JP2007007358A - High-speed radiographing digital x-ray image formation system for medical test collecting image data at low magnification ratio - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital X-ray image formation system for executing high-speed radiography with consideration given to scattered radiation and a subject. <P>SOLUTION: An X-ray generator 5 and an X-ray tube 11 capable of executing high-voltage radiography irradiate X-rays in a high voltage range, and information inside the subject 21 having movement is A/D converted by a digital image detecting system 31 highly sensitive to the energy band and imaged on an image display device 6. Then, the X-ray tube has a focus capable of executing magnification imaging and the subject 21 and the digital image detecting system 31 have a distance sufficient for Gradel effect. This constitution can thus magnify the image at a slight magnification ratio using the magnification imaging method, combinedly use the high-voltage radiographing method and Gradel method to produce a room for the mechanical output capacity of the X-rays, limits the non-acuteness caused by the movement of the subject by executing a short-time radiographing so as to improve the image quality. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high-speed digital X-ray image forming system for slightly enlarging an image by an enlargement imaging method and reducing difficulty in viewing and misidentification.

  When the focal point of the X-ray tube is a theoretical point, the X-ray image is emitted radially from the X-ray focal point, passes through the subject, and is projected onto the image detection system. When X-rays pass through the subject, energy is attenuated, so the image detection system shows this difference as an image. However, in reality, there is no point focus, and it always has an area. Therefore, the smaller the focal point of the X-ray tube, the better. However, the larger the capacity, the larger the focal point and the larger the penumbra because of the problem of X-ray output. A general imaging method is shown in FIG. In general imaging, in order to reduce penumbra, the distance a1 between the focus of the X-ray tube and the subject is set to a distance at which the X-ray can be approximated to a parallel line sufficiently mathematically depending on the size of the subject. The distance b1 between the image detection systems is made as small as possible.

  There is an enlarged shooting method when it is desired to sharply image a minute subject.

An enlarged photographing method is shown in FIG. The enlargement photographing method will be described by combining the terminology used in the text of a simple enlargement photographing method and an advanced magnification photographing method. The simple magnified imaging method considers the geometric positional relationship between the X-ray tube focal point, the subject, and the image detection system as X-rays are emitted from the X-ray tube focal point, and applies an image similar to a triangle. A method for enlarging and projecting an object larger than the X-ray focal spot size by the enlarging projection method. Furthermore, since the granularity of the image detection system is constant without depending on the geometric positional relationship between the X-ray tube focus, the subject, and the image detection system, the image detection system is expanded when the subject is magnified M times. Since the granularity of the object surface projected above is the square of M in area, it utilizes the fact that the S / N ratio increases and the discrimination performance improves. In addition, since the Gradell effect (described later) appears in the magnified photographing method, the Gradel technique (described later) is often used together. It is often used for mammography.
The advanced magnified imaging method is to enlarge and project a subject smaller than the X-ray focal spot size. The projected image is a smaller projected image than the subject due to the geometric penumbra, but the granularity of the image detection system does not depend on the geometric positional relationship between the focus of the X-ray tube and the subject to the image detection system. Therefore, when the subject is magnified M times, the granularity of the subject surface projected on the image detection system is M squared in area, so that the S / N ratio increases and is identified. It uses the ability to improve.
M is an enlargement ratio, and M = 1 + b2 ÷ a2 from FIG. 2, and the enlargement ratio M increases as a2 decreases and b2 increases.

  When you want to sharpen a moving subject, you can use high-pressure photography.

  When high-pressure imaging is performed, small focus and short-time imaging can be performed by reducing the load on the X-ray tube. Further, the contrast of the X-ray image is reduced due to the increase in bone permeability, and the diagnostic area is enlarged.

  When performing high-pressure photography or when the subject thickness is large and scattered rays affect image formation, there are the grid method and the Gradel method.

  In the grid method, a wall is made of an X-ray opaque material in a lattice shape so as to pass only in the incident main line direction of the projection image, and scattered rays incident from an angle outside the main line are blocked. Although it is an excellent scattered radiation removal device, the output dose is lost with respect to the X-ray grid incident dose, so depending on the X-ray energy band, the X-ray output needs to be increased from 2 to 4 times. There is. That is, the exposure dose of the subject increases, and the scattered radiation removal apparatus itself contributes to the degradation of image quality. Furthermore, it is incompatible with the digital image detection system. This is because a moire phenomenon due to the interaction between the grid pitch and the digital detection system element pitch occurs.

The Gradel method is explained by combining the terms used in the text of the Gradel effect and the Gradel technique. The Gradel effect is a phenomenon in which incident X-rays cause a scattering phenomenon in a subject and scatter radially from the scattering point, and the inverse square of the distance between the density per unit area of the scattered radiation and the distance from the scattering point. The law is established.
The main line in the same direction as the incident X-rays attenuates the energy when transmitted through the subject, but the density per unit area of the main line does not change greatly between the distance from the subject. Therefore, by separating the distance between the transmission X-ray output surface of the subject and the image detection system, only the scattered radiation can be greatly attenuated. This effect is called the Gradel effect.
Grader's technique pays attention to the fact that there is a point where the gradel effect is higher when the distance between the transmission X-ray output surface of the subject and the image detection system β2 is increased than when the scattered radiation removing device such as grit is used. , A technique that does not require the use of a scattered radiation removing device such as grit. The distance between the transmission X-ray output surface of the subject and the image detection system is said to be 15 to 20 cm or more, and at a distance of 40 cm, it is said that scattered rays that substantially affect the image quality can be removed.

Explanation of cited references

  Cited Document 1 describes an X-ray system in which the geometric positional relationship between the X-ray tube focus, the subject, and the image detection system is set using the Gradel technique, and the geometrical insensitivity increases. Are listed. Cited Document 2 describes the use of a detachable X-ray low-absorption table having a height at which enlarged photographing is performed. Cited Document 3 describes an X-ray image forming system in which a magnified imaging method and a Gradel technique are efficiently used and a refractive contrast phenomenon is generated using the method.

List of above cited references

1. Japanese Patent Laid-Open No. 9-2622332. 2. Microfilm of Japanese Patent Application No. 59-132951 (Japanese Utility Model Application No. 61-48711) Japanese Patent Application Laid-Open No. 2001-324772

  In order to use the magnified imaging method, the Gradel technique, and the high-pressure imaging method in combination, the setting of the imaging conditions was very difficult in terms of mathematical and X-ray output capability, and thus it was classified into the field of special imaging. However, in recent years, with the advancement from analog photography to digital photography, image processing such as density change can be performed by computer software, so that it is easy to set photographing conditions. In addition, since the enlargement ratio of the completed image can be easily changed, these combined methods can be applied to improve the sharpness and facilitate diagnostic interpretation when the subject's movement is not zero, but it is more than the existing technology. A digital X-ray image forming system for reducing image insensitivity and improving image quality by performing high-speed imaging is provided.

  In order to achieve the above object, the present invention corresponds to the setting of the magnification ratio of the subject, the setting of the imaging time by the movement of the subject, and the configuration of the X-ray image forming system for enabling the imaging time.

What magnification ratio is used when the magnified imaging method is used. Here, attention is paid to the MTF of the naked eye (MTF is a sharpness converted into a physical quantity). The MTF of the naked eye is shown in FIG. Although the lesion of 0.1 to 0.15 mm can be identified with the normal naked eye, the MTF rapidly decreases at a size smaller than that, and the rate of misperception increases even if the signal can be detected. In FIG. 3, the MTF of the naked eye has a peak at a position slightly smaller than 2 cycles / mm. In other words, MTF is very good when it is slightly larger than 0.15 to 0.2 mm, but 0.15 to 0.2 mm may be sufficient. For example, since the trabecular bone is about 0.1 mm, it is easy to see as it is enlarged. However, even if the enlargement is not greatly enlarged like a dedicated photographing machine, the signal can be detected and an accurate diagnosis can be made without misidentification. A degree of enlargement is sufficient. In other words, the diagnostic ability is improved simply by setting a 0.1 mm lesion to 0.11 mm at a magnification of 1.1 times, and if it can be reduced to 0.12 mm at a magnification of 1.2 times, the diagnostic ability will be greatly improved. To do.
Therefore, in order to enlarge a 0.1 to 0.15 mm subject to 0.15 to 0.2 mm, the enlargement ratio is required to be about 1.04 to 2.0 times. The X-ray tube focal point for that purpose may be 0.3 mm or more and 0.6 mm or less if an advanced magnification imaging method is used.

When the subject is dynamic, instability due to movement changes the image quality exponentially, so it is better to shoot for as short a time as possible.
For example, if there is a motion with an amplitude of 1.2 mm / s, a magnification of 2.0 times results in a projected image of 2.4 mm / s, so if 0.3 mm of unsharpness is allowed, a short time within 0.125 seconds You have to shoot. Similarly, when the amplitude is 1.5 mm / s, when the magnification is 1.5 times, a projected image of 2.25 mm / s is obtained. Therefore, it is necessary to shoot for a short time within 0.133 seconds.
Actually, since a geometric penumbra is taken into account, it is necessary to take a short time of 0.12 seconds or less. However, because of the granularity due to the X-ray quantum motor, it is desired to irradiate for 0.01 seconds or longer, so the imaging time is limited to a range of 0.01 to 0.12 seconds.
The reason why the amplitude is used for the movement is that the number of movements does not affect the image quality if the amplitude is the same.

Use the Gradel technique for short-time shooting. The instability due to the movement of the subject changes exponentially with the shooting time, so it is better to shoot in a short time. That is, it is good to take a short time with a higher voltage and a larger current. However, a scattered ray is generated from the subject as the tube voltage is higher. Therefore, a scattered ray removing device such as grit is used in the high voltage region. In addition, scattered radiation is generated depending on the thickness of the subject even when the voltage is not high, and thus a scattered radiation removing device such as grit may be used. This causes an output loss with respect to the input of X-rays, which is contrary to the intention because it is necessary to lengthen the imaging time. Therefore, the effective distance of the Gradel effect or the distance of the Gradel technique is maintained by using the Gradel effect without using a scattered radiation removing device such as a grid. However, since the distance depends on the thickness of the scatterer, that is, the thickness of the subject, it must be considered as the inspection contents.
If there is a distance that can adopt the Gradel technique, the output can be controlled while obtaining the same image quality.
That is, since high-speed shooting can be performed in a shorter time, when the movement of the subject is not zero but is small, the image quality of the Gredel technique is significantly improved as compared with the grid method.
The effect of the Gredel effect varies depending on the X-ray tube voltage used. This is because high-voltage X-ray energy is more likely to scatter when passing through the subject. This is a feature of the high voltage imaging method. In addition, the high-voltage imaging method enables small focal length and short time imaging by reducing the X-ray tube load.

The X-ray tube focus to the subject to the digital image detection system uses a tungsten target for high-pressure imaging, so the X-ray tube focus to the subject X-ray input is taken into account. The distance α2 between the surfaces is desired to be 50 cm or more. In order to use the Gradel effect, it is empirically desired that the distance between the transmission X-ray output surface of the subject and the digital image detection system β2 is 4 cm or more even for a thin subject. And if it is 40 cm, it is said that scattered radiation can be removed.
When the distance b2 between the subject and the digital image detection system is 50 cm, the distance a2 between the focal point of the X-ray tube and the subject needs to be 500 cm if the enlargement ratio is 1.1 times. Considering the necessary capacity of the X-ray apparatus, it is appropriate to set it to 150 cm or less.
Therefore, the distance a2 + b2 between the X-ray tube focal point and the digital image detection system is in the range of 54 to 200 cm.
As shown in FIG. 4, the subject thickness is 50 cm, the a4 + b4 between the X-ray tube focus and the digital image detection system is 150 cm, the α4 between the X-ray tube focus and the X-ray input surface of the subject is 50 cm, and the transmitted X-ray output surface of the subject is digital. When the inter-image detection system β4 is 50 cm, the enlargement ratio is 2.0 times, and when an advanced enlargement photographing method is used for a subject of 0.1 mm, the X-ray tube focus may be 0.3 mm, and an angiography system or CT It will be the range applied to the device. However, the angiography system and CT apparatus are not intended for such a small subject, so if the movement of the subject can be controlled, a larger X-ray tube focus may be used.

  As described above, the high-voltage imaging method is suitable for performing small focus and short-time imaging. However, in the digital image detection system, the image detection element is 100 μm and highly sensitive to 70 to 80 KV band X-ray energy. Some of them show a response. In order to generate X-rays that match this energy band, the continuous spectrum of the X-ray energy of the tungsten target matches if the tube voltage peak of the X-ray tube is about 100 KV or higher. Therefore, an X-ray generator having an X-ray tube voltage of about 100 KV or more is required. However, a rotary anode X-ray tube of a tungsten target has a limit of 200 KV because of its structure, but its X-ray continuous spectrum is sufficient. In order to perform the high voltage imaging method, 100 KV or more is desired, but it is 96 KV or more in consideration of the presence or absence of a filtration filter, and 150 KV or less if a general-purpose X-ray tube is used.

  In consideration of the total X-ray output for constructing an image under the above conditions, the X-ray high voltage generator needs 20 mA or more in the case of the single-phase full-wave rectification method.

Comparison between the invention of claim 1 and cited document 1

  The invention according to claim 1 and the invention described in the cited document 1 are exactly the same in that the gradel technique is used, and the transmission X-ray output surface of the subject recognized as necessary in the use of the gradel effect. The distance β2 of the image detection system is approximately the same. However, as a result, reference 1 specifies that geometrical sharpness increases. That is, while the image quality is deteriorated, the invention of the present application has the opposite effect of improving the image quality. This is because the cited document 1 is configured with an X-ray image forming system without considering the focus size of the X-ray tube and the necessity of short-time imaging due to the motion of the subject, which are important in the X-ray image forming system. This is because it is different from the present invention.

Comparison between the invention of claim 1 and cited references 2 and 3

The invention according to claim 1 and the inventions described in the cited documents 2 and 3 are exactly the same in that an enlarged photographing method is used. However, the magnified shooting method is for viewing a subject larger than the focal size in a geometrically enlarged manner, and a subject smaller than the focal size is blurred by a penumbra. Not subject. References 2 and 3 implicitly indicate that the focal point is smaller than the subject because it is an X-ray system for breasts, but the present invention is mainly intended for a subject smaller than the focal point size. This is different from the present invention.
Also, in the magnifying method, even if the magnification is different, the same evaluation is obtained if it is the same sharpness, or a higher magnification is obtained from the viewpoint of easy viewing. Since it is assumed that there is a certain amount of X-rays, it is necessary to increase the amount of X-rays when the enlargement ratio is increased. If the image quality is unsharp for the reason that it is not desirable to lengthen the shooting time, a lower magnification is better.
Further, the cited documents 2 and 3 are based on the premise that the subject has no motion, and the X-ray system having a photographing time unit of several seconds is configured, whereas the present invention is based on the premise that the subject has motion. This is different from the present invention in that the X-ray system is configured in units of a few hundredths of a second.

Comparison between the invention of claim 1 and cited document 3

  The invention according to claim 1 and the invention described in the cited document 3 describe the efficient combined use of the magnified photographing method and the Gradel technique, and these theoretical viewpoints are exactly the same. However, in configuring the X-ray system, the cited document 3 does not consider the motion of the subject. Therefore, when the individual components of the X-ray system are different and the movement of the subject is not zero but involves a slight movement, the result of the present invention cannot be obtained in the cited document 3.

Comparison between the invention of claim 1 and the combination of the cited references 1, 2 and 3

  From the viewpoint of short-time shooting, the invention of the present application is likely to be completed by the combination of Cited Document 1 and Cited Documents 2 and 3, but as described in Cited Document 1, dislikes the geometrical sharpness, Since there is a description of the purpose of giving up the adaptation of the Gradel technique, even those skilled in the art cannot easily conceive.

The invention's effect

  Since the present invention is configured as described above, the following effects can be obtained.

By constructing an X-ray image forming system from the viewpoint of short-time imaging and advanced magnified radiography, it is possible to obtain a sharper image than a normal radiography technique. As a result, an image sufficient to improve the diagnostic ability of a lesion of 0.1 to 0.15 mm required for medical diagnosis could be obtained. If applied, if it is a general-purpose X-ray image forming system equipped with a 0.6 mm focal point, an existing bed can be installed by adding an X-ray low-absorption table in order to increase the distance between the transmission X-ray output surface of the subject and the image detection system. If the thickness is increased and a certain distance is maintained, this is possible depending on the inspection contents.
Further, since a scattered radiation removing device such as a grid is not used, a moire phenomenon due to the interaction between the grid pitch and the digital detection system element pitch is not caused.
And the obtained image quality was more than expected.
Although research is currently being elucidated, it seems that high-pressure imaging is not suitable for diagnosing bone lesions, but it does not seem to be the case. When viewing images in trabecular units, bone tissue is present in the soft tissue, which is unexpectedly sparse. This is because there is enough space to recognize the projected image effectively.
Further, in the present invention, an image detecting element having a pitch of 100 μm is used. However, even if the pitch becomes rough, it is likely that a better image is formed if the X-ray sensitivity is improved. On the contrary, if the pitch becomes finer, the refraction contrast of X-rays may be detected.

  The embodiment will be described with reference to the drawings. In FIG. 5, an X-ray generator (single-phase full-wave rectification method) is used with an X-ray output condition of an X-ray tube voltage of 98 KV, a tube current of 20 mA, and an imaging time of 0.12 seconds. (5) is operated and X-rays are irradiated from the X-ray tube (11) having a focal point of 0.3 mm. A subject (21) having a thickness of 14 cm is supported by an X-ray low absorption table (4), and the transmitted X-rays reach a digital image detection system (31) having high sensitivity in the 70 KV to 80 KV band. The X-ray energy is A / D converted and sent to the image display device (6) to be imaged. Since the image displayed on the image display device can be changed in density and scaled by software, fine density setting can be performed. Images taken at a high speed in a short time in consideration of scattered radiation and subject motion have very good image quality. At this time, the geometrical system layout is 72 cm for the X-ray tube focal point to the subject a5, 28 cm for the subject to digital image detection system b5, and 65 cm for the distance between the X-ray tube focal point and the X-ray input plane of the subject to be 65 cm. Β5 between the transmission X-ray output surface and the digital image detection system is 21 cm, and a5 + b5 between the X-ray tube focus and the digital image detection system is 100 cm, and the enlargement ratio is about 1.39 times.

It is a figure which shows the conventional general imaging | photography method. It is a figure which shows the conventional magnified imaging method. It shows MTF of a human normal eye. The cited documents are excerpted from Nanedo Co., Ltd. Medical Radiation Technology Revised 5th edition. It is a figure which shows the Example of the geometrical X-ray system arrangement | positioning in this invention. It is a figure which shows the Example of the image forming system in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray tube 11 X-ray tube 2 for high-voltage imaging 2 Subject 210 Object which is not 0 but accompanied by minute movement 3 Image detection system 31 Digital image detection system X-ray high sensitivity in 70 KV to 80 KV band 4 X-ray low absorption Table 5 X-ray generator for high-voltage imaging 6 Image display device

Claims (1)

  It consists of a tungsten target with an effective focus of 0.3 mm or more and 0.6 mm or less so that a magnified photographing method with an enlargement ratio of 1.04 to 2.0 times is possible when the movement of the subject is not zero but is minute. The X-ray tube focal point, the X-ray input surface of the subject, the transmitted X-ray output surface of the subject, and the geometrical arrangement of the digital image detection system have a rotating anode X-ray tube. The distance between the transmission X-ray output surface of the subject and the digital image detection system is 4 cm or more and 50 cm or less so that the distance between the line input surfaces is 50 cm or more and 150 cm or less and the Gradel effect is effective. The distance of the detection system is 54 cm or more and 200 cm or less. Furthermore, it has a digital image detection system that exhibits a high-sensitivity response in the X-ray energy band of 70 KV to 80 KV, and an image display device that images the digital signal, and the digital image detection system reacts efficiently. In the case of a single-phase full-wave rectification method capable of high-voltage imaging with an X-ray tube voltage of 96 KV to 150 KV, and capable of short-time imaging of 0.01 seconds to 0.12 seconds, 20 mA or more X-ray image forming system having the function of having an X-ray generator

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