JP5211880B2 - X-ray tomography system - Google Patents

Description

  The present invention relates to an industrial X-ray tomography apparatus.

  In an X-ray tomography apparatus, generally, a sample stage for placing an object is provided between an X-ray generator and X-ray detection, and a pair of X-ray generator and X-ray detector and a sample are provided. By rotating the stage relatively and collecting X-ray projection data at a plurality of different angles in the rotation, the X-ray projection data of the object from many directions is collected, and the data is filtered. Then, back projection is performed to obtain a tomographic image of the object (see, for example, Patent Documents 1 and 2).

  For example, as shown in FIG. 7 (A), between the X-ray generator 1 and the X-ray detector 2, a rotary table 3 that rotates around a vertical rotation axis R orthogonal to the line connecting them is arranged. When an object W as shown in the figure is mounted on the rotary table 3 and irradiated with X-rays, the output of the X-ray detector 2, that is, the X-ray projection data of the object W is shown in FIG. It will be as illustrated in The line profile in the horizontal direction perpendicular to the vertical rotation axis R is as shown in FIG. 4C when the vertical central portion is taken as an example.

  The example shown in FIG. 8 shows an apparatus having a structure in which a pair of the X-ray generator 1 and the X-ray detector 2 is rotated about the rotation axis R. The X-ray generator 1 and the X-ray detector are shown in FIG. An object is placed between 2 and a sample stage (not shown) on which the object W is mounted is fixed without rotating, and a pair of the X-ray generator 1 and the X-ray detector 2 is rotated around the sample stage. . Even with such an apparatus structure, X-ray projection data similar to the above can be obtained.

  In the apparatus shown in FIG. 7A or FIG. 8, the rotary table 3 is rotated by a minute angle while irradiating the object W with X-rays, or the X-ray generator 1 and the X-ray detector 2 are rotated. The X-ray projection data in various directions (projection angles) can be collected by rotating the pair of each by a minute angle and capturing the X-ray projection data. A graph obtained by collecting and graphing X-ray projection data on a line at a certain position in the direction of the rotation axis R in the projection data at each projection angle and in a direction orthogonal to the rotation axis R is called a sinogram. An example is shown in FIG. This sinogram becomes data before the reconstruction operation is performed. The tomographic reconstruction calculation is realized by back-projecting a sinogram (projection data). That is, as illustrated in FIG. 10, for example, with the sinogram of the center line illustrated in FIG. 7C, the line profile data of the corresponding angle is used, so to speak, toward the focal point of the X-ray generator 1. The process of painting is repeated for the collected angles. As a result, a tomographic image at the center in the vertical direction of the object as illustrated in FIG. 11 is obtained. Actually, it is necessary to perform a filtering process on the projection data, but this is omitted here.

  In the above example, the processing of projection data on a line has been described. However, three-dimensional tomographic data (three-dimensional image information) is reconstructed from two-dimensional projection data obtained at various projection angles by a similar method. Can do.

  In such an X-ray tomographic imaging apparatus, the number of divisions for one round and the collection of projection data is referred to as the number of projections. The greater the number of projections, the higher the angular resolution and the higher the resolution (resolution) of the reconstructed tomographic image.

Further, the exposure time at the time of photographing each projection data also affects the image quality. The longer the exposure time, the higher the S / N of the projection data and the S / N of the tomographic image to be reconstructed.
JP 2005-300388 A JP-A-2005-283180

  As described above, in order to obtain a high-resolution, high-quality tomographic image, it is necessary to increase the number of projections, but the data collection time (imaging time) becomes long, and in industrial equipment, Data collection can range from tens of minutes to hours. Moreover, when the number of projections is increased, the reconstruction operation executed after data collection becomes longer in proportion to the number of projections, and it may take several tens of minutes to several hours. On the other hand, it is necessary to optimize various conditions, such as X-ray conditions and object positioning, and a tomogram obtained over such time may be completely wasted. .

  Here, with regard to the exposure time, in Patent Document 2 described above, the X-ray generation data and the X-ray detector pair and the object are relatively rotated over a plurality of rotations, and the X-ray projection data collected at each rotation is projected. The angle is the same, and X-ray projection data at the same projection angle is repeatedly collected multiple times, so that the exposure time is gradually increased and data is obtained when a satisfactory S / N tomographic image is obtained. A technique for stopping collection is disclosed. However, in the technique of Patent Document 2, the number of projections is constant, and the resolution of tomographic images and the time required for imaging are not considered at all.

  The problem of the present invention is that a tomographic image can be confirmed in a relatively short time, and if there is a point to be changed such as positioning of an object or X-ray conditions, it can be quickly changed to a suitable condition, In addition, it is an object of the present invention to provide an X-ray tomographic imaging apparatus that can obtain a tomographic image with a sufficient resolution in a shortest time.

In order to solve the above-described problems, an X-ray tomography apparatus according to the present invention is provided between an X-ray generator and an X-ray detector arranged opposite to each other, and between these X-ray generator and X-ray detector. A sample stage for placing an object, a rotation mechanism for relatively rotating the pair of the X-ray generator and X-ray detector and the sample stage, and driving and controlling the rotation mechanism, Control means for collecting X-ray transmission data of an object at a plurality of different angles and storing it in a data storage means, and X-ray transmission data at a plurality of angles stored in the data storage means, In the X-ray tomography apparatus provided with the reconstruction calculation means for constructing an X-ray transmission image, the control means rotates the rotation mechanism over a plurality of rotations, and for each rotation, Are different from each other. Angle to collect X-ray projection data, the reconstruction operation unit, each time the rotating mechanism rotates once, a tomogram subjected to reconstruction operation using all the X-ray projection data collected so far It is characterized by constructing (claim 1).

  Here, in the present invention, each time a tomographic image is constructed by the reconstruction calculation means, it has a determining unit that determines the image quality of the tomographic image, and when the tomographic image quality reaches a certain level. A configuration (claim 2) in which the collection of X-ray projection data is terminated can be suitably employed.

  In the present invention, a pair of an X-ray generator and an X-ray detector and a sample stage (object) are relatively rotated over a plurality of rotations, and the number of projections is increased by increasing the number of rotations. For example, an object is to solve the problem by constructing a tomographic image by reconstruction calculation using X-ray projection data collected so far for each rotation.

  In other words, a pair of X-ray generator and X-ray detector by a rotating mechanism and a sample stage are rotated relative to each other over a plurality of rotations, and X-ray projection data is collected at each rotation at an angular position different from other rotations. To do. Thereby, the number of projections increases by increasing the number of rotations. The reconstruction calculation means constructs a tomographic image every time the rotation speed reaches a predetermined number of times (for example, every time). Thereby, the resolution of the obtained tomographic image is improved as the number of rotations increases.

  It is possible to change other imaging conditions such as object positioning and X-ray conditions from the tomogram in the initial stage, and the operator confirms that the required resolution has been obtained, or claim 2 As in the invention according to the present invention, a means for determining the tomographic image quality is provided, and when a certain image quality is obtained, the photographing operation is terminated to collect useless data for a tomographic image with a sufficient resolution. It becomes possible to obtain without.

  According to the present invention, the pair of the X-ray generator and the X-ray detector and the sample stage on which the object is placed are relatively rotated over a plurality of rotations, and each rotation is different from the other rotations. By collecting X-ray transmission data at an angle, the number of projections is increased each time the number of rotations is increased, and each time rotation is performed a predetermined number of times, the tomography is performed by reconstruction calculation using the X-ray projection data collected so far. Since an image is constructed, it is possible to grasp the necessity of changing other conditions such as positioning of an object and X-ray conditions at a relatively early stage, and it is possible to prevent wasted time. In addition, when the required resolution of the tomographic image is obtained, the data collection is terminated, so that a tomographic image with a resolution that is not excessive or insufficient with respect to the required resolution can be obtained. It can be obtained without collecting, and the time required for imaging and reconstruction calculation can be shortened.

  Further, as in the invention according to claim 2, by providing the tomographic image quality judging means so that a tomographic image having a required resolution can be automatically obtained, the burden on the operator is greatly reduced. be able to.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an embodiment of the present invention, and is a diagram illustrating a schematic diagram showing a mechanical configuration and a block diagram showing a main functional configuration of a control device.

The X-ray generator 1 is arranged so that its X-ray optical axis is oriented in the horizontal direction, and the X-ray detector 2 is arranged facing the X-ray generator 1 in the horizontal direction. The X-ray generator 1 is supplied with a tube voltage and a tube current according to a signal from the X-ray controller 11 to generate cone beam X-rays. The X-ray detector 2 is a two-dimensional X-ray detector in which pixels are arranged two-dimensionally.

  Between the X-ray generator 1 and the X-ray detector 2, a rotary stage 3 for mounting the object W is disposed. The rotation stage 3 rotates around a rotation axis R along a vertical direction orthogonal to the X-ray optical axis. The rotary stage 3 is movable in three axial directions that are orthogonal to each other including the X-ray optical axis, and the movement in each axial direction and the rotational operation around the rotational axis R are performed by an axis control unit. 12 is controlled by a drive control signal supplied from 12.

  When collecting X-ray projection data of the object W, that is, CT imaging, the object W is mounted on the rotation stage 3, and the rotation stage 3 is rotated while irradiating X-rays, and X is set at every minute angle. This is done by taking the output of the line detector 2. Specifically, each pixel output of the X-ray detector 2 at each rotation angle is stored in the data storage unit 14 via the image data capturing circuit 13 as X-ray projection data at that angle.

  The X-ray projection data at each angle stored in the data storage unit 14 is subjected to a reconstruction calculation by the reconstruction calculation unit 15 at a later-described timing, and a tomographic image of the object W is constructed. The tomographic image is displayed on the display 16. Further, the tomographic image constructed by the reconstruction calculation by the reconstruction calculation unit 15 is simultaneously subjected to resolution determination by the resolution determination unit 17 as described later.

  The image data capturing circuit 13, the data storage unit 14, the reconstruction calculation unit 15, and the display unit 16 are placed under the control of the system control unit 18 together with the X-ray controller 11 and the axis control unit 12 described above. The system control unit 18 is connected to an operation unit 19 including a mouse, a keyboard, a joystick, and the like. By operating the operation unit 19, the rotary stage 3 can be positioned or various commands can be given. These are actually configured mainly by a computer and its peripheral devices, and realize functions according to installed programs. In FIG. 1, for convenience of explanation, these are represented by blocks for each major function. ing.

Next, the operation of the embodiment of the present invention having the above configuration will be described with reference to the flowchart shown in FIG.
The greatest feature of this embodiment is that the rotary stage 3 is rotated over a plurality of rotations, and X-ray projection data is acquired at a plurality of rotation angles at each rotation, and X-ray projection data is acquired at each rotation. This is to make the positions (angles) different. With this, the number of projections increases sequentially by increasing the number of rotations of the rotary stage 3. Further, each time the rotation stage 3 is rotated once, a tomographic image of the object W is constructed by reconstruction calculation using all X-ray projection data stored in the data storage unit 14 so far, and When the resolution reaches a certain level, the shooting operation is terminated.

  That is, for example, X-ray projection data from the M direction per rotation is collected, the maximum number of rotations is N, and the projection data collection position at one rotation is i (i = 0, 1,... M−1). ), Where each rotation is represented by j (j = 0, 1,... N−1), the rotary stage 3 is positioned at the i-th position (angle) at the j-th rotation, and the output of the X-ray detector 2 Are collected as X-ray projection data. When the acquisition of the X-ray projection data at the M-th position of the j-th rotation is completed, the process proceeds to the data acquisition of the j + 1-th rotation, but the data acquisition position is shifted at the j-th rotation and the j + 1-th rotation. The There are several methods for the shifting. For example, the projection data collection position at each rotation can be set at the position represented by the following expression (1). In Expression (1), Projection represents the angle (degree) from the initial position (0 °) of the i-th projection position of the j-th rotation of the rotary stage 3.

  The projection data collection position (hereinafter referred to as the projection position) shown in the equation (1) is as schematically shown in FIG. 3 at each rotation. In FIG. 3, the projection position at each rotation is represented by changing the type of line, the solid line represents the projection position at the first rotation, the broken line represents the second rotation, and the alternate long and short dash line represents the projection position at the third rotation. In this method, data is collected at a position that divides 360 ° into M at each rotation, and the initial position is shifted by a certain angle at the first and second rotations or between the second and third rotations. When the maximum rotation speed N is finished, X-ray projection data at a position obtained by equally dividing 360 ° by M × N is collected.

  Thus, every time the rotation of the rotary stage 3 is repeated, X-ray projection data from different directions is collected for each rotation. Each time the rotation stage 3 makes one rotation, the reconstruction calculation unit performs a reconstruction calculation using all the X-ray projection data collected so far to construct a tomographic image and display it on the display 16. In addition, the resolution determination unit 17 determines whether or not the tomographic image has reached a preset resolution level. The method of the determination is not particularly limited. For example, the degree of roughness of the image in a flat part on the tomographic image, that is, a part where the image is uniform is less than a preset degree. It can be determined by whether or not it is within. The part to be discriminated can be the part when the uniform part is known in the internal structure of the object W, or the air outside the tomographic image of the object W can be used. A partial tomographic image may be a discrimination target.

  Then, until the resolution of the tomographic image constructed for each rotation reaches a preset level, the process proceeds to the next rotation to continue collecting X-ray projection data, and the resolution of the tomographic image is preset. When the level reached is reached, the shooting operation is terminated.

  According to the above embodiment, a tomographic image with a small number of projections and thus a low resolution is obtained in a state where the number of rotations of the rotary stage 3 is small, and the resolution of the tomographic image gradually increases as the rotation is repeated. When the resolution is obtained, the photographing and calculation are automatically terminated. Therefore, for example, when other imaging conditions such as the mounting position of the object W on the rotary stage 3 and the X-ray conditions are not set correctly, this can be known at an initial stage, and wasted time. It is possible to change the setting of the conditions quickly without spending time, and the tomographic image finally obtained satisfies the required resolution.

Here, the projection data collection position at each rotation of the rotary stage 3 in the present invention can be set by the following method in addition to the expression (1).
One of them is a method of positioning the rotary stage 3 at a position represented by the following equation (2).

  In this equation (2), M is the number of projections per revolution, and N is the maximum number of revolutions, as in the previous example. In the equation (2), i is a numerical value that is continuous through each rotation, and i = 0, 1, 2,... M × N−1.

  In the method of the formula (2), data is collected at every rotation of a constant angle without shifting the data collection position for each rotation, and exactly 360 ° / (M × N ) Is a method of setting an angle α ° that is a projection interval.

That is, the angle for one view (the above-mentioned constant angle) is α °, and α ° may be determined so that the projection direction is shifted by α ° when N rotations are performed. The total number of projections after N rotations is M × N, and the rotation angle at that time is represented by α × (M × N). On the other hand, in order to obtain this total number of projections, since it is rotated by N rotation and α °,
α ° × (M × N) = N × 360 ° + α °
Holds. Therefore,

Thus, equation (2) can be derived. In the method (2), the projection position at each rotation is schematically shown in FIG. In FIG. 4, similarly to the previous example, the projection position at each rotation is represented by changing the line type. The solid line represents the projection position at the first rotation, the broken line at the second rotation, and the alternate long and short dash line at the third rotation. Represents.

  As another method, a method of positioning the rotary stage 3 at a position represented by the following formulas (4) and (5) may be employed.

  In the equations (4) and (5), when collecting data from the M direction in the first one rotation, the maximum number of rotations is N, and the jth rotation (j = 0, 1, 2,... N -1) represents the i-th data collection position.

  As shown in FIG. 5, this method collects data at the position where the first rotation is equally divided in the first rotation, collects data at the middle position of the data collection position of the first rotation, In the next third rotation, data is collected between the data collection positions of the first rotation and the second rotation. According to this method, at the end of all rotations, the data collection position is a position obtained by equally dividing one round.

  The data collection position in the present invention can employ any of the above-described methods, and may also be a method other than these methods. In short, each time the number of rotations is repeated, the data collection positions are from different directions. Any method can be employed as long as the projection data is collected and the number of projections increases.

  Here, in the above embodiment, each time the turntable 3 is rotated, the tomographic image is constructed by the reconstruction calculation using the X-ray projection data obtained so far. For example, a tomographic image may be constructed every time a predetermined rotational speed is reached.

  In the above embodiment, an example in which the resolution of the tomographic image is automatically determined every time a tomographic image is constructed is shown. However, the tomographic image constructed without the automatic resolution determination function is provided. However, it is also possible to determine the resolution based on the operator's judgment and give a command to end the photographing.

  Further, in the above embodiment, the apparatus configuration in which the pair of the X-ray generator 1 and the X-ray detector 2 is fixed and the rotary stage 3 is disposed between them is described. However, the stage on which the object is mounted is rotated. Of course, the present invention can be equally applied to an apparatus configuration in which a pair of an X-ray generator and an X-ray detector is rotated around the X-ray generator.

  In the above embodiment, the example in which the X-ray generator 1 and the X-ray detector 2 are arranged in the direction orthogonal to the rotation axis R is shown. However, as shown in FIG. The present invention can be applied even to an apparatus called a so-called tilted CT in which the line connecting the X-ray detector 2 and the rotation axis R of the rotary stage 3 on which the object W is mounted are not orthogonal to each other. it can. Note that the tilted CT may have a structure in which a pair of an X-ray generator and an X-ray detector is rotated around an object.

In the configuration diagram of the embodiment of the present invention, a schematic diagram showing a mechanical configuration and a block diagram showing a main functional configuration of a control device are shown together. It is a flowchart which shows the example of operation | movement of embodiment of this invention. It is a typical explanatory view of the collection position of X-ray projection data in an embodiment of the invention. It is typical explanatory drawing of the other example of the collection position of the X-ray projection data in embodiment of this invention. It is typical explanatory drawing of the further another example of the collection position of the X-ray projection data in the cross form of this invention. It is a schematic diagram which shows the structural example of inclination type CT which can apply this invention. It is explanatory drawing of the imaging system of an X-ray tomography apparatus, (A) is a typical block diagram of the imaging system using a rotary table, (B) is an example of the X-ray projection data obtained in the state of (A) (C) is a figure which shows the line profile in the vertical direction center part of (B). It is a figure which shows the other example of the imaging system of an X-ray tomography apparatus, and is a schematic diagram of the system which rotates the pair of an X-ray generator and an X-ray detector around an object. It is a figure which shows the example of the sinogram in the position of the line profile shown in FIG.7 (C). It is explanatory drawing of the reconstruction calculation process which constructs | assembles a tomogram from X-ray projection data with an X-ray tomography apparatus. It is a figure which shows the example of the tomogram obtained by a reconstruction calculation process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray generator 2 X-ray detector 3 Rotation stage 11 X-ray controller 12 Axis control part 13 Image data capture circuit 14 Data storage part 15 Reconstruction calculating part 16 Display 17 Resolution determination part 18 System control part 19 Operation part W Object

Claims (2)

An X-ray generator and an X-ray detector arranged opposite to each other, a sample stage provided between these X-ray generator and X-ray detector, for placing an object, and the X-ray generator A rotation mechanism for relatively rotating a pair of X-ray detectors and the sample stage, and driving and controlling the rotation mechanism to collect X-ray transmission data of the object at a plurality of different angles, thereby storing data. X-ray tomography having control means for storing the image and reconstruction calculation means for constructing an X-ray transmission image of the object using X-ray transmission data at a plurality of angles stored in the data storage means In the device
The control means rotationally drives the rotation mechanism over a plurality of rotations, collects X-ray projection data at a plurality of angles different from other rotations for each rotation, and the reconstruction calculation means An X-ray tomographic imaging apparatus that constructs a tomographic image by performing reconstruction calculation using all X-ray projection data collected so far each time the rotating mechanism makes one rotation .   Each time a tomographic image is constructed by the reconstruction calculation means, it has a determining means for determining the image quality of the tomographic image, and the collection of X-ray projection data is terminated when the image quality of the tomographic image reaches a certain level. The X-ray tomography apparatus according to claim 1, wherein the X-ray tomography apparatus is configured to