JP2006288719A - X-ray ct photographing method and device - Google Patents

X-ray ct photographing method and device Download PDF

Info

Publication number
JP2006288719A
JP2006288719A JP2005113437A JP2005113437A JP2006288719A JP 2006288719 A JP2006288719 A JP 2006288719A JP 2005113437 A JP2005113437 A JP 2005113437A JP 2005113437 A JP2005113437 A JP 2005113437A JP 2006288719 A JP2006288719 A JP 2006288719A
Authority
JP
Japan
Prior art keywords
ray
subject
image sensor
data
image
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
JP2005113437A
Other languages
Japanese (ja)
Inventor
Yoshinori Arai
Masakazu Suzuki
嘉則 新井
正和 鈴木
Original Assignee
Morita Mfg Co Ltd
株式会社モリタ製作所
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Morita Mfg Co Ltd, 株式会社モリタ製作所 filed Critical Morita Mfg Co Ltd
Priority to JP2005113437A priority Critical patent/JP2006288719A/en
Publication of JP2006288719A publication Critical patent/JP2006288719A/en
Pending legal-status Critical Current

Links

Abstract

<P>PROBLEM TO BE SOLVED: To make it possible to easily calibrate deviation of a rotary center in an X-ray CT photographing. <P>SOLUTION: An X-ray photographing data is acquired on the tomographic face of an object. A plurality of displacement quantities are then set in a direction of the rotation of a relative X-ray image sensor to the object, the reconstruction to which the displacement of the above displacement quantities are added from the same X-ray projecting date are carried out to make a plurality of tomographic image data. Among them a collection data for image reconstruction calculation is set from the displacement quantity by which the largest tomographic data with the largest width of gradation sequence is acquired. Alternatively a conversion table is made responding to each respective displacement quantity to make a plurality of tomographic images. Among them the conversion table by which the tomographic image with the largest width of the gradation sequence is acquired is used for the image reconstruction calculation. Alternatively, the tomographic image is made to determine the width of the blur of the image, so that the collection data used for the image reconstruction calculation is set from the displacement with the width of half width of the blur. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to image reconstruction in CT imaging.

  In an X-ray computed tomography (CT) apparatus, an X-ray generator and an X-ray image sensor are arranged on both sides of a subject. Then, while rotating the X-ray generator and the X-ray image sensor around the subject, the X-ray generator irradiates the subject with X-ray beams from multiple directions, and the intensity distribution of the X-rays transmitted through the subject (projection of the subject) ) With an X-ray image sensor. Then, from the X-ray projection data collected in one rotation, the distribution (image) of the X-ray absorption coefficient inside the subject is reconstructed two-dimensionally on the tomographic plane of the subject to obtain a tomographic image. This reconstruction calculation is performed for a plurality of surfaces perpendicular to the rotation center axis. Furthermore, a three-dimensional image is obtained from a plurality of tomographic images.

  Any of the X-ray generator and the X-ray image sensor and the subject may rotate. In the above example, the X-ray generator and the X-ray image sensor are rotated around the subject. However, in an X-ray CT imaging apparatus used for an industrial subject (see, for example, Japanese Patent Laid-Open No. 5-322802), The positions of the X-ray generator and the X-ray image sensor arranged on both sides of the subject are fixed, while the subject is placed on the rotary table. Then, the projection of the subject is photographed while rotating the rotary table. Then, a tomographic plane image of the subject is calculated from the X-ray projection data collected in one rotation.

  In a projection data acquisition system including an X-ray generator, a subject, and an X-ray image sensor, the relative positional relationship between these components is determined in advance. In image reconstruction in which the X-ray projection data is converted into the distribution of the X-ray absorption coefficient of the subject, a tomographic image is created by performing calculations based on this relative positional relationship. It is necessary to correct the positional distortion that occurs during photographing in the projection data collection system. For this reason, various correction data are obtained by photographing an appropriate phantom instead of the subject at the position of the subject. Then, using this correction data, X-ray projection data collected by the X-ray image sensor is corrected, and image reconstruction is calculated.

  In the X-ray CT imaging apparatus, the image can be enlarged or reduced by changing the position of the X-ray generator and / or the X-ray image sensor with respect to the subject. For example, in a CT apparatus capable of independently changing the positions of the X-ray generator and the X-ray image sensor, the image can be enlarged / reduced by changing the distance of the X-ray generator and / or the X-ray image sensor with respect to the subject. . Also, the magnification can be varied by moving the table on which the subject is placed. Some dental X-ray imaging apparatuses are capable of performing Cephalo X-ray imaging and panoramic X-ray imaging in addition to CT imaging. In such an apparatus, the position of the X-ray detector changes, for example, when CT imaging is performed after cephalo X-ray imaging or panoramic X-ray imaging. However, in order to obtain a good reconstructed image, as described above, the relative positional relationship between the X-ray generator, the subject, and the X-ray image sensor must be accurate. In particular, it is important to accurately know the position of the imaging system of the X-ray generator and the X-ray image sensor or the center of rotation of the subject. If the point set as the rotation center (the nominal rotation center) and the true rotation center are deviated, the reconstructed image will be blurred. Therefore, it is necessary to calibrate the rotation center every time the magnification of the subject image is changed and every time the X-ray image sensor or the X-ray generator is attached or detached. The same applies to a case where a positional shift occurs in the apparatus due to a change over time. Further, with the configuration in which the X-ray image sensor is detachable from the swivel arm, a positional shift may occur when the X-ray image sensor is once detached from the swivel arm and mounted again. In particular, the displacement of the rotation center position in the left and right direction with respect to the rotation axis as viewed from the X-ray generator has a very large influence. In this case, the reconstruction calculation becomes inaccurate due to the shift of the rotation center position, and the reconstructed image is blurred. Therefore, it is necessary to calibrate the rotation center for the X-ray image sensor.

  The magnification changing procedure including the creation of correction data including the center of rotation is, for example, as follows. First, the subject positioned at the shooting position is removed, then the physical position of the apparatus is changed to change the enlargement ratio, and then a fixture (jig) for creating correction data is attached. Next, photographing is performed, and correction data is calculated using the photographing data. Next, the fixture (jigs) for creating correction data is removed, and the subject is attached and positioned again. Next, the subject is photographed and the photographing data is reconstructed. Therefore, it takes time and effort to attach and remove the fixture (jig) and to shoot the correction data. Also, if the affected area is a minute part and it is necessary to take images frequently during treatment, the procedure of repeating the positioning of the subject (affected area) every time the image is taken is unacceptable. It was not practical. In addition, when the enlargement ratio is varied while the subject is positioned, it is impossible to acquire correction data, and thus it is actually necessary to reposition the subject. In addition, the X-ray image sensor can be attached to and detached from the swivel arm. When the X-ray image sensor is once removed from the swivel arm and mounted again, the rotation center position is set each time the X-ray image sensor is mounted. There was a need to calibrate.

In order to facilitate calibration of the center of rotation, for example, in a computed tomography apparatus described in Japanese Patent Application Laid-Open No. 2004-301860, it is obtained from transmission data (sinogram) of the subject itself without using a phantom. First, a transmission image for each angle is acquired by an X-ray detector. Then, on the sinogram created by the obtained plurality of transmission data, the correlation between the transmission data at a plurality of points and the transmission data at the plurality of points determined by setting the virtual rotation center is obtained. The correlation is obtained by changing the virtual rotation center, and the virtual rotation center that gives the best correlation is obtained as the rotation center position.
JP-A-5-322802 JP 2004-301860 A

  In X-ray CT imaging, if the rotation center is inaccurate, the reconstruction calculation is inaccurate and the reconstructed image is blurred. Therefore, calibration of the rotation center is important. It is desirable that the rotation center position be determined with an accuracy of 0.1 mm, for example. For this reason, the rotation center position has been calibrated each time the X-ray image sensor and / or the X-ray generator is removed or changed. However, the method using the sinogram described above has an advantage that the phantom need not be used, but the processing is complicated.

  An object of the present invention is to provide an X-ray CT imaging method and apparatus that can easily calibrate the shift of the rotation center in X-ray CT imaging. More specifically, the object of the present invention is to easily calibrate the shift of the rotation center when the magnification (magnification ratio) of the image is changed by changing the relative positional relationship between the X-ray generator, the X-ray image sensor, and the subject. To provide an X-ray CT imaging method and apparatus, and when the X-ray image sensor is detached from the swivel arm etc. and is mounted again in a configuration in which the X-ray image sensor is detachable from the swivel arm etc. It is also an object to provide an X-ray CT imaging method and apparatus that can be easily calibrated.

  In the first X-ray CT correction method according to the present invention, (1) an X-ray is generated while rotating an X-ray generator and an X-ray image sensor arranged opposite to each other with the subject interposed therebetween. The X-ray generated by the generator is irradiated to the subject, and the X-ray transmitted through the subject is detected by the X-ray image sensor to obtain X-ray projection data. Next, (2) the X-ray generator, the rotation center, and the X-ray image set in the calculation of the image reconstruction for converting the acquired X-ray projection data into the distribution of the X-ray absorption coefficient of the subject. In the relative positional relationship between the sensors, a displacement amount is set in the direction of rotation of the X-ray image sensor relative to the subject, and then the subject or a part of the subject portion is determined from the X-ray projection data. The tomographic image data is generated by performing the image reconstruction with the displacement corresponding to the displacement amount added. (3) The tomographic image data is created for a plurality of displacement amounts based on the same X-ray projection data. Next, (4) correction data for image reconstruction calculation is set based on the displacement amount from which the tomographic image data having the largest gradation spread among the obtained tomographic image data is obtained. Here and in other parts of the specification, “performing the image reconstruction with displacement corresponding to the displacement amount” means that “from the X-ray projection data at the position where displacement is equivalent to the displacement amount, “Tomographic image data is created by performing the image reconstruction on the subject or a part of the target part” also means “from the X-ray projection data, the subject part or a part of the target part is equivalent to the amount of displacement. It also includes “creating tomographic image data by performing the above-described image reconstruction for correcting displacement”.

  In the second X-ray CT correction method according to the present invention, (1) an X-ray is generated while rotating an X-ray generator and an X-ray image sensor arranged opposite to each other with the subject interposed therebetween. The X-ray generated by the generator is irradiated to the subject, and the X-ray transmitted through the subject is detected by the X-ray image sensor to obtain X-ray projection data. Next, (2) the X-ray generator, the rotation center, and the X-ray image set in the calculation of the image reconstruction for converting the acquired X-ray projection data into the distribution of the X-ray absorption coefficient of the subject. In the relative positional relationship between the sensors, a displacement amount is set in the direction of rotation of the X-ray image sensor relative to the subject. Next, (3) a conversion table for converting the coordinates of the position of the X-ray projection data acquired on the X-ray image sensor into the coordinates of the subject is converted by adding a displacement corresponding to the displacement amount. The tomographic image data is created by reconstructing the image of the subject or a part of the target portion from the X-ray projection data using the modified conversion table. Next, (4) the tomographic image data is created for a plurality of displacement amounts based on the same X-ray projection data. (5) Among the obtained plurality of tomographic image data, a conversion table from which tomographic image data having the largest gradation spread is set as a conversion table used for the image reconstruction.

  In the third X-ray CT correction method according to the present invention, (1) an X-ray is generated while rotating an X-ray generator and an X-ray image sensor disposed opposite to each other with the subject interposed therebetween. The X-ray generated by the generator is irradiated to the subject, and the X-ray transmitted through the subject is detected by the X-ray image sensor to obtain X-ray projection data. Next, (2) tomographic image data is created by performing image reconstruction calculation for converting the acquired X-ray projection data into a distribution of X-ray absorption coefficients of the subject for the subject or a part of the subject. Next, (3) in the created tomographic image data, a blur width in a plane perpendicular to the rotation axis of the rotation mechanism included in the tomographic image data is set. Next, (4) ½ of the set blur width is set as each displacement amount in the direction opposite to the rotation direction of the X-ray image sensor relative to the subject. The tomographic image data is created by performing the image reconstruction by adding displacements corresponding to the respective displacement amounts with respect to the subject or a part of the target portion from the line projection data. Then, (5) correction data for image reconstruction calculation is set based on the displacement amount from which the tomographic image data having the larger gradation spread out of the two obtained tomographic image data is obtained.

  In the X-ray CT imaging method according to any one of the above, the amount representing the spread of gradation is, for example, a density difference or a standard deviation of density in the reconstructed image. Preferably, in the first and second X-ray correction methods according to the present invention, the amount representing the spread of gradation is a density difference or a standard deviation of density in a tomographic image, and the density for the plurality of tomographic images. The standard deviation of the difference or concentration is plotted against the displacement amount, and the displacement amount in which the concentration difference or the standard deviation of the concentration is the maximum among the plurality of displacement amounts and the concentration difference between the plurality of displacement amounts adjacent thereto or Interpolation calculation is performed by approximating the standard deviation of density by quadratic curve approximation to calculate the displacement amount that maximizes the density difference or the standard deviation of concentration, and the displacement amount is the tomographic image with the largest gradation spread. The amount of displacement from which data can be obtained.

  In the first or second X-ray CT imaging method, preferably, after the creation of the plurality of tomographic image data, the plurality of tomographic image data are displayed side by side or sequentially on the screen of the image display device. The tomographic image data selected by the operator is tomographic image data having the largest gradation spread.

  An X-ray CT imaging method according to the present invention is generated by an X-ray generator while rotating an X-ray generator and an X-ray image sensor disposed opposite to each other with the subject interposed therebetween. The X-ray image sensor detects X-rays that are irradiated with X-rays and passes through the subject, and calculates the image reconstruction to convert the obtained X-ray projection data into the distribution of the X-ray absorption coefficient of the subject. An X-ray CT imaging method for generating tomographic image data of a tomographic plane of the subject, wherein any one of the above-described X-ray CT correction methods is executed before acquisition of the X-ray projection data. Alternatively, when a change in the relative position of the X-ray generator and / or the X-ray image sensor with respect to the subject is detected, one of the X-ray CT correction methods described above is executed.

  A first X-ray CT imaging apparatus according to the present invention includes an X-ray generator and an X-ray image sensor arranged opposite to each other with a subject interposed therebetween, and the X-ray generator and the X-ray image sensor disposed on the subject. The X-ray generator and the X-ray image sensor are rotated relative to the subject by the rotation mechanism, and the subject is irradiated with X-rays by the X-ray generator. Projection data acquisition means for acquiring X-ray projection data by the X-ray image sensor for the tomographic plane of the image, and image reconstruction for converting the X-ray projection data obtained by the X-ray image sensor into a distribution of X-ray absorption coefficients of the subject. Image reconstruction means for generating tomographic image data of the tomographic plane of the subject by calculating the composition, correction data for image reconstruction calculation using the projection data acquiring means and the image reconstruction means And a calibration means for setting. The calibration means includes the X-ray relative to the subject in the relative positional relationship between the X-ray generator, the center of rotation and the X-ray image sensor set in the calculation of the image reconstruction. A plurality of displacement amounts are set in the direction of rotation of the image sensor, and the image reconstruction is performed by adding a displacement corresponding to the displacement amount with respect to the subject or a part of the target portion from the X-ray projection data. Image data creation means for creating image data, and correction data for image reconstruction calculation based on the displacement amount from which the tomographic image data having the largest gradation spread among the obtained tomographic image data is obtained Correction data setting means for setting.

  According to a second X-ray CT imaging apparatus of the present invention, an X-ray generator and an X-ray image sensor arranged opposite to each other with a subject interposed therebetween, and the X-ray generator and the X-ray image sensor are attached to the subject. The X-ray generator and the X-ray image sensor are rotated relative to the subject by the rotation mechanism, and the subject is irradiated with X-rays by the X-ray generator. Projection data acquisition means for acquiring X-ray projection data by the X-ray image sensor for the tomographic plane of the image, and image reconstruction for converting the X-ray projection data obtained by the X-ray image sensor into a distribution of X-ray absorption coefficients of the subject. Image reconstruction means for generating tomographic image data of the tomographic plane of the subject by calculating the composition, correction data for image reconstruction calculation using the projection data acquiring means and the image reconstruction means And a calibration means for setting. The calibration means includes the X-ray relative to the subject in the relative positional relationship between the X-ray generator, the center of rotation and the X-ray image sensor set in the calculation of the image reconstruction. A conversion table that sets a plurality of displacement amounts in the rotation direction of the image sensor and converts the coordinates of the position of the X-ray projection data acquired on the X-ray image sensor in the reconstruction calculation into the coordinates of the subject. Using a conversion table that is corrected so as to be converted by adding a displacement corresponding to the amount of displacement, a plurality of tomographic image data is obtained by performing image reconstruction of the subject or a part of the target portion from the X-ray projection data. And the image data creation means for creating the image, and the image based on the displacement obtained from the tomographic image data having the largest gradation spread among the plurality of obtained tomographic image data. Setting the conversion table used in the configuration means and a correction data setting means.

  According to a third X-ray CT imaging apparatus of the present invention, an X-ray generator and an X-ray image sensor arranged opposite to each other with a subject interposed therebetween, and the X-ray generator and the X-ray image sensor are attached to the subject. The X-ray generator and the X-ray image sensor are rotated relative to the subject by the rotation mechanism, and the subject is irradiated with X-rays by the X-ray generator. Projection data acquisition means for acquiring X-ray projection data by the X-ray image sensor for the tomographic plane of the image, and image reconstruction for converting the X-ray projection data obtained by the X-ray image sensor into a distribution of X-ray absorption coefficients of the subject. An image reconstruction unit that calculates a configuration and generates tomographic image data of the tomographic plane of the subject, and an image reconstruction calculation using the projection data acquisition unit and the image reconstruction unit And a calibration means for setting a positive data. The calibration means includes first image data creation means for creating tomographic image data by performing the image reconstruction on the subject or a part of a target portion thereof from the acquired X-ray projection data; and the first image data In the tomographic image data created by the creating means, the blur width setting means for setting a blur width in a plane perpendicular to the rotation axis of the relative rotation included in the image data, and the blur set by the blur width setting means. Of the X-ray image sensor relative to the rotated subject in a direction opposite to the direction of rotation of the X-ray image sensor. A second image data creation unit that creates two tomographic image data by performing the image reconstruction calculation with the displacement corresponding to the respective displacement amounts for a part of the target portion And correction data setting means for setting correction data for image reconstruction calculation based on the displacement obtained from the tomographic image data having the larger gradation spread among the two obtained tomographic image data. Is provided. In addition, these X-ray CT imaging apparatuses are provided with the display means which displays the produced tomographic image data, for example.

  In any one of the X-ray CT imaging apparatuses, the amount representing the gradation spread is, for example, a density difference or a standard deviation of density in a tomographic image.

  In the first and second X-ray CT imaging apparatuses, the amount representing gradation expansion is a density difference or a standard deviation of density in a tomographic image, and the correction data setting means includes, for example, the plurality of correction data setting means The density difference or the standard deviation of the density is obtained for the tomographic image data, and the density difference or the standard deviation of the density as a function of the displacement amount is the largest of the plurality of displacement amounts. Interpolation calculation is performed by performing quadratic curve approximation on the concentration difference or concentration standard deviation of multiple displacement amounts adjacent to it, and the displacement amount that maximizes the concentration difference or concentration standard deviation is calculated. Then, this displacement amount is set as a displacement amount that provides tomographic image data having the largest gradation spread.

  In the X-ray CT imaging apparatus according to any one of the above, preferably, further after the setting by the calibration unit, using the projection data acquisition unit and the image reconstruction unit using the setting, An imaging control unit is provided that performs tomographic image data generation on the subject or a part of the target portion thereof to generate tomographic image data.

  Preferably, the X-ray CT imaging apparatus according to any one of the above, further includes a movement detection unit that detects a change in a relative position of the X-ray generator and / or the X-ray image sensor with respect to a subject. When the movement detecting means detects the relative position change, the calibration means is activated.

  The first program according to the present invention is (1) generated by an X-ray generator while rotating an X-ray generator and an X-ray image sensor disposed opposite to each other with respect to the subject. An X-ray image sensor for detecting X-rays transmitted to the subject by irradiating the subject with the X-rays and acquiring X-ray projection data; and (2) using the X-ray projection data as X-rays of the subject. For the relative positional relationship between the X-ray generator, the center of rotation and the X-ray image sensor set in the calculation of the image reconstruction converted into the distribution of absorption coefficients, A reconstruction step for calculating the image reconstruction by setting a displacement amount, and generating a tomographic image of the subject or a part thereof for each displacement amount; and (3) selecting from the obtained plurality of reconstruction images Was re Setting correction data for the relative positional relationship among the X-ray generator, the center of rotation, and the X-ray image sensor in the calculation of the image reconstruction based on the amount of displacement corresponding to the synthesized image. It is a program for making it run.

  The second program according to the present invention is (1) generated by an X-ray generator while rotating an X-ray generator and an X-ray image sensor arranged opposite to each other with respect to the subject relative to the subject. An X-ray image sensor for detecting X-rays transmitted to the subject by irradiating the subject with the X-rays and acquiring X-ray projection data; and (2) using the X-ray projection data as X-rays of the subject. With respect to the relative positional relationship among the X-ray generator, the center of rotation and the X-ray image sensor set in the calculation of the image reconstruction to be converted into the distribution of the absorption coefficient, the X relative to the subject A conversion table that sets a plurality of displacement amounts in the rotation direction of the line image sensor and converts the coordinates of the X-ray image sensor into the coordinates of the subject is obtained by using the X-ray projection data at a position shifted by the displacement amount. A reconstruction step of generating the tomographic image of the subject or a part thereof with respect to each displacement amount by performing the image reconstruction using a conversion table modified so as to convert to the coordinates of the subject; (3) A program for causing a computer to execute a correction step of setting a conversion table corresponding to a reconstructed image selected from a plurality of reconstructed images as a conversion table used for calculation of the image reconstruction.

  The third program according to the present invention is (1) generated by an X-ray generator while rotating an X-ray generator and an X-ray image sensor arranged opposite to each other with respect to the subject. An X-ray image sensor for detecting X-rays transmitted to the subject by irradiating the subject with the X-rays and acquiring X-ray projection data; and (2) using the X-ray projection data as X-rays of the subject. A first image reconstruction step of calculating an image reconstruction to be converted into an absorption coefficient distribution to generate a tomographic image of the subject or a part thereof; and (3) a blur width of an image in the obtained tomographic image. (4) ½ of the blur width as a displacement amount in the opposite direction to the rotation with respect to the current position, and the image for the X-ray projection data Perform reconstruction calculations and tomograms A second image reconstruction step for creating image data, and (5) image reconstruction calculation based on a displacement amount obtained from tomographic image data having a larger gradation spread among the two obtained tomographic images. And a correction step for setting correction data for the position of each pixel in the X-ray image sensor used in the above.

  The effect of the present invention is that calibration can be easily calibrated by creating and comparing reconstructed images with a plurality of displacement amounts even when a rotational center misalignment occurs in CT imaging.

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

  FIG. 1 shows an imaging system of an X-ray CT imaging apparatus using a turning arm. The portal frame 10 includes a beam 10a for pivotally supporting the swivel arm 16, a pair of horizontal beams 10b for supporting the base end of the beam 10a on both sides, a pair of vertical beams 10c for supporting the pair of transverse beams 10b, And it comprises a base 10d for fixing a pair of vertical beams 10c. An X-ray generator 12 and an X-ray image sensor 14 are arranged to face each other at both ends of the turning arm (rotating mechanism) 16. The turning arm 16 is turned by an arm rotation motor 18 (see FIG. 2) built in the beam 10a. For example, in cone beam CT, the X-ray generator 12 emits a conical beam, and the X-ray image sensor 14 is a two-dimensional X-ray image sensor. As a two-dimensional X-ray image sensor, for example, an X-ray image intensifier (XII) camera, an X-ray CCD sensor, a MOS sensor, a CMOS sensor, a TFT sensor, an FT sensor, or a sensor made of an X-ray solid-state image sensor is used. it can. The X-ray generator 12 and the X-ray image sensor 14 constitute projection data acquisition means for acquiring X-ray projection data. The chair 20 is provided on the base 10 d and is moved in the front-rear, left-right, up-down directions by a three-dimensional movement mechanism 22 provided at the lower portion of the chair 20. Further, a headrest 24 is provided above the chair 20. At the time of imaging, the subject 26 (see FIG. 3) sits on the chair 20 and its head is fixed to the headrest 24. The operator instructs the chair 20 to move by the operation device 28 (see FIG. 2), and the imaging region (subject) 30 on the subject's head is moved between the X-ray generator 12 and the X-ray image sensor 14. Position it between them. Next, by turning the turning arm 16, the X-ray generator 12 and the X-ray image sensor 14 are rotated around the subject along a circular path. At this time, X-rays generated by the X-ray generator 12 pass through the subject, and the X-ray image sensor 14 detects X-ray projection data.

  FIG. 2 shows an imaging control apparatus 32 of the X-ray CT imaging apparatus. The imaging control device 32 controls the imaging operation by the imaging system of the X-ray CT imaging device, and reconstructs a three-dimensional image from the X-ray projection data. The imaging control device 32 includes a CPU 34 that controls the whole, and the CPU 34 is connected to a keyboard 36, a mouse 38, a display device 40, various input / output interfaces 42, a storage device 44 that stores various programs and data, and the like. The input / output interface 42 is connected to the X-ray generator 12, the X-ray image sensor 14, the arm rotation motor 18, the three-dimensional moving mechanism 22, etc., in addition to the operation device (including the operation panel) 28.

  The storage device 44 includes a photographing operation control program 46, an image memory 48, an image reconstruction program 50, a conversion table 52, a correction table 54, a positional distortion correction program 56, and a rotational position calibration program 58. The imaging operation control program 46 controls an operation sequence of CT imaging including turning control. The image memory 48 stores projection images and reconstructed images (CT images). An image reconstruction program (image reconstruction means, image data creation means) 50 performs a known reconstruction calculation for reconstructing a projection image into a tomographic image. For the reconstruction calculation, a filtered back projection method or the like is used. When the X-ray beam generated by the X-ray generator 12 passes through the three-dimensional voxel position of the subject and is projected onto the two-dimensional pixel position on the X-ray image sensor 14, the conversion table 52 displays the three-dimensional voxel of the subject. A table for associating a position with a two-dimensional pixel position on the X-ray image sensor 14, that is, a table for converting the coordinates of the position of the X-ray projection data acquired on the X-ray image sensor into the coordinates of the subject, Used for reconstruction. The correction table 54 is various tables used for correcting positional distortion generated at the time of imaging such as rotational shake of the X-ray generator 12 and the X-ray image sensor 14 and magnetic distortion due to geomagnetism. The positional distortion correction program 56 is a program for correcting the positional distortion. The positional distortion is measured before photographing the subject by using, for example, a correction phantom, and the correction table 54 is obtained based on this measurement. The rotational position calibration program (calibration means) 58 will be described later.

  In the X-ray CT imaging apparatus, the magnification of the image can be changed by the relative positional relationship among the X-ray generator 12, the X-ray image sensor 14, and the subject. For example, as shown in FIG. 3, the image detected by the X-ray image sensor 14 is reduced and the magnification is reduced by moving the position of the chair 20 from the normal position toward the X-ray image sensor 14. In this way, the magnification of the image can be adjusted by making the positional relationship between the X-ray generator 12, the X-ray image sensor 14, and the subject 30 variable. Even when the positional relationship between the generator 12, the X-ray image sensor 14, and the subject 30 is changed, the correction can be made from the actual X-ray projection data at the changed position, and the correction data once set is used each time. Compared to, corrections that are more realistic are possible each time.

  Note that the CT apparatus for turning the X-ray generator and the X-ray image sensor around the subject only needs to be capable of turning while the X-ray generator and the X-ray image sensor are arranged to face each other, as shown in FIG. In addition to a CT apparatus using a U-shaped swivel arm, for example, a CT apparatus including a known gantry for imaging a patient horizontally may be used. Alternatively, a C-arm that turns around a horizontal rotation axis may be used. In addition, the relative angle of the swivel axis at which the X-ray generator and the X-ray image sensor swivel with respect to the subject can be arbitrarily set, for example, avoiding metal artifacts embedded in the body to avoid metal artifacts. You may be able to shoot. For example, the turning axis of the turning arm 16 may be configured to be tiltable, or the headrest 24 may be configured to be movable, and the head of the subject 26 may be configured to be tiltable.

  The X-ray generator and the X-ray image sensor need only be able to rotate relative to the subject, and as described above, the X-ray generator and the X-ray image sensor may be turned while being opposed to each other. Relative rotation of the X-ray generator and the X-ray image sensor with respect to the subject may be realized by fixing the X-ray generator and the X-ray image sensor and rotating the subject. FIG. 4 shows an X-ray CT imaging apparatus in which a subject 82 is placed on a rotary table 80. The X-ray generator 84 and the X-ray image sensor 86 are provided at corresponding positions across the subject on the rotary table 80. In this X-ray CT imaging apparatus, the positions of the X-ray generator 84 and the X-ray image sensor 86 are fixed during imaging, and the rotation table 80 is rotated by the rotation mechanism 88. The positions of the X-ray generator 84 and the X-ray image sensor 86 can be changed with respect to the rotation axis of the rotary table 80, respectively. The imaging control device of the X-ray CT imaging apparatus is the same as the imaging control apparatus of FIG. 2, but controls the rotation mechanism 88 instead of the arm rotation motor. In FIG. 1, columnar members provided with X-ray generators and X-ray image sensors at both ends are shown as an example of the swivel arm 16, but the shape of the swivel arm can be variously set. For example, an X-ray generator and an X-ray image sensor may be provided at both ends of the annular member, and the annular member may be rotated.

  In the reconstruction of the projection image, a three-dimensional image of the subject is calculated based on the two-dimensional data obtained by the X-ray image sensor. Here, the reference of the position (voxel coordinates) of the subject in the plane of rotation should be the center of rotation. However, in CT imaging, when the mechanical (geometric) positional relationship of the imaging system is intentionally changed, and when it is attempted to return the mechanical positional relationship to the original position, the intended mechanical position is set. Subtle misalignment occurs. Even if the relative position of the X-ray generator and / or X-ray image sensor with respect to the subject is detected, the nominal position and the true position may be misaligned. For example, as described above, when the magnification (magnification ratio) of the image is changed due to a change in the relative positional relationship among the X-ray generator 12, the X-ray image sensor 14, and the subject, the X-ray image sensor 14 is used as the swing arm 16. On the other hand, when the X-ray image sensor is detached from the swivel arm 16 and attached again, the position may be shifted. In particular, the positional deviation of the rotation center position in the right and left direction with respect to the rotation axis as viewed from the X-ray generator 12 has a very large influence. In that case, the reconstruction calculation becomes inaccurate due to the shift of the rotation center position, and the reconstructed image is blurred. Therefore, the rotation center position needs to be calibrated every time the position of the X-ray generator and / or the X-ray image sensor is changed. In particular, for an object including a fine imaging target (such as an affected part), for example, an accuracy of 0.1 mm or less is required. On the other hand, when the X-ray image intensifier, which is one of the X-ray image sensors, is rotated, reproducible positional distortion such as rotational distortion of the image generated by interaction with the geomagnetism is once corrected. If the correction table 54 is obtained by measurement, there is no need to correct it every time of shooting. (Such correction of positional distortion is described in JP-A-2002-336237, etc.)

  As described above, the rotational center position needs to be calibrated every time the mechanical positional relationship of the X-ray generator and / or the X-ray image sensor is changed. Therefore, when shooting with the magnification of the image changed, as shown in FIG. 5, the rotation center position is calibrated before the actual shooting every time the change is made. Now, the X-ray generator 12 and the X-ray image sensor 14 are moved to the position A, and preliminary imaging is performed, and the displacement amount (amount for correcting the projection blur) S1 at that time is determined. Then, actual shooting is performed at position A. Next, when moving to position B to change the magnification (change in relative position of the X-ray generator and / or the X-ray image sensor with respect to the subject), the movement is detected. For example, as a well-known movement detecting means, a potentiometer, a speed sensor, an angular velocity sensor, an angle sensor, a rotary encoder, etc. are appropriately provided on the turning arm, and the movement of the turning arm is detected by detecting the moving distance and the angular displacement. Yes. Next, preliminary photographing is performed, and a displacement amount (amount for correcting projection blur) S2 of the rotation center position at that time is determined. Then, actual shooting is performed at position B. The same applies hereinafter.

  The above is an example in which the main imaging is performed after the preliminary imaging is performed and the amount of displacement is determined. However, the main imaging is suddenly performed, and the displacement amount may be determined using the X-ray projection data obtained by the main imaging. In this case, the amount of X-ray projection data to be processed is increased, but there is an advantage that it is completed by one imaging.

  The calibration of the center of rotation will be further described. The image is actually reconstructed, and the sharpest image is selected from the reconstructed images to calibrate the center of rotation. First, X-ray projection data of one or more small number of tomographic planes (for example, a center plane) perpendicular to the rotation axis is acquired, and then X-ray generator, X-ray image sensor, and rotation center are used as original data. A tomographic image is created by reconstructing an image by shifting the relative positional relationship between the two. Note that the image to be reconstructed may be the entire subject or a part of the subject. When a part of the subject is reconstructed, there is an advantage that the calculation time is relatively short. As the relative positional relationship between the X-ray generator, the X-ray image sensor, and the rotation center, a plurality of displacement amounts are set in the direction of rotation of the X-ray image sensor 14 relative to the subject. That is, using each displacement amount, an image reconstruction that actually converts the X-ray projection data of each pixel in the X-ray image sensor at a position shifted by the displacement amount into an X-ray absorption coefficient distribution of the subject ( Try even part of the subject). Then, a plurality of reconstructed images, that is, tomographic images are displayed. The operator can easily select the clearest image by visually comparing the reconstructed images. Further, the clearest image may be automatically selected by calculating from the reconstructed image data, here, the tomographic image data. Note that a clear image is an image having the largest gradation spread, as will be described later. Then, correction data is set corresponding to the amount of displacement from which the selected image was obtained. At the time of actual photographing, it is possible to reliably obtain an image free from blur due to the shift of the rotation center position using the correction data. It is assumed that correction for reproducible positional distortion other than calibration of the rotation center position has already been performed.

  The relative positional relationship among the X-ray generator 12, the X-ray image sensor 14, and the center of rotation can be calculated by shifting by several methods. Here, a line passing through the X-ray generator 12, the rotation center, and the X-ray image sensor 14 indicates the relative position between the subject and the X-ray image sensor within a plane including, for example, one tomographic plane perpendicular to the rotation axis. May be calculated by shifting to one side or both sides.

  In the first method, the X-ray projection data corresponding to the position of each pixel in the X-ray image sensor 14 (captured original projection data) has the same direction as the rotation relative to the subject of the X-ray image sensor 14 or A predetermined displacement amount (for example, one pixel) is set in the opposite direction, the displacement amount is added, and image reconstruction is performed on the subject or a part of the target portion from the X-ray projection data at the shifted position. Create a tomographic image. As a result, the same calculation result is obtained as when the X-ray image sensor 14 is photographed at a position where a displacement amount is added relative to the rotation center. As will be described later, “X-ray projection data at a position to which a displacement amount has been added” is specifically X-ray projection data read out by shifting the coordinate position by the displacement amount, for example. Further, in the calculation formula used for image reconstruction, the coordinate value included in the calculation formula may be changed so as to incorporate the displacement amount, and the coordinate position may be read without being shifted. In this case, in the calculation formula, the X-ray projection data corresponds to X-ray projection data at a position shifted by a displacement amount. In any case, in the image reconstruction calculation, the X-ray projection data stored corresponding to the coordinate position of the X-ray image sensor 14 is handled as the coordinate position being shifted by the amount of displacement, and the displacement X-ray projection data at a position shifted by an amount is used in the calculation. That is, image reconstruction is performed by adding a displacement corresponding to the amount of displacement. Then, a reconstructed image, here a tomographic image or tomographic image data, is reconstructed with respect to a plurality of displacement amounts (deviation amounts) from the same original projection data. Then, the clearest image is manually or automatically selected from a plurality of reconstructed images (tomographic images). Then, the rotation center position is calibrated by the amount of displacement corresponding to the selected reconstructed image. That is, correction data for image reconstruction calculation is set based on the amount of displacement. The range and increment of the displacement amount may be appropriately determined in consideration of the physical size of the apparatus. For example, when shifting the coordinates of the pixel of the X-ray image sensor with respect to the rotation center, the amount of displacement is set in increments of 0.2 mm from −1 mm to +1 mm. (0.2 mm is a pixel pitch.) In this imaging, the pixel position of the X-ray image sensor 14 is corrected using the set correction data, and an image is reconstructed.

  In the second method, the rotation center position is calibrated not by reconstructing X-ray projection data at a position shifted by the amount of displacement, but by recreating a conversion table used for reconstruction calculation. In the image reconstruction, a conversion table (also referred to as a horizontal table) that associates the three-dimensional position of the voxel of the subject with the two-dimensional position of the pixel of the detection image sensor 14 is used. First, a displacement is set in the direction of rotation of the X-ray image sensor relative to the subject. Next, the conversion table basically converts the position of the X-ray projection data acquired on the X-ray image sensor, that is, the coordinates of the pixel into the coordinates of the subject. The conversion table is converted into a displacement amount (amount of deviation). ), The amount of the displacement is added, and the X-ray projection data at the shifted position is corrected so as to perform the image reconstruction on the subject or a part of the target portion. This conversion table is modified so as to convert the X-ray projection data at the position shifted by the displacement amount into the coordinates of the subject. That is, image reconstruction is performed using a conversion table that is modified so as to be converted by adding a displacement corresponding to the amount of displacement. A conversion table is created for each of a plurality of displacement amounts, and a reconstructed image, here a tomographic image or tomographic image data, is created from the same original projection data using these conversion tables. As in the first method, the sharpest image is manually or automatically selected from a plurality of reconstructed images (tomographic images), and the corresponding conversion table is used for image reconstruction. It is selected as a conversion table and the rotation center position is calibrated. In actual photographing, an image is reconstructed using the selected conversion table.

  In the above example, a conversion table is created every time. Instead, a conversion table corresponding to a plurality of displacement amounts is created and stored in advance, and is selected and read out during position calibration. May be.

  The first method for setting the displacement amount with reference to the pixel of the X-ray image sensor 14 will be described more specifically with reference to FIGS. FIG. 6 shows an ideal situation where there is no particular problem in the relative positional relationship between the X-ray generator 12, the center of rotation and the X-ray image sensor 14. In this case, the X-ray image sensor 14 is at the position PSa that should be originally with respect to the X-ray generator 12 and the center of rotation. The X-ray XB irradiated from the X-ray generator 12 passes through a specific point Pa of the subject 30 and enters the pixel PTa of the X-ray image sensor 14. At this position PSa, if the point Pa is at the rotation center, for example, the pixel PTa is at a coordinate position set as a position where X-rays passing through the rotation center are incident. The X-ray projection data of the X-rays incident on the pixel PTa is processed as X-ray projection data at the position of the point Pa by image reconstruction. In other words, reconstruction is performed to return to the position of the point Pa.

  In the example shown in FIG. 7, the X-ray image sensor 14 is not located at the position PSc that should originally exist with respect to the X-ray generator 12 and the center of rotation, but is shifted to the position PSb. The X-ray XB irradiated from the X-ray generator 12 passes through a specific point Pb of the subject 30 and enters the pixel PTb of the X-ray image sensor 14 at the position PSb that is not supposed to be. The positions of the pixels in the X-ray image sensor 14 with respect to the X-ray generator 12 and the rotation center are set in advance. Even if the X-ray image sensor 14 is misaligned, if the X-ray image sensor 14 is treated as being in an ideal position, the pixel PTc of the X-ray image sensor 14 at the position PSc is the X-ray at the position PSb. Although it corresponds to the pixel PTb of the image sensor 14, in the X-ray image sensor 14 at the position PSb, the position PSc is handled as a position shifted by the amount of displacement from PTb to PTc. That is, on the image processing means side, the X-ray projection data incident on the pixel PTc at the original position PSc is the X-ray at the point Pc shifted by an amount corresponding to the amount shifted from PTb to PTc. It is processed as projection data and the image is reconstructed. In other words, reconstruction to the position of the point Pc is performed, and this occurs as blurring of the reconstructed image. In order to obtain a clear image without causing this blur, the X-ray projection data of the pixel PTb may be processed not as the point Pc but as the X-ray projection data of the point Pb. In other words, the reconstruction may be performed so as to return to the position of the point Pb.

  In the first method described above, in order to process the X-ray projection data of the pixel PTb as the X-ray projection data of the point Pb, so as to return it to an ideal point Pb, A plurality of predetermined displacement amounts (for example, one pixel) are set in the rotation direction of the X-ray image sensor, displacements corresponding to the displacement amount are added, and the subject or one of them is determined from the X-ray projection data of the pixel at the shifted position. The tomographic image is created by performing the above-described image reconstruction on the target portion of the part, and the image that is the clearest is selected, thereby attempting to reconstruct the image to the ideal point Pb.

  As described above, the X-ray projection data is shifted by the amount of displacement. Specifically, when the X-ray projection data is read, the coordinate position is shifted by the amount of displacement. For example, in the example of FIG. 7, when reading the X-ray projection data of the pixel position PTb, the X-ray projection data of the coordinates corresponding to the pixel position PTc is read. In this example, tomographic image data is created by performing image reconstruction on the subject or a part of the target portion from the X-ray projection data at the position displaced by the amount of displacement. In another example, the amount of displacement is changed to be incorporated into a variable representing a coordinate value included in a calculation formula used for image reconstruction. That is, the X-ray projection data is read without changing the coordinate position, but calculation is performed using a calculation formula that is modified so that the coordinate value is shifted by the displacement amount in the calculation formula for processing the read X-ray projection data. In this example, tomographic image data is created by performing image reconstruction for correcting the displacement of the subject or a part of the target portion from the X-ray projection data.

  8 and 9, the second method for correcting the conversion table and producing the same effect as the first method will be described more specifically in the case of performing image reconstruction using the conversion table. To do.

  FIG. 8 shows an ideal situation where there is no particular problem in the relative positional relationship between the X-ray generator 12, the center of rotation, and the X-ray image sensor 14. In this case, the X-ray image sensor 14 is at the position PSa that should be originally with respect to the X-ray generator 12 and the center of rotation. X-rays XB emitted from the X-ray generator 12 pass through specific points Pd1 and Pd2 of the subject 30, respectively, and enter the pixels PTd1 and PTd2 of the X-ray image sensor 14 at the position PSa where they should be. The X-ray projection data of the X-rays incident on the pixels PTd1 and PTd2 are processed as X-ray projection data at the positions of the points Pd1 and Pd2, respectively, in the image reconstruction by a preset conversion table. In other words, reconstruction is performed to return to the positions of the points Pd1 and Pd2.

  In the example shown in FIG. 9, the X-ray image sensor 14 is not at the position PSc where it should be, but is shifted to the position PSb. In the figure, Pd0, Pd1, and Pd2 represent adjacent points (voxels), and the position PSb is shifted from the position BSc by one voxel. The X-ray XB emitted from the X-ray generator 12 passes through specific points Pd1 and Pd2 of the subject 30, and enters the pixels PTd2 and PTd3 of the X-ray image sensor 14 at the position PSb that is not supposed to be the original position. To do. On the image processing means side, as in FIG. 7, the X-ray projection data of the X-rays incident on the pixels of the X-ray image sensor at the original position PSc are converted from the pixels PTd1, PTd2 to PTd2, PTd3. As a result, the image is reconstructed as X-ray projection data at the positions of the points Pd0 and Pd1 shifted by an amount corresponding to the amount shifted to. In other words, reconstruction is performed to return to the positions of the points Pd0 and Pd1, and this occurs as a blur of the reconstructed image.

  In order to obtain a clear image without causing this blur, the conversion table is used so that the X-ray projection data of the pixels PTd2 and PTd3 are processed as the X-ray projection data of the points Pd1 and Pd2 instead of the points Pd0 and Pd1. Should be corrected. In other words, the conversion table may be corrected and reconstructed so that the X-ray projection data of the pixel PTd2 is returned to the position of the point Pd1, and the X-ray projection data of the pixel PTd3 is returned to the position of the point Pd2.

  In the second method described above, in order to process the X-ray projection data of the pixels PTd2 and PTd3 as the X-ray projection data of the points Pd1 and Pd2, so to speak, the purpose is to return to the ideal points Pd1 and Pd2. A plurality of predetermined displacement amounts (for example, one pixel) are set in the direction of rotation of the X-ray image sensor relative to the subject, and the respective displacement amounts are used to perform image reconstruction from pixels at positions shifted by the displacement amount. Modify the conversion table for. The correction of the conversion table only changes the position of the pixel corresponding to the voxel in the image reconstruction calculation. Therefore, in this sense, the first method using X-ray projection data at a position shifted by the displacement amount is used. It is common. An image is reconstructed from the X-ray projection data with respect to the subject or a part of the target portion to create a tomographic image, and by selecting the clearest image, an image at ideal points Pd1 and Pd2 is obtained. Reconfiguration is performed.

  In correcting the conversion table, a conversion table is created corresponding to the amount of displacement so that the X-ray projection data of the pixel PTd1 at the shifted position is returned to the ideal coordinates Pd1. In this example, tomographic image data is created by performing image reconstruction on the subject or a part of the target portion from the X-ray projection data at the position displaced by the amount of displacement. In addition, a conversion table corresponding to a plurality of displacement amounts is created and stored in advance, and by selecting a conversion table from these, the X-ray projection data of the pixel at the shifted position is returned to the ideal coordinates. Therefore, the conversion table itself may be exchanged. In this example, tomographic image data is created by reconstructing an image by selecting a conversion table for converting the X-ray projection data into a different position corresponding to the displacement amount of the subject or a part of the target portion. ing.

  In the first or second method, in manual selection, images reconstructed with respect to each shift amount are displayed in a list or sequentially on the display device, and the operator selects the clearest image. The closer to the true center of rotation, the more blurring of the image disappears, so the density difference between the images increases and the contour of the image becomes clearer. For example, an image reconstructed by intentionally shifting the original projection data by 0.4 mm in the horizontal direction is blurred as shown in FIG. The parts that should be bright and focused are blurred and the brightness decreases. In addition, the portions that are dark and concentrated are blurred and the darkness is reduced. On the other hand, when the image is not blurred, as shown in FIG. 11, the bright part concentrates brightly and the dark part concentrates darkly. Therefore, the clearest image is an image having the largest gradation spread, and can be easily selected only by looking at the reconstructed image. In this way, by selecting the clearest image, a tomographic image having the largest gradation spread is selected from the plurality of obtained reconstructed images, that is, tomographic images or tomographic image data, Based on the amount of displacement obtained from the tomographic image data, correction data for the position of each pixel in the X-ray image sensor 14 used for image reconstruction calculation can be set.

  In the automatic selection, for the tomographic image data reconstructed for each displacement amount, the amount representing the extent of gradation is used as the amount representing the sharpness of the image, and the displacement amount that maximizes the amount is selected. To do. As an amount representing the spread of gradation, for example, an amount representing a difference in density (gradation) or a distribution state of density (for example, standard deviation or variance) is used. As shown in the reconstructed images of FIGS. 10 and 11, the density (luminance) difference, for example, (maximum value−minimum value) tends to increase as the image becomes clearer. The same applies to the standard deviation.

  In the example shown in FIG. 12, in the case of the original projection data actually used in FIGS. 10 and 11, the displacement amount for shifting the original projection data in the horizontal direction is −0.4 mm, −0.2 mm, 0 mm, 0.2 mm. , The difference between the maximum value and the minimum value of the voxel value (luminance) of the reconstructed image is plotted. In this example, the size of one pixel is 0.2 mm. In the case of this reconstructed image, the difference becomes the largest when the shift amount is 0 mm. Then, the difference between the maximum and minimum values becomes smaller as it shifts to both sides. Therefore, 0 mm is determined as the displacement amount. In the X-ray image sensor used for the image reconstruction calculation based on the displacement amount from which the tomographic image data having the largest gradation spread among the plurality of obtained reconstructed images, that is, the tomographic images is obtained. Correction data for the position of each pixel can be set automatically.

  When it is desired to determine the rotation center position with higher accuracy, interpolation calculation is performed on the measurement data. For example, a displacement used to create a reconstructed image by interpolating with a quadratic curve based on data of a plurality of points (for example, three points) including a point having the largest difference between the maximum value and the minimum value and points on both sides thereof. The amount of displacement, that is, the difference between the maximum value and the minimum value is determined with a higher accuracy than the difference between the amounts, that is, 0.2 mm. In the example shown in FIG. 13, the correction amount obtained by interpolation is −0.08 mm.

  In the above, the displacement amount is determined for the density (luminance) difference, for example, (maximum value−minimum value), but the same tendency can be obtained by calculating the amount representing the state of the density distribution of the voxel value, for example, standard deviation or variance. Is seen. Therefore, (maximum value−minimum value) may be used to obtain the optimum displacement amount, or a standard deviation may be used. In either case, a displacement amount that maximizes these values may be obtained.

  FIG. 14 shows blurring in the projection onto the X-ray image sensor 14 when the nominal rotation center 90 and the true rotation center 92 are deviated. The beam passing through the center of rotation 90 should be incident on the pixel position 94C in the X-ray image sensor 14. However, in the situation on the left side, the true rotation center 92 is shifted to the leftmost as viewed from the X-ray image sensor 14, and the beam that should come to the pixel position 94C in the X-ray image sensor 14 is shifted to the pixel position 94L. On the contrary, in the situation on the right side rotated by 180 °, the beam that should come to the pixel position 94C in the X-ray image sensor 14 is shifted to the pixel position 94R. Therefore, since the X-ray beam that should be incident on one position 94C is incident between 94L to 94R during one rotation, the projection is blurred. Therefore, an image reconstructed based on such projection is also blurred. However, conversely, the true position of the rotation center 90 can be detected using this phenomenon.

  In the third method, a reconstructed image of the subject (or a part thereof) is created from the original projection data, and the amount of displacement is determined based on the blur of the reconstructed image. First, one reconstructed image is created from the original projection data within a cross section perpendicular to the rotation axis. Next, the operator detects the blur width of the image in the reconstructed image and inputs the width to set the blur width. Since the blur width includes the enlargement ratio of the image, the detected blur width is divided by the enlargement ratio. Further, the blur width may be automatically detected. For example, edge enhancement image processing is performed to detect an edge portion from the image, and the width of the edge portion is obtained using a predetermined threshold value to obtain the blur width. Next, ½ of the blur width is set as a displacement amount in the same direction as the rotation of the X-ray image sensor 14 relative to the subject or in the opposite direction. Since one of the two displacement amounts is the correct displacement amount, the displacement amount is set in both directions, and the image of the subject or a part of the target portion is reproduced from the X-ray projection data at the position shifted by the displacement amount. Constitute. The amount of displacement from which a clear reconstructed image, here a tomographic image or tomographic image data is obtained, corresponds to the true center position. The sharpness is determined by the gradation spread as in the first and second methods. The displacement amount thus obtained is set as the correction amount. That is, of the obtained two tomographic images, the position of each pixel in the X-ray image sensor used for the image reconstruction calculation is based on the displacement obtained from the tomographic image data having the larger gradation spread. Correction data is set. That is, the tomographic image data is generated by performing the image reconstruction with the displacement corresponding to each displacement amount, and the tomographic image data having the larger gradation spread among the obtained two tomographic image data. Based on the obtained displacement amount, correction data for the position of each pixel in the X-ray image sensor used for the image reconstruction calculation is set. In the main imaging, the image is reconstructed by correcting the pixel position of the X-ray image center 14 as in the first method. Note that, as in the second method, the conversion table may be modified in accordance with the displacement amount. In this case, in actual photographing, an image is reconstructed using the conversion table.

  FIG. 15 is a flowchart of the rotational position calibration program 58 in the first method. Here, the operator manually selects the clearest image. First, a misregistration condition (start position, end position, displacement amount) for setting a misregistration range in the rotational direction or the opposite direction is set (S10). This may be a default value, for example. Next, the subject is photographed by the X-ray image sensor 14 while turning the turning arm 16, and X-ray projection data of a plane perpendicular to the rotation axis is obtained (acquisition step) (S12).

  Using this X-ray projection data as original projection data, a plurality of reconstructed images are created as follows. First, one displacement amount (here, the start position) is set within the misalignment range (S14). Then, the original projection data is read by shifting by the displacement amount (S16). In another example, the calculation formula is corrected to use a position shifted by the amount of displacement. Then, image reconstruction is performed, and the obtained reconstructed image is stored in the image memory 48 (reconstruction step) (S18). If it is not the end position (NO in S20), the process returns to step S14, a new displacement amount is set within the position shift range, and image reconstruction is continued.

  When image reconstruction is completed for all displacement amounts within the misalignment range (YES in S20), the obtained reconstructed image is then displayed on the screen of the display device 40 (S22). The display may be arranged as a list on the screen or may be sequentially displayed. The operator can select the reconstructed image determined to be the clearest on the screen. When the selection input of the reconstructed image by the operator is received (S24), the displacement amount corresponding to the reconstructed image is set as correction data (correction step) (26). When automatically selecting the clearest image, in step 24, an amount representing the gradation spread in the tomographic image is calculated, and the displacement corresponding to the tomographic image having the largest gradation spread is selected. To do.

  In the main imaging, image correction is performed by correcting the position of the X-ray projection data using the correction data. Actually, the normal imaging operation control program 46 is started for the main imaging. For convenience of explanation, if the processing following the above-described rotational position calibration is described in FIG. 15, the X-ray projection data of the subject is acquired. Next, image reconstruction is performed based on the X-ray projection data (S30). Note that if the X-ray projection data necessary for image reconstruction of the subject or a part of the target portion has already been captured in step S12, step S28 can be omitted.

  FIG. 16 is a flowchart of the rotational position calibration program 58 in the first method. Here, the clearest image is automatically set. What is different from the flowchart of FIG. 15 is the processing of steps S22a and S24a. These will be described. When the image reconstruction is completed for all displacement amounts within the misregistration range (YES in S20), next, an amount representing the gradation spread for each reconstructed image (for example, the maximum density value) The difference between the minimum values is calculated (S22a). Then, the reconstructed image having the largest amount is selected (S24a). Then, the displacement corresponding to the selected reconstructed image is set as correction data (26). In this step, the rotational position calibration program 58 has a function of correction data setting means.

  FIG. 17 is a flowchart of the rotational position calibration program 58 in the second method. Here, the operator manually selects the clearest image. What is different from the flowchart of FIG. 15 is the process of step S16a. First, a misregistration condition (start position, end position, displacement amount) for setting a misregistration range in the rotational direction or the opposite direction is set (S10). This may be a default value. Next, the subject is photographed by the X-ray image sensor 14 while turning the turning arm 16 to obtain projection image data of one or more small numbers of planes perpendicular to the rotation axis (acquisition step) (S12).

  Using this projection image data as original projection data, a plurality of reconstructed images are created as follows. First, one displacement amount (here, the start position) is set within the misalignment range (S14). Then, a conversion table corresponding to the displacement amount is created (S16a), image reconstruction is performed using the conversion table, and the obtained reconstructed image is stored in the image memory 48 (reconstruction step) (S18). If it is not the end position (NO in S20), the process returns to step S14, a new displacement amount is set within the position shift range, and image reconstruction is continued. If a conversion table corresponding to a plurality of displacement amounts is created and stored in advance, a conversion table among them is selected corresponding to the set displacement amount in step S16.

  When image reconstruction is completed for all displacement amounts within the misalignment range (YES in S20), the obtained reconstructed image is then displayed on the screen of the display device 40 (S22). The display may be displayed in a list and may be displayed sequentially. The operator can select the reconstructed image determined to be the clearest on the screen. When the selection input of the reconstructed image by the operator is received (S24), the conversion table corresponding to the reconstructed image is set as correction data (correction step) (26). In this step, the rotational position calibration program 58 has a function of correction data setting means. When automatically selecting the clearest image, in step 24, an amount representing the gradation spread in the tomographic image is calculated, and the displacement corresponding to the tomographic image having the largest gradation spread is selected. To do.

  In the main imaging, the image reconstruction is performed by correcting the position of the X-ray projection data using the conversion table. Actually, the normal imaging operation control program 46 is started for the actual imaging. For convenience of explanation, if the processing following the above-described rotational position calibration is described in FIG. 17, the X-ray projection data of the subject is acquired. Next, image reconstruction is performed based on the X-ray projection data (S30). Note that if the X-ray projection data necessary for image reconstruction of the subject or a part of the target portion has already been captured in step S12, step S28 can be omitted.

  FIG. 18 is a flowchart of the rotational position calibration program 58 in the second method. Here, the clearest image is automatically set. What is different from the flowchart of FIG. 17 is the processing of steps S22a and S24a. These will be described. When the image reconstruction is completed for all displacement amounts within the misregistration range (YES in S20), next, an amount representing the gradation spread for each reconstructed image (for example, the maximum density value) The difference between the minimum values is calculated (S22a). Then, the reconstructed image having the largest amount is selected (S24a). Then, the displacement corresponding to the selected reconstructed image is set as correction data (26).

  FIG. 19 is a flowchart of the rotational position calibration program 58 in the third method. Here, the operator manually selects the clearest image. First, the subject is photographed by the X-ray image sensor 14 while turning the turning arm 16, and X-ray projection data of one or more small numbers of planes perpendicular to the rotation axis are obtained (acquisition step) (S10). Image reconstruction is performed using the X-ray projection data as original projection data (in this step, the image reconstruction program 50 has the function of first image data creation means), and the obtained reconstructed image is stored in the image memory 48. Store (first image reconstruction step) (S12). Next, the obtained reconstructed image is displayed on the screen of the display device 40 (S14). A reconstructed image may be printed. The operator determines and inputs the blur width of the image in the direction of rotation from the reconstructed image. When the input of the blur width of the image is received (S16), the image is reconstructed from the same X-ray projection data with ½ of the blur width as a displacement amount in the same direction as the rotation or in the opposite direction (S18). (In this step, the image reconstruction program 50 has the function of the second image data creation means) and displays it on the screen (second image reconstruction step) (S20). The operator selects the reconstructed image determined to be the clearest. When the selection input of the reconstructed image by the operator is received (S22), the displacement corresponding to the reconstructed image is set as correction data (correction step) (24) In this step, the rotational position calibration program 58 performs correction. It has a function of data setting means. Note that the blur width may be automatically detected. Further, the sharpness difference between the two reconstructed images may be automatically determined.

  In the actual photographing, the position of the projection image is corrected using the correction data, and image reconstruction is performed. Actually, the normal imaging operation control program 46 is started for the actual imaging, but for convenience of explanation, in FIG. 19, when the processing following the above-described rotational position calibration is described, X-ray projection data of the subject is acquired. Next, image reconstruction is performed based on the X-ray projection data (S28). In this case, the rotational position calibration program 58 uses the projection data acquisition unit and the image reconstruction unit as a photographing control unit after the correction data is set, and further uses the projection data acquisition unit and the image reconstruction unit to set the subject or a part of the target portion thereof. The tomographic image data is generated by performing the image reconstruction for. Note that if the X-ray projection data necessary for image reconstruction of the subject or a part of the target portion has already been captured in step S12, step S26 can be omitted.

  Needless to say, the above-described rotation center calibration can be performed using a correction phantom instead of the subject.

Schematic diagram of the imaging unit of an X-ray CT imaging apparatus using a swivel arm The figure which shows the imaging | photography control apparatus of X-ray CT imaging apparatus. The figure which shows the movement of the to-be-photographed object position in X-ray CT imaging apparatus Schematic diagram of the imaging unit of an X-ray CT imaging apparatus using a rotary table Flow chart showing the procedure for shooting with changing the enlargement ratio The figure for explanation of the 1st method of setting the amount of displacement on the basis of the pixel of an X-ray image sensor The figure for explanation of the 1st method of setting the amount of displacement on the basis of the pixel of an X-ray image sensor Explanatory drawing for demonstrating the 2nd method which corrects a conversion table and produces the same effect as a 1st method Explanatory drawing for demonstrating the 2nd method which corrects a conversion table and produces the same effect as a 1st method Illustration of an example of an image reconstructed from original projection data Illustration of another example of an image reconstructed from original projection data Graph of difference between maximum and minimum voxel values (luminance) of reconstructed image Graph showing interpolation by quadratic curve Diagram explaining blur of projection due to rotation Flowchart of rotational position calibration program in the case of manual selection by the first method Flowchart of rotational position calibration program in case of automatic selection by first method Flowchart of rotational position calibration program in the case of manual selection by the second method Flowchart of rotational position calibration program in case of automatic selection by second method Flowchart of rotational position calibration program when manual selection is performed by the third method

Explanation of symbols

10 frame, 12 X-ray generator, 14 X-ray image sensor, 16 swivel arm, 20 chair, 30 subject, 32 imaging control device 32, 34 CPU, 40 display device, 44 storage device, 48 image memory, 50 image reconstruction Program, 52 conversion table, 58 rotational position calibration program.

Claims (18)

  1. While rotating the X-ray generator and the X-ray image sensor arranged opposite to each other with respect to the subject relative to the subject, the subject is irradiated with the X-rays generated by the X-ray generator and transmitted through the subject. X-rays are detected by an X-ray image sensor to obtain X-ray projection data,
    Relative relation between the X-ray generator, the rotation center and the X-ray image sensor set in the calculation of image reconstruction for converting the acquired X-ray projection data into the distribution of the X-ray absorption coefficient of the subject In the positional relationship, a displacement amount is set in the direction of rotation of the X-ray image sensor relative to the subject, and then the amount of the displacement amount corresponding to the subject or a part of the target portion is determined from the X-ray projection data. The tomographic image data is created by performing the image reconstruction with the displacement added,
    This tomographic image data is created for a plurality of displacement amounts based on the same X-ray projection data,
    An X-ray CT correction method of setting correction data for image reconstruction calculation based on a displacement amount from which tomographic image data having the largest gradation spread is obtained among the plurality of obtained tomographic image data.
  2. While rotating the X-ray generator and the X-ray image sensor arranged opposite to each other with respect to the subject relative to the subject, the subject is irradiated with the X-rays generated by the X-ray generator and transmitted through the subject. X-rays are detected by an X-ray image sensor to obtain X-ray projection data,
    Relative relation between the X-ray generator, the rotation center and the X-ray image sensor set in the calculation of image reconstruction for converting the acquired X-ray projection data into the distribution of the X-ray absorption coefficient of the subject In the positional relationship, a displacement amount is set in the direction of rotation of the X-ray image sensor relative to the subject,
    A conversion table in which a conversion table for converting the coordinates of the position of the X-ray projection data acquired on the X-ray image sensor into the coordinates of the subject is corrected by adding a displacement corresponding to the displacement amount. Using the X-ray projection data to perform tomographic image data reconstruction of the subject or a part of the target portion thereof,
    This tomographic image data is created for a plurality of displacement amounts based on the same X-ray projection data,
    An X-ray CT correction method of setting a conversion table in which tomographic image data having the largest gradation spread among a plurality of obtained tomographic image data is obtained as a conversion table used for the image reconstruction.
  3. While rotating the X-ray generator and the X-ray image sensor arranged opposite to each other with respect to the subject relative to the subject, the subject is irradiated with the X-rays generated by the X-ray generator and transmitted through the subject. X-rays are detected by an X-ray image sensor to obtain X-ray projection data,
    The tomographic image data is generated by performing calculation of image reconstruction for converting the acquired X-ray projection data into the distribution of the X-ray absorption coefficient of the subject for the subject or a part of the subject portion,
    In the created tomographic image data, set the width of blur in a plane perpendicular to the rotation axis of the relative rotation included in the tomographic image data,
    One half of the set blur width is set as a displacement amount in the opposite direction to the rotation direction of the X-ray image sensor relative to the subject, and the subject from the X-ray projection data. Or, the tomographic image data is created by performing the image reconstruction with the displacement of the respective displacement amounts for a part of the target portion,
    An X-ray CT correction method in which correction data for image reconstruction calculation is set based on a displacement amount from which tomographic image data having a larger gradation spread among the two obtained tomographic image data is obtained.
  4.   The X-ray CT correction method according to claim 1, wherein the amount representing the spread of gradation is a density difference or a standard deviation of density in tomographic image data.
  5.   The amount representing the gradation spread is a density difference or density standard deviation in a tomographic image, and the density difference or density standard deviation is plotted against the displacement amount for the plurality of tomographic image data. Interpolation calculation is performed by performing a quadratic curve approximation for the displacement amount in which the concentration difference or the standard deviation of the concentration is the maximum and the concentration difference or concentration standard deviation of the plurality of displacement amounts adjacent thereto. 2. The displacement amount at which the density difference or the standard deviation of the density is maximized is calculated, and the displacement amount is set as a displacement amount at which tomographic image data having the largest gradation spread is obtained. 2. The X-ray CT correction method according to 2.
  6.   After the creation of the plurality of tomographic image data, the plurality of the tomographic image data are displayed side by side or sequentially on the screen of the image display device, and the tomographic image data selected by the operator is the tomographic image having the largest gradation spread. 4. The X-ray CT correction method according to claim 1, wherein the X-ray CT correction method is image data.
  7. While rotating the X-ray generator and the X-ray image sensor arranged opposite to each other with respect to the subject relative to the subject, the subject is irradiated with the X-rays generated by the X-ray generator and transmitted through the subject. X-ray image is detected by the X-ray image sensor, and the obtained X-ray projection data is converted into the distribution of the X-ray absorption coefficient of the subject to calculate the image reconstruction to generate tomographic image data of the tomographic plane of the subject An X-ray CT imaging method for
    An X-ray CT imaging method, wherein the X-ray CT correction method according to claim 1 is executed before the acquisition of the X-ray projection data.
  8. While rotating the X-ray generator and the X-ray image sensor arranged opposite to each other with respect to the subject relative to the subject, the subject is irradiated with the X-rays generated by the X-ray generator and transmitted through the subject. X-ray image is detected by the X-ray image sensor, and the obtained X-ray projection data is converted into the distribution of the X-ray absorption coefficient of the subject to calculate the image reconstruction to generate tomographic image data of the tomographic plane of the subject An X-ray CT imaging method for
    The X-ray CT correction according to claim 1, prior to acquisition of the X-ray projection data, when a change in relative position of the X-ray generator and / or the X-ray image sensor with respect to the subject is detected. An X-ray CT imaging method characterized by executing the method.
  9. An X-ray generator and an X-ray image sensor arranged opposite to each other with a subject interposed therebetween;
    A rotation mechanism for rotating the X-ray generator and the X-ray image sensor relative to a subject;
    While rotating the X-ray generator and the X-ray image sensor relative to the subject by the rotation mechanism, the subject is irradiated with X-rays by the X-ray generator, and the tomographic plane of the subject is irradiated by the X-ray image sensor. Projection data acquisition means for acquiring X-ray projection data;
    Image reconstruction means for calculating image reconstruction for converting X-ray projection data obtained by the X-ray image sensor into an X-ray absorption coefficient distribution of a subject and generating tomographic image data of the tomographic plane of the subject; ,
    A calibration means for setting correction data for image reconstruction calculation using the projection data acquisition means and the image reconstruction means;
    The calibration means includes
    In the relative positional relationship between the X-ray generator, the center of rotation and the X-ray image sensor set in the calculation of the image reconstruction, the rotation of the X-ray image sensor relative to the subject A plurality of displacement amounts are set in a direction, and a plurality of tomographic image data are created by performing the image reconstruction by adding displacements for the displacement amount for the subject or a part of the target portion from the X-ray projection data. Image data creation means;
    Correction data setting means for setting correction data for image reconstruction calculation based on the amount of displacement from which the tomographic image data having the largest gradation spread is obtained among the plurality of obtained tomographic image data X Line CT imaging device.
  10. An X-ray generator and an X-ray image sensor arranged opposite to each other with a subject interposed therebetween;
    A rotation mechanism for rotating the X-ray generator and the X-ray image sensor relative to a subject;
    While rotating the X-ray generator and the X-ray image sensor relative to the subject by the rotation mechanism, the subject is irradiated with X-rays by the X-ray generator, and the tomographic plane of the subject is irradiated by the X-ray image sensor. Projection data acquisition means for acquiring X-ray projection data;
    Image reconstruction means for calculating image reconstruction for converting X-ray projection data obtained by the X-ray image sensor into an X-ray absorption coefficient distribution of a subject and generating tomographic image data of the tomographic plane of the subject; ,
    A calibration means for setting correction data for image reconstruction calculation using the projection data acquisition means and the image reconstruction means;
    The calibration means includes
    In the relative positional relationship between the X-ray generator, the center of rotation and the X-ray image sensor set in the calculation of the image reconstruction, the rotation of the X-ray image sensor relative to the subject A displacement table that sets a plurality of displacement amounts in a direction and converts the coordinates of the position of the X-ray projection data acquired on the X-ray image sensor in the reconstruction calculation into the coordinates of the subject; Image data for generating a plurality of tomographic image data by performing image reconstruction of the subject or a part of a target portion thereof from the X-ray projection data using a conversion table modified so as to be converted by adding a minute displacement Creating means;
    Correction data setting means for setting a conversion table used for the image reconstruction means based on the displacement amount from which the tomographic image data having the largest gradation spread is obtained among the plurality of obtained tomographic image data. X-ray CT imaging apparatus provided.
  11. An X-ray generator and an X-ray image sensor arranged opposite to each other with a subject interposed therebetween;
    A rotation mechanism for rotating the X-ray generator and the X-ray image sensor relative to a subject;
    The X-ray generator and the X-ray image sensor are rotated relative to the subject by the rotation mechanism, the subject is irradiated with X-rays by the X-ray generator, and the tomographic plane of the subject is irradiated by the X-ray image sensor. Projection data acquisition means for acquiring X-ray projection data;
    Image reconstruction means for calculating image reconstruction for converting X-ray projection data obtained by the X-ray image sensor into a distribution of X-ray absorption coefficients of a subject and generating tomographic image data of the tomographic plane of the subject; ,
    A calibration means for setting correction data for image reconstruction calculation using the projection data acquisition means and the image reconstruction means;
    The calibration means includes
    First image data creation means for creating tomographic image data by performing the image reconstruction on the subject or a part of the target portion from the acquired X-ray projection data;
    In the tomographic image data created by the first image data creating means, a blur width setting means for setting a blur width in a plane perpendicular to the rotation axis of the relative rotation included in the image data;
    1/2 of the blur width set by the blur width setting means is set as each displacement amount in the direction opposite to the rotation direction of the X-ray image sensor relative to the rotated subject. Second image data creation means for creating two tomographic image data by performing the image reconstruction calculation for the subject or a part of the target portion from the X-ray projection data and adding displacements corresponding to the respective displacement amounts. When,
    Correction data setting means for setting correction data for image reconstruction calculation on the basis of the displacement obtained from the tomographic image data having the larger gradation spread among the two obtained tomographic image data. X-ray CT imaging device.
  12.   The X-ray CT imaging apparatus according to claim 9, wherein the amount representing the spread of gradation is a density difference or a standard deviation of density in a tomographic image.
  13. The amount representing the spread of gradation is a density difference or a standard deviation of density in a tomographic image,
    The correction data setting means obtains the density difference or density standard deviation for the plurality of tomographic image data, and the density difference or density standard deviation as a function of the displacement amount, among the plurality of displacement amounts, Interpolation calculation is performed by performing a quadratic curve approximation on the concentration difference or concentration standard deviation of multiple displacement amounts adjacent to the concentration difference or concentration standard deviation, and the concentration difference or concentration standard deviation. 11. The displacement amount at which the standard deviation is maximized is calculated, and the displacement amount is set as a displacement amount at which tomographic image data having the largest gradation spread is obtained. X-ray CT imaging device.
  14. The X-ray CT imaging apparatus according to any one of claims 9 to 13,
    Further, after the setting by the calibration unit, the image reconstruction is performed on the subject or a part of the target portion using the projection data acquisition unit and the image reconstruction unit using the setting, and the tomogram is obtained. An X-ray CT imaging apparatus comprising imaging control means for creating image data.
  15. The X-ray CT imaging apparatus according to any one of claims 9 to 14,
    Furthermore, it comprises movement detection means for detecting a change in relative position of the X-ray generator and / or the X-ray image sensor with respect to the subject, and when the movement detection means detects the change in relative position, An X-ray CT imaging apparatus characterized by activating calibration means.
  16. While rotating the X-ray generator and the X-ray image sensor arranged opposite to each other with respect to the subject relative to the subject, the subject is irradiated with the X-rays generated by the X-ray generator and transmitted through the subject. An X-ray image sensor to detect the acquired X-rays to acquire X-ray projection data;
    Relative positional relationship among the X-ray generator, the center of rotation and the X-ray image sensor set in the calculation of image reconstruction for converting the X-ray projection data into the distribution of the X-ray absorption coefficient of the subject A plurality of displacement amounts are set in the direction of the rotation direction of the X-ray image sensor relative to the subject, and a displacement corresponding to the displacement amount is obtained from the X-ray projection data for the subject or a part of the target portion thereof. Reconstructing step of generating tomographic image data for each of the plurality of displacement amounts by performing the image reconstruction added with,
    A correction step for setting correction data for calculation of the image reconstruction based on a displacement amount obtained from the tomographic image data having the largest gradation spread selected from the plurality of obtained tomographic image data. A program to be executed.
  17. While rotating the X-ray generator and the X-ray image sensor arranged opposite to each other with respect to the subject relative to the subject, the subject is irradiated with the X-rays generated by the X-ray generator and transmitted through the subject. An X-ray image sensor to detect the acquired X-rays to acquire X-ray projection data;
    Relative positional relationship among the X-ray generator, the center of rotation and the X-ray image sensor set in the calculation of image reconstruction for converting the X-ray projection data into the distribution of the X-ray absorption coefficient of the subject A plurality of displacements in the direction of rotation of the X-ray image sensor relative to the subject are set, and the coordinates of the position of the X-ray projection data acquired on the X-ray image sensor are set as the coordinates. An image reconstruction of the subject or a part of a target portion thereof from the X-ray projection data using a conversion table in which a conversion table for converting to the coordinates of the subject is modified so as to be converted by adding a displacement corresponding to the amount of displacement. Performing a reconstruction step of generating tomographic image data by performing
    A correction step for setting, as a conversion table used for the image reconstruction, a conversion table in which tomographic image data having the largest gradation spread selected from the obtained plurality of reconstructed images is obtained. program.
  18. While rotating the X-ray generator and the X-ray image sensor arranged opposite to each other with respect to the subject relative to the subject, the subject is irradiated with the X-rays generated by the X-ray generator and transmitted through the subject. An X-ray image sensor to detect the acquired X-rays to acquire X-ray projection data;
    A first image reconstruction step of generating tomographic image data by performing calculation of image reconstruction for converting the X-ray projection data into a distribution of an X-ray absorption coefficient of a subject for the subject or a part of the subject portion;
    In the created tomographic image data, a width setting step for setting a width of blur in a plane perpendicular to the rotation axis of the relative rotation included in the tomographic image data;
    One half of the set blur width is defined as a displacement amount in the direction opposite to the rotation direction of the X-ray image sensor relative to the subject. A second image reconstruction step of creating tomographic image data by performing the image reconstruction in which a displacement corresponding to each displacement amount is applied to a subject or a part of the target portion;
    A correction step for setting correction data for image reconstruction calculation is executed on the computer based on the displacement obtained from the tomographic image data having the larger gradation spread among the two obtained tomographic image data. Program to let you.
JP2005113437A 2005-04-11 2005-04-11 X-ray ct photographing method and device Pending JP2006288719A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2005113437A JP2006288719A (en) 2005-04-11 2005-04-11 X-ray ct photographing method and device

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP2005113437A JP2006288719A (en) 2005-04-11 2005-04-11 X-ray ct photographing method and device

Publications (1)

Publication Number Publication Date
JP2006288719A true JP2006288719A (en) 2006-10-26

Family

ID=37409977

Family Applications (1)

Application Number Title Priority Date Filing Date
JP2005113437A Pending JP2006288719A (en) 2005-04-11 2005-04-11 X-ray ct photographing method and device

Country Status (1)

Country Link
JP (1) JP2006288719A (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2009045092A (en) * 2007-08-13 2009-03-05 Canon Inc Ct equipment and control method thereof
JP2016116775A (en) * 2014-12-22 2016-06-30 キヤノン株式会社 Image reconstruction device, image reconstruction method, and program

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000201918A (en) * 1999-01-11 2000-07-25 Hitachi Medical Corp X-ray ct system and x-ray photographing method of x-ray image and phantom
JP2005040236A (en) * 2003-07-24 2005-02-17 Toshiba Corp X-ray ct apparatus and reverse projection operation method for x-ray ct

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000201918A (en) * 1999-01-11 2000-07-25 Hitachi Medical Corp X-ray ct system and x-ray photographing method of x-ray image and phantom
JP2005040236A (en) * 2003-07-24 2005-02-17 Toshiba Corp X-ray ct apparatus and reverse projection operation method for x-ray ct

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2009045092A (en) * 2007-08-13 2009-03-05 Canon Inc Ct equipment and control method thereof
US8340383B2 (en) 2007-08-13 2012-12-25 Canon Kabushiki Kaisha CT scanner and control method therefor
JP2016116775A (en) * 2014-12-22 2016-06-30 キヤノン株式会社 Image reconstruction device, image reconstruction method, and program

Similar Documents

Publication Publication Date Title
US9036776B2 (en) X-ray photography apparatus
US6292530B1 (en) Method and apparatus for reconstructing image data acquired by a tomosynthesis x-ray imaging system
CN103961130B (en) So that C-arm system adapts to the method to provide three-dimensional imaging information
JP4632891B2 (en) X-ray CT imaging apparatus and X-ray CT imaging method
JP3378401B2 (en) X-ray equipment
JP4509971B2 (en) X-ray CT system
US9541509B2 (en) Radiation imaging apparatus, radiation imaging method, body movement measuring method, and body movement measuring program
JP4163991B2 (en) X-ray CT imaging apparatus and imaging method
JP5274812B2 (en) X-ray CT apparatus and image processing apparatus
US7186023B2 (en) Slice image and/or dimensional image creating method
US7444010B2 (en) Method and apparatus for the reduction of artifacts in computed tomography images
JP4537129B2 (en) System for scanning objects in tomosynthesis applications
JP4360817B2 (en) Radiation tomography equipment
EP1004272B1 (en) Tomographic imaging using penetrating radiation
US7561659B2 (en) Method for reconstructing a local high resolution X-ray CT image and apparatus for reconstructing a local high resolution X-ray CT image
JP5085031B2 (en) X-ray angiography equipment
US6256370B1 (en) Method and apparatus for performing tomosynthesis
JP4054402B2 (en) X-ray tomography equipment
JP3926334B2 (en) X-ray CT imaging system
JP2012050848A (en) Radiographic imaging control apparatus using multi radiation generating apparatus
JP5090680B2 (en) X-ray CT system
US7583781B2 (en) X-Ray CT apparatus and method of controlling the same
JP4508789B2 (en) X-ray equipment
JP3785576B2 (en) Subject blur correction means and medical X-ray imaging apparatus using the same
JP4340334B2 (en) Method and apparatus for determining a conversion between an object and a three-dimensional representation of the object

Legal Events

Date Code Title Description
A711 Notification of change in applicant

Free format text: JAPANESE INTERMEDIATE CODE: A711

Effective date: 20080124

A521 Written amendment

Free format text: JAPANESE INTERMEDIATE CODE: A821

Effective date: 20080124

A621 Written request for application examination

Free format text: JAPANESE INTERMEDIATE CODE: A621

Effective date: 20080324

A977 Report on retrieval

Free format text: JAPANESE INTERMEDIATE CODE: A971007

Effective date: 20100126

A131 Notification of reasons for refusal

Free format text: JAPANESE INTERMEDIATE CODE: A131

Effective date: 20100302

A02 Decision of refusal

Free format text: JAPANESE INTERMEDIATE CODE: A02

Effective date: 20100629