JP4010101B2 - X-ray imaging device - Google Patents

Description

なお、表中の血管径は拡大撮影していないときのＸ線撮影で測定したものである。試料のＮｏ．６は９Ｅ≧Ｂを満たさないので、判定結果は最も低い値１となっている。また、試料Ｎｏ．５は（４式）で求めたＥの値は上記の通りであるが、（３式）で求めたＥの値は３６、９Ｅは３２４であり、９Ｅ≧Ｂを満たしている。
【００８２】
［実施例２］
実施例１と同様に胸部ファントムＸ線像の撮影を行った。コニカ製の輝尽製蛍光体を用い、レーザースポットサイズ８７μｍで画像信号を読み取り、コニカ製レーザイメージャＬｉ−７でコニカ製片面フィルム６７ＬＰにプリントし、自動現像機ＳＲＸ５０２で現像処理を行った。撮影条件はＲ１＝Ｒ２＝２ｍで拡大率２倍、焦点サイズ４０μｍで、ボケ幅Ｂ＝４０μｍ及び（４式）のＡを血管直径１ｍｍとするときエッジ強調幅Ｅ＝１６μｍで９Ｅ＝１４４μｍであり、９Ｅ≧Ｂであり、Ｅは０．１μｍより大きい。
【００８３】
撮影後に得られた画像を３倍拡大及び元のサイズに縮小した画像をプリントした。２枚のプリントとともに直径１ｍｍの横走行の擬似血管の周りが黒く縁取られてエッジ強調が認められ、判定は３倍拡大画像が５、原寸表示が４であった。なおＸ線量は７．８ｍＡｓであった。
【００８４】
［実施例３］
京都科学製の頭部のファントムを用いて頭蓋骨Ｘ線像の撮影を行った。このときのＸ線管の設定管電圧は７０ｋＶｐであった。増感紙はＳＲＯ２５０を用い、フィルムはＳＲＧを用いた。Ｒ１＝Ｒ２＝２ｍの拡大倍率２倍、焦点サイズ４０μｍでぼけ幅Ｂ＝４０μｍ、３式のＡの被写体幅１ｍｍとするとエッジ強調幅Ｅ＝１６μで９Ｅ＝１４４μｍとなり、９Ｅ≧Ｂである。また、Ｅ≧９μｍも満足する。実施例１と同様の現像処理後にシャウカステン上で画像を裸眼で観察したとこと、骨部境界部分に明瞭に黒く縁取りをした境界線が見られた。評価は４であった。このときの３６ｍＡｓであった。
【００８５】
［実施例４］
京都科学製の手ファントムを用いて手指骨Ｘ線像の撮影を行った。Ｘ線画像撮影装置の機器の配置は、図６の通りであった。テーブルの一部がくりぬけられて、この窓に厚さ約０．５ｍｍの透明のポリエステル板を張り、この上に手ファントムを置いて撮影を行なった。
【００８６】
このときのＸ線管の設定管電圧は５０ｋＶｐであった。増感紙はコニカ株式会社製Ｍ１００を用い、フィルムはコニカ株式会社製片面乳剤フィルムＣＭＨを用いた。このシステムの平均階調は３．２であった。実施例１と同様の現像処理後にシャウカステン上で１ｍｍ幅（４式のＡの値）の骨梁を裸眼で観察し、その評価結果を表２に示す。
【００８７】
【表２】

Ｎｏ．９，１０は「認識できる」（３）及び「良く見える」（４）の判定である。Ｎｏ．７は９Ｅ≧Ｂを満足しておらず判定は「見えない」の（１）、Ｎｏ．８については、９Ｅ≧Ｂを満足しているがＥ≧９μｍを満足しておらず判定は「極めて弱い」の（２）となっている。
【００８８】
【発明の効果】
前記したように、本発明のＸ線画像撮影方法及びＸ線画像撮影装置では、発散するＸ線を放射するＸ線管を用いて拡大撮影を行うときに、半影によるボケとエッジ強調の関係を最適化することにより鮮鋭性の優れる拡大撮影画像を得ることができる。
【図面の簡単な説明】
【図１】Ｘ線画像撮影装置を示す図である。
【図２】Ｘ線画像撮影のエッジ強調を示す図である。
【図３】エッジ部分の強度分布を示す図である。
【図４】Ｘ線管から放射されるＸ線エネルギーの指標を示す図である。
【図５】横型のＸ線画像撮影装置を模式的に示す図である。
【図６】縦型のＸ線画像撮影装置を模式的に示す図である。
【図７】デジタルＸ線画像検出器を用いたＸ線画像の出力システムを示す図である。
【符号の説明】
１ Ｘ線画像撮影装置
２ Ｘ線管
３ 被写体
４ Ｘ線画像検出器[0001]
BACKGROUND OF THE INVENTION
  The present invention, XBACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line image photographing apparatus, and in particular, when performing magnified photographing using an X-ray tube that emits diverging X-rays, X-rays that obtain an X-ray image with excellent sharpness by edge enhancement by X-ray refraction contrastPictureImageShadowRelated to the position.
[0002]
[Prior art]
X-ray images using the action of X-rays passing through a substance are widely used for medical image diagnosis, non-destructive inspection, and the like. This X-ray image is a shading line due to the X-ray transmission amount being different depending on the atomic amount of the substance constituting the subject when the X-ray passes through the subject. That is, a two-dimensional distribution of the X-ray dose emitted from the X-ray source and transmitted through the subject is detected by the X-ray image detector, and an X-ray image based on the X-ray absorption contrast of the subject is formed.
[0003]
[Problem to be Solved by the Invention]
Examples of X-ray tubes that emit divergent X-rays used in non-destructive inspections and general medical facilities include rotary anode X-ray tubes. In these X-ray tubes, thermionic electrons collide with the counter-cathode. X-rays generated in this manner spread radially. Taking advantage of this property, the X-ray image is magnified by separating the distance between the subject and the X-ray image detector. At this time, since the focal size of the X-ray is a finite size, it is well known that a blur called “penumbra” occurs in magnified imaging as shown in FIG.
[0004]
When the X-ray source is a point light source, or when it can be regarded as a point light source, that is, when the focal spot size is 0 or almost 0, blurring does not occur in such an enlarged X-ray image. On the other hand, in order to obtain a sufficient X-ray dose for transmitting through a thick subject such as a human body, a practically constant focal spot size is required. Therefore, in X-ray photography, this blur caused by a penumbra cannot be avoided. In particular, in the case of magnified photography, the sharpness of the X-ray image is lowered.
[0005]
When the enlargement ratio of the X-ray enlargement imaging is increased, the blur width is further enlarged. For example, in magnified imaging such as chest spot imaging and bone precise X-ray imaging, if the magnification ratio is increased, the sharpness of the image deteriorates, making it difficult to interpret, and the effect of enlarged imaging is halved.
On the other hand, the present inventors have found that when a subject is photographed, an edge enhancement phenomenon occurs due to the refractive contrast of X-rays at a portion where the subject has a refractive index.
[0006]
The present invention has been made in view of the above problems, and optimizes the relationship between blur caused by penumbra and edge emphasis when performing magnified imaging using an X-ray tube that emits diverging X-rays. The present invention provides an X-ray image capturing method and an image capturing apparatus capable of obtaining an enlarged captured image with excellent sharpness.
[0007]
[Means for solving the problems]
In order to solve the above problems and achieve the object, the present invention is configured as follows.
[0008]
  The invention of claim 1 is directed to “diverging X-rays.LightX-ray tubeWhen,
An object position setting tool for setting an object position with respect to the X-ray tube;
An X-ray image detector for detecting an X-ray image transmitted through the subject,
The bokeh width caused by the penumbra of the X-ray image is B (μm), and the X-ray dose reduction maximum value of the portion where the X-ray intensity is reduced due to X-ray refraction in the X-ray image transmitted through the interface portion having a different refractive index. , E (μm) is the edge emphasis width which is a half-value width with respect to the maximum X-ray dose increase at the portion where the X-ray intensity has increased due to X-ray refraction.When the X-ray radiated from the X-ray tube is transmitted through the subject and the X-ray enlarged photographing is performed, the subject position setting tool and the X-ray image detector can be installed so that 9E ≧ B.X-ray imagingapparatus.].
[0009]
  The invention of claim 2『BoThe X-ray image photographing according to claim 1, wherein the width B and the edge emphasis width E are expressed by the following two formulas and three formulas, respectively.apparatus.
B = D × (R2 / R1) (2 formulas)
E = 39 × R2 (1 + 0.045 / R1) × λ²× √A (3 formulas)
However, the focus size of the X-ray tube is D (μm), the distance from the focus of the X-ray tube to the subject is R1 (m), the distance from the subject to the X-ray image detector is R2 (m), and from the X-ray tube The wavelength of the maximum value of the X-ray dose in the emitted X-ray is λ (Å), and the diameter of the circle of the cross section when the subject object is a cylinder is A (mm). ].
[0010]
  The invention of claim 3『BoThe X-ray image photographing according to claim 1, wherein the width B and the edge emphasis width E are expressed by the following two formulas and four formulas, respectively.apparatus.
B = D × (R2 / R1) (2 formulas)
E = 27 × (1 + R2 / R1)^1/3× (λ²× R2 × √A)^2/3... (4 formulas)
However, the focus size of the X-ray tube is D (μm), the distance from the focus of the X-ray tube to the subject is R1 (m), the distance from the subject to the X-ray image detector is R2 (m), and from the X-ray tube The wavelength of the maximum value of the X-ray dose in the emitted X-ray is λ (Å), and the diameter of the circle of the cross section when the subject object is a cylinder is A (mm). ].
[0011]
  According to a fourth aspect of the present invention, “the X-rayThe subject position setting tool can be provided so that the distance between the tube and the subject is 0.5 m or more, and the distance between the subject and the X-ray image detector can be 1 m or more.The X-ray imaging according to claim 1, wherein the X-ray imaging is performed.apparatus. ].
[0012]
  According to a fifth aspect of the present invention, “the focal point of the X-ray tube”A rail or support with information on the distance starting from
An X-ray image detector holder for holding the X-ray image detector;
The subject position setting tool and the X-ray image detector holder are provided so as to be movable and temporarily fixable to the rail or the column.It is characterized byRepliesClaim4X-ray imaging as describedapparatus. ].
[0013]
  The invention of claim 6It has an X-ray tube capable of setting a 50 kVp to 150 kVp tube voltage, a subject position setting tool is disposed at a position 0.5 m or more away from the X-ray tube, and at a position 1 m or more away from the subject position setting tool. An X-ray image detector was placedX-ray imaging according to any one of claims 1 to 5,apparatus. ].
[0014]
  The invention of claim 7 is directed to “the X-ray.The magnification rate of magnified shooting is 1.1 to 10 timesThe X-ray imaging according to claim 1, wherein the X-ray imaging is performed.apparatus. ].
[0015]
  The invention of claim 8 is “the X-ray tubeThe focal spot size is 0.03mm to 0.3mmThe X-ray imaging according to claim 1, wherein the X-ray imaging is performed.apparatus. ].
[0016]
  The invention of claim 9The X-ray tube is a Coolidge X-ray tubeThe X-ray imaging according to claim 1, wherein the X-ray imaging is performed.apparatus. ].
[0017]
  The invention of claim 10The X-ray tube is a tungsten rotating anode X-ray tubeThe X-ray imaging according to any one of claims 1 to 9, whereinapparatus. ].
[0018]
  The invention of claim 1111. The X-ray image detector according to claim 1, wherein a screen film system having an average gradation G of 1.5 to 4.0 is used, and an edge emphasis width E is 9 [mu] m or more. Any one of the itemsX-ray imaging device. ].
[0019]
  The invention of claim 1211. The X-ray image detector according to claim 1, wherein a digital X-ray image detector having a pixel size of 1 μm to 200 μm is used as the X-ray image detector, and the edge enhancement width E is larger than 0.1 μm. Or in 1X-ray imaging device. ].
[0027]
In the X-ray imaging apparatus 1 shown in FIG. 1, the present invention transmits X-rays emitted from a Coolidge X-ray tube, which is an example of an X-ray tube 2 that emits diverging X-rays, to an object 3, An X-ray image is obtained by the image detector 4 and X-ray enlarged photographing is performed. Since the X-ray is an electromagnetic wave, it has the property of a wave, that is, the property of causing refraction at the interface when the X-ray passes through the object 3 having a different refractive index, like the visible light. Note that the magnified imaging is imaging in which an image magnified from the subject 3 is obtained on the X-ray image detector 4. The enlargement ratio in this case refers to enlargement with respect to the length. For example, in the system as shown in FIG. 1, the enlargement ratio (magnification) is used.
[0028]
As schematically shown in FIG. 2, in the X-ray transmission image on the X-ray image detector 4 at the interface portion having different refractive indexes, the portion where the X-ray intensity decreases due to X-ray refraction, and the refracted X There is a portion where the X-ray intensity increases due to the line overlapping with the X-ray that has traveled straight through the space. That is, in the negative image obtained here, a portion where the X-ray intensity decreases at the interface having different refractive indexes is whitened, and a portion where the X-ray intensity increases becomes blacker, resulting in a so-called edge-enhanced image. . This is a phenomenon called X-ray refraction contrast. Since the wavelength of X-ray is very short and its refractive index is small, this X-ray refraction contrast is weak enough to be overlooked in conventional X-ray imaging. That is, in the conventional X-ray image, the X-ray refraction contrast is not sufficiently utilized, and the X-ray image has only the absorption contrast due to the X-ray absorption difference.
[0029]
In the present invention, this X-ray refraction contrast is used as a means for solving the problem. In other words, even if an image blur due to a penumbra occurs in magnified photography, edge blur as described above is caused at the same time to eliminate this blur, and an enlarged X-ray photograph image with good sharpness is obtained. More specifically, the present invention solves the problem by the following method.
[0030]
That is, for example, when performing magnified imaging using an X-ray tube 2 that emits diverging X-rays, which is a Coolidge X-ray tube, a blur width B (μm) due to penumbra and an edge enhancement width E due to X-ray refraction contrast enhancement. (Μm)
9E ≧ B (1 formula).
[0031]
In addition, it is preferable that the magnification rate of X-ray expansion imaging here is 1.1 to 10 times. The focal spot size of the X-ray tube 2 used here is preferably 10 μm to 1000 μm. The X-ray tube voltage of the X-ray tube 2 is preferably 50 kVp to 150 kVp. The X-ray tube 2 preferably contains tungsten in the counter cathode.
[0032]
Here, the X-ray focal point refers to a window viewed from the direction of the subject from which X-rays generated when an electron beam collides with, for example, a rotating anode of the X-ray tube 2 are extracted. The size of this window is called the focus size. When the focus is a square, the length of one side is used. When the focus is a rectangle other than a square, the length of the short side is used. The diameter can be used as a focal size and measured as defined in JISZ4704. Further, when the focus shape is other than the above, it can be measured using a pinhole camera or a test chart as defined in JISZ4704.
[0033]
The X-ray image detector 4 for forming an image preferably uses a screen film system having an average gradation G of 1.5 to 4.0. At this time, the edge emphasis width E is preferably 9 μm or more as shown in FIG. By setting this range, it is possible to improve the accuracy of human visual diagnosis.
When a digital X-ray image detector is used as the X-ray image detector 4, the pixel size is preferably 1 μm or more and 200 μm or less, and the edge emphasis width E at this time is preferably larger than 0.1 μm. preferable. By setting this range, the accuracy of diagnosis can be improved.
[0034]
In the present invention, the subject 3 is preferably a human body or a sample removed from the human body. Further details will be described below.
[0035]
First, the X-ray source used in the present invention uses an X-ray tube in which X-rays radiate radially. For an X-ray tube in which X-rays radiate radially, the magnification of the X-ray image can be arbitrarily set by adjusting the distance between the subject and the X-ray image detector. The X-ray source used in the present invention is specifically a Coolidge X-ray tube in which X-rays can be obtained by thermionic electrons colliding with the counter-cathode, and an X-ray tube having a rotating anode for obtaining particularly strong X-rays. Is preferred. A self-bias X-ray tube, a plasma X-ray tube, or the like can be used.
[0036]
As shown in FIG. 1, the blur width B (μm) due to the penumbra includes the X-ray tube focus size D (μm), the distance R1 (m) from the X-ray focus to the subject 3, and the X-ray image detection from the subject 3. If the distance R2 (m) to the unit 4 is determined uniquely geometrically. That is,
B = D × (R2 / R1) (2 formulas)
Can be calculated.
[0037]
As shown in FIG. 2, the edge emphasis width E (μm) at the interface due to the X-ray refraction contrast is the half width of the maximum X-ray dose decrease value and the maximum X-ray dose increase value, and this value was obtained by the following equation. Things can be used.
[0038]
  E = 39 × R2 (1 + 0.045 / R1) × λ²× √A (3 formulas)
  At this time, R1 is the distance (m) from the X-ray source to the subject 3, R2 is the distance (m) from the subject 3 to the X-ray image detector 4, and λ is the wavelength of the maximum value of the X-ray dose (Å), A is the diameter (mm) of the circle of the cross section when the object 3 is a cylinder. This empirical formula was obtained as follows.
[0039]
A reference intensity distribution was first obtained by ray tracing in a model manner under the following conditions.
[0040]
Model: Plastic fiber diameter 1mm
Refractive index difference from air: 3 × 10^-6(Value for Cu characteristic X-ray 1.5 angstrom of plastic)
Arrangement: R1: Infinite, R2 = 0.25 The obtained intensity distribution of the edge portion is shown in FIG. On the other hand, the X-ray refraction contrast width (edge enhancement width) E is proportional to R2, the refractive index difference, and the square root of the object diameter A, and the increase amount of the edge enhancement width E when R1 is finite. It was found to be proportional to 1 / R1.
[0041]
Here, the refractive index difference is proportional to the square of the wavelength (λ) in the X-ray region. Therefore
E = a × R2 × (1 + b / R1) × λ²X√A can be written. a and b are constants. Next, from the edge emphasis width E in the intensity distribution obtained by computer simulation from a practical viewpoint, a = 39 and b = 0.045 were obtained, and finally (Expression 3) was obtained.
[0042]
As the value of the edge emphasis width E, a value obtained by the following equation can also be used.
[0043]
  E = 27 × (1 + R2 / R1)^1/3× (λ²× R2 × √A)^2/3... (4 formulas)
  At this time, R1 is the distance (m) from the X-ray source to the subject 3, R2 is the distance (m) from the subject 3 to the X-ray image detector 4, and λ is the wavelength of the maximum value of the X-ray dose (Å), A is the diameter (mm) of the circle of the cross section when the object 3 is a cylinder.
[0044]
More generally, as shown in FIG. 2, the edge enhancement width at the interface due to the X-ray phase contrast is the half width of the maximum X-ray dose decrease value and the maximum X-ray dose increase value, and this value is placed in the air. For cylindrical objects,
Theoretical formula E = 2.3 × (1 + R2 / R1)^1/3× (R2 × δ × √A)^2/3Can be obtained by:
[0045]
At this time, δ is a refractive index difference (δ> 0) between the object and air.
[0046]
This theoretical formula is based on X-rays refracted by an object, where W is the wavefront shape after passing through the object. Intensity distribution caused by the second-order derivative W ”of W”
It calculated | required from expressing with i = (1 + R2 / R1) / (1-R2 * W ").
[0047]
  δ to λ (Å) And can be expressed as the following equation for the human body composition.
[0048]
The above formulas are all obtained in consideration of the X-ray refraction effect.
[0049]
  Also, (4 formulas)soThe obtained value is closer to the true edge emphasis width than the value obtained in (Expression 3) and is more preferable.
[0050]
Japanese Patent Publication No. 11-50262 and the scientific journal “Nature, vol, 77, 2962 (1996)” discuss the edge enhancement effect of X-ray images due to X-ray interference. In the discussion there, it is assumed that the X-rays used have a high lateral spatial coherence, and the edge enhancement effect is caused by X-ray interference, that is, X-rays by the first-order approximation of Fresnel diffraction contrast. This is due to a decrease and increase in strength. Therefore, in order to obtain highly spatially coherent X-rays, it is necessary to take a sufficient distance from the subject to the X-ray image detector so that the focal point size of the X-ray source is as small as possible and can be regarded as a point light source, and the contrast is low. Since it changes directly with respect to the distance (R2) between the subject and the X-ray image detector, it is argued that a certain distance or more needs to be set for R2.
[0051]
In the present invention, since a contrast enhancement phenomenon due to refraction of X-rays is used, high spatial coherence of X-rays is not particularly required. Therefore, it is not essential that the focal spot size be a point light source or a point light source. In the present invention, the distance (R1) from the X-ray source to the subject and the distance (R2) between the subject and the X-ray image detector are determined based on the magnification of the X-ray image and other factors. It is. Further, R1 and R2 are determined by (Equation 2) of the relationship between the edge width obtained from (Equation 3) or (Equation 4) and the blur width obtained geometrically. Thus, the X-ray spatial coherence is not particularly required for solving the problems of the present invention, and high contrast is not realized only by the distance (R2) between the subject and the X-ray image detector. Therefore, the effects obtained by the present invention are different from the techniques disclosed in the patent publications and scientific journals.
[0052]
  In addition, a method of removing scattered X-rays by separating an X-ray image detector from a subject in order to obtain a sharp X-ray image is known as the Gradel effect. In particular, when zooming in, the distance increases, so the Gradel effect is used. On the other hand, since the X-ray refraction contrast according to the present invention is not particularly related to the scattered X-ray, (Expression 3) and (4formulaX-ray scattering factors are not incorporated in the). That is, the present invention is different from the Gradel effect, which removes scattered X-rays known in the art and improves the sharpness of the X-ray image.
[0053]
However, in the present invention, when scattered radiation becomes a problem, for example, when an X-ray grid for removing scattered radiation is not used, when setting the distance between the subject and the X-ray image detector, Needless to say, the impact may be taken into account.
From (Expression 2), the smaller the focal size of the X-ray tube, the smaller the blur width. At this time, the X-ray refraction contrast is observed more strongly. However, if the focal spot size is small, the X-ray dose from the X-ray source is reduced, so that the subject 3 and the X-ray image detector 4 are limited. On the other hand, as the focal spot size increases, the X-ray dose increases, but the blur width B caused by the penumbra increases and it becomes difficult to obtain the X-ray refraction contrast effect. Therefore, the focal spot size is preferably at least 0.03 mm to 0.3 mm from such balance.
In the present invention, the distance R1 from the focal point of the X-ray tube is preferably 0.15 m or more, and the distance R2 between the subject 3 and the X-ray image detector 4 is preferably 0.15 m or more. When R1 is 0.15 m or more, the geometric distortion in the X-ray image becomes smaller. If R2 is 0.15 m or more, it is difficult to pick up scattered X-rays from the subject, and the sharpness of the image by scattered X-rays can be further improved.
[0054]
In the present invention, the number of X-rays that reach the X-ray image detector 4 for performing magnified imaging is reduced. Therefore, it is preferable not to use an X-ray grid for removing scattered X-rays accompanied by X-ray loss. When the subject 3 is thick, both R1 and R2 are preferably larger than 0.5 m. When used for medical purposes, from the viewpoint of X-ray exposure, the distance R1 from the X-ray source to the subject is 1 m or more, and the distance R1 + R2 between the X-ray source and the X-ray image detector is 1.5 m or more. Is desirable. In consideration of the size of the X-ray imaging room and the X-ray dose reaching the X-ray image detector 4, R1 + R2 is preferably within 10 m, and more preferably R1 + R2 is within 5 m.
[0055]
In (Expression 3) and (Expression 4), the diameter A of the detected object at the position of the subject 3 is a value to be determined according to the purpose to be described by X-ray imaging. In non-destructive examinations, etc., it is necessary to search for cracking with a width of about 0.1 mm. For medical use, for example, a tumor with a size of about 1 mm or a calcified shadow is drawn for detection of early lung cancer in the chest. It is hoped that. The magnified imaging of the present invention is particularly useful for detecting structures smaller than 10 mm.
[0056]
As described above, the value of A in (Expression 3) and (Expression 4) is a value to be selected according to the purpose of X-ray imaging. In the present invention, A is 0.1 mm or more and 10 mm or less, and further 1 mm. Thus, 2 mm or less is taken into consideration.
[0057]
  As shown in (Expression 3) and (Expression 4), the edge enhancement width E depends on the wavelength of the X-ray used. Wavelength λ (in Equation (3) and Equation (4)Å) Is the X-ray wavelength of the maximum value of the X-ray dose of the continuous spectrum excluding the characteristic X-rays generated from the X-ray tube used. For example, in the Coolidge X-ray tube 2 having tungsten as a rotating anode, the calculation is made with λ = 0.4 angstrom (FIG. 4).
[0058]
Depending on the tube voltage of the X-ray tube used, the quality of X-rays, that is, the ease of transmission through the subject, differs. The higher the tube voltage, the higher the X-ray energy component that is generated, so that X-rays are more easily transmitted through the subject, and therefore the X-ray image contrast due to absorption decreases. When the tube voltage is low, X-rays are hardly transmitted. Therefore, it is necessary to set the tube voltage of the X-ray tube according to the purpose of use. In medical X-ray image diagnosis and nondestructive inspection, the X-ray tube voltage is in the range of 50 kVp to 150 kVp.
[0059]
The region of (formula 1) of the present invention is a region suitable for these X-ray energy regions. Here, “kVp” represents the X-ray component having the highest energy of the emitted X-ray, and is generally an index of the X-ray energy emitted from the X-ray tube, and is set as the X-ray tube voltage at the time of imaging. (FIG. 4).
[0060]
The horizontal and vertical X-ray imaging apparatuses according to the present invention are schematically shown in FIGS. When the X-ray image photographing apparatus 1 performs magnified photographing, the blur caused by the movement of the subject 3 is also magnified. Therefore, in order to reduce such blur as much as possible, the subject position setting tool 20 for fixing the subject 3 at the time of photographing is necessary. In order to provide mechanical strength, the subject position setting tool 20 is preferably provided with a frame made of metal or reinforced plastic resin, and a plastic resin plate that transmits as much X-rays as possible is attached to the frame that transmits X-rays. The thickness of the plate is preferably 0.05 mm to several mm. The patient who is the subject 3 can minimize the movement at the time of photographing by bringing the body or a part of the body into close contact with the subject position setting tool 20.
[0061]
The distance R1 from the focal position of the X-ray tube 2 to the subject position setting tool 20 and the distance R2 from the subject position setting tool 20 to the X-ray image detector 4 can be arbitrarily set within the scope of the present invention. . In order to perform this setting accurately, a distance having information on the distance from the focal point of the X-ray tube 2 connecting the X-ray tube 2, the subject position setting tool 20 and the X-ray image detector 4 is imprinted. It is preferable to install the rail 21. The X-ray image detector 4 and the X-ray image detector holder 25 can be moved to the rail 21 and can be temporarily fixed.
[0062]
In FIG. 6, the X-ray tube 2 is installed on the subject 3, but conversely, the X-ray tube 2 may be placed downward and the X-ray image detector 4 may be installed upward. In this apparatus, it is preferable to have a table 22 so that the patient who is the subject 3 can be photographed while lying down. The table 22 is provided with a subject position setting tool 20. Further, as in FIG. 5, in order to accurately set the distance R1 from the X-ray tube 2 to the subject 3 and the distance R2 from the subject 3 to the X-ray image detector 4, a column 23 with a distance stamp is installed. Is preferred. The X-ray image detector 4 and the X-ray image detector holder 25 can be moved to the support column 23 and can be temporarily fixed.
[0063]
Although the object holding side is shown as the object position setting tool 20, it is sufficient to determine the object position necessary for obtaining the X-ray image of the present invention without holding it. It may be a member or the like.
[0064]
Various X-ray image detectors 4 are currently used. For example, a screen film system comprising a photographic light-sensitive material coated with a silver halide emulsion and an X-ray fluorescent intensifying screen can be used. As the photographic light-sensitive material (film), one obtained by coating an emulsion layer on one side or both sides of a support can be used. When high resolution is required, it is preferable to use a single-sided film. When the enlargement ratio is large, it is preferable to use a high-sensitivity double-sided coated film. As the fluorescent intensifying screen (screen) used together with the photographic light-sensitive material, those that emit blue light or green light by X-ray irradiation can be used. Cadolinium oxysulfide (Gd) activated by terbium with particularly good X-ray absorption₂O₂A fluorescent screen made of a phosphor (S: Tb, hereinafter referred to as GOS) is preferable. The average gradation G of the screen / film system used is preferably 1.5 to 4.0. Further, since the X-ray image contrast is increased by the edge enhancement effect, the average gradation G of the screen / film system is more preferably 2 to 3.8, and the latitude is wide in a region lower than “fog density + 1.0”. A system is preferred. The average gradation G refers to the slope of a straight line connecting two points of the characteristic curve, the point having the “fog density + 0.25” density and the point having the “fog density + 2.0” density. The fog is a density obtained by developing a portion that has not been exposed.
[0065]
The characteristic curve here is used when a silver halide photographic light-sensitive material is used. For example, “Basics of Revised Photo Optics—Silver Salt Photo Edition” (Corona Corp., edited by Japan Photographic Society, 1998) ), The blackening density (optical density) D of a photographic image obtained by exposing the silver halide emulsion layer and then performing development or the like is expressed as an exposure amount E (= I × t, I is the D-log E curve plotted against the common logarithm of I (exposure illuminance, t is exposure time).
[0066]
There are two main factors that influence the average gradation of the screen / film system: film characteristics and development processing. In the case of a film, the average gradation is determined by the composition of the silver halide grains constituting the emulsion layer, the particle size distribution, additives such as a fog inhibitor, and the amount of silver halide grains in the emulsion layer. The silver halide photographic light-sensitive material used in the present invention is outlined in, for example, the above-mentioned “Revised Basics of Photographic Engineering—Silver Salt Photo Edition” (edited by the Japan Photographic Society, Corona 1998). As for development processing, the average gradation can be raised by raising the development processing temperature or extending the processing time. However, when performing automatic development processing, in principle, processing is performed under the development processing conditions specified by the film manufacturer. It is preferable to do.
[0067]
The image resolution of the screen / film system needs to be larger than the edge enhancement width E. In addition, since a medical image in a screen / film system is usually observed directly with the naked eye, it cannot be observed if the edge enhancement width is too narrow. As a result of intensive studies, it was experimentally found that the edge emphasis width E is preferably 9 μm or more when the screen / film system is used as an X-ray image detector.
[0068]
The digital X-ray image detector obtains an X-ray image as a digital image signal. For example, a computed radiography (CR) using an imaging plate coated with a stimulable phosphor, X-ray irradiation is performed by GOS. The light generated by the cesium iodide phosphor is converted into an electrical signal using a photodiode and read by the TFT, or the X-ray irradiation is received by a-Se and the generated charge is directly read by the TFT. There are flat-type X-ray image detectors (FPD), detectors that convert X-ray images obtained by X-ray irradiation with a GOS phosphor or the like into visible light, and read them with a CCD or CMOS.
[0069]
In an imaging system using these digital X-ray image detectors, X-ray image information is read by dividing a two-dimensional plane. The length of the side of the square having the minimum area to be read or the diameter of the circle is called the pixel size. For example, in the above-mentioned CR, it corresponds to the pitch for reading the photostimulated light emission, and the minimum reading diameter of the CCD or CMOS, and in the FPD, the reading diameter of the silicon photodiode or the minimum collecting charge generated in the X-ray conductive layer. This is the pixel size.
[0070]
Further, as shown in FIG. 7, when the digital X-ray image detector 10 is used, image processing is performed by the image processing means 11, and enlargement / reduction and adjustment of the image contrast can be easily performed by this image processing. 12. Output to image printer 13 or store in image storage device 14 and send to, for example, hospital LAN. By using the digital X-ray image detector 10 in this way, the image can be reduced to the actual image size and displayed after the enlargement photographing of the present invention. It is also possible to enlarge the image beyond the enlargement ratio at the time of shooting. In consideration of enlargement at the time of imaging or more, the edge enhancement width E read by the digital X-ray image detector 10 is preferably larger than 0.1 μm. Here, in the digital X-ray image detector 4, the minimum read image size is determined by the purpose of use and the capability of the system.
[0071]
In the present invention, when a photostimulable phosphor is used for X-ray image detection, reading of an image signal is generally performed by a laser exposure scan. Usually, the minimum pixel size is equal to the reading laser spot diameter. The diameter is preferably larger than 1 μm, but more preferably 20 μm or more in order to increase the reading speed. Further, it is preferably 200 μm or less in order to improve the sharpness of the read image itself. The same applies to other digital X-ray image detectors described in the present invention.
[0072]
As an X-ray tube, what contains tungsten in the counter cathode which is an anode currently widely used in the medical field is preferable. This is because the most preferable X-ray energy range can be taken in order to obtain non-destructive inspection and X-ray images of the human body. When a small animal such as a fish with good X-ray permeability is used as a subject, an X-ray source whose anode is copper, for example, is used.
[0073]
In the present invention, for example, there is a possibility that it can contribute to the discovery of an early lung cancer of 5 mm or less in the chest. This is because a structure with a size of 2 mm is enlarged and drawn to 16 mm if 8 × magnification is taken. Conventionally, when such a large magnified image is taken, it is difficult to interpret due to blur caused by penumbras. However, in the present invention, since a fine structure can be clearly depicted, it is easy to interpret.
[0074]
In addition, for the early detection of metabolic and leumatic disorders, magnified photography of the peripheral bone of the finger is performed. At this time, in order to attach importance to sharpness, there is known a method of performing non-screen photography without using an X-ray fluorescent intensifying screen (screen) and performing enlarged printing. When performing non-screen photography, the problem is that the X-ray exposure is large.
[0075]
In the present invention, it is possible to realize magnified photographing with a lower dose and better sharpness than non-screen photographing. In today's medical field, tungsten X-ray tubes of 50 to 150 kVp X-rays are widely used. If a screen film system is applied to the X-ray image detector, it can be easily introduced into the medical field. Therefore, the present invention is particularly useful when applied to the medical field.
[0076]
DETAILED DESCRIPTION OF THE INVENTION
[Example 1]
As an X-ray source, an X-ray tube L662202 manufactured by Hamamatsu Photonics Co., Ltd., whose focal size is 40 μm and the counter cathode is a tungsten anode, and an X-ray tube DRA manufactured by Toshiba Corporation, whose counter cathode is a tungsten anode and whose focal size is 300 μm. A chest phantom image made by Kyoto Science Co., Ltd. was taken using -3535HD. The X-ray tube voltage at this time was 120 kVp. The arrangement of the devices of the X-ray imaging apparatus is as shown in FIG. The frame of the subject position setting tool was made of vinyl chloride having a width of 2 cm, and a transparent polyester film having a thickness of about 0.2 mm was attached to the frame. Photographing was performed with a chest phantom in close contact with the subject position setting tool.
[0077]
A screen film system was used as the X-ray image detector. The film is a medical X-ray film SRIC manufactured by Konica Corporation in which a silver iodobromide emulsion is coated on one side of a film support, and a medical product manufactured by Konica Corporation in which a silver iodobromide emulsion is coated on both sides of a film support. An X-ray film SRG was used. As the fluorescent intensifying screen, an SRO125 back intensifying screen manufactured by Konica Corporation was used in combination with SRIC.
[0078]
The double-sided film SRG used was an intensifying screen SRO250 or SRO1000 manufactured by Konica Corporation. The combination of SRO125 and SRIC has the lowest sensitivity but the highest resolution. The fluorescent intensifying screen combined with SRG has higher sensitivity as the arithmetic number is larger, while the resolution is lowered. The average gradation G of SRIC was 2.6, and the average gradation G of SRG was 2.45.
[0079]
The film development processing after X-ray image photographing was performed at 35 ° C. for 90 seconds with an SRX502 automatic developing machine manufactured by Konica Corporation. After the development processing, a film was put on a shaukasten (light box) having a brightness of about 9000 lux, and it was observed with naked eyes to determine whether edge enhancement was recognized.
[0080]
That is, it was determined whether or not the periphery of the cylindrical pseudo blood vessel image running substantially parallel to the film surface of the chest lung field region was blackened. The pseudo blood vessel diameter was used as the value of A in the three equations. The evaluation rank was evaluated as 5 when it looks very good, 4 when it looks good, 3 when it can be recognized, 2 when it is very weak even if it looks, and 1 when it is not visible. The results are shown in Table 1. E represents a value obtained by using (Expression 4).
[0081]
[Table 1]

In addition, the blood vessel diameter in the table is measured by X-ray imaging when magnification imaging is not performed. Sample No. Since 6 does not satisfy 9E ≧ B, the determination result is the lowest value 1. Sample No. The value of E obtained by (Equation 4) is 5 as described above, but the value of E obtained by (Equation 3) is 36, 9E is 324, and 9E ≧ B is satisfied.
[0082]
[Example 2]
A chest phantom X-ray image was taken in the same manner as in Example 1. An image signal was read at a laser spot size of 87 μm using a Konica bright-excited phosphor, printed on a Konica single-sided film 67LP with a Konica laser imager Li-7, and developed with an automatic processor SRX502. The imaging conditions are R1 = R2 = 2m, double magnification, focus size of 40 μm, blur width B = 40 μm, and edge enhancement width E = 16 μm and 9E = 144 μm when A in (Formula 4) is 1 mm blood vessel diameter. 9E ≧ B, where E is greater than 0.1 μm.
[0083]
An image obtained by enlarging the image obtained after the photographing by 3 times and reducing the original size was printed. Along with the two prints, a 1 mm diameter laterally running pseudo blood vessel was bordered in black, and edge emphasis was recognized. The determination was 5 for a 3 × enlarged image and 4 for the original size display. The X-ray dose was 7.8 mAs.
[0084]
[Example 3]
A skull X-ray image was taken using a head phantom made by Kyoto Science. At this time, the set tube voltage of the X-ray tube was 70 kVp. SRO250 was used for the intensifying screen, and SRG was used for the film. If the magnification is R1 = R2 = 2m, the focal size is 40 μm, the blur width B = 40 μm, and the subject width of the three formulas A is 1 mm, the edge emphasis width E = 16 μ is 9E = 144 μm, and 9E ≧ B. Further, E ≧ 9 μm is also satisfied. After the same development processing as in Example 1, the image was observed with naked eyes on the shaukasten, and a borderline with a clear black border was seen at the bone boundary portion. The evaluation was 4. The current was 36 mAs.
[0085]
[Example 4]
A finger bone X-ray image was taken using a hand phantom made by Kyoto Kagaku. The arrangement of the devices of the X-ray imaging apparatus was as shown in FIG. A part of the table was hollowed out, and a transparent polyester plate having a thickness of about 0.5 mm was stretched on the window, and a hand phantom was placed on the transparent polyester plate to take a picture.
[0086]
At this time, the set tube voltage of the X-ray tube was 50 kVp. The intensifying screen used was M100 manufactured by Konica Corporation, and the film used was a single-sided emulsion film CMH manufactured by Konica Corporation. The average gradation of this system was 3.2. After development processing similar to that in Example 1, a trabecular bone having a width of 1 mm (value of A in Formula 4) was observed with naked eyes on the shaucus ten, and the evaluation results are shown in Table 2.
[0087]
[Table 2]

No. Reference numerals 9 and 10 are determinations of “recognizable” (3) and “visible” (4). No. No. 7 does not satisfy 9E ≧ B, and the determination is “I cannot see” (1). As for 8, although 9E ≧ B is satisfied but E ≧ 9 μm is not satisfied, the determination is “very weak” (2).
[0088]
【The invention's effect】
As described above, in the X-ray image capturing method and X-ray image capturing apparatus of the present invention, the relationship between blur due to penumbra and edge emphasis when performing magnified imaging using an X-ray tube that emits diverging X-rays. By optimizing, an enlarged photographed image with excellent sharpness can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing an X-ray imaging apparatus.
FIG. 2 is a diagram illustrating edge enhancement in X-ray image capturing.
FIG. 3 is a diagram showing an intensity distribution of an edge portion.
FIG. 4 is a diagram showing an index of X-ray energy emitted from an X-ray tube.
FIG. 5 is a diagram schematically showing a horizontal X-ray imaging apparatus.
FIG. 6 is a diagram schematically illustrating a vertical X-ray imaging apparatus.
FIG. 7 is a diagram showing an X-ray image output system using a digital X-ray image detector.
[Explanation of symbols]
1 X-ray imaging equipment
2 X-ray tube
3 Subject
4 X-ray image detector

Claims (12)

And X-ray tube that shot an X-ray diverging irradiation,
An object position setting tool for setting an object position with respect to the X-ray tube;
An X-ray image detector for detecting an X-ray image transmitted through the subject,
The bokeh width caused by the penumbra of the X-ray image is B (μm), and the X-ray dose reduction maximum value of the portion where the X-ray intensity is reduced due to X-ray refraction in the X-ray image transmitted through the interface portion having a different refractive index. When the edge emphasis width, which is a half-value width with respect to the maximum X-ray dose increase at the portion where the X-ray intensity has increased due to X-ray refraction, is E (μm), the X-ray irradiated from the X-ray tube is applied to the subject. An X-ray imaging apparatus, wherein the subject position setting tool and the X-ray image detector can be installed so that 9E ≧ B when performing X-ray magnified imaging with transmission. 2. The X-ray imaging apparatus according to claim 1, wherein the blur width B and the edge enhancement width E are expressed by the following two formulas and three formulas, respectively.
B = D × (R2 / R1) (2 formulas)
E = 39 × R2 (1 + 0.045 / R1) × λ ² × √A (3 formulas)
However, the focus size of the X-ray tube is D (μm), the distance from the focus of the X-ray tube to the subject is R1 (m), the distance from the subject to the X-ray image detector is R2 (m), and from the X-ray tube The wavelength of the maximum value of the X-ray dose in the emitted X-ray is λ (Å), and the diameter of the circle of the cross section when the subject object is a cylinder is A (mm). 2. The X-ray imaging apparatus according to claim 1, wherein the blur width B and the edge enhancement width E are expressed by the following two formulas and four formulas, respectively.
B = D × (R2 / R1) (2 formulas)
E = 27 × (1 + R2 / R1) ^1/3 × (λ ² × R2 × √A) ^2/3 (4 formulas)
However, the focus size of the X-ray tube is D (μm), the distance from the focus of the X-ray tube to the subject is R1 (m), the distance from the subject to the X-ray image detector is R2 (m), and from the X-ray tube The wavelength of the maximum value of the X-ray dose in the emitted X-ray is λ (Å), and the diameter of the circle of the cross section when the subject object is a cylinder is A (mm). The subject position setting tool can be provided so that the distance between the X-ray tube and the subject is 0.5 m or more, and the distance between the subject and the X-ray image detector can be 1 m or more. The X-ray imaging apparatus according to claim 1, wherein the X-ray imaging apparatus is provided . A rail or support column having information on the distance from the focal point of the X-ray tube ;
An X-ray image detector holder for holding the X-ray image detector;
The object position setting tool and the X-ray image detector retainer according to the rail or movable in said post, 請 Motomeko 4 you characterized that you have and temporarily mounted fixably X-ray imaging device . It has an X-ray tube capable of setting a 50 kVp to 150 kVp tube voltage, a subject position setting tool is disposed at a position 0.5 m or more away from the X-ray tube, and at a position 1 m or more away from the subject position setting tool. X-ray imaging apparatus according to any one of claims 1 to 5, characterized in that a X-ray image detector. The X-ray imaging apparatus according to any one of claims 1 to 6, wherein an enlargement ratio of the X-ray enlargement imaging is 1.1 to 10 times . The X-ray imaging apparatus according to any one of claims 1 to 7, wherein a focal spot size of the X-ray tube is 0.03 mm to 0.3 mm . The X-ray imaging apparatus according to any one of claims 1 to 8, wherein the X-ray tube is a Coolidge X-ray tube . The X-ray imaging apparatus according to any one of claims 1 to 9, wherein the X-ray tube is a tungsten rotary anode X-ray tube . As the X-ray image detector, using a screen-film system average gradation G is 1.5 to 4.0, claims 1 to 10 you, wherein the edge enhancement width E is 9μm or more The X-ray imaging apparatus according to any one of the above . 11. The X-ray image detector according to claim 1, wherein a digital X-ray image detector having a pixel size of 1 μm to 200 μm is used as the X-ray image detector, and the edge enhancement width E is larger than 0.1 μm. The X-ray imaging apparatus of Claim 1 .

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