JP2005278880A - X-ray computer tomographic unit and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray CT unit and method capable of carrying out tomography of high contrast. <P>SOLUTION: The X-ray CT unit irradiates a patient H having an iodine contrast agent injected with X-rays and reproduces the distribution of a physical quantity in the patient based on the intensity distribution of the X-rays which has passed through the patient. The X-ray CT unit is provided with: a first X-ray radiator 3 which is rotated around the patient and irradiates the patient with X-rays having first X-ray energy; a second X-ray radiator 4 which is rotated around the patient and irradiates the patient with X-rays having second X-ray energy different from the first X-ray energy; first and second X-ray detectors 7 and 8 for detecting the intensity distribution of the X-rays which is emitted from the first and second X-ray radiators 3 and 4 and has passed through the patient; and a controller 10 for reproducing the distribution of the physical quantity in the patient based on the intensity distribution of the X-rays detected by the first and second X-ray detectors 7 and 8. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an X-ray computed tomography apparatus and an X-ray computed tomography method for reproducing a physical quantity distribution in a subject from an X-ray intensity distribution transmitted through the subject.

  An inspection method in which a contrast medium is injected into a blood vessel and X-ray imaging is performed is known. This test method is called an angiography type, and it can detect the difference in the absorption rate of contrast medium for living tissues and blood vessels as contrast, so that the lesions and hemodynamics of the circulatory system itself such as the heart, arteries, veins, It is used for the presence diagnosis and qualitative diagnosis of each organ.

  At present, as an angiography-type inspection device, the radiation emitted from a large electron beam accelerator or electron beam storage ring is split into two, irradiated onto the subject, and the intensity distribution of X-rays transmitted through the subject is measured. An apparatus is disclosed in which a difference is taken to image an inspection target part with high contrast.

  However, this inspection apparatus can not only perform tomography, but also requires a large electron accelerator and an electron beam storage ring, which increases the size of the apparatus.

Therefore, in recent years, as an angiography-type inspection apparatus that has solved this problem, an X-ray computed tomography apparatus that performs tomography of an inspection target part by rotating a set of X-ray sources and an X-ray detector around a subject. The structure is disclosed (for example, refer nonpatent literature 1).
“From the site where multi-slice CT is in operation” Yoshida Ida, Department of Radiology, Fujita Health University Hospital

  However, the above-described angiography type X-ray computed tomography apparatus has a problem that sufficient contrast cannot be obtained when there is not much difference in the absorption rate of the projection agent with respect to a living tissue or blood vessel.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an X-ray computed tomography apparatus and an X-ray computed tomography method capable of performing high-contrast tomography.

  In order to solve the above problems and achieve the object, the X-ray computed tomography apparatus and X-ray computed tomography method of the present invention are configured as follows.

(1) In an X-ray computed tomography apparatus that irradiates a subject into which a contrast agent has been injected with X-rays and reproduces a physical quantity distribution within the subject based on an intensity distribution of the X-rays transmitted through the subject The first X-ray irradiation means for rotating around the subject and irradiating the subject with X-rays having the first X-ray energy, and the first X with the subject interposed therebetween X-rays that are disposed opposite to the X-ray irradiation means, rotate around the subject integrally with the first X-ray irradiation means, and are irradiated from the first X-ray irradiation means and transmitted through the subject First X-ray detection means for detecting the intensity distribution of the X-ray, and X rotating around the subject and having a second X-ray energy different from the first X-ray energy toward the subject A second X-ray irradiating means for irradiating the line; The body is placed opposite to the second X-ray irradiation means, rotates around the subject integrally with the second X-ray irradiation means, and is irradiated from the second X-ray irradiation means. Second X-ray detection means for detecting the X-ray intensity distribution transmitted through the subject and the X-ray intensity distribution detected by the first and second X-ray detection means. And regenerating means for regenerating the physical quantity distribution in the specimen.

(2) The X-ray computed tomography apparatus described in (1), wherein the reproducing means includes the intensity distribution of the X-rays detected by the first X-ray detecting means and the second X-ray. A difference from the X-ray intensity distribution detected by the detection means is taken, and the physical quantity distribution in the subject is reproduced based on the difference.

(3) In the X-ray computed tomography apparatus described in (1), the first X-ray energy is an energy value immediately outside the X-ray absorption edge across the X-ray absorption edge of the contrast agent. There is a peak of intensity in one of the large portion and the small portion of the energy value immediately outside the X-ray absorption edge, and the second X-ray energy is X across the X-ray absorption edge of the contrast agent. Of the portion having a large energy value near the outer edge of the line absorption edge and the portion having a small energy value near the outer edge of the X-ray absorption edge, an intensity peak is present in a region that is not near the first X-ray energy peak. It is characterized by.

(4) In an X-ray computed tomography apparatus that irradiates a subject with X-rays and reproduces a physical quantity distribution in the subject based on an intensity distribution of the X-rays transmitted through the subject. The first X-ray irradiating means for irradiating the subject with X-rays while rotating and the first X-ray irradiating means are disposed opposite to the first X-ray irradiating means, and the first X-rays around the subject. First X-ray detection means for detecting an intensity distribution of X-rays irradiated from the first X-ray irradiation means and transmitted through the subject while rotating integrally with the irradiation means, and around the subject The second X-ray irradiating means for irradiating the subject with X-rays while rotating the object and the second X-ray irradiating means are arranged opposite to each other, and the second X-rays are disposed around the subject. While being rotated integrally with the irradiation unit, the second X-ray irradiation unit is irradiated with the irradiation target. Second X-ray detection means for detecting an intensity distribution of X-rays transmitted through the body, and the first X-ray irradiation means, the second X-ray detection means, and the second X-ray irradiation. And the first X-ray detection means are close to each other in the circumferential direction of the subject.

(5) In an X-ray computed tomography apparatus that irradiates a subject into which a contrast medium has been injected with X-rays and reproduces a physical quantity distribution in the subject based on the intensity distribution of the X-rays transmitted through the subject The X-ray irradiation means for rotating around the subject and irradiating the subject with X-rays having X-ray energy, and the X-ray irradiation means arranged opposite to the subject, X-ray detection means for rotating around the subject integrally with the X-ray irradiation means and detecting an intensity distribution of X-rays irradiated from the X-ray irradiation means and transmitted through the subject; and the X-rays And a reproducing means for reproducing the physical quantity distribution in the subject based on the X-ray intensity distribution detected by the detecting means, and an energy switching means for changing the energy amount of the X-ray energy. Toss .

(6) In an X-ray computed tomography method for irradiating a subject injected with a contrast agent with X-rays and reproducing a physical quantity distribution in the subject based on an intensity distribution of the X-rays transmitted through the subject An irradiation step of irradiating a plurality of types of X-rays having different energies toward the subject, a detection step of detecting the intensity distribution of the X-rays transmitted through the subject for each type, and the intensity distribution A difference obtaining step for obtaining a difference and a reproduction step for reproducing the physical quantity distribution in the subject based on the difference are provided.

  According to the present invention, high-contrast tomography can be performed.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  First, a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is an overall view of an X-ray computed tomography apparatus according to a first embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line AA in FIG.

  As shown in FIGS. 1 and 2, this X-ray computed tomography apparatus (hereinafter referred to as “X-ray CT apparatus”) has a rotating body 1. The rotating body 1 is formed in a ring shape, and is arranged so that its axis is substantially horizontal. The rotator 1 is provided with a drive device (not shown). By operating the drive device, the rotator 1 can be rotated around the axial center line at a desired speed.

  On the inner side of the rotating body 1, a bed 2 is provided substantially horizontally for a subject H (subject) to lie down. The bed 2 is structured to be movable with respect to the direction of the axis of the rotating body 1, and the subject H on the bed 2 is moved relative to the rotating body 1 by operating a driving device (not shown). Positioning. Note that an iodine contrast medium (contrast medium) containing iodine is injected into the blood vessel in the vicinity of the examination target portion of the subject H.

  FIG. 3 is a graph showing a relationship between X-ray energy and iodine, bone, and muscle X-ray absorption coefficients according to the embodiment.

As shown in FIG. 3, it can be seen that the X-ray absorption coefficient of iodine changes abruptly in the vicinity where the X-ray energy is 33.17 [keV]. Hereinafter, the X-ray energy (33.17 [keV]) when the X-ray absorption coefficient changes rapidly is referred to as “X-ray K absorption edge energy I ₀ ”.

  The X-ray absorption edge is the energy when the absorption coefficient (that is, absorption) suddenly increases when the X-ray absorption spectrum of a substance is measured, and the X-ray K absorption edge energy is X-ray absorption. This is the energy when X-ray absorption by electrons on the K shell changes discontinuously when electrons are knocked out of the K shell by.

  As shown in FIG. 1 and FIG. 2, a first X-ray irradiation device 3 (first X-ray irradiation means) and a second X-ray irradiation device 4 (second X-ray irradiation means) is provided. These first and second X-ray irradiation apparatuses 3 and 4 are arranged so as to be shifted by an angle θ with respect to the circumferential direction of the rotating body 1, and their emission ports are both directed toward the subject H.

  The angle θ is determined by the first X-ray irradiation device 3 and the second X-ray detector 8 (described later), and the second X-ray irradiation device 4 and the first X-ray detector 7 (described later). Is preferably larger in a range in which the two do not interfere. That is, it is preferable that the angle θ of the angle θ is small.

  FIG. 4 is a configuration diagram of the first and second X-ray irradiation apparatuses 3 and 4 according to the embodiment.

  As shown in FIG. 4, the first and second X-ray irradiation apparatuses 3 and 4 have an electron gun 5 and a target material 6. The electron gun 5 and the target material 6 are disposed to face each other, and when an electron beam is irradiated from the electron gun 5 to the target material 6, part of the energy of the electron beam is emitted from the surface of the target material 6 as X-rays.

  This X-ray energy is determined by the material of the target material 6. Therefore, in the present embodiment, cerium is used as the material of the target material 6 mounted on the first X-ray irradiation apparatus 3, and barium is used as the material of the target material 6 mounted on the second X-ray irradiation apparatus 4. Used.

By selecting this material, as shown in FIG. 3, the energy of X-rays emitted from the first X-ray irradiation apparatus 3 (hereinafter referred to as “first X-ray energy”) is the X-ray K absorption edge. An intensity peak value I ₁ (34.72 [keV]) is present immediately above the energy I ₀ , that is, at a portion having a large energy value immediately outside the absorption edge across the X-ray absorption edge, and the second X-ray irradiation apparatus The energy of X-rays emitted from 4 (hereinafter referred to as “second X-ray energy”) is directly below the X-ray K absorption edge energy I ₀ , that is, energy immediately outside the absorption edge across the X-ray absorption edge. A portion having a small value has an intensity peak value I ₂ (32.07 [keV]).

  Further, as shown in FIG. 1, a first X-ray detector 7 (first X-ray detection means) and a second X-ray detector 8 (second X-ray detector 8) are disposed on the inner peripheral surface of the rotating body 1. Line detection means) is provided. The first X-ray detector 7 and the second X-ray detector 8 are opposed to the first X-ray irradiation device 3 and the second X-ray irradiation device 4, respectively, and the detection surface thereof is the first. , Directed to the second X-ray irradiation device 3, 4 side.

  The first and second X-ray detectors 7 and 8 are composed of a plurality of scintillators 9. These scintillators 9 are arranged side by side with substantially no gap. Each of the scintillators 9 converts the intensity of the X-rays incident on the detection surface into an electric signal and outputs the electric signal. It can be detected.

  The electrical signal output from each scintillator 9 is displayed on the monitor 11 as a tomographic image of the inspection target part by being subjected to various processes by the control device 10. The details of the processing performed by the control device 10 will be described in detail in the following description of action.

  Next, an operation when the X-ray CT apparatus having the above-described configuration is used will be described.

  When performing tomography of the subject H using an X-ray CT apparatus, an iodine contrast agent is injected into a blood vessel in the vicinity of the examination target portion in advance.

  When the subject H lies on the bed 2, the X-rays are emitted from the first X-ray irradiation device 3 and the second X-ray irradiation device 4 at regular intervals while rotating the rotating body 1 around the subject H. . As a result, the subject H is irradiated with X-rays a plurality of times while the rotating body 1 makes one round around the subject H. Note that the timing of X-ray emission from the first X-ray irradiation apparatus 3 and the second X-ray irradiation apparatus 4 may be the same or different, but the time can be shortened by simultaneous emission.

  X-rays sequentially irradiated to the subject H are absorbed by the contrast medium in the living tissue and blood vessels when passing through the subject H, and after the intensity decreases, the first and second X-ray detectors 7 and 8 respectively. Detected. Therefore, a spatial intensity distribution is generated in the X-rays detected by the first and second X-ray detectors 7 and 8 in accordance with the inspection target part.

  The intensity distributions detected by the first and second X-ray detectors 7 and 8 are converted into electric signals by the photoelectric conversion action of each scintillator 9 and sequentially input to the control device 10. The control device 10 synthesizes a plurality of intensity distributions detected by the first X-ray detector 7 to create a first tomographic image in the examination target portion, and the second X-ray detector 8 detects the first tomographic image. A plurality of X-ray intensity distributions thus synthesized are combined to create a second tomographic image in the inspection target portion.

  Next, the control device 10 takes a difference between the first tomographic image and the second tomographic image, and creates a diagnostic image of the examination target portion.

Meanwhile, as shown in FIG. 3, the peak value I ₁ of the first X-ray energy is a value just above the X-ray K-edge energy I _0, the peak value I ₂ of the second X-ray energy X-ray a value just below the K-absorption edge energy I _0. Therefore, the X-ray absorption coefficient of iodine is extremely different between when the first X-ray energy is irradiated and when the second X-ray energy is irradiated. On the other hand, the X-ray absorption coefficients of the bones and muscles constituting the subject H are almost the same between the case where the first X-ray energy is applied and the case where the second energy is applied.

  Therefore, if the difference between the first tomographic image and the second tomographic image is taken, the intensity distribution of X-rays indicating bones and muscles cancels out, so that only blood vessels containing a large amount of contrast agent are high in the diagnostic image. Projected with contrast. This diagnostic image is output to the monitor 11 as a processing result and used as diagnostic material for a doctor or the like.

  According to the X-ray CT apparatus according to the present embodiment, the first X and the second X-ray irradiation apparatuses 3 and 4 that rotate around the subject H into which the iodine contrast medium is injected are used as the first X Irradiate X-rays having line energy and second X-ray energy from various angles, and create a first tomographic image of the inspection target portion based on a plurality of intensity distributions detected by the first X-ray detector 7 At the same time, a second tomographic image of the inspection target part is created based on the plurality of intensity distributions detected by the second X-ray detector 8, and the difference between the first and second tomographic images is taken. Thus, a diagnostic image for displaying the inspection target portion with high contrast is created.

  That is, the X-ray CT apparatus according to the present embodiment is an angiography type X-ray CT apparatus that uses two energy X-rays.

  Therefore, it is possible to perform tomography with higher contrast than in the past.

  Further, the first X-ray irradiation device 3 and the second X-ray irradiation device 4 are arranged as far as possible with respect to the circumferential direction of the rotating body 1. Therefore, the angle φ between the first X-ray irradiation device 3 and the second X-ray detector 8 and the angle φ between the second X-ray irradiation device 4 and the first X-ray detector 7 are small. Become.

  As a result, even if the X-ray emitted from the first X-ray irradiation device 3 is reflected by the surface of the subject H, the reflected light hardly enters the second X-ray detector 8, and the second X-ray Even if the X-rays emitted from the irradiation device 4 are reflected on the surface of the subject H, the reflected light hardly enters the first X-ray detector 7, so that the noise due to the reflected light is reduced and a clearer fault Shooting can be performed.

  FIG. 5 is a graph showing the relationship between the incident angle of X-rays and the reflection coefficient when the X-rays are irradiated to carbon mainly constituting the subject H according to the embodiment.

As shown in FIG. 5, it can be seen that the reflectance gradually increases as the X-ray irradiation angle decreases. This reflectivity is extremely small on the order of 10 ⁻¹⁹ , but it has been confirmed that it increases to several percent as the wavelength of X-rays increases.

  However, in the present embodiment, since the X-ray incident angle with respect to the subject H is increased by using the arrangement as described above, X-ray detection is possible even when long-wavelength X-rays are used. The devices 7 and 8 do not blur the tomography by collecting reflected light.

  Next, a second embodiment of the present invention will be described with reference to FIG. In addition, the description about the same structure and operation as the above embodiment is omitted here.

  FIG. 6 is an overall view of an X-ray CT apparatus according to the second embodiment of the present invention.

  As shown in FIG. 6, the X-ray CT apparatus includes an X-ray irradiation device 21 (X-ray irradiation means) and an X-ray detector 22 (X-ray detection means) on the inner peripheral surface of the rotating body 1. . The X-ray irradiation device 21 and the X-ray detector 22 are disposed to face each other, and can rotate around the subject H integrally with the rotating body 1.

  A switching device 23 (switching means) is connected to the X-ray irradiation device 21. The switching device 23 converts X-ray energy emitted from the X-ray irradiation device 21 into first X-ray energy and second X-ray energy in accordance with a command from the control device 10.

  Even with such a configuration, almost the same effect as the first embodiment can be obtained. However, since there is only one X-ray detector 22, X-rays of two types of energy cannot be performed at the same time. Therefore, tomography of the examination target portion of the subject H can be performed by the X-ray computed tomography method according to the present invention. In order to do so, it is necessary to make two rotations of the rotating body 1.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  For example, the rotary body 1 is provided with three or more X-ray irradiation devices and X-ray detectors for detecting X-rays emitted from these X-ray irradiation devices, and these X-ray irradiation devices and X-ray detectors are provided. You may make it perform tomography of the test subject H using.

  In addition, if there is a large difference in the absorption rate of the iodine contrast medium for the cell tissue and blood vessel, the tomogram with sufficiently high contrast can be obtained without taking the difference between the first tomographic image and the second tomographic image as in the above embodiment. Shooting can be performed.

  In this case, if the X-rays of the same energy are irradiated from the first X-ray irradiation apparatus and the second X-ray irradiation apparatus and the rotating body 1 is made a half turn around the subject H, the subject H is observed from all directions. Since X-rays are emitted toward, the time required for imaging can be reduced to about ½.

  Further, a contrast agent containing gadolinium may be used instead of the contrast agent containing iodine.

1 is an overall view of an X-ray computed tomography apparatus according to a first embodiment of the present invention. Sectional drawing which cut | disconnected FIG. 1 along the AA line. The graph which shows the relationship of the energy of the X-ray which concerns on the same embodiment, and the X-ray absorption coefficient of an iodine, a bone | frame, and a muscle. The block diagram of the 1st, 2nd X-ray irradiation apparatus which concerns on the same embodiment. The graph figure which shows the relationship between the incident angle of X-ray | X_line, and a reflection coefficient at the time of irradiating the X-ray | X_line mainly to the test subject who concerns on the same embodiment. The whole figure of the X-ray CT apparatus concerning the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... 1st X-ray irradiation apparatus (1st X-ray irradiation means), 4 ... 2nd X-ray irradiation apparatus (2nd X-ray irradiation means), 7 ... 1st X-ray detector (1st X-ray detection means), 8 ... second X-ray detector (second X-ray detection means), 10 ... control device (reproduction means), 21 ... X-ray irradiation apparatus (X-ray irradiation means), 22 ... X-ray detector (X-ray detection means), 23 ... switching device (switching means), H ... subject (subject), I ₀ ... X-ray K absorption edge energy (X-ray absorption edge energy), I ₁ ... first X-ray energy intensity peak value, I ₂ ... Second X-ray energy intensity peak value.

Claims (6)

In an X-ray computed tomography apparatus that irradiates a subject injected with a contrast agent with X-rays and reproduces a physical quantity distribution in the subject based on an intensity distribution of X-rays transmitted through the subject.
First X-ray irradiation means for rotating around the subject and irradiating the subject with X-rays having first X-ray energy;
The first X-ray irradiation unit is disposed opposite to the subject, and rotates around the subject integrally with the first X-ray irradiation unit, and from the first X-ray irradiation unit. First X-ray detection means for detecting an intensity distribution of X-rays irradiated and transmitted through the subject;
A second X-ray irradiation means for rotating around the subject and irradiating the subject with X-rays having a second X-ray energy different from the first X-ray energy;
The second X-ray irradiation unit is disposed opposite to the subject, and rotates around the subject integrally with the second X-ray irradiation unit and from the second X-ray irradiation unit. Second X-ray detection means for detecting an X-ray intensity distribution that has been irradiated and transmitted through the subject;
Reproduction means for reproducing the physical quantity distribution in the subject based on the X-ray intensity distribution detected by the first and second X-ray detection means;
An X-ray computed tomography apparatus comprising:   The reproduction means takes a difference between the X-ray intensity distribution detected by the first X-ray detection means and the X-ray intensity distribution detected by the second X-ray detection means, and uses this difference as a difference. The X-ray computed tomography apparatus according to claim 1, wherein the physical quantity distribution in the subject is reproduced based on the X-ray computed tomography apparatus.   The first X-ray energy is one of a portion having a large energy value immediately outside the X-ray absorption end and a portion having a small energy value immediately outside the X-ray absorption end across the X-ray absorption end of the contrast agent. The region has an intensity peak, and the second X-ray energy includes a portion having a large energy value immediately outside the X-ray absorption edge and an energy immediately outside the X-ray absorption edge across the X-ray absorption edge of the contrast agent. 2. The X-ray computed tomography apparatus according to claim 1, wherein an intensity peak is present in a region that is not in the vicinity of the first X-ray energy peak among portions having a small value. In an X-ray computed tomography apparatus that irradiates a subject with X-rays and reproduces a physical quantity distribution in the subject based on an intensity distribution of the X-rays transmitted through the subject.
First X-ray irradiation means for irradiating the subject with X-rays while rotating around the subject;
The subject is disposed opposite to the first X-ray irradiating means, and is irradiated from the first X-ray irradiating means while rotating integrally with the first X-ray irradiating means around the subject. First X-ray detection means for detecting an intensity distribution of X-rays transmitted through
Second X-ray irradiation means for irradiating the subject with X-rays while rotating around the subject;
The subject is disposed opposite to the second X-ray irradiation unit, and is irradiated from the second X-ray irradiation unit while rotating integrally with the second X-ray irradiation unit around the subject. Second X-ray detection means for detecting the intensity distribution of the X-rays transmitted through
Comprising
The proximity of the first X-ray irradiation means and the second X-ray detection means, and the second X-ray irradiation means and the first X-ray detection means in the circumferential direction of the subject; A featured X-ray computed tomography apparatus. In an X-ray computed tomography apparatus that irradiates a subject injected with a contrast agent with X-rays and reproduces a physical quantity distribution in the subject based on an intensity distribution of X-rays transmitted through the subject.
X-ray irradiation means for rotating around the subject and irradiating the subject with X-rays having X-ray energy;
The X-ray irradiation unit is disposed opposite to the subject, rotates around the subject integrally with the X-ray irradiation unit, and is irradiated from the X-ray irradiation unit and passes through the subject. X-ray detection means for detecting an X-ray intensity distribution;
Reproduction means for reproducing the physical quantity distribution in the subject based on the X-ray intensity distribution detected by the X-ray detection means;
Energy switching means for changing the amount of energy of the X-ray energy;
An X-ray computed tomography apparatus comprising: In the X-ray computed tomography method of irradiating a subject into which a contrast agent has been injected with X-rays and reproducing the physical quantity distribution in the subject based on the intensity distribution of the X-rays transmitted through the subject.
An irradiation step of irradiating a plurality of types of X-rays having different energies toward the subject;
A detection step of detecting, for each type, the intensity distribution of X-rays transmitted through the subject;
A difference acquisition step of acquiring a difference between the intensity distributions;
A reproduction step of reproducing the physical quantity distribution in the subject based on the difference;
An X-ray computed tomography method comprising:

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