JP2012231879A - Photoacoustic imaging method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform imaging by superimposing optical absorber information in a living body on a reflection ultrasonic image by efficiently reconstituting a photoacoustic image and the reflection ultrasonic image.SOLUTION: A photoacoustic imaging device 10 having means 13, 21, 22 for irradiating a subject with pulse light, detecting acoustic waves emitted from the subject at the time, and generating photoacoustic data includes: means 11, 21, 22 for transmitting ultrasonic waves to the subject, detecting reflection ultrasonic waves reflected against the subject, and obtaining ultrasonic data; and a complex number conversion means 25 for generating complex number data where the reflection ultrasonic data is defined as a real part and the photoacoustic data is defined as an imaginary part. The device also includes: an image reconstitution means 26 for obtaining a reconstitution image from the complex number data by a Fourier transformation method; a phase information extraction means 71 for extracting phase information from the reconstitution image; and a display control means 73 for allowing an image display means 14 to display an image to which a color table is applied based on the phase information.

Description

  The present invention relates to a photoacoustic imaging method, that is, a method of irradiating a subject such as a living tissue with light and imaging the subject based on an acoustic wave generated by the light irradiation.

  The present invention also relates to an apparatus for performing a photoacoustic imaging method.

  Conventionally, as shown in Patent Document 1 and Non-Patent Document 1, for example, a photoacoustic imaging apparatus that images the inside of a living body using a photoacoustic effect is known. In this photoacoustic imaging apparatus, a living body is irradiated with pulsed light such as pulsed laser light. Inside the living body that has been irradiated with the pulsed light, the living tissue that has absorbed the energy of the pulsed light undergoes volume expansion due to heat and generates acoustic waves. Therefore, it is possible to detect the acoustic wave with an ultrasonic probe or the like and visualize the inside of the living body based on the electrical signal (photoacoustic signal) obtained thereby. The photoacoustic imaging method is suitable for imaging a specific tissue in a living body, such as a blood vessel, since an image is constructed based only on an acoustic wave emitted from a specific light absorber.

  By the way, the photoacoustic image has an advantage that blood vessels and the like in the living body that are light absorbers can be extracted and displayed, but only the blood vessels are displayed. In view of this point, a technique for superimposing and displaying blood vessels on a normal reflected ultrasound image has been proposed, and Patent Document 2 discloses an example thereof.

JP 2005-21380 A Special table 2010-512929

A High-Speed Photoacoustic Tomography System based on a Commercial Ultrasound and a Custom Transducer Array, Xueding Wang, Jonathan Cannata, Derek DeBusschere, Changhong Hu, J. Brian Fowlkes, and Paul Carson, Proc.SPIE Vol. 7564, 756424 (Feb. 23, 2010)

  However, in the prior art disclosed in Patent Document 2, since the reflected ultrasonic image and the photoacoustic image are reconstructed and then superimposed, it is necessary to perform image reconstruction twice. Problems such as the need for large-capacity storage means or the time required for arithmetic processing are recognized.

  The present invention has been made in view of the above circumstances, and efficiently reconstructs a reflected ultrasonic image and a photoacoustic image, and displays a light absorber in a living body by superimposing information on the reflected ultrasonic image. It is an object to provide an acoustic imaging method.

  It is another object of the present invention to provide a photoacoustic imaging apparatus that can implement such a photoacoustic imaging method.

The photoacoustic imaging method according to the present invention comprises:
The object is irradiated with pulsed light having a wavelength that is absorbed inside the object, thereby detecting an acoustic wave emitted from the object to obtain photoacoustic data, and imaging the object based on the photoacoustic data. In the photoacoustic imaging method for displaying on the image display means,
Transmitting ultrasonic waves toward the subject, thereby detecting reflected ultrasonic waves reflected by the subject to obtain ultrasonic data;
Create complex data with one of the ultrasonic data and photoacoustic data as a real part and the other as an imaginary part,
Reconstructed image is obtained from the complex data by Fourier transform method,
Extract phase information from this reconstructed image,
A color map based on the phase information is applied to the subject image and displayed on the image display means.

  In the photoacoustic imaging method according to the present invention, intensity information is further extracted from the reconstructed image, and a color map based on the phase information is applied to the intensity information and displayed on the image display means. desirable.

  In such a case, it is more desirable to apply a color map in which the hue is emphasized as the phase indicated by the phase information is larger at the point having the maximum intensity as the intensity information.

  Further, in the photoacoustic imaging method of the present invention, it is desirable to use pulsed light having wavelengths with different absorption characteristics at two different portions of the subject as the pulsed light. In that case, if the two parts are a human artery and a vein, it is particularly preferable that the center wavelength of the pulsed light is 756 nm.

On the other hand, the photoacoustic imager according to the present invention is:
The object is irradiated with pulsed light having a wavelength that is absorbed inside the object, thereby detecting an acoustic wave emitted from the object to obtain photoacoustic data, and imaging the object based on the photoacoustic data. In the photoacoustic imaging device for displaying on the image display means,
Means for transmitting ultrasonic waves toward the subject, thereby detecting reflected ultrasonic waves reflected by the subject and obtaining ultrasonic data;
Complex number generating means for creating complex number data having one of the ultrasonic data and photoacoustic data as a real part and the other as an imaginary part;
Image reconstruction means for obtaining a reconstructed image from the complex number data by Fourier transform;
Phase information extraction means for extracting phase information from the reconstructed image;
And a display control means for displaying on the image display means an image to which a color map based on the phase information is applied.

  In the photoacoustic imaging apparatus according to the present invention, intensity information extracting means for extracting intensity information from the reconstructed image is further provided, and the display control means is a color map based on the phase information. Is preferably applied to the intensity information for display. And when comprised in that way, the said display control means applies the color map with which a hue is emphasized, so that the phase which the said phase information shows is large about the point which has the maximum intensity | strength as said intensity | strength information. It is particularly desirable.

  In the photoacoustic imaging apparatus of the present invention, it is preferable that a light source that emits pulsed light having a wavelength different in absorption characteristics at two different portions of the subject is applied as the light source that emits the pulsed light. In that case, the center wavelength of the pulsed light is particularly preferably 756 nm.

  According to the photoacoustic imaging method of the present invention, the subject is irradiated with pulsed light having a wavelength absorbed therein, thereby detecting the acoustic wave emitted from the subject and obtaining photoacoustic data, Ultrasound is transmitted toward the subject, and reflected ultrasound reflected by the subject is detected to obtain ultrasound data. One of the ultrasound data and photoacoustic data is the real part and the other is the imaginary part. The complex number data is generated, a reconstructed image is obtained from the complex number data by Fourier transform, and a color map based on the phase information extracted from the reconstructed image is applied to the subject image and displayed on the image display means. Therefore, the reflected ultrasonic image and the photoacoustic image can be reconstructed efficiently and at high speed, and the light absorber in the living body can be displayed with the information superimposed on the reflected ultrasonic image.

  The Fourier transform method is originally performed in a complex space, and even when a reconstructed image is obtained only from photoacoustic data, the image reconstruction is processed with a complex number. Therefore, even when image reconstruction is performed from acoustic wave data and ultrasonic image data as in the method of the present invention, the processing is basically the same as when image reconstruction is performed only from photoacoustic data. Therefore, the reflected ultrasonic image and the photoacoustic image can be displayed efficiently and at high speed.

  In particular, in the photoacoustic imaging method of the present invention, when using pulsed light having a wavelength different in absorption characteristics in two different parts of the subject as the pulsed light, the two different parts are color maps. It is also possible to display them separately from each other.

On the other hand, as described above, the photoacoustic imaging apparatus according to the present invention irradiates a subject with pulsed light having a wavelength absorbed therein, thereby detecting an acoustic wave emitted from the subject to obtain photoacoustic data. In a photoacoustic imaging device to obtain,
Means for transmitting ultrasonic waves toward the subject, thereby detecting reflected ultrasonic waves reflected by the subject and obtaining ultrasonic data;
Complex number generating means for creating complex number data with one of ultrasonic data and photoacoustic data as a real part and the other as an imaginary part;
Image reconstruction means for obtaining a reconstructed image from the complex data by Fourier transform;
Phase information extraction means for extracting phase information from the reconstructed image;
And a display control unit that displays on the image display unit an image to which the color map based on the phase information is applied. According to this photoacoustic imaging apparatus, the above-described photoacoustic imaging method of the present invention is provided. Can be implemented.

The block diagram which shows schematic structure of the photoacoustic imaging device by one Embodiment of this invention. The figure explaining the data processing in the apparatus of FIG. 1, and the image display by it Diagram explaining complex number data The figure explaining ultrasonic image data and photoacoustic image data Graph showing molecular absorption coefficient for each light wavelength of oxyhemoglobin (oxy-Hb) and deoxyhemoglobin (deoxy-Hb)

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a basic configuration of a photoacoustic imaging apparatus 10 according to an embodiment of the present invention. The photoacoustic imaging apparatus 10 can acquire both a photoacoustic image and an ultrasonic image, and includes an ultrasonic probe (probe) 11, an ultrasonic unit 12, a laser light source unit 13, and an image display. Means 14 are provided.

  The laser light source unit 13 emits laser light having a center wavelength of 756 nm as an example. The subject is irradiated with the laser beam emitted from the laser light source unit 13. The laser light is preferably guided to the probe 11 using light guide means such as a plurality of optical fibers, and irradiated from the probe 11 portion toward the subject.

  The probe 11 performs output (transmission) of ultrasonic waves to the subject and detection (reception) of reflected ultrasonic waves reflected back from the subject. For this purpose, the probe 11 has, for example, a plurality of ultrasonic transducers arranged one-dimensionally. The probe 11 detects ultrasonic waves (acoustic waves) generated by the observation object in the subject absorbing the laser light from the laser light source unit 13 by using the plurality of ultrasonic transducers. The probe 11 detects the acoustic wave and outputs an acoustic wave detection signal, and also detects the reflected ultrasonic wave and outputs an ultrasonic detection signal.

  When the above-described light guide means is coupled to the probe 11, the end portion of the light guide means, that is, the tip portions of the plurality of optical fibers, are arranged along the arrangement direction of the plurality of ultrasonic transducers. From there, laser light is irradiated toward the subject. Hereinafter, the case where the light guide means is coupled to the probe 11 as described above will be described as an example.

  When acquiring a photoacoustic image or an ultrasonic image of the subject, the probe 11 is moved in a direction substantially perpendicular to the one-dimensional direction in which the plurality of ultrasonic transducers are arranged. Two-dimensional scanning is performed by sound waves. This scanning may be performed by an inspector moving the probe 11 manually, or a more precise two-dimensional scanning may be realized using a scanning mechanism.

  The ultrasonic unit 12 includes a reception circuit 21, an AD conversion unit 22, a reception memory 23, a data separation unit 24, a complex number conversion unit 25, an image reconstruction unit 26, and the data separation unit 24 and the complex number conversion unit 25. The 1/2 sampling means 28, the intensity information extraction means 70 that receives the output of the image reconstruction means 26, the phase information extraction means 71 that receives the output of the image reconstruction means 26, and the output of the intensity information extraction means 70 are It has a detection / logarithm conversion means 72 for receiving, an image construction means 73 for receiving the output of the detection / logarithm conversion means 72 and the phase information extraction means 71. The output of the image construction unit 73 is input to the image display unit 14 including, for example, a CRT or a liquid crystal display device. Further, the ultrasonic unit 12 includes a transmission control circuit 30 and a control unit 31 that controls the operation of each unit in the ultrasonic unit 12.

  The receiving circuit 21 receives the acoustic wave detection signal and the ultrasonic wave detection signal output from the probe 11. The AD conversion means 22 is a sampling means, which samples the acoustic wave detection signal and the ultrasonic detection signal received by the receiving circuit 21 and converts them into photoacoustic data and ultrasonic data, which are digital signals, respectively. This sampling is performed at a predetermined sampling period in synchronization with, for example, an externally input AD clock signal.

  The laser light source unit 13 includes a Q-switch pulse laser 32 made of a Ti: Sapphire laser or the like and a flash lamp 33 as an excitation light source. The laser light source unit 13 is supplied with a light trigger signal for instructing light emission from the control means 31. When the light trigger signal is received, the flash lamp 33 is turned on and the Q switch pulse laser is turned on. 32 is excited. For example, when the flash lamp 33 sufficiently excites the Q switch pulse laser 32, the control means 31 outputs a Q switch trigger signal. When receiving the Q switch trigger signal, the Q switch pulse laser 32 turns on the Q switch and emits a pulse laser beam having a wavelength of 756 nm.

  Here, the time required from when the flash lamp 33 is turned on until the Q-switch pulse laser 33 is sufficiently excited can be estimated from the characteristics of the Q-switch pulse laser 33 and the like. In place of controlling the Q switch from the control means 31 as described above, the Q switch may be turned on after the Q switch pulse laser 32 is sufficiently excited in the laser light source unit 13. In that case, a signal indicating that the Q switch is turned on may be notified to the ultrasonic unit 12 side.

  The control unit 31 inputs an ultrasonic trigger signal for instructing ultrasonic transmission to the transmission control circuit 30. When receiving the ultrasonic trigger signal, the transmission control circuit 30 transmits an ultrasonic wave from the probe 11. The control means 31 outputs the optical trigger signal first, and then outputs an ultrasonic trigger signal. The light trigger signal is output to irradiate the subject with laser light and the acoustic wave is detected, and then the ultrasonic trigger signal is output to transmit the ultrasonic wave to the subject and the reflected ultrasonic wave. Is detected.

  The control means 31 further outputs a sampling trigger signal that instructs the AD conversion means 22 to start sampling. The sampling trigger signal is output after the optical trigger signal is output and before the ultrasonic trigger signal is output, more preferably at the timing when the subject is actually irradiated with the laser light. Therefore, the sampling trigger signal is output in synchronization with the timing at which the control means 31 outputs the Q switch trigger signal, for example. When receiving the sampling trigger signal, the AD conversion means 22 starts sampling the acoustic wave detection signal output from the probe 11 and received by the receiving circuit 21.

  After outputting the optical trigger signal, the control means 31 outputs the ultrasonic trigger signal at the timing when the detection of the acoustic wave is finished. At this time, the AD conversion means 22 continues the sampling without interrupting the sampling of the acoustic wave detection signal. In other words, the control unit 31 outputs the ultrasonic trigger signal in a state where the AD conversion unit 22 continues sampling the acoustic wave detection signal. When the probe 11 transmits ultrasonic waves in response to the ultrasonic trigger signal, the detection target of the probe 11 changes from acoustic waves to reflected ultrasonic waves. The AD conversion unit 22 continuously samples the acoustic wave detection signal and the ultrasonic wave detection signal by continuously sampling the detected ultrasonic wave detection signal.

  The AD conversion unit 22 stores photoacoustic data and ultrasonic data obtained by sampling in a common reception memory 23. The sampling data stored in the reception memory 23 is photoacoustic data up to a certain point, and becomes ultrasonic data from a certain point. The data separation unit 24 separates the photoacoustic data and the ultrasonic data stored in the reception memory 23, the photoacoustic data is directly input to the complex numbering unit 25, and the ultrasonic data passes through the 1/2 sampling unit 28. Input to the complex numbering means 25. The time from when the ultrasonic trigger signal is output until the ultrasonic data sampling is completed is basically that the ultrasonic wave propagates in a reciprocating manner, until the optical data sampling is completed after the optical trigger signal is output. Takes twice as long. In view of this point, the ½ sampling means 28 makes the number of data coincide with the number of data of the acoustic wave data by re-sampling the input ultrasonic data every other time axis.

  Hereinafter, generation and display of an ultrasonic image and a photoacoustic image will be described with reference to FIG. As described above, the complex number converting means 25 in FIG. 1 receives the ultrasonic data after passing through the 1/2 sampling means 28 and the photoacoustic data obtained by irradiating the subject with pulsed laser light having a wavelength of 756 nm. The

  2A and 2B schematically show examples of the ultrasonic data and the photoacoustic data, respectively, with respect to a cross section along one scanning line of the probe 11. In FIG. 1A, the horizontal direction indicated by the arrow x indicates the direction in which the plurality of ultrasonic transducers of the probe 11 are arranged, and the vertical direction indicates the time when the ultrasonic waves are detected (FIG. 2B). The same applies to (3). That is, when a reflected ultrasonic wave is detected, the ultrasonic wave is detected according to the time / position relationship indicated by arcs in these figures, and the apex portion of each arc reaches the probe 11 earliest after transmitting the ultrasonic wave. This indicates the time at which a sound wave (that is, a reflected ultrasonic wave that travels directly from the ultrasonic reflection portion toward the probe 11) is detected. Since this time corresponds to the position in the depth direction of the ultrasonic reflection part, the apex part indicates the position in the depth direction of the part where the ultrasonic wave is reflected.

  The same applies to the photoacoustic data shown in FIG. That is, when an acoustic wave is detected, the acoustic wave is detected with a time / position relationship indicated by an arc in the figure, and the apex portion of each arc reaches the probe 11 earliest after light irradiation (that is, the acoustic wave). The time at which the acoustic wave traveling in the direction of the probe 11 directly from the wave generation site is detected is indicated. Since this time corresponds to the position in the light irradiation depth direction of the acoustic wave generation site, the vertex portion indicates the position in the depth direction of the portion that emitted the acoustic wave.

  Here, the wavelength of the pulse laser beam emitted when obtaining the photoacoustic data is set to 756 nm in consideration of the molecular absorption coefficient for each light wavelength of oxygenated hemoglobin and deoxygenated hemoglobin shown in FIG. Therefore, the photoacoustic data indicating the arterial portion has relatively higher intensity than the photoacoustic data indicating the vein portion. On the other hand, since the degree of ultrasonic reflection is not particularly different between the arterial part and the venous part, there is basically a difference in intensity between the ultrasonic data indicating the arterial part and the ultrasonic data indicating the venous part. Absent. Therefore, the ratio of the photoacoustic data to the ultrasound data is larger between the data indicating the arterial part than the data indicating the arterial part. From this point, the artery and vein are separated as described later. Can be displayed.

That is, the complex number generating means 25 creates complex number data with the above-described ultrasonic data as a real part and photoacoustic data as an imaginary part (see (3) in FIG. 2). Here, the complex data will be described with reference to the Gaussian plane shown in FIG. In the complex number data of coordinates (X, Y) indicated by black circles in FIG. 3, the value of r such that r ² = X ² + Y ² indicates the intensity, and the declination angle θ indicates the phase. The larger the ratio of the photoacoustic data to the ultrasonic data described above, the larger the declination angle θ. It should be noted that the creation of complex data described above is sequentially performed as the probe 11 is moved, whereby complex data is created for each of a plurality of cross sections in the scanning direction of the subject.

  The complex number data thus created is then input to the image reconstruction means 26 in FIG. The image reconstruction means 26 performs image reconstruction from the input complex number data by the Fourier transform method (FTA method). For image reconstruction by the Fourier transform method, for example, a conventionally known method described in the document “Photoacoustic Image Reconstruction-A Quantitative Analysis” Jonathan I. Sperl et al. SPIE-OSA Vol. be able to.

  The Fourier-transformed data representing the reconstructed image is sent to the intensity information extracting means 70 where it is used for extracting the intensity information, and also sent to the phase information extracting means 71 where it is used for extracting the phase information. . The detection / logarithm conversion means 72 generates an envelope of the data indicating the extracted intensity information, and then logarithmically converts the envelope to widen the dynamic range. The detection / logarithm conversion means 72 inputs these processed data to the image construction means 73. The image construction means 73 is also input with data indicating the extracted phase information.

  FIG. 2 (4) schematically shows the reconstructed image described above. That is, this reconstructed image corresponds to the ultrasonic data and acoustic wave data shown in FIGS. 1A and 1B, and the vertical position corresponds to the detection time of each element arranged in the x direction. doing. The result of reconstruction from the ultrasonic data and acoustic wave data detected by each element in this way to the depth of the position where the ultrasonic waves are actually reflected and the depth of the position where the acoustic waves are actually generated is (4). It becomes the point shown in the inside. Here, the line shown with the dotted line has shown the data before reconstruction.

  Based on the above, the image constructing means 73 is achromatic (white) when the phase θ is minimum, and the phase θ is large for the ultrasonic reflection portion and the acoustic wave generation portion obtained based on the intensity information. Color mapping is performed to emphasize the red hue. This point will be described in more detail with reference to FIG. The five rectangles shown in the figure schematically show five data groups each having a common phase θ. As for the data of each data group, data with lower intensity (data closer to the origin indicated by arrow B) is displayed with higher density, that is, lower luminance, and data with higher intensity is displayed with lower density, that is, with higher luminance. At this time, the point displayed with the maximum luminance is the point where the ultrasonic wave is actually reflected as described above, or the point where the acoustic wave is actually generated. Then, the image construction means 73 is achromatic (white) when the phase θ is minimum at the point displayed at the maximum luminance, and the red as the phase θ is larger (that is, as it goes in the direction indicated by the arrow A in FIG. 3). Color mapping is performed to emphasize the hue of the image.

  Therefore, in this color-mapped image, the red portion indicates an artery and the white portion indicates a vein. (5) in FIG. 2 shows the color mapping result, in which the black point in the figure is mapped to red with the strongest hue, and the white point is the point with the weakest hue, that is, the point displayed in white. Is shown. The color mapping described above is performed in the same manner for each cross section obtained sequentially with the scanning movement of the probe 11.

  The color mapping image created in this way is sent to the image display means 14 of FIG. 1 and displayed. Therefore, by observing this display image, it is possible to know how the artery and vein exist. It is also possible to construct a three-dimensional image based on complex data obtained from ultrasonic data and acoustic wave data relating to a plurality of cross sections, and to display the positions of arteries and veins three-dimensionally.

  The Fourier transform method described above is originally performed in a complex space, and even when a reconstructed image is obtained only from photoacoustic data, the image reconstruction is processed with a complex number. Therefore, even when image reconstruction is performed from acoustic wave data and ultrasound image data as in the present embodiment, the processing is basically the same as when image reconstruction is performed from photoacoustic data alone, in other words, in that case It is possible to distinguish and display the two parts efficiently and at high speed.

  As is clear from the above description, in this embodiment, the image construction means 73 constitutes the display control means in the present invention.

  Here, in the photoacoustic imaging apparatus 10 of the present embodiment, a normal photoacoustic image can be acquired and displayed in the same manner as a general photoacoustic imaging apparatus, or a normal ultrasonic image is acquired and displayed. It is also possible. FIG. 4 schematically shows these images. That is, for example, as shown in FIG. 1A, it is assumed that an arterial portion indicated by a black dot and a vein portion indicated by a white dot exist in a cross section of the living body. The x direction and depth shown here are the same as those already described.

  With respect to such a cross section, the ultrasonic image is as shown in FIG. That is, in the ultrasonic image, the arterial portion and the vein portion are displayed as indicated by black dots. For the same cross section, the photoacoustic image is as shown in FIG. In other words, in the photoacoustic image, for example, if only a portion where an acoustic wave having a strength equal to or greater than a predetermined value is detected, only the arterial portion is displayed as indicated by a black dot.

  In order to perform the display as described above, in the apparatus shown in FIG. 1, the photoacoustic data output from the data separation unit 24 and the ultrasonic data output from the 1/2 sampling unit 28 are passed through the complex numbering unit 25. Further, the image construction in the image construction means 73 may be performed based only on the intensity information.

  In addition, in order to display two parts of the subject as different display states, in addition to displaying by changing the intensity of one hue as described above, for example, by changing the hue according to the change of the phase θ, one part is displayed. May be red or the like, and other parts may be blue or the like. Furthermore, it is also possible to adopt a mode in which only one of the two parts is displayed with hatching.

  Further, the embodiment has been described above in which human arteries and veins are displayed separately from each other. However, the present invention is not limited to displaying arteries and veins separately. All of them can be effectively applied when it is desired to distinguish and display two objects having different light absorption characteristics.

  In addition, the photoacoustic imaging apparatus and method of the present invention are not limited to the above embodiment, and various modifications and changes made from the configuration of the above embodiment are also included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Photoacoustic imaging apparatus 11 Probe 12 Ultrasonic unit 13 Laser light source unit 14 Image display means 21 Reception circuit 22 AD conversion means 23 Reception memory 24 Data separation means 25 Complex number conversion means 26 Image reconstruction means 28 1/2 Sampling means 30 Transmission control circuit 31 Control means 32 Q switch laser 33 Flash lamp 70 Intensity information extraction means 71 Phase information extraction means 72 Detection / logarithm conversion means 73 Image construction means

Claims (10)

The object is irradiated with pulsed light having a wavelength that is absorbed inside the object, thereby detecting an acoustic wave emitted from the object to obtain photoacoustic data, and imaging the object based on the photoacoustic data. In the photoacoustic imaging method for displaying on the image display means,
Transmitting ultrasonic waves toward the subject, thereby detecting reflected ultrasonic waves reflected by the subject to obtain ultrasonic data;
Create complex data with one of the ultrasonic data and photoacoustic data as a real part and the other as an imaginary part,
Reconstructed image is obtained from the complex data by Fourier transform method,
Extract phase information from this reconstructed image,
A photoacoustic imaging method, wherein a color map based on the phase information is applied to a subject image and displayed on an image display means.   2. The photoacoustic imaging method according to claim 1, wherein intensity information is further extracted from the reconstructed image, and a color map based on the phase information is applied to the intensity information and displayed on the image display means.   3. The photoacoustic imaging method according to claim 2, wherein a color map in which the hue is emphasized as the phase indicated by the phase information is larger is applied to the point having the maximum intensity as the intensity information.   4. The photoacoustic imaging method according to claim 1, wherein light having wavelengths different from each other in absorption characteristics at two different portions of the subject is used as the pulsed light.   5. The photoacoustic imaging method according to claim 4, wherein the two parts are a human artery and a vein, and a center wavelength of the pulsed light is set to 756 nm. The object is irradiated with pulsed light having a wavelength that is absorbed inside the object, thereby detecting an acoustic wave emitted from the object to obtain photoacoustic data, and imaging the object based on the photoacoustic data. In the photoacoustic imaging device for displaying on the image display means,
Means for transmitting ultrasonic waves toward the subject, thereby detecting reflected ultrasonic waves reflected by the subject and obtaining ultrasonic data;
Complex number generating means for creating complex number data having one of the ultrasonic data and photoacoustic data as a real part and the other as an imaginary part;
Image reconstruction means for obtaining a reconstructed image from the complex number data by Fourier transform;
Phase information extraction means for extracting phase information from the reconstructed image;
A photoacoustic imaging apparatus comprising: a display control unit that causes the image display unit to display an image to which a color map based on the phase information is applied.   It further comprises intensity information extraction means for extracting intensity information from the reconstructed image, and the display control means is adapted to display a color map based on the phase information applied to the intensity information. The photoacoustic imaging apparatus according to claim 6.   8. The color map in which the display control unit applies a color map in which the hue is emphasized as the phase indicated by the phase information is larger at the point having the maximum intensity as the intensity information. Photoacoustic imaging apparatus.   9. The photoacoustic according to claim 6, wherein the light source that emits the pulsed light emits pulsed light having a wavelength different in absorption characteristics at two different portions of the subject. Imaging method.   The photoacoustic imaging apparatus according to claim 9, wherein a center wavelength of the pulsed light is 756 nm.