Patent Application
20180306766
The present application relates to an optical element, a biological information measuring apparatus including the optical element, and an illumination apparatus including the optical element.
A biological information measuring apparatus is widely used that irradiates an organism with light, detects reflected scattered light from the inside of the organism, and can thus contactlessly obtain useful information on the organism.
Irradiation light enters into the organism through the skin, is transmitted through an internal organ, such as a blood vessel, and then emerges as scattered light. Thus, the scattered light includes biological information on the heartbeat, the blood flow volume, the blood pressure, the saturation of peripheral oxygen, and so on. Detecting this scattered light with a biological information measuring apparatus makes it possible to obtain, for example, information on the pulse, the blood flow, the oxygen saturation, and so on. These pieces of information can be used in a medical examination or the like.
Japanese Unexamined Patent Application Publication No. 2003-337102 discloses an apparatus for measuring biological activities, and this apparatus noninvasively measures biological activities, such as brain activities, indicating the functions of an organism. This apparatus includes a light source unit that generates infrared light, a light detecting unit that detects infrared light coming from a human body, and an optical system that controls a position on the human body at which the human body is irradiated with the light. This apparatus irradiates substantially the entirety of a human forehead with near-infrared light and receives reflected scattered light with a photodetector such as a charge coupled device (CCD).
In one general aspect, the techniques disclosed here feature a biological information measuring apparatus. The biological information measuring apparatus includes a light source that emits emission light with which a portion to be examined is to be irradiated; a photodetector that detects light returning from the portion to be examined, the light being produced when the portion to be examined is irradiated with the emission light; and an optical element that includes at least one lens, the optical element being disposed in an optical path between the light source and the portion to be examined. At least one value selected from the group consisting of a thickness of the at least one lens and a refractive index of the at least one lens varies along a first direction extending from a center portion toward an outer edge portion, the center portion being a portion that includes a center of the at least one lens, and the at least one value is locally minimum at the center portion and locally maximum at a first portion that lies between the center portion and the outer edge portion.
Additional benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. The benefits and/or advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages.
Prior to describing embodiments of the present disclosure, underlying knowledge for forming a basis of the present disclosure will be described.
The present inventors have found the following problem. Specifically, when biological information on a portion to be examined having a surface that is not planar, such as a forehead, an arm, or a leg, is to be acquired, the intensity of irradiation light becomes lower in a peripheral region of the portion to be examined than in a center region, which thus leads to a lower signal-to-noise ratio (S/N). Hereinafter, this problem will be described.
In the following descriptions, the XYZ-coordinates indicated in
The biological information measuring apparatus illustrated in
First, with reference to
Unlike the case illustrated in
Meanwhile, when the distance d is small as illustrated in
Next, an example in which a diffuser is disposed in an optical path between the light source 101 and the portion 106 to be examined at a position in proximity to the light source 101 to transform the light 108 into light with a Lambertian distribution will be described. The light 108 of the Lambertian distribution has a broad radiation angle, and the full width at half maximum of this radiation angle is 120 degrees. When the distance d is small, the light 108b in the peripheral portion is obliquely incident on the portion 106 to be examined. As the optical path length of the light 108b in the peripheral portion is increased, the intensity of the light 108b in the peripheral portion is lower than the intensity of the light 108a in the center portion in the A-A plane. As a result, although the S/N of a biological signal from the peripheral region improves due to the diffuser, the S/N is still lower than that of a biological signal from the center portion. Since the light 108b in the peripheral portion is obliquely incident on the portion 106 to be examined, the smaller the distance d is, the greater is the extent by which the S/N decreases.
When the distance d is relatively large-for example, when d=300 mm, the longitudinal and lateral sizes of the portion 106 to be examined are each 100 mm, and the optical intensity of the light 108a in the center portion is 1, the optical intensity of the light 108b in the outermost peripheral portion in the A-A plane is 0.97. In this manner, when the distance d is large, the optical intensity of the light 108b in the peripheral portion decreases to a lesser extent. In such a case, the use of a diffuser can solve the problem that the optical intensity decreases in the peripheral portion.
However, when the distanced is small-for example, when d=100 mm, the optical intensity of the light 108b in the outermost peripheral portion decreases to 0.74. Furthermore, when d=50 mm, this optical intensity decreases to 0.4. In this manner, it has been found that, as the distance d is smaller, the optical intensity in the peripheral portion decreases further.
Next, a case in which the curved portion 106a to be examined is irradiated with the divergent light 108 emitted from the light source 101, as illustrated in
Furthermore, the degree of the decrease in the S/N of a biological signal differs at different portions to be examined. For example, the shape of an arm or a leg is close to a column or a cylindroid, and the curvature of a forehead differs for the horizontal direction (X-direction) and for the vertical direction (Y-direction). Therefore, when such portions to be examined are to be measured, the degree of the decrease in the S/N of a biological signal from the peripheral region differs in the two orthogonal directions. As the curvature of a portion to be examined is greater, the degree of the decrease in the S/N is greater.
The present inventors have found the above problem and have conceived of a novel biological information measuring apparatus and a novel optical element.
The present disclosure includes a biological information measuring apparatus and an optical element set forth in the following items.
In the biological information measuring apparatus according to any one of Items 1 to 4,
α1r2+α2r4,
α1xx2+αiyy2+α2xx4+α2yy4,
In the biological information measuring apparatus according to any one of Items 1 to 6,
α1xx2+α2xx4 or
α1yy2+α2yy4,
In the biological information measuring apparatus according to any one of Items 1 to 9,
The biological information measuring apparatus according to any one of Items 1 to 10 may further include
In the biological information measuring apparatus according to any one of Items 1 to 11,
In the optical element according to any one of Items 13 to 15,
In the optical element according to any one of Items 13 to 17,
α1r2+α2r,
α1xx2+α1yy2+α2xx4+α2yy4,
α1xx2+α2xx4 or
as a function of y including a term
α1yy2+α2yy4,
In the optical element according to any one of Items 13 to 20,
In the present disclosure, all or a part of any of circuit, unit, device, part or portion, or any of functional blocks in the block diagrams may be implemented as one or more of electronic circuits including, but not limited to, a semiconductor device, a semiconductor integrated circuit (IC) or an LSI. The LSI or IC can be integrated into one chip, or also can be a combination of plural chips. For example, functional blocks other than a memory may be integrated into one chip. The name used here is LSI or IC, but it may also be called system LSI, VLSI (very large scale integration), or ULSI (ultra large scale integration) depending on the degree of integration. A Field Programmable Gate Array (FPGA) that can be programmed after manufacturing an LSI or a reconfigurable logic device that allows reconfiguration of the connection or setup of circuit cells inside the LSI can be used for the same purpose.
Further, it is also possible that all or a part of the functions or operations of the circuit, unit, device, part or portion are implemented by executing software. In such a case, the software is recorded on one or more non-transitory recording media such as a ROM, an optical disk or a hard disk drive, and when the software is executed by a processor, the software causes the processor together with peripheral devices to execute the functions specified in the software. A system or apparatus may include such one or more non-transitory recording media on which the software is recorded and a processor together with necessary hardware devices such as an interface.
Hereinafter, embodiments of the present disclosure will be described in more concrete terms. However, descriptions that are more elaborate than necessary may not be provided. For example, features that are already well known may not be described in detail, or duplicate descriptions of substantially identical configurations may be omitted. This is for preventing the following descriptions from becoming more lengthy than necessary and for facilitating understanding of a person skilled in the art. It is to be noted that the present inventors provide the appended drawings and the following descriptions to help a person skilled in the art understand the present disclosure at a sufficient level, and these drawings and descriptions are not intended to limit the subject set forth in the claims. In the following descriptions, identical or similar constituent elements are given identical reference characters.
Hereinafter, embodiments will be described with reference to the drawings.
First, a biological information measuring apparatus and an optical element according to a first embodiment of the present disclosure will be described.
A biological information measuring apparatus 17 according to the first embodiment includes a light source 1, a photodetector 2, a control circuit 7, and an optical element 3. The light source 1 emits emission light with which a portion 6 to be examined is irradiated. The photodetector 2 detects light that has been emitted from the light source 1 and reflected by the portion 6 to be examined. The optical element 3 is disposed in an optical path between the light source 1 and the portion 6 to be examined. The optical element 3 includes at least one lens. The control circuit 7 controls the light source 1 and the photodetector 2.
The control circuit 7 according to the present embodiment includes a signal processing circuit 30 that processes an electric signal (hereinafter, simply referred to as a signal) output from the photodetector 2. The signal processing circuit 30 generates information pertaining to the blood flow in the portion 6 to be examined on the basis of a signal indicating the quantity of light detected by the photodetector 2. The signal processing circuit 30 is used while being connected to the photodetector 2.
The control circuit 7 may, for example, be an integrated circuit that includes a processor, such as a central processing unit (CPU), and a memory. The control circuit 7, for example, executes a program recorded in the memory to thus cause the light source 1 to emit light and, in synchronization therewith, to cause the photodetector 2 to detect light.
The signal processing circuit 30 may be implemented, for example, by a digital signal processor (DSP), a programmable logic device (PLD) such as a field programmable gate array (FPGA), or a combination of a central processing unit (CPU) or a graphics processing unit (GPU) and a computer program. The control circuit 7 and the signal processing circuit 30 may be a single integrated circuit or may be individual separate circuits.
The biological information measuring apparatus 17 according to the present embodiment includes the control circuit 7. Alternatively, the control circuit 7 may be an element external to the biological information measuring apparatus 17.
The light source 1 may, for example, be a laser light source, such as a laser diode (LD), that successively emits pulsed light or a light emitting diode (LED). The light source 1 can start or stop emitting light and can change the emission power in accordance with an instruction from the control circuit 7 and can thus generate generally desired pulsed light.
The light source 1 emits light at a wavelength of no shorter than 650 nm nor longer than 950 nm, for example. This wavelength range is within a wavelength range of from red light to near-infrared rays. The above wavelength range is referred to as the biological window and is known for its low absorptance within a body. The descriptions are based on the assumption that the light source 1 according to the present embodiment emits light in the above wavelength range, but light in other wavelength ranges may also be used. In the present specification, the term “light” is used not only for visible light but also for infrared rays.
In the present embodiment, a diffuser 16 is disposed in an optical path between the light source 1 and the optical element 3 at a position in proximity to the light source 1. The diffuser 16 broadens the radiation angle of the emission light with a Gaussian distribution emitted from the light source 1 to transform the emission light to light with a Lambertian distribution, for example. The light diffused by the diffuser 16 is incident on the optical element 3. The optical element 3 further transforms the optical intensity distribution of light 8 to increase the optical intensity in the peripheral portion. The light transformed by the optical element 3 hits a surface (A-A plane) of the portion 6 to be examined that is spaced apart from the optical element 3 by a distance WD. The diffuser 16 is not an essential constituent element. However, providing the diffuser 16 renders it easier to design and manufacture the optical element 3.
The light source 1 including the diffuser 16 may be integrated with the optical element 3 to form a light source module 4. This renders it even easier to handle the light source 1 and the optical element 3.
In the following descriptions, “scattered light” includes reflected scattered light and transmitted scattered light. The reflected scattered light may simply be referred to as “reflected light.”
An organism is a scattering body. When a subject 5 is an organism, some of the light 8 incident on the portion 6 to be examined returns to the biological information measuring apparatus 17 as direct reflected light. The remaining portion of the light enters into the subject 5 through the skin on the surface of the portion 6 to be examined and is diffused, while some of that light is absorbed by the subject 5, to result in internal scatted light 9. Reflected scattered light 11 that has emerged from the inside of the subject 5 is detected by the photodetector 2. Incident on the photodetector 2 are direct reflected light that results in intense noise light and the reflected scattered light 11 having information on the internal blood flow. The optical path length of the reflected scattered light 11 is greater than the optical path length of the direct reflected light. Therefore, the arrival time of the reflected scattered light 11 at the photodetector 2 is later than the arrival time of the direct reflected light at the photodetector 2. Detecting light at a timing later than the time when the direct reflected light arrives at the photodetector 2 makes it possible to reduce the component of the direct reflected light, namely, the noise light component to be included in a detection signal and to increase the proportion of the component of the reflected scattered light 11.
The reflected scattered light 11 from the inside of the organism is light that has been transmitted through a blood vessel and so on and thus includes biological information on the heartbeat, the blood flow volume, the blood pressure, the saturation of peripheral oxygen, and so on. These pieces of biological information can be used for a variety of purposes including a medical examination and an estimation of an emotional state.
The optical element 3 according to the present embodiment includes a substrate 13 and a lens 12 provided at a center portion of the substrate 13. The lens 12 has a circular shape as viewed in the optical axis direction, or the Z-direction. The lens 12 has a shape that is rotationally symmetric about an axis that passes through the center of the lens 12, or the optical axis. The thickness of the lens 12 varies along a first direction, and the first direction extends from a center portion C of the lens 12 toward an outer edge portion E. The thickness of the lens 12 is locally minimum at the center portion C and locally maximum at a first portion (hereinafter, may be referred to as a “local maximum portion”) that lies between the center portion C and the outer edge portion E. To be more specific, the first portion at which the thickness of the lens 12 is locally maximum, or the local maximum portion, is present at each of a plurality of points that lie between the center portion C of the lens 12 and a plurality of points on the outer periphery, or the outer edge portion, of the lens 12.
In the present embodiment, the thickness of the lens 12 varies in accordance with the distance from the center portion C. Instead of the thickness of the lens 12 or in addition to the thickness of the lens 12, the refractive index of the lens 12 may be varied in a similar manner. In other words, it suffices that at least one of the thickness and the refractive index of the lens 12 in the optical element 3 vary in a direction extending from the center portion C of the lens 12 toward the outer edge portion E. The lens 12 is designed such that at least one of the thickness and the refractive index of the lens 12 is locally minimum at the center portion C and locally maximum at the first portions that lie between the center portion C and the outer edge portion E. The use of such a lens 12 makes it possible to collect more light onto a peripheral portion.
The center portion C coincides with the optical axis center in the present embodiment, and the center axis of the emission light from the light source 1 coincides with this optical axis center. Therefore, the center portion C may be referred to as the optical axis center in the present embodiment. The portion at which the thickness of the lens 12 is locally minimum need not strictly coincide with the optical axis center. It suffices that the thickness or the refractive index be locally minimum at a point in the vicinity of the optical axis center and that the thickness or the refractive index be locally maximum at points outside the aforementioned point. In the present specification, the term “center portion” refers to a point within a region with some spread containing the optical axis center and therearound.
The substrate 13 and the lens 12 may be fabricated from the same material, such as a cycloolefin resin (e.g., ZEONEX (registered trademark) available from Zeon Corporation). Alternatively, the substrate 13 and the lens 12 may be formed of different materials.
The substrate 13 and the lens 12 may be formed of a material that is substantially transparent to the light from the light source 1. The substrate 13 and the lens 12 can also be formed of a resin other than a cycloolefin resin, such as polycarbonate, a polymethyl methacrylate resin (PMMA), a norbornene resin (e.g., ARTON (registered trademark) available from JSR Corporation), or glass. The use of a resin can render it easier to integrally form the substrate 13 and the lens 12 from the same material.
The shape of the optical element 3 or the lens 12 can be expressed by a distribution of the sag amount indicating the difference between the thickness of the lens 12 at each point and the thickness of the lens 12 at the center portion C. The sag amount of the optical element 3 according to the present embodiment has a local minimum value at the center portion C, or the optical axis center, and has a local maximum value at a portion other than the center portion C. This local maximum value is also the global maximum value. The lens 12 in the optical element 3 has a structure that is rotationally symmetric about the center portion C, or the optical axis center. When loci obtained by connecting the portions of the lens 12 at which the lens 12 has the same thickness are projected onto an XY-plane, the loci result in concentric circles with their centers lying at the center portion C.
Hereinafter, a physical action of the optical element 3 according to the present embodiment will be described. The lens 12 in the optical element 3 has an effective diameter a. The lens 12 has a concave lens shape around the center portion and a convex lens shape at the peripheral portion. Thus, the optical element 3 disperses light, of the light emitted from the light source 1, incident on the center portion and therearound and condenses light incident on the peripheral portion. In other words, the optical element 3 functions to make the intensity of the light 8 higher at the peripheral portion than at the center portion and therearound in the A-A plane where the portion 6 to be examined is present.
The present inventors have found that the optical element 3 having such a sag amount distribution can be treated as an even-order aspherical lens. Furthermore, the present inventors have found that the sag amount can be expressed as a function of r including the term α1r2+α2r4, in which r is the distance from the center portion C, or the optical axis center, of the optical element 3, α1 is a positive real number, and α2 is a negative real number. Here, |α1|>|α2| holds. Describing with the use of the xy-coordinates yields r2=x2+y2, and thus the aforementioned sag amount can be expressed as a function of x and y including the term α1(x2+y2)+α2(x2+y2)2=α1x2+α2x4+α1y2+α2y4+2α2x2y2.
It is also possible to employ a design method in which the optical element 3 is treated as a lens other than an even-order aspherical lens. For example, a design technique for a refractive optical element having an odd-order aspherical surface, a toroidal surface, a Zernike standard sag surface, or the like may be employed. Furthermore, a design technique for a diffractive optical element having a hologram surface, a grating surface, or the like can also be employed. Regardless of with which technique the optical element 3 is designed, it suffices that the optical element 3 have a shape or a function of a concave lens and a convex lens at the center portion C and the peripheral region, respectively, of the lens 12. As long as the optical element 3 is designed in this manner, the optical element 3 can provide an advantageous effect equivalent to the advantageous effect of the present embodiment in which the optical element 3 increases the intensity of the light 8 at the peripheral portion.
As an example, the distance WD between the optical element 3 and the portion 6 to be examined is set to 100 mm, the distance from the surface of the diffuser 16 to the optical element 3 is set to 2 mm, the thickness of the substrate 13 is set to 3 mm, the sizes of the portion 6 to be examined in the X-direction and the Y-direction are each set to 100 mm, and the effective diameter a of the lens 12 is set to 4.24 mm. Then, when α1=0.01 and α2=−0.0025, the sag amount of the lens 12 can be expressed as a function of r including the term α1r2+α2r4, or in this case, expressed by α1r2+α2r4, for example. When r=1.41 mm, the local maximum value (global maximum value) of the sag amount is 10.1 μm.
As indicated by the dotted line in
Next, a biological information measuring apparatus and an optical element according to a modification of the first embodiment of the present disclosure will be described.
A difference from the biological information measuring apparatus according to the first embodiment described above is that the diffuser 16 is not disposed in an optical path between the light source 1 and the optical element 3 and the optical element 3 has a structure that functions as a diffuser as well. The light source 1 and the optical element 3 is integrated into the light source module 4.
The optical element 3 transforms the light 8 of the Gaussian distribution emitted from the light source 1 such that the intensity of the light at the peripheral portion is increased by the optical element 3. The transformed light 8 hits the portion 6 to be examined in the A-A plane. In this case, it has been found that, with a real number α3 being added, the sag amount can be expressed as a function of r including the term α1r2+α2r4+α3r6.
As an example, the distance WD between the optical element 3 and the portion 6 to be examined is set to 100 mm, the thickness of the substrate 13 is set to 3 mm, the sizes of the portion 6 to be examined in the X-direction and the Y-direction are each set to 100 mm, and the effective diameter a of the lens 12 is set to 4.24 mm. Then, when α1=0.13, α2=−0.018, and α3=0.004; the sag amount of the lens 12 can be expressed as a function of r including the term α1r2+α2r4+α3r6, or in this case, expressed by α1r2+α2r4+α3r6, for example. When r=2.05 mm, the local maximum value (global maximum value) of the sag amount is 258 μm.
In this modification, the optical element 3 functions as a diffuser as well. Therefore, as compared to the optical element according to the first embodiment, |α1|, |α2|, and the maximum sag amount increase. In this example, |α1|>|α2|>|α3| holds.
As indicated by the dotted line in
The optical element 3 includes a lens array 15 that includes a plurality of lenses arrayed two-dimensionally along a plane intersecting the center axis of the light emitted from the light source 1. At least one of the thickness and the refractive index of each lens is locally minimum at the center portion C of each lens and locally maximum at a portion that lies between the center portion C and the outer edge portion E of each lens.
Hereinafter, an example in which the thickness of each lens varies in accordance with the distance from the center will be described, but the configuration may be such that the refractive index of each lens varies in accordance with the distance from the center.
The optical element 3 according to this modification includes the substrate 13 and the lens array 15 disposed on the substrate 13. The lens array 15 includes a plurality of lenses arrayed in the X-direction and the Y-direction. In the example illustrated in
The sag amount of each lens has a local minimum value at the center portion C, or the optical axis center, and a local maximum value at a portion other than the center portion C. In this example as well, the locus 14 obtained by connecting the portions at which the sag amount of each lens is locally maximum has a circular shape. A difference from the optical element 3 according to the first embodiment is that the lens array 15 is used instead of a single lens. Thus, the tolerance in the positioning of the optical element 3 in the X- and Y-directions in which the lenses are arrayed improves. The sag amount of each lens can be expressed as a function of r including the term α1r2+α2r4, in a similar manner to the example illustrated in
In the present modification, the lenses constituting the array all have the same structure. However, not all the lenses need to have the same structure. The structure of the lens array may be modified in accordance with the distribution of light from the light source 1.
Next, a biological information measuring apparatus according to a second embodiment of the present disclosure will be described. The following descriptions center on the differences from the biological information measuring apparatus according to the first embodiment described above.
A subject 5a according to the present embodiment is, for example, a portion of an organism having a shape that can be approximated to an cylindroid, such as an arm or a leg. As illustrated in
When the curvature of the portion 6 to be examined differs in the X-direction and in the Y-direction, an optimal sag amount distribution is obtained for each of the directions, and the obtained results are combined. Then, an optimal optical element 3a can be designed. It has been found that the loci obtained by connecting the portions at which the sag amount has an identical value in the sag amount distribution obtained as described above result in concentric ellipses.
In the present embodiment as well, the sag amount of a lens 12a in the optical element 3a has a local minimum value at the center portion C, or the optical axis center, and a local maximum value at a portion other than the center portion C. The shape of a locus 14a obtained by connecting the portions at which the sag amount of the lens 12a is locally maximum is approximately an ellipse having a major axis extending in the X-direction and a minor axis extending in the Y-direction. It has been found that the use of the lens 12a having a minor axis extending in the Y-direction makes it possible to obtain an advantageous effect in that the intensity of the light 8 along the A-A plane is greater at the peripheral portions in the Y-direction than at the peripheral portions in the X-direction.
The optical axis center of the element serves as the origin, α1x and α1y are positive real numbers, and α2x and α2y are negative real numbers. Then, the present inventors have found that the sag amount of the optical element 3a can be expressed as a function of x and y including the term α1xx2+α2xx4+α1yy2+α2yy4.
As an example, the distance WD between the optical element 3a and the center portion of the portion 6 to be examined is set to 100 mm, the distance from the surface of the diffuser 16 to the optical element 3a is set to 2 mm, the thickness of the substrate 13 is set to 3 mm, the sizes of the portion 6 to be examined in the X-direction and the Y-direction are each set to 100 mm, and the effective diameter a of the lens 12a is set to 4.24 mm. Then, when α1y=0.013 and α2y=−0.004, the sag amount in the Y-direction can be expressed as a function of y including the term α1yy2+α2yy4, or in this case, expressed by α1yy2+α2yy4, for example. When y=1.28 mm, the local maximum value (global maximum value) of the sag amount is 10.6 μm. When α1x=0.01 and α2x=−0.0025, the sag amount in the X-direction can be expressed as a function of x including the term α1xx2+α2xx4, or in this case, expressed by α1xx2+α2xx4, for example. When x=1.41 mm, the local maximum value (global maximum value) of the sag amount is 10.6 μm.
Therefore, the shape of the locus 14a is approximately an ellipse having a major axis extending in the X-direction. In this example, the eccentricity e is 0.43. When the sizes of the ellipse in the major axis direction and the minor axis direction are represented by Sx and Sy, respectively, the eccentricity is defined as e=(1−(Sy/Sx)2)0.5.
As indicated by the dotted line in
The shape of the locus 14a obtained by connecting the portions at which the sag amount of the lens 12a is locally maximum is not limited to an ellipse.
Next, a biological information measuring apparatus and an optical element according to a modification of the second embodiment of the present disclosure will be described.
The optical element 3a according to the present modification includes the substrate 13 and a lens array 15a disposed on the substrate 13. The sag amount of each lens has a local minimum value at the center portion C, or the optical axis center, and a local maximum value at a portion other than the center portion C. The shape of the locus 14a obtained by connecting the local maximum portions in each lens is an ellipse. A difference from the optical element 3a according to the second embodiment is that the lens array 15a including a plurality of lenses is used instead of a single lens. Constituting the optical element 3a as an array improves the tolerance in the positioning of the optical element 3a in the X-direction and the Y-direction. The sag amount of the each lens can be expressed similarly as a function of x and y including α1xx2+α2xx4+α1yy2+α2yy4. In the above, |α1x|>|α2x| and |α1y|>|α2y| hold. The optical element 3a has a concave lens shape and a convex lens shape at the center portion C and therearound and at the peripheral region, respectively, of each lens.
Not all the lenses constituting the array need to have the same structure. The structure of each lens may be modified in accordance with the distribution of light from the light source 1. The shape of the locus 14a obtained by connecting the local maximum portions is not limited to an ellipse. The shape of the locus 14 or 14a may be a rhombus or a rhombus with four rounded corners, for example.
Next, a biological information measuring apparatus according to a third embodiment of the present disclosure will be described. The following descriptions center on the differences from the biological information measuring apparatus according to the second embodiment described above.
A biological information measuring apparatus 17b according to the third embodiment is, for example, an apparatus that contactlessly measures a brain function. The photodetector 2 is an image sensor having an electronic shutter function. The diffuser 16 transforms the divergent light with a Gaussian distribution emitted from the light source 1 to light with a Lambertian distribution, for example. An optical element 3b increases the intensity of the transformed light at the peripheral portion. The light 8 transmitted through the optical element 3b hits the portion 6 to be examined of a subject 5b. The portion 6 to be examined in the present embodiment is a forehead. The size of the portion 6 to be examined in the X-direction is designated by W, and the size in the Y-direction is designated by h. The light 8 may be continuous light but is pulsed light in the present embodiment. The light source 1 repeatedly emits pulsed light in accordance with the sensitivity of the photodetector 2. The pulse duration is, for example, no less than 0.1 ns nor more than 1 μs and is 11 ns in a certain example. The light source 1 and the optical element 3b are integrated into a light source module 4b.
Present inside the forehead serving as the portion 6 to be examined are, sequentially from the surface side, the scalp (thickness of approximately 3 mm to 6 mm), the cranial bone (thickness of approximately 5 mm to 10 mm), the cerebrospinal fluid layer (thickness of approximately 2 mm), and the brain tissue. The thickness ranges indicated in the parentheses represent individual differences. Some of the light 8 emitted toward the portion 6 to be examined returns to the biological information measuring apparatus 17b as direct reflected light. The remaining portion of the light results in the internal scatted light 9 that enters inside the portion 6 to be examined through the surface thereof. Some of the internal scatted light 9 is absorbed, and the remaining portion thereof is diffused and emerges from the surface of the portion 6 to be examined. The internal scatted light 9 that has entered inside the portion 6 to be examined includes information on the cerebral blood flow at a portion approximately 10 mm to 18 mm deep from the surface. The internal scatted light 9 that has emerged from the portion 6 to be examined returns to the biological information measuring apparatus 17b as the reflected scattered light 11 from the inside. Incident on the photodetector 2 are the direct reflected light that results in intense noise light and the reflected scattered light 11 having information on the cerebral blood flow. The optical path length of the reflected scattered light 11 is greater than the optical path length of the direct reflected light. Therefore, the arrival time of the reflected scattered light 11 at the photodetector 2 is later than the arrival time of the direct reflected light at the photodetector 2. Detecting the light with the use of the electronic shutter function of the image sensor at a timing later than the arrival time of the direct reflected light makes it possible to reduce the noise light and to improve the S/N of a signal pertaining to the cerebral blood flow.
The light source 1 is a multi-wavelength light source that emits light with at least two wavelengths. The light source 1 separately emits the light 8, which is pulsed light, at each wavelength in accordance with an instruction from the control circuit 7.
The light source 1 includes, for example, a structure in which a plurality of laser chips are embedded within a package. The two wavelengths to be used may be 750 nm and 850 nm, for example. The absorptance of light by oxidized hemoglobin and reduced hemoglobin varies in the wavelengths of 750 nm and 850 nm, for example. Therefore, carrying out a computation with a combination of two electric signals obtained by using the two respective wavelengths makes it possible to measure information pertaining to the cerebral blood flow in the portion 6 to be examined, such as the proportions of oxidized hemoglobin and reduced hemoglobin. This computation is executed by the signal processing circuit 30 (refer to
When the portion 6 to be examined is a forehead region of a head portion of an organism, the amount of change in the cerebral blood flow in the frontal lobe or the amount of change in the oxidized hemoglobin concentration and the reduced hemoglobin concentration can be measured. On the basis of these pieces of information, information on the emotional state or the like can be sensed. For example, under the concentrated state, the cerebral blood flow volume increases, and the amount of oxidized hemoglobin increases. The signal processing circuit 30 detects, for example, an increase in the cerebral blood flow volume or an increase in the amount of oxidized hemoglobin and can thus estimate the degree of concentration or the emotional state of the subject.
A variety of combinations of wavelengths are possible. The light with a wavelength of 805 nm has an equal absorption amount for oxidized hemoglobin and for reduced hemoglobin. Therefore, when light at a wavelength of less than 805 nm and light at a wavelength of greater than 805 nm are combined, information on each of oxidized hemoglobin and reduced hemoglobin can be acquired. Furthermore, in addition to the stated two wavelengths, three wavelengths including the wavelength of 805 nm can be used. The use of three wavelengths necessitates three laser chips. However, this configuration makes it possible to obtain information from the third wavelength as well, and the use of this information can facilitate the computation.
The light source 1 may have a structure in which a plurality of light source packages are arranged. A single laser chip is embedded in each light source package. In this case, the optical element 3b and the diffuser 16 may be provided for each light source package.
The size of the forehead, serving as the portion 6 to be examined, in the X-direction is designated by W, and the size in the Y-direction is designated by h. Then, although there are individual differences, these sizes are, for example, approximately as follows: W=100 mm, and h=50 mm. As can be seen from
The present inventors have found the above-described characteristics of the optical intensity distribution held when the portion 6 to be examined is a forehead and examined a configuration of the optical element 3b suitable for these characteristics. As a result, the present inventors have conceived of the use of the optical element 3b that has a shape that can be approximated to an ellipse having a minor axis extending in the X-direction, in which the sag amount has a local minimum value at the center portion C, or the optical axis center, and a local maximum value at a portion other than the center portion C, and in which the shape of the locus 14a obtained by connecting the portions at which the sag amount is locally maximum can be approximated to an ellipse. Making the direction in which the curvature of the portion 6 to be examined is large (the X-direction in the drawings) coincide with the minor axis direction of the ellipse makes it possible to bring the illuminance distribution on the portion 6 to be examined closer to being more uniform.
It has been found that, when the portion 6 to be examined is a forehead, although there are individual differences, it suffices that a lens in which the eccentricity e of the above-described ellipse satisfies 0<e<0.6 be used.
In the present embodiment as well, the optical element 3b may include a lens array. The sag amount of each lens has a local minimum value at the center portion C, or the optical axis center, and a local maximum value at a portion other than the center portion C, or the optical axis center. The shape of the locus 14a obtained by connecting the local maximum portions can be approximated to an ellipse.
The shape of the locus 14a obtained by connecting the local maximum portions is not limited to an ellipse. The accurate shape of the locus 14a obtained when the sag amount of the optical element 3b can be expressed as a function of x and y including the term α1xx2+α2xx4+α1yy2+α2yy4 can be derived mathematically. The shape of the locus 14a can be approximated to an ellipse as described above and can also be a rhombus or a rhombus with four rounded corners, for example, depending on the conditions.
A difference from the optical elements according to the foregoing embodiments is that the thickness of a lens 12b in the optical element 3b is substantially constant in the Y-direction that is orthogonal to both the X-direction and the thickness direction of the lens 12b.
The optical element 3b according to the present modification increases the intensity of the light at the peripheral portions in the X-direction. The optical element 3b does not change the optical intensity distribution in the Y-direction.
As illustrated in
The sag amount of the lens 12b in such an optical element 3b can be expressed as a function of x including α1xx2+α2xx4, in which the center portion C, or the optical axis center, serves as the origin, α1x is a positive real number, and α2x is a negative real number. The use of such an optical element 3b also makes it possible to constitute a biological information measuring apparatus suitable when the portion 6 to be examined is a forehead.
An optical element that increases the intensity of the transmitted light at peripheral portions not in the X-direction but in the Y-direction alone may instead be used. The sag amount of such an optical element can be expressed as a function of y including α1yy2+α2yy4, in which the optical axis center of the element serves as the origin, α1y is a positive real number, and α2y is a negative real number.
In the biological information measuring apparatus according to the present modification, the X-direction in which the optical element 3b increases the optical intensity at the peripheral portions is made to coincide with the lateral direction in which the curvature of the forehead is large, and thus an advantageous effect of reducing a decrease in the S/N of a biological signal from the peripheral region can be obtained.
In the first through third embodiments and the modifications thereof, an optical element in which primarily a lens has a nonuniform thickness is used. In place of the thickness of the lens or in addition to the thickness of the lens, an optical element in which the refractive index of a lens is nonuniform may be used, and still a similar advantageous effect can be obtained.
The present disclosure is not limited to the foregoing embodiments. A biological information measuring apparatus obtained by combining configurations of the biological information measuring apparatuses of the embodiments is also encompassed by the present disclosure, and a similar advantageous effect can be obtained.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-085091 | Apr 2017 | JP | national |
