JP2001120509A - Bloodstream signal extracting apparatus and bloodstream signal extracting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove a random mode hop of an oscillating wave length, and to remove the scattered light incident on a photoelectric conversion element in an apparatus for extracting a power spectrum correlating with a bloodstream signal. SOLUTION: An alternating current supplied via an AC power source 3 and an AC coupling capacitor 4 is superimposed on a direct current supplied to a laser diode 1. A laser beam reflected by subject by being oscillated from the laser diode 1 is received via a diffraction means 8. A temperature change in the laser diode 1 is detected by a first photodiode 5, and a Peltier element 6 absorbs heat of the laser diode 1 according to a detecting result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for irradiating a living tissue with a laser beam and using a beat signal of a Doppler shift caused by the laser beam scattered in the living tissue to obtain a power spectrum as a tissue blood flow signal. The present invention relates to an apparatus and a method for extracting.

[0002]

2. Description of the Related Art When a laser beam emitted from a laser diode is applied to a living tissue, a Doppler effect occurs due to reflection on the surface of the living tissue, diffusion in the living tissue and reflected return light. A technique for obtaining blood flow distribution data in a subject using the Doppler effect has been established.

For example, Japanese Patent Application Laid-Open No. 5-277111 discloses that an ultrasonic beam is radiated into a subject, a Doppler signal is detected using an obtained reflected wave signal, and a Doppler signal is detected based on the Doppler signal. An apparatus for obtaining blood flow distribution data is disclosed.

[0004]

When extracting a power spectrum as a tissue blood flow signal using a laser beam, when the oscillation wavelength of a laser diode that emits the laser beam is stable, that is, when the temperature is constant and the output Constant,
When there is no return light due to the reflection of laser light, FIG.
As shown in (A), the mode of the oscillation wavelength is single.

However, when laser light is directly irradiated on the surface of a living tissue from a laser diode, reflected return light is incident on the laser diode, causing optical self-coupling or heat generated by the laser diode itself. When the resonator length of the diode changes, a mode hop 20 having a random oscillation wavelength occurs, as shown in FIG. For this reason, laser light is received at peaks of different magnitudes, and it has been difficult to receive light in a single mode.

[0006] Further, the laser light reflected by the living tissue forms a scattered field called "Apple beam". Therefore, the laser light reflected by the living tissue enters the photoelectric conversion element as scattered light, similarly to the light emitted from a random point light source from multiple directions. As a result, the stray light component increases.

For the above reasons, the power spectrum generated as the diffraction phenomenon of the Doppler-shifted beat signal scattered in the living tissue fluctuates greatly, so that an accurate power spectrum correlated with the tissue blood flow signal can be extracted. It was difficult.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the prior art, and has a random oscillation wavelength generated by reflected light returning from the surface of a living tissue and heat generated by the light source itself. It is an object of the present invention to provide a power spectrum extracting device and a power spectrum extracting method capable of removing mode hops and removing scattered light, that is, stray light incident on the surface of a photoelectric conversion element.

[0009]

In order to achieve this object, a first aspect of the present invention is a laser light source that oscillates a longitudinal single mode laser beam, and a wavelength stabilizing device that stabilizes the wavelength of the laser beam. And, a photoelectric conversion unit that converts the laser light reflected from the subject into an electric signal,
An apparatus for extracting a power spectrum as a tissue blood flow signal is provided.

According to a second aspect of the present invention, the apparatus further comprises diffraction means for generating a diffraction phenomenon in a reflected laser beam when the living tissue is irradiated with a laser beam emitted from a laser light source. Is preferred.

According to a third aspect of the present invention, the wavelength stabilizing means is constituted as a means for superimposing an alternating current on a direct current which is an operating current capable of oscillating laser light in a single longitudinal mode. Can be.

By generating a small mode on the side of the fundamental mode (state oscillating in a single mode) by the wavelength stabilizing means, the coherence between the oscillated laser light and the reflected laser light is generated. And the optical self-coupling in the laser light source due to the return light can be prevented. As a result, random mode hops of the oscillation wavelength can be reduced.

Further, as described in claim 4,
Preferably, the alternating current has a frequency of 100 to 200 KHz and is in the range of 0.4 to 2.5 mA.

According to a fifth aspect of the present invention, there is provided a laser light source that oscillates a laser beam in a longitudinal single mode, a DC power supply for supplying a DC current to the laser light source, an AC power supply for supplying an AC current to the laser light source, and a reflection from the subject. Provided is an apparatus for extracting a power spectrum as a tissue blood flow signal, comprising: a diffracting means for diffracting the laser light, and a photoelectric converting means for converting the laser light passing through the diffracting means into an electric signal.

[0015] As described in claim 6, the apparatus for extracting a power spectrum as a tissue blood flow signal preferably further includes an AC coupling capacitor disposed between an AC power supply and a laser light source. The laser light source is supplied with an alternating current having a frequency of 100 to 200 KHz and 0.4 to 2.5 mA.

According to a seventh aspect of the present invention, the apparatus for extracting a power spectrum as a tissue blood flow signal detects a temperature change of a laser light source and issues a detection signal corresponding to the detected temperature change. It is preferable to further include a temperature sensor and heat absorbing means for absorbing heat in the laser light source in accordance with the detection signal.

With this temperature sensor and heat absorbing means,
The heat generation of the laser light source can be suppressed, and as a result,
A random mode hop of the oscillation wavelength of the laser light source can be eliminated.

As described in claim 8, as the diffraction means, a pinhole having a diameter of 50 to 200 μm,
Either a lens or a 50 to 200 μm graded index optical fiber can be selected.

The temperature sensor may be configured to detect a change in the laser output of the laser light source to detect a change in the temperature of the laser light source.

As described in claim 10, as the heat absorbing means, for example, a Peltier element can be used.

[0021] As described in claim 11, the laser light emitted from the laser light source is 500 to 900 nm.
Preferably, it has a wavelength of

A twelfth aspect is a first step of oscillating a longitudinal single mode laser beam, a second step of stabilizing the wavelength of the laser beam, and a step of applying a laser beam emitted from a laser light source to a living tissue. A third process of generating a beat signal of Doppler shift scattered in the living tissue when irradiated as a diffraction phenomenon, and a fourth process of converting laser light into an electric signal, as a tissue blood flow signal A method for extracting a power spectrum.

[0023] As described in claim 13, the second step can be constituted, for example, as a step of superimposing an alternating current on an operating current capable of oscillating laser light in the longitudinal single mode. .

In this case, the alternating current preferably has a frequency of 100 to 200 KHz and is in the range of 0.4 to 2.5 mA.

[0025] As described in claim 15, the method includes a fifth step of detecting a temperature change of the laser light source that emits the laser light, and a method of detecting a temperature change in the laser light source according to the detected temperature change. And a sixth step of absorbing heat.

The temperature change of the laser light source in the fifth step is detected, for example, by detecting a change in the laser output of the laser light source.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A blood flow signal extracting apparatus according to one embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a blood flow signal extraction device according to one embodiment of the present invention.

The blood flow signal extraction device according to the present embodiment supplies a laser diode 1 as a laser light source that oscillates a longitudinal single mode laser beam 1a having a wavelength of 500 to 900 nm, and supplies a direct current to the laser diode 1. A DC power supply 2, an AC power supply 3 for supplying an AC current, an AC coupling capacitor 4 disposed between the AC power supply 3 and the laser diode 1, and a laser diode disposed on the side opposite to the emission end of the laser diode 1. 1, a first photodiode 5 as a temperature sensor for detecting a temperature change and generating a detection signal according to the detected temperature change, a Peltier element 6 as a heat absorbing means for absorbing heat generated by the laser diode 1, and A detection signal transmitted by one photodiode 5 is received, and the amount of heat absorbed by the Peltier element 6 is determined in accordance with the detection signal. A control circuit 7 for controlling the subject 11
Diffraction means 8 for diffracting the laser light 1b reflected from the object, a second photodiode 9 for receiving the laser light 1b reflected from the subject 11 via the diffraction means 8,
A photoelectric conversion circuit 1 as a photoelectric conversion means for converting the laser beam 1b received by the second photodiode 9 into an electric signal
0.

The AC coupling capacitor 4 is supplied with AC current from the AC power supply 3 and has a frequency of 100 to 200 KH.
z, an alternating current of 0.4 to 2.5 mA is supplied to the laser diode 1.

As the diffraction means 8 in the present embodiment,
A pinhole having a diameter of 50 to 200 μm is used. Instead of this pinhole, it is also possible to select a lens or a 50 to 200 μm Ggraded Index optical fiber.

The first photodiode 5 detects a change in the laser output of the laser diode 1 to
The temperature change of the laser diode 1 is detected.

The blood flow signal extraction device according to the present embodiment having the above configuration operates as follows.

The DC power supply 2 supplies a DC current to the laser diode 1, and the AC power supply 3 has a frequency of 100 to 200 KHz, 0.4 to 2.
An alternating current of 5 mA is supplied to the laser diode 1.
This AC current is superimposed on the DC current inside the laser diode 1. As a result, as will be described later, a peak occurring in a high frequency band of the blood flow signal can be eliminated.

The laser diode 1 scans the subject 11 with a laser beam 1a having a wavelength of 500 to 900 nm.

The laser beam 1 reflected on the subject 11
b passes through a pinhole having an inner diameter of 50 to 200 μm as the diffraction means 8. When passing through the pinhole, a diffraction phenomenon occurs in the laser beam 1b. Next, after the laser beam 1b is received by the second photodiode 9,
In the photoelectric conversion circuit 10, the light is converted into an electric signal corresponding to the intensity of the laser light 1b.

Based on this electric signal, a power spectrum as a living tissue blood flow signal can be extracted.

The first photodiode 5 detects a temperature change of the laser diode 1 and transmits a detection signal corresponding to the detected temperature change to the control circuit 7. The control circuit 7
The amount of heat absorbed by the Peltier element 6 is controlled according to the temperature change of the laser diode 1 indicated by the detection signal.

In order to confirm the effectiveness of the AC power supply 3 and the AC coupling condenser 4 as the wavelength stabilizing means and the Peltier element 6 as the heat absorbing means, the AC power supply 3 and the AC coupling 3 were obtained from the blood flow signal extracting device shown in FIG. The power spectrum under static scattering conditions of the polyacetal resin was measured both when the capacitor 4 and the Peltier element 6 were removed and when the AC power supply 3, the AC coupling capacitor 4 and the Peltier element 6 were directly attached.

The results are shown in FIGS. 3A and 3B.
When the AC power supply 3, the AC coupling capacitor 4, and the Peltier element 6 are removed from the blood flow signal extraction device shown in FIG. 1, as shown in FIG. A peak 30 occurs at a high frequency, which is a frequency band as a signal. On the other hand, the AC power supply 3, the AC coupling capacitor 4, and the Peltier element 6
In the case where is attached as it is, as shown in FIG. 3B, the peak 30 at a high frequency seen in FIG. 3A has disappeared.

That is, by providing the AC power supply 3, the AC coupling capacitor 4, and the Peltier element 6, the configuration shown in FIG.
It can be seen that the random mode hop 20 as shown in FIG.

Further, in order to confirm the effectiveness of the diffraction means 8, the laser light 1b reflected from the subject 11 is received without passing through the diffraction means 8 and the laser light 1b is received through the diffraction means 8, respectively. , The power spectrum, which is the Brownian motion of the latex particles, was measured.

FIG. 4A shows the result when the laser beam reflected from the subject 11 is received without passing through the diffraction means 8.
FIG. 4 shows the result when light is received through the diffraction means 8.
(B) shows each. As is clear from the comparison between FIGS. 4A and 4B, the area of the power spectrum when the laser beam 1b reflected from the subject 11 is received without passing through the diffraction means 8 (FIG. 4A). ) Is the area of the power spectrum when light is received via the diffraction means 8 (FIG. 4).
(B)). This indicates that the use of the diffracting means 8 makes it possible to obtain a power spectrum having a higher degree of correlation with the blood flow signal as compared to the case where the diffracting means 8 is not used.

As described above, according to the blood flow signal extraction device of the present embodiment, a random mode as shown in FIG. The hop 20 can be removed by supplying a high-frequency current to the laser diode 1 via the AC power supply 3 and the AC coupling capacitor 4.

Further, the mode hop 20 caused by the heat generation of the laser diode 1 itself can be removed by the first photodiode 5 as the temperature sensor and the Peltier element 6 as the heat absorbing means.

Further, by using the diffraction means 8 for generating a diffraction phenomenon, it becomes possible to extract a more accurate power spectrum of a blood flow signal.

[0046]

According to the present invention, the following effects can be obtained.

It is possible to prevent optical self-coupling due to interference between laser light oscillated from a laser light source and light reflected from a biological tissue reflecting surface, and to extract a more accurate power spectrum as a biological tissue blood flow signal. be able to.

Further, random mode hops caused by return light reflected from the subject or heat generated by the laser light source itself can be eliminated.

Further, by generating a diffraction phenomenon with respect to the reflected laser light reflected from the subject, a more accurate power spectrum of the blood flow signal can be extracted.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a structure of a blood flow signal extraction device according to one embodiment of the present invention.

FIG. 2A shows a mode measurement result when no interference occurs between an oscillated laser beam and a reflected laser beam, and FIG. 2B shows a mode measurement result of the oscillated laser beam and the reflected laser beam. 9 shows a mode measurement result in the case where interference occurs between the mode and the mode.

FIGS. 3A and 3B are power spectra under static scattering conditions of a polyacetal resin measured under different conditions, respectively.

FIGS. 4A and 4B are power spectra in the Brownian motion of latex particles measured under different conditions, respectively.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser diode 2 DC power supply 3 AC power supply 4 AC coupling capacitor 5 First photodiode 6 Peltier element 7 Control circuit 8 Diffraction means 9 Second photodiode 10 Photoelectric conversion circuit 11 Subject 20 Mode hop 30 Peak

Claims (16)

[Claims] 1. A laser light source that oscillates a laser beam in a longitudinal single mode, a wavelength stabilizing unit that stabilizes a wavelength of the laser beam, and a photoelectric conversion unit that converts a laser beam reflected from an object into an electric signal. An apparatus for extracting a power spectrum as a tissue blood flow signal, comprising: 2. The tissue blood flow according to claim 1, further comprising diffraction means for generating a diffraction phenomenon in a reflected laser light when the living tissue is irradiated with the laser light emitted from the laser light source. A device that extracts a power spectrum as a signal. 3. The tissue according to claim 1, wherein said wavelength stabilizing means is means for superimposing an alternating current on a direct current capable of oscillating a laser beam in a longitudinal single mode. A device that extracts a power spectrum as a blood flow signal. 4. The method according to claim 1, wherein the alternating current is 100 to 200 KH.
4. The apparatus for extracting a power spectrum as a tissue blood flow signal according to claim 3, wherein the alternating current has a frequency of z and is in a range of 0.4 to 2.5 mA. 5. A laser light source that oscillates laser light in a longitudinal single mode; a DC power supply that supplies a DC current to the laser light source; an AC power supply that supplies an AC current to the laser light source; An apparatus for extracting a power spectrum as a tissue blood flow signal, comprising: a diffraction unit for diffracting the laser light; and a photoelectric conversion unit for converting the laser light having passed through the diffraction unit into an electric signal. 6. The apparatus according to claim 1, further comprising an AC coupling capacitor disposed between the AC power supply and the laser light source, wherein the laser light source has a frequency of 100 to 200K.
6. The apparatus for extracting a power spectrum as a tissue blood flow signal according to claim 5, wherein an alternating current of 0.4 to 2.5 mA at Hz is supplied. 7. Detecting a temperature change of the laser light source,
The temperature sensor according to any of claims 1 to 6, further comprising: a temperature sensor that emits a detection signal according to the detected temperature change; and a heat absorbing unit that absorbs heat in the laser light source according to the detection signal. An apparatus for extracting a power spectrum as a tissue blood flow signal according to claim 1. 8. The diffraction means has a diameter of 50 to 200.
The tissue blood flow signal according to any one of claims 1 to 6, wherein the tissue blood flow signal is formed of one of a pinhole, a lens, and a 50 to 200 µm graded index optical fiber. A device that extracts the power spectrum. 9. The temperature sensor according to claim 5, wherein a temperature change of the laser light source is detected by detecting a change of a laser output of the laser light source. An apparatus for extracting a power spectrum as a tissue blood flow signal according to the paragraph. 10. The apparatus for extracting a power spectrum as a tissue blood flow signal according to claim 5, wherein the heat absorbing means comprises a Peltier element. 11. The power spectrum as a tissue blood flow signal according to claim 1, wherein the laser light emitted from the laser light source has a wavelength of 500 to 900 nm. Equipment to extract. 12. A first step of oscillating longitudinal single mode laser light, a second step of stabilizing the wavelength of the laser light, and irradiating a living tissue with laser light emitted from the laser light source. A third process of generating a beat signal of Doppler shift scattered in the living tissue as a diffraction phenomenon when performing, and a fourth process of converting the laser light into an electrical signal, comprising: To extract the power spectrum of 13. The tissue blood flow according to claim 12, wherein the second step is a step of superimposing an alternating current on an operating current capable of oscillating laser light in a longitudinal single mode. A method of extracting a power spectrum as a signal. 14. The AC current is 100 to 200K.
The method for extracting a power spectrum as a tissue blood flow signal according to claim 13, wherein the alternating current has a frequency of Hz and is in a range of 0.4 to 2.5 mA. 15. A fifth step of detecting a temperature change of the laser light source that emits the laser light, and a sixth step of absorbing heat in the laser light source according to the detected temperature change. The method for extracting a power spectrum as a tissue blood flow signal according to any one of claims 12 to 14, wherein the power spectrum is provided. 16. The method according to claim 15, wherein the detecting of the temperature change of the laser light source in the fifth step is performed by detecting a change in the laser output of the laser light source. A method of extracting a power spectrum as a tissue blood flow signal.