JPH03279843A - Method for suppressing scattered component in light transmitted through specimen - Google Patents

Abstract

PURPOSE:To suppress the influence by scattered light and to visualize the information in a specimen with a high resolving power by detecting the sum of the rectilinear component and scattered light component of the light transmitted in the specimen and a scattered light component. CONSTITUTION:The sum of the rectilinear light component and scattered light component which are emitted from a light source 2 and are passed through a sample 3 is detected by a photodetector (1)5. On the other hand, a collimator (2)b disposed with a specified angle theta with beam light is connected to the photodetector (2)7 and only the scattered light component which is emitted from the light source 2 and is past the sample 3 is detected by a photodetector (2)7. The respective outputs of the photodetector (1)5 and the photodetector (2)7 are inputted to a differential amplifier 8. The output of the photodetector (2)7 weighted with theta is subtracted from the output of the photodetector (1)5 by the differential amplifier 8, by which the scattered light component is drastically removed. The influence of the scattering by the specimen is eliminated in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to scattering components in light passing through a subject, which are suitable for visualizing information inside a subject using light, such as transparent viewing of a living body. Concerning suppression methods.

[Prior Art] In recent years, with the increase in cardiovascular and cerebrovascular diseases and the increasing use of images in medical treatment, angiography has become increasingly important. However, although angiography has become relatively easy due to advances in digital radiography, there are still risks that cannot be ignored when applying it to the human body and the pain that patients experience.

Furthermore, conventionally, non-invasive, non-contact measurement of information inside a subject such as a living body has been mainly performed using X-rays. However, the use of X-rays is known to have problems such as radiation exposure and difficulty in imaging biological functions. Also,
There is a problem that NMR-CT multi-method equipment is large-scale and expensive, and fluoroscopy using ultrasonic waves has a problem of limited spatial resolution.

By the way, blood hemoglobin (
1-1b) is known to exhibit a unique spectral change depending on the degree of oxygenation. Utilizing this feature, for example, as shown in "Biological measurement using light" published in RO PLUS E1 magazine from May 1987 to March 1988, information inside the living body such as measuring blood oxygen saturation can be obtained. Research on non-invasive measurement of Furthermore, since blood hemoglobin (Hb) has higher absorbance in the infrared region than biological tissue, it is possible that blood vessels in tissue can be detected as images using light.

[Problems to be Solved by the Invention] However, when the inside of a living body is observed from outside the body using light, the contrast decreases due to strong light scattering in the body or body surface tissues, making it difficult to visualize information inside the living body. is difficult. If we can solve this light scattering problem,
It is believed that the shape of blood vessels in the body and its changes can be visualized and measured in real time without using contrast agents or the like. From the in-vivo information obtained in this way, it is thought that information on not only the shape but also the metabolic functions of the living body can be obtained based on the rich knowledge system of spectroscopy.

The present invention has been made in view of the above circumstances, and is intended to suppress the influence of scattering of the object and to visualize information inside the object using light with high resolution. The purpose of this invention is to provide a method for suppressing scattered components.

[Means for Solving the Problems] The method for suppressing scattered components in light passing through a subject according to the first invention includes a step of irradiating light onto a subject, and a method for suppressing light that is irradiated by the irradiation step and passing through the subject. a step of detecting the sum of a straight light component and a scattered light component of the light; a step of detecting only the scattered light component of the light that has passed through the subject after being irradiated by the illuminating step; and a step of suppressing the scattered light component by calculation using a detection output obtained by the step of detecting the scattered light component and a detection output obtained by the step of detecting only the scattered light component.

Further, the method for suppressing scattered components in light passing through a subject according to the second invention includes a step of irradiating a subject with pulsed light, and a time-resolved waveform of the light that is irradiated and passes through the subject through the irradiation step. The method includes a detecting step and a step of suppressing the scattered light component by separating a part of the time-resolved waveform detected by the detecting step.

[Operation] In the first invention, the sum of the straight light component and the scattered light component of the light that has passed through the subject, and only the scattered light component of the light that has passed inside the subject, are respectively detected. , the scattered light component is suppressed by the operation using these.

Further, in the second invention, the subject is irradiated with pulsed light,
A time-resolved waveform of light passing through the subject is detected, and a part of this FR gate-resolved waveform is separated to suppress scattered light components.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

1 and 2 relate to a first embodiment of the present invention, FIG. 1 is an explanatory diagram showing the configuration of an apparatus for implementing the method of suppressing scattered components, and FIG. FIG. 5 is a characteristic diagram showing a beam measuring 5 of the amount of transmitted light near the edge using .

As shown in FIG. 1, the scattered component suppressing device 1 for realizing the method for suppressing scattered components of this embodiment includes a light source 2 as a light irradiation means, and a device facing the light source 2 with a sample 3 in between. It includes a photodetector (1) 5 and a photodetector (2) 7. The light source 2 is provided on the light receiving side of the photodetector (1) 5.
A remeter (1) 4 is connected to the photodetector (1) 5 which is correctly aligned on the optical axis of the beam light from the
Accordingly, the sum of the straight light component and the scattered light component emitted from the light source 2 and passing through the sample 3 is detected. On the other hand, the photodetector (2) 7 is connected to a collimator (2) 6 arranged at a constant angle θ with respect to the beam light. The photodetector (2) 7 detects only the scattered light component that is emitted from the light source 2 and passes through the light source 3. The photodetector (
The respective outputs of the photodetector (1) 5 and the photodetector (2) 7 are input to a differential amplifier 8. Then, by this differential amplifier 8, the output of the photodetector (1) 5 is weighted by θ, and a photodetector (
2) By subtracting the output of 7, it becomes possible to significantly remove the scattered light component. This is tentatively called the differential principle.

Next, with reference to FIG. 2, an experiment to demonstrate the effects of this embodiment will be described.

In this experiment, the light source 2 was a He-Ne laser (wavelength 63
2.8nm, output 2mW), ]remeter (1) 4
For this, a combination of objective lens (focal path II 1110 mm) and pinhole (diameter 30 μm) is used, and a collimator (
2) A beam expander (xlo) was used for 6.

In addition, for Sample 3, an acrylic container with an inner wall thickness of 20 mm containing the etiquette suspension was used as a scattering material. A knife was placed in the center of this sample solution, and the amount of transmitted light near the edge was measured.

The results are shown in FIG. In FIG. 2, the horizontal axis shows the position of the beam center with respect to the knife, and the vertical axis shows the normalized light intensity. In addition, A is the output of the photodetector (1) 5 without using the collimator (1) 4, and B is the output of the collimator (1) 5.
1) In the case of the output of photodetector (1) 5 using collimator (1) 4, C is weighted by θ when based on the differential principle, that is, from the output of photodetector (1) 5 using collimator (1) 4. In the case of the output of the differential amplifier 8 after subtracting the output of the photodetector (2) 7, D indicates the case of only water without scattering.

As can be seen from FIG. 2, in the case (A) where no collimator is used, the signal is significantly smoothed compared to the case <D> in which only water is used due to the strong influence of scattered light.

On the other hand, using only a collimator (B) also suppresses the scattered components to some extent, and when using the differential principle (
In C), a result very close to the state of water without scattering (D) was obtained.

As described above, according to this embodiment, it is possible to extract the straight light component while suppressing the scattered component υ1. Also, transmission image measurement with high spatial resolution becomes possible.

3 to 13 relate to the second embodiment of the present invention, in which FIG. 3 is an explanatory diagram showing a transmission image of the palm of the hand using near-infrared light, and FIG.
The figure is a block diagram showing the configuration of the blood vessel image analysis system.
The figure is an explanatory diagram showing the settings for measuring the contrast of blood vessel images, Figure 6 is a histogram showing the distribution of brightness in the area set as in Figure 5, and Figure 7 is the measurement of the contrast of blood vessel images. A characteristic diagram showing the results. Figure 8 is a characteristic diagram showing the wavelength characteristics of the transmitted light intensity of the finger. Figure 9 is a characteristic diagram showing the results of measurement to determine the visible depth of blood vessels. Figure 10 is a characteristic diagram showing the wavelength characteristics of the transmitted light intensity of the finger. A characteristic diagram showing the relationship between the concentration and contrast of skim milk powder and hemoglobin in a solution, FIG. Figure 13 shows the change in pulse waveform when the scattered component is not spatially suppressed in the device shown in Figure 11 (characteristic diagram). Figure 13 shows the change in the pulse waveform when the scattered component is spatially suppressed in Figure 14 shows the Naifetsuji spatially resolved waveform.
The figure shows the amount of transmitted light near the edge using the device shown in Figure 11.
FIG. 4 is a characteristic diagram showing four measurement results.

The method of this example is a method of temporally suppressing scattered light υj, but before explaining the method, we will explain the bio-penetration of near-infrared light, the wavelength characteristics of blood vessel images, and the visible depth of blood vessels. explain.

First, the permeability of near-infrared light to living bodies will be explained with reference to FIG.

First, we investigated the biological penetration characteristics of light. It is known that biological tissue has low absorption in the near-infrared wavelength region. Therefore, we first conducted an experiment to investigate how much light can be obtained when light passes through a living body. The results are shown in FIG.

As a light source, a near-infrared light emitting diode (wavelength 880 nm,
Optical output 30mW/piece), 100 pieces in total, 10 pieces vertically and horizontally, 8
They were arranged on a plane of 0 x 80 mm.

Figure 3 shows this light source applied to the palm of the hand, and the transmitted light from the back side of the palm of the hand as an image intensifier.
1ntensif'1er). In this figure, the part indicated by the reference numeral 10 is a transmitted image, and the hatched part is a dark part of the background. Even with this amount of light, a transmitted image can be observed without the need for image accumulation, and because of the absorbency of Hb and its high concentration in this wavelength range, blood in blood vessels can be visualized as bright and dark images. Do you get it. However, the blood vessel images obtained in this way are strongly influenced by light scattering in the living body, and there are many unknowns about the actual thickness, depth, etc. of the blood vessels. Therefore, in order to clarify the phenomena of light scattering and absorption in living organisms and to visualize the actual state of blood in the body, we conducted the following basic research.

Next, wavelength characteristics of blood vessel images will be explained with reference to FIGS. 4 to 8.

That is, in order to find the optimal wavelength effective for visualizing blood vessel images, the wavelength characteristics of the obtained blood vessel images were investigated.

An outline of the blood vessel image analysis system 11 for this purpose is shown in FIG. This system 11 includes a light source 12. CCD tele camera 152 image processing device [16, (personal) combination coater 17. It is composed of a VTR 19 and a monitor (display device) 18. First, light in the visible to near-infrared range is generated from a light source 12 such as a laser or an LED, and is irradiated onto the object to be measured 14 through the aperture 13 . Transmits the object 14 to be measured.

The scattered light is detected by a CDD television camera 15 from the direction opposite to the direction of incidence, and a transmitted image is obtained as a television signal.

At this time, since blood absorbs more light than other tissues, blood vessels are detected as bright and dark images. The blood vessel image thus obtained is imported into the image processing device 16 and computer 17, and processed and analyzed.

Here, contrast was selected as an evaluation parameter when quantitatively analyzing the obtained blood vessel image, and the contrast of the blood vessel image with respect to the background (tissue) image was determined as follows.

As shown in FIG. 5, first, a region 23 including the target blood vessel 22 is set in the obtained image of the finger 21 and the like. Next, shine all over this area! ! ! When the histogram distribution of (intensity) is obtained, a bimodal peak as shown in FIG. 6 is obtained. Here, the luminance distribution of the blood vessel part has one peak (
Ib), and the background distribution around the inner tube is concentrated at the other peak (It). These peak positions were determined as the brightness of the blood vessel portion and the brightness of the background portion, respectively, and the contrast M of the blood vessel image was defined as shown in the following equation.

M-(It-1b)/(It+lb) Next, the contrast of the blood vessel image and the wavelength characteristics of the transmitted light intensity of the finger were measured. A dye laser (argon laser excitation, output 200 mW, dye Rhodamine 6G) was used as a light source,
The wavelength was varied between 570 and 620 nm. The index finger 21 of an adult male was used as the measurement object. A laser beam with a beam diameter of 5 mm was irradiated between the first and second joints on the ventral side of the index finger 21, and the transmitted image was detected by a television camera placed dorsally. An optical sensor (light-receiving surface 4 mmφ, PIN photodiode) was attached immediately behind the back side of the mouse, and measurements were taken.

FIGS. 7 and 8 show the contrast of the blood vessel image and the wavelength characteristics of the transmitted light intensity of the finger, which are the measurement results. Note that three samples A were used for the measurements shown in FIG.

B and C were used. As seen in FIG. 7, the contrast increases on the shorter wavelength side. This seems to be because absorption by hemoglobin increases significantly in the short wavelength region compared to other tissues. On the other hand, as seen in FIG. 8, the transmitted light intensity increases on the longer wavelength side. This is thought to be due to the fact that as the wavelength becomes longer, both tissue absorption and blood absorption decrease.

These Il! The results revealed that in order to visualize blood vessels in the body, it is necessary to select a wavelength according to the purpose and conditions.

Next, the depth of the blood vessel will be explained with reference to FIGS. 9 and 10.

The results so far have shown that it is possible to visualize blood vessels in the body by selecting an appropriate wavelength. However, with this type of trans-illumination method, blood vessels located deep in the body when viewed from the observation side of the body are difficult to visualize. Due to strong diffuse scattering, it does not appear clearly in the image. Therefore, we investigated the depth of blood vessels that can be detected in images.

The experimental system is the same as that shown in FIG. 4 except for the light source 12 and the object to be measured 14. As the light source 12, a planar light source in which light emitting diodes used to obtain the image shown in FIG. 3 were arranged was used. As the object to be measured 14, a transparent acrylic container filled with a sample was used. As a sample solution, the same scattering as biological tissue.

A mixture of etiquette suspension and hemoglobin solution formulated to have absorption properties was used. However, the scattering and absorption values of tissues are as reported by Wray et al. (Blochimica
et Biophysica Acta 993,1
84-192 (1988). A glass capillary tube (inner diameter: 11 mm) containing blood was placed in this solution to create a model that optically simulates blood vessels in a living body. In addition, for comparison with the blood vessel model, a black-painted wire (outer diameter 1 mm) was used.
) was used as a perfect absorber.

Using this experimental system, we first measured the visible depth of blood vessels. A glass capillary tube or wire with a variable distance from the wall is erected in an acrylic container with an inner wall interval of 10 mm.
We sought the relationship between their depth and contrast. next,
We investigated how the scattering and absorption characteristics of tissues affect the contrast of blood vessel images.The experiment was conducted with an inner wall spacing of 20
A wire is placed in the center of a mm container (depth 10 mm), and the skim milk powder (scatterer) and hemoglobin (absorber) in the sample solution are
The contrast at this time was measured by changing the density.

Figure 9 shows the experimental results. In this figure, the horizontal axis is the distance (depth) from the observation side inner wall surface of the acrylic container filled with the sample to the glass tube (full surface) or wire. Although the visibility limit is limited by the S/N ratio of the observation system, we were able to obtain a visibility depth of approximately 3 mm on the entire surface and approximately 8 mm on the wire.

Next, FIG. 10 shows the results when the scattering and handling properties of the target substance (here, the ratio) and the background substance (here, the sample solution) were varied. The degree of scattering of matter in ancient times (
It was found that the contrast was increased by increasing the absorbance (Hb concentration) while keeping the skim milk powder (1 degree) constant. In particular, we obtained an interesting result in that when scattering is strong, objects that are invisible when the absorbance is low become visible as the number of absorbers increases. This seems to be because the presence of the absorber suppresses scattering, and although the overall amount of transmitted light decreases, the contrast of the transmitted image increases.

Considering this result, we believe that the increase in contrast on the short wavelength side shown in Figure 7 is not simply due to an increase in the absorption of hemoglobin, but also to a synergistic effect with the scattering suppression phenomenon associated with increased absorption in the background tissue. It will be done. These factors are considered to be one of the reasons why a certain degree of transmission image can be obtained in biological tissue despite strong scattering.

The results obtained so far have revealed that in order to visualize blood vessels in the body, it is necessary to suppress the strong diffusive scattering caused by living tissue. Therefore, we devised a method to temporally and spatially suppress the scattered components.

The method will be explained below. When a beam of light enters a large number of randomly distributed particulate scatterers from one direction, the light is repeatedly scattered between the particles, and after a time delay due to scattering, is emitted in a wide h direction. Therefore, when a temporally short pulsed light is incident on an object, the pulse width of the emitted pulsed light is expanded due to scattering, and the scattered component has a long tail. Therefore, this pulsed light is regarded as a time-resolved waveform, and the rising part of the pulse is divided into minutes 1i11? l
It is thought that the scattered components can be suppressed. In addition, particles that are not affected by scattering do not have their optical axes bent and travel straight along the optical axis. Therefore, by selectively extracting straight light by using a light receiving system with a small acceptance angle that directly faces the incident light,
It is thought that the scattered components can also be suppressed spatially. Here, we experimentally examined the effectiveness of these two methods.

FIG. 11 shows a system for evaluating the suppressing effect of scattered components in the emitted light in the trans-illumination method, and also shows the configuration of the scattered component suppressing device 31 for realizing the scattered component suppressing method of this embodiment. be.

This system includes a Nd:YAG laser 32 as a light irradiation means, and a collimator 36 that correctly aligns the optical axis of the incident beam with the optical axis of the incident beam is provided so as to face the laser 32 with a sample 34 in between. . This collimator 36
consists of a lens 37 with a focal length of 10 mm and a pinhole 38 with a diameter of 50 μm. The collimator 3
6, the light passes through an optical fiber bundle (inner diameter 3 mm, length 600
mm) to the streak camera 40. The output of this streak camera 40 is processed by a signal processing device M42 and a (personal) computer 43, so that the time-resolved waveform of the emitted pulse can be observed. Note that between the laser 32 and the sample 34,
A half mirror 33 is provided, and the light reflected by the half mirror 33 is received by a photodiode 41 and is used as a trigger signal for a streak camera 40, as is well known.

Next, with reference to FIGS. 12 to 14, an experiment in which changes in spatial resolution were measured will be described in order to demonstrate the effects of this embodiment.

In this experiment, a sample 34 is irradiated with optical pulses (output 8 mJ, wavelength 532 r1 m, beam diameter 1 mm, pulse half width 55 ps measured at the fiber output end) from a YAG laser 32 at intervals of 30 H2.

Sample 34 has 1ftllB of milk in an acrylic container W with an inner wall spacing of 20mm! (11 fat 1 & milk 1.5)/100m
j) was used. A knife 35 was placed at the center of the sample 34 (distance 10 mm from the inner wall surface), and the spatial resolution near the edges of the transmitted image was measured. Light emitted from the sample 34 is guided to a streak camera 40 via an optical fiber bundle 39. Then, the output of the streak camera 40 is processed by a signal processing device 42 and a computer 43, and the time-resolved waveform of the emitted pulse is observed. Furthermore, the incident angle was slightly limited by the collimator 36, and the effect of spatially suppressing scattering was investigated.

The results are shown below. Pinhole 3 in the measurement system
FIG. 12 shows changes in pulse waveforms when scattering components are not spatially suppressed except for case No. 8. Furthermore, Figures 12 and 13
In the figure, the horizontal axis is time, the vertical axis is the light intensity, and the depth direction is the distance l from the beam center to the knife edge (the position of the beam center with respect to the knife edge). In this case, the 12th
It can be seen that the output light waveform is significantly influenced by scattering both temporally and spatially compared to the incident light waveform shown in the upper left of the figure. On the other hand, when the scattered components are spatially suppressed by the collimator 36, as shown in FIG. You can see that it's getting easier.

FIG. 15 shows spatially resolved images of the naifetsu obtained by these methods. In the figure, curves A to C show spatially resolved images based on the light intensity at points A to C shown in FIG. 14 in the time-resolved waveform when the collimator 36 is not used. Note that the light intensity at any point in the time-resolved waveform is extracted by the signal processing unit 42 and the combi coater 43.

From FIG. 15, it can be seen that the spatial resolution of the rising portion (Δ) of the emitted light pulse is the best, and that the later times are strongly influenced by scattering. Here, the reason why the influence of scattered light is considerably seen even in case A is considered to be because suppression of scattered components is limited due to the finite width of the incident pulsed light and the finite spread of the acceptance angle. Indicated by D in Figure 15 4
The curve is a spatially resolved image obtained from the light intensity peak value of the partially resolved waveform when the collimator 3G is used.

Thus, it can be seen that the spatial resolution can be greatly improved by adding spatial scattering suppression.

Based on the above results, the scattered component suppression l111 of this example
In the device 31, a streak camera 40. Signal processing device 4
2 and the computer 43 to separate the portion corresponding to the straight light component in the time-resolved waveform of the emitted light from the sample 34,
More preferably, the collimator 36 spatially extracts the straight light component.

As described above, according to this embodiment, it is possible to suppress the scattered components temporally and spatially, thereby suppressing strong diffuse scattering and obtaining information inside the object with high spatial resolution. Visualization becomes possible.

[Effects of the Invention] As described above, according to the present invention, the influence of scattering of the object can be suppressed, so that it is possible to visualize information inside the object using light with high resolution.

[Brief explanation of drawings]

1 and 2 relate to the first embodiment of the present invention, FIG. 1 is an explanatory diagram showing the configuration of an apparatus for realizing the method for suppressing scattered components, and FIG. Characteristic diagrams showing the measurement results of the amount of transmitted light near the edge using
FIG. 3 relates to the second embodiment of the present invention, FIG. 3 is an explanatory diagram showing a transmission image of the palm by near-infrared light, FIG. 4 is a block diagram showing the configuration of a blood vessel image analysis system, and FIG. An explanatory diagram showing the settings for measuring the contrast of blood vessel images. Figure 6 is a histogram showing the distribution of brightness in the area set as shown in Figure 5. Figure 7 shows the measurement results of the contrast of blood vessel images. Figure 8 is a characteristic diagram showing the wavelength characteristics of the transmitted light intensity of the finger, Figure 9 is a characteristic diagram showing the results of measurement to determine the visible depth of blood vessels, and Figure 10 is a characteristic diagram showing the wavelength characteristics of the transmitted light intensity of the finger. The relationship between the concentration and contrast of skim milk powder and hemoglobin is shown.
A characteristic diagram, FIG. 11 is an explanatory diagram showing the configuration of an apparatus for realizing the scattered component suppression method of this embodiment, and FIG.
Figure 13 shows the change in pulse waveform when the scattered component is not spatially suppressed in the apparatus shown in Figure 11 (characteristic diagram). 14 is an explanatory diagram showing the spatially resolved waveform of the knife edge, and FIG. 15 is a characteristic diagram showing the measurement results of the amount of transmitted light near the edge using the apparatus shown in FIG. 11. 1...Scattered component Suppression device 2...Light source 4.6...Collimator 5.7...Photodetector 8...Differential amplifier Fig. 2 Fig. 7 Fig. 8 Liquid length fnml Fig. 9 Fig. 10 Figure HbjlI+mMoffil Figure 11 Figure 14 Figure 12 (ps) Procedural amendment (gi) October 3, 1990, relationship with the person making the amendment case

Claims (2)

[Claims] (1) A step of irradiating the object with light; a step of detecting the sum of a straight light component and a scattered light component of the light irradiated by the irradiation step and passing through the object; and the irradiation step. A procedure for detecting only the scattered light component of the light that was irradiated by and passed through the object, a detection output from the procedure for detecting the sum, and a detection output from the procedure for detecting only the scattered light component. A method for suppressing scattered light components in light passing through a subject, comprising: a step of suppressing the scattered light components by a computation performed by a subject. (2) A procedure for irradiating the subject with pulsed light, a procedure for detecting the time-resolved waveform of the light that was irradiated by the irradiation procedure and passed through the subject, and the time-resolved waveform detected by the detecting procedure. A method for suppressing scattered components in light passing through a subject, comprising: suppressing the scattered light components by separating a part of the waveform.