JP4909132B2 - Optical tomography equipment - Google Patents

Description

  The present invention provides a tomographic image (distribution of an ultrasonic velocity change distribution inside an object by measuring a change in sound velocity inside the object before and after irradiation when the inside of the object such as a living body is irradiated with light. The present invention relates to an optical tomography apparatus for acquiring a tomographic image.

  Ultrasound diagnostic devices used in the medical field transmit ultrasonic signals (ultrasound beams) oscillated from ultrasonic transducers into the living body and receive and detect ultrasonic echo signals from the living body. This is tomographic image. Some of these ultrasonic diagnostic apparatuses, such as the so-called B mode and M mode, image the intensity of the received ultrasonic echo signal by luminance modulation, etc. Various ideas have been made, such as calculation of blood flow and development of other application software. Recently, an apparatus for displaying a tomographic image in real time by adopting electronic scanning by an array type probe or the like has been widely used, and it exerts great power for noninvasive diagnosis in the body.

  As one of the new diagnostic methods using such an ultrasonic diagnostic apparatus, a mechanism for irradiating light to the measurement area is provided, and the received signals (super It has been proposed to obtain a tomographic image (optical tomographic image) by obtaining the distribution of the ultrasonic velocity change in the measurement region due to light irradiation from the change in the acoustic echo signal) (see Patent Document 1).

  This optical tomographic image represents a tomographic image of a temperature change in the measurement region due to absorption of the irradiated light. In other words, when light is irradiated into the living body, if the light absorption characteristics are different for each part in the living body, a temperature distribution is generated in the living body according to the light absorption characteristic of each part. Since the sound velocity of the ultrasonic wave propagating in the living body changes depending on the temperature, by calculating the sound velocity change of the ultrasonic echo signal before and after the light irradiation for each part and tomographic imaging, It can be displayed as a tomographic image of ultrasonic velocity change distribution, temperature change distribution, or light absorption distribution. Therefore, in the following description, the tomographic image related to the ultrasonic velocity change distribution includes tomographic images of the ultrasonic velocity change distribution, the temperature change distribution, and the light absorption distribution.

FIG. 6 is a diagram showing a device configuration for displaying an optical tomographic image described in Patent Document 1. As shown in FIG. The subject 100 is irradiated with light by a light source 40 composed of an infrared laser. On the emission side of the light source 40, a shutter 42 for intermittently irradiating the subject 100 with light is provided. The shutter 42 is controlled to be opened and closed by the light absorption analysis unit 60.
Transmission / reception of ultrasonic waves is performed by the linear array probe 50. The linear array probe 50 is excited by a drive signal from the transmission / reception unit 52 to generate an ultrasonic signal, and returns a reception signal (ultrasonic echo signal) from the inside of the subject with respect to the ultrasonic signal to the transmission / reception unit 52. The scanning control unit 54 scans a plurality of ultrasonic signals by sequentially switching transducers that transmit and receive waves.
The reception signal of the linear array probe 50 is input to the B-mode signal processing circuit 56 and the light absorption analysis unit 60. The B-mode signal processing circuit 56 performs a well-known B-mode tomographic image forming process on the received signal to form a tomographic image in the beam scanning range, and writes it in a DSC (digital scan converter) 58. Further, the light absorption analysis unit 60 analyzes the received signal and forms an image of the light absorption distribution (that is, the ultrasonic velocity change distribution) in the beam scanning range. This light absorption distribution is obtained by calculating the phase change of the received signal before and after the light irradiation.

  A control procedure for obtaining a light absorption distribution image by the above apparatus will be described below. First, the light absorption analysis unit 60 closes the shutter 42 and stores the reception signal (the reception signal for the B-mode image) of the probe 50 in a state where the temperature of the subject 100 is not increased due to light absorption for one scan. . At this time, the light absorption analysis unit 60 distinguishes and stores the received signal for each scanning line (beam) based on the scanning information from the scanning control unit 54. Next, the light absorption analysis unit 60 opens the shutter 42 to irradiate the subject 100 with light, and a time during which a detectable temperature rise occurs in each part of the subject (this is obtained and set in advance by experiments). After the elapse of time, the reception signal of the probe 50 is again acquired for one scan. Then, the light absorption analysis unit 60 compares the received signals before and after the light absorption for each scanning line, and analyzes the change in the sound velocity of the ultrasonic wave from the phase change. The analysis result is written in the DSC 58. The DSC 58 displays a light absorption distribution image (that is, an ultrasonic velocity change distribution) that is an analysis result of the light absorption analysis unit 60 on the display device 62. At this time, the light absorption distribution image may be displayed in color by being superimposed on the B-mode image. For example, since the light absorption distribution corresponds to the temperature rise of each part of the subject, a warm color is used so that the higher the absorption rate (the greater the phase difference before and after irradiation), the higher the lightness. If an image such as this is taken, an image that can be easily grasped intuitively by a diagnostician can be obtained.

In this way, different from the ultrasonic echo signal intensity (reflection intensity) (B-mode image), it is possible to display a distribution of different physical quantities called a distribution of light absorption characteristics (that is, an ultrasonic velocity change distribution). A multifaceted understanding of the organization is possible.
Note that a contrast agent is also injected by the contrast agent injector 70. That is, after injecting a material that has a high light absorption rate as a contrast agent and that is easily taken up specifically by a target tissue (for example, a lesion 110 such as a cancer cell) in a subject, Since the temperature rise due to light absorption of the tissue of interest is greater than other portions, a tomographic image highlighting the tissue of interest can be formed.
JP 2001-145628 A

FIG. 7 is an example of a B-mode image created based on the ultrasonic echo signal measured by the array type probe. This B-mode image is an image obtained by luminance-modulating 345 lines of ultrasonic echo signals. FIG. 8 shows an example of an ultrasonic echo signal for one line of the 345 lines. Ultrasound is reflected at the interface between tissues with different acoustic impedances. Therefore, as a reception signal (ultrasonic echo signal) when a pulsed ultrasonic signal is transmitted into the living body, echoes reflected at the boundary between the tissues appear as reflected pulses in the order closer to the probe.
The B-mode image is obtained by modulating the amplitude of the reflected pulse as luminance information, and is displayed in black as the amplitude increases. The reception signals of all 345 lines are displayed and imaged, whereby a B-mode image as shown in FIG. 7 is obtained.

  Separately from this B-mode image, when an optical tomographic image showing the above-described light absorption distribution (ultrasonic velocity change distribution) is to be displayed, ultrasonic echo signals of each line before and after the light irradiation are acquired, Signal analysis before and after light irradiation is performed for each line.

  The signal analysis at this time will be described. As shown in FIG. 9, for each line of the ultrasonic echo signal, the waveform on the line is divided into equal intervals for about one wavelength, and the waveform before and after light irradiation in each interval. The cross correlation is calculated and the difference is detected. Based on the detected difference, the change in the sound speed of the ultrasonic wave in each section is calculated, and the same change in the sound speed is calculated for all lines. The calculated distribution of sound speed changes is displayed as an ultrasonic speed change image or a temperature distribution image (or a light absorption distribution image).

However, when the waveform data on one line is divided into equal intervals and the cross-correlation of each interval is calculated, a large error may occur in the calculated sound speed change value in some intervals.
In general, in a section including a large-amplitude ultrasonic echo signal (section in which the B-mode image is black), the signal and the artifact can be distinguished. Therefore, if the cross-correlation is calculated, a difference detection with a small error can be performed. However, in a section that includes only a signal having a small amplitude (a section in which the B-mode image is white), the S / N ratio is small, so that the signal and the artifact are difficult to be distinguished from each other. It is easy to include.

  FIG. 5 shows a B-mode image and a sound velocity change distribution image obtained by creating a biological pseudo sample including a region where an ultrasonic echo signal with a small amplitude that makes it difficult to distinguish between a signal and an artifact is obtained. FIG. This pseudo sample is prepared using agar, for example. FIG. 5A is a B-mode image of a biological pseudo sample having an ultrasonic echo signal area with a small amplitude at the center. The central part of the sample is made of a material that does not absorb the irradiation light. FIG. 5B is a diagram in which the distribution of the change in ultrasonic velocity before and after light irradiation is calculated and imaged. In the central part where the ultrasound echo signal with a small amplitude (the part where the B-mode image is white) cannot be distinguished from the signal and the artifact, the cross-correlation cannot be calculated accurately, resulting in an error. In the center of the image, a ghost image is generated as if there was a change in the sound speed despite no change in the ultrasonic velocity.

  In this way, when an ultrasonic velocity change distribution image is created by adopting a conventional signal processing method of dividing the ultrasonic echo signal of each line into equal intervals and calculating the cross-correlation of each interval, There has been a problem that an image in which an erroneous change in ultrasonic velocity appears is displayed in a region where the amplitude of the ultrasonic echo signal is small.

  Accordingly, the present invention provides an optical tomography apparatus capable of displaying an accurate ultrasonic velocity change image (temperature change image or light absorption image) by devising signal processing for an ultrasonic echo signal. Objective.

  In addition, depending on the measurement site in the living body and the state of the measurement site (for example, a state in which a contrast medium that enhances the light absorption rate is injected), when light is irradiated into the living body, The light absorption rate may be different at each part in the living body. Therefore, even when light is irradiated from a light source, a temperature change may be efficiently generated depending on a part in the living body, or a sufficient temperature change may not be generated.

  Therefore, the present invention can be adapted to the situation depending on which part in the living body the measurement part is in or the state of the measurement part (for example, a state in which a contrast medium that increases the light absorption rate is injected). Accordingly, another object is to provide an optical tomography apparatus that can acquire an appropriate ultrasonic velocity change image.

  An optical tomography apparatus of the present invention made to solve the above-described problems includes a light source that irradiates light to a measurement region, an ultrasonic signal that is transmitted to the measurement region, and an ultrasonic echo signal that is received from the measurement region. Based on the ultrasonic transmission / reception mechanism to be used, the non-irradiation ultrasonic echo signal received from the measurement region when light is not irradiated, and the post-irradiation ultrasonic echo signal received from the measurement region after light irradiation An ultrasonic tomography device comprising an ultrasonic velocity analysis unit that obtains ultrasonic velocity changes with respect to light irradiation to a measurement region and displays them as a tomographic image relating to the distribution of ultrasonic velocity changes, and an ultrasonic echo signal when not irradiated And an envelope data extraction unit for extracting the envelope of the signal waveform of each of the ultrasonic echo signals after irradiation and the non-irradiation ultrasonic echo signal and the post-irradiation ultrasonic echo based on the extracted envelope data. -An interest signal interval extraction unit that extracts an interest signal interval in each signal waveform of the signal, and the ultrasonic velocity analysis unit includes a non-irradiation ultrasonic echo signal and a post-light irradiation ultrasonic echo signal within the interest signal interval. An ultrasonic velocity change is obtained based on the signal.

  According to the present invention, when determining the ultrasonic velocity change in the measurement region based on the non-irradiation ultrasonic echo signal and the post-irradiation ultrasonic echo signal, the entire echo signal is divided into equal intervals and analyzed. Instead, first, envelope data of each echo signal is extracted by the envelope data extraction unit. By extracting the envelope data, the true echo signal and the artifact included in the received echo signal can be distinguished. Further, the interest signal section extraction unit extracts a section that is a true echo signal in the echo signal as the interest signal section based on the extracted envelope data. Then, the ultrasonic velocity analysis unit calculates the cross-correlation based on the signal within the signal of interest in the non-irradiation ultrasonic echo signal and the post-irradiation ultrasonic echo signal, and calculates the ultrasonic velocity change in the measurement region. To do. As a result, a change in ultrasonic velocity is obtained based only on the true echo signal that does not include artifacts, and a tomographic image is created.

  According to the present invention, an image showing an erroneous change in ultrasonic velocity is not displayed in a region where the amplitude of the ultrasonic echo signal is small, and an accurate ultrasonic velocity change image (or temperature distribution image, light absorption) is eliminated. Image) can be displayed.

(Means and effects for solving other problems)
In the above invention, the interest signal section extraction unit may detect a signal peak larger than a predetermined threshold for the envelope data, and extract a feeling signal section based on the detected signal peak.
According to this, since only a signal peak larger than a preset threshold value is extracted as an echo signal for the envelope data, artifacts can be further eliminated and an ultrasonic velocity change image without noise can be displayed.

Moreover, in the said invention, you may make it use the laser light source from which the wavelength of irradiation light is variable in the range of 700 nm-1000 nm.
Here, the “laser light source having a variable wavelength” may be a laser light source capable of continuously changing the wavelength of the output light, or a plurality of laser groups that output light of different wavelengths are prepared, It is also possible to use a laser light source that switches between any of these to emit light.
The reason why the wavelength range is 700 nm to 1000 nm is that light in this wavelength range can generally pass through the living body to the deep part, which is convenient for obtaining an ultrasonic velocity change image of the deep part of the living body. Because.
Specifically, a titanium sapphire laser (the output wavelength is variable in a wavelength range of 700 nm to 1000 nm) can be used as a laser light source capable of continuously changing the wavelength in a range of 700 nm to 1000 nm. Further, as a laser light source composed of a laser group that outputs a plurality of light beams having different wavelengths, for example, a laser light source that combines a plurality of semiconductor laser groups that emit light at 808 nm, 880 nm, 940 nm, 980 nm, or the like can be used.

According to the present invention, light having a wavelength that allows the measurement site to efficiently absorb light depending on the measurement site of the living body or the state of the measurement site (a state in which the contrast medium is injected to increase the light absorption rate of light). Since the light can be effectively absorbed, a clearer ultrasonic velocity change image can be acquired. In particular, when a contrast agent having the property of selectively increasing the light absorption rate for light of a specific wavelength is injected into the living body, laser light having a wavelength close to the specific wavelength is selected from the variable wavelengths of the laser light source. By irradiating, the light absorption at the site where the contrast agent is injected is emphasized, so that a clearer ultrasonic velocity change image can be obtained.
In addition, by using the present invention in combination with a drug delivery system in a living body, a drug carrier such as a liposome carrying a drug selects and irradiates light having a wavelength that is easy to absorb light, thereby allowing in vivo drug dragging. The distribution state of the carrier can be observed, and the timing for releasing the drug from the drug carrier can be accurately grasped.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an optical tomography apparatus according to an embodiment of the present invention.
An optical tomography apparatus 1 includes a linear array probe 2, a probe 5 including an infrared laser light source 3, a transmission / reception unit 6, a scanning control unit 7, an ultrasonic velocity analysis unit 8 (light absorption analysis unit), and envelope data extraction. A control system 11 including a unit 14, an interest signal section extraction unit 15, a B-mode signal processing unit 9, a DSC 10 (digital scan converter), and a display device 12.

  While the probe 5 is pressed against the subject 100, an ultrasonic signal is transmitted from the linear array probe 2 and infrared light is irradiated from the infrared laser light source 3. The infrared laser light source 3 is controlled to be turned on by the ultrasonic velocity analysis unit 8.

The linear array probe 2 has a plurality of transducers arranged in a straight line, and each transducer is excited by a drive signal from the transmission / reception unit 6 to generate an ultrasound signal. An ultrasonic echo signal from the inside of the subject is returned to the transmission / reception unit 6. The scanning control unit 7 scans a plurality of (for example, 345) ultrasonic signals by sequentially switching transducers that transmit and receive waves.
The reception signal (ultrasonic echo signal) of the linear array probe 2 having such a structure is input to the B-mode signal processing circuit 9 and the ultrasonic velocity analysis unit 8. The B-mode signal processing circuit 9 performs a well-known B-mode tomographic image forming process on the received signal to form a tomographic image in the beam scanning range and writes it in the DSC 10.

  On the other hand, the ultrasonic velocity analysis unit 8 analyzes the received signal (ultrasonic echo signal) and forms an image of the distribution of ultrasonic velocity changes in the beam scanning range. At that time, the envelope data extraction unit 14. Control the interest signal section extraction unit 15.

  The envelope data extraction unit 14 performs a process of executing an envelope process for extracting an envelope for each waveform of the ultrasonic echo signal after light irradiation when the received signal is not irradiated. The envelope processing calculation itself is performed using known software. FIG. 2A is an example of envelope data, which is extracted from the ultrasonic echo signal shown in FIG.

  The interest signal section extraction unit 15 performs a process of extracting an interest signal section for calculating a change in ultrasonic velocity from the entire extracted envelope data. That is, a section including a signal peak on the envelope data is extracted as a signal section of interest. At this time, a processing time may be shortened by setting a threshold value in advance, extracting only signal peaks equal to or higher than the threshold value, and removing small peaks as artifacts.

  Specifically, the process of extracting the interest signal section from the envelope data is performed as follows. As shown in FIG. 3 (a), comparison is made with respect to each data (set as M = ± 160 points in FIG. 3) within a predetermined section M centered on one maximum point j on the envelope data. When the central maximum point is the maximum value in the predetermined interval M, the predetermined interval M centering on the maximum point j is extracted as one of the interest signal intervals. If the central maximum point j ′ is not the maximum value in the predetermined section M as shown in FIG. 3B, the section M is not extracted as an interest signal section, and the next maximum point is not extracted. Move the section so that becomes a new center, and repeat the same operation. For example, in the example of FIG. 2, four sections are extracted by this method. Except for the interest signal section, it is processed as an artifact.

  Then, the ultrasonic velocity analysis unit 8 performs ultrasonic echoes at the time of non-irradiation and after light irradiation for the portion of the ultrasonic echo signal (colored portion in FIG. 2B) corresponding to each extracted interest signal section. The signal cross-correlation ΔM is calculated. This cross-correlation calculation can also be performed using known software. The ultrasonic velocity analysis unit 8 performs the same analysis on the signal sections of interest of all the 345 ultrasonic beams that have been measured, and acquires the cross correlation data ΔM. The acquired cross-correlation data ΔM represents the waveform shift amount before and after the light irradiation of the ultrasonic echo signal, and ΔM / M represents a change in the ultrasonic velocity. Then, based on the calculated ΔM / M, a tomographic image (optical tomographic image) is created and displayed on the display device 12.

Although detailed explanation is omitted, when displaying as an image of a temperature change (ΔT) rather than an image of an ultrasonic velocity change before and after the light irradiation, the temperature correction term of the following equation (1) is added accurately. It is converted into an image with the collected data.

ΔT = (4.821−0.095124T + 0.00040623T ² ) ⁻¹ · (ν · ΔM / M) (1)
Here, T is temperature (° C.), and ν is sound velocity (m / s).

Next, an example of measurement operation by the optical tomography apparatus 1 will be described with reference to the flowchart of FIG.
The probe 5 is set toward the measurement region of the subject and measurement is started. A control signal for irradiating light to the infrared laser light source 3 is sent (S11). As a result, the subject 100 is irradiated with light from the infrared laser light source 3.

Then, after a lapse of a predetermined time from the start of irradiation, the scanning control unit 7 sequentially sends a signal to the transmission / reception unit 6 to drive the linear array probe 2 to transmit a pulsed ultrasonic signal and to the subject 100. An ultrasonic echo signal which is a received signal from the receiver is received (S12). Here, the predetermined time from the start of light irradiation to the start of transmission / reception of ultrasonic waves is a time required for each part of the subject 100 to absorb sufficient light energy, and is measured in advance through experiments or the like, and the control system 11 is not shown. Set in the storage unit. The scanning control unit 7 refers to this and adjusts the transmission / reception timing.
And the waveform of the ultrasonic echo signal (reception signal) acquired in the light irradiation state is memorize | stored as an ultrasonic echo signal after light irradiation (S13).

When storage of the received waveform of the ultrasonic echo signal after light irradiation ends, a control signal for stopping light irradiation is sent (S14). Thereby, the light irradiation with respect to the subject 100 is stopped.
When the temperature of the subject 100 is sufficiently lowered after a lapse of a predetermined time from the stop of the irradiation, the scanning control unit 7 sends a signal to the transmission / reception unit 6 to drive the linear array probe 2 and transmit an ultrasonic signal. At the same time, an ultrasonic echo signal is received from the subject 100 (S15). And the waveform of the ultrasonic echo signal (reception signal) acquired in the light irradiation stop state is stored as the non-irradiation ultrasonic echo signal (S16).

  Subsequently, envelope data is extracted for the ultrasonic echo signals after the light irradiation and at the time of non-irradiation (S17). Further, a signal peak equal to or greater than a predetermined threshold is extracted on the envelope data, and an interest signal section is extracted based on the signal peak (S18). Subsequently, with respect to the ultrasonic echo signals after the light irradiation and at the time of non-irradiation, the cross-correlation between the signals in the interest signal section is calculated, and the change in the ultrasonic velocity due to the presence or absence of the light irradiation in the signal section of interest is analyzed (S19). . The distribution of the ultrasonic velocity change of the analysis result is imaged and displayed on the display device (S20).

  As described, FIG. 5A is a B-mode image for a biological pseudo sample, and FIG. 5B is a tomographic image (comparative example) acquired by signal processing according to a conventional method for the same sample. . On the other hand, FIG. 5C is a tomographic image of changes in ultrasonic velocity acquired by the signal processing method of the present invention. The ghost signal that appears in the signal processing of the conventional method does not appear in the tomographic image by the signal processing method of the present invention.

FIG. 10 is a diagram showing an example of a tomographic image taken using the optical tomography apparatus of the present invention. FIG. 10A is a photograph of chicken used as a sample, and FIG. It is a mode image. FIG. 10C is an ultrasonic velocity change image when the light irradiation time is changed.
As shown in FIG. 10 (a), this tomographic image is obtained by creating a black colored portion on a part of a chicken sample to promote light absorption and irradiating it with 809 nm infrared light. is there. At this time, the tomographic images were taken while changing the irradiation time of the infrared light to 20 seconds, 40 seconds, 60 seconds, 100 seconds, and 140 seconds.

When the irradiation time is short and the temperature in the sample hardly changes, the entire image is white. At this time, no ghost image appears. As the irradiation time becomes longer, a temperature distribution in the sample is generated, and the portion where the ultrasonic velocity change is caused by the temperature change becomes black.
Thus, in the tomographic image of the ultrasonic velocity change, the influence of the artifact can be completely removed, and the change accompanying the temperature change can be reliably imaged.

  The present invention can be used in an optical tomography apparatus that displays tomographic images of changes in a subject before and after light irradiation.

1 is a block diagram showing a configuration of an optical tomography apparatus that is an embodiment of the present invention. The figure which shows an example of an envelope. The figure explaining the example of extraction of an interest signal area. The flowchart which shows the measurement operation | movement procedure by the optical tomography apparatus which is one Embodiment of this invention. The figure which shows the example of the B mode image and ultrasonic velocity change image by a biological pseudo sample. The block diagram which shows the structure of the conventional optical tomography apparatus (sonic wave measuring device). The figure which shows an example of a B mode image. The figure which shows an example of the received waveform of an ultrasonic echo signal. The figure explaining the example of extraction of an interest signal area. The figure explaining the signal processing implemented with the conventional optical tomography apparatus. The figure which shows the example of an ultrasonic velocity change image by this invention.

Explanation of symbols

1: Optical tomography device 2: Linear array type probe 3: Infrared laser light source 5: Probe 8: Ultrasonic velocity analysis unit 12: Display device 14: Envelope data extraction unit 15: Interest signal section extraction unit

Claims (3)

From a light source that irradiates light to the measurement area, an ultrasonic transmission / reception mechanism that transmits ultrasonic signals to the measurement area and receives ultrasonic echo signals from the measurement area, and a measurement area when light is not irradiated Change in ultrasonic velocity based on the received ultrasonic echo signal during non-irradiation and the post-irradiation ultrasonic echo signal received from the measurement region after light irradiation. An optical tomography device comprising an ultrasonic velocity analysis unit for displaying as a tomographic image relating to the distribution of
An envelope data extraction unit that extracts envelopes of the signal waveforms of the non-irradiation ultrasonic echo signal and the post-light irradiation ultrasonic echo signal, and
An interest signal interval extraction unit that extracts an interest signal interval in the signal waveforms of the non-irradiation ultrasonic echo signal and the light irradiation ultrasonic echo signal based on the extracted envelope data,
An ultrasonic tomography apparatus characterized in that an ultrasonic velocity analysis unit obtains an ultrasonic velocity change based on signals within a signal section of interest of a non-irradiation ultrasonic echo signal and a post-irradiation ultrasonic echo signal. 2. The optical tomo according to claim 1, wherein the interest signal section extraction unit detects a signal peak larger than a predetermined threshold for the envelope data, and extracts the interest signal section based on the detected signal peak. Graphic equipment. 2. The optical tomography apparatus according to claim 1, wherein a laser light source whose wavelength of irradiation light is variable in a range of 700 nm to 1000 nm is used as the light source.