JP2005062200A - Computerized tomographic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the image quality of cross-sectional images by a CT scanner, in computerized tomographic equipment used for nondestructive tests. <P>SOLUTION: The computerized tomographic equipment is provided with a radiation source; a radiation detecting means; a drive means for relatively rotating or moving the radiation source, a measuring system constituted of the radiation detection means, and a subject at a specified speed; and a reconstruction means for creating cross-sectional images of the subject from radiation transmission signals detected. The computerized tomographic equipment is provide with both a plurality of radiation filters for changing the energy components of radiation radiated from the radiation source and a filter changeover means for inserting a radiation filter, selected from among the plurality of radiation filters, between the radiation source and the radiation detecting means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an improvement in a computer tomography apparatus used for nondestructive inspection.

  In a conventional industrial computer tomography apparatus (CT scanner), a translation / rotation method (hereinafter referred to as “TR method”) in which a subject performs a translation operation and step rotation, or a so-called rotation in which only rotation is performed. Rotation method (hereinafter referred to as “RR method”) is mainly adopted.

  FIG. 12 is a block diagram showing a conventional typical TR type computed tomography apparatus. The computer tomography apparatus shown in FIG. 12 is viewed from the top.

  The X-ray tube 1 is a radiation source that emits X-rays 2 that are transmitted radiation, and an internal focal point S is a radiation source. The X-ray tube 1 is fixed to a vertically moving frame 7.

  The collimator 3 shapes the X-ray 2 emitted from the X-ray tube 1 into a fan shape having a fan angle θ. The collimator 3 and the collimator 4 have a function of allowing only effective components of the X-ray 2 to pass therethrough.

  The radiation detector 5 is for detecting the X-ray 2 emitted from the X-ray tube 1 and transmitted through the subject 6, and is geometrically fixed to the vertically moving frame 7 at a position facing the X-ray tube 1. ing.

  The radiation detector 5 detects the X-ray 2 with a one-dimensional resolution, and outputs the detection result to the data collection unit 8 as a radiation transmission signal. As described above, the X-ray 2 measuring system is configured by the X-ray tube 1 and the radiation detector 5 fixed to the vertically moving frame 7.

  The vertical movement mechanism 9 is a mechanism for moving the vertical movement frame 7 up and down. The vertical movement of the vertical movement frame 7 adjusts the position of the measurement system so that the X-ray 2 is irradiated to the cross-sectional image photographing position of the subject. Is done.

  In this computed tomography apparatus, a translation mechanism 10 and a rotation mechanism 11 are provided as drive means for relatively driving the subject 6 and the measurement system during tomographic imaging (scanning).

  The translation mechanism 10 moves the subject 6 in the horizontal direction, whereby the translation operation of the subject 6 is performed. The translation mechanism 10 can execute a translation operation at two speeds.

  The rotating mechanism 11 supports a rotating table 12 so that it can rotate horizontally at the top, and the rotating table 12 is rotated by the same angle as the fan angle θ to perform step rotation of the subject 6.

  The mechanism control unit 13 controls the operation of each drive mechanism including the vertical movement mechanism 9, the translation mechanism 10, the rotation mechanism 11, and the like. The mechanism control unit 13 outputs a synchronization signal for synchronizing the translation operation by the translation mechanism 10 and data collection to the data collection unit 8.

  The X-ray control unit 14 performs a focus selection operation such as determining which focus S generates X-rays 2 when there are a plurality of focal points S of the X-ray tube 1 or the tube voltage of the X-ray tube 1. Control the tube current.

  The data collection unit 8 collects the radiation transmission signal detected by the radiation detector 5 in synchronization with the translation operation by the synchronization signal from the mechanism control unit 13 and outputs the collected signal to the data processing unit 15.

  The data processing unit 15 reconstructs a cross-sectional image based on, for example, the filtered back projection method (FBP method) based on the radiation transmission signal input from the data collection unit 8, and displays the cross-sectional image obtained by this reconstruction. To the unit 16.

  The display unit 16 displays the cross-sectional image input from the data processing unit 15. The operation of the conventional computed tomography apparatus having such a configuration will be described below.

  In the TR method, a radiation transmission signal is collected by a relative translation operation and a relative step rotation between the subject 6 and the measurement system. Here, in the TR system, the translation operation and the step rotation of the same angle as the fan angle θ are alternately repeated, and in order to obtain a radiation transmission signal from the 180 ° direction, 180 ° / θ translation is performed. The action is executed. That is, for example, when the fan angle θ is set to 30 °, six translation operations are executed.

  In this conventional computer tomography apparatus based on the TR system, one cross-sectional image is created by the radiation transmission signal from the 180 ° direction. Further, in the conventional computed tomography apparatus, one of two types of scans (normal scan and fine scan) having different translation operation speeds can be selected and selected by the operator according to the subject 6.

  In normal scan and fine scan, the speed of translation operation is different, but the data collection pitch and the number of data points are the same, and the method for reconstructing a cross-sectional image is also the same.

  In the fine scan, the speed of the translation operation is set slower than that in the normal scan, and thereby the integration time when the X-ray detection signal is integrated between the data collection pitches by the radiation detector 5 becomes long.

  As a result, there is little noise in the created cross-sectional image, and a high-quality cross-sectional image can be obtained. In the conventional computed tomography apparatus, the slice width of the fan-shaped X-ray 2 can be switched by switching the width of the slit provided in the collimator 3 or the collimator 4. As a result, in the case of the subject 6 in which the X-ray 2 is difficult to transmit, or in the case of the subject 6 with little change in the same direction as the slice width, the slit width of the X-ray 2 is increased by widening the slit width of the collimator 4. The image quality of the cross-sectional image is improved by widening and increasing the X-ray dose irradiated to the radiation detector 5.

  Further, in some conventional computed tomography apparatuses, the X-ray tube 1 has a plurality of focal points S having different focal point sizes, and the X-ray 2 focal point size can be selected and irradiated. In such a conventional computed tomography apparatus capable of switching the focus size, when the subject 6 is difficult to transmit X-rays 2, the focus S is switched to a focus with a large focus size (large focus), and the radiation detector 5. The X-ray dose irradiated to the is increased. As a result, a high-quality cross-sectional image with low noise but low noise can be obtained.

  Some conventional computed tomography apparatuses can switch the resolution of cross-sectional images. In this conventional computed tomography apparatus capable of switching the resolution, a comb-like or rectangular hole is placed in the same direction as the arrangement of the detection elements (channels) of the radiation detector 5 in the previous stage of the radiation detector 5, that is, in the resolution direction. In the case of the subject 6 in which the X-ray 2 is not easily transmitted, the radiation detector 5 is expanded by widening the aperture width. As a result, the X-ray dose applied to the laser beam is increased, whereby a high-quality cross-sectional image with less noise is obtained although the spatial resolution is lowered.

  By the way, in such a conventional computed tomography apparatus, fine scan is a scan method for obtaining a high-quality cross-sectional image over time, but if it takes too much time, the integral which is a component of the radiation detector 5 is integrated. There is a first problem that a sufficient time cannot be secured because there is a limit because the amplifier and the amplifier may be saturated.

  Further, in the conventional computed tomography apparatus, the geometric position of each drive mechanism such as a vertical movement mechanism, a translation mechanism, and a rotation mechanism must be accurately set. For example, the center point of the translation operation is shifted. In some cases, radial artifacts (false images) occur in the created cross-sectional image.

  FIG. 13 is a diagram illustrating an example when radial artifacts occur in the cross-sectional image of the pin-shaped subject. Here, FIG. 13A shows a cross-sectional image when the center point of the translation operation is always shifted to one side. For example, during the translation operation by the conventional computed tomography apparatus, the rotary table is The cross-sectional images of the radial artifacts 18a and 18b and the pin 17 that are generated when they are always in the same direction are shown. Radial black line artifacts 18a and white line artifacts 18b that are different in black and white are generated every 180 ° in total. doing.

  FIG. 13B shows a cross-sectional view when the center point of the translation operation is shifted in the opposite direction between the even-numbered translation operation and the odd-numbered translation operation. For example, FIG. In the case of a translation operation that moves from one side to the other side, the center point of the translation operation shifts from one side to the other side, and conversely, a translation that moves from the other side to one side. In the case of operation, the cross-sectional images of the radial artifacts 18a and 18b and the pin 17 generated when the center point of the translation operation is shifted from the other side to the one side are shown. A total of ten black line artifacts 18a and white line artifacts 18b are generated every 30 °.

  As described above, the conventional computed tomography apparatus creates a cross-sectional image using a radiation transmission signal in the 180 ° direction, but if the geometric position of each drive mechanism is shifted, a radial artifact is generated sensitively to the created cross-sectional image. There is a second problem.

  Further, in the conventional computed tomography apparatus, when switching the slice width of the fan-shaped X-ray, there is a restriction for preventing the components of the radiation detector from being saturated, which is sufficient to create a cross-sectional image. There is a third problem that a fan-shaped X-ray slice width cannot be realized.

  Furthermore, in the case of using a large focal point in a conventional computed tomography apparatus capable of switching the focal spot size, the components of the radiation detector are saturated, so that the X-ray dose cannot be increased sufficiently to create a cross-sectional image. There is a fourth problem.

  Furthermore, in the conventional computed tomography apparatus capable of switching the resolution, when the resolution is lowered, the components of the radiation detector are saturated, so that there is a fifth problem that the resolution cannot be lowered.

  Among the above problems, the first problem and the third to fifth problems can be prevented from being saturated by lowering the gain of the integrator or amplifier that is a component of the radiation detector. Alternatively, when the gain of the amplifier is lowered, the gain becomes insufficient when scanning is performed in a normal state, and as a result, the image quality of the cross-sectional image is lowered.

  Further, if the radiation detector has a gain switching function, there is a problem that the size of the radiation detector becomes enormous and the structure of the radiation detector becomes complicated. The present invention has been made in consideration of the above-mentioned actual situation. It is a first object of the present invention to provide a computer tomography apparatus capable of creating a cross-sectional image so as to prevent artifacts and improving the image quality of the cross-sectional image. Computerized tomography that aims to improve the image quality of the created cross-sectional image by enabling long-time scans or scans with a large amount of radiation without saturating the components of the radiation detector. A second object is to provide a photographing apparatus.

  In order to achieve the second object, the invention of claim 1 is a radiation source that radiates radiation to a subject, and radiation detection that detects radiation emitted from the radiation source and passed through the subject as a radiation transmission signal. Means, a measurement system constituted by the radiation source and the radiation detection means, and a driving means for relatively rotating or moving the subject at a specified speed, and radiation transmission detected by the radiation detection means during the rotation or movement In a computed tomography apparatus comprising a reconstruction means for creating a cross-sectional image of a subject from a signal, a plurality of radiation filters for changing the energy component of radiation emitted from a radiation source, and a speed of rotation or movement by a driving means When a change is made, a radiation filter selected from a plurality of radiation filters is selected according to the changed speed. A computer tomography apparatus and a filter switching means for inserting between the detecting means.

  Therefore, in the computed tomography apparatus according to the first aspect of the present invention, the optimum radiation filter is a filter so that the integrator which is a component of the radiation detecting means does not overflow even when the scanning speed by the driving means is lowered. Since it is selected by the switching means, the time during which the radiation detection means detects the radiation, that is, the integration time of the integrator of the radiation detection means, can be lengthened, so that even a subject that is difficult to transmit the radiation has high image quality. Can be obtained.

  Next, the invention of claim 2 is directed to a radiation source that emits radiation to a subject, radiation detection means that detects radiation emitted from the radiation source and transmitted through the subject as a radiation transmission signal, and the radiation source and radiation detection. A driving unit that relatively rotates or moves the measurement system constituted by the unit and a subject, and a reconstruction that creates a cross-sectional image of the subject from the radiation transmission signal detected by the radiation detecting unit during the rotation or movement A collimator that forms radiation into a fan-shaped radiation having a designated slice width, a plurality of radiation filters that change the energy component of the radiation emitted from the radiation source, and a slice width When a change is made, a radiation filter selected from multiple radiation filters is selected according to the changed slice width. A computer tomography apparatus and a filter switching means for inserting between the ray source and the radiation detecting means.

  Therefore, in the computed tomography apparatus according to the second aspect of the present invention, an optimum filter is provided so that the integrator, which is a component of the radiation detection means, does not overflow even if the slice width of the fan-shaped radiation is increased. Since it is selected by the filter switching means, the slice width can be increased to increase the amount of radiation applied to the radiation detection means, thereby producing a high-quality cross-sectional image even for a subject that is difficult to transmit radiation. Can be obtained.

  Next, the invention of claim 3 is a radiation source capable of changing the focal point of the generated radiation to a specified size and changing the radiation dose emitted to the subject, and the radiation emitted from the radiation source and transmitted through the subject. Radiation detection means for detecting radiation as a radiation transmission signal, drive means for relatively rotating or moving the measurement system formed by the radiation source and the radiation detection means, and the radiation detection means during this rotation or movement In a computed tomography apparatus comprising a reconstruction means for creating a cross-sectional image of a subject from a radiation transmission signal detected by the step, a plurality of radiation filters for changing an energy component of radiation emitted from a radiation source, When there is a change in size, a radiation filter selected from a plurality of radiation filters is selected according to the changed focus size. A computer tomography apparatus and a filter switching means for inserting between the radiation detecting means.

  Therefore, in the computed tomography apparatus of the invention of claim 3, even if radiation is emitted from a radiation generating source having a large radiation generation amount, that is, a large focal point, the integrator as a component of the radiation detecting means overflows. The optimal radiation filter is selected by the filter switching means so that the amount of radiation irradiated to the radiation detection means can be increased, and thus a high-quality cross section even for a subject that is difficult to transmit radiation. An image can be obtained.

  Finally, the invention of claim 4 is directed to a radiation source that emits radiation to a subject, radiation detection means that detects radiation emitted from the radiation source and transmitted through the subject as a radiation transmission signal, radiation source and radiation detection A driving unit that relatively rotates or moves the measurement system constituted by the unit and a subject, and a reconstruction that creates a cross-sectional image of the subject from the radiation transmission signal detected by the radiation detecting unit during the rotation or movement A resolution varying means for changing the resolution of the radiation detecting means to a specified resolution by changing the aperture width of each of a number of detection elements constituting the radiation detecting means, and radiation from the radiation source. When there are multiple radiation filters that change the energy component of the emitted radiation and the resolution is changed, Te is a computer tomography apparatus and a filter switching means for inserting between the radiation source and the radiation detecting means selected radiation filter from the plurality of radiation filters.

  Therefore, in the computer tomography apparatus of the invention of claim 4, even if the resolution is changed by changing the aperture width of the plurality of radiation detection elements provided in the radiation detection means, Since the optimum filter is selected by the filter switching means so that an integrator does not overflow, the aperture width can be widened to increase the radiation dose irradiated to the radiation detection means, thereby transmitting the radiation. A high-quality cross-sectional image can be obtained even for a subject that is difficult to perform.

  As described above, according to the computed tomography apparatus of another invention, a scan with an arbitrary degree of overlap is executed, and the same number of cross-sectional images as the obtained arbitrary degree of overlap are synthesized to obtain a final cross-sectional image. Therefore, it is possible to scan for a long time without saturating the components of the radiation detection means, and a high-quality cross-sectional image with less noise can be obtained.

  In addition, when compositing the same number of cross-sectional images as the number of arbitrary overlaps, the compositing is performed so as to cancel out the artifacts occurring in each cross-sectional image, thus preventing the occurrence of artifacts in the final cross-sectional image. Can do.

  Furthermore, even before the end of scanning with an arbitrary degree of overlap, the cross-sectional image being created during the process is displayed, and if the cross-sectional image being created during the process is of sufficient quality, the scan can be stopped. The time until an image is obtained can be shortened.

  Further, according to the computed tomography apparatus of the present invention, even when the scan speed, the slice width of the radiation, the focal point of the radiation, the resolution of the radiation, etc. are changed, and the radiation dose incident on the radiation detection means changes, In order not to saturate the components of the radiation detection means, an appropriate radiation filter is selected and the radiation is filtered. Therefore, the radiation dose can be increased within a range not to saturate the components of the radiation detection means. A quality cross-sectional image can be obtained.

  Hereinafter, another embodiment and an embodiment of the present invention will be described in detail with reference to the drawings.

(First embodiment)
In this embodiment of another invention, the degree of overlap of scans can be selected, and when a scan of two or more scans is executed, the cross-sectional images for the executed scans are combined to obtain a final cross-sectional image. This is a computer tomography apparatus to be created.

  FIG. 1 is a block diagram showing a system configuration of a computed tomography apparatus according to the present embodiment. The same parts as those in FIG. 12 are denoted by the same reference numerals and the description thereof is omitted or briefly described. Here, only different parts will be described in detail.

  In FIG. 1, the base 19 fixedly supports the X-ray tube 1 and the radiation detector 5 so as to face each other. In the computer tomography apparatus shown in FIG. 1, the X-ray 2 is shaped into a fan shape by the collimators 3 and 4 so that the fan angle θ is 30 °.

  The translation frame 20 supports the rotation mechanism 11 via the vertical movement mechanism 9, and the rotation mechanism 11 is moved up and down by the vertical movement mechanism 9, so that the X-ray 2 is at the cross-sectional image photographing position of the subject 6. It is adjusted to be irradiated.

  The translation frame 20 is supported by the base 19 via the translation mechanism 10 and is movable in the horizontal direction. The vertical movement mechanism 9 and the translation mechanism 10 each have two guide rails and one ball screw, and are moved by rotating the ball screw with a motor.

  The subject 6 placed on the rotary table 12 is moved along the X-ray 2 so as to cross the X-ray 2 and rotated horizontally. As described above, the vertical movement by the vertical movement mechanism 9 is performed. The slice plane of the cross-sectional image created by is changed.

  The X-ray tube 1 is connected to the data processing unit 15 via the X-ray control unit 14. The X-ray control unit 14 supplies power to the X-ray tube 1, controls the tube voltage and the tube current, and turns on / off the X-ray 2 according to a signal from the data processing unit 15.

  The mechanism control unit 13 is connected to each drive mechanism of the vertical movement mechanism 9, the translation mechanism 10, and the rotation mechanism 11, and is also connected to the data processing unit 15. The mechanism control unit 13 stores various operation sequences of each drive mechanism, and controls each drive mechanism in accordance with an operation signal input from the data processing unit 15.

  The mechanism control unit 13 is connected to the data collection unit 8 and outputs a synchronization signal to the data collection unit 8 in conjunction with the operation of the translation mechanism 10. The radiation detector 5 is connected to the data processing unit 15 via the data collection unit 8.

  When the synchronization signal is input from the mechanism control unit 13, the data collection unit 8 collects the radiation transmission signal detected by the radiation detector 5, converts the collected radiation transmission signal into a digital signal, and the data processing unit 15. Output to.

  The data processing unit 15 mainly includes a CPU 21, an image memory 22, an interface device 23, a system bus 24, and an image bus 25. The data processing unit 15 stores an entire scan program, a reconstruction process program, and the like. The CPU 21 executes these programs to perform a scan operation, and a cross-sectional image is generated from a digitally converted radiation transmission signal. The created cross-sectional image is stored in the image memory 22.

  The interface device 23 relays the connection between the other components connected to the data processing unit 15 and the system bus 24 or the image bus 24 inside the data processing unit 15.

  The system bus 24 is a bus for transmitting various data and signals, and the image bus 25 is a bus for transmitting cross-sectional image data. The data processing unit 15 is connected to a keyboard 26 which is a human interface device and a display unit 16.

  The operator uses the keyboard 26 and the display unit 16 to perform system activation, menu selection, scan activation, device status display, cross-sectional image display, cross-sectional image analysis, and the like.

  In addition, this computed tomography apparatus includes an X-ray shielding means (not shown), a slice light indicating the position of the X-ray 2, a comparison detector for measuring X-ray intensity changes, and the like.

  Next, the operation of the computed tomography apparatus according to this embodiment configured as described above will be described. The operator first drives the vertical movement mechanism 9 so that the X-ray 2 is irradiated to the slice position of the subject 6 by manual operation before scanning.

  Next, a single scan, double scan, or quad scan is selected by menu selection, and a scan operation is started. Here, the double scan and the quad scan are selected when it is desired to obtain a high-quality cross-sectional image even if it takes more time than the single scan.

  Then, the data processing unit 15 executes a process corresponding to the selected scan, and creates a cross-sectional image. The operation of the computer cross-sectional imaging apparatus in each scan is shown below.

(Single scan)
In the single scan, first, the subject 6 on the rotary table 12 is set at the reset position (one end side of the translation operation), and offset data is collected.

  Next, the X-ray 2 is turned on by the X-ray control unit 14, the subject 6 is moved from one end side to the other end side of the translation operation, and data 1 t is collected while the subject 6 crosses the X-ray 2. Collected by part 8.

  Next, the subject 6 is rotated stepwise in the CW direction by 30 °, the same angle as the fan angle θ, and moved from the other end side to the one end side of the translation operation, and the data 2t is collected by the data collecting unit 8. .

  When the subject 6 on the rotary table 12 returns to one end side of the translation operation again, the subject 6 is rotated in the CW direction by 30 °, which is the same angle as the fan angle θ. When such translation operation from one end side to the other end side, step rotation, translation operation from the other end side to one end side, and step rotation are repeated in the same manner and data is collected up to 6t, the X-ray 2 is turned off, The scan ends.

  Here, the speed of each translation operation is constant, the integration time per data is constant, the data is detected by the radiation detector 5 at every constant pitch, collected by the data collection unit 8, and the data processing unit 15 is input.

  The transmission data 1t to 6t at the slice position in the 180 ° direction are obtained as described above, and the data processing unit 15 reconstructs the transmission data 1t to 6t by the FBP method to create cross-sectional images, and the cross-section created on the display unit 16 An image is displayed.

(Double scan)
In the double scan, as described in the operation in the single scan, the subject 6 on the rotary table 12 is set at the reset position (one end side of the translation operation) and the offset data is collected. The X-ray 2 is turned on by the X-ray control unit 14 to translate from one end to the other end, 30 ° CW direction step rotation, translate from the other end to the one end, 30 ° CW The direction step rotation is repeated, and data 1t to 12t, which are transmission data at slice positions in the 360 ° direction, are obtained in the data processing unit 15 via the radiation detector 5 and the data collection unit 8.

  Here, the speed of each translation operation is constant, data is collected at a certain pitch, the integration time per data is constant, and the speed, pitch, and integration time of each translation operation are described above. Is set to be the same as the single scan.

  In this manner, data 1t to 12t, which are transmission data at slice positions in the 360 ° direction, are obtained, the X-ray 2 is turned off, and the scan ends. The data processing unit 15 performs reconstruction by the FBP method based on the data 1t to 6t among the data 1t to 12t, and creates a first cross-sectional image. Similarly, the data processing unit 15 performs reconstruction by the FBP method based on the data 7t to 12t. A second cross-sectional image is created.

  Then, the data processing unit 15 rotates the second cross-sectional image by 180 °, and adds and averages the first cross-sectional image and the rotated second cross-sectional image to create a final cross-sectional image, and the display unit 16 is displayed.

  In the case of this double scan, even when the scan operation is being executed, when the data 6t is collected, a first cross-sectional image is created, and as soon as this first cross-sectional image is created, the display section 16 is displayed as a half-way cross-sectional image. Is displayed. The first cross-sectional image continues to be displayed on the display unit 16 until the final cross-sectional image is displayed.

  The operator can confirm the intermediate cross-sectional image by the function of displaying the intermediate cross-sectional image even during the scan, and as a result of the confirmation, the intermediate cross-sectional image is sufficiently high quality and does not need to be scanned any more. If it is determined, the scan can be stopped by inputting a scan stop command to the keyboard 26.

  In this double scan, since the first cross-sectional image and the second cross-sectional image rotated by 180 ° are added and averaged, the artifacts caused by the shift of the translation operation cancel each other, and the cross-section with good image quality An image is obtained.

  2, 3, and 4 are cross-sectional images of the pin 17, FIG. 2 is a first cross-sectional image, FIG. 3 is a second cross-sectional image, and FIG. 4 is an example of a final cross-sectional image. In the first cross-sectional image and the second cross-sectional image, the center point C of the translation operation is shifted in the opposite direction between the even-numbered translation operation and the odd-numbered translation operation, and the even-numbered transformer The average center point of the rate operation and the odd-numbered translation operation is also shifted to one side, and black line artifact 18a and white line artifact 18b are generated. When the direction of the deviation of the center point is reversed, the black line artifact 18a and the white line artifact 18b are reversed.

  The occurrence of artifacts is characterized in that black line artifacts 18a and white line artifacts 18b are generated in opposite directions across the cross-sectional image of the pin 17, respectively.

  The first cross-sectional image collects data before the turntable 12 rotates, that is, from 0 ° rotation, whereas the second cross-sectional image collects data after 180 ° rotation, The position of the pin 17 appearing in the second cross-sectional image is a position obtained by rotating the position of the pin 17 appearing in the first cross-sectional image by 180 °.

  Therefore, when the first cross-sectional image and the cross-sectional image obtained by rotating the second cross-sectional image by 180 ° are added and averaged, the artifacts 18a and 18b caused by the shift of the translation operation cancel each other, and the cross-section with good image quality. An image is obtained.

(For quad scan)
In the quadruple scan, the subject 6 on the rotary table 12 is set at the reset position (one end side of the translation operation), as described in the operations in the case of the single scan and the double scan. The offset data is collected and the X-ray 2 is turned on by the X-ray controller 14 to translate from one end side to the other end side, 30 ° CW direction step rotation, translation from the other end side to the one end side The operation and the CW direction step rotation of 30 ° are repeated, and data 1t to 24t, which are transmission data of slice positions in the 720 ° direction, are obtained in the data processing unit 15 via the radiation detector 5 and the data collection unit 8.

  Here, the speed of each translation operation is constant, data is collected at a certain pitch, the integration time per data is constant, and the speed, pitch, and integration time of each translation operation are described above. Is set to be the same as the single scan.

  In this manner, data 1t to 24t, which are transmission data at the slice position in the 720 ° direction, are obtained, the X-ray 2 is turned off, and the scan is completed. The data processing unit 15 performs reconstruction by the FBP method using the data 1t to 6t, the data 7t to 12t, the data 13t to 18t, and the data 19t to 24t, and the first cross-sectional image, the second cross-sectional image, 3 sectional images and a fourth sectional image are created.

  Then, among the first to fourth cross-sectional images, the even-numbered cross-sectional image is rotated by 180 °, and the odd-numbered cross-sectional image and the rotated even-numbered cross-sectional image are added and averaged to obtain the final result. Are created and displayed on the display unit 16.

  In the case of the fourth scan, reconstruction processing of each cross-sectional image is performed in parallel with the scanning operation, and the created cross-sectional image is displayed on the display unit 16. Therefore, first, the first cross-sectional image is reconstructed and displayed on the display unit 16 as an intermediate cross-sectional image.

  Next, when the second cross-sectional image is reconstructed, the second cross-sectional image is rotated 180 °, and the first cross-sectional image and the second cross-sectional image rotated 180 ° are added and averaged. The mid-section image is updated, and the updated mid-section image is displayed on the display unit 16.

  Next, when the third cross-sectional image is reconstructed, the first cross-sectional image, the second cross-sectional image rotated by 180 °, and the third cross-sectional image are added and averaged to update the intermediate cross-sectional image. The updated mid-section image is displayed on the display unit 16.

  When the fourth cross-sectional image is reconstructed, the fourth cross-sectional image is rotated by 180 °, the first cross-sectional image, the second cross-sectional image rotated by 180 °, the third cross-sectional image, 180 The fourth cross-sectional image that has been rotated is added and averaged to create a final cross-sectional image, and the final cross-sectional image thus created is displayed on the display unit 16.

  As described above, the even-numbered cross-sectional image is rotated by 180 °, and the odd-numbered cross-sectional image and the even-numbered cross-sectional image rotated by 180 ° are added and averaged, so that the artifacts caused by the shift of the translation operation can be reduced. They can cancel each other out, and a high-quality cross-sectional image can be obtained.

  In the case of double scanning or quadruple scanning, the operator can check the intermediate cross-sectional image by the display unit 16 even during the scan, and determines that the intermediate cross-sectional image is sufficiently high quality. The scan can be stopped at an arbitrary degree of overlap by inputting a scan stop command to the keyboard 26.

  Hereinafter, effects of the computed tomography apparatus according to the present embodiment will be described. Since the computed tomography apparatus according to the present embodiment can select the degree of overlap of scans, the operator desires to obtain a cross-sectional image in a short time or to create a high-quality cross-sectional image over time. A cross-sectional image can be created according to the above.

  In other words, even if the integration time of the radiation detector 5 in each scan is not changed, the scan time can be lengthened by increasing the degree of overlap of the scans. In addition, by creating a cross-sectional image by increasing the scan redundancy, it is possible to prevent overflow due to saturation of the integrator and amplifier that are components of the radiation detector 5, as in the case of increasing the integration time, A high-quality cross-sectional image with less noise can be obtained.

  In addition, since the reconstruction process can be performed by the same reconstruction process as the single scan even in the double scan and the quad scan, it is possible to prevent a decrease in operability and an increase in installation cost due to the complexity of the apparatus.

  Further, in the case of performing the double scan and the quadruple scan, among the plurality of cross-sectional images, either one of the even-numbered cross-sectional image or the odd-numbered cross-sectional image is rotated by 180 ° and averaged. It is possible to obtain a high-quality cross-sectional image by canceling out the artifacts caused by the shift of the translation operation.

  In addition, when a double scan or quadruple scan is performed, an intermediate cross-sectional image is displayed on the display unit 16, so that when the operator determines that a sufficiently accurate cross-sectional image has been obtained, an arbitrary degree of overlap can be obtained. The scanning can be stopped by this, so that the unnecessary scanning until the cross-sectional image is reconstructed can be deleted, and the time until the cross-sectional image is obtained can be shortened.

  In the computed tomography apparatus according to the present embodiment, the X-ray tube 1 is used as a radiation source and a cross-sectional image is created by the X-ray 2. However, the present invention is not limited to this, and other transmissive radiation is used. You can also.

  In the computed tomography apparatus according to the present embodiment, a cross-sectional image is created every time the subject 6 is rotated by 180 °, and the images are added later to obtain the average. Image addition can be omitted by projecting. Here, at the time of back projection, every time the subject 6 rotates 180 °, the back projection is continued by rotating 180 °.

  Furthermore, before reconstruction processing, data of 0 ° to 360 ° or 0 ° to 720 ° data in the same direction and in the opposite direction is averaged and collected into data of 0 ° to 180 °. Then, a cross-sectional image may be created.

  Further, in the computed tomography apparatus according to the present embodiment, the even-numbered cross-sectional image is rotated by 180 °, and the odd-numbered cross-sectional image and the rotated even-numbered cross-sectional image are added and averaged. In contrast to this, the odd-numbered cross-sectional image is rotated by 180 °, and the even-numbered cross-sectional image and the rotated odd-numbered cross-sectional image are added and averaged. The cross-sectional image may be created.

  In addition, the computer tomography apparatus according to the present embodiment has been described for the case of single scan, double scan, and quadruple scan, and the fan angle θ is 30 °. The fan angle θ is not limited to this, and the cross-sectional image can be reconstructed with various degrees of overlap and the fan angle θ. In particular, this computer tomography apparatus is suitable for the double scan, the quad scan, the 6 scan, and the 8 scan because of the relationship between the time until obtaining the cross section image and the image quality of the cross section image. The fan angle θ is suitably 30 °, 36 °, 45 °, or 60 °.

(Second Embodiment)
The computed tomography apparatus according to the present embodiment of the present invention, when the radiation irradiation situation is changed, for example, when the radiation dose irradiated to the radiation detector is changed, the changed radiation irradiation. By switching the radiation filter according to the situation, it is possible to always create a high-quality cross-sectional image.

  FIG. 5 is a block diagram showing a system configuration of the computed tomography apparatus according to the present embodiment. The same parts as those in FIGS. 1 and 12 are denoted by the same reference numerals, and description thereof is omitted or simplified. Only different parts will be described in detail here. In the computer tomography apparatus shown in FIG. 5, a case where a cross-sectional image is created by the RR method is taken as an example.

  The X-ray tube 1 generates X-rays 2 by either the small focal point S1 or the large focal point S2, and the generated X-rays 2 are emitted to the radiation detector 5. Here, the X-ray dose generated by the small focus S1 is small, and the X-ray dose generated by the large focus S2 is large.

  In this X-ray tube 1, even if the X-ray focal points S1 and S2 are switched, the focal point movement (movement from the small focal point S1 to the large focal point S2 or movement from the large focal point S2 to the small focal point S1) is performed horizontally. Are arranged with a small focal point S1 and a large focal point S2.

  The X-ray control unit 14 supplies electric power to the X-ray tube 1 and controls the tube voltage and the tube current, switches the X-ray focal points S1 and S2 according to the signal from the data processing unit 15, and the X-ray 2 ON / OFF.

  The filter case 27 is provided with a plurality of X-ray filters that change the energy component of the X-ray 2. The filter switching mechanism 28 switches the X-ray filter used for the X-ray 2.

  FIG. 6 is a view showing the relationship between the filter case 27 and the filter switching mechanism 28, FIG. 6 (a) is a view seen from the X-ray irradiation direction, and FIG. FIG.

  The filter case 27 is formed in a fan shape, and is provided with four copper X-ray filters 27a to 27d having radially different thicknesses from the central corner portion to the arc portion.

  The filter switching mechanism 28 includes a support plate 28a and a motor 28b. The filter case 27 is supported by a support plate so as to be rotatable at the central corner portion, and is rotated by the rotation operation of the motor 28b in contact with the arc portion to switch the X-ray filters 27a to 27d. The X-ray 2 passing through the opening 28c provided in the plate 28a is filtered.

  The slice width switching mechanism 29 switches the slice width of the fan-shaped X-ray 2 by switching the slit width of the collimator 4. FIG. 7 is a diagram showing the relationship between the collimator 4 and the slice width switching mechanism 29, as viewed from the X-ray irradiation direction.

  The collimator 4 includes an upper slit plate 4a and a lower slit plate 4b, and the slice width switching mechanism 29 includes a first shaft 29a, a second shaft 29b, and a motor 29c.

  One end of the upper slit 4a and one end of the lower slit 4b are connected by a first shaft 29a, and the other end of the upper slit 4a and the other end of the lower slit 4b are connected by a second shaft 29b.

  A gear is formed on the first shaft 29a, and the inclination of the first shaft 29a changes due to the rotational operation of the motor 29c engaged with the gear, and the change in the inclination causes the upper slit 4a to change. And the width of the slit opening of the lower slit 4b is switched, and the slice width of the X-ray 2 is changed.

  The radiation detector 5 mainly includes a detection element array 30, a circuit unit 31, a resolution collimator 32, and a resolution switching mechanism 33, and the X-ray 2 detected by the detection element array 30 is processed by the circuit unit 31 to generate radiation. The transmitted signal is output to the data collecting unit 8.

  The detection element array 30 is irradiated with the X-ray 2 via the resolution collimator 32. The resolution of the X-ray 2 to be detected can be changed via the resolution collimator 32, and this resolution is a resolution switching mechanism. 33.

  FIG. 8 is a diagram showing the relationship between the detection element array 30, the resolution collimator 32, and the resolution switching mechanism 33, as viewed from the X-ray irradiation direction. In the detection element array 30, a plurality of detection elements 30a are arranged one-dimensionally in the horizontal direction.

  The resolution switching mechanism 33 includes a guide rail 33a, a screw 33b, and a motor 33c. The resolution collimator 32 provided immediately before the detection element row 30 has the same interval as the detection element 30a, and is provided with a comb-like groove 32a in the same direction as the detection element. Therefore, it is supported so as to be movable in the vertical direction.

  The resolution collimator 32 is provided with a nut 32b, and a screw 33b is inserted into the nut 32b. The motor 33c rotates the screw 33b, whereby the comb-like groove 32a portion of the resolution collimator 32 is pushed out to the front surface of the detection element row 30, and the opening width of each detection element 30a is changed, thereby each detection element 30a. The X-ray receivable area changes.

  Although the resolution collimator 32 shown in FIG. 8 has a comb-like groove 32a, the present invention is not limited to this, and the comb-like groove 32a may be a row of rectangular holes. Further, although the screw 33b and the motor 33c are used as the drive means of the resolution switching mechanism 33 shown in FIG. 8, the present invention is not limited to this, and other drive means may be used. Further, in FIG. 8, the number of the detection elements 30a in the detection element array 30 is significantly reduced.

  The drive mechanisms such as the rotation mechanism 11, the filter switching function 28, the slice width switching mechanism 29, and the resolution switching mechanism 33 are connected to the data processing unit 15 via the mechanism control unit 13. The mechanism control unit 13 stores various operation sequences of each drive mechanism, and moves each drive mechanism in accordance with a command from the data processing unit 15.

  The mechanism control unit 13 is connected to the data collection unit 8 and outputs a synchronization signal linked to the operation of the rotation mechanism 11 to the data collection unit 8. The data processing unit 15 outputs commands and information for operating each driving mechanism to the mechanism control unit 13 according to the scanning conditions input by the operator through the keyboard 26, and outputs the X-ray 2 to the radiation detector 5. The X-ray filters 27 a to 27 d suitable for the incident state are selected, and a command and information for setting the selected X-ray filter are output to the mechanism control unit 13.

  Further, the data processing unit 15 creates a cross-sectional image based on the radiation transmission signal converted into a digital signal from the data collection unit 8 in order to create a cross-sectional image by the operation of the RR method, and displays the cross-sectional image as a display unit. 16 is displayed.

Next, the operation of the computed tomography apparatus according to this embodiment configured as described above will be described. The operator installs the subject 6 so that the X-ray 2 is irradiated to the slice position of the subject 6, and refers to the menu screen as shown in FIG. 26, selection is made for each item of scan speed, slice width, focus size, and resolution. In accordance with this selection, the data processing unit 15 obtains a total dB number p that is the total number of dBs assigned to each item, and selects the X-ray filters 27a to 27d based on the total dB number p. The number of dB assigned to each item is a value preset to a number (10 × log (X dose / reference X dose)) proportional to the logarithm of the X dose. Here, when selecting the X-ray filters 27a to 27d from the total dB number p, for example, the selection is made according to the criteria shown in Table 1.

  Among the X-ray filters 27a to 27d, the X-ray filter 27a is the thinnest, and gradually increases in the order of the X-ray filter 27b, the X-ray filter 27c, and the X-ray filter 27d.

  The X-ray filters 27a to 27d absorb the lower energy component having a smaller transmission capability among the energy components of the X-ray 2 better, and the subject 6 also absorbs the lower energy component having the smaller transmission capability similarly.

  Therefore, even if the X-ray filters 27a to 27d are passed, the energy component of the X-ray 2 that passes through the subject 6 does not change much, but the energy component of the X-ray 2 that passes through both sides of the subject 6 is low. Since many energy components are included, the low energy components are attenuated and changed through the X-ray filters 27a to 27d.

  Therefore, the total energy of the X-ray 2 that passes through the subject 6 containing a large amount of high energy components is not changed much even through the X-ray filters 27a to 27d, and the total energy of the X-ray 2 that passes through both sides of the subject 6 is not changed. This reduces the saturation of the integrators and amplifiers that are components of the radiation detector 5.

  When the X-ray filters 27a to 27d are selected, the data processing unit 15 outputs a filter setting signal to the mechanism control unit 13 so that the X-ray 2 is filtered by the selected X-ray filter, and also scan speed. A command for setting the slice width, the X-ray focal point, and the resolution to the state selected by the operator is output to the mechanism control unit 13, and the mechanism control unit 13 drives each drive mechanism to set the scanning condition.

  The scan is performed by continuously rotating the rotary table 12 at a constant speed, as in a computer tomography apparatus using a normal RR method, and the radiation transmission signal detected by the radiation detector 5 is converted into a data collection unit 8 at equal angular pitches. Are collected, and the data processing unit 15 creates a cross-sectional image from 360 ° data.

  Here, the integration time per data varies depending on the set scan speed, and the integration time per data becomes longer during fine scan (low speed). The reconstruction process is performed by a method similar to that of a normal computed tomography apparatus. However, when the focal points S1 and S2 are switched, detection elements (center channel) existing on a straight line connecting the focal points S1 and S2 and the rotation center c. ) Since N1 and N2 also change, the center channels N1 and N2 are switched and executed.

  Next, the operation of the X-ray filters 27a to 27d will be described in more detail with reference to FIGS. In FIG. 10 and FIG. 11, it is assumed that the X-ray dose has changed by 2 times (+3 dB) by 8 times by switching the items of scan speed, slice width, X-ray focus, and resolution. X-ray energy spectra when the X-ray filters 27a to 27d are selected are shown.

  Here, FIG. 10 shows an X-ray energy spectrum of the X-ray 2 detected by the radiation detector 5 when air passes through, that is, when the subject is not installed. In FIG. 10, the thicker the X-ray filter, the higher the X-ray energy spectrum is shifted to the higher energy side, but the integrated value of the X-ray energy spectrum is approximately 120 Mev (relative). This is because an X-ray filter having a thickness (1 mm, 5 mm, 9.9 mm, and 15.3 mm, respectively) that does not change the total energy for each X-ray dose is selected.

  On the other hand, FIG. 11 shows an X-ray energy spectrum of the X-ray 2 detected by the radiation detector 5 when aluminum having a thickness of 200 mm is used as a subject and the aluminum is transmitted.

  In FIG. 11, the integral value increases as the X-ray filter is thicker. Therefore, by selecting an appropriate X-ray filter, the X-ray dose irradiated to the radiation detector 5 when passing through the subject can be increased while preventing saturation of the components of the radiation detector 5.

  Hereinafter, effects of the computed tomography apparatus according to the present embodiment will be described. Since the computed tomography apparatus according to the present embodiment can switch the scan speed, does the operator want to obtain a cross-sectional image in a short time or a high-quality cross-sectional image over time? Can be selected.

  In addition, a total dB number p indicating the X-ray dose when the scan speed, slice width, X-ray focus, and resolution are switched is calculated, and X-ray filters 27a to 27d adapted to the X-ray dose according to the total dB number p. Is set automatically.

  Here, in the computed tomography apparatus according to the present embodiment, since the radiation detector 15 detects the X-ray dose through the automatically set X-ray filters 27a to 27d, the component parts of the radiation detector 15 are used. Since the integrator or amplifier overflow is prevented and the integration time can be increased or the X-ray dose can be increased within the range where this overflow does not occur, a high-quality cross-sectional image with less noise can be created. .

  That is, in the computed tomography apparatus according to the present embodiment, even if the slice width of the X-ray 2 is increased by the slice width switching mechanism 29, the constituent parts of the radiation detector 15 are passed through the selected X-ray filter. Even in the case of the subject 6 that is difficult to transmit the X-ray 2 or the subject 6 with little change in the width direction, it is possible to increase the X-ray dose by widening the slice width. Since a cross-sectional image can be created with an appropriate X-ray dose, the image quality of the cross-sectional image can be improved.

  Similarly, the computed tomography apparatus according to the present embodiment filters the emitted X-ray 2 with an appropriate X-ray filter, so that the components of the radiation detector 15 are not saturated, and the X-ray focal point S1. , The X-ray dose can be changed by switching S2, and even in the case of the subject 6 or the like that does not easily transmit X-rays 2, the X-ray dose is increased by switching to the large focal point S2, and the spatial resolution is lowered. However, a high-quality cross-sectional image with less noise can be obtained.

  Similarly, the computed tomography apparatus according to the present embodiment filters the emitted X-ray 2 with an appropriate X-ray filter, so that the resolution switching mechanism 33 is within a range in which the components of the radiation detector 15 are not saturated. Therefore, even in the case of the subject 6 that does not easily transmit the X-ray 2, the spatial resolution is reduced but the noise is reduced by increasing the opening width of each detection element 30a. A cross-sectional image with image quality can be obtained.

  In addition, the computed tomography apparatus according to the present embodiment can obtain a cross-sectional image by the same reconstruction process because the angle pitch at the time of data collection is the same without being affected by the scan speed. There are also advantages.

  Furthermore, the computed tomography apparatus according to the present embodiment not only increases the X-ray dose in a range in which the components of the radiation detector 15 are not saturated by automatic setting of the X-ray filters 27a to 27d, but also the X-ray filters 27a to 27a. The attenuation of the low energy component by passing through 27d can prevent the occurrence of artifacts due to the line quality effect such as cupping and improve the cross-sectional image.

  In the computed tomography apparatus according to the present embodiment, the X-ray tube 1 is used as a radiation source, but the present invention is not limited to this, and other transmissive radiation can be used.

  Although the case where the cross-sectional image is reconstructed by the RR method has been described as an example, the present invention can be similarly applied to other types of computer tomography apparatuses, and similar effects can be obtained by similar operations.

  Furthermore, in the computed tomography apparatus according to the present embodiment, each item of scan speed, slice width, X-ray focus, and resolution can be selected, but not all items can be selected in this way. Any combination of items may be selectable.

  Further, the selection of the X-ray filters 27a to 27d does not necessarily need to be calculated logarithmically, and an amount proportional to the X-ray dose may be used as it is. The X-ray filters 27a to 27d may be selected.

  In addition, the thicknesses of the X-ray filters 27a to 27d do not need to be 1 mm, 5 mm, 9.9 mm, and 15.3 mm exemplified above, and may be other numerical values. There is no need to be a step, and any step of two or more steps can be applied. Further, the material of the X-ray filter is not limited to copper, and other materials may be used, and it is not necessary to use the same material.

  The present invention is effective in the field of computer tomography apparatuses.

The block diagram which shows the system configuration | structure of the computed tomography apparatus which concerns on 1st Embodiment by another invention. The figure which shows the example of the 1st cross-sectional image produced by the computer tomography apparatus which concerns on the embodiment. The figure which shows the example of the 2nd cross-sectional image produced by the computer tomography apparatus which concerns on the embodiment. The figure which shows the example of the 3rd cross-sectional image produced by the computer tomography apparatus which concerns on the embodiment. The block diagram which shows the system configuration | structure of the computed tomography apparatus which concerns on 2nd Embodiment by this invention. The figure which shows the relationship between a filter case and a filter switching mechanism. The figure which shows the relationship between a collimator and a slice width switching mechanism. The figure which shows the relationship between a detection element row | line | column and a resolution collimator. The figure which shows the example of a menu screen. The figure which shows the example of the X-ray energy spectrum at the time of air permeation | transmission. The figure which shows the example of the X-ray energy spectrum at the time of aluminum permeation | transmission. 1 is a block diagram showing a conventional TR computed tomography apparatus. The figure which shows the example when an artifact generate | occur | produces in the cross-sectional image of a pin-shaped subject.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... X-ray tube, 2 ... X-ray, 3, 4 ... Collimator, 5 ... Radiation detector, 6 ... Subject, 8 ... Data collection part, 9 ... Vertical movement mechanism, 10 ... Translation mechanism, 11 ... Rotation mechanism , 12 ... Rotary table, 13 ... Mechanism control unit, 14 ... X-ray control unit, 15 ... Data processing unit, 16 ... Display unit, 19 ... Base, 20 ... Translate frame, 21 ... CPU, 22 ... Image memory, 24 ... System bus, 25 ... Image bus, 26 ... Keyboard

Claims (4)

A radiation source that radiates radiation to the subject, radiation detection means that detects radiation emitted from the radiation source and passed through the subject as a radiation transmission signal, and a measurement system constituted by the radiation source and the radiation detection means; A reconstructing unit that creates a cross-sectional image of the subject from a driving unit that relatively rotates or moves the subject at a specified speed, and a radiation transmission signal detected by the radiation detecting unit during the rotation or movement. A computed tomography apparatus comprising:
A plurality of radiation filters for changing the energy component of radiation emitted from the radiation source;
When the rotation or movement speed is changed by the driving means, a radiation filter selected from the plurality of radiation filters is inserted between the radiation source and the radiation detection means according to the changed speed. A computed tomography apparatus comprising: a filter switching means. A radiation source that emits radiation to the subject, radiation detection means that detects radiation emitted from the radiation source and transmitted through the subject as a radiation transmission signal, and a measurement system constituted by the radiation source and the radiation detection means; Drive means for relatively rotating or moving the subject, and reconstructing means for creating a cross-sectional image of the subject from the radiation transmission signal detected by the radiation detecting means during the rotation or movement. In computed tomography equipment,
A collimator for shaping the radiation into fan-shaped radiation having a specified slice width;
A plurality of radiation filters for changing the energy component of radiation emitted from the radiation source;
A filter switching means for inserting a radiation filter selected from the plurality of radiation filters between the radiation source and the radiation detection means in accordance with the changed slice width when the slice width is changed; A computed tomography apparatus comprising: A radiation source capable of changing the focal point of the generated radiation to a specified size and changing the amount of radiation emitted to the subject, and radiation that detects radiation emitted from the radiation source and transmitted through the subject as a radiation transmission signal Detection means, measurement means constituted by the radiation source and the radiation detection means, and drive means for relatively rotating or moving the subject, and radiation detected by the radiation detection means during this rotation or movement In a computed tomography apparatus comprising a reconstruction means for creating a cross-sectional image of the subject from a transmission signal,
A plurality of radiation filters for changing the energy component of radiation emitted from the radiation source;
A filter that inserts a radiation filter selected from the plurality of radiation filters between the radiation source and the radiation detecting means according to the changed focal spot size when the focal spot size is changed. A computed tomography apparatus comprising: a switching unit. A radiation source that emits radiation to the subject, radiation detection means that detects radiation emitted from the radiation source and transmitted through the subject as a radiation transmission signal, and a measurement system constituted by the radiation source and the radiation detection means; Drive means for relatively rotating or moving the subject, and reconstructing means for creating a cross-sectional image of the subject from the radiation transmission signal detected by the radiation detecting means during the rotation or movement. In computed tomography equipment,
A resolution variable means for changing the resolution of the radiation detection means to a designated resolution by changing the aperture width of each of the multiple detection elements constituting the radiation detection means;
A plurality of radiation filters for changing the energy component of radiation emitted from the radiation source;
A filter switching means for inserting a radiation filter selected from the plurality of radiation filters between the radiation source and the radiation detection means in accordance with the changed resolution when the resolution is changed; The computer tomography apparatus characterized by the above-mentioned.

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