Patent Application
20200214602
The present disclosure relates to a measurement apparatus.
Techniques have been known in which optical methods are used to diagnose or inspect an internal state of a scatterer and changes thereof, the internal state and the changes being undetectable by the human eye.
For example, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2010-503475 discloses an apparatus that uses an optical method to inspect skin damaged by a burn. Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2010-503475 discloses estimating the depth of a burn by using laser speckle analysis.
In one general aspect, the techniques disclosed here feature a measurement apparatus for obtaining information about a target object that is present inside a scatterer. The measurement apparatus includes: a light source that emits laser light to the scatterer; an imaging device; a signal processing circuit; and a controller that controls the light source and the imaging device and that controls an irradiation position of the laser light on the scatterer. The controller causes the light source to irradiate a first portion of the scatterer with the laser light and causes the imaging device to output a first image signal representing a first image resulting from the laser light emitted from a first target area that is away from the first portion. The controller causes the light source to irradiate a second portion of the scatterer with the laser light and causes the imaging device to output a second image signal representing a second image resulting from the laser light emitted from a second target area that is away from the second portion. The signal processing circuit generates data regarding a position of the target object inside the scatterer based on the first image signal and the second image signal and outputs the data. A first distance between the first portion and a center of the first target area is equal to a second distance between the second portion and a center of the second target area, or a difference between the first distance and the second distance is smaller than 10% of a smaller one of the first distance and the second distance.
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.
Before an embodiment of the present disclosure is described, a description will be given of findings underlying the present disclosure.
Heretofore, various techniques have been developed in which optical methods are used to diagnose or inspect the internal state of a scatterer or changes thereof, the internal state and the changes being undetectable with the human eye. For example, measurement apparatuses, such as photoplethysmographic sensors, near-infrared spectroscopy (NIRS) apparatuses, and optical coherence tomography (OCT) apparatuses, have been developed in addition to the technique disclosed in Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2010-503475.
For the photoplethysmographic sensors, the surface of skin is irradiated with light-emitting diode (LED) irradiation light other than green or near-infrared light. Blood including hemoglobin flows in subcutaneous arteries. Hemoglobin has a property of absorbing green or near-infrared light. When the artery pulses, the state of blood flow in the artery changes. As a result, the amount of light absorbed by hemoglobin in an area irradiated with the light changes. When components of irradiation light multiple-scattered by the artery or subcutaneous tissue and emitted from the surface of the skin are detected using a photodiode, it is possible to observe in reception-light intensity changes according to the artery pulsation. Thus, pulse wave signals are detected. The photoplethysmographic sensor detects the interval state of a scatterer as a light intensity.
Another example is a brain function measurement apparatus employing MRS. In NIRS, the scalp is irradiated with near-infrared laser irradiation light or LED irradiation light. Part of irradiation light that is multiple-scattered inside the head portion penetrates the skull and reaches the brain surface layer portion in the skull while scattering. When the amount of hemoglobin contained in the cerebral blood changes, part of the irradiation light is further multiple-scattered in the brain surface layer portion. As a result, the intensity of light emitted from the surface of the scalp changes. This change is observed using a photodiode to thereby estimate the state of activity of the brain surface layer portion. In NIRS, the internal state of a scatterer is also detected as the magnitude of the light intensity, similarly to the photoplethysmographic sensor.
A further example is an optical coherence tomography (OCT) apparatus. The OCT apparatus is one type of optical interferometer. A beam splitter splits irradiation light having a coherence length of about several tens of micrometers into two light beams. One of the light beams is reflected by a mirror to provide reference light. The other light beam is incident on a scatterer, such as a living body, is scattered inside the scatterer, and is emitted from the surface thereof to provide signal light. When the signal light and the reference light are combined together by the beam splitter, interference light is generated through interference of signal light components having an optical path length that is equal to the optical path length of the reference light. The signal light components that contribute to the interference are only light components that travel in straight lines inside the scatterer, are reflected therein, and are emitted from the surface. The light components are referred to as “straight-traveling reflection light”. The signal light components that contribute to the interference do not include light components multiple-scattered inside the scatterer. When the mirror for the reference light is moved in the optical-axis direction to change the optical path length, and the light intensity of the interference light is detected using a photodiode, the distribution of the intensity of reflection light in the depth direction of the scatterer can be measured with a resolution equivalent to the coherence length. The OCT apparatus utilizes an interference phenomenon to detect the intensity of reflection light at a specific depth inside the scatterer.
With a method using the above-described photoplethysmographic sensor, NIRS, or the like, it is difficult to obtain information regarding the depth of a target object that is present inside a scatterer. In addition, although the information regarding the depth of a target object can be obtained with a method using OCT or the like described above, the mirror for the reference light and the beam splitter are required, thus complicating the optical system
The present inventors have found the above-described problems and have conceived a novel measurement apparatus.
The present disclosure includes a measurement apparatus described in the following items.
A measurement apparatus according to the present disclosure item 1 is a measurement apparatus for obtaining information about a target object that is present inside a scatterer, and includes:
The controller
The signal processing circuit generates data regarding a position of the target object inside the scatterer based on the first image signal and the second image signal and outputs the data.
A first distance between the first portion and a center of the first target area is equal to a second distance between the second portion and a center of the second target area, or a difference between the first distance and the second distance is smaller than 10% of a smaller one of the first distance and the second distance.
In the measurement apparatus according to item b 1,
In the measurement apparatus according to item 1 or 2,
In the measurement apparatus according to one of item 1 to 3,
In the measurement apparatus according to item 4,
In the measurement apparatus according to item 1,
The measurement apparatus according to item 7 of the present disclosure is a measurement apparatus for obtaining information about a target object that is present inside a scatterer, and includes:
The controller causes the light source to irradiate a first portion of the scatterer with the laser light and causes the imaging device to output image signals indicating an image including a first image resulting from the laser light emitted from a first target area that is away from the first portion and a second image resulting from the laser light emitted from a second target area that is away from the first portion.
The signal processing circuit generates data regarding a position of the target object inside the scatterer based on a first signal representing the first image and a second signal representing the second image, the first signal and the second signal being included in the image signals, and outputs the data.
A first distance between the first portion and a center of the first target area is equal to a second distance between the second portion and a center of the second target area, or a difference between the first distance and the second distance is smaller than 10% of a smaller one of the first distance and the second distance.
In the measurement apparatus according to item 7,
In the measurement apparatus according to item 7,
In the measurement apparatus according to item 3 or 8,
In the measurement apparatus according to one of items 1 to 10,
In the measurement apparatus according to one of items 1 to 10,
In the measurement apparatus according to one of items 1 to 10,
In the measurement apparatus according to one of items 1 to 13,
In the measurement apparatus according to one of items 1 to 13,
In the measurement apparatus according to one of items 1 to 15,
In the measurement apparatus according to one of items 1 to 16,
In the present disclosure, all or a part of any of circuits, units, apparatuses, devices, parts, or portions 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 a large-scale integration (LSI). The LSI or IC can be integrated into one chip or also can be a combination of a plurality of chips. For example, functional blocks other than a memory may be integrated into one chip. Although the name used here is an LSI or IC, it may also be called a system LSI, a very large scale integration (VLSI), or an ultra large scale integration (ULSI) 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 also be used for the same purpose.
In addition, the functions or operations of all or a part of the circuits, units, apparatuses, devices, parts, or portions can be 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.
A more specific embodiment in the present disclosure will be described below. However, an overly detailed description may be omitted herein. For example, a detailed description of already well-known things and a redundant description of substantially the same configuration may be omitted herein. This is to avoid the following description becoming overly redundant and to facilitate understanding of those skilled in the art. The accompanying drawings and the following description are provided so as to allow those skilled in the art to fully understand the present disclosure and are not intended to limit the subject matters recited in the claims. In the following description, the same or similar constituent elements are denoted by the same reference numerals.
(Background from which Configuration in Embodiment of Present Disclosure was Derived)
The present inventors studied a measurement apparatus for obtaining information about the depth of a substance that is present inside an optical scatterer having a scattering property that is different from that of the substance. Study was conducted based on an analytical model of such a measurement apparatus. The substance is hereinafter referred to as a “foreign object” or a “target object”. By using a Monte Carlo method, the present inventors calculated the distribution of multiple scattering light emitted from the surface of a scatterer in the analytical model when the scatterer is irradiated with irradiation light.
In this analytical model, a foreign object 102, which is a measurement target, is contained at a position at a depth d [mm] inside the scatterer 101. The scatterer 101 is a material having an absorption coefficient of μa=0.002 mm−1 and a reduced scattering coefficient of μs=0.24 mm−1. The size of the foreign object 102 is 10×10×10 mm. The foreign object 102 is a substance having a low-scattering property than the scatterer 101 and has a reduced scattering coefficient μs of zero. Light with a sufficiently small-size spot is used as the irradiation light.
An area that is 4 mm away from the irradiation portion 105 in the X direction and that has a size of 3.2×3.2 mm is selected as an area to be photographed, that is, the target area 306. The distance between the irradiation portion 105 and the center of the target area 306 is hereinafter referred to as a “source-detector distance”. In this analytical model, the source-detector distance is 4 mm. Scatter light emitted from the target area 306 forms an image through an optical system 107 having a numerical aperture (NA) of 1.0. The depth d from the surface of the scatterer 101 to the surface of the foreign object 102 was changed to three depths: 2 mm, 5 mm, and 10 mm. Light intensities and optical-phase spatial dispersions (hereinafter referred to as “phase dispersions”) in an image plane (not illustrated) corresponding to the target area 306 were calculated for the respective depths. In this analysis, standard deviations of the light intensities in the image plane was calculated as the phase dispersions.
Light that enters the inside of a scatterer is multiple-scattered, and the optical path length of each light ray varies on a far greater order of magnitude than the wavelength of the irradiation light. Thus, the phase in the image plane becomes spatially random. However, there is a possibility that the random phase dispersions can be observed as interference images. The possibility changes depending on the relationship between the coherence length of the irradiation light and the average optical path length of a large number of light rays that pass through the scatterer.
The absolute quantity of variations in the optical path lengths of a large number of light rays that pass through the scatterer 101 (the absolute quantity is hereinafter referred to as “optical-path-length deviation”) increases, as the average optical path length increases. When the coherence length of the irradiation light is greater than or equivalent to the optical-path-length deviation, two light rays that are adjacent to each other in the image plane interfere with each other. Thus, the phase difference between the two light rays appears in an interference image. On the other hand, when the coherence length of the irradiation light is smaller than the optical-path-length deviation, the probability that the two light rays that are adjacent to each other in the image plane interfere with each other decreases. Thus, the probability that the phase difference appears in an interference image also decreases.
Hence, the average optical path length of light rays that are multiple-scattered from when the light rays from the irradiation portion 105 enter the inside of the scatterer 101 until the light rays reach the target area 306 is reflected in the phase dispersion observed as an interference image.
The examples illustrated in
In this analysis, the coherence length of irradiation light is 10 mm. When the coherence length is too small, the interference of the multiple scattering light decreases. Thus, changes in the phase dispersion depending on the presence/absence of a foreign object decrease. On the other hand, when the coherence length is too large, the interference of the multiple scattering light stays strong regardless of the presence/absence of a foreign object. Thus, changes in the phase dispersion decrease. Therefore, an appropriate coherence length is in a certain range.
The example illustrated in
The example illustrated in
The reason why the decrease tendency with respect to the depth of the foreign object 102 varies between the change rate of the light intensity and the change rate of the phase dispersion is thought to be as follows. When the irradiation light is incident on the surface of the scatterer 101, the number of light rays that reach a deeper portion from the surface decreases. The change rate of the light intensity due to the foreign object 102 that is present at a certain depth directly reflects the number of light rays that reach the depth.
On the other hand, the change rate of the phase dispersion reflects changes in the average optical path length from the irradiation portion 105 to the target area 306, When the foreign object 102 is present at a very shallow portion, the optical path lengths of light rays that are scattered inside the foreign object 102 decrease. However, since the foreign object 102 has a low-scattering property, the number of light rays that are scattered inside the foreign object 102 and that return to the surface also decreases. As a result, the effect of the decrease in the average optical path length is thought to be limited.
It was found that when the foreign object 102 having a scattering property that is different from that of the scatterer 101 is present inside the scatterer 101, the change rate of the light intensity and the change rate of the phase dispersion exhibit different decrease tendencies with respect to the depth of the foreign object 102.
In this analytical model, the foreign object 102 has a lower-scattering property than the scatterer 101. However, the configuration with which the phenomenon in which the change tendency with respect to the depth differs between the change rate of the light intensity and the change rate of the phase dispersion occurs is not limited to the above-described configuration. For example, when the foreign object 102 has a higher-scattering property than the scatterer 101, the light intensity can increase and the phase dispersion can decrease in an area where the foreign object 102 is present inside the scatterer 101. In any configuration with which at least one of the absorption coefficient and the reduced scattering coefficient differs between the scatterer 101 and the foreign object 102, the phenomenon in which the change tendency with respect to the depth differs can occur.
The measurement apparatus 100 in the present embodiment includes a light source 103, an imaging device 108, a signal processing circuit 110, and a controller 130.
The light source 103 emits light 104 having a coherence length of 1 mm or more and 400 mm and less to the scatterer 101. As described above, the light source 103 may emit light having, for example, a coherence length of 2 mm or more and 100 mm or less. In one example, the light source 103 may emit light having a coherence length of 5 mm or more and 20 mm or less. The light source 103 may be, for example, a laser light source that emits laser light having a coherence length in any of the ranges described above.
The controller 130 includes a control circuit that controls the light source 103 and the imaging device 108. The control circuit in the controller 130 controls an actuator 140 to thereby control a light irradiation position of the scatterer 101, The actuator 140 is coupled to a table on which the scatterer 101 is placed and enables the scatterer 101 to move in a direction parallel to an image capture plane of the imaging device 108.
The controller 130 causes the light source 103 to irradiate a first portion 105a of the scatterer 101 with the light 104. In this state, the controller 130 causes the imaging device 108 to output a first image signal representing a first interference image 109, which is a first image resulting from light emitted from a first target area 106 that is a distance SD away from the first portion 105a. Upon the output of the first image signal, the first image capture is completed,
Subsequently, the controller 130 causes the light source 103 to irradiate a second portion 105b of the scatterer 101 with the light 104. In this state, the controller 130 causes the imaging device 108 to output a second image signal representing a second interference image 113, which is a second image resulting from light emitted from a second target area 112 that is away from the second portion 105b. Upon the output of the second image signal, the second image capture is completed.
The signal processing circuit 110 performs computational operation using the first image signal and the second image signal to generate data regarding the depth of a foreign object 102 that is present inside the scatterer 101 and outputs the data.
The controller 130 executes the above-described control, for example, by executing a program recorded in a memory. The controller 130 may include, for example, an integrated circuit, such as a central processing unit (CPU) or a microcomputer. The controller 130 and the signal processing circuit 110 may be integrated into a single unit.
In
In the present embodiment, the distance between the first portion 105a and the center of the first target area 106 is equal to the distance between the second portion 105b and the center of the second target area 112, Thus, when the first portion 105a, the first target area 106, the second portion 105b, and the second target area 112 are present in an area where the foreign object 102 is not present, the detection light intensity in the first image capture and the detection light intensity in the second image capture can be made to have approximately the same value. Herein, two distances being “equal” means that the absolute value of the difference between the two distances is smaller than 10% of the smaller one of the two distances. The distance between the first portion 105a and the center of the first target area 106 may be different from the distance between the second portion 105b and the center of the second target area 112. In such a case, the signal processing circuit 110 may be adapted to correct at least one of the first and second image signals in accordance with the difference between the distances, so as to allow comparison of the first and second image signals.
In the example illustrated in
The operation of the measurement apparatus 100 in the present embodiment will be described below.
In accordance with an instruction from the controller 130, the light source 103 irradiates the first portion 105a on the surface of the scatterer 101 with the light 104, which has a predetermined coherence length, Scatter light emitted from the first target area 106 that is a distance SD away from the first portion 105a passes through the optical system 107, and an image of the scatter light is formed in the image capture plane of the imaging device 108. The imaging device 108 captures the formed image as a first interference image 109 and outputs a first image signal representing the interference image 109.
Next, as illustrated in
In the present embodiment, the foreign object 102 is present directly inside the first target area 106 of the scatterer 101, and the foreign object 102 is absent directly inside the second target area 112. Thus, signal processing using the first image signal and the second image signal can provide information about the depth at which the foreign object 102 is present. It is sufficient as long as the foreign object 102 is present directly inside one of the first target area 106 and the second target area 112.
There are also cases in which, in actual image capture, at which position inside the scatterer 101 the foreign object 102 is present is unknown. In such a case, the first target area 106 and the second target area 112 may be selected based on images of a large number of target areas, the images being captured while moving the scatterer 101. In such a case, the controller 130 causes the light source 103 to sequentially irradiate a plurality of portions including the first portion 105a and the second portion 105b of the scatterer 101 with light. The controller 130 causes the imaging device 108 to sequentially output image signals indicating interference images resulting from light emitted from target areas that are located at an equal distance from the respective portions, The signal processing circuit 110 performs computational operation using the image signals to thereby generate data regarding the depth of a target object and outputs the data. Those portions are typically arranged at regular intervals in one direction along the surface of the scatterer 101, but does not necessarily have to be arranged at regular intervals.
The signal processing circuit 110 calculates a light intensity and a phase dispersion with respect to each of the first interference image 109 and the second interference image 113 by using a method described below, and estimates at what degree of depth the foreign object 102 is present, based on the calculation result, The signal processing circuit 110 outputs information regarding the depth onto a display 111. Details of signal processing performed by the signal processing circuit 110 are described later.
Next, the operation of the signal processing circuit 110 will be described in more detail.
In step S101, the signal processing circuit 110 calculates a light intensity a1 and a phase dispersion σ1 of the first interference image 109 and a light intensity a2 and a phase dispersion σ2 of the second interference image 113.
The light intensity represents an average luminance of the interference image and is also referred to as an “average luminance”. The average luminance can be determined by, for example, calculating an average value of luminance values of the entire area of the interference image.
The phase dispersion represents a luminance dispersion of the interference image and is also referred to as a “luminance dispersion”. The luminance dispersion can be determined by, for example, a method described below.
(1) The area of the interference image is divided into a plurality of areas according to a two-dimensional grid pattern, and average values of luminances are determined for the respective areas.
(2) Using all of the divided areas as a parameter, a standard deviation of the average values of the luminances is determined as a phase dispersion.
A distribution may be used instead of the standard deviation. Another value that numerically expresses the degree of dispersion in the luminance distribution may also be used as the phase dispersion.
In step S102, the signal processing circuit 110 calculates a change rate of the light intensity and a change rate of phase dispersions. The change rate of the light intensity can be determined by computational operation ri=|a2−a1|/a1. The change rate of the phase dispersion can be determined by computational operation rp=|σ2−σ1|/σ1.
In step S103, the signal processing circuit 110 calculates a ratio ri/rp of the change rate of the light intensity to the change rate of the phase dispersion.
In step S104, the signal processing circuit 110 determines whether or not the ratio ri/rp is larger than or equal to a predetermined threshold c. The threshold c is appropriately determined according to image-capture conditions, such as optical properties of the scatterer 101 and the foreign object 102, the coherence length of the light source 103, and the source-detector distance.
When the ratio ri/rp is larger than or equal to the threshold c, the signal processing circuit 110 determines that the foreign object 102 is present at a relatively shallow portion of the first target area 106 or the second target area 112 (step S105). On the other hand, when the ratio ri/rp is smaller than the threshold c, the signal processing circuit 110 determines that the foreign object 102 is present at a relatively deep portion of the first target area 106 or the second target area 112 (step S106). The inside of the scatterer 101 may be divided into areas at three or more different depths, and in which depth area the foreign object 102 is present may be determined based on the value of the ratio ri/rp.
The signal processing circuit 110 sends data indicating a result of the determination made in step S105 or S106 to the display 111. The signal processing circuit 110 may send the data to a recording medium (not illustrated) instead of the display 111. The display 111 displays the result of the determination. For example, the display 111 displays at least one of an image of the relatively deep portion in the scatterer 101 and an image of the shallow portion in the scatterer 101. In still another example, at least one of the probability that the foreign object 102 is present at the relatively deep portion in the scatterer 101 and the probability that the foreign object 102 is present at the relatively shallow portion in the scatterer 101 is displayed as a numerical value. In a further example, the scatterer 101 is a living body, and at least one of information regarding blood flow at the relatively shallow portion and information regarding blood flow at the relatively deep portion is displayed as a numerical value. In yet another example, at least one of an optical property at the relatively deep portion in the scatterer 101 and an optical property of the relatively shallow portion in the scatterer 101 is displayed as a numerical value. The optical property is, for example, the intensity of reflection light. In yet another example, the information displayed as the numerical value is displayed, for instance, as “normal” or “abnormal or an index converted into symbols, such as “○”, “Δ”, or “x”. In a yet further example, the above-described image(s) or information may be sent to an analyzing device, inspection equipment, a computer, or the like that is located external to the measurement apparatus 100, instead of being displayed.
As described above, the signal processing circuit 110 in the present embodiment executes operations described below.
(1) A first average luminance indicating the average of luminance of the first interference image 109 and a first luminance dispersion indicating a luminance dispersion of the first interference image 109 are determined based on the first image signal.
(2) A second average luminance indicating the average of luminance of the second interference image 113 and a second luminance dispersion indicating a luminance dispersion of the second interference image 113 are calculated based on the second image signal.
(3) Computational operation using the first and second average luminances and the first and second luminance dispersions is performed to generate data regarding the depth of the target object, and the data is output. The “data regarding the depth” is not limited to the above-described example and may be any data or signal indicating the degree of the depth of a measurement target object from the surface of the scatterer.
More specifically, in step (3) described above, the signal processing circuit 110 executes operations described below.
(3a) The absolute value of the difference between the first average luminance and the second average luminance is divided by the first or second average luminance to thereby calculate a change rate of the average luminance.
(3b) The absolute value of the difference between the first luminance dispersion and the second luminance dispersion is divided by the first or second luminance dispersion to thereby calculate a change rate of the luminance dispersion.
(3c) In which area of two or more different depth areas inside the scatterer 101 the foreign object 102 is present is determined based on the ratio of the change rate of the average luminance to the change rate of the luminance dispersion.
With the above-described configuration and operations in the present embodiment, information regarding the depth of a target object that is present inside a scatterer can be obtained with a simple optical system.
In the present embodiment, the actuator 140, which moves the scatterer 101, is used in order to change the position of the first target area 106 and the position of the second target area 112. An actuator that moves the light source 103, the optical system 107, and the imaging device 108 may be used, instead of moving the scatterer 101. It is sufficient as long as the actuator has a mechanism that changes the position of the scatterer 101 relative to the light source 103 and the imaging device 108 in the measurement apparatus 100. The actuator may be included in the controller 130 or may be an element external to the controller 130.
Also, a configuration described below may be employed instead of the configuration for moving the scatterer 101.
Differences from the embodiment described above are mainly described below.
The measurement apparatus 100 in the present embodiment does not include an actuator. A controller 130 causes a light source 103 to irradiate a first portion 105a of a scatterer 101 with light 104. The controller 130 causes an imaging device 108 to output image signals indicating an image including a first interference image 109 resulting from light emitted from a first target area 106 that is away from the first portion 105a and a second interference image 113 resulting from light emitted from a second target area 112 that is away from the first portion 105a. As a result, two rounds of image capture are completed.
A signal processing circuit 110 performs computational operation using a signal representing the first interference image 109 and a signal representing the second interference image 113, the signals being included in the image signals, to generate data regarding the depth of a foreign object 102, which is a target object that is present inside the scatterer 101, and outputs the data.
The distance between the first portion 105a and the center of the first target area 106 is equal to the distance between the first portion 105a and the center of the second target area 112. The distance between the first portion 105a and the center of the first target area 106 may be different from the distance between the first portion 105a and the center of the second target area 112. In such a case, in accordance with the difference between the distances, the signal processing circuit 110 may be adapted to be able to correct at least one of the signal representing the first interference image 109 and the signal representing the second interference image 113, the signals being included in the image signal, to make it possible to compare both the signals.
The signal processing circuit 110 in the present embodiment executes operations described below.
(1) A first average luminance indicating an average luminance of the first interference image 109 and a first luminance dispersion indicating a luminance dispersion of the first interference image 109 are calculated based on the signal representing the first interference image 109.
(2) A second average luminance indicating an average luminance of the second interference image 113 and a second luminance dispersion indicating a luminance dispersion of the second interference image 113 are calculated based on the signal representing the second interference image 113.
(3) Computational operation using the first and second average luminances and the first and second luminance dispersions are performed to generate data regarding the depth of the foreign object 102 that is present inside the scatterer 101, and the data is output. A specific method for generating the data is the same as or similar to that described above.
As illustrated in
A description will be given of an example in which calculation was performed in order to confirm the advantages of the present disclosure.
In this example, two 10-millimeter-square bar-shaped foreign objects 102a and 102b are embedded in the scatterer 101. The absorption coefficient and the reduced scattering coefficient of the scatterer 101 are the same as the absorption coefficient and the reduced scattering coefficient of the scatterer 101 described above in the example illustrated in
With the exemplary configuration of the measurement apparatus 100 in the above-described embodiment, the scatterer 101 is irradiated with irradiation light, the scatterer 101 is moved 25 steps at intervals of 5 mm in the X direction, and images of a total of 25 target areas are captured. A method that is similar to the method in the above-described embodiment was used to calculate a light intensity and a phase dispersion on the basis of the luminance distributions of the interference images corresponding to the respective target areas.
In the following description, the position of the foreign object 102a at a depth of 2 mm and the position of the foreign object 102b at a depth of 5 mm are separated based on the light intensity and the phase dispersion.
When the value of the change rate of the phase dispersion is close to zero, a foreign object is assumed to be absent or is assumed to be present at a depth where it is not detectable. Accordingly, it is rational to estimate that no foreign object is present at the depth of 2 mm or 5 mm. In the example, for ri/rp<0.05, correction for setting the ratio of the change rates to zero was performed.
Lastly, a description will be given of graph separation based on whether or not the corrected ratio of the change rates is larger than a certain value.
In the above-described embodiment, the respective change rates are calculated based on the light intensity and the phase dispersion, and information about the depth is obtained based on the ratio of the change rate of the light intensity to the change rate of the phase dispersion. However, the information may be obtained based on a difference or a magnitude relationship, not the ratio. The information regarding the depth may also be obtained based on the light intensity and the phase dispersion, instead of the change rate of the light intensity and the change rate of the phase dispersion. Also, another calculation method may be used in accordance with the optical properties of the scatterer or the foreign object(s). In addition, the relationship between the state of a foreign object and the change rate of the light intensity and the change rate of the phase dispersion may be machine-learned, and the information regarding the depth may be obtained based on the result of the learning. Also, the relationship between the state of a foreign object and the light intensity and the phase dispersion may be machine-learned, and the information regarding the depth may be obtained based on the result of the learning.
In an actual scatterer, the absorption properties and the scattering properties of foreign objects that are present inside the scatterer may be different from each other. In such a case, a method in which images of a target area are captured by irradiating the scatterer while changing the coherence length of a light source to a plurality of lengths is effective in order to obtain the information regarding the depths of respective foreign objects. The reason will be described below.
For example, two foreign objects, that is, a foreign object having a low-scattering property and a foreign object having a high-scattering property, are assumed to be present inside a scatterer. The average optical path length of light that travels through the foreign object having a high-scattering property becomes larger than the average optical path length of light that travels through the foreign object having a low-scattering property. This means that the optical-path-length deviation of light that travels through the foreign object having a high-scattering property increases. In order to cause interference to occur in the image plane with respect to the light, a light source having a larger coherence length is necessary. In other words, it can be said that the relationship between the coherence length of a light source and the interference changes depending on the scattering property of a foreign object.
Hence, it can be said that the use of a light source with different coherence lengths makes it possible to obtain the information regarding the depth even when foreign objects having different diffusion properties are present inside a scatterer. Also, the same concept can be applied to a case in which foreign objects having absorption properties that are different from each other are present inside a scatterer.
An actual scatterer may also have an absorption property and a scattering property that are not spatially uniform. In such a case, an average light intensity and a spatial distribution of the phase dispersion are pre-measured in a target area where there is apparently no foreign object. Next, the average light intensity and the phase dispersion in a target area where there is a foreign object are measured. It is possible to obtain the information regarding the depth by finding positions that are respectively spatially close to a target area where no foreign object is present and a target area where a foreign object is present and calculating the change rates of average light intensities and the change rates of phase dispersions with respect to the positions.
The configurations of the measurement apparatus used in the embodiment and the example are not limited to the above-described configurations, The configuration of the measurement apparatus may be changed to an appropriate configuration within a scope in which the disclosed configuration and the advantages are satisfied.
An application example of the measurement apparatus according to the present embodiment will be described below.
In the example illustrated in
Use of the measurement apparatus 200 in the embodiment makes it possible to separately detect the distribution of blood flow at a deep portion from the surface of the scalp and the distribution of blood flow in a brain surface layer portion located at a shallow portion from the surface of the scalp. A display 203 may display those blood flow distributions.
In the example in
Use of the measurement apparatus 204 in the embodiment makes it possible to separately detect the distribution of blood flow in a peripheral blood vessel part located at a shallow portion from the surface of skin and the distribution of blood flow in an artery part or vein part located at a deep portion. A display 207 may display the blood flow distribution as a numerical value corresponding to a blood flow rate.
Temporally continuously obtaining the distribution of the hemoglobin concentration and performing computational operation makes it possible to estimate a pulse waveform, a blood pressure value, and so on of only a deep artery part or only a shallow peripheral blood vessel part.
In the example in
With the measurement apparatus 208 in the embodiment, whether or not the content 213 is placed at a correct depth can be determined based on the information regarding the depth of the content 213 viewed from the image capture side, and a determination can be made as to whether each food product 212 is an acceptable product or unacceptable product. A display 211 may display the determination result.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-206083 | Oct 2017 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2018/036206 | Sep 2018 | US |
| Child | 16826477 | US |
