KR101049180B1 - Semi monochrome X-ray - Google Patents

Abstract

The present invention is to develop a quasi-monochrome X-ray apparatus using an optical filter composed of a multi-layer thin film reflector, and to develop a quasi-monochrome X-ray imaging apparatus that can obtain an image image of a uniform beam intensity for a subject using the quasi-monochrome X-rays The purpose is.

Technical configuration of the present invention for achieving the above object, the light source tube including a beam source for generating multi-color X-rays; An optical filter 20 mounted with one or more multilayer thin film reflectors 26 at regular intervals to reflect multicolor X-rays incident from the light source tube 10 as quasi-monochrome X-rays; The light source tube 10 and the optical filter 20 are rotated together at a predetermined angle about the light source focal point 12 positioned at the beam source so that the quasi-monochrome X-rays can be irradiated to the subject 60 at a constant speed. Main frame 1; And an image detector unit 6 which acquires an image image readable from the semi-monochrome X-rays transmitted through the subject 60.

Monochromatic X-rays, optical filters, multilayer thin-film reflectors, image detectors

Description

Semi-monochrome X-ray equipment {QUASI-MONOCHROMATIC X-RAY IMAGING SYSTEM}

The present invention relates to a quasi-monochrome X-ray imaging apparatus, and more particularly, to create one or multiple quasi-monochrome X-rays using an optical filter composed of a multilayer thin film reflector, and irradiate the quasi-monochrome X-rays with a uniform beam intensity on a subject. The present invention relates to a quasi-monochrome X-ray imaging apparatus developed to be able to do so.

The basic three elements of the X-ray imaging apparatus are a beam source for generating X-rays, a subject to be photographed, and an image detector for detecting X-rays passing through the subject. In X-ray imaging, X-rays originating from the beam source are attenuated (absorbed and scattered) as they pass through the subject, and some of them reach the image detector. The degree of arrival varies depending on the thickness of the subject and the type of material. Information of a subject projected in two dimensions can be obtained from an X-ray photograph.

Since the attenuation rate varies depending on the exposed X-ray energy, if the X-ray energy is different, the amount of radiation absorbed by the human body and the picture quality are different. The damping rate is high in the low energy region and low in the high energy region. In other words, as the energy increases, the attenuation rate decreases.

The difference between the damping rates of the two materials is larger on the lower energy side and smaller on the larger one. Therefore, the contrast is large at low energy. Therefore, low-energy X-rays should be used to increase contrast in order to distinguish between materials with small differences in attenuation.

On the other hand, if the attenuation rate is high, X-rays are difficult to pass because a large amount of X-rays are attenuated. If the attenuation rate is low, it is easy to pass. Heavy atomic materials, such as heavy metals, have attenuation rates of tens to hundreds of times higher than those of the lower atomic numbers (carbon, oxygen, hydrogen, nitrogen) that make up the body. Higher attenuation means more absorption of the human body, so lower energy X-rays are more harmful than higher energy X-rays when the human body is exposed to the same number of X-ray photons.

Higher attenuation means that the number of X-ray photons that reach the detector when the same number of photons is exposed to the subject is smaller. The photographic image obtained by the image detector may be readable when the photo detector reaches a certain level or more. This level can be determined by the SNR (Singnal to Noise Ratio), which is the ratio of signal to noise. Thick subjects have to enter a large amount of X-ray photons to get a proper SNR. In this case, it is advantageous for SNR to use a high energy region so that a large number of photons can pass through the subject and reach the image detector because of the increased absorption dose, but the contrast decreases because the difference in the attenuation rate is small.

Therefore, it is necessary to adjust the exposure dose and the X-ray energy range so that the dose is the minimum and the contrast and the SNR value to obtain the image quality suitable for the reading purpose according to the thickness or type of the subject to be photographed. Since ordinary X-ray sources are polychromatic light sources with a broad spectrum, there is a limit to adjusting the light source to the desired spectrum. Optimum image quality can be obtained compared to dose.

In other words, a monochromatic light source having a narrow energy width can provide a solution of the energy change problem according to the thickness of a subject when using multicolored light. Since the X-ray attenuation coefficient changes depending on the X-ray energy value, the energy spectrum at the time of incidence changes according to the length of the object.

The first part of the multi-color X-rays attenuates more of the low-energy X-rays, so that higher energy remains at the back of the object, and the contrast decreases as the thickness of the object increases. On the other hand, when the monochromatic X-ray is used, the contrast does not change greatly depending on the thickness of the object because the difference between the incident spectrum and the spectrum after passing through the object is not large, thereby providing more accurate information on the object.

Due to these advantages, imaging apparatuses using monochrome X-rays have been used in recent years. However, since it is very difficult to convert a multi-color X-ray to a complete monochromatic X-ray having one energy value, most imaging apparatuses convert and use multi-color X-rays to quasi-monochromatic X-rays. The multi-layer thin film filter is a representative apparatus for converting multicolor X-rays into quasi-monochrome X-rays in these imaging devices.

An example of a quasi-monochrome X-ray imaging apparatus using a multilayer thin film filter is disclosed in Korean Patent No. 719497 (a breast cancer diagnosis apparatus using a multilayer filter, hereinafter referred to as "primary invention 1"). The breast cancer diagnosis apparatus includes a multilayer filter unit in which basic filters having a multilayer thin film structure are arranged in parallel / parallel to reflect multicolor X-rays into quasi-monochrome X-rays having a specific energy band (15-20 keV). It is configured to obtain an accurate image by irradiating the semi-monochrome X-rays reflected on the breast fixation unit.

However, this diagnostic apparatus should be further provided with a linear motion guide to obtain a blank portion of the image generated due to the stacked structure of the multi-layered filter portion, and separately obtained before and after the scanning operation by the linear motion guide. Since only a software for combining them can be obtained to obtain a complete breast image, there is a problem in that the configuration and the photographing method of the device are very complicated.

Another quasi-monochrome X-ray imaging apparatus using a multilayer thin film filter is disclosed in Korean Patent No. 801186 (a quasi-monochrome X-ray filter and an X-ray imaging apparatus using the same, hereinafter referred to as "conventional invention 2"). This imaging device is a quasi-monochromatic X-ray filter consisting of reflectors in which two coating layers of different densities are repeatedly stacked to satisfy the Bragg diffraction equation, and the angular velocity at which the quasi-monochrome X-ray filter can be rotated at a constant angular velocity with respect to the X-ray source. The rotation mechanism is provided to allow a uniform X-ray photon to reach the subject to obtain an accurate image.

However, the imaging device not only rotates the quasi-monochrome X-ray filter within a short time without any vibration within an angle range smaller than the angle between the reflector and the reflector (division angle, Φ), but also the quasi-monochrome X-rays reflected from all reflectors. Because of the same or very similar intensity profiles and spacing, extremely uniform and precise reflector production is required. This photographing apparatus has not been commercialized to date due to such limitations.

SUMMARY OF THE INVENTION The present invention has been proposed to solve such a conventional problem, and includes a light source tube for generating multicolor X-rays and an optical filter for reflecting the multicolor X-rays incident from the light source tube with quasi-monochrome X-rays at a constant angle with respect to the light source focal point. It is a main object to provide a quasi-monochrome X-ray imaging apparatus configured to rotate so that the quasi-monochrome X-rays irradiated onto a subject have a profile of uniform intensity.

The present invention provides a technical configuration for achieving the above object, a light source tube including a beam source for generating multi-color X-rays; An optical filter having one or more multilayer thin film reflectors mounted at regular intervals to reflect multi-color X-rays incident from the light source tube as quasi-monochrome X-rays; A main frame mounted to allow the quasi-monochrome X-rays to be irradiated on the subject at a constant speed by rotating the light source tube and the optical filter together at a predetermined angle around a focal point of the light source positioned at the beam source; And an image detector unit for obtaining a readable image image from the quasi-monochrome X-rays passing through the subject.

According to the present invention configured as described above, since all quasi-monochromatic X-rays pass through the subject at a constant speed by the integral rotation of the light source tube and the optical filter, the intensity of the X-rays can be projected to a constant integral value at any arbitrary point, thereby making it more accurate. Image images may be obtained.

In addition, even if the stacking density of the multilayer thin film reflectors constituting the optical filter is somewhat uniform, since the projection is performed as an integral value of all quasi-monochrome X-rays reflected while passing through the subject, a uniform intensity profile can be finally obtained. Therefore, since a strict manufacturing condition that all the multilayer thin film reflectors have the same stacking density is not required, it is easy to commercialize the photographing apparatus using the same.

In addition, since the light source tube and the optical filter are integrally rotated, the light source tube and the optical filter can be rotated up to 360 °, which is advantageous for photographing a large-area subject.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

1 is a perspective view of a quasi-monochrome X-ray imaging apparatus according to the present invention, and FIGS. 2A and 2B are partial front views showing two rotating mechanisms of the imaging apparatus, and FIGS. 3A and 3C show three alignment mechanisms. Some front view.

The quasi-monochrome X-ray photographing apparatus according to the present invention includes a light source tube 10 including a beam source that largely generates multi-color X-rays, and an optical filter 20 that reflects multi-color X-rays incident from the light source tube 10 to quasi-monochrome X-rays. ), The main frame 1 mounted so that the light source tube 10 and the optical filter 20 can be rotated together with respect to the light source focal point, and the quasi-monochrome X-rays reflected from the optical filter 20 are irradiated onto the subject. And an image detector unit 6 for acquiring the generated image.

The light source tube 10 is configured in a cylindrical shape, and a beam source for generating multi-color X-rays, such as Mo and W target sources, is mounted therein. The light source focal point is located at this beam source, and the multicolor X-rays emitted from the beam source are irradiated to the optical filter 20 with a constant divergence angle.

The optical filter 20 is configured such that one or two or more multilayer thin film reflectors are mounted at predetermined intervals to reflect the multi-color X-rays incident from the light source tube 10 as quasi-monochrome X-rays. A detailed configuration of the optical filter 20, including the laminated structure of the multilayer thin film reflector and the principle of reflecting the quasi-monochrome X-rays by the Bragg diffraction law, will be described later with reference to FIGS. 4 to 7.

The main frame 1 is a vertical frame constituting the basic frame of the photographing apparatus. As the light source tube 10 and the optical filter 20 are rotated together at a predetermined angle around the light source focal point positioned at the beam source, the semi-monochrome X-rays It is mounted so that the subject can be irradiated at a constant speed.

The image detector unit 6 is installed on a stand 5 on which a subject, such as a human body, is placed. The image detector unit 6 is a readable image image of a shade generated by a difference in the transmittance of semi-monochrome X-rays generated according to the density of each part of the subject. Configured to obtain.

The quasi-monochrome X-ray imaging apparatus according to the present invention includes an integral rotation mechanism of the light source tube 10 and the optical filter 20, and includes two rotation mechanisms and three alignment mechanisms of the main frame. It is attached to (1). To this end, the rotation frame 3 is mounted on the main frame 1 so as to be movable up and down via the slider 2, and the rotation frame 3 is rotated inclined at a predetermined angle about the rotation shaft 4. It is equipped to be. In addition, the light source tube 10 and the optical filter 20 is mounted on the rotary frame (3) rotatably mounted at regular intervals up and down the rotatable frame 3 is the most characteristic technical configuration of the present invention The integrated rotation of the phosphor light source tube 10 and the optical filter 20 is realized.

In addition, the optical filter 20 is mounted to the rotary mount 7 via a three-axis moving mechanism 8 and a rotating disk 9. The three-axis moving mechanism 8 allows the optical filter 20 to be moved in three axes xyz, and the rotating disk 9 allows the optical filter 20 to be rotated about its disc origin.

2a and 2b show two rotating mechanisms according to the invention. These rotating mechanisms are intended to obtain a more accurate image image by implementing the imaging of the rotary quasi-monochrome X-ray according to the present invention.

The first rotation mechanism is to allow the light source tube 10 and the optical filter 20 installed to be rotated up and down at a predetermined interval as shown in Figure 2a at a predetermined interval. The integrated rotation mechanism of the light source tube 10 and the optical filter 20 allows uniform quasi-monochrome X-ray irradiation to a large-area subject, which will be described in detail with reference to FIGS. 8 to 10. It will be described later.

The second rotating mechanism rotatably mounts the optical filter 20 to the rotary mount 7 via the rotating disk 9 as shown in FIG. 2B, whereby the optical filter 20 causes the light filter tube 10 to be rotated. ) So that it can be rotated separately. As such, when the optical filter 20 is rotated independently, the incident angle with respect to the light source focal point of the multilayer thin film reflectors mounted at regular intervals in the optical filter 20 is changed, thereby changing the energy value of the reflected semi-monochrome X-ray. This allows the generation of quasi-monochrome X-rays having two or more multiple energies. The operation and effects of the multiple energies will be described later with reference to FIGS. 14 and 15.

3a to 3b show three alignment mechanisms according to the invention. These alignment mechanisms align the distance and position of the light source tube 10 and / or the optical filter 20 to enable accurate X-ray imaging.

The first alignment mechanism allows the distance between the light source tube 10 / optical filter 20 and the image detector unit 6 to be adjusted as shown in FIG. 3A. To this end, the rotary frame 3 on which the light source tube 10 / optical filter 20 is mounted is mounted to the main frame 1 via a slider 2 so as to be movable up and down. This alignment mechanism adjusts the distance between the focus of the light source and the subject placed on the image detector unit 6, thereby controlling the X-ray dose irradiated onto the subject to obtain an optimum image quality.

The second alignment mechanism allows to adjust the inclination of the light source tube 10 / optical filter 20 and the image detector unit 6. To this end, the light source tube 10 / optical filter 20 is the optical filter 20 in a straight line connecting the focus of the light source positioned in the light source tube 10 and the center of the subject placed on the image detector unit 6. And rotatable around an arbitrary point located between the object and the subject.

In FIG. 3B, as an embodiment of this alignment mechanism, a rotating frame 3 equipped with a light source tube 10 / optical filter 20 is mounted on the main frame 1 at an angle about the rotational axis 4. The rotatably mounted form is shown. This alignment mechanism allows the subject to be photographed at an oblique angle so that the subject can be photographed regardless of the form of the subject. In particular, the image is synthesized by capturing dozens of images while rotating within a certain inclination angle range. It allows the imaging apparatus of the present invention to support a shooting technique such as Digital Tomosynthesis, which is a method of acquiring a digital signal.

The third alignment mechanism is to move the optical filter 20 in the xyz 3-axis as shown in Figure 3c to adjust its position. To this end, the optical filter 20 is installed to be vertically / horizontally moved to the main frame 1 through the three-axis moving mechanism 8 installed in the form of a square plate. This alignment mechanism allows the optical filter 20 to be moved separately from the light source tube 10 to adjust the relative distance and angle with respect to the light source focal point to determine the energy band of the quasi-monochrome X-rays suitable for the subject. The optical filter 20 may also be configured to generate multiple energies as in the second rotating mechanism by moving the optical filter 20 in the horizontal direction (y direction).

Optical filter 20 is equipped with one or more multilayer thin film reflectors to reflect the multi-color X-rays to quasi-monochrome X-rays by the Bragg diffraction law to achieve an important technical configuration of the present invention, as shown in Figure 4 to The configuration and operation of the optical filter 20 will be described in more detail with reference to FIG. 7.

4 illustrates one embodiment of the optical filter 20 according to the present invention. The housing 22 of the optical filter 20 has a wider front in which the semi-monochrome X-rays are reflected than the rear in which the multi-color X-rays are incident to form a trapezoidal cross section. At this time, the angle between the rear and front of the housing 22 is preferably manufactured to correspond to the divergence angle of the X-rays emitted from the light source tube. In addition, Figure 4 is shown in the form of a plurality of openings formed on the circumferential surface of the housing 22, in actual use except for the semi-monochrome X-ray cover to block harmful X-rays scattered or passed through the housing 22 It is desirable to be manufactured in the form of the cover.

A plurality of slots 24 are provided in the housing 22 at regular intervals, and one or more multilayer thin film reflectors 26 are mounted in the slots 24. The multilayer thin film reflector 26 is a structure in which several tens to hundreds of nm thin films 26a and 26b are coated on a substrate 27 having a thickness of less than 1 mm and having a very flat surface, as shown in FIG. Multicolored X-rays are reflected as quasi-monochrome X-rays by the incident angle corresponding to the incident angle of the diffraction law and the thickness of the pair of thin film materials.

In other words, the semi-monochrome X-rays reflect the multi-colored X-rays on the multilayer thin-film reflector 26 which alternately arranges a material having a large element symbol and a thin film of a small material, thereby causing constructive and destructive interference between beams reflected by the Bragg diffraction law. It can be created by reflecting only monochromatic X-rays of a certain wavelength. The Bragg diffraction law is as follows.

E = (12.4 * n) / (2 * d * sin θ)

Here, E is energy in diffraction kiloelectron Volt (keV) units, n is an integer greater than or equal to 1, d is a diffraction grating distance in units of ,, and θ represents an incident angle between the incident beam and the incident surface.

As such, the multilayer thin film reflector 26 reflects only a specific energy portion in the multi-color X-rays incident on the reflector, and the spectrum has a slightly narrow energy band width. Since the reflection energy and the band width are inherent to the reflector determined by the adjustment of the incident angle, the type of material, the thickness and the number of layers of the multilayer thin film material, the ideal values can be predicted. For example, if the thickness of a pair of multilayer thin films is 1.5 to 8 nm, the angle of incidence is less than 1 degree, and the number of layers is adjusted to 5 to 200 layers, the energy range of the semi-monochrome X-rays reflected is controlled to be about 10 to 100 keV. can do.

Pairs of multilayer thin film materials 26a and 26b need not be limited to have a constant thickness over the entire length of the reflector. Preferably, the multilayer thin film reflector 26 is arranged along the longitudinal direction of the reflector such that the Bragg diffraction conditions where the pairs 26a and 26b of the multilayer thin film materials having different electron densities reflect quasi-monochrome X-rays of a specific energy are satisfied. It is repeatedly stacked obliquely in the form of gradually increasing thickness. More preferably, the pairs 26a and 26b of the multilayer thin film material may be stacked such that a slope obtained by dividing the difference in thicknesses of both ends in the longitudinal direction of the reflecting mirror by the length thereof is constant. As such, according to the inclined coating method of inclining the thickness of the multilayer thin film to be gradually thickened in the longitudinal direction of the reflector, the width of the energy deviation reflected by the multilayer thin film reflector 26 is narrowed more easily to implement the quasi-monochrome X-rays. Do it.

In more detail, when Bragg's equation is applied to each of the angles of incidence i1 and i2 formed by a straight line connecting the light source focal points at the beginning and end of the reflector and the reflector at a predetermined reflection energy, a pair of high layers to be coated at both points The electron density-low electron density thin film thickness can be calculated, and if the thickness is mt1 and mt2, it becomes a relationship of mt2> mt1 and gradually thickens from mt1 to mt2 thickness in the longitudinal direction.

The thickness of each portion of the reflector is a thickness that satisfies the Bragg diffraction law, and the thickness (tilt) in the longitudinal direction should be larger as i2 is closer to i2 than i1. However, when i2 is 0.15 degrees or more and the difference between i1 and i2 is small or the manufacturing process needs to be simplified, the thickness of the multilayer thin film of the reflector is inclined to the length L of the reflector {(mt2-mt1) / L} can be coated at a constant angle, and the area of reflected energy shifts slightly to the smaller side, but can still be used as a multilayer thin film reflector effective for producing quasi-monochrome X-rays.

The inclined coated thin film may be manufactured by applying various vacuum deposition processes that are widely used, and may incline only the high electron density material, incline only the low electron density material, or give a thickness gradient in both materials. In the case of the substrate 27, various materials such as glass, various metals, and silicon single crystal wafers can be used. However, it is preferable that the substrate surface is very flat and not rough, and more preferably, the root mean square of the substrate surface roughness is 1.0. It is good that the transmittance of X-rays is lower than nm. Substrate materials having a low X-ray transmittance are heavy metals having a high atomic number, and are preferably nickel, iron, molybdenum, tungsten, or lead, and these substrates 27 also help block X-rays through the optical filter 20.

6 illustrates a principle of quasi-monochrome X-ray generation according to the present invention.

A plurality of multilayer thin film reflectors 26 are arranged at right angles on a concentric circle having a radius r about the light source focal point 12 of the multi-color X-rays 14 and closest to the light source focal point 12 of the multilayer thin film reflector 26. The end point e21 of the side surface is located on a concentric circle with the radius r. The multilayer thin film reflectors 26 are arranged to be inclined by the same angle of incidence θ i with respect to the radial line centering on the light source focal point 12. Further, the lengths of the multilayer thin film reflectors 26 are set to L + Δl and the thickness to t.

This arrangement ensures that all multilayer thin film reflectors 26 have the same angle of incidence with respect to the point where any concentric circle about the light source focal point 12 is located, and each of the multilayer thin film reflectors 26 is in the longitudinal direction of the reflector. Have the same angle of incidence distribution. The spacing dg of the multilayer thin film reflectors 26 is set to reflect quasi-monochrome X-rays of a specific wavelength by the Bragg diffraction law, which is related to L, t, and θ i. That is, when L and t are fixed when θ i is fixed, dg is calculated. When t and dg are fixed, L is calculated, and so is t.

In the state where the values of L, t, and θ i are determined, the value of dg is set, and the value of this dg is set to the value at which the intensity of the reflected semi-monochrome X-rays 28 is greatest. The dg value when the intensity of the quasi-monochrome x-rays 28 is greatest can be determined by the following method.

For any multilayer thin film reflector 26, the line connecting the light source focal point 12 and the end point e12 of the surface furthest from the light source focal point 12 has an angle θ i2 with respect to the surface of the reflector. And an end of the back side closest to the light source focus 12 of the multilayer thin film reflector 26 adjacent to the line connecting the light source focus 12 and the end point e12 of the surface farthest from the light source focus 12. Let the branches meet. This method can be repeated to arrange the multilayer thin film reflectors 26 at the same arrangement interval dg.

Given L, t, dg and θ i in this way, assuming that the multilayer thin-film reflectors 26 connect the end points of the surface closest to the light source focal point 12 with the light source focal point 12, respectively, The angle between the straight lines of two adjacent multilayer thin film reflectors 26 is formed by dividing the portion where the multilayer thin film reflectors 26 are located among concentric circles centered on the light source focal point 12 by the number of multilayer thin film reflectors 26. The dividing angle Φ is obtained. As described above, according to the present invention, the plurality of multilayer thin film reflectors 26 are disposed at a predetermined interval defined by the division angle Φ, thereby reflecting the semi-monochrome X-rays 28 having a specific wavelength to cover a certain area. .

The advantages of such monochromatic X-rays can be clearly seen in FIG. 7, which compares contrast differences between polychromatic and quasi-monochrome X-rays. In order to determine the contrast difference between multi-color and semi-monochrome X-rays, experiments were conducted as follows. First, the acrylic block and aluminum are used as the subject phantom, and the thickness of the X-ray passing through the acrylic and acrylic + aluminum parts is placed on the acrylic block with a thickness of 1 mm aluminum while changing the thickness of the acrylic from 10 to 60 mm in units of 10 mm. Was calculated to calculate the contrast of the two parts.

As a multi-color X-ray, the tube voltage from the Mo target source is adjusted with (a) 22 keV, (b) 26 keV, (c) 33 keV, (d) 40 keV, and (e) 40 keV + Mo 50 μm prefilter. The contrast in one case was measured. For quasi-monochrome X-rays, (f) the energy value of (g) was left in the 17.5 keV characteristic peak region using a multilayer thin film filter at the Mo target source, and the quasi-monochrome X-rays produced using the W target source and the multilayer thin film filter (g) 25.1 The contrast in the case of keV, (h) 28.5 keV and (i) 35.3 keV was measured, respectively.

As a result of the experiment, in the case of (a) to (e) using multi-color X-rays, contrast decreases significantly as the thickness difference of the subject increases, whereas in (f) to (i) using quasi-monochrome X-rays of the subject It can be seen that the contrast is almost constant regardless of the thickness difference. Therefore, the use of quasi-monochrome X-rays provides a uniform contrast regardless of the thickness of the subject, thereby obtaining a more accurate image.

As such, when the quasi-monochrome X-rays having a specific energy are reflected and irradiated to the subject by using an optical filter, a more accurate image image may be obtained than when the multi-color X-rays are used. However, in the case of the optical filter, as the multilayer thin film reflector 26 is disposed at regular intervals by the division angle Φ, a serious problem occurs as follows. The multi-color X-rays incident on the multilayer thin film reflector 26 collide with the end portion not corresponding to the surface of the multilayer thin film reflector 26, that is, the cross section corresponding to the thickness of the multilayer thin film reflector 26, thereby absorbing the multi-color X-rays or Shadows appear in the image image generated by the final semi-monochrome X-rays scattered and passed through the optical filter 20.

As described above, in order to prevent such a shadow phenomenon, the photographing apparatuses disclosed in the "Prior Invention 1" and the "Prior Invention 2" have been developed, but the former acquires the images before and after scanning the subject separately and then combines them. The configuration of the device is complicated, and the latter is restricted by the fact that all the multilayer thin film reflectors 26 must be uniformly coated and rotated precisely within a range smaller than the division angle Φ between the multilayer thin film reflectors 26. All are not commercialized.

The present invention has a main object to effectively prevent such a shadow phenomenon to commercialize a semi-monochrome X-ray imaging apparatus using an optical filter, and for this purpose, the first rotating mechanism described above has been developed, with reference to FIGS. 8 to 10. The operation and effects of the first rotating mechanism will be described in detail.

As shown in FIG. 8, according to the first rotating mechanism according to the present invention, the light source tube 10 and the optical filter 20 are rotated together with respect to the light source focal point 12 to the entire area of the subject 60. Scan once at constant speed. In this case, a collimating unit 30 may be installed between the optical filter 20 and the subject 60 to allow the quasi-monochrome X-rays to be irradiated onto the subject 60 only. The metal shutter 40 may be installed to cut off and reflect only the quasi-monochrome X-rays having one energy value for a certain time.

Each quasi-monochrome X-rays reflected by the multilayer thin film reflectors arranged in the optical filter 20 are converted to have a constant intensity profile over the entire area of the subject 60 during rotational scanning, see FIG. 9 for the principle. This will be described in detail. First, as shown in FIG. 9A, the semi-monochrome X-rays reflected while the optical filter 20 is not rotated each have an intensity profile separated by a predetermined interval. A represents the intensity profile of the quasi-monochrome X-rays reflected by one multilayer thin film reflector, and B is the distance between the quasi-monochrome X-rays and corresponds to the spacing of the multilayer thin film reflectors. Here, the portion of zero energy intensity between each semi-monochrome X-ray A becomes a shadow portion of the final image image.

When the quasi-monochrome X-ray having such an intensity profile is scanned once at a constant speed with respect to the entire area of the subject 60 while rotating the light source tube 10 and the optical filter 20 together, as shown in FIG. Likewise, the energy intensity values of the respective monochromatic X-rays are summed according to the rotation angle. In this case, it is very important to scan the light source tube 10 and the optical filter 20 while rotating the light source tube 10 and the optical filter 20 at constant speed (equivalent rotational angular velocity) over the entire area of the subject 60 in order to uniformly sum the respective energy values.

When the one-time scanning is completed, all quasi-monochromatic X-rays reflected by the respective multilayer thin film reflectors are irradiated once to one point of the subject 60, and the energy intensity values are summed up, as shown in FIG. 9C. As shown, it will have an intensity profile with the same integral over all distances. As a result, as shown in (a) of FIG. 9, the energy gap between the semi-monochrome X-rays A can be eliminated, thereby preventing the shadow phenomenon appearing in the final image image.

The photographing apparatus of the present invention configured as described above can be implemented much more easily than the "prior invention 1", which requires to acquire two images before and after scanning and combine them in that it is completed by only one scanning. In addition, unlike the conventional invention 2, the photographing apparatus of the present invention can be easily commercialized because stringent manufacturing conditions in which each of the multilayer thin film reflectors have the same energy value are not required. The reason is that even if the quasi-monochrome X-rays reflected by each multilayer thin-film reflector have slightly different energy values, the final image image is made by adding up the energy values of each quasi-monochrome X-rays and projecting the same integral value. .

At this time, the spectrum of the semi-monochrome X-rays used is 15 ~ 80 keV in the center reflection energy, the half width of the energy at each center energy is 1 ~ 20 keV, the energy resolution ΔE / E is adjustable in the range of 5 ~ 20%. The central energy, half energy width, and energy resolution can be adjusted to suit the application.

The rotational angular velocity may be adjusted according to the photographing time selected by the rotational scanning. For example, when the distance between the light source focal point and the image detector is 1 m, the rotational angular velocity may be at least 0.4 m per second when rotated at an angular velocity of 30 degrees per second. In particular, when the breast is taken, the energy can be finely adjusted to the breast thickness between 17 and 25 keV, thereby reducing the dose and the effect of contrast.

Meanwhile, according to the present invention, X-ray imaging of a large area can be easily performed. That is, since the photographing apparatus of the present invention can control the rotation angles of the light source tube 10 and the optical filter 20 within a maximum 360 degree range, the reflector can be controlled only within an angle range smaller than the dividing angle Φ of the multilayer thin film reflectors. Larger subjects can be taken more easily than "traditional invention 2" which can be rotated.

FIG. 10 is an example of photographing a large area by rotational scanning of the present invention. FIG. 10 is a photograph obtained by rotating a 197 mm x 238 mm large area with a shooting time of about 400 msec and an exposure amount of 5.4 mR using uniform semi-monochrome X-rays. . FIG. 10A illustrates a blank image image photographed without using a CDMAM phantom, and FIG. 10B illustrates the same blank image image captured using a CDMAM phantom. As described above, according to the present invention, a subject having a length of several hundred mm can be photographed by only one rotational scanning.

On the other hand, the penetration depth through which multi-color X-rays incident on the multilayer thin-film reflector can pass through without disappearing by scattering and absorption by the thin film and the substrate material is not so great at low incidence angles of less than 1 degree. When the energy range is up to hundreds of keVs, high-energy regions of tens of keVs or more can pass through thin substrates. X-rays other than the semi-monochrome X-rays reflected in this way, that is, X-rays passing through the multilayer thin-film reflector 26 or X-rays scattered from a portion other than the multilayer thin-film reflector 26 are elements that inhibit the quasi-monochromatic properties. Should be removed.

X-rays other than the semi-monochrome X-rays that are reflected are formed when the rear surface of the substrate is heavy when the multi-layer thin film reflector 26 has a large array spacing or when a small number of the multi-layer thin film reflectors 26 are used. Although shielding may be performed by shielding the material, when the multilayer thin film reflector 26 is arranged as closely as possible or the number of the multilayer thin film reflectors 26 is large, a separate blocking device should be provided.

According to the present invention, as shown in Figure 11 by installing a slit-shaped structure in front of the housing 22 of the optical filter 20, X-rays passing straight through the multilayer thin film reflector 26 without being absorbed or scattered Can be configured to block. The metal slit 50 is placed on a concentric circle having the same origin as the concentric circle on which the multilayer thin film reflector 26 is arranged, thereby opening or blocking a part of the metallic slit 50 based on the space on the circumferential line of the concentric circle.

The metal slit 50 is formed to have a groove 52 that is open to allow X-rays to move and a wall 54 that blocks the path of the X-ray between the grooves 52, and a gap or wall between these grooves 52. The gap between 54 may be determined to have an appropriate value depending on the thickness of the multilayer thin film reflector and the substrate thickness. That is, the gap between the groove 52 or the wall 54 is determined by the width and spacing of the quasi-monochrome X-rays reflected by the geometry of the optical filter 20 shown in FIG.

In FIG. 11, the metal slit 50 is positioned in front of the optical filter 20, that is, between the optical filter 20 and the subject 60 to block a part of X-rays reflected from the optical filter 20. Although shown, the metal slit 50 may be installed in addition to one or more in various locations shown in FIG. This installation position is the most effective point to block the X-rays other than the semi-monochrome X-rays reflected, the divergence angle and tube voltage energy band of the multi-color X-rays incident on the optical filter 20, the reflection angle of the quasi-monochrome energy, the reflected energy value and This is determined by comprehensively considering the distance to the subject and the like.

For example, the metal slit 50 is positioned between the light source tube 10 and the optical filter 20 to be incident from the beam source to the optical filter 20 as shown in points (a) and (b) of FIG. 12. It may be installed to block a part of the X-rays. In this case, the interval between the grooves 52 formed in the metal slit 50 may be configured to be narrower as the light source focal point 12 approaches the light source 12 in consideration of the divergence angle of the X-rays. Therefore, the gap of the metal slit 50 becomes the largest when it is closely attached to one side close to the light source tube 10 of the optical filter 20 as shown in FIG.

Meanwhile, the metal slit 50 is positioned between the optical filter 20 and the subject 60 to block a part of X-rays reflected from the optical filter 20 as illustrated in (c) and (d) of FIG. 12. It can also be installed to. In particular, when the metal slit 50 is installed in close contact with the light source tube 10 of the optical filter 20 as shown in point (c) of FIG. 12, rotational scanning is performed by adjusting the width of the reflected monochromatic X-rays. It is effective to irradiate uniform light source.

The effect of using the metal slit 50 thus configured is shown in FIG. 13. As shown in (a) of FIG. 13, the beam intensity profile of the quasi-monochrome X-ray reflected from the optical filter without using the metal slit 50 is greater than about 25 keV, which is an energy band of the predetermined quasi-monochrome X-ray. It can be seen that the leaked X-rays (Leakage beam) exists in the high energy band (about 70 keV), the uniformity of the light source is degraded by the leaked X-rays. In contrast, when the metal slit 50 is used under the same conditions, as shown in FIG. 13B, leaked X-rays are blocked in the high energy band, and the beam intensity of the predetermined 25 keV energy band is higher. As a result, the uniformity and intensity of the light source are increased to obtain a clearer image.

Finally, according to the present invention, a clearer image can be obtained by using multiple energies. To this end, the optical filter 20 is configured to irradiate the subject 60 with quasi-monochrome X-rays having two or more energies. The method of irradiating quasi-monochrome X-rays with multiple energies can be implemented by the following two principles. Hereinafter, the dual energy will be described as an example. However, the technical idea of the present invention is not limited thereto, and the present invention will also include all methods of irradiating quasi-monochrome X-rays having three or more multiple energies.

In the first dual energy irradiation method, a plurality of multilayer thin film reflectors 26 disposed in the optical filter 20 are mounted to have the same angle of incidence with respect to the light source focal point 12 to reflect quasi-monochrome X-rays having only one energy. After irradiating the subject 60 once, all the multilayer thin film reflectors 26 are rotated at the same angle by using the second rotating mechanism shown in FIG. 2B to change the incident angle of the multi-color X-rays. The quasi-monochrome X-rays having energy are configured to be irradiated to the subject 60 twice.

The principle of changing the energy of the quasi-monochrome X-rays by rotating the multilayer thin film reflector 26 will be briefly described with reference to FIG. The center of the multilayer thin film reflectors 26 on a concentric circle having a radius r is c, and when the multilayer thin film reflectors 26 are rotated by θr with respect to the circle center while the relative arrangement position is maintained, the multilayer thin film reflector 26 All angles of incidence are changed uniformly. In this case, when the multilayer thin film reflectors 26 are rotated in the direction of θ r, the incident angle becomes large, and thus the reflection energy is decreased. When the multilayer thin film reflectors 26 are rotated in the opposite direction, the incident angle becomes small, and the energy becomes large.

In the second dual energy irradiation method, as shown in FIG. 14, the optical filter 20 alternately mounts two kinds of multilayer thin film reflectors 26 reflecting quasi-monochrome X-rays having different energies. In front of the optical filter 20, as shown in FIG. 8, a metal shutter 40 is installed to allow only one quasi-monochrome X-ray having a specific energy to be irradiated in one irradiation of the subject 60. will be.

The two kinds of multilayer thin film reflectors 26 are arranged by alternately arranging multilayer thin film reflectors having different incidence angles θ1 and θ2 one by one (FIG. 14 (a)), or arranged in groups of two [FIG. 14 (b)], and can be arranged in groups of 3 each (Fig. 14 (c)). Substantially, as shown in (c) of FIG. 14, it is easiest to install the metal shutter 40 by dividing the whole multilayer thin film reflectors 26 bilaterally.

The dual energy irradiation method can be effectively utilized for dual energy subtraction. In the dual energy subtraction method, the subjects are photographed with quasi-monochrome X-rays (E1, E2) having different energy bands, and then the log values are subtracted appropriately. Depending on the result of the subtraction, the signal value of one substance of the same substance having one attenuation coefficient can be zeroed, so that the image of one substance can disappear.

Mammography can facilitate the discovery of cancer cells by erasing the components of the breast, including the mammary glands and fats. As such, the dual energy irradiation method makes it easier to detect lesions by using a so-called background cancellation effect that can process a particular material into the background and make the background disappear. What is important in the above-described dual energy subtraction imaging method is that the X-ray spectra of the two energy bands E1 and E2 should be well separated from each other, and the width of one energy band should be narrow so that the noise component can be easily removed.

15 shows the experimental results for the background cancellation effect of the dual energy subtraction method. The subject phantom of the triple structure of acrylic + silver paste + Teflon was photographed by multicolor X-ray and quasi-monochrome X-ray, respectively. The quasi-monochrome X-rays were rotated using a plurality of multilayer thin-film reflectors with 22 keV and 36 keV center energy, and the multi-color X-rays were two types using a 40 kV tube voltage of W target source and a 70 keV + W 0.5 mm filter. X-ray was used. The silver paste corresponds to breast tissue and was applied in the shape of a breast to the surface of the acrylic block using a brush. Since SNR is an important factor in determining the level of image quality, the noise level of multi-color X-ray and quasi-monochromatic X-ray is almost equally adjusted.

In FIG. 15, the Teflon fragment corresponding to the lesion is a Teflon fragment corresponding to the lesion. Referring to FIG. 15A, which is an image of general X-ray imaging, the Teflon fragment is almost indistinguishable. 15 (b) which is a subtracted image image, the silver paste (breast tissue) is background processed to clearly identify the Teflon fragment (lesion tissue). As compared with FIG. 15C, which is an image image obtained by subtracting dual energy using multi-color X-rays and subtracting the image, it can be seen that subtractive imaging using quasi-monochrome energy is more effective.

As described above, the quasi-monochrome X-ray imaging apparatus of the present invention uses a quasi-monochrome X-ray, which has a narrow energy width and easy selection of various energy values, as a light source by using a multilayer thin film reflector. In addition, the shadow problem generated when using a plurality of multi-layer thin film reflector was solved by rotating the multi-layer thin film reflector around the light source focal point to be irradiated to the subject with a uniform beam intensity. In addition, two rotation mechanisms and three alignment mechanisms are provided to perform various functions such as rotational photographing, focusing with a light source, adjusting energy bands of X-rays, adjusting distance to a subject, and tilting.

Accordingly, the practical quasi-monochromatic X-ray apparatus according to the present invention uses mammography, contrast X-ray imaging, dual energy mammography, dual energy subtraction, dual image synthesis (Tomosynthesis), and dual energy. It may be widely used for dual energy tomosynthesis.

1 is a view showing a quasi-monochrome X-ray photographing apparatus according to the present invention.

2A and 2B show a rotation mechanism of the photographing apparatus according to the present invention.

3A to 3C show an alignment mechanism of the photographing apparatus according to the present invention.

Figure 4 shows an optical filter made of a multilayer thin film reflector according to the present invention.

5 is a view showing a cross-sectional structure of a multilayer thin film reflector according to the present invention.

6 is a diagram illustrating a principle of quasi-monochrome X-ray generation according to the present invention.

7 is a graph comparing the contrast of multicolor and quasi-monochrome X-rays.

8 illustrates a rotational scanning method according to the present invention.

9 is a graph showing a beam intensity profile according to rotational scanning of the present invention.

10 is a photograph taken a large area by rotational scanning of the present invention.

11 is a view illustrating an installation form of a metal slit according to the present invention.

12 is a view showing an installation position of a metal slit according to the present invention.

13 is a graph showing the effect of the metal slit according to the present invention.

14 shows a dual energy irradiation method according to the present invention.

15 is a photograph comparing the dual energy irradiation effect according to the present invention.

[Description of Reference Numerals]

1: main frame 2: slider

3: rotating frame 4: rotating shaft

5: stand 6: image detector

7: Rotating Mounting Device 8: 3-Axis Moving Mechanism

9: rotating disc 10: light source tube

12: light source focus 14: multi-color X-ray

20: optical filter 22: housing

24: mounting slot 26: multilayer thin film reflector

28: semi-monochrome X-rays 30: collimated part

40: metal shutter 50: metal slit

60: subject

Claims (14)

A light source tube (10) comprising a beam source for generating multicolor X-rays; An optical filter 20 mounted with one or more multilayer thin film reflectors 26 at regular intervals to reflect multicolor X-rays incident from the light source tube 10 as quasi-monochrome X-rays; The light source tube 10 and the optical filter 20 are rotated together at a predetermined angle about the light source focal point 12 positioned at the beam source so that the quasi-monochrome X-rays can be irradiated to the subject 60 at a constant speed. Main frame 1; And And an image detector unit (6) which obtains an image image readable from the semi-monochrome X-rays passing through the subject (60). The method according to claim 1, The multilayer thin film reflector 26 is repeatedly stacked in such a manner that a pair of thin film materials having different electron densities gradually increases in thickness along the longitudinal direction of the reflector such that a Bragg diffraction condition reflecting a quasi-monochrome X-ray of a specific energy is satisfied. Semi-monochrome x-ray apparatus characterized by. The method according to claim 2, The multi-layer thin film reflector (26) is a semi-monochromatic X-ray imaging apparatus, characterized in that the inclination divided by the length of the difference in the thickness of both ends of the longitudinal direction of the reflector is repeatedly laminated the pair of thin film material. The method according to claim 1, The optical filter 20 is a semi-monochromatic X-ray imaging apparatus, characterized in that configured to irradiate the subject (60) quasi-monochrome X-rays having two or more energies. The method according to claim 4, The optical filter 20 is equipped with a multilayer thin film reflector 26 reflecting a semi-monochrome X-ray having one energy, and rotates the multilayer thin film reflector 26 after one irradiation of the subject 60. Semi-monochrome X-ray photographing apparatus, characterized in that installed so as to change the incident angle of the X-rays. The method according to claim 4, The optical filter 20 is alternately mounted with a multilayer thin film reflector 26 reflecting quasi-monochrome X-rays having different energies, and in front of the optical filter 20 when irradiating the subject 60 once. Semi-monochrome x-ray apparatus, characterized in that the metal shutter 40 is installed so that only one quasi-monochrome X-rays having a specific energy can be irradiated. The method according to claim 1, The light source tube (10) and the optical filter (20) is a semi-monochromatic X-ray imaging apparatus, characterized in that the movable to the main frame (1) to adjust the distance between the image detector (6). The method of claim 7, The light source tube 10 and the optical filter 20 may be arranged at an arbitrary point located between the optical filter 20 and the subject 60 on a straight line connecting the light source focal point 12 and the center of the subject 60. Semi-monochrome X-ray photographing apparatus, characterized in that installed rotatably around the center. The method according to claim 8, The optical filter 20 is a semi-monochrome X-ray imaging apparatus, characterized in that installed on the main frame (1) to be movable in three axes xyz. The method according to claim 1, Quasi-monochromatic X-ray imaging, characterized in that between the light source tube 10 and the optical filter 20, a metal slit 50 for blocking a portion of the X-rays incident from the beam source to the optical filter 20 is installed. Device. The method according to claim 10, The metal slit (50) is a near monochrome X-ray imaging apparatus, characterized in that installed close to the side of the light source tube (10) of the optical filter (20). The method according to claim 1, Semi-monochromatic X-ray photographing apparatus, characterized in that between the optical filter 20 and the subject 60 is provided with a metal slit (50) for blocking a part of the X-ray reflected from the optical filter (20). The method according to claim 12, The metal slit (50) is a semi-monochrome X-ray imaging apparatus, characterized in that in close contact with one side of the light source tube 10 of the optical filter (20). The method according to claim 1, A semi-monochrome X-ray photographing apparatus, characterized in that a collimating unit (30) is installed between the optical filter (20) and the subject (60) so that the quasi-monochrome X-rays can be irradiated only to the subject (60).

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