JP2009257791A - X-ray tomographic imaging equipment and x-ray tomographic imaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the imaging time, without causing the brightness of projected image acquired by means of an X-ray two-dimensional detector to be lowered. <P>SOLUTION: A synchronization signal is sent from a synchronization signal generating part 26 to the X-ray two-dimensional detector 2 so that a first pulse zone arises for longer pulse widths (periods), at imaging an inspected body 7 (in time of its still standing), while a second pulse zone arises for shorter pulse widths (periods), at rotating the inspected body 7 to control the imaging of projection images by means of the two-dimensional detector 2. Projected images of respective angle phases are imaged by means of the two-dimensional detector 2, to perform the reconstruction calculation of internal structure data from the acquired projected images acquired. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an X-ray tomographic imaging apparatus and an X-ray tomographic imaging method for inspecting internal structure data of an object to be examined using X-rays or the like.

  Conventionally, non-destructive three-dimensional analysis is required in the field of research and development of semiconductor elements and the like in order to inspect cracks, breaks, and the like that exist inside a micro-inspection object. As one of the methods, there is a method using a computed tomography apparatus using X-rays (hereinafter referred to as “X-ray tomography apparatus”).

  An X-ray tomographic imaging apparatus, for example, irradiates a subject to be examined in a conical shape (cone beam shape) through an X-ray source (an X-ray generator configured with an X-ray tube or the like) and an X-ray focal point from the X-ray source. Provided between the X-ray source and the X-ray two-dimensional detector, and from the X-ray focal point to the X-ray two-dimensional detector. A rotation base portion is provided with an angular displacement based on the setting with the object to be inspected placed around a rotation axis perpendicular to a perpendicular line dropped on the detection surface. In such an X-ray tomographic imaging apparatus, the X-ray source irradiates the object to be inspected with X-rays, and the transmitted X-ray projection image of the object to be inspected is picked up by the X-ray two-dimensional detector and digitized. Each is processed as a plurality of image data (projection data). Then, the internal structure data is reconstructed from the plurality of image data, thereby facilitating inspection and observation inside the object to be inspected.

  In an industrial X-ray tomographic imaging apparatus that inspects minute parts such as semiconductor elements, cone beam X-rays are generally used as described above. The smaller the focal spot size of the cone-beam X-rays, the more the blurring of the edges (ends) caused by the enlargement of the transmitted X-ray projection image is suppressed. Therefore, a fine projection image (tomographic image) is obtained by the X-ray two-dimensional detector. Is obtained. In recent years, an open X-ray tube has been developed in place of a conventional sealed X-ray tube for a microfocus X-ray source having an X-ray focal spot size of a micron unit or less. Since this open X-ray tube has a very small focal spot size, a clear image with high resolution and no blur can be obtained. In addition, the structure is characterized in that the object to be inspected can be placed near the X-ray focal point and the magnification is high.

For example, using an X-ray two-dimensional detector placed in an apparatus having a limited space, the X-ray two-dimensional detector is swung along a cylindrical surface centering on the X-ray source, An X-ray tomographic imaging apparatus that improves the magnification ratio of a projected image while suppressing luminance attenuation has been disclosed (see, for example, Patent Document 1).
JP 2007-101247 A

  By the way, since the industrial X-ray tomographic imaging apparatus described in Patent Document 1 requires a high-resolution projection image, the focal size of X-rays irradiated from the X-ray source is very small. And it is designed to obtain a projection image with a large magnification.

  However, since the brightness of X-rays with a small focus is generally low, the projection image obtained by the X-ray two-dimensional detector becomes dark. Therefore, the X-ray two-dimensional detector needs to be exposed to transmitted X-rays for a certain period of time, and the object to be inspected must be fixed so that the image projected on the X-ray two-dimensional detector does not blur during that time. There is.

  In addition, when the magnification ratio of the projected image is large, the distance from the X-ray focal point to the object to be inspected is short, and the distance from the X-ray focal point to the X-ray two-dimensional detector is far and wide. The brightness of X-rays captured by the two-dimensional detector is lowered, and as a result, the projected image is darkened. Therefore, the X-ray two-dimensional detector needs to be exposed for a certain time or more, and the object to be inspected needs to be fixed so that the image projected on the X-ray two-dimensional detector does not blur during that time.

  As described above, in the imaging of the projection image of each angle phase (tomographic imaging process) in the X-ray tomographic imaging apparatus, it is necessary to perform exposure for a certain period of time or more in order to obtain a clear projection image. It is desirable that the object to be inspected (rotation base) is stationary so that the image projected on the X-ray two-dimensional detector does not blur.

  Currently, in a tomographic imaging process, first, X-rays emitted from an X-ray source are continuously irradiated to an X-ray two-dimensional detector through an object to be inspected. Then, the X-ray two-dimensional detector outputs image data of the captured projection image to the outside in synchronization with a synchronization signal having a pulse having a constant interval and a constant length.

  FIG. 1 is a timing chart showing a synchronization signal supplied to an X-ray two-dimensional detector from a synchronization signal generator (not shown) and a state of an object to be inspected in the prior art. In the figure, (A) shows the synchronization signal, (B) shows the exposure on the detection surface, (C) shows the object to be inspected, and (D) shows the state of capturing the projected image.

  As shown in FIG. 1A, in the conventional synchronization signal, a pulse having a high level (on) width H1 and a pulse having a low level (off) width L1 are regularly and alternately repeated. The combination of the pulse with the width L1 is repeated. In this example, the total length of the high-level width H1 pulse and the low-level width L1 pulse is, for example, about 1000 msec.

  Conventionally, the synchronization signal is configured by regular repetition of a pulse having a high level of width H1 and a pulse having a low level of width L1, and the object to be inspected must be kept stationary during imaging. The following imaging process has been performed.

  First, when the first high-level pulse of width H1 is supplied from the synchronization signal generator to the X-ray two-dimensional detector (FIG. 1A), the X-ray two-dimensional detector detects the pulse of width H1. The rise is detected, and the detection surface is exposed (FIG. 1B).

  When the X-ray two-dimensional detector detects the falling of the high-level width H1 pulse, the X-ray two-dimensional detector ends the exposure on the detection surface, and stores the image data of the projected image of the subject at the initial angle phase in a main memory (not shown). Memorize temporarily.

  Subsequently, the image data of the projection image temporarily stored in the main memory or the like is taken in and stored in a storage device (projection image storage unit) (not shown) (FIG. 1D). This storage device is constituted by non-volatile storage means such as a hard disk.

  In parallel with the capture to the projection image storage unit, the second high-level width H1 pulse is supplied to the X-ray two-dimensional detector after the low-level width L1 pulse, and the rotation control signal is received. Supplied to the rotating base on which the inspection object is placed. The motor of the rotation base operates in response to the rotation control signal, and moves the object to be inspected to the second angle phase rotated by a predetermined angular displacement from the initial angle phase (FIG. 1C). As described above, the X-ray two-dimensional detector also has the second high-level width H1 pulse and the low-level width L1 pulse while the rotating base on which the object to be inspected is rotating. The X-ray two-dimensional detector performs exposure on the detection surface and temporarily stores the image data of the projection image in the main memory.

  However, the projection image obtained by the exposure here has a large shake because the object to be inspected is rotating, and cannot be used for an image for reconstruction. Therefore, the projection image obtained during the second high-level pulse of width H1 is discarded without being stored in the projection image storage unit. Actually, it is overwritten with the image data of the projection image obtained during the next pulse of the third high level width H1. Is overwritten on the image data of the projection image obtained during the second pulse of the high level width H1. Thereby, the image data of the projection image obtained during the second high-level pulse with the width H1 is not stored.

  Next, when the X-ray two-dimensional detector detects that the third high-level pulse of width H1 has been input, exposure at the second angular phase rotated by a predetermined angular displacement from the initial angular phase is performed. Execute and temporarily store in main memory or the like.

  When the falling edge of the third high-level pulse of width H1 is detected, the rotation base is rotated to the third angle phase and the image data of the projection image at the second angle phase is projected. Capture to the image storage unit. In this way, the X-ray two-dimensional detector repeats the projection image capturing process at each set angular phase. This series of processing is performed until the image data of the number of projection images required for the reconstruction of the inspection object is acquired, and the image data of all the projection images is reconstructed to obtain the internal structure data of the inspection object. obtain.

  However, the image data of the projected image captured during the rotation of the object to be inspected must be discarded because the object to be inspected is not stationary. It took twice as long as the pulse width (H1 and L1). On the other hand, since the exposure time depends on the pulse width of the synchronizing signal, shortening the pulse width of the pulses that are regularly repeated at regular intervals is very effective for shortening the imaging time, but on the other hand, the projected image due to insufficient exposure of X-rays. There is a problem that the brightness is lowered.

  The present invention has been made in view of such a situation, and makes it possible to shorten the imaging time without reducing the brightness of the projected image obtained by the X-ray two-dimensional detector. .

  An X-ray tomographic apparatus according to one aspect of the present invention includes an X-ray source, two-dimensional detection means for detecting transmitted X-rays of a subject based on a pulse included in a synchronization signal, a first pulse region, A synchronization signal generating unit that generates a synchronization signal alternately including a second pulse region shorter than the first pulse region, and a transmission detected by the two-dimensional detection means between the first pulse region of the synchronization signal A projection image storage unit for storing a projection image by X-rays, rotation control means for generating a rotation control signal synchronized with the second pulse region of the synchronization signal, an X-ray focal point of the X-ray source, and the two-dimensional Based on the rotation control signal generated between the rotation control unit and the detection unit, the object to be inspected is placed on the detection surface at the initial position of the two-dimensional detection unit from the X-ray focal point. Set around the axis of rotation perpendicular to the lowered perpendicular Characterized in that it comprises rotating means for rotating at the angular displacement, a.

  An X-ray tomographic imaging method according to one aspect of the present invention includes an X-ray source, two-dimensional detection means for detecting transmitted X-rays of an object to be inspected based on a pulse included in a synchronization signal, and the X-ray of the X-ray source. Based on a rotation control signal generated between the focal point and the two-dimensional detection unit and generated by the rotation control unit, the inspection object is placed and an initial state of the two-dimensional detection unit is determined from the X-ray focal point. X-ray tomography by an X-ray tomographic imaging apparatus including a rotating means that rotates at a set angular displacement about a rotation axis perpendicular to a perpendicular drawn to a detection surface at a position and that captures a projected image for each angular phase This is an imaging method. That is, a step of generating a synchronization signal alternately including a first pulse region and a second pulse region shorter than the first pulse region, and the two-dimensional detection means being included in the synchronization signal Detecting the transmitted X-ray of the object to be inspected based on the pulse region and the second pulse region, and the rotation means based on the rotation control signal synchronized with the second pulse region of the synchronization signal Rotating the set angular displacement, and storing only a projection image of transmitted X-rays detected by the two-dimensional detection means between the first pulse regions of the synchronization signal. It is characterized by including.

  In one aspect of the present invention, the object to be inspected is stationary when a projection image of the object to be inspected is captured, and a sufficient exposure time can be secured, and a delay in image data acquisition time due to the required time when the object is rotated. Can be minimized. Therefore, it is possible to shorten the time required to capture the projected image of the stationary object to be inspected at each angle phase, and to shorten and speed up the acquisition of the necessary number of image data.

  According to the present invention, the imaging time can be shortened without reducing the brightness of the projected image obtained by the X-ray two-dimensional detection means.

  Hereinafter, examples of embodiments of the present invention will be described with reference to the accompanying drawings.

  The embodiment described below is a specific example of a preferred embodiment for carrying out the present invention, and therefore various technically preferable limitations are given. However, the present invention is not limited to these embodiments unless otherwise specified in the following description of the embodiments. Therefore, for example, the materials used in the following description, the amounts used, the processing time, the processing order, and the numerical conditions of each parameter are only suitable examples, and the dimensions, shapes, and arrangements in the drawings used for the description are also examples. The relationship and the like are also schematic showing an example of the embodiment.

  That is, although an X-ray tomographic imaging apparatus widely used among computer tomographic imaging apparatuses will be described as an example, the present invention irradiates an object with X-rays and other radiations from multiple directions and images the projection image thereof. The present invention can be applied to a computer tomography apparatus that reconstructs internal structure data from a plurality of projection data.

2A and 2B are schematic views showing a configuration example of the first embodiment of the X-ray tomographic imaging apparatus of the present invention, where FIG. 2A is a front view and FIG. 2B is a side view.
The X-ray tomographic imaging apparatus according to the present embodiment includes, as major elements, an X-ray tube 1, an X-ray two-dimensional detector 2, and a rotating base 3 on which an inspected object 7 is placed. It is installed and covered with a shield cover 11.

  The X-ray tube 1 is, for example, an X-ray generator (X-ray source) that generates cone-beam X-rays. The X-rays generated in the X-ray tube 1 are irradiated on the entire inspection object 7 or a part thereof.

  The X-rays irradiated from the X-ray tube 1 are configured to form a minimal X-ray focal point having a focal size of about 1 μm or less, for example. Since the X-ray focal spot size is a large factor that determines the resolution of the X-ray tomographic imaging apparatus, the smaller the numerical value, the more preferable it is possible to observe a minute size of damage inside the object to be inspected.

  The X-ray two-dimensional detector 2 detects X-rays that are emitted from the X-ray tube 1, pass through the inspection object 7, and enter the detection surface. As the X-ray two-dimensional detector 2, for example, a flat panel detector (FPD) can be applied, and the X-ray two-dimensional detector 2 detects the perpendicular line dropped from the X-ray focal point of the X-ray tube 1 to the detection surface. It arrange | positions so that it may be located in the center of a surface. The position of the X-ray two-dimensional detector 2 can be adjusted left and right and up and down (XYZ directions) by the X-ray two-dimensional detector driving mechanism 14. Furthermore, the X-ray two-dimensional detector 2 can be rotated about the axis parallel to the Z-axis by the X-ray two-dimensional detector rotation drive mechanism 15.

  As an example, FPD is disclosed in Japanese Patent Laid-Open No. 6-342098 (hereinafter referred to as “Document 1”). The FPD described in Document 1 absorbs X-rays transmitted through a subject by a photoconductive layer, generates charges according to the X-ray intensity, and detects the amount of charges for each pixel. In the FPD of the method disclosed in this document 1, since the X-ray dose is directly converted into the charge amount for each pixel, the sharpness degradation in the FPD is small and an image with excellent sharpness can be obtained. As an example of other types of FPDs, as disclosed in, for example, JP-A-9-90048, X-rays are absorbed in a phosphor layer such as an intensifying screen to generate fluorescence, and the intensity of the fluorescence Is detected by a photoelectric conversion element.

  As other fluorescence detection means, there is a method using a CCD (Charge Coupled Devices) or a C-MOS (Complementary Metal Oxide Semiconductor) sensor. As described above, the X-ray two-dimensional detector 2 of this example may be any device that can detect the transmitted X-rays of the inspection object 7 and process each pixel to obtain an image signal.

  The rotating base 3 is an example of a rotating means for placing the object to be inspected 7 and rotating in a state where the object to be inspected 7 is placed. Hereinafter, the entire rotation base portion including a motor (not shown) for rotating the rotation base portion and a bearing described later is referred to as a rotation base. The rotation base portion includes a Z-axis drive mechanism 3a for moving the rotation base 3 in the direction parallel to the rotation axis, that is, in the Z-axis direction as shown in FIG. Furthermore, a Y-axis drive mechanism 6 is provided for moving the device under test 7 in the Y-axis direction. The inspected object 7 is configured to be held and fixed by a holding jig 8 on the rotary base.

  The rotary base 3 is supported by an air bearing 4, and a servomotor (not shown) having an angular positioning accuracy of, for example, 0.2 minutes or less is directly connected to the air bearing 4 and a rotational phase. Detection means are provided. By means of these servo motors and rotational phase detection means, the rotation base 3 can be synchronized with the projection data capture period required for the reconstruction of the internal structure data at each angular displacement corresponding to the resolution of the servo motors and rotational phase detection means. Quiesced.

  The rotation axis of the bearing 4 that supports the rotation base 3 is orthogonal to a perpendicular line that descends from the focal point of the X-ray tube 1 to the vicinity of the center of the detection surface of the X-ray two-dimensional detector 2. In this example, the bearing 4 is composed of an air bearing capable of controlling the rotational base 3 with a minute angular displacement. However, the bearing 4 is not limited to this, and the minute angular displacement required by supporting the rotational base 3 and rotating smoothly. Any device can be used as long as it can control the above.

  The XY table 5 moves the X-ray tube 1 on an XY plane orthogonal to the rotation axis of the bearing 4. The turning radius of the inspected object 7 is appropriately fed back to the XY table 5, and projection data can be acquired in a state where the inspected object 7 and the XY table 5 are in close proximity as necessary. The highest element that controls the enlargement ratio is the distance between the X-ray focal point and the object 7 to be inspected held on the rotating base 3. If the enlargement ratio is large, the internal structure of a finer part is analyzed. It becomes possible to do.

  The vibration isolation table 10 mounts all the devices, members, and the like that constitute the above-described X-ray tomographic imaging apparatus, and removes vibrations so that no error occurs in the X-ray irradiation position. The shield cover 11 is made of lead or the like, and covers the entire apparatus so that X-rays do not leak outside the X-ray tomographic imaging apparatus.

  FIG. 3 is a block diagram showing an internal configuration of the X-ray tomographic imaging apparatus shown in FIG.

  As described above, the X-ray tube 1 irradiates the inspection object 7 placed on the rotation base 3 with X-rays. The intensity and quality of X-rays irradiated at this time are controlled by the control operation unit 22 through the X-ray control unit 20 which is X-ray control means.

  The mechanism control functioning as a mechanism control means (rotation control means) for controlling the position and movement of the rotation base 3 such as the position, rotation angle displacement, and initial angle phase of the rotation base 3 on which the inspection object 7 is placed. It is controlled by the control operation unit 22 through the unit 21 (rotation control unit). The inspected object 7 placed on the rotating base 3 is rotated at a predetermined rotational speed by the angular displacement specified by the control signal from the control operation unit 22, and the projection image is taken by the X-ray two-dimensional detector 2. Is done.

  The control operation unit 22 controls and calculates each block constituting the X-ray tomographic imaging apparatus. The control operation unit 22 includes a control unit 22A that generates a control signal to be output to each block and executes arithmetic processing, and a non-volatile memory that is used as a work area when the control unit 22A performs control / arithmetic processing. 22B and an input unit 22C as an interface through which setting information and the like are input from the outside. As the control operation unit 22, for example, a personal computer (hereinafter referred to as “PC”) to which input means such as a keyboard and display means for displaying a GUI (Graphical User Interface) screen, a reconstruction result of a subject image, and the like are connected. .) Etc. can be applied.

  The control operation unit 22 performs calculation / control of an X-ray tomographic imaging process, which will be described later, according to a program stored in a non-volatile memory (not shown) such as a ROM (Read Only Memory) by the control unit 22A. In addition, the control operation unit 22 displays information such as the X-ray intensity of the X-rays emitted from the X-ray tube 1 on the display unit, or an operation signal input to the input unit by the user via the input unit. Based on this, a control command is output to the X-ray control unit 20 or a command for appropriately positioning the object to be inspected 7 is output to the rotating base 3. Also, a command is output to the synchronization signal generator 26 so as to generate a synchronization signal. Further, the control operation unit 22 issues a command to the X-ray two-dimensional detector 2 through the mechanism control unit 21 to control the turning angle (rotation angle), movement in the X-axis direction, and the like.

  The synchronization signal generator 26 is shorter than the first pulse region for the X-ray two-dimensional detector 2 to capture the transmitted X-rays of the inspection object 7 and the first pulse region for rotating the rotating base 3. A synchronization signal alternately including the second pulse region is generated. The generated synchronization signal is supplied to the X-ray two-dimensional detector 2 and the mechanism control unit 21.

  The mechanism control unit 21 extracts the second pulse region from the synchronization signal supplied from the synchronization signal generation unit, generates a rotation control signal including the second pulse region, and outputs the rotation control signal to the rotation base 3 (motor). Is. Further, a stop signal including information indicating that the rotation base 3 is stopped is supplied to the control operation unit 22.

  The X-ray two-dimensional detector 2 synchronizes the X-rays emitted from the X-ray tube 1 and transmitted through the inspection object 7 in synchronization with a pulse included in the synchronization signal, that is, the first pulse region or the second pulse region. , Capture and detect. The X-ray two-dimensional detector 2 includes a memory 2a (projection image holding unit) that stores a projection image, and temporarily stores the detected projection data of transmitted X-rays in the projection image holding unit 2a. This process is executed for the number of sheets instructed from the control operation unit 22 (for each angle phase). Then, the X-ray two-dimensional detector 2 supplies the detected transmitted X-ray information as a projection image to a projection image storage unit 23 as a projection image storage unit. In this example, the projection image holding unit 2a is assumed to be volatile such as a main memory, but a nonvolatile storage unit may be applied. Further, the memory 22B of the control operation unit 22 may be used as a place for temporarily storing projection data captured by the X-ray two-dimensional detector 2.

  The projection image storage unit 23 associates the projection image supplied from the X-ray two-dimensional detector 2 with the angle phase at the time of imaging as digitized projection data in response to an instruction from the control unit 22A of the control operation unit 22. save. Further, the projection data supplied from the X-ray two-dimensional detector 2 is stored in the projection image storage unit 23 in association with not only the angle phase but also information such as the angular displacement at the time of imaging, the initial angle phase, and the X-ray intensity. May be. The projection image storage unit 23 only needs to have a capacity capable of recording projection data, and includes various types including a large-capacity magnetic recording device, a removable recording medium such as an optical recording medium and a semiconductor memory, and the like. Can be applied.

  The projection data stored in the projection image storage unit 23 is supplied to a reconstruction calculation computer 24 that functions as reconstruction means connected thereto. The reconstruction calculation computer 24 reconstructs the internal structure data of the inspection object 7 from the input projection data. The reconstructed internal structure data (reconstruction data) is stored in the projection image storage unit 23 or another recording medium, and is input to the reconstruction result display device 25 as display means via a display memory (not shown). It is displayed on a display such as a liquid crystal display device.

  The reconstruction calculation computer 24 may have an arithmetic processing capability capable of collecting input projection data and reconstructing internal structure data, and may be shared with the control operation unit 22. The reconstruction result display device 25 may be shared with display means connected to the control operation unit 22.

  With the configuration as described above, the internal structure data of the inspection object 7 is generated, and the internal structure of the inspection object 7 is displayed on the reconstruction result display device 25. The operator (operator) determines the presence and state of defects such as cracks and breaks in the object to be inspected, such as multilayer film plates and minute electronic component elements, by the internal structure displayed on the reconstruction result display device 25. It can be confirmed visually.

  Next, with reference to the timing chart of FIG. 4, the operation timing of each part in the X-ray tomographic imaging apparatus according to the first embodiment will be described.

  When receiving a synchronization signal generation command from the control operation unit 22, the synchronization signal generation unit 26 generates a synchronization signal shown in FIG. The synchronization signal includes a pulse 31 having a high level width H1, a pulse 32 having a low level width L1, a pulse 33 having a high level width H2 shorter than the pulse 31, a pulse 34 having a low level width L2, and so on. Furthermore, a pulse 35 having a high level width H1, a pulse 36 having a low level width L1, a pulse 37 having a high level width H2, a pulse 38 having a low level width L2, and so on, at a predetermined cycle. The pulses are repeated.

  Here, a combination of the pulse 31 having the high level width H1 and the pulse 32 having the low level width L1 is defined as a “first pulse region”. Similarly, the combination of the pulse 35 having the high level width H1 and the pulse 36 having the low level width L1 is defined as a “first pulse region”. On the other hand, a combination of a high-level pulse H2 having a width H2 shorter than the pulse 31 and a low-level pulse L2 having a width L2 is defined as a “second pulse region”. Similarly, a combination of the high-level pulse H2 having a width H2 and the low-level pulse L2 having a width L2 is also referred to as a “second pulse region”.

  As described above, the synchronization signal is configured by repeating the “first pulse region” and the “second pulse region”. As will be described later, the first pulse region is an effective imaging period in which a projection image exposed by the X-ray two-dimensional detector 2 during this period is used for reconstruction of internal structure data. The second pulse region is an invalid imaging period in which the projection image exposed by the X-ray two-dimensional detector 2 during this period is not used.

  The length of the first pulse region is such that a sufficient time can be secured for the X-ray two-dimensional detector 2 to expose the X-rays irradiated on the detection surface. For example, if the time required for exposure is 1000 msec, the length of the first pulse region is set to 1000 msec.

  On the other hand, the length of the second pulse region is calculated based on the set angular displacement and the rotation speed of the rotary base 3, and the angular displacement of the rotary base 3 is set. Is determined based on the time required to rotate the motor. For example, when the time required for the rotation base 3 to rotate 1 ° as a predetermined angle is 200 msec, it may be set to 250 msec, which is a little longer than that.

  In this way, by shortening the second pulse region from the first pulse region, the time required for capturing the projected image of the stationary object to be inspected at each angle phase is shortened, and the number of sheets necessary for the tomographic imaging method is reduced. The acquisition of the image data can be shortened and speeded up.

  As a specific example, the first pulse region is set to 1000 msec and the second pulse region is set to 250 msec. However, the present invention is not limited to this example, and may be set as appropriate within the range satisfying the above conditions.

  The low level pulse 32 only needs to be able to detect that the period of the high level pulse 31 has ended. Therefore, the width L1 of the low level pulse 32 is sufficiently smaller than the width H1 of the high level pulse 31. Shall. The same applies to the relationship between the pulse H2 and the pulse L2. In this case, the length of the first pulse region is substantially equal to the width H1 of the high level pulses 31, 35, and the length of the second pulse region is substantially equal to the width H2 of the high level pulses 33, 36.

  The X-ray two-dimensional detector 2 receives the synchronization signal supplied from the synchronization signal generator 26 and performs exposure on the detection surface. As shown in FIG. 4B, this exposure is performed at a timing based on a high level pulse of the synchronization signal. Actually, the rising of the high-level pulses 31, 33, 35, 37 is detected to start exposure, and the falling of each pulse 31, 33, 35, 37 (or the low-level pulses 32, 34, 36, 37). 38) is detected and the exposure is terminated. The X-ray two-dimensional detector 2 temporarily stores the image data of the projected image in the memory 2a when the exposure on the detection surface in each pulse is completed.

  On the other hand, the mechanism control unit 21 generates a rotation control signal shown in FIG. 4C based on the synchronization signal supplied from the synchronization signal generation unit 26 and outputs the rotation control signal to the rotation base 3. The rotation control signal is generated by extracting the second pulse region included in the synchronization signal, that is, the pulses 33 and 37 having a high level width H2 in the mechanism control unit 21.

  The rotation base 3 rotates in the second pulse region (pulses 33 and 34, pulses 37 and 38) of the synchronization signal based on the high level pulse included in the rotation control signal supplied from the mechanism control unit 21. (FIG. 4D).

  As described above, the X-ray two-dimensional detector 2 is based on the first pulse region and the second pulse region of the synchronization signal supplied from the synchronization signal generator 26, and the object to be inspected is irradiated on the detection surface. Captures and detects transmitted X-rays. However, the X-ray two-dimensional detector 2 outputs a projection image captured when the rotation base 3 is stationary under the control of the control operation unit 22 to the projection image storage unit 23, and the rotation base 3 rotates. Discard the projected image taken when

  Therefore, as shown in FIG. 4E, after the pulses 31 and 35 having the high level width H1 in the first pulse region are completed, the reading to the memory 2a and the loading to the projection image storage unit 23 are performed. That is, when the projection image capturing operation includes at least the second pulse region (pulses 33 and 34, pulses 37 and 38) after the pulses 31 and 35 having the high-level width H1 in the first pulse region. Is set to be valid (high level).

  On the other hand, the image data of the projected image captured when the rotation base 3 is rotating is overwritten with the image data of the projected image obtained in the next exposure. Therefore, as shown in FIG. 4E, the image data of the projection image obtained in the second pulse region (pulses 33 and 34, pulses 37 and 38) is not taken into the projection image storage unit 23. In other words, the projection image capturing operation is invalid when the second pulse region (pulses 33 and 34, pulses 37 and 38) includes at least the high pulse widths H1 and 31 in the first pulse region ( Low level).

  Next, imaging processing by the X-ray tomographic imaging apparatus according to the first embodiment will be described with reference to the flowchart of FIG.

  First, in step S1, after the positioning of the X-ray tube 1, the inspected object 7 (rotation base 3), and the X-ray two-dimensional detector 2 is completed, an instruction to start imaging is given to the control operation unit 22. The control operation unit 22 outputs a control signal for generating a synchronization signal to the synchronization signal generation unit 26 to instruct generation of the synchronization signal. The generated synchronization signal is supplied to the X-ray two-dimensional detector 2 and the mechanism control unit 21. After the process of step S1 is completed, the process proceeds to step S2.

  In step S2, the control operation unit 22 sets the count value of the number of captured images to zero. The number of captured images can be counted by receiving information indicating the number of pulses included in the synchronization signal or the imaging processing status output from the X-ray two-dimensional detector 2. After the process of step S2 is completed, the process proceeds to step S3.

  In step S3, the X-ray two-dimensional detector 2 detects the rising edge of the high level pulse included in the synchronization signal (see FIG. 4A) supplied from the synchronization signal generator 26 and performs exposure. Then, after the process of step S3 for temporarily storing the captured projection image in the memory 2a is completed, the process proceeds to step S4.

  In step S <b> 4, the control operation unit 22 determines whether or not a stop signal indicating the end of the rotation operation of the inspection object 7, that is, the rotation base 3, has been received from the mechanism control unit 21. Here, when the stop signal is received, that is, when the rotation base 3 is stationary, the process proceeds to step S5.

  On the other hand, in the determination process of step S4, when it is determined that the stop signal has not been received, that is, the rotation base 3 is rotating, the process returns to step S3. Then, after the rising edge of the high level pulse included in the synchronization signal is detected and a projected image is taken, the determination process in step S4 is performed again to determine whether or not the subject 7 is stationary.

  In step S5, the control operation unit 22 determines that the projection image captured by the X-ray two-dimensional detector 2 in step S3 is a pulse having the width H1 and the width L1 of the synchronization signal, that is, between the first pulse regions. It is determined whether the image is captured. If the projected image is captured in the first pulse region, the process proceeds to step S6.

  On the other hand, if the projected image is not captured in the first pulse region, the process returns to step S3. Then, after the rising edge of the high level pulse included in the synchronization signal is detected and a projected image is taken, the determination process in step S4 is performed again to determine whether or not the subject 7 is stationary.

  In step S6, the projection image temporarily stored in the memory 2a of the X-ray two-dimensional detector 2 is stored in the projection image storage unit 23 based on the projection image capture timing shown in FIG. After the process of step S6 ends, the process proceeds to step S7.

  In step S7, the rotation base 3 is set based on the rotation control signal supplied from the mechanism control unit 21 after the pulses of the width H1 and the width L1 of the synchronization signal are completed, that is, when the first pulse region is completed. Rotate by the specified angular displacement. Thereby, the to-be-inspected object 7 mounted on the rotation base 3 is rotated by the set angular displacement. After the process of step S7 is completed, the process proceeds to step S8.

  In step S <b> 8, the projection image captured in the projection image storage unit 23 is displayed on a display unit (not shown) connected to the control operation unit 22 or the reconstruction result display device 25. This display process is not always necessary. After the process of step S8 is completed, the process proceeds to step S9.

  In step S9, the control operation unit 22 adds 1 to the current count value of the number of captured images to obtain a new count value. After the process of step S9 ends, the process proceeds to step S10.

  In step S10, the control operation unit 22 compares the new count value with the requested total number of images to be imaged and determines whether the new count value is the same as the total number of images to be imaged. If the result of determination is the same, a series of imaging processing ends.

  On the other hand, if it is determined in step S10 that the new count value is not the same as the total number of captured images, the process returns to step S3, and the above-described steps S3 to S11 are performed. Then, the X-ray tomographic imaging apparatus repeats a series of processing from step S3 to step S10 until imaging of the projected images for the total number of imaging is completed.

  As described above, in the first embodiment, the X-ray two-dimensional detector 2 has the first pulse region having a long pulse width (period) at the time of imaging of the inspection object 7 (at rest), the inspection target. When the body 7 is rotated, a synchronization signal is sent from the synchronization signal generator 26 so as to be a second pulse region having a short pulse width (period), and the imaging of the projected image by the X-ray two-dimensional detector 2 is controlled. Then, the X-ray two-dimensional detector 2 picks up the projection images of the respective angle phases, and the reconstruction calculation of the internal structure data is performed from the obtained projection images.

  As a result, the inspected object 7 is stationary when the projection image of the inspected object 7 is captured, and a sufficient exposure time can be secured. When the inspected object 7 rotates, the image data acquisition time is delayed due to the required time. The impact can be minimized. Therefore, it is possible to shorten the time required to capture the projected image of the stationary object 7 to be inspected at each angle phase, and to shorten and speed up the acquisition of image data for the number of sheets necessary for the tomographic imaging method.

  Further, since the second pulse region shorter than the first pulse region is set simultaneously with the end of the first pulse region with respect to the synchronization signal, the rotation base that rotates the inspection object 7 at the start of the rotation of the inspection object 7. The control system of the table 3 can react instantaneously, and it is possible to further reduce the time required for the rotating operation of the inspection object 7.

  For example, assuming that an exposure time of 1 second (1000 msec) is secured for capturing a projected image of an object to be inspected, it is assumed that an image is captured by a synchronization signal (see FIG. 1) having a pulse width of 1 second, which is a conventional X-ray tomographic imaging method. For example, it takes 96 minutes for the X-ray tomographic imaging method that captures 2880 projection images to reconstruct one internal structure data. On the other hand, in the X-ray tomographic imaging apparatus according to this embodiment, in the synchronization signal shown in FIG. 4A, the long pulse width (first pulse region) is 1 second (1000 msec) and the short pulse width (second By controlling the imaging operation of the X-ray two-dimensional detector using a synchronization signal in which the pulse area is set to 0.25 seconds (250 msec), the imaging time can be shortened to 60 minutes, and the imaging time is greatly reduced. Can be realized.

  Next, an X-ray tomographic imaging apparatus according to the second embodiment of the present invention will be described.

  FIG. 6 is a timing chart showing the operation timing of each unit in the X-ray tomographic imaging apparatus according to the second embodiment. The difference from the timing chart shown in FIG. 4 is that the first pulse region included in the synchronization signal is divided into a plurality of sub-pulse regions, and the total length of the plurality of sub-pulse regions is calculated by X-ray two The point is that it is equal to or longer than the time required for the exposure of the dimension detector 2. In this example, only the same case is displayed.

  The synchronization signal shown in FIG. 6 (A) divides the long first pulse region composed of the pulses 31 and 32 shown in FIG. 4 (A) into four, and four sub-pulse regions in the first pulse region. This is an example of formation. That is, one sub pulse region is formed from the sub pulse 41 having the high level width H1 and the sub pulse 42 having the low level width L1. Similarly, a sub-pulse 43 with a high level width H1, a sub-pulse 44 with a low level width L1, a sub-pulse 45 with a high level width H1, a sub-pulse 46 with a low level width L1, and a high level width H1. A sub-pulse region is formed by the sub-pulse 47 and the sub-pulse 48 having a low level width L1. Then, the first pulse region is constituted by these four sub-pulse regions.

  On the other hand, the second pulse region is the same as the pulses 33 and 34 shown in FIG. 4A, and is composed of a sub-pulse 49 having a high level width H2 and a sub-pulse 50 having a low level width L2.

  Similarly, the sub-pulses 51 to 58 of the synchronization signal constitute the first pulse region, and the sub-pulse 59 and the sub-pulse 60 constitute the second pulse region.

  As described above, the length of the first pulse region may be long enough to ensure a sufficient time for the X-ray two-dimensional detector 2 to expose the X-rays irradiated on the detection surface. Therefore, when the necessary exposure time in one angular phase is set to 1000 msec, for example, the length of one sub-pulse area in this case is 250 msec.

  On the other hand, the length of the second pulse region is calculated by the set angular displacement and the rotation speed of the rotation base 3 as in the case of FIG. 4A, and the angle at which the rotation base 3 is set. It is determined based on the time required to rotate the displacement. For example, when the time required for the rotation base 3 to rotate 1 ° as a predetermined angle is 200 msec, it may be set to 250 msec, which is a little longer than that.

  As shown in FIG. 6B, the exposure of the X-ray two-dimensional detector 2 in the present embodiment is executed at a timing based on the high-level pulse of the synchronization signal in FIG. Actually, the rising of the high level pulses 41, 43, 45, 47, 49, 51, 53, 55, 57, 59 is detected to start the exposure, and each pulse 41, 43, 45, 47, 49, The trailing edge of 51, 53, 55, 57, 59 (or low level pulses 42, 44, 46, 48, 50, 52, 54, 56, 58, 60) is detected and the exposure is terminated. The X-ray two-dimensional detector 2 temporarily stores the image data of the projected image in the memory 2a when the exposure on the detection surface in each pulse is completed.

  In capturing the projection image, the four pulses 41, 43, 45, and 47 having the high-level width H1 of the first pulse region are collectively captured in the projection image storage unit 23. That is, when the exposure of the four pulses 47 having the fourth high-level width H1 is completed, the projection image of each pulse is stored in the projection image storage unit 23, and thus the fourth high-level width H1. It is set to be effective (high level) after the end of the four pulses 47 and when the second pulse region is included.

  On the other hand, as in the case of the first embodiment, the image data of the projection image captured when the rotation base 3 is rotating is overwritten with the image data of the projection image obtained in the next exposure. Therefore, as shown in FIG. 6E, the image data of the projection image obtained in the second pulse region (pulses 49 and 50, pulses 59 and 60) is not taken into the projection image storage unit 23. That is, in the projection image capturing operation, after the second pulse region (pulses 49 and 50, pulses 59 and 60), at least the pulses 41, 43, 45, 47, and 49 having a high pulse width H1 in the first pulse region. , 51, 53, 55, 57, 59 are set to be invalid (low level).

  As described above, according to the second embodiment, a single projection image is obtained by superimposing the projection images captured in a plurality (four in this example) of sub-pulse regions. In addition to the function and effect of the first embodiment, the brightness (density) of each projection image can be added to obtain one projection image with enhanced brightness, and the first pulse region (FIG. 4A) that is not divided. The lightness equivalent to that of the projected image captured in (1) can be obtained.

  Further, by superimposing a plurality of projection images, it is possible to cancel random noise included in each projection image and improve the S / N ratio (Signal to Noise ratio) of the reconstructed image.

  Note that an X-ray tomographic imaging apparatus to which the present invention is applied detects transmission radiation or fluorescent radiation, etc., which is applied to an object to be inspected moving with a predetermined angular displacement, using a two-dimensional detector. Any X-ray tomography method in which the control of the two-dimensional detector is performed before the internal structure data of the object to be inspected is reconstructed from the projection image obtained by the two-dimensional detector may be used.

  Further, in this specification, the processing steps describing the tomographic imaging method are executed in parallel or individually even if they are not necessarily processed in time series, as well as processes performed in time series in the described order. (For example, parallel processing or object processing).

  In addition, the present invention is not limited to the above-described embodiments, and various modifications and changes can be made without departing from the scope of the present invention.

It is a timing chart of the conventional imaging process. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which shows the X-ray tomography apparatus based on the 1st Example of this invention, (A) represents a front view, (B) represents a side view. 1 is a block configuration diagram of an X-ray tomographic imaging apparatus according to a first embodiment of the present invention. It is a timing chart of the imaging process which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the imaging process which concerns on the 1st Embodiment of this invention. It is a timing chart of the imaging process which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... X-ray tube, 2 ... X-ray two-dimensional detector, 3 ... Rotation base, 7 ... Test object, 22 ... Control operation part, 22a ... Control part, 22b ... Memory, 22c ... Input part, 23 ... Projection Image storage unit, 24... Computer for reconstruction calculation, 25... Reconstruction result display device, 26... Synchronization signal generation unit, 31, 35... (Long) pulse, 33, 37 ... (short) pulse, 41, 43, 45 , 47, 51, 53, 55, 57 ... Sub pulse

Claims (6)

An X-ray source;
Two-dimensional detection means for detecting transmitted X-rays of the object to be inspected based on pulses included in the synchronization signal;
A synchronization signal generating unit that generates a synchronization signal alternately including a first pulse region and a second pulse region shorter than the first pulse region;
A projection image storage unit for storing a projection image by transmitted X-rays detected by the two-dimensional detection means during the first pulse region of the synchronization signal;
Rotation control means for generating a rotation control signal synchronized with the second pulse region of the synchronization signal;
Based on a rotation control signal generated between the X-ray focal point of the X-ray source and the two-dimensional detection means and generated by the rotation control unit, the object to be inspected is placed from the X-ray focal point. Rotating means that rotates at a set angular displacement around a rotation axis that is orthogonal to a perpendicular drawn to the detection surface at the initial position of the two-dimensional detection means;
X-ray tomographic imaging apparatus. The length of the second pulse region of the synchronization signal is determined based on the time required for the rotation means to rotate the angular displacement, which is calculated from the set angular displacement and the rotation speed of the rotation means. The X-ray tomographic imaging apparatus according to claim 1. A projection image holding unit that stores a projection image of transmitted X-rays detected by the two-dimensional detection unit;
The two-dimensional detection means temporarily stores a projection image by transmission X-rays detected in the first pulse region of the synchronization signal in the projection image holding unit, and the rotation means stores the second pulse of the synchronization signal. When the region is rotated by the angular displacement, the projection image stored in the projection image holding unit is output to the projection image storage unit, and transmitted X-rays detected in the second pulse region of the synchronization signal The X-ray tomographic imaging apparatus according to claim 2, wherein the projected image is erased. The X-ray tomographic imaging apparatus according to claim 3, further comprising: a reconstruction unit configured to reconstruct the internal structure data of the object to be inspected from the projection images of each angular phase stored in the projection image imaging unit. The first pulse region of the synchronization signal is composed of a plurality of sub-pulse regions, and the total length of the plurality of sub-pulse regions is equal to or longer than the exposure time required by the two-dimensional detection means. X-ray tomographic imaging apparatus according to claim 1. An X-ray source, a two-dimensional detection means for detecting transmitted X-rays of the object to be inspected based on a pulse included in the synchronization signal, and an X-ray focal point of the X-ray source and the two-dimensional detection means are arranged. A rotation axis orthogonal to a perpendicular line placed on the detection surface at the initial position of the two-dimensional detection means from the X-ray focal point on the basis of the rotation control signal generated by the rotation control unit An X-ray tomographic imaging method using an X-ray tomographic imaging apparatus that captures a projected image for each angular phase, and a rotating means that rotates at a set angular displacement around
Generating a synchronization signal including alternating first pulse regions and second pulse regions shorter than the first pulse regions;
The two-dimensional detection means detecting transmitted X-rays of the inspected object based on the first pulse region and the second pulse region included in the synchronization signal;
The rotating means rotating the set angular displacement based on a rotation control signal synchronized with the second pulse region of the synchronization signal;
Storing only a projection image by transmitted X-rays detected by the two-dimensional detection means during the first pulse region of the synchronization signal;
X-ray tomographic imaging method including:

Images