D indicates the signal intensity of the photoacoustic wave signal, and the horizontal axis indicates the detection time. Note that since the sound speed of the photoacoustic wave in the subject multiplied by the detection time is the distance from the probe, assuming that the sound speed of the photoacoustic wave in the subject is constant, FIG. The distance from the probe shown in b) and the photoacoustic wave detection time shown in FIGS. 3C and 3D correspond to each other. That is, the distance r in FIG. 3B corresponds to the time t1 in FIGS. 3C and 3D, and the distance r + R in FIG. 3B corresponds to the time t2 in FIGS. 3C and 3D. doing. Also, the photoacoustic wave signal 320 shown in FIG. 3C includes photoacoustic wave signals 321 and 323 that are multiple-reflected on the surface of the probe 130. These signals are the cause of artifacts.

  Therefore, the weighting module 151 is weighted by making the weighting coefficient corresponding to the region of interest 312 larger than the weighting coefficient corresponding to the regions 313 and 314 other than the region of interest among the weighting factors performed on the photoacoustic wave signal 320. A photoacoustic wave signal 330 is acquired. Here, as shown in FIG. 3, the weighting coefficient corresponding to the region of interest 312 is made larger than 1, and the weighting coefficients corresponding to the regions 313 and 314 other than the region of interest are made smaller than 1.

  Note that the weighting module 151 may perform a weighting process that makes the weighting coefficient corresponding to the region of interest smaller than 1 or makes the weighting coefficient corresponding to the region other than the region of interest larger than 1. The weighting module 151 may multiply the signal intensity of the photoacoustic wave signal by a weighting coefficient that reduces the signal intensity of the photoacoustic wave signal corresponding to the area other than the region of interest by a dynamic range.

  When the feature information is high in the region where the light absorber exists (for example, when the observation target is a tumor having a high elastic modulus measured by elastography measurement), the weighting module 151 calculates the value of the feature information. May be used as a weighting coefficient. In addition, when the value of the feature information of the region where the light absorber 101 exists is small (for example, when the observation target is a tumor having a low strain measured by elastography measurement), the reciprocal of the feature information. May be used as a weighting coefficient.

  Further, weighting may be performed using a ratio between feature information and an arbitrary value as a weighting coefficient. For example, the feature information corresponding to the region of interest can be multiplied by N, the feature information corresponding to the region other than the region of interest can be multiplied by M, and the signal intensity of the photoacoustic wave signal corresponding to each region can be multiplied. .

  Further, the same weighting coefficient may be applied to the photoacoustic wave signals corresponding to the entire region of the region of interest 312. Further, the same weighting coefficient may be applied to the photoacoustic wave signals corresponding to all the regions 313 and 314 other than the region of interest. At this time, you may multiply the photoacoustic wave signal of each area | region by the average value of the feature information corresponding to each area | region.

  Further, a value obtained by dividing the average value of the feature information corresponding to the region of interest 312 by the average value of the feature information corresponding to the region other than the region of interest may be multiplied by the photoacoustic wave signal corresponding to the region of interest. Further, the photoacoustic wave signal corresponding to the region other than the region of interest can be multiplied by the value obtained by dividing the average value of the feature information corresponding to the region other than the region of interest by the average value of the feature information corresponding to the region of interest. Such a method is especially suitable for measurement that identifies the observation target by measuring the relative difference in strain value and elastic modulus between the region of interest and the region other than the region of interest, such as elastography measurement. It is particularly effective.

  Thus, in this step, by performing weighting processing, it is possible to relatively reduce the photoacoustic wave signals corresponding to regions other than the region of interest that causes artifacts and noise images.

(S600: Step of acquiring weighted optical characteristic value distribution of subject based on weighted photoacoustic wave signal)
In this step, the image reconstruction module 152 in the signal processing device 150 performs image reconstruction based on the weighted photoacoustic wave signal acquired in S500, thereby weighting the initial sound pressure distribution (optical) of the subject. Acquire characteristic value distribution). Then, the weighted optical characteristic value distribution is stored in a memory inside the signal processing device 150.

  Since the image reconstruction module 152 performs image reconstruction using the weighted photoacoustic wave signal acquired in S500, the optical characteristic value distribution obtained in this step is weighted based on the characteristic information. Distribution. That is, since image reconstruction is performed using a photoacoustic wave signal in which the photoacoustic wave signal corresponding to a region other than the region of interest that causes the artifact or noise image is relatively reduced, the artifact or noise image is A relatively reduced weighted optical property value distribution can be obtained.

  Here, the image reconstruction module 152 can use an image reconstruction algorithm such as back projection in the time domain or Fourier domain that is normally used in tomography technology. Note that if it is possible to have a lot of reconstruction time, an image reconstruction method such as an inverse problem analysis method using an iterative process may be used.

(S700: Step of displaying optical characteristic value distribution of subject)
In this step, the display device 160 displays the weighted optical characteristic value distribution acquired by the weighting module 151 in S600 as an image on the display. At this time, the image after weighting and the image before weighting may be switched.

  Note that the program including the above steps may be executed by the signal processing device 150 as a computer.

(Effect of the present invention)
Next, an example of an image obtained by the subject information acquisition method of the present embodiment will be described with reference to FIG.

  FIG. 4A is a diagram showing an optical characteristic value distribution obtained by reconstructing an unweighted photoacoustic wave signal obtained when a living body including a tumor covered with new blood vessels is an observation target. . In FIG. 4A, a white region indicates a region having a larger optical characteristic value. Here, the blood vessel image 400 and the tumor image 410 covered with new blood vessels are emphasized.

  The image shown in FIG. 4A is an image obtained by reconstructing a photoacoustic wave signal including a photoacoustic wave signal corresponding to a region other than the region of interest. Therefore, in the optical characteristic value distribution before weighting shown in FIG. 4A, an artifact 420 due to a false signal appears in addition to the blood vessel image 400 and the tumor image 410 covered with the new blood vessel.

  On the other hand, FIG. 4B shows a strain distribution by elastography measurement in an observation object similar to the observation object shown in FIG. As described above, since the tumor part is typically harder than other tissues, a characteristic signal can be obtained by elastography measurement. In addition, tumors and new blood vessels can be distinguished by elastography measurement. Here, the regions of interest 430 and 431 and the region 440 other than the region of interest of the elastomer are set by the method shown in S300.

  Then, the pre-weighted photoacoustic wave signals corresponding to the regions of interest 430 and 431 and the region 440 other than the region of interest are weighted by the method shown in S500. The weighted photoacoustic wave signal obtained as a result is reconstructed to obtain a weighted optical characteristic value distribution shown in FIG.

  Here, when FIG. 4A is compared with FIG. 4C, the artifact 420 due to the false signal exists in FIG. 4A, whereas the artifact is reduced in FIG. 4C. The blood vessel image 400 and the tumor image 410 can be easily identified. Further, the blood vessel image 400 and the tumor image 410 can be easily identified.

  As described above, the object information acquisition method shown in the present embodiment weights the photoacoustic wave signal and reconstructs the weighted photoacoustic wave signal to reconstruct the weighted optical characteristic value distribution. Have acquired. In the weighted optical characteristic value distribution obtained in this way, artifacts and noise images in regions other than the region of interest are relatively reduced, so light with high contrast between the region of interest and the region other than the region of interest. An acoustic imaging image can be acquired.

  Furthermore, according to the subject information acquisition method of the present invention, after acquiring the optical characteristic value distribution as shown in FIG. 4A by reconstructing the image of the photoacoustic wave signal before weighting, the acquired optical characteristic value is obtained. It is also possible to obtain a weighted optical characteristic value distribution by performing weighting similarly to the weighting shown in S500. That is, although the photoacoustic wave signal is weighted in the present embodiment, according to the present invention, the optical characteristic value itself can be weighted similarly. Thereby, since artifacts and noise images in regions other than the region of interest can be relatively reduced, a photoacoustic imaging image with high contrast between the region of interest and the region other than the region of interest can be acquired.

  The preferred embodiments have been described above, but the present invention is not limited to these embodiments, and includes various modifications and application examples without departing from the scope of the claims.

DESCRIPTION OF SYMBOLS 130 Probe 150 Signal processing apparatus 151 Weighting module 152 Image reconstruction module 153 Feature information acquisition module 154 Area setting module

Claims (19)

A processing device for displaying on a display means a photoacoustic image obtained based on a photoacoustic wave generated by irradiating a subject with light,
Display control means for causing the display means to display an ultrasonic image obtained based on an ultrasonic echo transmitted to the subject;
Obtaining means for obtaining information indicating a region of interest in the ultrasound image, which is determined based on an instruction from an operator;
Have
The display control means causes the photoacoustic image corresponding to the region of interest to be displayed with a higher contrast ratio than the photoacoustic image corresponding to a region other than the region of interest based on information indicating the region of interest. A processing apparatus characterized by the above. The acquisition unit determines, as the region of interest, a region determined based on an operator's instruction and a region in which the value of characteristic information constituting the ultrasonic image is within a predetermined numerical value range. The processing apparatus according to claim 1, wherein information to be acquired is acquired. The processing apparatus according to claim 2, wherein the acquisition unit determines the predetermined numerical range based on the feature information. The processing apparatus according to claim 2, wherein the acquisition unit determines the predetermined numerical range based on an instruction from an operator. 5. The information acquisition apparatus according to claim 1, wherein the acquisition unit acquires information indicating the plurality of regions of interest in the ultrasonic image determined based on an instruction from an operator. Processing equipment. The processing apparatus according to claim 1, wherein the ultrasonic image is an image based on B-mode information, elastography information, or flow velocity information. The said photoacoustic image is an image based on the information regarding initial stage sound pressure distribution, light absorption energy density distribution, absorption coefficient distribution, or oxygen saturation distribution, The any one of Claim 1 to 6 characterized by the above-mentioned. The processing apparatus as described. The processing apparatus according to any one of claims 1 to 7,
A light source that emits light;
Transmitting means for transmitting ultrasonic waves to the subject;
A photoacoustic wave signal is output by receiving a photoacoustic wave generated by irradiating the subject with light, and an ultrasonic signal is received by receiving an echo of the ultrasonic wave transmitted from the transmitting unit. Receiving means for outputting;
A subject information acquisition apparatus characterized by comprising: The object information acquiring apparatus according to claim 8, wherein the transmission unit and the reception unit include a single probe. The display control means can switch between a photoacoustic image in which the region of interest is highlighted with a higher contrast ratio than a region other than the region of interest and a photoacoustic image that is not highlighted. The processing apparatus of any one of Claim 1 to 9. A photoacoustic image display method obtained based on a photoacoustic wave generated by irradiating a subject with light,
Displaying an ultrasound image obtained based on the echo of the ultrasound transmitted to the subject, obtaining information indicating a region of interest in the ultrasound image, determined based on an operator's instruction,
Based on the information indicating the region of interest, the photoacoustic image corresponding to the region of interest is displayed with a higher contrast ratio than the photoacoustic image corresponding to the region other than the region of interest. How to display the image. The step of acquiring information indicating the region of interest includes, as the region of interest, a region determined based on an operator's instruction and a region in which the value of characteristic information constituting the ultrasonic image is within a predetermined numerical range. The method for displaying a photoacoustic image according to claim 11, further comprising a determining step. The method of displaying a photoacoustic image according to claim 11, wherein the step of acquiring information indicating the region of interest includes a step of determining the predetermined numerical range based on the feature information. The photoacoustic image display method according to claim 11, wherein the step of acquiring information indicating the region of interest includes a step of determining the predetermined numerical range based on an instruction from an operator. The step of acquiring information indicating the region of interest includes acquiring information indicating the plurality of regions of interest in the ultrasonic image determined based on an instruction from an operator. The display method of the photoacoustic image of any one of these. The photoacoustic image display method according to any one of claims 11 to 15, wherein the ultrasonic image is an image based on B-mode information, elastography information, or flow velocity information. The photoacoustic image is an image based on information on an initial sound pressure distribution, a light absorption energy density distribution, an absorption coefficient distribution, or an oxygen saturation distribution, according to any one of claims 11 to 17. The display method of the photoacoustic image of description. 18. The photoacoustic image in which the region of interest is highlighted with a higher contrast ratio than the region other than the region of interest and the photoacoustic image that is not highlighted can be switched. The display method of the photoacoustic image of any one of Claims 1.   A program for causing a computer to execute the method for displaying a photoacoustic image according to any one of claims 11 to 18.

Images