JP2005111165A - Instrument and method for measuring scattering absorbing medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an instrument and method for measuring a scattering absorbing medium for realizing the measurement of the scattering absorbing medium by a PMS method under a stable condition in spite of a change in environmental temperature and light quantity. <P>SOLUTION: The scattering absorbing medium SM is irradiated from a laser diode 10 with measurement light which is modulated by a modulation signal with a reference signal outputted from a reference signal generator 20 as a source. Then internally propagated light is detected by a light detector 15. A phase difference between a detection signal from the light detector 15 and the reference signal is detected by a phaser detector 21 to measure the scattering absorbing medium by the PMS method. A light branch mirror 14 for branching a part of the measurement light from the laser diode 10 is arranged. Then a PLL circuit for stabilizing the phase of the measurement light from the laser diode 10 is constituted of a light detector 30 for monitoring, a phase detector 31 for monitoring, and a VCO 32. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a scattering medium measuring apparatus and a measuring method for measuring internal information of a scattering medium such as a living body.

  In recent years, biological measurement using light has attracted attention because of its non-destructive and non-invasive advantages. In this measurement method, measurement light having a predetermined wavelength such as near-infrared light is applied to a scattering medium such as a living body to be measured and propagated through the inside. And the light which propagated the inside is detected with a photodetector, and the internal information of a scattering medium is acquired from the detection result (for example, refer to patent documents 1).

Such a measurement method can be used, for example, in an optical topography measurement device that acquires oxygenated / deoxygenated hemoglobin concentration information in a living body and visualizes the oxygen metabolism function in blood. Research has been conducted to dynamically visualize changes in oxygen metabolism during tasks given to humans.
JP-A-11-169361 JP 2000-77768 A

  In a scattering medium measuring apparatus using light that is currently on the market, CW light is used as the measuring light with which the scattering medium is irradiated. In the measurement method using CW light, changes in hemoglobin concentration and the like are mapped from the distribution of changes in the detected light intensity. However, in such a method, since the average optical path length in which light propagates in the living body is not measured, the value of the concentration change cannot be obtained as an absolute value, and it can be used for advanced medical examinations in the clinical field. There is a problem that you can not.

  Attempts have also been made to determine the average optical path length by irradiating the scattering medium with pulsed light. However, in such a method, a measurement system constructed using a photodetector and a light source may be expensive. Further, there is a PMS (Phase Modulation Spectroscopy) method for obtaining an average optical path length by irradiating a scattering medium with intensity-modulated light and measuring a phase delay with respect to the phase in the intensity-modulated periodic optical waveform. It is being considered.

  When scattering absorber measurement by the PMS method is applied to clinical sites and the like, it is important to be able to measure under a wide range of environmental temperatures and to be measured with a wide dynamic range. On the other hand, a laser diode, which is a semiconductor light emitting element, is used as a light source for supplying measurement light. Here, in the operation of the laser diode, the operating condition of the laser diode changes when the environmental temperature changes or when the light quantity is changed by the excitation current in order to measure in a wide dynamic range. Thus, when the operating condition of the laser diode changes, there is a problem that the phase of the measurement light changes and the scattering medium measurement by the PMS method cannot be performed stably.

  As a method for preventing changes in operating conditions of the laser diode due to changes in the environmental temperature, a configuration in which the temperature of the laser diode is controlled by a Peltier element is used. However, when the Peltier element is used in this way, the Peltier element requires a sufficient current, so that the power supply becomes large, the entire apparatus becomes large, and the apparatus becomes expensive. Regarding the change in the operating conditions of the laser diode due to the change in the amount of light, a configuration in which the amount of light output from the laser diode is constant and the amount of light is controlled by installing an ND filter or the like at the subsequent stage of the laser diode is conceivable. However, in such a configuration, there is a problem that the light quantity control mechanism is complicated, and the device is expensive as in the temperature control by the Peltier element.

  The present invention has been made to solve the above problems, and a scattering absorber measurement apparatus capable of performing scattering absorber measurement by the PMS method under stable conditions regardless of changes in environmental temperature and light amount, and An object is to provide a measurement method.

  In order to achieve such an object, a scattering medium measuring apparatus according to the present invention is set for (1) a reference signal generating means for outputting a reference signal of a predetermined reference frequency and (2) a scattering medium. A light supply means for supplying measurement light having a predetermined wavelength for irradiation from a light irradiation position and capable of modulating the measurement light by a modulation signal based on a reference signal; and (3) from the light irradiation position to the scattering medium. A light detection means for detecting light that has propagated through the inside of the irradiated measurement light and has reached the light detection position and outputting a detection signal; and (4) generation of a detection signal and a reference signal from the light detection means. Measuring phase detecting means for detecting the phase difference of the reference signal from the means, (5) monitoring means for monitoring the light output from the light supplying means and outputting a monitor signal, and (6) monitor signal from the monitoring means And reference signal generating means By detecting the phase difference between al of the reference signal, characterized in that it comprises a monitoring phase detecting means for outputting a reference signal for detecting the phase difference by the measurement phase detecting means.

  Further, the scattering absorber measuring method according to the present invention includes (1) a reference signal generating step for outputting a reference signal having a predetermined reference frequency, and (2) a reference signal from a light irradiation position set for the scattering absorber. A light irradiation step for irradiating measurement light of a predetermined wavelength from the light supply means modulated by the modulation signal based on the above, and (3) propagating through the measurement light irradiated to the scattering medium from the light irradiation position A light detection step for detecting light that has reached the light detection position and outputting a detection signal; and (4) for detecting a phase difference between the detection signal from the light detection step and the reference signal from the reference signal generation step. A phase detection step; (5) a monitor step for monitoring a light output from the light supply means and outputting a monitor signal; and (6) a monitor signal from the monitor step and a reference signal generation step. By detecting the phase difference between the signals, characterized in that it comprises a monitoring phase detecting step of outputting a reference signal for detecting the phase difference in the measurement phase detecting step.

  In the scattering absorber measuring apparatus and the measuring method described above, the scattering absorber measurement is performed by the PMS method using the measurement phase detector. Then, the monitor phase detection means compares the phase of the monitor signal corresponding to the measurement light with the phase of the reference signal, detects a change in the phase of the measurement light with respect to the reference signal, and detects the phase difference by the PMS method. A reference signal for is generated. By using such a reference signal, it is possible to perform scattering absorber measurement by the PMS method under stable conditions, reflecting changes in the operating conditions of the light supply means due to changes in environmental temperature, light quantity, and the like. .

  Regarding the reflection of the reference signal to the scattering medium measurement, the measuring device outputs an oscillation signal of a predetermined frequency and includes an oscillator capable of controlling the oscillation condition by an external signal, and the oscillation signal from the oscillator is used as a modulation signal. It is preferable that the oscillation condition of the oscillation signal is controlled by the reference signal from the monitoring phase detection means in the oscillator while being input to the light supply means.

  Similarly, the measurement method includes an oscillation signal generation step for outputting an oscillation signal having a predetermined frequency whose oscillation condition is controlled by an external signal, and the oscillation signal from the oscillation signal generation step is input to the light supply means as a modulation signal. In addition, the oscillation condition of the oscillation signal is preferably controlled by the reference signal from the monitoring phase detection step in the oscillation signal generation step.

  According to such a configuration, the PLL circuit that stabilizes the phase of the modulated measurement light from the light supply unit is configured by the monitoring unit, the monitoring phase detection unit, and the oscillator, and the PMS under stable conditions is formed. Scattering absorber measurement by the method can be realized.

  Alternatively, the measuring apparatus inputs the reference signal from the reference signal generating means to the light supplying means as a modulation signal, and uses the reference signal from the monitoring phase detecting means to detect the detection result of the phase difference by the measuring phase detecting means. It is preferable to correct.

  Similarly, in the measurement method, the reference signal from the reference signal generation step is input to the light supply means as a modulation signal, and the detection result of the phase difference in the measurement phase detection step by the reference signal from the monitor phase detection step Is preferably corrected.

  According to such a configuration, even when the phase of the modulated measurement light from the light supply unit changes, the change in the phase is reflected in the detection result of the phase difference by the PMS method, and stable. Scattering absorber measurement by the PMS method under conditions can be realized.

  Here, the measurement device is based on an attenuation rate analysis unit that obtains an attenuation rate of light in the scattering medium based on a detection signal from the light detection unit, a detection result of a phase difference by the measurement phase detection unit, and an attenuation rate analysis unit. It is good also as providing the density | concentration calculation means which calculates the density | concentration of the absorber in the scattering medium based on the analysis result of an attenuation factor. Similarly, the measurement method includes an attenuation rate analysis step for obtaining an attenuation rate of light in the scattering medium based on a detection signal from the light detection step, a detection result of a phase difference in the measurement phase detection step, and an attenuation rate analysis step. It is good also as providing the density | concentration calculation step which calculates the density | concentration of the absorber in the scattering medium based on the analysis result of an attenuation factor.

  The measurement apparatus preferably includes a light amount control unit that monitors the DC component of the light output from the light supply unit and controls the light amount of the measurement light supplied from the light supply unit. Similarly, the measurement method preferably includes a light amount control step for monitoring the DC component of the light output from the light supply unit and controlling the light amount of the measurement light supplied from the light supply unit.

  Alternatively, the measurement apparatus preferably includes a measurement light adjustment unit that adjusts the measurement light supplied from the light supply unit so that the DC component or the AC component of the light output from the light supply unit falls within a desired range. . Similarly, the measurement method includes a measurement light adjustment step for adjusting the measurement light supplied from the light supply unit so that the DC component or the AC component of the light output from the light supply unit falls within a desired range. preferable.

  In this way, by controlling and adjusting the DC component or AC component of the light output from the light supply means, the light amount, amplitude, optical waveform, etc. of the measurement light are suitably set, and the scattering absorber measurement by the PMS method is performed. This condition can be further stabilized.

  According to the scattering medium measuring apparatus and the measuring method according to the present invention, the ambient temperature and the light amount are measured by performing the measurement using the reference signal indicating the comparison result between the phase of the monitor signal corresponding to the measurement light and the phase of the reference signal. Regardless of the change of, scattering absorber measurement by the PMS method can be performed under stable conditions.

  Hereinafter, preferred embodiments of a scattering medium measuring apparatus and a scattering medium measuring method according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings do not necessarily match those described.

  FIG. 1 is a block diagram schematically showing the configuration of the first embodiment of the scattering medium measuring apparatus according to the present invention. This scattering medium measuring apparatus measures the internal information of a scattering medium noninvasively using light of a predetermined wavelength such as near infrared light. Examples of the scattering absorber to be measured by this measuring apparatus include a living body. The internal information to be measured includes, for example, the concentration of hemoglobin that is an absorbing substance in the living body, oxygen saturation, and the like. In this specification, “phase” refers to a phase in an intensity-modulated periodic optical waveform.

  The measurement apparatus shown in FIG. 1 includes a laser diode 10 that is a semiconductor light emitting element, a photodetector 15, a reference signal generator 20, a phase detector 21, and an analysis device 22. The laser diode 10 is a light supply unit that supplies measurement light having a predetermined wavelength used for measuring internal information of the scattering medium SM, and can radiate measurement light from a light irradiation position set for the scattering medium SM. Is arranged. Further, the laser diode 10 is configured to be capable of modulating the measurement light by the modulation signal from the outside, and supplies the modulated light whose intensity is modulated by the modulation signal as the measurement light to the scattering medium SM. Further, a DC current source 11 that supplies a DC current for exciting the laser diode 10 to the laser diode 10 is provided.

  The reference signal generator 20 outputs an electric signal having a predetermined reference frequency as a reference signal. This reference signal is a signal that is the source of the modulation signal input to the laser diode 10, and the reference frequency is the modulation frequency of the measurement light.

  The light detector 15 supplies light that has been supplied from the laser diode 10 and that has traveled through the scattering medium SM and reached the light detection position out of the measurement light irradiated on the scattering medium SM from the light irradiation position described above. To detect. And the photodetector 15 outputs the detection signal according to the intensity | strength, time change, etc. of the detected light.

  A phase detector 21 and an analysis device 22 are provided for the detection signal output from the photodetector 15. The phase detector 21 is a phase detector for measurement used for scattering medium measurement by the PMS method. The phase detector 21 receives the detection signal from the photodetector 15 and the reference signal from the reference signal generator 20, and detects the phase difference between the detection signal and the reference signal. The phase difference detected by the phase detector 21 is the phase delay (delay time) of the light detected by the photodetector 15 with respect to the measurement light irradiated from the laser diode 10 to the scattering medium SM. This phase delay corresponds to the average optical path length of light in the scattering medium SM.

  The analysis device 22 includes an attenuation rate analysis unit 23 and a concentration calculation unit 24. A detection signal from the photodetector 15 is input to the attenuation factor analysis unit 23, and the amplitude of the detection signal is calculated, and the attenuation factor of light in the scattering medium SM is obtained from the calculated amplitude. As for the input to the attenuation rate analysis unit 23, the amplitude of the AC component output from the phase detector 21 may be input, and thereby the attenuation rate of light may be obtained.

  The detection result of the phase difference by the phase detector 21 and the analysis result of the light attenuation rate by the attenuation rate analysis unit 23 are input to the concentration calculation unit 24. Based on these results, the concentration calculation unit 24 calculates the concentration of the absorbing substance (for example, hemoglobin) in the scattering medium SM.

  In the measurement apparatus of the present embodiment, in addition to the reference signal generator 20, the monitoring light detector 30, the monitoring phase detector 31, and the VCO (VCO) are used for the intensity-modulated measurement light supplied from the laser diode 10. A voltage-controlled oscillator (voltage-controlled oscillator) 32 is provided. Further, an optical branching mirror 14 that branches a part of the measurement light emitted from the laser diode 10 is disposed at a predetermined position on the optical path between the laser diode 10 and the scattering medium SM.

  The monitoring photodetector 30 is monitoring means for monitoring the light output from the laser diode 10. In the configuration shown in FIG. 1, a part of the measurement light branched by the light branching mirror 14 is incident on the monitoring photodetector 30 and detected, thereby monitoring the light output from the laser diode 10. . And the photodetector 30 outputs the monitor signal according to the intensity | strength, time change, etc. of the detected measurement light.

  The monitor phase detector 31 receives the monitor signal from the monitor photodetector 30 and the reference signal from the reference signal generator 20, and compares the phases of the monitor signal and the reference signal. Detect phase difference. The phase difference detected by the phase detector 31 is a phase shift between the reference signal that is the source of the modulation signal input to the laser diode 10 and the measurement light from the laser diode 10 that is actually intensity-modulated.

  By monitoring such a phase shift of the measurement light, a temporal change in the phase of the measurement light accompanying a change in the operating condition of the laser diode 10 is monitored. Then, the monitoring phase detector 31 outputs a reference signal for detecting the phase difference by the phase detector 21 in accordance with the detected phase difference.

  The VCO 32 is an oscillator that can output an oscillation signal having a predetermined frequency and can control an oscillation condition by an external signal. In the present embodiment, the oscillation signal from the VCO 32 is input to the laser diode 10 as a modulation signal based on a reference signal for modulating the measurement light. Further, the reference signal from the monitoring phase detector 31 is input to the VCO 32, and the phase of the oscillation signal is controlled based on this reference signal. Thereby, in the VCO 32, the phase of the oscillation signal from the VCO 32 is controlled so that the phase of the measurement light emitted from the laser diode 10 is aligned.

  In the scattering medium measuring method using the measuring apparatus shown in FIG. 1, first, a reference signal having a reference frequency is output from the reference signal generator 20 (reference signal generation step). Then, in addition to the DC current from the DC current source 11, an oscillation signal from the VCO 32 based on the reference signal is input to the laser diode 10 as a modulation signal. The laser diode 10 generates measurement light having a predetermined wavelength modulated by the modulation signal, and irradiates the measurement light from the light irradiation position to the scattering medium SM to be measured (light irradiation step). The irradiated measurement light propagates inside the scattering medium SM while receiving absorption, scattering, and the like.

  Of the light that has been irradiated to the scattering medium SM from the light irradiation position and propagated through it, the light component that has reached the light detection position is detected by the light detector 15. The light detector 15 outputs a detection signal corresponding to the detected light intensity or the like (light detection step).

  The phase detector 21 detects the phase difference between the detection signal from the photodetector 15 and the reference signal from the reference signal generator 20 (measurement phase detection step). The attenuation factor analysis unit 23 of the analyzer 22 obtains the attenuation factor of light in the scattering medium SM based on the detection signal from the photodetector 15 (attenuation factor analysis step). Further, the concentration calculation unit 24 calculates the concentration of the absorbing material in the scattering medium SM based on the detection result of the phase difference and the analysis result of the attenuation rate (concentration calculation step).

  On the other hand, a part of the measurement light branched by the light branching mirror 14 is detected by the monitoring photodetector 30 and the light output from the laser diode 10 is monitored. The photodetector 30 outputs a monitor signal corresponding to the monitoring result of the light output (monitoring step). The monitoring phase detector 31 detects the phase difference between the monitor signal from the photodetector 30 and the reference signal from the reference signal generator 20, and outputs a reference signal (monitoring phase detection step). The VCO 32 outputs an oscillation signal at a frequency and phase controlled by the reference signal from the phase detector 31 (oscillation signal generation step). The oscillation signal is input to the laser diode 10 as a modulation signal for modulating the measurement light.

  The effects of the scattering medium measuring apparatus and the measuring method according to the above embodiment will be described.

  In the scattering medium measuring apparatus and the measuring method using the same shown in FIG. 1, the supply of the modulated measuring light from the laser diode 10 and the phase of the detection signal from the photodetector 15 by the phase detector 21. Using the detection, scattering absorber measurement by the PMS method is performed. The monitoring phase detector 31 compares the phase of the monitor signal corresponding to the measurement light with the phase of the reference signal, detects a change in the phase of the measurement light with respect to the reference signal, and detects the phase difference in the PMS method. A reference signal for detection is generated. By using such a reference signal, even if the phase of the measurement light changes with a change in the operating condition of the laser diode 10 due to a change in the environmental temperature or the amount of light, the change is reflected in the measurement. It becomes possible to perform scattering absorber measurement by the PMS method under stable conditions.

  Thus, in the configuration in which the light output from the laser diode 10 is monitored and the scattering medium measurement is performed by the PMS method, the measurement is performed under stable conditions without installing a temperature control Peltier element or the like for the laser diode 10. Can be executed. This eliminates the need for supplying the current used for the Peltier element, reduces the size of the entire apparatus including the power supply, and reduces the cost of the apparatus. In this case, an air cooling fan or the like may be used for temperature control of the laser diode 10. The installation of such a fan is effective in suppressing an excessive temperature change of the laser diode 10 and preventing a change in the wavelength of the measurement light.

  In addition, regarding the reflection of the reference signal to the scattering medium measurement, in this embodiment, a VCO 32 is provided separately from the reference signal generator 20, and the oscillation signal from the VCO 32 is used as the modulation signal, and the phase detection for monitoring is performed. The VCO 32 is feedback controlled by the reference signal from the device 31. According to such a configuration, the monitoring photodetector 30, the phase detector 31, and the VCO 32 constitute a PLL circuit that stabilizes the phase of the modulated measurement light from the laser diode 10 that is the light supply means. Thus, scattering absorber measurement can be realized under stable conditions.

  Here, with respect to the frequency of the reference signal from the reference signal generator 20 that is the source of the modulation signal for intensity-modulating the measurement light irradiated to the scattering medium SM, the measurement of the average optical path length by the PMS method is accurately performed. It is necessary to set to a frequency that can be performed. Specifically, this reference frequency is preferably set to a frequency of 1 MHz or more. As for the wavelength of the measurement light, a suitable wavelength may be selected depending on the characteristics of the scattering medium SM to be measured, the type of internal information to be acquired (for example, the concentration of the absorbing material), and the like. If there is, light having two or more wavelengths may be used.

  For irradiation of the measurement light beam from the laser diode 10 to the scattering medium SM, an irradiation optical system including the laser diode 10 may be directly arranged at the light irradiation position of the scattering medium SM, or a laser The measurement light emitted from the diode 10 may be guided to the light irradiation position by an irradiation probe such as an optical fiber. Such a configuration is the same for the detection of light by the photodetector 15. In addition to the laser diode (LD), various light sources such as LEDs may be used as the light supply means for supplying the measurement light to the scattering medium SM.

  As for the monitoring means for monitoring the operation of the laser diode 10, in the configuration shown in FIG. 1, a part of the measurement light is branched by the light branching mirror 14 and the photodetector 30 for detecting it is used as the monitoring means. However, various other configurations can be used as the monitoring means. Generally, this monitoring means may be any means that monitors the light output from the light supply means.

  FIG. 2 is a block diagram showing a modification of the configuration of the scattering medium measuring apparatus shown in FIG. In this modification, a light branching mirror is not disposed between the laser diode 10 and the scattering medium SM and a part of the measurement light is branched, but the light emitted behind the laser diode 10 is detected. The monitoring photodiode 33 is used as monitoring means for monitoring the light output from the laser diode 10. Such a monitoring photodiode 33 is usually housed in the same package as the laser diode 10. As the laser diode 10, the DC current source 11, the reference signal generator 20, the monitoring photodiode 33, the monitoring phase detector 31, and the VCO 32, for example, the circuit system shown in FIG. 3 can be used.

  Note that Patent Document 2 describes the incorporation of a PLL circuit into a light source. However, the device described in Patent Document 2 is an optical pulse generator, and does not describe phase difference measurement using the generated optical pulse, influence of phase change in such phase difference measurement, or the like. .

  On the other hand, in the above scattering absorber measuring apparatus and measuring method, the modulated measuring light is applied to the scattering absorber measurement by the PMS method. Then, a reference signal based on the monitoring result of the measurement light is generated for the detection of the phase difference between the detection signal and the reference signal in such measurement, and the scattering absorber measurement with high accuracy is performed by using this reference signal. It is possible.

Here, the acquisition of the internal information of the scattering medium by the measurement apparatus and the measurement method described above will be described by taking, as an example, the concentration measurement of oxygenated hemoglobin (HbO ₂ ) and deoxygenated hemoglobin (Hb) that are absorbing substances in the living body. Keep it. In vivo measurement using light cannot directly measure oxygen in the body, but chromoproteins such as hemoglobin in the blood involved in oxygen metabolism absorb light in a state of being bound to oxygen and in a dissociated state. Since the spectra (wavelength dependence of light absorption characteristics) are different, information on oxygen metabolism in the living body can be obtained indirectly using this spectrum.

ここで、＜Ｌ１＞、＜Ｌ２＞はそれぞれ波長λ_１、λ_２での平均光路長（位相差に対応）、ΔＯＤ^λ１、ΔＯＤ^λ２はそれぞれ波長λ_１、λ_２での光強度変化（減衰率に対応）、ε^λ１ _ＨｂＯ２、ε^λ２ _ＨｂＯ２はそれぞれ波長λ_１、λ_２での酸素化ヘモグロビンの吸光係数、ε^λ１ _Ｈｂ、ε^λ２ _Ｈｂはそれぞれ波長λ_１、λ_２での脱酸素化ヘモグロビンの吸光係数である。 For example, when two-wavelength light having wavelengths λ ₁ and λ ₂ is used as the modulated measurement light emitted from the laser diode 10 to the scattering medium SM, the concentration change Δ [HbO ₂ ] of oxygenated hemoglobin, and The concentration change Δ [Hb] of deoxygenated hemoglobin is obtained as shown in the following formulas (1.1) and (1.2), respectively, based on the attenuation rate of light in the living body and the average optical path length.

Here, <L1>, <L2> each wavelength lambda _1, (corresponding to the phase difference) the mean path length in ^{λ _2,} ΔOD λ1, ΔOD λ2 each wavelength lambda _1, the light intensity change at lambda ₂ (attenuation corresponding to the ^{_{rate), ε λ1 HbO2, ε λ2}} HbO2 each wavelength lambda _1, the absorption coefficient of oxyhemoglobin at ^{_{λ 2, ε λ1 Hb, ε}} λ2 Hb each wavelength lambda _1, deoxygenated hemoglobin in lambda ₂ Is the extinction coefficient.

に示すように、リニアな関係式が成り立つ。ここで、ｃ’は媒質（散乱吸収体）中での光速を示している。上記の式より、位相情報Ｐを平均光路長＜Ｌ＞に換算することにより、減衰率の計測結果と合わせて、ヘモグロビンの濃度変化を絶対値として求めることができる。特に、安定した条件でＰＭＳ法による散乱吸収体計測を実行可能な上記した計測装置及び計測方法を用いれば、ヘモグロビンの濃度、及びその時間変化を定量的に精度良く求めることが可能となる。なお、計測対象での吸収係数μ_ａについて、μ_ａ≪２πｆ／ｃ’の条件が満たされない場合には、計測精度を上げるために式（２．１）に補正項を入れても良い。 In such hemoglobin concentration measurement, the measurement using CW light cannot determine the average optical path length <L> in the living body, and therefore cannot determine the change in hemoglobin concentration as an absolute value. On the other hand, when the phase shift P (radian) is measured using modulated light as measurement light, the phase P and the average optical path length <L> are expressed by the following equations (2.1) and (2.2):

As shown, a linear relational expression is established. Here, c ′ represents the speed of light in the medium (scattering absorber). By converting the phase information P to the average optical path length <L>, the change in hemoglobin concentration can be obtained as an absolute value together with the attenuation rate measurement result. In particular, if the above-described measurement apparatus and measurement method capable of performing scattering absorber measurement by the PMS method under stable conditions are used, the concentration of hemoglobin and its change over time can be obtained quantitatively and accurately. When the condition of μ _a << 2πf / c ′ is not satisfied with respect to the absorption coefficient μ _a on the measurement target, a correction term may be added to the equation (2.1) in order to increase measurement accuracy.

  FIG. 4 is a block diagram schematically showing the configuration of the second embodiment of the scattering medium measuring apparatus according to the present invention.

  The measurement apparatus shown in FIG. 4 has an analysis including a laser diode 10, a current source 11, a photodetector 15, a reference signal generator 20, a phase detector 21, an attenuation rate analysis unit 23, and a concentration calculation unit 24. And a device 22. About these structures, it is the same as that of the measuring apparatus shown in FIG. In the present embodiment, the reference signal itself from the reference signal generator 20 is input to the laser diode 10 as a modulation signal for modulating the measurement light.

  In the measurement apparatus of the present embodiment, in addition to the reference signal generator 20, a monitor photodetector 30 and a monitor phase detector 31 are provided for the intensity-modulated measurement light supplied from the laser diode 10. ing. Further, an optical branching mirror 14 that branches a part of the measurement light emitted from the laser diode 10 is disposed at a predetermined position on the optical path between the laser diode 10 and the scattering medium SM.

  The monitor photodetector 30 receives and detects part of the measurement light branched by the light branching mirror 14 and outputs a monitor signal according to the intensity of the detected measurement light, a temporal change, or the like. The monitoring phase detector 31 detects the phase difference by comparing the phase of the monitor signal from the monitoring photodetector 30 with the reference signal from the reference signal generator 20, and responds to the detected phase difference. Output a reference signal.

  The reference signal from the monitoring phase detector 31 is input to the analysis device 22. In the analysis device 22, the detection result of the phase difference by the phase detector 21 is corrected by the input reference signal. Based on the detection result of the phase difference by the phase detector 21 corrected by the reference signal from the monitoring phase detector 31 and the analysis result of the light attenuation rate by the attenuation rate analysis unit 23, the density calculation unit 24 performs scattering. The concentration of the absorbing substance in the absorber SM is calculated.

  In the scattering medium measuring apparatus shown in FIG. 4 and the measuring method using the same, the monitor phase detector 31 compares the phase of the monitor signal with the phase of the reference signal to obtain a phase difference in the PMS method. A reference signal for the detection of. Thereby, it becomes possible to perform scattering absorber measurement by the PMS method under stable conditions.

  In addition, regarding the reflection of the reference signal to the scattering medium measurement, in this embodiment, the reference signal from the monitoring phase detector 31 is input to the analysis device 22, thereby detecting the phase difference by the phase detector 21. The result is corrected. According to such a configuration, even when the phase of the modulated measurement light from the laser diode 10 serving as the light supply means changes, the change in the phase is reflected in the detection result of the phase difference by the PMS method. Thus, it is possible to realize scattering absorber measurement by the PMS method under stable conditions.

  FIG. 5 is a block diagram schematically showing the configuration of the third embodiment of the scattering medium measuring apparatus according to the present invention.

  The measurement apparatus shown in FIG. 5 has an analysis including a laser diode 10, a current source 11, a photodetector 15, a reference signal generator 20, a phase detector 21, an attenuation rate analysis unit 23, and a concentration calculation unit 24. And a device 22. About these structures, it is the same as that of the measuring apparatus shown in FIG. Further, the configuration of the optical branching mirror 14, the monitoring photodetector 30, the monitoring phase detector 31, and the VCO 32 is the same as that of the measurement apparatus shown in FIG.

  In the measurement device of the present embodiment, a measurement light adjustment device 40, a differential amplifier 41, and an RF amplifier 42 are further installed.

  The differential amplifier 41 is a light amount control unit that monitors the DC component of the light output from the laser diode 10 that is a light supply unit and controls the light amount of the measurement light. The differential amplifier 41 is supplied with the DC component of the detection signal corresponding to the measurement light detected by the monitoring photodetector 30 and the reference voltage from the measurement light adjusting device 40. The differential amplifier 41 sends a control signal for keeping the amount of measurement light constant to the DC current source 11 based on the comparison result between the DC component of the detection signal and the reference voltage. Thereby, APC control for stabilizing the light amount of the measurement light supplied from the laser diode 10 is performed (light amount control step).

  On the other hand, an oscillation signal from the VCO 32 that is a modulation signal for modulating the measurement light is amplified with a predetermined gain by the RF amplifier 42 and then input to the laser diode 10. Further, the amplification gain of the oscillation signal in the RF amplifier 42 is controlled by a gain instruction signal from the measurement light adjusting device 40. As a result, the amplitude of the AC component in the measurement light supplied from the laser diode 10 is controlled.

  The measurement light adjustment device 40 is an adjustment unit that adjusts the measurement light so that the DC component or AC component of the light output from the laser diode 10 is within a desired range. The measurement light adjusting device 40 receives an adjustment instruction signal from the analysis device 22 that instructs setting or changing of the DC component value and the AC component value of the measurement light. The measuring light adjusting device 40 sets or changes the reference voltage to be sent to the differential amplifier 41 and the gain indication signal to be sent to the RF amplifier 42 based on the instruction signal from the analyzing device 22, thereby changing the laser diode. The DC component and AC component of the measurement light supplied from 10 are adjusted (measurement light adjustment step).

  In the present embodiment, an instruction signal indicating the operating conditions and the like is input from the laser diode 10 to the analysis device 22. The analysis device 22 sets the adjustment conditions of the measurement light by the measurement light adjustment device 40 in consideration of the contents of the instruction signal from the laser diode 10. Thereby, various measurement control according to the operating condition of the laser diode 10 becomes possible. The instruction signal from the laser diode 10 includes a signal indicating temperature information measured by a temperature sensor 12 (see FIG. 3) provided for the laser diode 10, for example. As the temperature sensor 12, for example, an element or a thermistor whose resistivity changes with temperature can be used. In FIG. 3, a change in resistance value is converted into a voltage change by using the fact that the resistance division ratio changes due to a change in resistance value due to temperature by connecting in series with a fixed resistor. However, the element used for the temperature sensor 12 is not limited to the thermistor.

  Information on the temperature sent from the laser diode 10 to the analysis device 22 may be reflected in a parameter used for calculation in the concentration calculation unit 24. For example, when the spectral characteristic of the measurement target for which the concentration is to be calculated depends on the wavelength, it is preferable to change the parameter used for the concentration calculation due to a temperature change. In this case, it is possible to improve the measurement accuracy by preparing a parameter table for the temperature value or an equation for obtaining the parameter in advance and changing the parameter to be used according to the temperature value. By performing such control, strict temperature control using a Peltier element or the like becomes unnecessary. At this time, in order to prevent thermal runaway of the laser diode 10, the laser diode 10 may be cooled by an air cooling fan or water cooling.

  In the scattering medium measuring apparatus shown in FIG. 5 and the measuring method using the same, the monitor phase detector 31 compares the phase of the monitor signal with the phase of the reference signal, and the phase difference in the PMS method. A reference signal for the detection of. Thereby, it becomes possible to perform scattering absorber measurement by the PMS method under stable conditions.

  Further, a measurement light adjusting device 40, a differential amplifier 41, and an RF amplifier 42 are provided for the measurement light supplied from the laser diode 10. Using such a configuration, by controlling and adjusting the DC component or AC component of the light output from the laser diode 10, the light amount, amplitude, optical waveform, etc. of the measurement light is suitably set, and scattering by the PMS method Absorbent measurement conditions can be further stabilized. In addition, the measurement conditions can be easily changed as necessary.

  The scattering medium measuring apparatus and the measuring method according to the present invention are not limited to the above-described embodiments, and various modifications are possible. For example, in the above-described embodiment, the analysis device 22 having the attenuation rate analysis unit 23 and the concentration calculation unit 24 is provided. However, when it is not necessary to derive the attenuation rate or the concentration, or when an external device performs the calculation For example, the attenuation rate analysis unit 23 and the concentration calculation unit 24 may be omitted. As a method for modulating the measurement light in the light supply means, the measurement light may be modulated by an optical modulator provided at the subsequent stage of the light source. In this case, the modulation signal is input to the optical modulator, and the modulation operation is controlled.

  In addition, a signal component within a predetermined frequency range may be provided between the monitoring photodetector 30 and the monitoring phase detector 31 or between the monitoring phase detector 31 and the VCO 32 as necessary. A frequency filter that selectively passes may be inserted. For example, FIG. 6 shows a configuration in which a frequency filter 35 is installed between the monitoring photodetector 30 and the monitoring phase detector 31 as a modification of the configuration of the scattering medium measuring apparatus shown in FIG. ing.

  In the configuration shown in FIG. 1 and the like, the reference signal generator 20 and the VCO 32 may be connected using a synchronization signal so as to operate stably in synchronization. In this case, generally, a signal of 10 MHz is often used. As for the phase control of the oscillation signal in the VCO 32, the phase is controlled by the VCO 32 itself in the above configuration, but the phase control method is not limited to this. For example, the VCO may be operated at a fixed phase, and the phase may be controlled by an element that delays the phase according to an electric signal. As the modulation signal for the laser diode 10, signals having various waveforms such as a sine wave and a rectangular wave may be used as long as the signals have a predetermined period.

  Various elements other than the light branching mirror 14 shown in FIG. 1 may be used as the light branching means for branching a part of the measurement light emitted from the laser diode 10. For example, a fiber having a branching function may be used by guiding light from a light source such as a laser diode to the fiber. Further, a bundle fiber, a fiber having the number of inputs and outputs of 1 input to 2 outputs by fusion, or the like may be used.

  The scattering medium measuring apparatus and the measuring method according to the present invention can be used as a measuring apparatus and a measuring method capable of performing scattering medium measurement by the PMS method under stable conditions regardless of changes in environmental temperature and light quantity.

It is a block diagram which shows the structure of 1st Embodiment of a scattering medium measuring device. It is a block diagram which shows the modification of a structure of the scattering medium measuring device shown in FIG. It is a figure which shows an example of the circuit system used for the PLL circuit provided with respect to a laser diode. It is a block diagram which shows the structure of 2nd Embodiment of a scattering medium measuring device. It is a block diagram which shows the structure of 3rd Embodiment of a scattering medium measuring device. It is a block diagram which shows the modification of a structure of the scattering medium measuring device shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Laser diode (light supply means), 11 ... DC current source, 12 ... Temperature sensor, 14 ... Optical branching mirror, 15 ... Photo detector, 20 ... Reference signal generator, 21 ... Phase detector for measurement, 22 ... Analyzing device, 23... Attenuation factor analyzing unit, 24... Concentration calculating unit, 30... Monitoring photodetector, 31... Monitoring phase detector, 32 .. VCO (voltage controlled oscillator), 33. ... Measurement light adjusting device, 41 ... differential amplifier, 42 ... RF amplifier.

Claims (12)

Reference signal generating means for outputting a reference signal of a predetermined reference frequency;
A light supply means for supplying measurement light of a predetermined wavelength for irradiation from a light irradiation position set to the scattering medium, and capable of modulating the measurement light by a modulation signal based on the reference signal;
Among the measurement light irradiated to the scattering medium from the light irradiation position, light detection means for detecting the light that has propagated through the interior and reached the light detection position and outputting a detection signal;
A phase detector for measurement that detects a phase difference between the detection signal from the light detector and the reference signal from the reference signal generator;
Monitoring means for monitoring a light output from the light supply means and outputting a monitor signal;
Monitor phase detection means for detecting a phase difference between the monitor signal from the monitor means and the reference signal from the reference signal generation means and outputting a reference signal for detection of the phase difference by the measurement phase detection means And a scattering medium measuring apparatus. An oscillator that outputs an oscillation signal of a predetermined frequency and that can control oscillation conditions by an external signal is provided.
The oscillation signal from the oscillator is input to the light supply unit as the modulation signal, and the oscillation condition of the oscillation signal is controlled by the reference signal from the monitoring phase detection unit in the oscillator. The scattering medium measuring apparatus according to claim 1.   The reference signal from the reference signal generation means is input to the light supply means as the modulation signal, and a phase difference detection result by the measurement phase detection means by the reference signal from the monitoring phase detection means The scattering medium measuring apparatus according to claim 1, wherein: An attenuation rate analysis means for obtaining an attenuation rate of light in the scattering medium by the detection signal from the light detection means;
A concentration calculating means for calculating the concentration of the absorbing substance in the scattering medium based on the detection result of the phase difference by the measurement phase detecting means and the analysis result of the attenuation rate by the attenuation rate analyzing means. The scattering medium measuring apparatus according to any one of claims 1 to 3.   5. The apparatus according to claim 1, further comprising a light amount control unit that monitors a DC component of light output from the light supply unit and controls a light amount of the measurement light supplied from the light supply unit. The scattering medium measuring apparatus according to one item.   The measurement light adjusting means for adjusting the measurement light supplied from the light supply means so that the DC component or AC component of the light output from the light supply means falls within a desired range. Item 6. The scattering medium measuring apparatus according to any one of Items 1 to 5. A reference signal generation step for outputting a reference signal of a predetermined reference frequency;
A light irradiation step of irradiating measurement light having a predetermined wavelength from the light supply means modulated by the modulation signal based on the reference signal from the light irradiation position set for the scattering medium;
Among the measurement light irradiated to the scattering medium from the light irradiation position, a light detection step of detecting light that has propagated through the measurement light and reached the light detection position and outputting a detection signal;
A phase detection step for measurement for detecting a phase difference between the detection signal from the light detection step and the reference signal from the reference signal generation step;
A monitoring step of monitoring a light output from the light supply means and outputting a monitor signal;
A monitoring phase detection step for detecting a phase difference between the monitoring signal from the monitoring step and the reference signal from the reference signal generation step and outputting a reference signal for detection of the phase difference in the measurement phase detection step A scattering absorber measurement method comprising: An oscillation signal generating step for outputting an oscillation signal of a predetermined frequency whose oscillation condition is controlled by an external signal;
The oscillation signal from the oscillation signal generation step is input to the light supply means as the modulation signal, and the oscillation condition of the oscillation signal is determined by the reference signal from the monitoring phase detection step in the oscillation signal generation step. The scattering absorber measurement method according to claim 7, wherein:   The reference signal from the reference signal generation step is input as the modulation signal to the light supply means, and the detection result of the phase difference in the measurement phase detection step by the reference signal from the monitoring phase detection step The method of measuring a scattering medium according to claim 7, wherein: An attenuation rate analysis step for obtaining an attenuation rate of light in the scattering medium by the detection signal from the light detection step;
A concentration calculation step of calculating a concentration of the absorbing substance in the scattering medium based on a detection result of the phase difference in the measurement phase detection step and an analysis result of the attenuation rate in the attenuation rate analysis step. The scattering medium measuring method according to any one of claims 7 to 9.   The light quantity control step of monitoring the DC component of the light output from the light supply means and controlling the light quantity of the measurement light supplied from the light supply means. The scattering absorber measurement method according to one item.   The measurement light adjustment step of adjusting the measurement light supplied from the light supply means so that the DC component or AC component of the light output from the light supply means falls within a desired range. Item 12. The scattering medium measuring method according to any one of Items 7 to 11.

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