JP2008054831A - Radiographic equipment and radiographic method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide radiographic equipment which obtains mutually different tomograms concerning the same section of a subject by photographing the subject in a short period in the equipment which photographs the same section of the subject using radiation having two parts whose energy distributions are different from each other. <P>SOLUTION: The equipment has a radiation source generating the radiation for irradiating the subject, a detection means detecting the radiation transmitted through the subject, and a rotation means relatively rotating the radiation source and the subject around a rotary shaft. The energy distributions of the radiation for irradiating the subject are made to be different from each other between the two parts sandwiching a plane including the rotary axis and crossing with the radiation source. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radiation imaging apparatus and a radiation imaging method.

  Conventionally, X-ray CT (Computed Tomography) apparatuses are often used for the purpose of medical diagnosis or nondestructive inspection. The X-ray CT apparatus is an apparatus that scans a subject with X-rays and constructs a tomographic image representing a state inside the subject by a computer based on obtained data. In the X-ray CT apparatus, X-rays are emitted from an X-ray tube to a subject, and X-rays transmitted through the subject are detected by an X-ray detector. This is called X-ray imaging, and the subject is imaged from an arbitrary angle while the X-ray tube and the X-ray detector are rotated together. On the other hand, X-ray imaging can be similarly performed even when the X-ray tube and the X-ray detector are fixed and the subject is rotated. When the subject is imaged a plurality of times from an arbitrary angle direction, the data obtained by the X-ray detector can be analyzed by a computer to obtain an image (tomographic image) in a cross section of the subject.

  In an X-ray CT apparatus, a dual energy scan is used in which the same part of a subject is imaged using a plurality of X-rays having different X-ray energy distributions. By taking such an image, tomographic images corresponding to the respective X-rays can be obtained, and the tomographic images are different from each other. This is because each part of the subject has different radiation absorption spectrum characteristics, and the X-ray transmittance in each part varies depending on the wavelength of the X-ray. Therefore, when a plurality of X-rays having different energy distributions are emitted to the subject, different tomographic images are obtained. Different tomographic images are used, for example, when a tomographic image of only a specific part is extracted by performing a difference calculation process between them.

  As an X-ray imaging apparatus using this dual energy scan, an X-ray computed tomography apparatus equipped with a multi-slice X-ray detector is known (see Patent Document 1). This imaging apparatus is configured to change the X-ray quality (X-ray energy distribution) along the slice direction (the direction of the rotation axis of the X-ray tube and the X-ray detector) using an X-ray filter. In this way, the X-ray tube and the X-ray detector are rotated in an integrated manner in order to obtain different tomographic images of the same part of the subject by imaging while changing the X-ray quality. There is no need to replace the X-ray filter.

In addition, there is an X-ray CT apparatus in which an X-ray filter is arranged so that X-ray quality is different between even channels and odd channels in the X-ray detector group (see Patent Document 2). In this apparatus, as described above, in the dual energy scan, it is not necessary to replace the X-ray filter while the X-ray tube and the X-ray detector are rotating integrally. Further, different X-ray energy data can be collected by one scan.
JP 2000-229076 A JP 63-82628 A

  However, in the X-ray imaging apparatus described in Patent Document 1, in order to obtain different tomographic images for the same part of the subject, the X-ray tube and the X-ray detector are integrally rotated once for imaging. Then, after that, the X-ray tube and the X-ray detector must be moved in the direction of their rotation axes and further rotated once to take an image. That is, since the X-ray tube and the X-ray detector are rotated a plurality of times in order to obtain different tomographic images for the same part of the subject, imaging takes a long time. This is more noticeable when imaging is performed with the X-ray tube and the X-ray detector fixed and only the subject rotated. This is because when the subject is rotated, the rotational speed of the subject cannot be increased, so that a long time is required for imaging.

  Further, in the X-ray CT apparatus described in Patent Document 2, since the X-ray filters are arranged so that the X-ray quality of the X-ray detector group is different between the even-numbered channel and the odd-numbered channel, it is used for imaging. The number of channels is halved. Therefore, although the spatial resolution is halved, it is compensated by devising a data processing method. However, the processing method is complicated, and it takes a lot of time for processing, and the demerit due to halving the spatial resolution is great.

  Accordingly, the present invention provides a radiation imaging apparatus capable of imaging a subject in a short time in an apparatus for imaging the same part of the subject using radiation having two portions having different energy distributions. With the goal.

  The present invention also provides a radiation imaging method capable of imaging a subject in a short time in a method for imaging the same part of the subject using radiation having two portions having different energy distributions. With the goal.

  In the present invention, in order to solve the above-described problems, a radiation source that generates radiation for irradiating the subject, detection means for detecting radiation that has passed through the subject, the radiation source, and the subject And a rotating means for relatively rotating about the rotation axis, and the energy distribution of the radiation irradiated to the subject is in two parts sandwiching a plane including the rotation axis and intersecting the radiation source A radiographic apparatus characterized by being different from each other is provided.

  In the present invention, a radiation source generates radiation for irradiating the subject, a step of rotating the radiation source and the subject relative to each other about a rotation axis, and transmission through the subject. And the step of detecting the radiation, wherein the energy distribution of the radiation applied to the subject is different from each other in two portions including a plane that includes the rotation axis and intersects the radiation source. A radiography method is provided.

  According to the present invention, imaging of a subject using radiation having two portions having different energy distributions can be performed in a short time.

  Embodiments of the present invention will be described below with reference to the drawings. In the following embodiments, an X-ray CT imaging apparatus that images an object using X-rays will be described. However, the present invention can also be applied to an imaging apparatus using other radiation.

  FIG. 1 shows an outline of an X-ray CT imaging apparatus in Embodiment 1 of the present invention. FIG. 2 is a view of the X-ray CT imaging apparatus of FIG. A subject 3 is disposed between an X-ray tube 1 that is a radiation source that generates radiation and an X-ray detector 2 that is detection means for detecting radiation. The subject 3 is placed on a rotary table 4 that is a rotating means, and rotates around the rotary shaft 6 in the direction of the arrow shown in FIG. As shown in FIGS. 1 and 2, X-rays are emitted radially from the focal point 1a of the X-ray tube 1 in the direction of the rotation axis 6 (Y direction shown in FIGS. 1 and 2). This direction is the X-ray traveling direction.

  Between the X-ray tube 1 and the subject 3, an X-ray filter 5 that changes the quality of X-rays emitted from the X-ray tube 1 is disposed.

  Regarding the quality of X-rays, X-rays with strong penetrating power are called hard X-rays and X-rays with low penetrating power are soft X-rays, based on whether or not X-rays easily pass through substances (transmitting power) However, it expresses qualitative differences in X-rays. Specifically, this will be described with reference to FIG. As X-rays pass through the material, they cause an interaction that reduces their strength. The intensity after a single wavelength of X-rays passes through the material is expressed as an exponential function of the thickness of the material through which the X-rays pass and the attenuation coefficient. Here, the attenuation coefficient indicates the degree of interaction between the X-ray and the substance, and is determined by the type of the substance and the energy of the X-ray. FIG. 7A shows the relationship between the X-ray energy and the attenuation coefficient when X-rays pass through a certain substance. As can be seen from FIG. 7A, when the X-ray energy is small, the attenuation coefficient is large, and when the X-ray energy is large, the attenuation coefficient is small. That is, when the X-ray energy is small, the penetrating power is weak and called soft X-ray, and when the X-ray energy is large, the penetrating power is strong and called hard X-ray. Since the energy of X-rays is inversely proportional to the wavelength, the difference in the quality of the beam can be expressed by the magnitude of the wavelength.

  The X-ray filter 5 has an action of changing the X-ray quality. The X-ray filter 5 is, for example, an aluminum plate, a titanium plate, an iron plate, a copper plate, or the like. FIG. 7B shows the relationship between the X-ray energy and the attenuation coefficient when X-rays pass through the aluminum plate, titanium plate, and iron plate. As shown in FIG. 7B, it can be seen that the attenuation coefficient for a certain X-ray energy differs depending on the substance (filter) that passes therethrough. Usually, the X-rays radiated from the X-ray tube 1 are continuous spectrum X-rays, and the energy distribution of the X-rays is a curve in the case of no filter shown in FIG. The relative value on the vertical axis is the relative intensity of X-rays. When the X-rays radiated from the X-ray tube 1 pass through the filter having the above characteristics, the relative value peaks shift as shown in 81 and 82 shown in FIG. 8A, and the relative value decreases. 81 is a case of a high energy region pass filter made of a copper plate, for example, and 82 is a case of a low energy region pass filter called a so-called K absorption edge filter made of La, Y or the like. That is, the energy distribution of X-rays can be changed by providing a filter. Note that even if the filters are made of the same material as shown in FIG. 8B, the energy distribution of the X-rays can be changed by changing the thickness thereof.

  The X-ray filter 5 includes two filters 5A and 5B that change the energy distribution of transmitted X-rays to different energy distributions, and the filters 5A and 5B are arranged as shown in FIGS. That is, the X-ray filter 5 crosses the X-ray energy distribution irradiated to the subject 3 with the X-ray tube 1 including the plane 1 including the focal point 1 a of the X-ray tube 1 and the rotation axis 6, that is, the rotation axis 6. The two parts across the plane are different from each other. For example, as described above, 5A can be a high energy region pass filter, and 5B can be a low energy region pass filter. When the X-rays generated from the X-ray tube 1 pass through the X-ray filter 5, the energy distribution is changed, and the subject 3 is irradiated. Here, the energy distribution of the X-rays transmitted through the X-ray filter 5 is a direction perpendicular to the rotation axis 6 and perpendicular to the traveling direction of the X-rays radiated from the X-ray tube 1 (see FIG. 1). The X direction is different). However, the X-ray energy distribution is not different in the direction of the rotation axis 6.

  Then, X-ray imaging of the subject 3 is performed by detecting the emitted X-rays including the X-rays transmitted through the subject 3 with the X-ray detector 2. The X-ray detector 2 includes an electric circuit such as a scintillator, a light detection element, and an AD converter, and converts X-rays detected by the light detection element into a digital signal via the AD converter. Here, instead of the scintillator and the light detection element, an element that directly converts an X-ray into an analog signal may be used.

  FIG. 3 shows a block diagram of the X-ray CT imaging apparatus in the present embodiment. When an imaging start signal is input from the input unit 31 to the control unit 32, the control unit 32 sends an imaging start signal to the X-ray tube 1, the X-ray detector 2, and the drive unit 33 of the rotary table 4. Then, radiation is generated from the X-ray tube 1, X-rays are irradiated to the subject 3 through the X-ray filter 5, and X-rays transmitted through the subject 3 are detected by the X-ray detector 2. The digital signal converted by the X-ray detector 2 is sent to the control unit 32 as X-ray data detected by the X-ray detector 2. In the control unit 32, data calculation processing is performed using data appropriately stored in the storage unit 34. The control part 32 and the memory | storage part 34 comprise the computer 35 mentioned later, and can be used as a part of X-ray CT imaging apparatus. Further, it may be provided separately from the device, and data storage and arithmetic processing can be performed outside the device.

  FIG. 4 shows a flow of signal processing performed in the X-ray imaging and the computer 35. When the shooting start signal is input to the control unit 32, first, shooting is performed (S1). The X-ray is detected by the X-ray detector 2, and the digital signal converted by the X-ray detector 2 is sent to the control unit 32 as X-ray data detected by the X-ray detector 2. The X-ray data sent to the control unit 32 is temporarily stored in the storage unit 34 (S2).

  When imaging of the subject is performed, the rotary table 4 rotates, and X-ray imaging of the subject 3 is repeated at a predetermined rotation angle interval, and the data obtained from the X-ray detector 2 is sequentially transferred to the data. It is stored in the storage unit 34. The rotation angle of the turntable 4 is detected by the angle detector 36 and sent to the controller 32. When the rotation angle reaches a predetermined rotation angle, an imaging signal is input to the X-ray detector 2 and imaging is performed. When the turntable 4 is rotated 360 degrees (one rotation) (S3), the photographing is finished. Then, using the data stored in the data storage unit 34, a tomographic image of the subject 3 in the imaging region 8 shown in FIG. 1 is obtained. Obtaining a tomographic image in this way is called reconstruction.

  As shown in FIG. 8, the X-rays radiated to the subject have different energy distributions in the two portions described above. Therefore, on the surface of the X-ray detector 2 irradiated with X-rays, the X-ray data detected on the left surface 2A with the line 7 connecting the focal point 1a of the X-ray tube 1 and the rotating shaft 6 as a boundary is the line 7 is different from the X-ray data detected on the right surface 2B. Therefore, the data obtained from the X-ray detector 2 includes X-ray data having different energy distributions.

  When reconstructing, first, X-ray data having different energy distributions are separated for each type of X-ray, and a tomographic image of the subject corresponding to each is reconstructed. Specifically, the X-ray data obtained by the X-ray detector 2 is separated into the data obtained on the surface 2A and the data obtained on the surface 2B, and the object 3 corresponding to each data is separated. The tomographic image is reconstructed, and two different tomographic images are obtained simultaneously or sequentially (S4). The obtained tomographic image is stored in the storage unit 34 (S5), and is displayed on the image display unit 37 such as a display as it is (S8) when the difference calculation described later is not performed. When the difference calculation is performed, a difference calculation between tomographic images described later is performed (S7), and then displayed on the image display unit 37 (S8).

  The above difference calculation is called so-called subtraction. In this subtraction, two radiographic images taken under different conditions are photoelectrically read out to obtain digital image signals, and then these digital image signals are subtracted by associating each pixel of both images. Here, each image is appropriately weighted, and a subtraction process is performed. And the difference signal for forming the image in the specific site | part in each image is obtained. A radiographic image in which only a specific structure is extracted can be reproduced using the difference signal thus obtained. Therefore, by extracting and displaying only a specific part of the subject, it is possible to observe only the specific part.

  The above image reconstruction and subtraction are digital signal information processing, and can be implemented as a software function (program) of a computer system. Here, the software function of the computer system includes programming including executable code, and can perform image reconstruction and subtraction. The software code can be executed on a general purpose computer. During software code operation, the code or associated data record is stored within a general purpose computer platform. In other cases, however, the software may be stored elsewhere or loaded into a suitable general purpose computer system. Thus, the software code can be held on at least one machine-readable medium as one or more modules. The invention described below can be described in the form of the code described above and can function as one or more software products. The software code is executed by the processor of the computer system. The computer platform may implement the methods shown herein or the software download function.

  A computer 35 shown in FIG. 3 is a computer that executes image processing from data reconstruction (S4) to difference calculation (S7) shown in FIG. 4, and may be incorporated in the X-ray CT imaging apparatus. It may be a remote computer connected by a network. The control unit 32 is, for example, a CPU, GPU, DSP, or microcomputer, and further includes a cache memory for temporary storage. The display unit 37 is a display device such as a CRT display or a liquid crystal display. The storage unit 34 is, for example, a memory or a hard disk. The input unit 31 is, for example, a keyboard or a mouse. The machine-readable medium is a floppy (registered trademark) disk, a CD-ROM, a USB memory, or the like.

  According to the present embodiment, since the subject 3 is imaged by rotating the subject 3 once, imaging can be completed in a short time, and different tomographic images can be obtained for the same part of the subject 3.

  Therefore, the radiation exposure amount of the radiation that the subject 3 is exposed to is reduced, and between the different tomographic images at the same position in the rotation axis direction, due to the data collection timing shift by the X-ray detector and the body movement of the subject. The displacement of the shape and position of the part of the subject can be reduced.

  Furthermore, in this embodiment, the positional deviation of the part of the subject between the tomographic images due to the data collection timing deviation and the body movement of the subject 3 is reduced, and the difference calculation processing between the tomographic images can be performed satisfactorily. . This is because different tomographic images are reconstructed based on data obtained during one rotation of the subject 3.

  In the above description, the subject 3 is rotated for imaging, but the subject 3 is fixed and the X-ray tube 1 and the X-ray detector 2 are rotated integrally as shown in FIG. But there are similar effects. Alternatively, the X-ray detector 2 may be arranged in a cylindrical shape around the subject 3 and only the X-ray tube 1 may be rotated around the subject 3 to perform imaging. Further, imaging may be performed by rotating the subject 3 and also rotating the X-ray tube 1 and the X-ray detector 2 together.

  In addition, as shown in FIG. 6, the same effect can be obtained even when the X-ray filter 5 is emitted only to 5A, that is, only to one side of the imaging region 8, the radiation transmitted through the X-ray filter 5 is emitted.

  Further, the same effect can be obtained if the X-ray tube 1 generates X-rays having different energy distributions and the energy distributions on the left and right sides of the line 7 are different. On the surface of the X-ray detector 2 that is irradiated with X-rays, the energy distribution of X-rays detected on the left surface 2A with the line 7 connecting the X-ray tube 1 and the rotary shaft 6 as the boundary is the right side of the line 7 This is different from the X-ray energy distribution detected on the surface 2B.

1 is a schematic view of an X-ray CT imaging apparatus according to the present invention. 2 is a schematic view of the X-ray CT imaging apparatus of FIG. 1 is a block diagram of an X-ray CT imaging apparatus according to the present invention. It is a figure which shows the flow of the signal processing performed in the X-ray imaging and computer in this invention. 1 is a schematic view of an X-ray CT imaging apparatus in which an X-ray tube and an X-ray detector rotate integrally. 1 is a schematic view of an X-ray CT imaging apparatus using an X-ray filter only on one side. It is a figure which shows the relationship between the energy of X-ray | X_line, and an attenuation coefficient. It is a figure which shows energy distribution of X-ray | X_line.

Explanation of symbols

1 X-ray tube 2 X-ray detector 3 Subject 4 Rotating table 5 X-ray filter 6 Rotating shaft

Claims (6)

A radiation source for generating radiation for irradiating the subject;
Detection means for detecting radiation transmitted through the subject;
Rotating means for relatively rotating the radiation source and the subject around a rotation axis,
A radiation imaging apparatus, wherein energy distributions of radiation irradiated to the subject are different from each other in two portions including a plane that includes the rotation axis and intersects the radiation source.   The radiation imaging apparatus according to claim 1, further comprising a radiation filter that makes the energy distribution different from each other in the two portions.   The radiation imaging apparatus according to claim 1, wherein the radiation sources generate radiation having different energy distributions, and the energy distributions differ from each other in the two portions.   2. The apparatus according to claim 1, further comprising means for obtaining different tomographic images at the same part of the subject based on radiation data detected by the detecting means, and calculating a difference between the tomographic images. The radiation imaging apparatus according to any one of 3. A radiation source generating radiation for irradiating the subject; and
Rotating the radiation source and the subject relative to each other about a rotation axis;
Detecting the radiation transmitted through the subject,
A radiation imaging method, wherein energy distributions of radiation irradiated to the subject are different from each other in two portions including a plane that includes the rotation axis and intersects the radiation source.   A computer performs a step of obtaining different tomographic images at the same part of the subject based on radiation data detected by the radiographic method according to claim 5 and performing a difference calculation between the tomographic images. Program for.

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