JPH10332577A - Correction method for surface effect - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a correction method in which an error can be corrected even when an angle of incidence is changed by a method wherein incident light is incident on the surface of a standard sample from a plurality of angles, transmitted light is measured, the dependence on the angle of a quantity of transmitted light of the standard sample is found and the error which is caused by the angle of incidence on the surface of an object to be measured is corrected on the basis of the dependence on the angle. SOLUTION: In the case of computed tomography, an angle in a case in which light is incident on a part near the center of an object to be measured is different from an angle in a case in which light is incident on a part around its end, and an error which is comtained in a measured value is different in both cases. At this time, an angle which is formed by a perpendicular line with reference to the surface of a standard sample 60 and by the optical path of incident light is designated as θ. The standard sample 60 is turned, a quantity of transmitted light 80 corresponding to various angle θ of incidence is measured by a measuring device 90, and the dependence on the angle of the quantity of transmitted light 80 is obtained. On the basis of the dependence on the angle, an error which is contained in the measured value of the transmitted light is corrected. A continuous function which approximates the measured value of the transmitted light is found. A method in which the error contained in the measured value of the transmitted light is estimated and corrected by using the function is suitable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a correction method for correcting an error of a measured value in optical CT or the like.

[0002]

2. Description of the Related Art Conventionally, light scattering and
2. Description of the Related Art In order to investigate properties such as absorption, optical measurement is known in which light is incident on a measurement target and the amount of light transmitted through the measurement target is measured. In recent years, computed tomography using light (optical CT; optical computed tomography)
aphy) has also been actively studied. In this case, it is necessary to make light incident on various positions of a measurement object from various directions and measure the amount of transmitted light corresponding to each. In these optical measurements, it is necessary to know the amount of decrease in light due to transmission through the measurement object, which represents the state inside the measurement object.

[0003]

However, when light measurement is performed by placing the object to be measured in air, the refractive index of the object to be measured is generally different from that of air. , The amount of transmitted light greatly decreases due to a change in the polarization plane, and the like. In addition, the amount of reduction is often larger than the amount of reduction of light that represents scattering or absorption of light inside the measurement target, which should be originally obtained in optical measurement for measuring the amount of transmitted light. Furthermore, since the reflection and refraction of light on the surface of the measurement target greatly depend on the angle of incidence of light on the measurement target,
When it is necessary to obtain a measured value corresponding to various incident directions and positions of light as in the case of the light CT, the measured value is included in the measured value.
It is particularly difficult to correct an error due to light reflection / refraction on the surface of the measurement target.

The present invention has been made in view of the above circumstances, and provides a correction method capable of correcting an error due to light reflection or the like on the surface of a measurement object even when the angle of incidence of light on the measurement object changes. The purpose is to:

[0005]

According to the present invention, there is provided a method for correcting a surface effect, comprising the steps of: irradiating incident light on a measuring object; measuring transmitted light transmitted through the measuring object to obtain a measured value; Determining the angle dependence of the amount of transmitted light of the standard sample by irradiating the incident light onto a predetermined standard sample at a plurality of angles with respect to the surface of the standard sample and measuring the transmitted light at each angle. And, based on the angle dependence of the amount of transmitted light of the standard sample, included in the measured value, the step of correcting an error caused by the incident angle to the surface of the measurement target, of the light incident on the measurement target. Features.

[0006]

Embodiments of the present invention will be described below. FIG. 1 is a diagram illustrating a step of obtaining a measurement value of transmitted light transmitted through a measurement target in one embodiment of the present invention. The cylindrical measuring object 10 has a cylindrical scatterer 2 inside.
When the incident light 30 is applied to the measuring object 10, a part of the incident light is first reflected on the surface thereof, and the rest enters the measuring object 10. Next, the light that has entered the measurement target 10 travels to the scatterer 20 and is partially scattered while passing through the scatterer 20. The primary purpose of optical measurement is to obtain information inside the measurement object by knowing the amount of decrease in light due to scattering by the scatterer 20. The light transmitted through the scatterer 20 travels to the surface of the measurement target 10, a part of which is reflected on the surface, and the rest goes out of the measurement target 10. Of the incident light 30, the transmitted light 40, which is light not reflected or scattered by the measurement object 10, is measured by the measuring device 50 to obtain a measured value.

In the present invention, the shape of the object to be measured and the number, shape, distribution, etc. of the scatterers are not limited to the above description. The measurement object may have an absorber instead of a scatterer, and may have a scatterer and an absorber. In any measurement object, only the decrease in light due to reflection or the like on the surface of the measurement object is an error in the measurement value, and the decrease in light due to scattering, absorption, or the like at a portion other than the surface of the measurement object is originally the measurement value It should be reflected in

In the case of optical CT or the like, information on a tomographic plane is obtained by measuring the object 10 by moving it in parallel or rotating it. For example, as shown by a left-right arrow in FIG. 1, when a case is considered in which the light is translated in a direction perpendicular to the optical path of the incident light 30, light is incident near the center of the measurement target 10 and around the end. Incident light, the incident light 3
The angle between the zero optical path and the surface of the measurement target 10 is significantly different, and the light reflectance and the like on the surface are also greatly different. Accordingly, the error included in the measured value differs greatly between the case where light is incident near the center of the measurement target 10 and the case where light is incident near the end, and the change in the error depends on the internal structure of the measurement target. , Often exceeds the change in measured value.

FIG. 2 is a diagram showing steps in the present embodiment for determining the angle dependence of the amount of light transmitted through the standard sample. The standard sample 60 is the measurement target 10 shown in FIG.
This is a plate-shaped sample having the same surface structure as that of Example 1 and having no scatterer inside. In the present invention, the shape of the standard sample need not be a plate as long as the shape is suitable for measuring the angle dependence of the transmitted light amount. Also, assuming that the surface of the measurement sample is, for example, ground glass, the surface structure of the standard sample is sufficient if the surface of the standard sample is ground glass at first glance, and strict identity is not required. Of course there are. When the measurement target is, for example, a living body, the standard sample may be a sample having a scatterer or the like inside, such as a part of the skin.

Similar to the step of obtaining the measured value of the transmitted light 40 shown in FIG. 1, the incident light 70 is incident on the standard sample 60, and the measured value is obtained by measuring the amount of the transmitted light 80 with the measuring instrument 90. Here, the angle formed between the perpendicular to the surface of the standard sample 60 and the optical path of the incident light 70 is defined as θ, and the standard sample 60 is rotated to measure the amount of transmitted light 80 corresponding to various incident angles θ. The angle dependence of the light intensity of the light 80 is obtained.

As a method of correcting an error included in the measured value of the transmitted light 40 based on the angle dependency, a continuous function approximating the measured value of the transmitted light 80 is obtained as described later. The method of estimating and correcting the error included in the measurement value of the transmitted light 40 using the above method is preferable. Further, an error included in a measured value of the transmitted light 40 corresponding to the incident angle of the transmitted light 80 may be estimated and corrected directly from a measured value corresponding to one incident angle.

[0012]

EXAMPLES Examples of the above embodiment will be described below. A 30-mm-diameter acrylic cylinder whose surface was polished with sandpaper and made into a 30-mm-diameter acrylic cylinder, a 12-mm-diameter hole was formed, and a 10-mg intralipid solution of 2 mg / liter was placed as a scatterer in the measurement object. did.

A laser beam is incident on the object to be measured, and the transmitted light is measured by a light heterodyne method, so that only the portion of the incident laser light which is not affected by the reflection or scattering of light by the object to be measured. Was extracted and measured. Also, the measurement object is translated a little at a time in a direction perpendicular to the optical path of the incident light, and a series of measurement values corresponding to each incident position is obtained, thereby obtaining projection data when the measurement object is viewed from one direction. I got An example of this projection data is
A graph in which the horizontal axis indicates the incident position and the vertical axis indicates the measured value of the amount of transmitted light indicates that the height is substantially the same over the entire range corresponding to the position where the measurement target is present, as indicated by a black square in FIG. Became a trapezoidal graph. After obtaining the projection data viewed from one direction, the object to be measured was slightly rotated, and the projection data in a new direction was obtained by the same procedure as above. By repeating these procedures, each projection data obtained by viewing the measurement target from each direction was obtained. By analyzing these projection data with a computer, an image of a tomographic plane as described later was obtained.

As a standard sample corresponding to the above-mentioned measurement object,
Using an acrylic plate whose surface was polished with a sandpaper in the same manner as the measurement object, a series of measurement values of the transmitted light transmitted through the standard sample corresponding to a plurality of angles θ were obtained by the measurement method shown in FIG. When a series of these measured values is plotted on the vertical axis of the amount of transmitted light and the angle θ shown in FIG. 2 on the horizontal axis, a graph having a peak near 0 radians as shown by a white square in FIG. 3 is obtained. In this embodiment, this series of measured values is represented by a Gaussian function y = -87 + indicated by a solid line in FIG.
The approximation was performed by 42 * exp (-x * x / 0.4), and the error included in the projection data was estimated and corrected using this Gaussian function. When a result of correcting the example of the projection data shown in FIG. 4 using this Gaussian function is shown in a graph, as shown by a white square in FIG. 4, only a range corresponding to the position where the scatterer exists is greatly raised. Could be obtained.

Hereinafter, the effect of the present embodiment will be described using an image of a tomographic plane reconstructed from the projection data and the corrected projection data. FIG. 5 is an image of a tomographic plane obtained using projection data without correction. FIG. 6 is an image of a tomographic plane obtained using the corrected projection data. FIG. 7 is an image of a tomographic plane obtained using projection data that has been corrected and then smoothed.

The inside of a circle inscribed in the black square forming the outer periphery common to the images of these tomographic planes is an image range calculated by the computer, and the black part outside the inscribed circle is a physical meaning. Do not have. Also, the whiter part of the screen indicates that the part is more strongly scattered. Comparing the above three figures, FIG. 5 first shows a clear white ring-shaped image, which corresponds to the surface of the measurement object. In addition, there is almost no structure-like thing inside the white ring-shaped image. On the other hand, in FIG. 6, the portion corresponding to the surface of the measurement target is hardly discriminated, and a clear white round image having a diameter of about one third of the diameter of the measurement target appears near the center of the screen. And this is the part corresponding to the scatterer. Further, in FIG. 7, only the image of the scatterer clearly appears in white, and portions other than the scatterer are almost uniformly black.

As described above, according to the present embodiment, errors due to reflection on the surface of the object to be measured and the like can be corrected.

[0018]

As described above, according to the surface effect correction method of the present invention, even if the angle of incidence of light on the object to be measured changes, the error due to the reflection of light on the surface of the object to be measured, etc. Can be corrected.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a step of obtaining a measurement value of transmitted light transmitted through a measurement target according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a step of obtaining an angle dependency of transmitted light transmitted through a standard sample in one embodiment of the present invention.

FIG. 3 is a graph showing the angle dependence of the amount of transmitted light transmitted through a standard sample.

FIG. 4 is a graph showing an example of projection data of a measurement target.

FIG. 5 is an image of a tomographic plane obtained using projection data without correction.

FIG. 6 is an image of a tomographic plane obtained using corrected projection data.

FIG. 7 is an image of a tomographic plane obtained using projection data that has been corrected and then smoothed.

[Explanation of symbols]

 10 Measurement target 30,70 Incident light 40,80 Transmitted light 60 Standard sample

Continuing from the front page (72) Inventor Takao Akatsuka 2-2-1 Matsuei, Yamagata City, Yamagata Prefecture Inside the Bio-Optical Information Laboratory Co., Ltd. (72) Inventor Fumio Inaba 35-1 Kasumi-cho, Yagiyama, Taishiro-ku, Sendai College of business

Claims (1)

[Claims] 1. A step of irradiating incident light on a measurement target and measuring a transmitted light transmitted through the measurement target to obtain a measurement value; and transmitting the incident light to a predetermined standard sample and to a surface of the standard sample. Incident from each of a plurality of angles, measuring the transmitted light at each angle, to determine the angle dependence of the transmitted light amount of the standard sample, based on the angle dependence of the transmitted light amount of the standard sample, Correcting an error caused by an incident angle of the incident light on the measurement target with respect to the surface of the measurement target, which is included in the measurement value.