Calibration apparatus and calibration method

A calibration apparatus includes an insertion portion into which a measurement probe is inserted and a reference reflection plate that is arranged at a position away from a distal end of the measurement probe by a predetermined distance in a state in which the measurement probe has been inserted in the insertion portion and that has uniform reflectivity of light in a range of a wavelength to be measured in an irradiation plane of an illumination light, wherein a material forming the reference reflection plate has a scattering mean free path that is greater than a spatial coherence length at the predetermined distance.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a calibration apparatus and a calibration method that calibrate an optical measurement apparatus that measures, as an amount of scattering and absorption of light, information related to an internal structure of an object to be measured.

2. Description of the Related Art

Conventionally, backward scattered returned light from a comparatively weak scattering medium such as body tissue has been known to be observed as light that increases interference according to a degree of spatial coherence of illumination light thereof (see Young L. Kim, et. al: Low-Coherence Enhanced Backscattering; Review of Principles and Applications for Colon Cancer Screening, Journal of Biomedical Optics, 11(4), 041125 2006). A technique of measuring spectroscopic information using this phenomenon is called low-enhanced backscattering spectroscopy (LEBS), and characteristics of an interference pattern with respect to a scattering mean free path (a reciprocal of a scattering coefficient) in a scattering medium have been well studied (see V, Turzhitsky, et. al: Characterization of Light Transport in Scattering Media at Subdiffusion Length Scales with Low-Coherence Enhanced Backscattering, IEEE journal of selected topics in quantum electronics, Vol. 16, No. 3, 619 (2010)). This scattering mean free path has a correlation with an internal structural change in the scattering medium and is used in detecting a minute tissue structural change as seen in early cancer. For example, distinguishment of colorectal cancer using an interference pattern of scattered returned light has been known to be possible (see Hemant K. Roy, et. al: Association Between Rectal Optical Signatures and Colonic Neoplasia: Potential Applications for Screening, Cancer Research, 69(10), 4476 (2009)).

A technique of applying the above mentioned LEBS to noninvasive measurement within a body through a small diameter probe inserted in an endoscope is known (see U.S. Patent Application Publication No. 2009/0009759). In this technique, in order to obtain an interference pattern, detection fibers are arranged at different plural positions in a plane on which the interference pattern is formed, and signals are detected by detectors corresponding to the respective detection fibers.

SUMMARY OF THE INVENTION

A calibration apparatus according to one aspect of the present invention obtains a plurality of calibration data used when an optical measurement apparatus corrects returned light from an object to be measured, the optical measurement apparatus including: a measurement probe having an illumination fiber that irradiates to the object to be measured illumination light including at least light of wavelength to be measured and a plurality of detection fibers that receive the returned light, which is of the illumination light reflected and/or scattered by the object to be measured; and a plurality of detection units that detect the returned light respectively received by the plurality of detection fibers, and the calibration apparatus includes: an insertion portion into which the measurement probe is inserted; and a reference reflection plate that is arranged at a position away from a distal end of the measurement probe by a predetermined distance in a state in which the measurement probe has been inserted in the insertion portion and that has uniform reflectivity of light in a range of the wavelength to be measured in an irradiation plane of the illumination light, wherein a material forming the reference reflection plate has a scattering mean free path that is greater than a spatial coherence length at the predetermined distance.

A calibration method according to another aspect of the present invention of obtaining calibration data using a calibration apparatus with respect to an optical measurement apparatus that includes: a measurement probe having an illumination fiber that irradiates to an object to be measured illumination light including at least light of wavelength to be measured and a plurality of detection fibers that receive, at different angles, returned light of the illumination light reflected and/or scattered by the object to be measured; and a plurality of detection units that detect the returned light respectively received by the plurality of detection fibers, includes: a first step of obtaining data for internal reflection calibration of the measurement probe detected by the detection units when the measurement probe is caused to irradiate the illumination light to an insertion portion that is provided, inside the calibration apparatus, with a light absorption member that absorbs light; and a second step of obtaining reference reflection plate calibration data detected by the detection units when the measurement probe irradiates the illumination light to a reference reflection plate in the calibration apparatus, the reference reflection plate being arranged at a position away from a distal end of the measurement probe by a predetermined distance and having uniform reflectivity of light over a range of the wavelength to be measured in an irradiation plane of the illumination light, wherein a material forming the reference reflection plate has a scattering mean free path that is greater than a spatial coherence length at the predetermined distance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of an optical measurement apparatus and a calibration apparatus according to the present invention will be described in detail with reference to the drawings. Further, in describing the drawings, the same portions are appended with the same reference signs. Further, the drawings are schematic, and it is to be noted that the relation between the thickness and width of each component and the ratios among the respective components are different from the actual. Further, a portion is included, which has different size relations and ratios among the drawings. The present invention is not limited by the embodiments.

First Embodiment

FIG. 1is a block diagram that schematically illustrates a configuration of an optical measurement apparatus and a calibration apparatus according to a first embodiment of the present invention and is a diagram that illustrates a state in which the calibration apparatus has been connected to the optical measurement apparatus.

First, the optical measurement apparatus is described. An optical measurement apparatus1illustrated inFIG. 1includes a main body unit2that performs optical measurement with respect to an object to be measured such as body tissue, which is a scattering media, and measures characteristics (properties) of the object to be measured, and a measurement probe3that is detachable from the main body unit2, inserted into a subject.

The main body unit2has a power source20, a light source unit21, a connector unit22, a first detection unit23, a second detection unit24, a third detection unit25, an input unit26, an output unit27, a recording unit28, and a control unit29. The power source20supplies electric power to each component of the main body unit2.

The light source unit21irradiates to the measurement probe3, via the connector unit22, illumination light to be irradiated onto the object to be measured. The light source unit21is realized by using a light source such as a white light emitting diode (LED), a xenon lamp, a tungsten lamp, a halogen lamp, and a laser, and a plurality of lenses. Examples of such lenses include condenser lenses and collimator lenses. The light source unit21irradiates illumination light having a wavelength component included in a predetermined wavelength band.

To the connector unit22, the measurement probe3is detachably connected. The connector unit22propagates, to the measurement probe3, the illumination light irradiated by the light source unit21, and propagates a plurality of light beams entering from the measurement probe3respectively to the first detection unit23, the second detection unit24, and the third detection unit25.

The first detection unit23detects returned light of the illumination light that has been irradiated from the measurement probe3and reflected and/or scattered by the object to be measured, and outputs a result of this detection to the control unit29. Specifically, the first detection unit23detects a spectral component and an intensity distribution of scattered light entering from the measurement probe3, and outputs a result of this detection to the control unit29. The first detection unit23is realized using a spectrometer, a light receiving sensor, or the like.

The second detection unit24is realized by the same configuration as that of the first detection unit23, detects the returned light of the illumination light that has been irradiated from the measurement probe3and reflected and/or scattered by the object to be measured, and outputs a result of this detection to the control unit29.

The third detection unit25is realized by the same configuration as that of the first detection unit23, detects the returned light of the illumination light that has been irradiated from the measurement probe3and reflected and/or scattered by the object to be measured, and outputs a result of this detection to the control unit29.

The input unit26receives and outputs to the control unit29, input of an instruction signal instructing activation of the main body unit2, an instruction signal instructing start of measurement of a measurement object S1by the main body unit2, an instruction signal instructing a calibration process, and the like. The input unit26is realized using a push-type switch, a touch panel, or the like.

The output unit27outputs, under control by the control unit29, various information in the main body unit2, for example, a result of measurement on the object to be measured. The output unit27is realized using a display of a liquid crystal, organic electroluminescence (EL), or the like, and a speaker or the like.

The control unit29comprehensively controls the main body unit2by carrying out transfer or the like of instruction information or data corresponding to each component of the main body unit2. The control unit29is configured using a central processing unit (CPU) or the like. The control unit29has a calculation unit291.

The calculation unit291performs a plurality of calculation processes based on detection results respectively detected by the first detection unit23, the second detection unit24, and the third detection unit25, to calculate characteristic values related to the characteristics of the object to be measured.

Next, the measurement probe3will be described.FIG. 2is a diagram that schematically illustrates a cross section of the distal end of the measurement probe3, the cross section being cut to include a central axis in a longitudinal direction of the measurement probe3.FIG. 3is a front view of the measurement probe3viewed from the distal end thereof.

The measurement probe3illustrated inFIGS. 1 to 3includes an illumination fiber31, a first detection fiber32, a second detection fiber33, a third detection fiber34, a fiber holding portion35, and a rod lens (optical element)36. The illumination fiber31, the first detection fiber32, the second detection fiber33, and the third detection fiber34are each realized using an optical fiber having a core diameter of ρ1and a cladding thickness of ρ2.

The illumination fiber31irradiates, via the rod lens36, the illumination light entering, via the connector unit22, from the light source unit21, to the object to be measured or a calibration apparatus4.

The first detection fiber32detects (receives), via the rod lens36, the returned light of the illumination light that has been irradiated by the illumination fiber31and reflected and/or scattered by the object to be measured or the calibration apparatus4, and propagates the received returned light to the first detection unit23.

The second detection fiber33detects, via the rod lens36, the returned light of the illumination light that has been irradiated by the illumination fiber31and reflected and/or scattered by the object to be measured or the calibration apparatus4, and propagates the received returned light to the second detection unit24.

The third detection fiber34detects, via the rod lens36, the returned light of the illumination light that has been irradiated by the illumination fiber31and reflected and/or scattered by the object to be measured or the calibration apparatus4, and propagates the received returned light to the third detection unit25.

The fiber holding portion35holds respective distal ends of the illumination fiber31, the first detection fiber32, the second detection fiber33, and the third detection fiber34to be arranged in a straight line or irregularly. Specifically, the fiber holding portion35holds the illumination fiber31, the first detection fiber32, the second detection fiber33, and the third detection fiber34so that optical axes of the illumination fiber31, the first detection fiber32, the second detection fiber33, and the third detection fiber34become parallel to one another. Further, the fiber holding portion35fixes the illumination fiber31, the first detection fiber32, the second detection fiber33, and the third detection fiber34respectively at predetermined positions so that the returned light of the illumination light enters therein at different angles. For example, the fiber holding portion35holds the illumination fiber31and the first detection fiber32so that a return of the illumination light irradiated from the illumination fiber31enters the first detection fiber32at an angle θ. The fiber holding portion35is realized using a glass, a resin, a metal, or the like.

The rod lens36is provided on a distal end of the fiber holding portion35. The rod lens36is realized using a glass, a plastic, or the like having a predetermined transmissivity, and is column-shaped so that distances from the respective distal ends of the illumination fiber31, the first detection fiber32, the second detection fiber33, and the third detection fiber34to the object to be measured or to the calibration apparatus4become constant.

Next, the calibration apparatus4will be described. The calibration apparatus4includes a container41, a stopper portion42that prevents insertion of the measurement probe3, and a reference reflection plate43used in a calibration process.

The container41is tubular and has an insertion portion41athrough which the measurement probe3is insertable, and an accommodation portion41bthat accommodates the reference reflection plate43. The container41is integrally formed of the insertion portion41aand the accommodation portion41b.

The stopper portion42is ring-shaped and provided in the accommodation portion41b. The stopper portion42prevents the measurement probe3from being inserted into the accommodation portion41b. An inner diameter of the stopper portion42is smaller than an outer diameter of the measurement probe3. The stopper portion42keeps a predetermined distance L from an end of the rod lens36of the measurement probe3to the reference reflection plate43constant.

The reference reflection plate43is arranged at a position which is away by the predetermined distance L from a distal end portion of the measurement probe3in a state in which the measurement probe3has been inserted in the insertion portion41a. The reference reflection plate43formed of a material having light reflectivity that is uniform over a wavelength range to be measured in an irradiation plane of the illumination light irradiated by the measurement probe3. Specifically, a scattering mean free path of a material forming the reference reflection plate43is set to be of a larger value than that of a spatial coherence length at the predetermined distance L.

In the optical measurement apparatus1configured as described above, after a calibration process is performed by the calibration apparatus4, as illustrated inFIG. 4, the measurement probe3is inserted into the subject via a treatment tool channel51aprovided in an endoscopic device51(endoscope) of an endoscopic system5, the illumination fiber31irradiates the illumination light to the object to be measured, and the first detection fiber32, the second detection fiber33, and the third detection fiber34respectively detect, at different scattering angles, the returned light of the illumination light that has been reflected and/or scattered by the object to be measured and propagate the detected returned light to the first detection unit23, the second detection unit24, and the third detection unit25. Thereafter, the calculation unit291calculates the characteristic values representing the characteristics of the object to be measured, based on detection results detected respectively by the first detection unit23, the second detection unit24, and the third detection unit25.

Next, calibration items of the optical measurement apparatus1will be described in detail.FIG. 5is a diagram that schematically illustrates an interference pattern detected by the optical measurement apparatus1.FIG. 6is a diagram that schematically illustrates intensities of signals detected by the optical measurement apparatus1. InFIGS. 5 and 6, the illumination fiber31is described as an illumination fiber S, and the first detection fiber32, the second detection fiber33, and the third detection fiber34are respectively described as a first detection fiber d1, a second detection fiber d2, and a third detection fiber d3. Further, inFIGS. 5 and 6, the first detection fiber d1and the second detection fiber d2correspond to intensities at skirt portions of the interference pattern, and the third detection fiber d3corresponds to an intensity of a scattered light component of a degree that allows influence of interference to be ignored. Further, inFIG. 6, an intensity detected by a detection fiber S for a case in which the illumination fiber31is supposed to be the detection fiber S is also illustrated. InFIG. 6, signal values corresponding to particular wavelengths are illustrated.

As illustrated inFIGS. 5 and 6, because the signal value detected by the detection fiber S corresponds to the maximum value of the interference pattern, the intensity thereof is the largest. Further, the signal values detected respectively by the first detection fiber d1and the second detection fiber d2are of the same intensities, because they are at positions away from the detection fiber S by the same distances. Further, the signal value detected by the third detection fiber d3is of the smallest intensity. However, the signal values are influenced by variation in light guiding efficiency of detection routes, and variation in detection sensitivity of each of the first detection unit23, the second detection unit24, and the third detection unit25. Accordingly, as illustrated inFIG. 7, even if light of uniform intensity is irradiated to the measurement probe3, the signal values detected respectively by the first detection fiber d1, the second detection fiber d2, and the third detection fiber d3do not become constant (seeFIG. 8). Therefore, as illustrated inFIG. 9, calibration to make detection intensities respectively detected by the first detection fiber d1, the second detection fiber d2, and the third detection fiber d3constant is needed.

Further, as illustrated inFIG. 10, an illumination area A to which the illumination fiber31irradiates the illumination light does not coincide with a detection area B for which the first detection fiber32, the second detection fiber33, and the third detection fiber34each detect the returned light of the illumination light, and thus variation in the signal values is generated. For example, as illustrated inFIG. 10, the illumination area A to which the illumination fiber31irradiates the illumination light and the detection area B over which the third detection fiber34detects the returned light of the illumination light are different from each other. Therefore, the optical measurement apparatus1needs to perform correction of detection signals according to variation in a detection range of the object to be measured.

Next, the reference reflection plate43of the calibration apparatus4will be described in detail. In the calibration apparatus4, for the above mentioned calibration items, material properties of the reference reflection plate43are set, correspondingly with a degree of spatial coherence on the reference reflection plate43, i.e., a spatial coherence length Lsc, to satisfy Condition (1) or Condition (2).
ls*≧2Lsc, ANDg≦0.85  (1):
ls*≈2Lsc, ANDg>0.85  (2):
Herein, ls* represents the scattering mean free path of the material forming the reference reflection plate43, and “g” represents an anisotropic parameter in a scattering direction of the reference reflection plate43. For Condition (2), a range of ls*/Lsc=1 to 3 is only needed.

Further, as illustrated inFIG. 1, when a length in a fiber longitudinal direction of the rod lens36is “R”, a distance from the distal end of the measurement probe3to the reference reflection plate43is “L”, a refractive index of the rod lens36at a prescribed wavelength λ is “n”, and a core diameter of the illumination fiber31is ρ1, the spatial coherence length Lsc at a detection position of the reference reflection plate43is defined by Equation (3) below.
Lsc=λ(R/n+L)/πρ1(3)

As described above, in the calibration apparatus4, based on Condition (1) or Condition (2): the scattering mean free path ls* of the reference reflection plate43is preset and the distance L is set such that the spatial coherence length Lsc satisfies Condition (1) or Condition (2); or the distance L of the reference reflection plate43is preset and the material of the reference reflection plate43is adjusted or selected such that the scattering mean free path ls* satisfies Condition (1) or Condition (2). In this case, because for the reference reflection plate43, a material having reflectivity that is constant regardless of wavelength needs to be selected, preferably, the scattering mean free path ls* of the reference reflection plate43is set, and the distance L is set such that the spatial coherence length Lsc satisfies Condition (1) or Condition (2). Even if a value of the scattering mean free path ls* of the material forming the reference reflection plate43is not accurately known, intensity change detected by any of the first detection fiber32, the second detection fiber33, and the third detection fiber34may be detected by changing a position of the reference reflection plate43and the distance L may be set to a position at which the detection intensities of the first detection fiber32and the second detection fiber33are of the minimum values.

Condition (1) and Condition (2) will now be described in detail. According to Condition (1) and Condition (2), a shape of the interference pattern, which is formed at the distal end of the measurement probe3when the illumination light from the measurement probe3is reflected and/or scattered and becomes the returned light, is determined by the spatial coherence length Lsc at a position of the reference reflection plate43and the scattering mean free path ls* of the reference reflection plate43(see Non-Patent Literature 2).

FIG. 11is a diagram that illustrates a relation between a value of a ratio of the scattering mean free path ls* to the spatial coherence length Lsc and a value of a ratio obtained by dividing an apparent light source size by a full width at half maximum (FWHM) w of the interference pattern.FIG. 12is a diagram that schematically illustrates the full width at half maximum w.

As illustrated inFIG. 11, when the anisotropic parameter g in the scattering direction of the reference reflection plate43is less than 0.85, a value of α/w tends to converge from around where a value of ls*/Lsc becomes greater than 2. Further, when the anisotropic parameter g in the scattering direction of the reference reflection plate43is greater than 0.85, the value α/w becomes maximum around where the value of ls*/Lsc is 2. Therefore, when the value becomes maximum around where the value of ls*/Lsc is 2, the full width at half maximum w of the interference pattern becomes the smallest.

As described above, under the condition where the full width at half maximum w of the interference pattern becomes the smallest, the interference pattern does not enter the first detection fiber32to the third detection fiber34and at a position of the detection fiber, a luminous flux of uniform intensity is obtained. Accordingly, from a relation between the full width at half maximum w and scattering properties of a scattering medium (ls*/Lsc and g) illustrated inFIG. 11, Condition (1) and Condition (2) are able to be derived as conditions under which the full width at half maximum w becomes the smallest.

Further, the apparent light source size a illustrated inFIGS. 11 and 12, is, as illustrated inFIG. 13, a quantity represented by Equation (4) below where a numerator is the core diameter ρ1of the illumination fiber31and a denominator is a sum of the distance L from the illumination fiber31to the reference reflection plate43and a value R/n obtained by dividing the length R of the rod lens36by the refractive index n of the rod lens36.
α=ρ1/(R/n+L)  (4)
When α of Equation (4) is small (α<0.1), α becomes equal to an angle α′ [rad] illustrated inFIG. 13. Therefore, the vertical axis α/w ofFIG. 11can be said to be an index indicating the extent to which the full width at half maximum w of the interference pattern fits in an angle range a corresponding to the core ρ1of the illumination fiber31.

FIG. 14is a diagram when α/w=1, and an interference peak corresponding to the full width at half maximum w of the interference pattern fits in the core ρ1of the illumination fiber31.

As illustrated inFIG. 14, the optical measurement apparatus1considers a condition under which skirt of the interference pattern is not in the respective cores of the first detection fiber32and the second detection fiber33. Under this condition, the core of the detection fiber32is positioned outer than about a position corresponding to twice (2w) the full width at half maximum w. Specifically, it is important that the skirt of the interference pattern is not in the respective cores of the first detection fiber32and the second detection fiber33. InFIG. 14, a case in which α/w=1 is illustrated, but the full width at half maximum w is not necessarily in the core ρ1of the illumination fiber31. For example, if α/w=1 is not true, the full width at half maximum w just needs to be not in the respective cores of the first detection fiber32and the second detection fiber33. Such a situation would be a case in which the thicknesses of the claddings of the first detection fiber32to the third detection fiber34and the illumination fiber31are thick.

Further, as illustrated inFIG. 3, when the core diameter of the illumination fiber31is ρ1and the thickness of the cladding thereof (hereinafter, “cladding thickness”) is ρ2, the full width at half maximum w satisfies Condition (5) below.
(ρ1+4ρ2)/(R/n+L)>2w(5):

As illustrated inFIG. 15, when the core diameter of the illumination fiber31is ρ1, the cladding thickness thereof is ρ2, the respective core diameters of the first detection fiber32, the second detection fiber33, and the third detection fiber34are ρ3, and the cladding thicknesses thereof are ρ4, the full width at half maximum w satisfies Condition (6) below.
(ρ1+2ρ2+2ρ4)/(R/n+L)>2w(6):

As described above, in the measurement probe3, because a light guiding property of each fiber is maintained and thus the cladding thicknesses are set to be thick, the above Condition (5) or Condition (6) is satisfied.

Next, a calculation process including the calibration process performed by the optical measurement apparatus1is described.FIG. 16is a flow chart that illustrates an outline of the calculation process including the calibration process performed by the optical measurement apparatus1. Hereinafter, “ch” represents each detection fiber number and λ represents wavelength.

As illustrated inFIG. 16, the optical measurement apparatus1obtains internal reflection calibration data BA (ch, λ) by inserting absorbing apparatus as illustrated inFIG. 17. (Step S101).FIG. 17is a diagram that schematically illustrates a cross section of an absorbing apparatus according to the first embodiment of the present invention. A absorbing apparatus6illustrated inFIG. 17includes a container61that is approximately a cuboid and a stopper portion62that prevents insertion of the measurement probe3.

The stopper portion62is ring-shaped and provided in the accommodation portion61b. The stopper portion62prevents the measurement probe3from being inserted into the accommodation portion61b. An inner diameter of the stopper portion62is smaller than an outer diameter of the measurement probe3. The stopper portion62keeps a distance L from the end of the rod lens36of the measurement probe3to a bottom surface of the accommodation portion61bconstant.

The container61has an insertion portion61ainto which the measurement probe3is insertable, and an accommodation portion61bhaving an inner surface formed of a light absorption portion61cprovided with a member that does not reflect light or a light absorption member that absorbs wavelength of light irradiated by the light source unit21. Specifically, the light absorption portion c1cis coated in black. Specifically, the optical measurement apparatus1obtains, by irradiating, in the insertion portion61aof the calibration apparatus6, the illumination light to the illumination fiber31, internal reflection calibration data in a measurement probe detected by the first detection unit23, the second detection unit24, and the third detection unit25.

Subsequently, the optical measurement apparatus1obtains, in a state in which the distal end of the measurement probe3has come into contact with the stopper portion42, reference reflection plate calibration data IS (ch, λ) of the reference reflection plate43(Step S102). Specifically, the optical measurement apparatus1, obtains, by the illumination fiber31irradiating the illumination light to the reference reflection plate43in a state in which the distal end of the rod lens36of the measurement probe3has come into contact with the stopper portion42, reference reflection plate calibration data of the reference reflection plate43, the reference reflection plate calibration data having been detected by each of the first detection unit23, the second detection unit24, and the third detection unit25.

Thereafter, the optical measurement apparatus1obtains measured data T (ch, λ) of the object to be measured (Step S103). Specifically, the optical measurement apparatus1obtains, by the illumination fiber31irradiating the illumination light to the object to be measured, measured data detected by each of the first detection unit23, the second detection unit24, and the third detection unit25.

Subsequently, the calculation unit291converts, using the internal reflection calibration data BA (ch, λ) and the reference reflection plate calibration data IS (ch, λ), the measured data T (ch, λ) into calibrated data S (ch, λ) (Step S104). Specifically, the calculation unit291converts the measured data T (ch, λ) into the calibrated data S (ch, λ) by Equation (7) below.
S(ch,λ)=(T(ch,λ)−BA(ch,λ))/(IS(ch,λ)−BA(ch,λ))  (7)

According to the above described first embodiment of the present invention, the reference reflection plate43is included, which is arranged at the position away by the predetermined distance L from the distal end portion of the measurement probe3in the state in which the measurement probe3has been inserted in the insertion portion41a, and for the reference reflection plate43, the scattering mean free path of the material forming the reference reflection plate43is set to be larger than the spatial coherence length Lsc determined using the predetermined distance L. As a result, complicated plural calibration items are readily obtainable in one operation.

Second Embodiment

Next, a second embodiment of the present invention will be described. In the second embodiment, a configuration of a calibration apparatus is different from the calibration apparatus according to the above described first embodiment. Therefore, hereinafter, the configuration of the calibration apparatus according to the second embodiment will be described. Configurations that are the same as those of the optical measurement apparatus1and the calibration apparatus4according to the above described first embodiment will be described being appended by the same reference signs.

In the second embodiment, a spherical formation may be employed.FIG. 18is a diagram that schematically illustrates a cross section of a calibration apparatus according to a second embodiment. A calibration apparatus7illustrated inFIG. 18includes a container71that is approximately spherical and a stopper portion72that prevents insertion of the measurement probe3.

The container71has an insertion portion71ainto which the measurement probe3is insertable, and an accommodation portion71bthat accommodates the reference reflection plate43.

Third Embodiment

Next, a third embodiment of the present invention will be described. The third embodiment has a different configuration for a calibration apparatus. Therefore, hereinafter, the configuration of the calibration apparatus according to the third embodiment will be described. Configurations that are the same as those of the optical measurement apparatus1and the calibration apparatus4according to the above described first embodiment will be described being appended by the same reference signs.

FIG. 19is a diagram that schematically illustrates a cross section of the calibration apparatus according to the third embodiment. A calibration apparatus8illustrated inFIG. 19includes a container81, a stopper portion42, and the reference reflection plate43.

The container81has an insertion portion81athrough which the measurement probe3is insertable, and an accommodation portion81bthat accommodates the reference reflection plate43, and the container81is formed integrally of the insertion portion81aand the accommodation portion81b.

The insertion portion81ahas, on an inner surface thereof, a light absorption portion81cprovided with a member that does not reflect light or a light absorption member that absorbs wavelength of light irradiated by the light source unit21. Specifically, the light absorption portion81cis coated in black.

A calibration process performed using the calibration apparatus8configured as above will be described.FIG. 20is a diagram that schematically illustrates an outline of the calibration process, which the optical measurement apparatus1performs, using the calibration apparatus8.

As illustrated inFIG. 20, the optical measurement apparatus1obtains, when the illumination fiber31irradiates the illumination light to the light absorption portion81cin the insertion portion81a, internal reflection calibration data detected by each of the first detection unit23, the second detection unit24, and the third detection unit25(FIG. 20(a) toFIG. 20(b)). In this case, the optical measurement apparatus1may obtain the internal reflection calibration data when a user stops the insertion of the measurement probe3midway through the insertion portion81a. Further, the calculation unit291may continuously obtain the internal reflection calibration data until the measurement probe3comes into contact with the stopper portion42and select, as an internal reflection calibration data to be used in the calibration process, data indicating the minimum intensity, from the obtained internal reflection calibration data. This step is corresponds to the step S101inFIG. 16.

Subsequently, the optical measurement apparatus1obtains the reference reflection plate calibration data detected by the first detection unit23, the second detection unit24, and the third detection unit25when the illumination fiber31irradiates the illumination light to the reference reflection plate43(FIG. 20(b)). Preferably, the calculation unit291selects, as the reference reflection plate calibration data, data indicating the maximum intensity detected by the first detection unit23, the second detection unit24, and the third detection unit25when the distal end of the measurement probe3comes into contact with the stopper portion42. This step is corresponds to the step S102inFIG. 16.

According to the above described third embodiment of the present invention, just by a single operation of inserting the measurement probe3into the insertion portion81aof the calibration apparatus8, plural calibration items are able to be performed simultaneously. As a result, complicated operations are able to be lessened, and damage to the measurement probe3during calibration processes and forgetting to take calibration data are preventable.

Further, according to the third embodiment, plural calibration items are able to be performed simultaneously with a simple configuration.

In the third embodiment of the present invention, a position of the reference reflection plate43may be movably provided by a drive unit such as a motor, and while adjusting the distance from the measurement probe3to the reference reflection plate43, the optical measurement apparatus1may measure the reference reflection plate calibration data and the internal reflection calibration data.

Fourth Embodiment

Next, a fourth embodiment of the present invention will be described. The fourth embodiment has a different configuration for a calibration apparatus. Therefore, hereinafter, the configuration of the calibration apparatus according to the fourth embodiment will be described. Configurations that are the same as those of the optical measurement apparatus1and the calibration apparatus4according to the above described first embodiment will be described being appended by the same reference signs.

FIG. 21is a diagram that schematically illustrates a cross section of the calibration apparatus according to the fourth embodiment. A calibration apparatus9illustrated inFIG. 21includes a container91, the stopper portion42, and the reference reflection plate43.

The container91has an insertion portion91athrough which the measurement probe3is inserted, and an accommodation portion91bthat accommodates the reference reflection plate43. The container91is integrally formed of the insertion portion91aand the accommodation portion91b. The insertion portion91ais tubular and connected to the accommodation portion91bwith a portion of the insertion portion91abeing bent.

When a calibration process is performed using the calibration apparatus9configured as above, the optical measurement apparatus1obtains internal reflection correction data before the bend of the insertion portion91a. When this is done, the illumination light irradiated from the measurement probe3will not be irradiated to the reference reflection plate43and thus the returned light of the illumination light is preventable from influencing the measurement probe3.

According to the above described fourth embodiment of the present invention, because the portion of the insertion portion91ais bent, upon the calibration of the internal reflection correction, the influence by the returned light from the reference reflection plate43is preventable and thus an accurate calibration process is able to be performed.

According to the fourth embodiment, an angle of the bend of the insertion portion91ais approximately 90 degrees, but the insertion portion91aonly needs to be bent to an extent such that the reference reflection plate43is not visible at the front of the measurement probe3and the angle of the bend may be changed as appropriate in order to ensure operability.

In the fourth embodiment of the present invention, the position of the reference reflection plate43may be movably provided by a drive unit such as a motor, and while adjusting the distance from the measurement probe3to the reference reflection plate43, the optical measurement apparatus1may measure the reference reflection plate calibration data and the internal reflection calibration data.

Fifth Embodiment

Next, a fifth embodiment of the present invention will be described. The fifth embodiment has a different configuration for a calibration apparatus. Therefore, hereinafter, the configuration of the calibration apparatus according to the fifth embodiment will be described. Configurations that are the same as those of the optical measurement apparatus1and the calibration apparatus4according to the above described first embodiment will be described being appended by the same reference signs.

FIGS. 22 and 23are diagrams that each schematically illustrates a cross section of the calibration apparatus according to the fifth embodiment. A calibration apparatus10illustrated inFIGS. 22 and 23includes a container101, the stopper portion42, the reference reflection plate43, a shutter102, and a drive unit103.

The container101has an insertion portion101athrough which the measurement probe3is inserted, and an accommodation portion101bthat accommodates the reference reflection plate43. The container101is integrally formed of the insertion portion101aand the accommodation portion101b. Further, the insertion portion101ahas a hole101cprovided therein, through which the shutter102is retractably insertable. Further, the insertion portion101ahas the stopper portion42provided therein.

The shutter102is circular and shields the illumination light irradiated by the measurement probe3. The shutter102is formed using a black plate, which uses a light absorption member or the like.

The drive unit103retractably drives the shutter102with respect to the hole101c. The drive unit103is configured using a DC motor, a stepping motor, or the like.

A calibration process performed by the optical measurement apparatus1using the calibration apparatus configured as above will be described. The optical measurement apparatus1obtains the internal reflection calibration data. In this case, as illustrated inFIG. 22, the shutter102is arranged on an optical axis of the illumination light irradiated by the measurement probe3, and shields the illumination light irradiated by the measurement probe3.

Subsequently, by driving the drive unit103, the calibration apparatus10retracts the shutter102from the hole101cof the insertion portion101a(seeFIG. 23).

Thereafter, the optical measurement apparatus1obtains the reference reflection plate calibration data by irradiating the illumination light to the reference reflection plate43.

According to the above described fifth embodiment of the present invention, calibration items of the optical measurement apparatus1are automatically changeable, and thus plural calibration items are able to be readily performed in one operation.

Sixth Embodiment

Next, a sixth embodiment of the present invention will be described. The sixth embodiment has a different configuration for a calibration apparatus. Therefore, hereinafter, the configuration of the calibration apparatus according to the sixth embodiment will be described. Configurations that are the same as those of the optical measurement apparatus1and the calibration apparatus4according to the above described first embodiment will be described being appended by the same reference signs.

FIG. 24is a diagram that schematically illustrates a cross section of the calibration apparatus according to the sixth embodiment. A calibration apparatus11illustrated inFIG. 24includes: an accommodation unit111b, which has a space inside, and into which the measurement probe3is inserted through an insertion portion111a; the stopper portion42, which is provided in the accommodation unit111band prevents insertion of the measurement probe3; a rotation plate112, which rotates about a predetermined axis; a drive unit113, which causes the rotation plate112to rotate; a first container114, which has an inner surface provided with a light absorption member and used when the internal reflection calibration data are obtained; and a second container115, which accommodates the reference reflection plate43that is away from the stopper portion42by a distance L.

A calibration process performed by the optical measurement apparatus1using the calibration apparatus11configured as above will be described. The optical measurement apparatus1inserts the measurement probe3into the insertion portion111a. In this case, in the calibration apparatus11, by the drive unit113driving, the rotation plate112rotates and the first container114moves to a position of the insertion portion111a. Accordingly, the optical measurement apparatus1is able to obtain the internal reflection calibration data.

Subsequently, in the calibration apparatus11, by the drive unit113driving, the rotation plate112rotates and the second container115moves to the position of the insertion portion111a. Accordingly, the optical measurement apparatus1is able to obtain the reference reflection plate calibration data.

According to the above described sixth embodiment of the present invention, calibration items of the optical measurement apparatus1are automatically changeable and thus without performing complicated operations, data of calibration processes are obtainable in one operation.

In the sixth embodiment of the present invention, a positional relation between the measurement probe3and the first container114or the second container115need only be relatively changeable, and for example, the insertion portion111amay be rotatably provided with respect to a principal plane of the accommodation unit111b.

Seventh Embodiment

Next, a seventh embodiment of the present invention will be described. In the seventh embodiment, a calibration process is performed in a state in which a calibration apparatus is installed to a measurement probe. Therefore, hereinafter, the configuration of the calibration apparatus according to the seventh embodiment will be described. Configurations that are the same as those of the optical measurement apparatus1and the calibration apparatus4according to the above described first embodiment will be described being appended by the same reference signs.

FIG. 25is a diagram that schematically illustrates a cross section of a state in which a measurement probe of an optical measurement apparatus is installed in the calibration apparatus according to the seventh embodiment. A calibration apparatus12illustrated inFIG. 25is a bottomed cuboid and has the reference reflection plate43at a position that is away from the measurement probe3by the predetermined distance L. Further, the calibration apparatus12protects the distal end of the measurement probe3from an external force.

The calibration apparatus12configured as above is removed from the measurement probe3after the optical measurement apparatus1obtains the reference reflection plate calibration data. Thereafter, the optical measurement apparatus1obtains the internal reflection calibration data by irradiating the illumination light to the container provided with the light absorption member inside thereof.

According to the above described seventh embodiment of the present invention, variation in the predetermined distance L from the measurement probe3to the reference reflection plate43is preventable and a more accurate calibration process is able to be performed.

In the seventh embodiment of the present invention, when the treatment tool channel51aof the endoscopic device51is usable as a light absorption space, the optical measurement apparatus1may obtain the internal reflection correction data inside the treatment tool channel51aof the endoscopic device51.