JPH03218443A - Tomographic image pickup method and device using beam - Google Patents

Abstract

PURPOSE:To obtain one kind of distribution as a tomographic image out of transmissivity, absorbance and diffusion strength in a cross sectional surface by irradiating the prescribed cross sectional surface of an object with beam from plural parallel directions and reconstituting data obtained by measuring the transmission strength. CONSTITUTION:A light source 2 and a photodetection part 3 are arranged so as to be faced each other with an object 1 between and the both light source 2 and photodetection part 3 can be respectively simultaneously parallelly moved on the prescribed cross section and parallel plane of the object 1 by linear motors 4 and 5. Then, the center of an intermediate point O between them can be rotated at 180 deg.. The light source 2 executes light scanning in the prescribed cross section of the object 1 and the photodetection part 3 measures the strength of the beam from the light source 2 passing through the object 1. The light source 2 and the photodetection part 3 are parallelly moved by the motors 4 and 5 and light irradiation scan from a certain direction and the passed light intensity measurement is executed. Next, while changing an angle theta and repeating this operation, the set of the projection data from all the angles necessary for reconstituting the tomographic image in the prescribed cross section is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a tomography method and apparatus that use light to obtain information within a predetermined cross section of an object as a tomographic image.

(Prior Art) A method that quantitatively deals with the internal structure of a substance is particularly useful when the substance is non-uniform. Such methods are often required to elucidate the morphological mechanisms or dynamics of nonlinear and non-dimensional phenomena, which have been of increasing interest in recent years. For example, in a reaction system or a diffusion reaction system where a lipid-impregnated membrane is placed at the boundary of an ionic solution, the ion concentration oscillates on both sides of the membrane.
The concentration gradient of a substance in solution is driving the reaction. By quantitatively measuring the spatial dispersion state of substances caused by such reactions and their temporal changes, it becomes possible to elucidate the reaction mechanism, and furthermore, new devices and process technologies that utilize such phenomena can be developed. It is believed that this will be useful for the development of

Non-destructive and non-contact methods are essential for measuring the phenomena described above. IL using light? + constant is very suitable for non-destructive and non-contact measurements.

Furthermore, it is a particularly excellent measurement method in terms of the sensitivity and time resolution of the detection system. Specifically, by measuring the transmitted light, reflected light, or scattered light from the sample, the optical constants, spectrum, etc. of the sample can be obtained, and the molecular species, molecular structure, vibrational structure, etc. can be determined. Further, laser light having monochromaticity, linearity, pervasiveness, etc. can extract detailed information about substances to the extent that it can be used for molecular structure analysis, surface structure analysis, and the like. In particular, for compounds that absorb light in the ultraviolet, i+J, and infrared regions, there is an absorption spectrum specific to each molecular species, so the optical At1 constant can also provide chemical information about the substance.

Historically, light source systems can be miniaturized by guiding a laser diode or a light source located elsewhere to the device using an optical fiber, and the light receiving system can also be made smaller by using a photodiode array or by guiding the light source through an optical fiber. There are advantages in device design. In addition, it has the advantage of being able to perform spectroscopy using a diffraction grating, the ability to freely set the optical path by using optical fibers, the ability to adjust the optical path using optical elements such as lenses, mirrors, and prisms, and the ability to polarize light using polarizing elements. be.

However, in measurements using reflected light, the object of optical constant p1 is the surface of the sample, and in measurements using transmitted light, it is assumed that absorbers are uniformly distributed on the optical path of the material. , the measured values are interpreted as average values. In any case, the non-uniform structure inside the sample itself cannot be handled, and therefore it is insufficient for investigating the internal structure of a substance.

A non-destructive, non-contact method of investigating the internal structure of a material is to scan a cross-section of an object from all directions with X-rays, measure the transmitted dose, and use a computer to create an image based on each measured transmitted dose. By reconstructing the object's t
X-ray CT (Comp
utcd tosography) is widely used in medical diagnosis and other fields. The mathematical principles of this method were published in the 1910s, and the combination of mathematical analysis of the reconstruction and experiments using gamma rays was published in the 1960s. Furthermore, in recent years, methods using not only X-rays but also magnetic resonance phenomena of atoms with nuclear spin have been put into practical use. In this way, image reconstruction methods are non-destructive and
This is an effective method that is widely used to obtain cross-sectional images without contact.

However, when it comes to X-ray CT, the X-rays emitted from the radiation source have poor directivity, and the sensitivity and time resolution of the detector are also not as high as in optical measurements.

Moreover, high-energy electromagnetic waves such as X-rays used in tomography only interact non-specifically with molecular species, so the information obtained is limited to physical information. Methods using magnetic resonance phenomena also usually provide only positional information of specific atoms (for example, hydrogen atoms).

(Problems to be Solved by the Invention) As described above, conventional optical measurements have not been able to examine non-uniform internal structures within substances that transmit light in the ultraviolet, iJ, or infrared regions.

In addition, X-ray CT is an excellent method for examining the internal structure of substances that do not transmit light in a non-destructive and non-contact manner, but there are some issues such as X-ray directivity, detector sensitivity and resolution. And optics? This is disadvantageous compared to IF1 constant, and only physical information, not chemical information, can be obtained.

The present invention has been made in view of the above points, and is capable of optically transmitting an object within a desired arbitrary cross section for a subject that is first transparent and has absorbers or scatterers unevenly dispersed inside. The object of the present invention is to provide a tomography method and apparatus using light, which makes it possible to obtain characteristics such as transmittance, absorbance, or distribution of scattering intensity as a tomographic image.

[Structure of the Invention] (Means for Solving the Problems) The tomography method of the present invention irradiates light onto a predetermined cross section of an object from a plurality of directions, and measures the amount of light transmitted from the object. The present invention is characterized in that a distribution of at least one of transmittance, absorbance, and scattering intensity within the cross section is obtained as a tomographic image by measuring the intensity of light and reconstructing the obtained JIJ constant data.

The tomography apparatus of the present invention also includes a light scanning means that is disposed on a plane passing through a predetermined cross section of a subject and scans the cross section with light from a plurality of directions, and a light scanning means that receives transmitted light from the subject and scans the cross section with light. Image reconstruction that obtains a tomographic image of the distribution of at least one of transmittance, absorbance, and scattering intensity within the cross section by reconstructing the data of the transmitted light intensity measured by the light receiving means and the light receiving means that measures the intensity. It is characterized by comprising a configuration means.

The present invention also measures the intensity of transmitted light for each wavelength by dispersing transmitted light from all directions within an arbitrary cross section for an object in which multiple types of absorbers are unevenly distributed. The present invention is characterized in that image reconstruction is performed based on these ill constant values to obtain a tomographic image of the transmittance within the cross section, and furthermore, an absorption spectrum of an arbitrary point within the tomographic image is obtained.

(Function) The present invention uses light to measure the transmittance, absorbance, or scattering intensity at the measurement wavelength for a desired arbitrary cross section of an object that has an optically non-uniform internal structure due to the presence of absorbers or scatterers. 41 minutes are obtained as tomographic images non-destructively and non-contact. Light has higher intensity and better directivity than X-rays, and detectors for the light have higher sensitivity and resolution.

With the present invention, it is possible to obtain the internal structure of an object not only from one cross section but also from various angles, and to understand the three-dimensional internal structure of the object by taking multiple parallel cross sections. By utilizing the high time resolution of the detector, it is also possible to obtain temporal changes in the internal structure at fixed time intervals in one cross section.

Furthermore, if the wavelength of light is selected from the ultraviolet region through the visible light region to the infrared region, it is possible to take advantage of the fact that each molecular species has its own unique absorption spectrum. A spectral distribution within a desired cross section can be obtained, and as a result, it becomes possible to obtain tomographic images containing chemical information, which is theoretically impossible with X-rays. Although it is not possible to obtain distribution information of multiple types of substances by simply imaging the wavelength-independent transmitted light intensity distribution of a subject through which light is transmitted, it is possible to obtain information on the distribution of multiple types of substances. By obtaining this information, it is possible to know the mixed state of multiple substances.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure shows a schematic configuration of a tomography apparatus according to an embodiment of the present invention.

In FIG. 1, a subject 1 is made of a material that transmits light, and a pair of light sources 2 and a light receiving section 3 are arranged to face each other with the subject 1 in between. Light source 2 and light receiving section 3
can be simultaneously translated in the same direction within a plane parallel to a predetermined cross section of the subject 1 by a linear motor 4.5, respectively,
Also, centering on the midpoint 0 between the two, at least tgo'
It can be rotated.

The light source 2, together with a linear motor 4 that moves the light source in parallel, constitutes a pre-scanning means that scans a predetermined cross section of the subject 1 with light. The light source 2 is not particularly limited as long as it emits light in any of the ultraviolet, visible, and infrared wavelength ranges, or all wavelength ranges depending on the purpose, but may include semiconductor lasers, light emitting diodes, other light emitting elements, or various solid states. and those configured to guide only light in a specific wavelength range selected by a spectrometer, color filter, interference filter, etc., or gas lasers, xenon lamps, tungsten lamps, deuterium lamps, etc. Examples include.

Further, the light from these light sources may be converted into parallel light beams by a lens and irradiated onto the subject 1. Furthermore, in order to obtain more information regarding the structure of the subject 1, it is also effective to irradiate the subject 1 with only specific polarized light components of the light obtained from these light sources.

The light receiving section 3 is moved in parallel by a linear motor 4, and the light receiving section 3 is moved in parallel by a linear motor 4.
A photoelectric conversion element, such as a photodiode, a photodiode array, an image intensifier, a CCD, which outputs an electrical signal according to the intensity, receives the light emitted from the object and passes through the object 1, and measures its intensity.
A photodetector or the like may be used, or a structure may be adopted in which the transmitted light from the subject 1 is received by an optical fiber and then the intensity of the light is measured by a charging conversion element, a photomultiplier tube, or the like.

Ideally, the light detected by the light receiving section 3 is only on a predetermined straight optical path, so it is desirable that the solid angle sensed by the light receiving section 3 is small.

This can be achieved by installing a via hole several times thicker than the hole diameter on the light receiving surface as a window for the light receiving section 3, or if using only light of a specific wavelength, using a transmission type diffraction grating and a method that diffracts the wavelength. One method is to place the light-receiving element in the direction in which the light is detected.

There is also a method of measuring the intensity of transmitted light from a plurality of light sources with one light receiving section by changing the light receiving direction of the light receiving section whose solid angle of light reception is narrowed.

The light source 2 and the light receiving section 3 are connected by linear motors 4 and 5.
By moving the object 1 in a certain direction, scanning with light irradiation from a certain direction and measuring the intensity of transmitted light, the same operation is repeated gradually changing the angle θ until θ - IH'. A collection (data set) of projection data from all angles necessary to reconstruct the tomographic image of the image is obtained.

The output signal of the light receiving section 3 is amplified to an appropriate level by an amplifier 6, and then inputted to an A/D converter 7, where it is converted into digital data. This digital data is manually input to an image reconstruction unit 8 using a computer, and a tomographic image within a cross section of the subject 1 scanned by the light source 2 is reconstructed. The reconstructed image is displayed or recorded in nine output copies.

The image reconstruction method may be the same as that used in conventional X-ray CT, and specifically, for example, a successive approximation method or an analytical method may be used.

For the latter, a general filter-corrected back projection method or a Fourier transform method is used, which may be selected as appropriate depending on the situation. The filter correction function is Chester
r) type, Shepp-at-gun (Shepp-Logan)
) type, etc., but it is sufficient to determine an appropriate correction function using a subject (so-called phantom) whose absorbance distribution is known in advance.

Next, other embodiments of the present invention will be described with reference to FIGS. 2 to 7.

In the embodiment shown in FIG. 2, a plurality of light sources 2 and a plurality of light receiving sections 3 are each arranged in the same plane, whereas in FIG. 1 only one set of light R2 and light receiving section 3 is used. By rotating the group of pairs as shown by the arrows while maintaining their relative positions, data sets from all angles necessary to reconstruct a tomographic image within a predetermined cross section of the subject 1 are obtained. This is what I did.

In the embodiment shown in FIG. 3, one light source 2 and a plurality of light receiving sections 3 are arranged, and the operation of collecting data within a certain angle range by deflecting the light from the light source 2 as shown by the broken line arrow is performed. By maintaining the relative relationship between the light source 2 and the light receiving section 3 and rotating the same as shown by the solid arrow, a similar data set is obtained.

Incidentally, for the pair of light source 2 and light receiving section 3, both parallel movement and rotation may be performed in combination.

In the embodiment shown in FIG. 4, a sufficient number of light sources 2 and light receiving units 3 are arranged in a matrix in a plane passing through a predetermined cross section of the subject 1 to obtain a data set necessary for image reconstruction. . According to this configuration, there is no need to mechanically move the subject 1, the light source 2, and the light receiving section 4 relative to each other.

5 to 7 each show an example in which data sets of a plurality of cross sections are obtained in order to obtain the three-dimensional structure of the subject 1.

In the embodiment shown in FIG. 5, a set of light source 2 and light receiving unit 3 that can obtain the data set necessary to reconstruct a tomographic image of the subject 1 is used as the cross-section for obtaining a tomographic image of the subject 1. By moving in parallel at regular intervals in the vertical direction, tomographic images in a plurality of parallel cross sections are obtained.

Furthermore, in the embodiment shown in FIG. 6, similar pairs of light sources 2 and light receiving units 3 are arranged at regular intervals in a direction perpendicular to the cross section in which tomographic images of the subject 1 are to be obtained. It was designed to give one image.

Furthermore, FIG. 7 is an extension of FIG. 6, in which a similar pair of light source 2 and light receiving section 3 are arranged at regular intervals in a cylindrical shape as a whole in a direction perpendicular to the cross section in which a tomographic image of the subject 1 is to be obtained. This makes it possible to obtain a more detailed three-dimensional structure.

In the embodiments shown in FIGS. 5 to 7, light 1! A2
Any of the configurations shown in FIGS. 1 to 4 may be used as a set of the light receiving section 3 and the light receiving section 3.

In addition, in the above embodiments, by changing the light receiving direction of the light receiving section, it is possible to measure the transmitted light intensity of multiple optical paths with one light receiving section, or to measure only the light from a specific light source from among the light coming from multiple light sources. It is also possible to measure by receiving transmitted light.

Furthermore, by repeating the measurements described in the above embodiments at regular intervals, it is also possible to track changes in the cross-sectional structure over time.

FIG. 8 schematically shows the configuration of an embodiment for obtaining a transmitted light intensity distribution that is projection data sufficient to obtain an absorption spectrum at an arbitrary point in a tomographic image of the subject 1. FIG. Although the input optical system may include only a light emitting element such as a lamp, the figure shows a case where light from a light emitting element 11 is guided to a light irradiation section 13 through an optical fiber 12. The light irradiation unit 13 also includes a color filter used for wavelength selection.

The light receiving optical system includes a light receiving section 14 that receives the light emitted from the light irradiating section 13 and transmitted through the subject 1, a spectroscopic element 15 that separates the received light, and a photoelectron that determines the intensity of the separated light l1-1. It includes a converter 16.

In the f-plane, the light irradiation part and
By moving the pair of light receiving sections in parallel while measuring the transmitted light intensity, or by arranging multiple pairs of light emitting sections and light receiving sections in parallel, the transmitted light intensity for each wavelength from that angular direction can be measured. Obtain a distribution, ie a set of projection data.

By repeating this operation over a range of 1800 while changing the angle little by little, a collection of projection data for each wavelength from all angles, that is, a data set can be obtained.

To track changes in the fault structure over time, it is sufficient to repeat the measurement at regular intervals.

As the data set on which the image is reconstructed based on the obtained signal, an appropriate wavelength may be selected from the measurement wavelength range and a data set at that wavelength or the sum of all measurement wavelengths may be used. One way to specify the position in the image where you want to obtain the absorption spectrum is to specify it by moving the cursor on the display, and the absorption spectrum at that position is obtained from tomographic image data (spatial distribution of transmittance) at each wavelength. can be obtained by rearranging the wavelength distribution.

Next, an example of an experiment conducted to confirm the effects of the present invention will be described. Cylindrical quartz container containing water (not shown)
A cylindrical body 10 having a uniform light transmission composition as shown in FIG. This subject 1 (
The shaded part of the cylinder 10) has a wavelength of 532 nm.
It is assumed that the absorbance at is known to be 0.1. A Nd:YAG laser is used as the light source 2, and its double wave (532 ns) is guided to the measuring section through an optical fiber.
The object was irradiated with a light flux of 0.5ssφ. Light receiving part 3
A pin photodiode was used, and the light source 2 and the light receiving section 3 were placed facing each other with the subject 1 in between and separated by approximately 20 cm.

The measurement is performed by moving the pair of light source 2 and light receiving part 3 in parallel by 0.5 s in one direction using linear motors 4 and 5 (stepping motors), and emitting 8 pulses of laser light at each position. In order to determine the transmitted light intensity for each pulse n1, the output voltage of the pin photodiode of the light receiving section 3 was measured, and the average value thereof was taken as the transmitted light intensity at that position.

The scanning takes into consideration the symmetry of the shape of the object 1, and after calculating the projection data for 180 degrees by performing a rotation pot change on the computer based on the transmitted light intensity distribution (projection data) only in the direction,
Image reconstruction was performed. The filtered back projection method is used for image reconstruction, and the filter function is Cheste.
The r type was used. As a result, a tomographic image as shown in FIG. 10 was obtained.

Next, the absorption spectrum at a predetermined position in a predetermined tomographic image of a similar subject was measured. It is known in advance that the absorbance of the shaded portion in FIG. 9 is 0.1 at a wavelength of 310 rv.

A deuterium lamp was used as the light source, and an infrared cut filter was used to remove infrared light before illuminating the subject. The light-receiving optical system was configured such that transmitted light was guided through an optical fiber through a light-receiving window to a spectroscopic element, a transmission type diffraction grating was used for the spectroscopic element, and the separated light was received by a photodiode array. The received light signals were processed using a multichannel analyzer.

The light emitting part and the light receiving part were placed 20 cm apart and facing each other. The measurement was carried out by moving the light irradiation part and light receiving part pair in parallel by 0.5L in one direction using a stepping motor, and at each position.
0 0 sssec integration was performed and the transmitted light intensity was measured. Scanning takes into account the symmetry of the subject and performs a rotational conversion on the computer from the transmitted light intensity distribution (projection data) in only one direction to obtain projection data for 180 degrees.
Image reconstruction was performed.

When the absorption spectrum at the position of the absorber on the tomographic image was determined, the results shown in FIG. 11 were obtained. On the other hand, the absorption spectrum of this absorber alone was measured using a general-purpose device, and the results are shown in FIG.

Both showed good agreement, confirming the validity of the method of the present invention.

[Effects of the Invention] As explained above, according to the present invention, light can be transmitted in a plurality of directions on one predetermined cross section for a subject that transmits light in the ultraviolet, visible, or infrared regions, or all of these wavelength regions. By reconstructing the results of measuring light intensity as an image, the distribution of light absorbers or scatterers in the irradiation wavelength range within a predetermined cross section of the object is expressed as a tomographic image of transmittance, absorbance, or scattering intensity distribution. This makes it possible to take tomographic images, which was impossible with conventional optical measurements. Furthermore, it goes without saying that with this method, the internal structure of an object can be measured in a non-destructive and non-contact manner, similar to conventional optical measurement.

The light in the wavelength range used for measurement in the present invention can be spectroscopy, optical path adjustment, and polarization, and a small light source such as a laser diode can be used, and the light source and
The optical path can be set freely and extremely small, and laser light with excellent monochromaticity and straightness can also be used, making it possible to achieve tomography with excellent spatial resolution from the standpoint of device design. .

Furthermore, since detectors for light in the ultraviolet, visible, or infrared regions have extremely high sensitivity and temporal resolution,
Not only is the accuracy high and measurement time can be shortened, but it is also possible to track temporal changes in tomographic images.

Furthermore, since molecular species that absorb in the wavelength region of light have their own unique absorption spectra, the present invention allows chemical It also becomes possible to represent information on the image as a tomographic image.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic configuration of a tomography apparatus using light according to one embodiment of the present invention, FIG. 2 is a diagram showing the arrangement of a light source and a light receiving section in another embodiment of the present invention, and FIG. 4 is a diagram showing the arrangement of a light source and a light receiving section in another embodiment of the present invention. FIG. 5 is a diagram showing the arrangement of a light source and a light receiving section in another embodiment of the present invention. FIG. 6 shows the arrangement of the light source and light receiving section in the sixth embodiment. 7 is a diagram showing the configuration of the light source and the light receiving section in the seventh embodiment, FIG. 8 is a diagram showing the configuration of the light source and the light receiving section in another embodiment of the present invention, and FIG. 9 is a diagram showing the configuration of the light source and the light receiving section in the seventh embodiment. Figure 10 is a diagram showing the structure of a subject used in an experiment to confirm the effects of the invention; Figure 10 is a diagram showing a tomographic image obtained by the present invention for the subject in Figure 9; Figure 11 is a diagram showing the tomographic image obtained by the present invention of the subject shown in Figure 9. FIG. 12 is a diagram showing the absorption spectrum distribution at a predetermined position in the tomographic image of the subject. FIG. 12 is a diagram showing the absorption spectrum distribution obtained for the absorber by a general-purpose device. 1... Subject, 2... Light source (light scanning means), 3...
- Light receiving unit, 4.5... Linear mode controller, 6... Amplifier, 7... A/D converter, 8... Image reconstruction unit, 9.
... Output part, lO... Cylindrical body, 11... Light emitting element,
12... Optical fiber, 13... Light irradiation section, 14...
- Light receiving section, 15... Spectroscopic element, 16... Photoelectric conversion section.

Claims (3)

[Claims] (1) By irradiating light into a predetermined cross section of the object from multiple directions parallel to the cross section, measuring the intensity of the transmitted light from the object, and reconstructing the obtained measurement data,
A tomography method using light, characterized in that the distribution of at least one of transmittance, absorbance, and scattering intensity within the cross section is obtained as a tomographic image. (2) Obtain a tomographic image by dispersing the transmitted light from the subject and reconstructing a set of data obtained by measuring the intensity of each wavelength, and based on the data of the obtained tomographic image. 2. The tomography method according to claim 1, further comprising obtaining an absorption spectrum at a predetermined position within the tomographic image of the subject. (3) A light scanning means that is arranged on a plane passing through a predetermined cross section of the subject and scans the cross section with light from a plurality of directions; and a light receiving means that receives transmitted light from the subject and measures its intensity. and image reconstruction means for obtaining, as a tomographic image, a distribution of at least one of transmittance, absorbance, and scattering intensity within the cross section by reconstructing data of transmitted light intensity measured by the light receiving means. A tomography device using light, which is characterized by: