JP2010017375A - Ultrasonically modulated light tomography apparatus and ultrasonically modulated light tomography method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the cost of an ultrasonically modulated light tomography apparatus. <P>SOLUTION: The ultrasonically modulated light tomography apparatus has a measurement light irradiating means for irradiating a subject part with measurement light and an ultrasonic wave irradiating means for irradiating the subject part with ultrasonic waves, and acquires a tomographic image of the subject part on the basis of detection signals of ultrasonically modulated light modulated by interactions between the measurement light and the ultrasonic wave within the subject part. Tomographic information is acquired by detecting heterodyne signals due to modulation of the measurement light and the ultrasonic wave and analyzing the frequency of the heterodyne signals. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ultrasonic modulation optical tomographic imaging apparatus that acquires a tomographic image of a biological tissue based on light modulated by ultrasonic waves.

  Conventionally, various optical measurement devices are used in the field of biological measurement. In these optical measurement devices, for example, measurement light (near infrared light or the like) is irradiated from outside the body to the living body, and the measurement light emitted through interaction with the living tissue is detected. Then, based on the detection signal of the measurement light including the biological tissue information, tomographic imaging processing, collection of metabolic information (for example, quantification of hemoglobin), and the like are performed. For example, an optical tomographic imaging apparatus using OCT (Optical Coherence Tomography) measurement is known as one of them. This optical tomographic imaging apparatus divides broadband light emitted from a light source into measurement light and reference light by an optical interferometer, and then irradiates the measurement light to a test part through an optical axis scanning means and performs optical axis scanning. The optical axis of the measurement light is scanned in one or two-dimensional directions perpendicular to the optical axis by the means, the reflected light from the test part is returned to the interferometer, and the reflected light is combined with the reference light and reflected. An optical tomographic image of the scanning region is acquired based on the interference light intensity between the light and the reference light.

  By the way, the living tissue is a light scattering medium, and most of the measurement light that has entered the living body is multiply scattered. Therefore, in the living body measurement using the optical measuring device, the measurement range is limited to the vicinity of the living body surface. For example, in the case of the above OCT measurement based on the optical interference of the measurement light itself, the measurement depth is at most 2 to 3 mm from the living body surface. Thus, the measurement range of the test part is limited only by irradiating the measurement light from outside the living body.

  Therefore, a method of combining with ultrasonic waves that can penetrate deeper into the living body has been attracting attention, and as one of them, an ultrasonic modulated optical tomographic imaging apparatus (UOT: Ultrasound modulated) using ultrasonic modulated light measurement. Optical Tomography) is known.

For example, in the method described in Non-Patent Document 1, ultrasonic waves are applied to the light scattering medium from a direction orthogonal to the measurement light. As can be seen with existing ultrasonic measurement devices, the ultrasonic waves can be locally concentrated on a part to be examined in the living body. And the elastic wave in the living body generated by irradiating the living body with ultrasonic waves forms a dense state of the living tissue, and forms a refractive index distribution with respect to the measuring light. At this time, when the measurement light travels through the test part while being scattered, the temporal change in the density of the living tissue acts on the measurement light, and the measurement light is modulated (hereinafter, the modulated measurement light is ultrasonically modulated). Called light). As a result, by analyzing only the modulation component from the detection signal of the ultrasonic modulation light, it is possible to acquire biological tissue information of the observation site.
Lihong V. Wang, Geng Ku, OPTICS LETTERS, Vol. 23, No. 12, p.975-977 (1998)

  However, in the conventional method, there are problems in reducing the cost on the electric circuit side and reducing the size, for example, devices for detection signal processing are expensive and the types are limited. This is because, in UOT measurement, a method in which the light detection means detects ultrasonically modulated light (for example, 1 to 20 MHz) that matches the ultrasonic frequency component is the main.

  For example, in Non-Patent Document 1, assuming that ultrasonic modulated light is detected at a frequency lower than the frequency of the ultrasonic wave to be modulated, the frequency sweep ultrasonic wave that encodes the depth position of the test part is modulated with the gain of the photodetector. Thus, a method for detecting an interference signal of ultrasonically modulated light is described. However, the method of detecting the signal by modulating the gain is difficult unless it is a photomultiplier tube (PMT), and high voltage modulation is also necessary for the gain modulation, and an increase in cost is inevitable.

  The present invention has been made in view of the above problems, and an object thereof is to provide a low-cost ultrasonic modulation optical tomographic imaging apparatus that does not require an expensive apparatus such as a PMT.

  The inventor has focused on the fact that in UOT measurement, an interference signal of ultrasonically modulated light can be generated by modulation of measurement light and ultrasonic wave, and the present invention has been achieved.

That is, the ultrasonic modulation optical tomographic imaging apparatus according to the present invention is
Measuring light irradiating means for irradiating the test part with measuring light, ultrasonic irradiating means for injecting ultrasonic waves to the test part, ultrasonic modulating means for modulating the ultrasonic waves, and measuring light and ultrasonic test The first ultrasonic modulated light detected by the light detecting means for detecting the first ultrasonic modulated light that is part of the measurement light, the optical characteristics of which are modulated by the interaction in the unit, and the light detecting means In the ultrasonic modulation optical tomographic imaging apparatus comprising a tomographic image acquisition means for acquiring a tomographic image of the test part based on the detection signal of
Measuring light modulating means for modulating the measuring light;
It comprises synchronization control means for synchronizing the modulation of the measurement light and the modulation of the ultrasonic wave.

  Furthermore, in the ultrasonic modulation optical tomographic imaging apparatus according to the present invention, the first ultrasonic modulation light is caused by the interaction between the measurement light and the ultrasonic wave whose frequency is modulated by the ultrasonic modulation means. It is preferable that it is due to the interaction between the measurement light and the pulsed ultrasonic wave modulated by the ultrasonic modulation means.

Further, a reference light irradiation means for irradiating the test part with reference light having a wavelength different from the wavelength of the measurement light,
A reference light modulation means for modulating the reference light,
The tomographic image acquisition means is based on respective detection signals of the second ultrasonic modulated light and the first ultrasonic modulated light whose optical characteristics are modulated by the interaction of the reference light and the ultrasonic wave in the test portion. It is preferable that a tomographic image of the test part is acquired using a calculation result between the two ultrasonic modulated lights.

  In the ultrasonic modulation optical tomographic imaging apparatus according to the present invention, an interference signal of ultrasonic modulation light is generated by modulation of measurement light and ultrasonic modulation. Therefore, since it is not necessary to modulate the gain of the light detection means, an expensive device such as a PMT is not required. As a result, the cost of the ultrasonic modulation optical tomographic imaging apparatus can be reduced.

  Hereinafter, although an embodiment of the present invention is described using a drawing, the present invention is not limited to this.

"Ultrasound-modulated optical tomographic imaging system"
A first embodiment of an ultrasonically modulated optical tomographic imaging apparatus (UOT apparatus) according to the present invention will be described. FIG. 1 is a schematic diagram showing the overall configuration of the UOT device 101 of the present embodiment.

  As shown in FIG. 1, the UOT device 101 includes a personal computer (PC) 110 that controls the device and a light source 122 that is measurement light irradiating means for irradiating measurement light 123 a to a test portion 150 of a living body (light scattering medium). And a light source driver (L driver) 121 that drives the light source 122, a function generator (FG) 120 that is a measurement light modulation unit that modulates the measurement light 123a, an ultrasonic transducer 132 that is an ultrasonic irradiation unit, and an ultrasonic vibration An ultrasonic transducer driver (U driver) 131 that drives the child 132, a function generator (FG) 130 that is an ultrasonic modulator for modulating the ultrasonic wave 133, a photodetector 142 that is a light detector, and a detection signal. A signal processing unit 141 that is a tomographic image acquisition unit that acquires a tomographic image of the test unit 150 based on And an image display device 111 for displaying a tomographic image that has been. The light source 122 and the photodetector 142 are arranged so as to face each other with the test portion 150 interposed therebetween, and the ultrasonic transducer 132 is arranged so that the irradiation direction of the measurement light 123a and the irradiation direction of the ultrasonic wave 133 are perpendicular to each other. Has been placed.

  The PC 110 controls the operation content of each component on the apparatus and controls the timing of each operation. Further, by controlling the timing of waveform generation of the FG 120 and the FG 130 by the PC 110, the PC 110 also serves as a synchronization control means for synchronizing the modulation of the measurement light 123a and the modulation of the ultrasonic wave 133.

  The light source 122 emits measurement light 123a having a wavelength of 750 nm. Examples of the light source 122 include a semiconductor laser and an LD excitation solid laser. The light source 122 can also be used in combination with a fiber optical system or a condensing lens that guides measurement light. The L driver 121 is connected to the FG 120 and drives the light source 122 according to the waveform of a signal generated by the FG 120.

  The ultrasonic transducer 132 is a single transducer or an array transducer. The ultrasonic transducer 132 is preferably provided with an acoustic lens for acoustic focusing, and in the case of an array transducer, electronic focusing is preferably applied. In this example, the arrangement is such that the irradiation direction of the ultrasonic wave 133 and the irradiation direction of the measuring light 123a are orthogonal to each other, but it is sufficient that the ultrasonic wave passes through the light scattering region, and this arrangement is particularly limited. It is not something that can be done. The irradiated ultrasonic wave 133 may be a pulse wave (PW) or a continuous wave (CW). In addition, when CW ultrasonic waves are used, a higher S / N ratio is obtained than when PW ultrasonic waves are used, and therefore the measurement time can be shortened. The U driver 131 is connected to the FG 130 and drives the ultrasonic transducer 132 according to the waveform of the signal generated by the FG 130.

  The FG 120 and the FG 130 generate waveforms of the measurement light 123a and the ultrasonic wave 133, respectively, and receive the trigger from the PC 110, thereby transmitting the waveforms to the L driver 121 and the U driver 131, respectively. If the waveforms of the measurement light 123a and the ultrasonic wave 133 are the same, one driver may be used. In this case, it is preferable to set the trigger for the measurement light 123a and the trigger for the ultrasonic wave 133 so that they can be processed separately so as to shift the generation timing of the measurement light 123a and the ultrasonic wave 133.

  The light detector 142 detects the measurement light 123a (scattered light 123b) that has traveled while being scattered multiple times in the test portion 150. A part of the scattered light 123b is detected as frequency-modulated ultrasonic modulated light 123c due to the interaction from the ultrasonic wave 133 when passing through the sound ray of the ultrasonic wave 133. The photodetector 142 is connected so as to transmit a detection signal to the signal processing unit 141. Further, the photodetector 142 may receive a trigger from the PC 110 as shown in FIG.

  Note that because of the scattering of the measurement light 123a in the test unit 150, the detection of the scattered light 123b from the test unit 150 is not limited to the case where the detection is performed on the optical axis as described above. That is, the arrangement position of the photodetector 142 can be arranged at a position that can secure as much signal amount as possible, for example, according to the shape of the test part 150. For example, as shown in FIG. 2, when the light source 122, the ultrasonic transducer 132, and the photodetector 142 are arranged in the vicinity, they can be combined into a measurement probe, and the shape dependency of the test part 150 is Since it is reduced, it is preferable. In such a case, the scattered light 123b incident on the photodetector 142 includes a lot of scattered light 123b that has passed through a specific path 124a (banana shape) in the test portion 150 as shown in FIG. 3A. Become. Therefore, as shown in FIG. 3B, by using a plurality of photodetectors 143, the role is divided so that scattered light from the depth position corresponding to each banana shape (124b and 124c) is detected. Can be made. Thereby, the photodetector 143 can be reduced in size, and the measurement probe can be reduced in size.

  The signal processing unit 141 receives the interference signal of the ultrasonic modulated light 123c detected by the photodetector 142, performs signal processing based on the A / D converted interference signal, and acquires tomographic information of the test unit 150. Then, a tomographic image is generated based on the tomographic information, and the tomographic image is transmitted to the PC 110. Details of the signal processing will be described later.

  The image display device 111 displays a tomographic image transmitted from the PC 110.

  And UOT measurement using the UOT device concerning this embodiment is shown below. First, the measurement light 123a and the ultrasonic wave 133 are synchronized with each other, the measurement light 123a and the ultrasonic wave 133 are irradiated onto the test part 150, the scattered light 123b traveling through the test part 150 is detected, and the scattered light 123b is detected. Signal processing is performed based on the interference signal of the ultrasonic modulated light 123c included in the detection signal, and a tomographic image for one line is acquired. Then, while scanning along the measurement area of the test unit 150, the above operation is repeated to obtain a plurality of lines of tomographic images, and the tomographic images of the test unit 150 are combined by combining the tomographic images of the plurality of lines. Get an image.

This UOT measurement is based on the heterodyne signal detection of the ultrasonic modulated light 123c caused by the modulation of the measurement light 123a and the modulation of the ultrasonic wave 133. Specifically, the modulation frequency _{f l} and modulation frequency _{f u} of ultrasonic 133 of the measuring light 123a is a compound represented by the following formula respectively against time t (1), when given in (2), modulated in depth position z The heterodyne frequency f _h of the received ultrasonic modulated light 123c is given by the following equation (3). The depth position z is a distance from the surface of the test part 150 along the sound ray of the ultrasonic wave 133. Thus, to detect a heterodyne signal having information of depth position z, and the heterodyne frequency f _h can acquire a tomographic information by frequency component analysis.
f ₁ = a ₁ + b · t (1)
f _u = a _u + b · t (2)
f _h = | a _u −a ₁ −b · z / v _u | (3)
(Here, a _l and a _u are the initial values of f _l and f _u , b is the sweep rate, and v _u is the speed of sound in the test section 150.)

For example, when the ultrasonic wave 133 is CW, the modulation of the measurement light 123a and the ultrasonic wave 133 is synchronized so that the irradiation start of the measurement light 123a and the ultrasonic wave 133 coincides. On the other hand, when the ultrasonic wave 133 is PW, these synchronizations are synchronized at the time when one ultrasonic pulse having one frequency enters the living tissue, and modulation on the light source side is started. until the pulse exits the area to be measured performed by sweeping the modulation frequency f _l, as represented by the above formula (1). In the latter case, the formula (2) _{f u} = _a u, and the above equation (3) becomes _{f h = a l -a u +} b · z / v u.

  As shown in FIG. 4, in the signal processing of the ultrasonic modulated light 123c, the signal processing unit 141 receives the detection signal from the photodetector 142 (ST1), removes the DC component (ST2), and performs square detection ( ST3), all the signal data for one line is extracted from the detection signal (ST4, ST5), the obtained data of the same line is added (ST6), and the added signal data is subjected to Fourier transform processing to obtain spectral data. (ST7, ST8), reference data is acquired (ST9), the spectrum data and the reference data are compared and calculated (ST10), and the spectrum data obtained by the comparison calculation using the above equation (3) is obtained. The depth position is obtained from the frequency component (ST11), and tomographic information for one line is obtained (ST12).

  The reference data is the same as the above UOT measurement and signal processing (excluding ST9 and ST10) using, for example, reference light having a wavelength that is different from the wavelength of the measurement light 123a and is not easily absorbed by the test unit 150. Data obtained by the method. Specifically, the UOT device further includes reference light irradiating means for irradiating the reference light, and the ultrasonic modulated light whose optical characteristics are modulated by the interaction between the reference light and the ultrasonic wave in the test portion. Reference data can be obtained by detecting and acquiring spectrum data based on the reference light based on the detection signal of the ultrasonically modulated light. This reference data may be created separately such as immediately before or after the measurement, or may be created simultaneously with the UOT measurement using the measurement light 123a.

  5A and 5B schematically show spectrum data and reference data obtained as described above, respectively. By comparing these data, the relative intensity of the spectrum data can be obtained (FIG. 6). As a result, the baseline fluctuation due to the distribution of the scattered light 123b can be canceled and tomographic information with a higher S / N ratio can be acquired. In general, the signal level also varies depending on the amount of light in the baseline. Therefore, by performing the comparison operation as described above, the variation in the measurement system can be removed, and specific absorption spectrum information of the test unit 150 can be obtained. It becomes possible. Therefore, for example, it is possible to measure a light absorption coefficient or blood oxygen concentration.

  As described above, in the UOT device according to the present invention, the interference signal of the ultrasonic modulated light is generated by the modulation of the measurement light and the modulation of the ultrasonic wave. Therefore, since it is not necessary to modulate the gain of the light detection means, an expensive device such as a PMT is not required. As a result, the cost of the UOT device can be reduced.

"Measurement probe"
Next, a measurement probe used in the UOT device according to the present invention will be described.

<First Embodiment>
FIG. 7 shows a first embodiment of the measurement probe. The measurement probe 201 is used, for example, in contact with the neck of the living body 150, and is for analyzing blood in the carotid artery, for example. In the casing of the measurement probe 201, the above-described light source 122 and photodetector 142 are provided, and an ultrasonic transducer 132 is provided therebetween. The ultrasonic transducer 132 emits the ultrasonic wave 133 along the central axis of the measurement probe 201, and the directivity directions of the light source 122 and the photodetector 142 are set so as to be substantially parallel to the central axis. Is set. The light source 122 and the ultrasonic transducer 132 are connected to measurement light modulation means and ultrasonic modulation means (not shown in FIG. 7), as detailed in the UOT device. According to such a measurement probe 201, there is an advantage that desired measurement can be performed only by bringing the probe into contact with the living body as in the conventional ultrasonic diagnosis.

<Second Embodiment>
FIG. 8 shows a second embodiment of the measurement probe. The measurement probe 202 is inserted into a blood vessel or a lumen. A light source 122 and a photodetector 142 are provided in the distal end portion, and an ultrasonic transducer 132 is provided between them. Similarly to the above, in the measurement probe 202, the ultrasonic transducer 132 radiates the ultrasonic wave 133 along the central axis of the measurement probe 201, and the light source is substantially parallel to the central axis. The directivity directions of 122 and the photodetector 142 are set. The light source 122 and the ultrasonic transducer 132 are connected to measurement light modulation means and ultrasonic modulation means (not shown in FIG. 8), as detailed in the UOT device. According to such a probe 202, for example, the biological tissue 150 in the vicinity of the blood vessel 151 can be analyzed.

<Third Embodiment>
FIG. 9 shows a third embodiment of the measurement probe. In the present embodiment, the measurement probe includes an ultrasonic probe 132 and a measurement optical probe 203. The measurement optical probe 203 is inserted into the blood vessel 151 of the living body 150, for example. A light source 122 and a photodetector 142 are provided in the distal end portion, and the measurement light is transmitted and received in the blood vessel 151. On the other hand, the ultrasonic probe 132 has an ultrasonic transducer 132 and is used in contact with the surface of a living body, and an ultrasonic wave 133 is emitted by the ultrasonic probe 132. Here, as described in detail in the UOT device, the light source 122 and the ultrasonic transducer 132 are connected to measurement light modulation means and ultrasonic modulation means (not shown in FIG. 9), respectively.

  Further, in the measurement optical probe 203 shown in FIG. 9, both the light source 122 and the photodetector 142 may be provided on the distal end surface, and blood in front of the probe may be analyzed. Further, light may be transmitted and received outside the body while transmitting the ultrasonic wave 133 inside the body.

  In the above-described embodiment, an apparatus for measuring a living body has been described. Of course, the present invention can also be applied to measuring an object other than a living body.

Schematic configuration diagram showing an example of a UOT device according to the present invention (part 1) Schematic configuration diagram showing an example of a UOT device according to the present invention (part 2) Schematic showing an arrangement example of a light source, an ultrasonic transducer, and a photodetector (part 1) Schematic showing an arrangement example of a light source, an ultrasonic transducer and a photodetector (part 2) The flowchart which shows the flow of the signal processing in this invention Schematic diagram of spectral data Schematic diagram of reference data Schematic diagram of spectral data obtained by calculation with reference data First embodiment of measurement probe Second embodiment of measurement probe Third embodiment of measurement probe

Explanation of symbols

101 UOT device 110 Control unit 111 Image display device 120, 130 Function generator 121 Light source driver 122 Light source 123a Measurement light 123b Scattered light 123c Ultrasound modulated light 131 Ultrasonic transducer driver 132 Ultrasonic transducer 133 Ultrasonic wave 141 Signal processing unit 142 Photodetector 150 Test part 201 Measuring probe

Claims (4)

Measuring light irradiating means for irradiating the test part with measuring light, ultrasonic irradiating means for irradiating the test part with ultrasonic waves, ultrasonic modulating means for modulating the ultrasonic waves, the measuring light and the ultrasonic waves The first ultrasonic modulated light that is part of the measurement light, the optical characteristics of which are modulated by the interaction in the test part with the light detection means, and the light detection means In an ultrasonically modulated optical tomographic imaging apparatus comprising tomographic image acquisition means for acquiring a tomographic image of the test part based on a detection signal of the first ultrasonically modulated light,
Measuring light modulating means for modulating the measuring light;
An ultrasonic modulation optical tomographic imaging apparatus comprising synchronization control means for synchronizing the measurement light modulation and the ultrasonic modulation.   2. The ultrasonic wave according to claim 1, wherein the first ultrasonic modulation light is caused by an interaction between the measurement light and the ultrasonic wave whose frequency is modulated by the ultrasonic modulation unit. Sound modulation optical tomography imaging device.   The supersonic wave according to claim 1, wherein the first ultrasonic modulation light is caused by an interaction between the measurement light and the ultrasonic wave modulated by one pulse by the ultrasonic modulation means. Sound modulation optical tomography imaging device. Reference light irradiating means for irradiating the test portion with reference light having a wavelength different from the wavelength of the measurement light;
Reference light modulation means for modulating the reference light,
Each of the tomographic image acquisition means includes a second ultrasonic modulated light whose optical characteristics are modulated by the interaction of the reference light and the ultrasonic wave in the test portion, and the first ultrasonic modulated light, respectively. 4. The ultrasonograph according to claim 1, wherein a tomographic image of the part to be examined is acquired based on a detection signal obtained by using a calculation result between the two ultrasonic modulated lights. 5. Sound modulation optical tomography imaging device.

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