JP2013146480A - X-ray detector, x-ray computed tomography method utilizing the x-ray detector, and x-ray computed tomography system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and system to measure soft tissue, a contrast medium and a bone in a subject by X-ray transmission imaging.SOLUTION: In an X-ray detector 3, a plurality of X-ray detecting elements 3a-3d generating a charge by energy applied by X rays incident after transmitting a subject S are arranged in a row on an X-ray incident line such that their distances from an incident end are different from one another, and absorbents 3e, 3f absorbing and attenuating a part of the X rays are disposed at a plurality of points between the detecting elements in the X-ray detecting elements row. The X-ray detector determines the thicknesses of soft tissue, a contrast medium and a bone by thickness operation from ratios of output current values of the plurality of the X-ray detecting elements of the X-ray detector.

Description

  The present invention relates to an X-ray detector, an X-ray computed tomography (X-ray CT) method and an X-ray computed tomography system using the X-ray detector. Specifically, the X-ray detector arranges a plurality of X-ray detection elements that generate electric charges by the energy applied by the incident X-rays and output a current in a line in the X-ray traveling direction. A configuration in which an absorber is arranged on the X-ray incident side of a plurality of X-ray detection elements excluding the frontmost of the line detection elements, and X-ray transmission from two directions of the subject using this X-ray detector is used. The present invention relates to an X-ray computed tomography (X-ray CT) method and an X-ray computed tomography system for obtaining a preferable CT image (data) by performing imaging.

  In order to observe a lesion inside a human body (subject), particularly a cancer tissue, an X-ray transmission imaging method is used. It is possible to detect cancer tissue by so-called X-ray imaging in which X-rays are incident from one direction of the human body and the number of X-rays transmitted to the opposite side across the human body is measured. Computed tomography in which such measurement is performed from a direction of 360 degrees with respect to the human body to acquire a large number of X-ray transmission image data, and the data is processed by a computer to reconstruct an image (data). By performing (CT), a more detailed image (data) can be obtained, and a smaller cancer tissue can be found. According to this image processing, it is possible to obtain a tomographic image as if the human body was cut in a circle, and for example, it becomes easy to observe cancer tissue on the back side of the bone.

  In this X-ray CT, in order to measure the X-ray, for example, the X-ray is absorbed by a NaI (Tl) scintillator, the light generated by this scintillator is converted into electrons by a photomultiplier tube, etc., and further amplified. taking measurement. At this time, the energy of each X-ray is not measured, the light generated by a large number of X-rays absorbed by the NaI (Tl) scintillator is measured as a current value, and the amount of X-rays that have passed through the human body is measured. The average X-ray absorption coefficient on the line through which the X-ray has passed is derived to determine the presence or absence of cancer tissue.

  However, originally, cancer tissue is also a kind of human tissue, and the X-ray absorption coefficient of cancer tissue is not much different from that of normal tissue. For this reason, it is not easy to distinguish cancer tissue from normal tissue only by the amount of X-ray absorption. Therefore, in general, an iodine contrast agent is injected into the human body in advance to facilitate identification. That is, since the ratio of blood vessels in cancer tissues is larger than that in normal tissues, the ratio of iodine contrast medium injected into the blood vessels in the cancer tissues is larger than that in normal tissues. Since iodine has an X-ray absorption edge at 33.2 keV and a large absorption, a tissue with a high iodine content can be identified as a cancer tissue.

  Although the absorption of X-rays can be increased by using an iodine contrast agent, it cannot be determined that the absorption is due to iodine only by the amount of X-ray absorption. That is, X-rays are absorbed even by calcium adhering to blood vessels, and iodine and calcium are often indistinguishable. In order to identify such a substance, when a conventional X-ray CT apparatus is used, the X-ray tube voltage is changed to, for example, 100 kVp and 140 kVp, and X-ray irradiation is performed twice. The effective energy of X-rays at each acceleration voltage is 62 keV and 74 keV, and the absorption coefficient differs for each substance as a function of energy, so that iodine and calcium can be distinguished.

In such a conventional measurement method, in order to identify a substance, the acceleration voltage is changed two or more times.
Since CT measurement is required and X-ray transmission image data needs to be acquired by performing imaging a number of times from 360 degrees at a time, the exposure dose of the subject increases. Further, when X-rays are measured as current, low energy X-rays are preferentially absorbed while the X-rays pass through the subject, and the ratio of high energy X-rays increases after passing through the subject. This is called a beam hardening effect. When this beam hardening effect occurs, the number of X-rays having an energy of about 33.2 to 40 keV, which is easily absorbed by iodine, is reduced, so that it is difficult to observe the effect of absorption by iodine.

  In order to overcome such drawbacks, a “transXend detector” has been developed that obtains X-ray energy information while measuring X-rays as current as usual (Non-patent Document 1).

  The transXend detector includes a plurality of X-ray detection elements arranged in the X-ray traveling direction. According to this transXend detector, an X-ray energy distribution can be obtained by unfolding by obtaining a response function of each X-ray detection element to the X-ray.

It is desirable that the response functions of the X-ray detection elements in this transXend detector change mutually. The transXend detector, which consists of X-ray detectors with similar response functions, has a large number of initial estimated energy distributions because the unfolding result greatly affects the initial estimated energy distribution. An analysis method of selecting an energy distribution is taken.

On the other hand, by using a scintillator having a different effective atomic number and density as the X-ray detection element, the response function of each X-ray detection element changes, and a stable solution that does not depend on the initial estimated energy distribution can be obtained. It has been proposed that CT measurement using a smaller X-ray dose is possible (Patent Document 4, Non-Patent Document 2).

However, since these X-ray detectors are arranged with X-ray detection elements of the same form, the configuration is simplified, and an excellent feature is that detection of high-dose X-rays and collection of energy information can be performed simultaneously. However, since the response characteristics with respect to the energy of the incident X-ray of each X-ray detection element are similar, there has been a problem that a large amount of calculation is required to obtain energy information with high accuracy. In addition, in order to accurately obtain the thickness of iodine on the X-ray passing line as an analysis result, it was necessary to prepare a large number of initial estimated X-ray energy distributions and input them to the unfolding code. Furthermore, it is necessary to use the response function obtained with respect to the distance that the X-ray has passed through the subject for the analysis. For this reason, the X-ray is measured at each measurement point using the CT image data reconstructed from the measured current value. It was necessary to calculate the distance that passed through the subject.

Japanese Patent Laying-Open No. 2005-077752 JP 2004-223158 A JP 2007-071602 A Japanese Patent Application No. 2011-050851 and drawings Japanese Patent Application No. 2011-195023 specification and drawings

I. Kanno, R. Imamura, K. Mikami, A. Uesaka, M. Hashimoto, M. Ohtaka, K. Ara, S. Nomiya, and H. Onabe, "A Current Mode Detector for Unfolding X-ray Energy Distribution" , J. Nucl.Sci. And Technol., 45, 1165-1170 (2008). I. Kanno, Y. Minami, R. Imamura, H. Shimazaki, K. Fukuda, M. Ohtaka, M. Hashimoto, K. Ara and H. Onabe, "Advantages of Resopnse Function Change in a transXend Detector with Various Scintillators as Substrates of Segment Detectors ", J. Nucl. Sci. And Technol., 48, 1377-1384 (2011).

  In view of the problems of the prior art, an object of the present invention is an X-ray computed tomography method capable of simplifying image analysis after imaging, with a small number of X-ray transmission imaging, the imaging direction being about two directions, An object of the present invention is to realize an X-ray computed tomography method, an X-ray computed tomography system and a radiation detector with a small exposure dose of a human body as a subject.

  Specifically, the "radiation detector" proposed in Japanese Patent Application No. 2011-050851 (Patent Document 4) and Japanese Patent Application No. 2011-195023 (Patent Document 5), which the inventors of the present application studied and applied for a patent, is further improved. By adopting it, the above-mentioned problems are solved.

  One feature of the X-ray detector of the present invention is that a plurality of X-ray detection elements that generate charges by energy applied by X-rays that have passed through the subject and incident are incident on the X-ray incident line from the incident end. It is arranged in a line so that the distances are different from each other, and an absorber that absorbs and attenuates part of the X-rays is installed at a plurality of positions between the detection elements in the X-ray detection element column. There is.

  The absorber is a material containing an element from Al of atomic number 13 to Bi of atomic number 83 (excluding Tc of atomic number 43 and Pm of atomic number 61).

  Each of the X-ray detection elements is composed of a detection medium made of the same material, and at least four of them are arranged in a line on the X-ray incident line, and the absorber is the X-ray detection element of the X-ray detection element. It is characterized in that it is arranged on the X-ray incident end side of the X-ray detection element in the middle part of the row and the last X-ray detection element.

  One feature of the X-ray computed tomography method of the present invention is that X-ray transmission imaging of a subject is performed using the X-ray detector, and output currents of a plurality of X-ray detection elements of the X-ray detector. The thickness of the soft tissue, contrast medium, and bone in the subject is measured by calculating the thickness from the ratio of the values.

  The plurality of tissues in the subject are human soft tissue, cancer tissue, and bone tissue.

  The outer shape of the subject is obtained based on surface shape image data obtained by surface shape measurement using a laser and soft tissue image data in the subject obtained by X-ray transmission imaging. In addition, the shapes of soft tissue, contrast medium (cancer tissue) and bone tissue are synthesized and displayed.

  One feature of the X-ray computed tomography system of the present invention is that the X-ray detector, means for performing X-ray transmission imaging of a subject using the X-ray detector, and the X-ray detector An object of the present invention is to provide a calculation apparatus that measures the thickness of soft tissue, contrast medium, and bone in a subject by calculation from the ratio of output current values of a plurality of X-ray detection elements.

Then, the outer shape of the subject is obtained based on the surface shape image data obtained by measuring the surface shape of the subject using a laser and the image data of the soft tissue in the subject obtained by the X-ray transmission imaging. The shape of the soft tissue, contrast medium, and bone is synthesized and displayed in the outer shape of the display.

  According to the present invention, the presence or absence of a cancer tissue containing an iodine contrast agent can be identified by X-ray transmission imaging with a small exposure dose.

  In addition, two-dimensional transmission image data that can identify the position and shape of cancer tissue in the human body can be obtained by two X-ray transmissions with different imaging directions. Can be done in time.

  Therefore, it is possible to realize an X-ray CT measurement method and system that can reduce the exposure dose by X-ray transmission imaging as compared with conventional X-ray CT.

  Furthermore, this low exposure X-ray CT can be applied to a wide range of medical fields including health checkups because the cumulative exposure dose is low even after many visits.

  Moreover, according to the X-ray detector, X-ray computed tomography method and system of the present invention, it can be applied not only to iodine but also to detection of other substances having an X-ray absorption edge of several tens keV. .

It is a schematic block diagram which shows the Example of the X-ray inspection apparatus using the radiation detector of this invention. It is the schematic which shows the Example of the radiation detector of this invention. It is a two-dimensional map of acrylic thickness-iodine thickness. 4 is a stepped phantom of acrylic and iodine used to obtain the two-dimensional map shown in FIG. This is a phantom used for measurement to verify acrylic thickness and iodine thickness. FIG. 5 shows distributions of acrylic thickness and iodine thickness obtained as a result of measuring the phantom shown in FIG. 5 for verification. It is a three-dimensional map of acrylic thickness, iodine thickness, and aluminum thickness. (A) is a two-dimensional map of acrylic thickness-iodine thickness, and (b) is a two-dimensional map of acrylic thickness-aluminum thickness. This is a phantom used for measurement for verification of acrylic thickness, iodine thickness and aluminum thickness. As a result of measuring the phantom shown in FIG. 9 for verification, it is the distribution of acrylic thickness-iodine thickness and acrylic thickness-aluminum thickness obtained. It is distribution of acrylic thickness, iodine thickness, and aluminum thickness which were obtained by analyzing the results obtained as shown in FIG. It is a flowchart of an imaging process. (A) is a flowchart of elemental three-dimensional image creation processing, and (b) is a conceptual diagram showing the relationship between elemental thickness data obtained by imaging from two directions. (C) is a conceptual diagram showing the relationship between elemental thickness data obtained by imaging from two directions.

In the X-ray detector of the present invention, a plurality of X-ray detection elements that generate charges by energy applied by X-rays that have passed through a subject and are incident on the X-ray incident line have different distances from the incident end. It is arranged in a row so as to be in a position, and an absorber that absorbs and attenuates a part of the X-rays is installed at a plurality of positions between the detection elements of this X-ray detection element row,
The absorber is selected from materials containing elements from Al of atomic number 13 to Bi of atomic number 83 (except for Tc of atomic number 43 and Pm of atomic number 61), and upstream of the X-ray traveling direction Arranged so that the element number increases from the
Each of the X-ray detection elements is composed of a detection medium made of the same material, and at least four of them are arranged in a line on the X-ray incident line, and the absorber is arranged in a row of the X-ray detection elements. The X-ray detection element in the middle part and the last X-ray detection element are arranged on the X-ray incident end side.

  In the X-ray computed tomography method of the present invention, X-ray transmission imaging is performed from two directions of a subject using the X-ray detector, and a ratio of output current values of a plurality of X-ray detection elements of the X-ray detector is measured. The thickness of the soft tissue, contrast medium, and bone (human soft tissue, cancer tissue, bone tissue) in the subject is measured by calculating the thickness. The outer shape of the subject is obtained based on the surface shape image data obtained by surface shape measurement using a laser and the image data of the soft tissue in the subject obtained by the X-ray transmission imaging, and the soft tissue is included in the outer shape of the subject. The contrast agent and the shape of the bone are synthesized and displayed.

  The X-ray computed tomography system of the present invention includes means for performing X-ray transmission imaging from two directions of a subject using the X-ray detector, and output currents of a plurality of X-ray detection elements of the X-ray detector. A configuration is provided with a calculation device that measures the soft tissue, contrast medium, and bone thickness in the subject by calculation from the ratio of the values. The outer shape of the subject is measured by measuring the surface shape of the subject using a laser. It is obtained on the basis of the surface shape image data and the image data of the soft tissue in the subject obtained by the X-ray transmission imaging, and the soft tissue, the contrast agent and the shape of the bone are synthesized and displayed in the outer shape of the subject.

In the X-ray computed tomography method and system, the ratios I ₂ / I ₁ and I _{3 of the} current values I _{1 to} I ₃ output from the X-ray detection element of the X-ray detector by the X-rays passing through the subject.
By calculating and using / I ₁ , it is possible to estimate the thickness of the soft tissue and iodine of the human body on the line through which X-rays pass and to identify the presence or absence of cancer tissue by one transmission imaging. . Here, I ₁ is an output current value obtained from the frontmost X-ray detection element in the X-ray traveling direction, and I ₂ is an output current obtained from the X-ray detection element located behind the frontmost X-ray detection element. The value I ₃ is an output current value obtained from the X-ray detection element positioned further rearward of the X-ray detection element positioned rearward. The absorber functions to increase the values of the current value ratios I ₂ / I ₁ and I ₃ / I ₁ to facilitate thickness calculation.

  In addition, by performing X-ray transmission imaging from the front and side directions of the human body, the position and shape of the cancer tissue in the human body can be identified three-dimensionally with a small exposure dose. This is what makes shooting possible.

In the human body, there are bones in addition to soft tissues and cancer tissues, but soft tissue, cancer tissues (iodine) and bones can be identified by this X-ray transmission imaging. At this time, the output current value I ₄ output from the X-ray detection element located further rearward is also used, and I ₄ / I ₁ or I ₄ / I ₃ is further calculated and used.

  Embodiments of an X-ray computed tomography method, an X-ray computed tomography system, and an X-ray detector according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing an embodiment of an X-ray inspection apparatus using an X-ray detector, and FIG. 2 is a schematic diagram showing an embodiment of the X-ray detector.

As shown in FIG. 1, an X-ray inspection apparatus 1 according to the first embodiment includes an X-ray detector array 4 having a X-ray tube 2 and an X-ray detector 3 arranged vertically and horizontally, a preamplifier 5, and a main amplifier. 6 and 2 to 3 types of dividers 7 and 8, a soft tissue thickness-contrast agent thickness and bone thickness calculation device 9, a thickness calculation support means 10, an imaging device 11 and the like.
<X-ray detector>
The X-ray detector 3 of the present embodiment will be described in detail. In the following description, an embodiment in which a Si (Li-containing) semiconductor is used as the material (medium) of the X-ray detection element will be described with reference to FIG. 2, but other types of semiconductors such as CdTe can also be used. Further, a base material of a general X-ray detector such as various scintillators can be used.

  In addition, the number of X-ray detection elements arranged in the X-ray traveling direction is preferably 3 or more because energy information can be obtained more accurately as the number increases. However, if the number is excessively large, the cost for manufacturing the X-ray detector increases. Three are sufficient to determine the thickness of soft tissue and iodine (cancer tissue), and four are sufficient to determine the thickness of bone.

As shown in FIG. 2, the X-ray detector 3 of the present embodiment includes four X-ray detection elements 3a, 3b, 3c, and 3d made of Si (Li-containing) semiconductor. The four X-ray detection elements 3a, 3b, 3c, and 3d are installed in a line in order along the X-ray incident (advance) direction. Currents I _{1 to} I ₄ output from the four X-ray detection elements 3a, 3b, 3c, and 3d are input to the preamplifier 5 (5a to 5d) described above. In front of the third and fourth X-ray detection elements 3c and 3d in the X-ray traveling direction, a tin absorber 3e having a thickness of 60 μm that absorbs and attenuates a low energy component of the passing X-ray and a thickness of 75 μm. A gadolinium absorber 3f is provided. The thicknesses of the absorbers 3e and 3f are not limited to 60 μm and 75 μm, but are shown as an example. The substance of the absorber 3f is not limited to gadolinium, but a substance having an atomic number close to gadolinium is suitable. The materials of the absorbers 3e and 3f are not limited to tin and gadolinium, but other materials can be used. However, a material having a large element number is used as a material for the absorber located further rearward. It is desirable.

  In this X-ray inspection apparatus 1, when X-rays are irradiated from the X-ray tube 2 to the subject S, the X-rays transmitted through the subject S enter the X-ray detector 3 in the X-ray detector array 4. . The X-ray irradiated from the X-ray tube 2 is not particularly limited. For example, low-energy X-rays are removed from the white X-rays emitted by colliding electrons accelerated to 120 kV with a tungsten target by an aluminum filter. X-rays and the like are preferably used.

When X-rays to the X-ray detector 3 are incident, the X-ray detecting elements 3a, 3b, 3c, 3d, respectively outputs a current I ₁ ~I ₄ in response to energy imparted by incident X-rays. Current I ₁
˜I ₄ is amplified by the preamplifier 5 and the main amplifier 6. Dividers 7 and 8 calculate I ₂ / I ₁ and I ₃ / I ₁ , respectively. Soft tissue thickness-contrast agent thickness and bone thickness calculator 9
Then, based on the calculation results of the dividers 7 and 8, the soft tissue thickness in the subject S and the thickness of the iodine contrast agent are calculated with reference to the conversion reference table preset in the thickness calculation support means 10. . Then, the imaging device 11 generates an X-ray transmission image (image data) based on the calculation result.

  In order to obtain the soft tissue thickness and the contrast agent thickness by the soft tissue thickness-contrast agent thickness and bone thickness calculator 9, soft tissue (equivalent to acrylic) thickness-iodine (equivalent to cancer tissue) thickness as shown in FIG. A two-dimensional map (conversion reference table) is created in advance and stored in the thickness calculation support means 10. In order to create this conversion reference table, a stepped phantom made of acrylic and iodine is used. This phantom is, for example, as shown in FIG.

In order to verify, an X-ray transmission image of a phantom containing iodine (corresponding to a cancer tissue portion) in acrylic (corresponding to the soft tissue portion of the human body) as shown in FIG. When measuring the thicknesses of the two types of substances, the measured current values I ₁ , I ₂ and I ₃ at each measurement point are used to display I ₂ / I ₁ at each measurement point on the two-dimensional map of FIG. I ₃ / I
Each thickness can be obtained by referring to _one two-dimensional data (a conversion reference calculation table). The obtained example is shown in FIG. By performing such a measurement on the subject S from the front direction and the side direction, the position and shape of the iodine (equivalent to cancer tissue) portion in the subject S can be determined.

  However, what is obtained by the above method is the thickness of acrylic and iodine on the line through which the X-rays have passed, and the shape of the subject S cannot be determined. In the conventional X-ray CT, since the X-ray transmission imaging is performed over 360 degrees, the outline shape of the subject S can be determined. However, since the method of this embodiment is intended to determine the position and shape of the cancer tissue from two transmission images with a low exposure dose (to obtain image data), the outline shape of the subject S is determined. As a supplementary measurement, the surface shape is measured using a laser without using X-rays. Since this surface shape measuring method is a laser scanning technique used for measuring unevenness of a human body by an underwear manufacturer or the like, a description thereof is omitted. Before and after the X-ray CT, a frontal shape can be determined by laser scanning a half body portion of the subject S that can be seen from the front, for example, and the soft tissue thickness measured by X-ray transmission imaging of the frontal shape data. Is added, the back surface shape data of the subject S can be obtained. From this, the position and shape of the cancer tissue in the subject S are determined based on the front shape data of the subject S obtained by laser scanning and the image data obtained by X-ray transmission imaging from two different directions. It becomes possible.

Next, the case where the subject S has soft tissue, iodine (cancer tissue), and bone will be described. Since it is common to use aluminum as the bone equivalent, aluminum thickness measurement will be described. Since there are three types of substances whose thicknesses are to be measured, the four output currents I _{1 to} I ₄ of the X-ray detection elements 3a to 3d in the X-ray detector 3 are used.

  Acrylic (equivalent to soft tissue) -iodine (equivalent to cancer tissue)-to a thickness encompassing the thickness of each substance that may exist in the specimen S in order to measure the thickness of three types of substances- Using aluminum (equivalent to bone tissue), a phantom with a step shape as shown in Fig. 4 with an aluminum staircase added in front of the iodine staircase is constructed, and the 3D map data of this phantom is obtained for conversion reference It is desirable to store the thickness calculation support means 10 as a table. FIG. 7 shows the three-dimensional map data (conversion reference table) created at this time.

However, since this method is complicated, as an alternative, a stepped phantom made of acrylic and iodine and a stepped phantom made of acrylic and aluminum as shown in FIG. Two kinds of two-dimensional map data of two-dimensional map data and acrylic-aluminum-thickness two-dimensional map data are obtained in advance and stored in the thickness calculation support means 10 as two conversion reference tables. Anyway. However, when the current value I ₄ is measured by the X-ray detecting element 3d is small, instead vertical axis I ₄ / I ₁ I ₄ /
It is preferred to use I ₃ . In this case, the horizontal axis may be I ₃ / I ₁ instead of I ₂ / I ₁ . An example of this is shown in FIGS. 8 (a) and 8 (b).

For verification, a phantom in which an acrylic cylinder (corresponding to soft tissue) having a diameter of 30 mm and an iodine layer (corresponding to cancer tissue) having a diameter of 5 mm and an aluminum rod having a diameter of 2 mm (corresponding to bone tissue) shown in FIG. 9 was measured. The acrylic thickness-iodine thickness and acrylic thickness-aluminum thickness estimated from the results are shown in FIGS. 10 (a) and 10 (b). The thickness of each substance inferred from two two-dimensional map data (conversion reference table) is that the acrylic thickness-iodine thickness is overestimated in the place where aluminum is present, and the acrylic thickness- As for the aluminum thickness, the acrylic thickness and the aluminum thickness are overestimated where iodine is present.

For this evaluation result, the acrylic thickness in terms of acrylic thickness-iodine thickness is defined as P ₁ (x)
The iodine thickness is set to P ₂ (x), and the acrylic thickness in the acrylic thickness-aluminum thickness is set to Q ₁ (x), and the aluminum thickness is set to Q ₂ (x). Further, when the acrylic thickness at each position x is A (x), the iodine thickness is B (x), and the aluminum thickness is C (x), the following relational expression is obtained.

これらを用いることにより、アクリル厚さ、ヨウ素厚さ、及びアルミニウム厚さは図１１のように得られる。

By using these, the acrylic thickness, iodine thickness, and aluminum thickness are obtained as shown in FIG.

  From the above, it can be verified that the method of this example can be applied even when soft tissue, iodine (cancer tissue), and bone are present in the subject.

  The above mathematical formula depends on the X-ray energy spectrum, and depends on the arrangement of the X-ray tube 2, the subject S, and the X-ray detector 3 in the measurement. By obtaining an equation for the measurement arrangement, it can be applied to various subjects. Also, instead of using two two-dimensional maps (conversion reference table) of acrylic thickness-iodine thickness and acrylic thickness-aluminum thickness, acrylic thickness-iodine thickness-aluminum as shown in FIG. By obtaining a three-dimensional map (conversion reference table) of thickness in advance, the acrylic thickness, iodine thickness, and aluminum thickness shown in FIG. 11 can be obtained without using such a mathematical expression.

The measurement example described above uses the transXend detector 3 in which four X-ray detection elements 3a to 3d made of Si (Li-containing) semiconductors having dimensions of 1 cm × 1 cm × 1 mm are arranged in the X-ray traveling direction. I went. In front of the X-ray detector 3, a collimator was placed so that X-rays passed through only 2 mm wide, and the subject S was moved for measurement.

  By further reducing the area of the Si (Li-containing) semiconductor and using it as a two-dimensional array of transXend detectors arranged on a plane as shown in the figure, it is possible to perform faster measurement.

Further, by arranging two-dimensional detectors such as an imaging plate having high position resolution in the X-ray traveling direction, measurement with a position resolution of 100 μm or less is possible. The imaging plate is a detector used for X-ray photography, and by using a transXend detector using this, the presence or absence of cancer can be confirmed with the same resolution as that of the X-ray photograph.

  Here, the imaging process will be described with reference to FIGS. 12, 13-1, and 13-2.

  The imaging process is basically performed from the steps shown in FIG.

  Step S-1 The imaging data obtained by the individual X-ray detection elements 3a to 3d of the X-ray examination apparatus 1 are processed by the soft tissue thickness-contrast medium thickness and bone thickness calculation device 9 and the thickness calculation support means 10. Data of the calculated soft tissue thickness, contrast agent thickness, and bone thickness, which are imaged for each element and from two different directions (hereinafter, abbreviated as thickness data), are combined into an imaging device 11. Read in.

  Step S-2: The read thickness data is developed three-dimensionally for each element, and is made three-dimensional image data for each element.

  Step S-3 Three-dimensional synthesized image data is created by synthesizing all the elements of the elemental three-dimensional image data created in Step S-2.

  Step S-4: For the three-dimensional composite image data and the element-specific three-dimensional image data, the form of the image to be displayed is selected from the input means of the image display device 11 and input. The contents to be selected and input are, for example, “display by element or display all elements” or “input a cutting plane instruction for cutting and displaying which part”.

  Step S-5: For each element designated in step S-4, the angle of the cut surface, and the like are determined, and the elemental 3D image data and the 3D composite image data are coordinate-converted to display an image. Here, the coordinate conversion performed according to the angle of the cut surface can be performed by a general coordinate conversion program.

  The processes relating to these steps S-1 to S-5 are performed by starting corresponding processing programs that are individually known in the image display apparatus according to instructions from the input means of the image display apparatus 11.

The processing contents of elemental three-dimensional image creation in step S-2, which is the basis of imaging, are performed as shown in FIG. Here, (b) and (c) show as a conceptual diagram the relationship between soft tissue thickness, contrast agent thickness, and bone thickness data, so-called elemental thickness data obtained by imaging from two directions. It is a thing. A thickness data group measured from one direction is displayed as R, and a thickness data group measured from the other direction is displayed as T. When the thickness data of R (i, m) and the thickness data of T (i, n) are crossed and both thickness data of R (i, m) and T (i, n) exist, The element is specified as a portion where an element exists, and the thickness data at that time is synthesized as a value of Z (i, m, n) to create a three-dimensional image for each element. (This corresponds to “1” in FIG. 13-2 (c).)
Further, the thickness data of R (i, m) and the thickness data of T (i, n) are interlaced, and both thickness data of R (i, m) and T (i, n) exist. If the thickness data are not equal, R (i, m) is greater than T (i, n), or T (i, n) is greater than R (i, m). Perform the process.

When R (i, m) is larger than T (i, n), the smaller thickness data value is specified as the portion where the element exists, and the thickness data at that time is expressed as Z (i, m, n). ) Value. The following processing is performed in which the difference between the thickness data values of R (i, m) and T (i, n) is compared with other T (i, n ′). (It corresponds to “2” in (c) of FIG. 13-2, and the part indicated by the alternate long and short dash line in FIG. 13-2 represents comparison with other T (i, n ′).)
On the other hand, when T (i, n) is larger than R (i, m), the smaller thickness data value is specified as the portion where the element exists, and the thickness data at that time is expressed as Z (i, m). , N). The following processing is performed in which the difference between the thickness data values of R (i, m) and T (i, n) is compared with other R (i, m ′). (It corresponds to “3” in (c) of FIG. 13-2, and the part indicated by the alternate long and short dash line in FIG. 13-2 represents comparison with other R (i, n ′).)
Here, i and m are two-dimensional array numbers of the radiation detector when imaged from one direction, and m and n are two-dimensional array numbers of the radiation detector when imaged from the other direction. . N ′ and m ′ represent sequence numbers other than n and m.

  Specifically, it is performed according to the procedure shown in (a). This process is created for the sake of convenience with a priority of R (i, m)> T (i, n), but may be changed as appropriate.

  Steps S2, S3, and S4 are control key processes for the maximum values Nmax, Mmax, and Imax.

  Steps S5 and S6 are processes for skipping because there is no interlaced T data although the value of R (i, m) is not "0" and the value of R (i, m) is not "0".

  Step S7 is a process of comparing R (i, m) and T (i, n) whose thickness data value is not “0” and selecting a process for specifying Z (i, m, n). . If R (i, m) = T (i, n), the process proceeds to step S8. If R (i, m)> T (i, n), the process proceeds to step S10. Further, if R (i, m) <T (i, n), the process proceeds to step S12 to perform processing.

Steps S8 and S9 specify Z (i, m, n) when there is T data that intersects R (i, m) and R (i, m) and T data match. It is processing. (This corresponds to “1” in FIG. 13-2 (c).)
In steps S10 and S11, when there is T data intersecting with R (i, m) and R (i, m)> T data, T (i, n) which is the smaller value. Is specified as Z (i, m, n), and a portion with an excess value is left as R (i, m), and is assigned to another T data. (This corresponds to “2” in FIG. 13C.)
In steps S12 and S13, T data that intersects with R (i, m) exists, but conversely, when R (i, m) <T data, R (i, m) is the smaller value. This is a preparatory process for specifying m) as Z (i, m, n), leaving the portion with the excess value as T data, and allocating it to another R (i, m). (This corresponds to “3” in FIG. 13C.)
By performing this series of processing for each element, three-dimensional image data for each element can be created.

  The synthesis of the elemental three-dimensional image data in step S-3 in FIG. 12 is the elemental three-dimensional image data Z (i, m, n) is a process of combining in accordance with the positions of i, m, and n.

  Next, an application example of elemental three-dimensional image creation described based on FIGS. 13A and 13B will be described.

  When examining whether or not cancerous tissue exists in the human body as the subject S and in which part of the human body the cancerous tissue exists, the objective of X-ray transmission imaging is achieved by focusing on iodine. be able to. That is, based on R (i, m) of the thickness data group measured from one direction for iodine and T (i, n) of the thickness data group measured from the other direction, FIG. 13-1 (a) By changing the processing of steps S-5 to S-13 to the following series of processing, a three-dimensional image shows whether or not cancerous tissue exists in the human body and in which part of the human body cancerous tissue exists Can be expressed as

In particular,
(1) An operation of R (i, m) × T (i, n) is performed.

  (2) When the calculation result is “0”, it is assumed that iodine (cancer tissue) does not exist.

  (3) When the calculation result is not “0”, the calculation result is compared with the threshold value.

  (4) When the calculation result is lower than the threshold, the calculation result is regarded as “0”, and it is assumed that iodine (cancer tissue) does not exist.

  (5) If the calculation result is higher than the threshold value, it is assumed that iodine (cancer tissue) exists, and Z (i, m, n) is, for example, the square root of R (i, m) × T (i, n). Is specified as thickness data.

  (6) A three-dimensional image of iodine (cancer tissue) is created by repeating (1) to (5) above.

  (7) Further, by appropriately changing this threshold value, it is possible to improve the accuracy of discrimination between iodine in the blood vessels of normal tissue and iodine in the cancer tissue.

DESCRIPTION OF SYMBOLS 1 X-ray inspection apparatus 2 X-ray tube 3 X-ray detector 3a-3d X-ray detection element 3e, 3f Absorber 4 X-ray detector array 5 Preamplifier 6 Main amplifier 7 Divider 8 Divider 9 Soft tissue thickness- Contrast agent thickness and bone thickness calculation device 10 Thickness calculation support means 11 Imaging device

Claims (8)

  A plurality of X-ray detection elements that generate charges by energy applied by incident X-rays that have passed through the subject are arranged in a row on the X-ray incident line so that the distances from the incident end are different from each other. An X-ray detector characterized in that an absorber that absorbs and attenuates a part of the X-rays is installed at a plurality of positions between the detection elements in the row of X-ray detection elements.   2. The material according to claim 1, wherein the absorber is a material containing an element from Al of atomic number 13 to Bi of atomic number 83 (excluding Tc of atomic number 43 and Pm of atomic number 61). X-ray detector. In claim 1 or 2, each of the X-ray detection elements is a detection medium made of the same material, and at least four of them are arranged in a line on an X-ray incident line,
The X-ray detector, wherein the absorber is disposed on an X-ray incident end side of an X-ray detection element in an intermediate portion and a rearmost X-ray detection element of the row of X-ray detection elements.   An X-ray transmission imaging of a subject is performed using the X-ray detector according to any one of claims 1 to 3, and a thickness is calculated from a ratio of output current values of a plurality of X-ray detection elements of the X-ray detector. An X-ray computed tomography method, comprising: measuring a soft tissue, a contrast medium, and a bone thickness in a subject.   5. The X-ray computed tomography method according to claim 4, wherein the plurality of compositions in the subject are soft tissue, cancer tissue, and bone of a human body.   In claim 4 or 5, the outer shape of the subject is obtained based on surface shape image data obtained by surface shape measurement using a laser and image data of soft tissue in the subject obtained by the X-ray transmission imaging, An X-ray computed tomography method characterized in that a soft tissue, a contrast medium, and a bone shape are synthesized and displayed within an outer shape of a subject.   An X-ray detector according to any one of claims 1 to 3, means for performing X-ray transmission imaging of a subject using the X-ray detector, and a plurality of X-ray detection elements of the X-ray detector An X-ray computed tomography system comprising an arithmetic unit that measures the thickness of soft tissue, contrast medium, and bone in a subject by calculation from a ratio of output current values of the subject.   In claim 7, the external shape of the subject is obtained based on surface shape image data obtained by measuring the surface shape of the subject using a laser and image data of soft tissue in the subject obtained by the X-ray transmission imaging, An X-ray computed tomography system characterized in that a soft tissue, a contrast medium, and a bone shape are synthesized and displayed within an outer shape of a subject.

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