JP6238549B2 - SUBJECT INFORMATION ACQUISITION DEVICE AND METHOD FOR CONTROLLING SUBJECT INFORMATION ACQUISITION DEVICE - Google Patents

Description

  The present invention relates to a subject information acquisition apparatus that acquires information inside a subject and a control method thereof.

  In the medical field, a photoacoustic imaging apparatus that images a form and function inside a tissue by irradiating a living body with light such as laser light and receiving ultrasonic waves generated from inside the living body due to the light. Many are used. When the subject is irradiated with measurement light such as pulsed laser light, an acoustic wave is generated when the measurement light is absorbed by the living tissue in the subject. The photoacoustic imaging apparatus can visualize the information (function information) related to the optical characteristics inside the subject by receiving and analyzing the generated acoustic wave with the probe. Such a technique is called photoacoustic imaging.

  In addition, in order to acquire ultrasonic waves from a wide range, an image diagnostic apparatus having a mechanism for mechanically scanning a probe has been proposed. For example, Patent Document 1 describes a photoacoustic imaging apparatus that can acquire ultrasonic waves from a wide range by mechanically scanning a probe.

JP 2010-104816 A

In the photoacoustic imaging apparatus described above, scanning is performed by moving the probe on the surface of the subject. Therefore, if the subject moves during scanning, there may be a problem that the acquired image is deviated or the data scheduled to be acquired cannot be acquired.
Thus, in an apparatus that acquires information on an object using acoustic waves, care must be taken so that the object does not move during measurement. However, when it is noticed after the measurement that the subject is displaced during the measurement, it is necessary to restart the measurement while holding the subject under pressure, which is a heavy burden on the subject.

  The present invention has been made in view of the above-described problems of the prior art, and provides an object information acquisition apparatus that can detect a change in the position of an object during measurement and can appropriately change a scanning path. With the goal.

The subject information acquisition apparatus according to the present invention includes:
An object information acquisition apparatus for acquiring information in the subject by receiving and analyzing an acoustic wave coming from within the subject, and scanning the probe for receiving the acoustic wave with respect to the subject Scanning means for making the path, path setting means for determining a first path that is the scanning path of the probe, and position information acquisition means for acquiring position information that is information relating to the position of the surface of the subject relative to the apparatus. The path setting means determines whether to change the scanning path to a second path different from the first path based on the position information, and when changing the scanning path, The first route and the second route are presented to the user .

In addition, the control method of the subject information acquisition apparatus according to the present invention includes:
A subject having an acoustic wave receiving probe and a scanning mechanism for moving the probe, and receiving and analyzing an acoustic wave arriving from within the subject to acquire information in the subject A method for controlling an information acquisition apparatus, comprising: a scanning step of determining a first path which is a scanning path of the probe, and scanning the object using the probe; and acquiring the object information A position information acquisition step of acquiring position information that is information relating to the position of the subject surface with respect to the apparatus , wherein the scanning step uses a second scanning path different from the first path based on the position information. It is determined whether to change to the first path, and when changing the scanning path, the first path and the second path are presented to the user .

  According to the present invention, it is possible to provide an object information acquisition apparatus that can detect that the position of an object has changed during measurement and can appropriately change a scanning path.

The block diagram of the photoacoustic measuring device which concerns on 1st embodiment. The figure explaining the scanning path | route of the photoacoustic measuring device which concerns on 1st embodiment. The process flowchart figure of the photoacoustic measuring device which concerns on 1st embodiment. The figure explaining the operation screen of the photoacoustic measuring device which concerns on 1st embodiment. The figure explaining the operation timing of each component which a photoacoustic measuring device has. The figure explaining the operation screen of the photoacoustic measuring device which concerns on 2nd embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In principle, the same components are denoted by the same reference numerals, and description thereof is omitted.

(First embodiment)
The photoacoustic measurement apparatus according to the first embodiment of the present invention irradiates a subject with laser light, receives and analyzes photoacoustic waves generated in the subject due to the laser light, An apparatus for imaging information related to optical characteristics in a subject. The information related to the optical characteristics is generally an initial sound pressure distribution, a light absorption energy density distribution, an absorption coefficient distribution, or a concentration distribution of substances constituting the tissue.

<System configuration>
The configuration of the photoacoustic measurement apparatus according to the first embodiment will be described with reference to FIG. The photoacoustic measurement apparatus according to the first embodiment includes a light source 11, an optical system 13, an acoustic wave probe 17, a scanning unit 18, a signal processing unit 19, a data processing unit 20, an input / output unit 21, a measurement unit 22, A route setting unit 23 is included.

The measurement is performed by inserting a subject 15 (for example, a breast) into an opening (not shown) provided in the apparatus.
First, pulsed light 12 emitted from the light source 11 is irradiated to the subject 15 via the optical system 13. When a part of the energy of light propagating through the subject is absorbed by a light absorber such as blood, an acoustic wave is generated from the light absorber due to thermal expansion. The acoustic wave generated in the subject is received by the acoustic probe 17 and analyzed by the signal processing unit 19 and the data processing unit 20. The analysis result is converted into image data (optical characteristic value information) representing the characteristic information in the subject and output through the input / output unit 21. The path setting unit 23 determines the scanning path of the acoustic wave probe.
Further, the photoacoustic measurement device according to the present embodiment acquires information (position information) representing the position of the subject when the measurement unit 22 acquires a change in the position of the subject that affects the measurement. 23 detects this and resets the scanning path. Thereby, even when the position of the subject changes during measurement, it is possible to prevent incomplete information from being generated or information from being lost.
Hereinafter, each means which comprises the photoacoustic measuring device which concerns on this embodiment is demonstrated.

<< light source 11 >>
The light source 11 is a device that generates pulsed light that irradiates a subject. The light source is preferably a laser light source in order to obtain a large output, but a light emitting diode, a flash lamp, or the like may be used instead of the laser. When a laser is used as the light source, various lasers such as a solid laser, a gas laser, a dye laser, and a semiconductor laser can be used. The timing, waveform, intensity, etc. of irradiation are controlled by a light source control unit (not shown). The light source control unit may be integrated with the light source.
In order to effectively generate photoacoustic waves, light must be irradiated in a sufficiently short time according to the thermal characteristics of the subject. When the subject is a living body, the pulse width of the pulsed light generated from the light source is preferably about 10 to 50 nanoseconds. Further, the wavelength of the pulsed light is preferably a wavelength at which the light propagates to the inside of the subject. Specifically, when the subject is a living body, the thickness is desirably 500 nm or more and 1200 nm or less. Furthermore, it is desirable that the wavelength of the pulsed light has a high absorption coefficient relative to the observation target.

<< Optical system 13 >>
The optical system 13 is a means for guiding the pulsed light 12 generated by the light source 11 to the subject 15, and typically includes a mirror that reflects the light, a lens that collects, enlarges, or changes the shape of the light, and the light. It consists of a diffuser plate that diffuses. Using these optical members, the irradiation conditions such as the irradiation shape of the pulsed light, the light density, and the irradiation direction of the subject can be set arbitrarily. Note that it is preferable to spread the light over a certain area rather than condensing it with a lens from the viewpoint of expanding the safety of the subject and the diagnostic area. The light source 11 and the optical system 13 are a light irradiation unit in the present invention.

<< Subject 15 >>
The subject 15 and the light absorber 14 do not constitute the present invention, but will be described here. The subject 15 is an object to be subjected to photoacoustic measurement, and is typically a human body or animal breast, finger, limb or the like. Here, a human breast is used as a subject.
In the photoacoustic measurement apparatus according to the present embodiment, it is possible to image the light absorber 14 present inside the subject 15 and having a relatively large light absorption coefficient. When the subject is a living body, the light absorber 14 is specifically water, lipid, melanin, collagen, protein, oxygenated hemoglobin, reduced hemoglobin, or the like. Or a blood vessel containing a lot of oxidized or reduced hemoglobin, a malignant tumor containing a lot of new blood vessels, and the like. By imaging the light absorber, the photoacoustic measurement apparatus according to the present embodiment can perform blood vessel contrast, diagnosis of human or animal malignant tumors or vascular diseases, follow-up of chemical treatment, and the like.

<< Acoustic wave probe 17 >>
The acoustic wave probe 17 is a means for receiving an acoustic wave generated inside the subject due to the light irradiated on the subject 15 and converting it into an analog electric signal. The acoustic wave in the present invention is typically an ultrasonic wave, and includes an elastic wave called a sound wave, an ultrasonic wave, a photoacoustic wave, and an optical ultrasonic wave. The acoustic wave probe 17 receives these elastic waves generated or reflected in the subject.
The acoustic wave probe 17 is also called a probe or a transducer. The acoustic wave probe 17 may be composed of a single acoustic detector or a plurality of acoustic detectors.
The acoustic wave probe 17 may be one in which a plurality of receiving elements are arranged one-dimensionally or two-dimensionally. When a multidimensional array element is used, acoustic waves can be received at a plurality of locations at the same time, so that measurement time can be shortened and influences such as vibration of the subject can be reduced.

Further, it is desirable that the acoustic wave probe 17 has high sensitivity and a wide frequency band. Specific examples include PZT (piezoelectric ceramics), PVDF (polyvinylidene fluoride resin), CMUT (capacitive micromachined ultrasonic transducer), and those using a Fabry-Perot interferometer. However, the present invention is not limited to those described here, and any one may be used as long as the function as an acoustic wave probe is satisfied.

<< Scanning section 18 >>
The scanning unit 18 is means for moving the acoustic probe 17 in a two-dimensional direction, and includes a scanning mechanism and its control means. By using the scanning unit 18, photoacoustic measurement can be performed while the acoustic wave probe 17 is scanned two-dimensionally. In the present embodiment, the subject 15 is fixed, and the relative position between the subject and the acoustic wave probe is changed by moving the acoustic wave probe on the XY stage.
In the present embodiment, the acoustic wave probe 17 is moved by the scanning mechanism. However, the acoustic wave probe may be fixed and the subject may be moved. In this case, a support unit (not shown) that supports the subject may be moved by a scanning mechanism.

Note that both the subject 15 and the acoustic wave probe 17 may be configured to be movable. When the subject 15 is moved, the measurement unit 22 preferably follows the subject and makes the same movement, but other methods may be used as long as the movement of the subject can be captured. The scanning is preferably performed while the probe is moved continuously, but may be performed while the probe is moved intermittently. The scanning mechanism for performing scanning is desirably an electric type using a stepping motor or the like, but may be a type in which scanning is performed manually.
Note that the types and methods of scanning are not limited to those listed here, and any scanning is possible as long as at least one of the subject 15 and the acoustic probe 17 can be moved. There may be.

<< Signal processing unit 19 >>
The signal processing unit 19 is means for amplifying the electric signal obtained by the acoustic wave probe 17 and converting it into a digital signal. The signal processing unit 19 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 probe, it is desirable that a plurality of signals can be processed simultaneously.

<< Data processing unit 20 >>
The data processing unit 20 is means for generating image data (image reconstruction) by processing the digital signal obtained by the signal processing unit 19. Examples of the image reconstruction method executed by the data processing unit 20 include a Fourier transform method, a universal back projection method, a filtered back projection method, a sequential reconstruction method, and the like. I do not care. Further, the signal processing unit 19 and the data processing unit 20 may be integrated. The signal processing unit 19 and the data processing unit 20 are image acquisition means in the present invention.

<< Input / output unit 21 >>
The input / output unit 21 is a unit that outputs an image generated by the data processing unit 20 and receives an input operation from an operator, and is typically a touch panel display. The input / output unit 21 is a means for displaying detailed information about the positional deviation when the path setting unit 23 described later detects the positional deviation of the subject. The input / output unit 21 is not necessarily integral with the photoacoustic measurement device, and may be a device connected to the outside.

<< Measurement unit 22 >>
The measurement unit 22 is a measurement unit for acquiring position information of the subject, and specifically, a visible light camera that captures the surface of the subject, an infrared camera, a distance sensor that measures the shape of the subject, and the like. is there. When a camera is used for the measurement unit 22, the frame rate and resolution need only be such that a change in the position of the subject that affects the measurement can be detected. The measurement unit 22 is position information acquisition means in the present invention.
Further, the measurement unit 22 may be a plurality of visible light cameras, or may be one or more sensors that can measure the distance to the subject. Also, any infrared camera capable of measuring the blood vessel shape on the surface of the subject may be used as long as it can capture the movement or deformation of the subject.
In the first embodiment, a visible light camera capable of capturing the entire measurement target region of the subject is used as the measurement unit 22.

<< Route setting unit 23 >>
The path setting unit 23 is a unit that generates a moving path (scanning path) of the acoustic wave probe 17 at the time of measurement and controls the movement of the acoustic wave probe 17 through the scanning unit 18. Further, it is a means for detecting the deviation of the subject generated during scanning based on the subject image obtained by the measuring unit 22 and regenerating the scanning path. The route setting unit 23 is route setting means and route change means in the present invention.
Here, the displacement of the subject will be described. In photoacoustic measurement, an acoustic wave generation source is estimated by receiving an acoustic wave generated in a subject with a probe. That is, if the subject moves or deforms during the photoacoustic measurement, the positional relationship with respect to the probe is shifted, so that an image is generated based on erroneous information.
The path setting unit 23 detects or shifts the subject that affects such measurement (hereinafter, simply referred to as “position shift”), and recovers or prevents the lack of information by changing the scanning path. The positional deviation includes parallel movement, expansion / contraction, rotation, distortion, etc. of the subject in the measurement target region. The detection target may be any movement as long as the movement of the subject affects the measurement.
The path setting unit 23 acquires a plurality of subject images via the measurement unit 22 and detects that the subject has been misaligned using each of the images. A specific method will be described later.

Note that the scanning path to be set at the start of measurement may be designated by the operator, or may be automatically set by the path setting unit 23 based on the obtained subject image.
Further, the signal processing unit 19, the data processing unit 20, and the path setting unit 23 may be a computer having a CPU, a main storage device, and an auxiliary storage device, or a hardware such as a microcomputer or a specially designed FPGA. It may be wear.

・・・式（１） <Position detection method>
Next, a method in which the path setting unit 23 detects the displacement of the subject will be described. In this example, a target region (region of interest) for detecting a displacement is determined from the subject image, and the displacement in the region is detected. The region of interest may be designated in advance by the operator, or may be automatically set by the apparatus.
The position shift is detected by comparing the template image with the subject image periodically acquired during the measurement. First, a subject image is acquired before the measurement is started, and the image is temporarily stored as a template image. Then, after starting the measurement, a subject image is acquired at regular intervals, and the template image and the subject image in each frame are matched. More specifically, a normalized cross-correlation (ZNCC) as shown in Equation 1 is calculated to calculate the amount of change in the position of the subject.
In this embodiment, the calculation based on the normalized cross-correlation is performed. However, the calculation may be performed by another method as long as it indicates a change in the position of the subject. For example, any method such as SSD (Sum of Squared Difference) or SAD (Sum of Absolute Difference) may be used as long as it can understand the change in the position of the subject. In this example, the entire subject image is set as the region of interest. However, when the region of interest is designated, the region of interest may be cut out from each image for calculation.

... Formula (1)

Here, M and N are the numbers of pixels in the X and Y directions in the XY coordinate system of each image. I (i, j) is a luminance value in the region of interest of the subject image being measured, and I _avg is an average value of luminance in the region of interest. T (i, j) is a luminance value in the region of interest of the template image, and _Tavg is an average value of luminance in the region of interest.
Using Equation 1, the similarity R between the region of interest of the template image and the region of interest of the subject image can be obtained. Further, by performing matching while shifting the coordinates and acquiring the shift amount with the highest similarity, the shift widths in the X direction and the Y direction can be acquired. The deviation width is the amount of movement of the subject that occurs after the start of measurement.

  The path setting unit 23 acquires the deviation widths in the X direction and the Y direction as described above, and determines that the positional deviation has occurred in the subject based on the deviation widths. Details of the determination method will be described later.

<Scanning path change method>
Next, a method for changing the scanning path when the path setting unit 23 detects a displacement of the subject will be described. As a method of changing the scanning path, it is conceivable to change a part of the path or to change the entire path.
The description will be given with reference to FIG. Here, before the measurement is performed on the subject 15, the operator sets the measurement target region 24 that is the target region to be scanned, and the scanning path 25 is automatically generated for the measurement target region 24. To do. The generated scanning path is shown in FIG. Scanning is performed by repeating main scanning for acquiring photoacoustic data while moving the acoustic probe 17 in the X-axis direction and sub-scanning for moving the acoustic probe 17 by a certain distance in the Y-axis direction. An area scanned by main scanning is called a scanning stripe. In FIGS. 2B to 2D, the notation of the X axis and the Y axis is omitted.

  In the example of FIG. 2A, an example in which there are three scanning stripes has been shown. However, any number of scanning stripes may be used as long as the target region can be scanned. Further, the order of scanning the scanning stripes may be arbitrary. Further, the scanning stripes may be partially overlapped, or the same stripe may be scanned multiple times by the acoustic wave probe. By doing in this way, the S / N ratio of the acquired signal can be improved.

Here, it is assumed that when the acoustic probe has reached the position indicated by reference numeral 26 in FIG. Here, it is assumed that the subject has moved parallel to the lower right. In this case, if measurement is continued as it is, photoacoustic measurement is performed with the coordinates shifted, and an inaccurate image is generated. The following three methods can be considered as methods for preventing this.
The first method is a method of continuing the measurement by shifting the acoustic probe by the amount of movement of the subject. That is, the scanning path is moved following the movement of the subject, and the acoustic wave probe is moved on the new scanning path to continue scanning. In the example of FIG. 2B, at the time when the displacement of the subject is detected, the unscanned path is discarded from the scan path 25, and the scan path 28A is generated by shifting the unscanned path to the lower right. To do. The acoustic wave probe moves onto a new scanning path 28A and continues scanning. A reference numeral 15A indicated by a dotted line represents the position of the subject after movement. Reference numeral 27A indicated by a dotted line is a new scanning stripe.

As in the first method, the second method shifts the scanning path by the amount of movement of the subject. However, the acoustic wave probe is moved backward to a position that is not affected by the positional deviation, and scanning is performed again. Is the method. In the first method, since the acoustic wave probe is moved onto a new scanning path at the time when a positional deviation is detected, there is a possibility that data will not be continuous at that location. In order to avoid this, in the second method, the acoustic wave probe is moved backward to perform scanning again.
In the example of FIG. 2C, a new scanning path 28B is generated as in the first method. However, since the probe needs to be retracted, the already scanned path is also subject to change. In this example, the entire scanning path 25 is replaced with the scanning path 28B, the acoustic probe is moved to the head (scanning start point) of the scanning path 28B, and scanning is performed again. Reference numeral 27B is a new scanning stripe.
In this example, the entire scanning path 25 is the object to be changed, and the acoustic wave probe is retracted to the head of the scanning path 28B. However, for example, only the part after the head of the second stripe in the scanning path 25 is used. It may be changed. The scanning path may be changed within a range in which the acoustic probe can be moved back to a position where it is not affected by the displacement of the subject.

The third method is a method for re-generating a scanning path when a positional deviation occurs. In the first and second methods, the scanning path is shifted by an amount corresponding to the shift width, but in the third method, a new scanning path is generated again, and scanning is performed from the beginning using the newly set scanning path. I do. A new scanning path is automatically determined based on the measurement target region.
In the example of FIG. 2D, it is assumed that the area indicated by reference numeral 29 is a new measurement target area after the occurrence of the positional deviation. At the time when the positional deviation is detected, the scanning path 25 is discarded, a new scanning path 30 covering the measurement target region 29 is generated, and scanning is performed again. The new measurement target area 29 may be reset manually or may be reset automatically.

<Process flowchart>
Processing performed by the photoacoustic measurement apparatus according to the present embodiment will be described with reference to FIG.
First, the operator inputs a threshold value of the displacement width of the subject, that is, an allowable maximum value of the movement amount in the number of pixels (S1). The threshold value is preferably input from the input / output unit 21, but the threshold value may be stored in advance as a predetermined value in the apparatus, or the apparatus may automatically calculate it.

Next, a living body (for example, a breast) as a subject is inserted into the photoacoustic measurement apparatus. At this time, the measurement unit 22 (visible light camera) captures the images before and after inserting the subject, and acquires the difference between the two images (S2). The image acquired here is a template image for comparison. In the following description, the subject image is a difference between an image captured with the subject inserted and an image captured before the subject is inserted (that is, an image representing only the subject). Suppose that
Next, the path setting unit 23 determines a scanning path (S3). The scanning path is a path that can scan the entire measurement target region. The measurement target region may be the entire region where scanning is possible or only the region where the subject exists. In the present embodiment, the measurement target region is divided into stripes, and a path for scanning all the stripes is automatically generated. However, the operator may manually specify the scan path.
When step S3 is completed, photoacoustic measurement is started. First, the measurement unit 22 acquires a subject image, and the path setting unit 23 detects a positional deviation of the subject (S4). Here, as described above, the deviation width (that is, the number of moved pixels) between the subject image acquired before the start of measurement and the subject image captured multiple times at regular intervals during the measurement is acquired and set in advance. Comparison with the threshold value. As a result, when the deviation width exceeds the threshold value, it is determined that the subject is displaced.
In addition to this, every time the subject image is acquired, the deviation width from the start of measurement is integrated, and when the accumulated deviation width exceeds the threshold value, it is determined that the subject position deviation has occurred. Also good.

Step S5 is a step of determining whether to change the scanning path based on the detection result of the displacement of the subject. As a result of executing Step S4, when the deviation width is within the threshold value, the scanning path is not changed, pulse light is generated from the light source 11, and the subject is irradiated with the pulse light through the optical system 13 (S6).
Then, the acoustic wave generated in the subject due to the pulsed light is acquired by the acoustic wave probe 17 (S7). When the predetermined number of pulse lights are emitted and the acquisition of the acoustic wave is completed, it is determined whether all the measurements are completed (S8), and if completed, the process is terminated. If it is not completed, the process returns to step S4, and the acquisition of the subject image is executed again.
As a result of executing step S5, if the deviation width exceeds the threshold value, the process proceeds to step S9, where the scanning path is changed and the acoustic wave probe is moved.

Step S9 is a step of notifying the operator that the positional deviation has occurred through the input / output unit 21 and changing the scanning path.
When resetting the scanning path, the scanning path may be shifted by the amount of deviation generated in the subject, or a new scanning path may be generated. When a new scanning path is generated, the acoustic wave probe is moved onto the new scanning path. In this case, scanning may be resumed immediately, or scanning may be resumed after the acoustic wave probe has been retracted by an amount that can cover the deviation. Further, the scanning may be performed again from the beginning. In step S9, these instructions are received from the operator, and the acoustic wave probe is moved.

FIG. 4 shows an example of a screen for notifying the operator that the subject has been displaced. In the present embodiment, the input / output unit 21 is a touch panel display, and FIG. 4 is an example of a screen output by the input / output unit 21. In FIG. 4, reference numeral 31 is a graphic that notifies the subject that a positional shift has occurred. Reference numeral 32 denotes an area for displaying detailed information on positional deviation. Reference numeral 33 denotes an area illustrating a change in the position of the subject. Reference numeral 34 denotes an area for displaying options.
The screen of FIG. 4 is an example, and the screen presented to the operator may be configured in any manner as long as it can be notified that the position of the subject has changed. For example, the position change amount and the change vector may be displayed as numerical values, or may be displayed superimposed on the subject image. Further, the position change amount of the subject may be displayed as a length (millimeter), or may be displayed as a change voxel value or a vector of the change amount. Further, when the number of change pixels in the Z direction can be detected, it may be displayed together. Any value that can be handled by the device may be displayed.

Further, the scanning path before and after the change may be displayed graphically. For example, the subject image may be displayed on the screen, and the scan path before the change and the scan path after the change may be superimposed and displayed in different colors and styles. The style is a line thickness, a solid line, a dotted line, or the like, but any display may be used as long as it can express how the scanning path has changed.
The scanning path is preferably changed automatically by the apparatus, but options may be displayed on the screen to allow the operator to select subsequent processing. For example, in the example of FIG. 4, “redo measurement”, “continue measurement by causing the probe to follow the movement of the subject”, and “re-measure by newly generating a scanning path that follows the movement of the subject”. Four options for “measurement interruption” are presented. Of course, any other option may be presented as long as the method can be realized in the apparatus.

  FIG. 5 is a diagram illustrating the relationship between the operation timing of the measurement unit 22, the path setting unit 23, and the scanning unit 18 and the laser beam irradiation timing. The measurement unit 22 acquires the subject image and transmits it to the path setting unit 23. Then, when the path setting unit 23 compares the template image and the acquired subject image and determines that no positional deviation has occurred, the path setting unit 23 performs laser light irradiation while scanning the acoustic wave probe. When it is determined that a positional deviation has occurred, the scanning path is changed and the acoustic wave probe is moved.

  According to the first embodiment, in the photoacoustic measurement apparatus, it is possible to detect that the position of the subject under measurement has changed and change the scanning path. Thereby, it is possible to prevent the measurement data from being deteriorated due to the change in the position of the subject and improve the accuracy.

  In the present embodiment, the positional deviation of the subject is detected by obtaining a normalized cross-correlation between the template image and the subject image acquired at regular intervals, but other methods may be used. . For example, contour extraction may be performed on the subject image in each frame, and the shift width may be calculated by matching the contours to detect the positional shift.

  Alternatively, a blood vessel image obtained by using an infrared camera may be used as a template image, and a position shift of the subject may be detected by calculating a normalized cross-correlation between frames. Further, the displacement of the subject may be detected by comparing the center of gravity of the template image, or the template image is cut out using the region of interest set by the operator and matched with the subject image. You may make it detect the position shift of a test substance.

(Second embodiment)
In the first embodiment, the deviation width between the template image acquired before the start of photoacoustic measurement and the subject image acquired during the measurement is acquired. That is, the displacement of the subject is expressed by one vector. On the other hand, the second embodiment is an embodiment in which feature points on the surface of the subject are extracted and the amount of displacement is determined for each feature point, and the occurrence of misalignment is comprehensively determined.

The configuration of the ultrasonic diagnostic apparatus according to the second embodiment is the same as that of the first embodiment, but the measurement unit 22 is not a normal camera but a stereo camera that can acquire a distance. This is different from the first embodiment.
In addition, the path setting unit 23 according to the second embodiment does not perform pattern matching between captured images, but extracts feature points from each image, and detects the movement of the extracted feature points to detect positional deviation. It differs from the first embodiment in that occurrence is determined.
Known techniques can be used to extract feature points. For example, feature points may be extracted from edge information obtained by filtering the image, or anatomical features in the image (eg, nipple in breast, blood vessel shadow, melanin pigmentation, breast contour, wrinkles) Feature points may be extracted from The feature point extraction method is not particularly limited as long as the change in the position of the feature point can be traced between frames.
Further, these pieces of information may be integrated between frames for a certain period of time, and feature points may be extracted from information obtained by averaging after integration. In addition, when obtaining feature points from each photographed frame, only a part of the image or all of the image may be used. Further, the operator may set a region of interest through the input / output unit 21 and track feature points in the region of interest.
The feature point is a minute region for tracking the movement of the subject and does not necessarily have to correspond to one pixel.

A process flowchart of the photoacoustic measurement apparatus according to the second embodiment will be described focusing on differences from the first embodiment.
Similar to the first embodiment, step S1 is a step of setting a threshold value for the positional deviation of the subject, that is, an allowable maximum value of the deviation width. In the second embodiment, the amount of movement of the whole subject is set. Instead of the corresponding value, the allowable maximum value of the deformation amount is set as the threshold value. Specifically, “the maximum allowable deviation value of the feature point having the largest displacement amount” is set as the threshold value. The allowable deviation width may be input as the number of pixels, or may be input as a voxel converted value, a distance converted value, or the like.
The threshold value may be set automatically. For example, the displacement information (for example, motion vector value and its absolute value) corresponding to each feature point is acquired after the subject is inserted into the apparatus and the measurement preparation is completed and before the measurement is started. May be used as a threshold value. These calculations may be performed by the measurement unit 22 or the route setting unit 23.

In step S2, instead of acquiring a template image, the coordinates of feature points in a state before the start of measurement are acquired. Specifically, the state before the start of measurement of the subject inserted in the apparatus is photographed with a stereo camera. Then, a plurality of corresponding feature points are extracted from the obtained set of images, and a set of coordinates of the obtained plurality of feature points is acquired. The feature points are preferably extracted from the subject portion of the subject image. The coordinates of the feature points are expressed in a stereo coordinate system with the midpoint of the stereo camera as the origin, but any coordinate system can be used as long as each point can be set.
The scanning path generation process performed in step S3 is the same as in the first embodiment.

  In step S4, a plurality of feature points acquired in step S2 are tracked, and a motion vector connecting the corresponding feature points in the original frame and a frame after a certain time is calculated. The feature point may be obtained from one frame, or the center of gravity of the corresponding feature point in a plurality of frames may be used.

  The determination (S5) of whether or not the deviation of the subject is within the threshold is performed using the motion vector calculated for each feature point. In the present embodiment, the feature point having the longest moving distance is specified and the moving distance is compared with the threshold value. However, the determination may be performed using another method. For example, the average value of the movement distances of all feature points between two frames may be obtained and the average value may be compared with a threshold value, or the integrated value from the start of measurement of the movement distances of all feature points may be obtained. It may be compared with a threshold value. Any method can be used to determine whether or not a positional shift has occurred.

If it is determined that a positional deviation has occurred, RANSAC (Random Sample Consensus
) Method can be used to further estimate whether the subject is moving in parallel or deformed. In the RANSAC method, n feature points are extracted at random, and a transformation matrix is obtained between corresponding feature points. Then, the transformation matrix is applied to other feature points extracted at random.
As a result, when a significant number of transformation matrices that minimize the residual sum of squares are obtained, it can be determined that a shift due to parallel movement has occurred. On the other hand, when many cannot be obtained, it can be determined that rotation or deformation has occurred. Of course, the present invention is not limited to the above method, and other methods may be used.

The processes in steps S6 to S8 are the same as in the first embodiment.
In step S9, as in the first embodiment, the operator is notified by screen display, and the scanning path is changed. When the parallel movement is detected, the scanning path may be shifted by the amount of the deviation generated in the subject, or a new scanning path may be generated, as in the first embodiment. When rotational movement or deformation is detected, it is preferable to generate a new scanning path and scan again from the beginning. However, if the position shift can be covered without scanning from the beginning, scanning is performed from the middle of the new scanning path. May be resumed. That is, when only a part of the subject is deformed, only the scanning path related to the deformed part may be regenerated.

  Also in the second embodiment, detailed information about misalignment is displayed through the input / output unit 21 as in the first embodiment, but in the second embodiment, the motion vector of the feature point is acquired. Therefore, information regarding the deformation of the subject may be presented to the operator. For example, a value representing the most frequent motion vector amount may be displayed in the region 32, or a value representing the maximum motion vector amount may be displayed.

Further, a graphic representing the motion vector of each feature point may be generated and displayed superimposed on the subject image. Thereby, it is possible to notify the operator of a minute position change of the subject. FIG. 6 is an example of a screen when a display representing a motion vector of a feature point is generated and superimposed on the subject image 33. Here, feature points having similar motion vectors are clustered and displayed. Thereby, it is possible to easily show the operator how the subject has been deformed.
Note that the motion vector may be indicated by a method other than the exemplified method. For example, similar motion vectors may be displayed in similar colors, or the colors of lines to be grouped may be changed. In addition, the motion vector may be represented using other than the arrows, or only the region where the motion vector is large may be enlarged and displayed without displaying the entire subject.

  As described above, in the second embodiment, by extracting feature points and acquiring motion vectors, it is possible to more accurately detect a change in the shape of the subject, and as a result, the accuracy of measurement data is further improved. Can be improved.

(Modification)
The description of each embodiment is an exemplification for explaining the present invention, and the present invention can be implemented with appropriate modifications or combinations without departing from the spirit of the invention. The present invention can also be implemented as a method for controlling a subject information acquisition apparatus including at least a part of the above processing. The above processes and means can be freely combined and implemented as long as no technical contradiction occurs.

For example, in the description of the embodiment, an example in which the subject image is pattern-matched and an example in which the coordinates of the feature points are compared are given, but other information is used as information for detecting the positional deviation of the subject. May be. For example, the background portion of the subject, inter-frame difference information, inter-frame difference information with a frame after a certain period of time, histogram information of the subject portion, subject texture information, optical flow information by gradient method or block matching method, etc. It may be.
In addition, the mobile tracking method by the Moravec operator, KLT (Kanade-Lucas-Tomasi)
) Method, a method based on association of local correlations, or information based on a method considering global consistency. Alternatively, it may be determined that a positional deviation has occurred when the subject protrudes from a preset region. Any information may be used to determine the occurrence of positional deviation as long as the information indicates the change in the position and outer shape of the subject.

In addition to the number of displaced pixels from the initial state as described in the present embodiment, the value set as the threshold and the value presented to the operator may be as follows. For example, the displacement amount of each feature point between frames, the integrated value of the displacement amount of the feature point within a certain time, the change direction of the feature point in the space, the voxel conversion value of the acquired change data, the millimeter-centimeter conversion value Etc.
In addition, the result of classifying the amount of displacement into large, medium, and small, the type of displacement (for example, “translation” and “partial distortion”), the displacement value from the initial state on each axis in the coordinate system It may be. Any value may be used as long as it can express what the positional deviation is.

  In each embodiment, the photoacoustic measurement device has been described as an example. However, the present invention includes an acoustic wave transmission unit that transmits ultrasonic waves to the subject, and receives the ultrasonic waves reflected in the subject. By doing so, you may apply to the ultrasonic measuring device which visualizes the information relevant to the acoustic characteristic in a subject. The present invention can be applied to any apparatus that acquires information in a subject by receiving an acoustic wave coming from within the subject.

  17 ... acoustic wave probe, 18 ... scanning unit, 22 ... measurement unit, 23 ... path setting unit

Claims (18)

An object information acquisition apparatus for acquiring information in the subject by receiving and analyzing an acoustic wave coming from within the subject,
Scanning means for scanning the subject with a probe that receives acoustic waves;
Path setting means for determining a first path which is a scanning path of the probe;
Position information acquisition means for acquiring position information which is information related to the position of the subject surface relative to the own apparatus ;
Have
The path setting means determines whether to change the scanning path to a second path different from the first path based on the position information, and when changing the scanning path, the first path The subject information acquisition apparatus is characterized in that the path and the second path are presented to the user . The path setting means acquires a movement amount of the subject based on the position information, and changes the scanning path when the movement amount exceeds a predetermined value. 2. The object information acquiring apparatus according to 1. The object information acquiring apparatus according to claim 2, wherein the second path is a path obtained by translating the first path following the movement of the subject. When changing the scanning path, the path setting unit changes the path including the already scanned path from the first path to the second path,
The object information acquiring apparatus according to claim 2, wherein the scanning unit performs scanning again using the second path. The path setting means, when changing a scanning path, changes an unscanned path from the first path to a second path,
The object information acquiring apparatus according to claim 3, wherein the scanning unit continues scanning using the second path. The path setting unit acquires a deformation amount of the subject based on the position information, and changes the scanning path when the deformation amount exceeds a predetermined value. The subject information acquisition apparatus according to any one of? The path setting means, when changing a scanning path, changes a scanning path related to a deformed portion of the subject in the first path to a second path based on the position information. The object information acquiring apparatus according to claim 6, wherein: A subject information acquisition apparatus for acquiring information in the subject by irradiating the subject with light and receiving and analyzing an acoustic wave generated in the subject due to the light,
A light irradiation unit for irradiating the subject with light; and
Image acquisition means for imaging information related to optical characteristics in the subject by analyzing the acoustic wave received by the probe;
The object information acquiring apparatus according to claim 1, further comprising: An object information acquisition apparatus for acquiring information in the subject by transmitting an acoustic wave in the subject and receiving and analyzing the acoustic wave reflected in the subject,
Acoustic wave transmitting means for transmitting an acoustic wave into the subject using the probe;
Image acquisition means for imaging information related to acoustic characteristics in the subject by analyzing the acoustic wave received by the probe;
The object information acquiring apparatus according to claim 1, further comprising: A subject having an acoustic wave receiving probe and a scanning mechanism for moving the probe, and receiving and analyzing an acoustic wave arriving from within the subject to acquire information in the subject A method for controlling an information acquisition device, comprising:
A scanning step of determining a first path which is a scanning path of the probe, and scanning the subject using the probe;
A position information acquisition step of acquiring position information which is information related to the position of the object surface with respect to the object information acquisition apparatus ;
Including
The scanning step determines whether or not to change the scanning path to a second path different from the first path based on the position information, and when changing the scanning path, the first path A method for controlling a subject information acquiring apparatus, wherein a route and a second route are presented to a user . The scanning path is changed when the movement amount of the subject is acquired based on the position information and the movement amount exceeds a predetermined value in the scanning step. The control method of the object information acquisition apparatus of description. The method for controlling a subject information acquiring apparatus according to claim 11, wherein the second route is a route obtained by translating the first route following the movement of the subject. In the scanning step, when changing the scanning path, the path including the already scanned path in the first path is changed to the second path, and scanning is performed again using the second path. The method for controlling an object information acquiring apparatus according to claim 11 or 12, wherein: In the scanning step, when a scanning path is changed, an unscanned path among the first paths is changed to a second path, and scanning is continued using the second path. The method for controlling the subject information acquiring apparatus according to claim 12. The scanning step is characterized in that, in the scanning step, a deformation amount of the subject is acquired based on the position information, and the scanning path is changed when the deformation amount exceeds a predetermined value. The control method of the subject information acquisition apparatus according to any one of claims 14 to 14. In the scanning step, when changing the scanning path, based on the position information, the scanning path related to the deformed portion of the subject in the first path is changed to the second path. The method for controlling an object information acquiring apparatus according to claim 15, wherein the object information acquiring apparatus is a control method. Object information that includes a light irradiation unit that irradiates light in the subject, and acquires information in the subject by receiving and analyzing an acoustic wave generated in the subject due to the light An acquisition device control method comprising:
A light irradiation step for generating light from the light irradiation unit;
An image acquisition step of imaging information related to optical characteristics in the subject by analyzing the acoustic wave received by the probe;
The method for controlling an object information acquiring apparatus according to any one of claims 10 to 16, further comprising: A control method for an object information acquisition apparatus that acquires information in the subject by transmitting an acoustic wave from the probe into the subject and receiving and analyzing the acoustic wave reflected in the subject. There,
An acoustic wave transmitting step for generating an acoustic wave from the probe;
An image acquisition step of imaging information related to acoustic characteristics in the subject by analyzing the acoustic wave received by the probe;
The method for controlling an object information acquiring apparatus according to any one of claims 10 to 16, further comprising:

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