JP5458771B2 - Radiation tomography system - Google Patents

Description

  The present invention relates to an industrial radiation tomography apparatus.

  In an industrial radiation tomographic tomography apparatus, generally, a radiation source that generates radiation such as X-rays and a radiation detector that detects the radiation are disposed opposite to each other, and the radiation source and the radiation are disposed therebetween. By rotating the pair of detectors and the sample stage relative to each other and capturing the output of the radiation detector at every predetermined minute angle, radiation projection data of the object from many directions is obtained (see, for example, Patent Document 1). ).

  In such a radiation tomography apparatus, conventionally, a pair of a radiation source and a radiation detector and a sample stage are relatively rotated over a plurality of rotations, and radiation projection data at the same projection angle is repeatedly collected over a plurality of times. By superimposing projection data at the same angle in rotation, the substantial exposure time is gradually increased, and when the projection data, that is, the S / N of the fluoroscopic image is satisfied, the projection data is collected. And a technique for constructing a tomographic image has been proposed (see, for example, Patent Document 2). In this way, it is possible to obtain a tomographic image from the beginning under appropriate imaging conditions even with a sample that captures a tomographic image for the first time.

JP 2005-300388 A JP 2005-183180 A

  By the way, in order to obtain a tomographic image of an object by reconstruction calculation of radiation projection data, radiation projection data is generally backprojected. In this back projection, basically, radiation projection data is acquired on the assumption that the pair of the radiation source and the radiation detector rotate relative to each other in a predetermined trajectory with respect to the object. The collected radiation projection data is back-projected based on the premised trajectory.

  Therefore, if the actual apparatus rotates relative to a trajectory different from the set trajectory, the image quality of the tomographic image obtained by the reconstruction calculation is adversely affected. That is, the image is doubled or a virtual image (artifact) is generated. In particular, when the rotation center shifts, that is, the actual relative rotation axis at the time of photographing is shifted from the assumed rotation axis, the tomographic image is seriously affected. Other misalignments also cause virtual images (artifacts).

  The reason why the relative rotation trajectory is different from the set trajectory, that is, the actual rotation center of the rotary table or the actual rotation center of the radiation source and radiation detector pair deviates from the set rotation center. Possible causes of inconsistency include insufficient strength of the device, deformation of the member due to temperature changes, and movement of the position of the radiation (focal position) generated from the radiation source. Similarly, parts above the rotary table (object holding mechanism, object itself, object drive mechanism, etc.) moved due to insufficient strength of the equipment, deformation of the member due to temperature change, etc. It may be different from the orbit.

  In particular, as in the technique disclosed in Patent Document 2 described above, when radiation projection data is repeatedly collected by relatively rotating a radiation source / radiation detector pair and an object over a plurality of rotations, As a result of accumulating the deviation, the S / N is improved by increasing the number of rotations for photographing, but the problem is that the image quality is lowered.

  In general, in the radiation tomography apparatus, after the radiation projection data is prepared, the radiation projection data is subjected to preprocessing such as sensitivity correction, distortion correction, weighting correction, and filter processing, and then before that. Although the tomographic image of the object is obtained by back projection processing using the processed data, collection of radiation projection data and arithmetic processing using the collected projection data are performed in series. Here, in a tomographic imaging apparatus using a cone-shaped radiation beam such as a cone beam X-ray CT apparatus, three-dimensional information of an object is obtained using pre-processed data. Therefore, the time required from the start of the collection of projection data, that is, the start of CT imaging until the three-dimensional image information is obtained becomes longer.

  In particular, when the technique disclosed in Patent Document 2 described above is applied to a tomographic imaging apparatus using cone-beam radiation, the sum of the imaging time and the data processing time for obtaining three-dimensional image information is There is a problem that it becomes quite long.

  Furthermore, in the technique disclosed in Patent Document 2, the radiation source and the radiation detector pair and the object are relatively rotated over a plurality of rotations in order to collect the radiation projection data, and the projection data obtained in each rotation are the same. Are constructed by superimposing the projection angles at the projection angles, and when the S / N of the fluoroscopic image is satisfied, the photographing is stopped and the construction of the tomographic image is started. There is also a problem that whether or not the S / N is satisfied can be determined only after the final tomographic image is constructed.

  The present invention has been made in view of such circumstances, and repeatedly collects radiation projection data by relatively rotating a radiation source / radiation detector pair and an object multiple times, and the data for the multiple rotations is collected. In a tomographic imaging apparatus for constructing tomographic images or three-dimensional image information of an object by using a tomographic image or three-dimensional image from the start of imaging without degrading the image quality even if there is a shift in the locus of relative rotation. An object of the present invention is to provide a radiation tomography apparatus capable of significantly shortening the time required for obtaining information.

  Another object of the present invention is that the operator can observe the tomographic image or the three-dimensional image information of the object during the photographing operation over a plurality of rotations, and the decision to stop the photographing operation is made. An object of the present invention is to provide a radiation tomography apparatus capable of directly judging from information.

In order to solve the above-described problems, a radiation tomography apparatus according to the present invention is provided with a radiation source and a radiation detector arranged to face each other, and between the radiation source and the radiation detector, and arranges an object. And a rotation mechanism that relatively rotates the sample stage and the pair of the radiation source and the radiation detector and the sample stage, while irradiating the object on the sample stage with radiation from the radiation source, Radiation tomographic image that obtains tomographic information of an object by sequentially collecting radiation projection data at a plurality of projection angles obtained by driving the rotating mechanism in a computer-based arithmetic unit and using it for back projection processing In the imaging apparatus, the calculation device collects radiation projection data by rotating the rotation mechanism over a plurality of rotations, and at the same projection angle obtained by each rotation. The mutual projection amount of the data is calculated, and the parameters for performing the back projection processing are corrected based on the calculation result of the deviation amount, and the radiation projection data obtained by each rotation is used as the tomographic information of the object. The computer of the arithmetic unit has a parallel processing function, and includes a data collection process for collecting radiation projection data from the radiation detector, a calculation process for the deviation amount of each data, and a back projection process. Numerical calculation processing including construction of dimensional image information is executed in parallel, and the computer of the arithmetic device is obtained from the first rotation to the time point every time projection data for one rotation is used for back projection processing. It is characterized by displaying an image based on the tomographic information that is present (claim 1).

  Here, in the present invention, the computer of the arithmetic device divides the numerical calculation process into preset projection angles, and divides the divided numerical processing into a plurality of processes within the divided processes. (Claim 2) can be suitably employed.

  Further, in the present invention, the computer of the arithmetic unit includes a pre-processing including a sensitivity correction, a distortion correction, a weight correction, a filter process, and a deviation amount calculation process within each of the divided processes, a back projection process, It is possible to adopt a configuration (claim 3) in which the divided processes are executed in parallel.

  Furthermore, in the present invention, the CPU of the computer shares the preprocessing including the sensitivity correction, distortion correction, weighting correction, filter processing, and shift amount calculation processing, while the back projection processing is mounted on the computer. It is desirable to adopt a configuration (claim 4) shared by the GPUs that are present.

  The present invention relates to radiation projection data at a certain projection angle and the projection angle if the rotation of the rotation mechanism that relatively rotates the pair of the radiation source and the radiation detector and the sample stage (object) is normal. In consideration of the fact that the radiation projection data at the same projection angle rotated 360 ° should be exactly the same projection data, the projection data collected by rotating the rotation mechanism a plurality of times is the same at each rotation. A tomogram that appears due to a shift in the orbit of relative rotation by calculating the amount of deviation between the projection angle data and correcting the parameters related to the position of each projection data based on the amount of deviation and using it for back projection processing In addition, the projection data collection processing and the numerical calculation processing including the above-described projection data shift calculation and back projection processing are executed in parallel. Ri, it is intended to Hakaro to shorten the time required to tomographic information can be obtained.

  That is, for example, with respect to the data of each projection angle after the second rotation, a deviation amount with respect to the data at the same projection angle of the first rotation is calculated, and when being used for back projection processing, the coordinates (positions) of each data are based on the deviation amount. More specifically, parameters relating to the position of the center of rotation on the fluoroscopic image and the position of the radiation optical axis based on the projection data are corrected. The tomographic information obtained in this way can be attributed to the relative rotation deviation because each projection data is reconstructed after the deviation is corrected even if there is a deviation in the relative rotation trajectory. The deterioration of the image quality is suppressed. Further, since the shift amount of the projection data is absorbed by the parameters inside the back projection process, it is possible to suppress a decrease in resolution caused by the correction of the shift amount.

In addition, since the projection data collection and the numerical calculation processing including the calculation of the shift amount and the back projection processing are executed in parallel, the time required for obtaining the tomographic information can be shortened.
Here, such parallel processing can be realized by using a parallel processing function using HPC (High Performance Computing) technology. For example, by using a computer having an HPC function using a multi-core made of CELL (product name, IBM / SONY / TOSHIBA), CUDA (product name, Nvidia), or AMD or INTEL as an arithmetic unit, projection data Collection and numerical calculation processing of the collected projection data can be executed in parallel.
Further, since the projection data collection and the numerical calculation processing including the calculation of the deviation amount and the back projection processing are executed in parallel, the tomographic information is obtained during the collection of the projection data. If it is configured to display an image based on tomographic information obtained from the first rotation to the point in time each time the projection data is subjected to back projection processing, is it necessary for the operator to collect more data than this? It becomes possible to judge directly from a tomogram.

  Further, as in the invention according to claim 2, numerical calculation processing is also performed by dividing the projection angle, dividing the processing into a plurality of divisions, and executing the divided processing in parallel. The processing itself can be shortened.

  Here, the numerical calculation to be divided is divided into pre-processing of X-ray projection data for performing back projection processing and back projection processing as in the invention according to claim 3, and each processing is vector-type. For example, a method of sharing between a CPU and a GPU (Graphics Processing Unit) can be employed.

  According to the present invention, a pair of a radiation source and a radiation detector and a sample stage on which an object is arranged are relatively rotated a plurality of times, and projection data is collected at a plurality of angles in each rotation, and the collected projection data is collected. The tomographic information of the object is obtained by backprojection processing using, and the projection data used for the backprojection processing calculates the amount of deviation between the same angles collected at each rotation, and uses the calculation results to Since the parameters of the coordinates used for the projection processing are corrected, even if the relative rotation trajectory gradually shifts, it is possible to suppress the deterioration in the image quality of the tomographic image due to the accumulation of the shift.

  Moreover, since the projection data collection process, the deviation amount calculation, and the back projection process are executed in parallel, the tomographic information is sequentially constructed while collecting the projection data over a plurality of rotations. The time required from the start until finally obtaining the fault information can be greatly shortened.

  In addition, using the fact that tomographic information is obtained during the collection of projection data, each time a back projection process of projection data for one rotation is completed, a tomographic image or three-dimensional image information based on the tomographic information of the object is obtained. By displaying, it is possible to accurately determine the interruption of data collection by the operator.

It is a block diagram of embodiment of this invention. It is a figure which shows typically the method of the process by the computer in embodiment of this invention. It is a figure which shows typically the flow of data in embodiment of this invention. It is explanatory drawing of the example of how to obtain | require the shift | offset | difference of projection data in embodiment of this invention.

DESCRIPTION OF SYMBOLS 1 X-ray generator 2 X-ray detector 3 Sample stage 4 Computer 5 Operation part 6 Display 7 X-ray controller 8 Axis control part W Target object

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration diagram in which the present invention is applied to a cone-beam X-ray CT apparatus. An X-ray generator 1 is arranged so that its X-ray optical axis is oriented in the horizontal direction, and the X-ray generator 1 The X-ray detector 2 is provided opposite to the horizontal direction. And between these, the sample stage 3 for mounting the target object W is provided. In this example, the sample stage 3 rotates around a vertical rotation axis R perpendicular to the X-ray optical axis. In addition, the sample stage 3 can be moved in three orthogonal directions including the X-ray optical axis by driving a moving mechanism (not shown), and an imaging magnification, an imaging range, and the like can be set by this movement. . The X-ray generator 1 generates cone beam X-rays, and the X-ray detector 2 is a two-dimensional X-ray detector.

  CT imaging is performed by collecting the output of the X-ray detector 2 at each minute rotation angle while rotating the sample stage 3 while irradiating the object W with X-rays from the X-ray generator 1. Is called.

  That is, during CT imaging, the output of the X-ray detector 2 is taken into the computer 4 at every minute rotation angle of the sample stage 3 and stored in the memory or hard disk as X-ray projection data at each projection angle. In this example, the sample stage 3 rotates over a plurality of rotations, and the computer 4 stores projection data for a plurality of rotations.

  The computer 4 performs pre-processing as will be described later on the X-ray projection data collected at each angle as described above, and applies 2 to the X-ray projection data in the reference rotation, here the first rotation. After calculating the shift amount of the X-ray projection data after the rotation, a program for obtaining the three-dimensional image information of the object W is written by performing the back projection process. The calculation program is executed at a timing described later. The three-dimensional image information of the object W obtained in this way is stored in the memory of the computer 4 or the hard disk.

  An operation unit 5 including a keyboard, a mouse, a joystick, and the like is connected to the computer 4. By operating the operation unit 5, an arbitrary plane can be obtained based on the stored three-dimensional image information of the object W. Can be displayed on the display 6 as a three-dimensional image by MPR display or VR display.

  The computer 4 is also under control of an X-ray controller 7 that controls a tube current and a tube voltage to be supplied to the X-ray generator 1, and a rotating mechanism and a moving mechanism of the sample stage 3 are also provided. Control is performed via the axis control unit 8. Such commands and settings relating to control can also be performed by operating the operation unit 5 described above.

  The computer 4 uses HPC technology, is equipped with a multi-core CPU having a plurality of CPUs and a GPU, collects X-ray projection data by the CT imaging, and collects the collected data. A numerical calculation process for obtaining three-dimensional image information of the object W by the numerical calculation used is processed in parallel. FIG. 2 schematically shows a processing method of the computer 4 in a block diagram.

  In the data collection process A, the output from the X-ray detector 2 in each view (each projection angle) obtained by the above-described CT imaging is stored in a memory such as a RAM via a capture board A1 and a DMAC (Direct Memory Access Controller) A2. Alternatively, write processing A3 to the hard disk is performed.

  On the other hand, in the numerical calculation process B, this is divided into a back projection pre-process Ba, a shift amount detection process Bb, and a back projection process Bc, and the processes are executed in parallel for each predetermined number of views. That is, for example, if the number of views of CT imaging is 600, every time the number of views reaches 12, X-ray projection data for 12 views is read out and used for the back projection preprocessing Ba, and the back projection preprocessing is performed. The completed 12-view data is subjected to the shift amount detection process Bb and then to the back projection process Bc. Here, the deviation amount detection process Bb is omitted for the X-ray projection data collected in the first rotation, and the X-ray projection data for the second and subsequent rotations have the same projection angle with reference to the data for the first rotation. This is done by comparing things.

  In the back projection pre-processing Ba, the X-ray projection data written by CT imaging is read out from the memory or the hard disk for every 12 views, and this is stored in the memory (work area) Ba2 and stored. After the sensitivity correction and distortion correction processing Ba3 is performed on the data, the data is subjected to weighting processing Ba4 and filter processing Ba5 such as FFT.

  As described above, the deviation amount detection process Bb is performed for the data after the second rotation, and as schematically shown in FIG. Are compared at the same projection angle, and shift amounts δx and δy in the x direction and y direction of the projection data after the second rotation with respect to the projection data of the first rotation are obtained. The deviations δx and δy are used for parameter correction in the following back projection process Bc. Here, the detection method of the shift amount of the projection data is not particularly limited. For example, general image processing such as a method of measuring the degree of coincidence of images while shifting the perspective image that is the projection data is adopted. be able to.

  In the backprojection process Bc, the data for 12 views for which the above-described backprojection preprocessing Ba has been completed is subjected to a copy process Bc1 to the graphic memory (GMEM), which is stored in the graphic memory Bc2, and backprojection calculation process is performed. Subject to Bc3. In this backprojection calculation process Bc3, for the data after the second rotation, rotation on the X-ray fluoroscopic image is performed based on the shift amounts δx and δy in the x and y directions detected by the shift amount detection process Bb. The process is executed by changing the center by δx and changing the X-ray optical axis position by δy.

  By executing the back projection process Bc described above, three-dimensional image information of the object W is obtained. However, every time data collection for 360 ° and back projection process are completed, in other words, for one rotation. Each time data back projection processing is completed, a tomographic image along the plane designated by the operation unit 5 is copied from the graphic memory to the RAM and displayed on the display device 6.

  According to the above-described embodiment of the present invention, the X-ray projection data after the second rotation are compared with each other at the same projection angle as the first rotation X-ray projection data, and the amount of deviation is obtained. Since the parameters in the back projection process are corrected based on the amount of deviation, even if the rotation center of the rotation mechanism is deviated from the initial position, it is possible to suppress deterioration in the image quality of the tomographic image due to accumulation of the deviation.

  Moreover, the process of collecting the output from the X-ray detector 2 by CT imaging and the numerical calculation process for performing the back projection process using the collected data are executed in parallel, and in the numerical calculation process, Since back-projection preprocessing such as sensitivity correction, shift amount detection processing, and backprojection processing are executed in parallel, compared with this type of apparatus that performs these conventional processes in series, the CT imaging to tomography The time required to obtain an image can be greatly shortened.

  Furthermore, when the data collection for one rotation and the back projection processing are completed, a tomographic image based on the processing results up to that time is displayed on the display 6, so that the operator can see a sufficient S / N while viewing the image. It is possible to directly recognize whether or not the image has been obtained, and it is possible to accurately determine whether or not to continue the shooting operation.

  In the above embodiment, the sample stage is rotated with respect to the pair of the X-ray generator and the X-ray detector. However, the pair of the X-ray generator and the X-ray detector is the sample stage. Of course, it is possible to adopt a configuration in which the rotation is performed around the center.

Claims (4)

A radiation source and a radiation detector arranged to face each other, a sample stage provided between the radiation source and the radiation detector, for placing an object, a pair of the radiation source and the radiation detector, and the sample Radiation projection data at a plurality of projection angles obtained by driving the rotation mechanism while irradiating an object on the sample stage with radiation from the radiation source while rotating the stage relative to the stage. In a radiation tomography apparatus for obtaining tomographic information of an object by sequentially collecting the information in a computer-based arithmetic device and subjecting it to back projection processing,
The arithmetic device collects radiation projection data by rotating the rotation mechanism over a plurality of rotations, calculates a mutual shift amount between data at the same projection angle obtained by each rotation, and calculates the shift amount The radiation projection data obtained in each rotation by correcting the parameters for performing the back projection process based on the above are used for constructing the tomographic information of the object,
The computer of the arithmetic unit has a parallel processing function, and constructs three-dimensional image information by data collection processing for collecting radiation projection data from the radiation detector, calculation processing for the shift amount of each data, and back projection processing. and numerical processing including, performed in parallel,
The computer of the arithmetic unit displays a radiation tomographic image that displays an image based on tomographic information obtained from the first rotation to the time point each time projection data for one rotation is subjected to back projection processing. Shooting device.   The computer of the arithmetic device divides the numerical calculation process for each preset projection angle, divides into a plurality of processes within each divided process, and executes the divided processes in parallel. The radiation tomography apparatus according to claim 1.   The computer of the arithmetic device divides the divided processing into preprocessing including sensitivity correction, distortion correction, weighting correction, filter processing, and calculation processing of the deviation amount, and back projection processing within the divided processing. The radiation tomography apparatus according to claim 2, wherein each process is executed in parallel.   The CPU of the computer shares the preprocessing including the sensitivity correction, distortion correction, weighting correction, filter processing, and the shift amount calculation processing, while the back projection processing is shared by the GPU mounted on the computer. The radiation tomography apparatus according to claim 3, wherein

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