JP2007097977A - X-ray ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce time to transfer X-ray detector data or projection data of a conventional scan (an axial scan), a cine scan, or a helical scan of an X-ray CT apparatus with a two-dimensional area X-ray detector of a matrix structure typified by a multi-row X-ray detector or a flat-panel X-ray detector to achieve a reduction in the imaging time and the image reconstruction time. <P>SOLUTION: The X-ray detector data or a projection data of the X-ray CT apparatus is divided into a region of interest and a region of non-interest, and the volume of the data is reduced by compressing the X-ray detector data or the projection data of the region of non-interest to reduce the transfer time to input in/output from a storage device during the collection of the X-ray detector data and the reconstruction of images. Consequently, the imaging time and the image reconstruction time of the X-ray CT apparatus are reduced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an X-ray CT (Computed Tomography) imaging method and an X-ray CT apparatus in a medical X-ray CT apparatus or an industrial X-ray CT apparatus, and relates to a conventional scan (axial scan), a cine scan, or a helical scan. The present invention relates to shortening of photographing time or shortening of image reconstruction time.

  Conventionally, in a multi-row X-ray detector X-ray CT apparatus or an X-ray CT apparatus using a two-dimensional X-ray area detector with a matrix structure represented by a flat panel, the data acquisition system is in the view direction as shown in FIG. For example, data of about 1000 channels x about 1000 views x 256 columns was collected with only one rotation. FIG. 12 shows a view of the data acquisition system composed of the X-ray tube 21 and the multi-row X-ray detector 24 as seen from the xy plane and a view as seen from the yz plane. In addition, the X-ray detector data for one rotation obtained from this data collection system is visually shown as about 1000 channels x about 1000 views x the number of columns (256 columns). If one channel of data is 16 bits, the data volume is about 512 megabytes, the data transfer capacity of the data transfer bus of the image reconstruction processing device, a disk that stores projection data and X-ray detector data, etc. From the viewpoint of the technical limit of the data transfer capacity of the data input / output bus of the storage device, it is becoming increasingly difficult to handle such large-capacity X-ray detector data and projection data.

  If the size of X-ray detector data and projection data is simply reduced, the spatial resolution and gradation resolution of the X-ray detector will be lowered, and the density resolution and spatial resolution of the X-ray CT device will be reduced. It was also a problem from a viewpoint.

  The following Patent Document 1 is characterized by having an image reconstruction means having a means for compressing projection data in the image reconstruction means and a data restoration means for restoring the compressed projection data. As an effect according to this document, since both the data compression means and the data decompression means exist in the image reconstruction means, the projection data transfer system inside the image reconstruction means, for example, the inside of the data processing device It aims to improve the efficiency of the data transfer means between the data storage means and the arithmetic processing means.

However, this document does not mention data transfer between the data collection unit and the image reconstruction unit. Further, this document does not refer to a region of interest on a tomographic image or projection data, and only an air region is simply extracted on the projection data by threshold processing or the like. For this reason, if you want to see subtle details of the contour of the subject with the air, in some cases, a part of the projection data may be destroyed by simple threshold processing. Met.
JP 2003-290216 A

  However, in the development trend of X-ray CT devices with multi-row X-ray detectors, X-ray CT devices or two-dimensional X-ray area detectors typified by flat panels, This is the direction in which the cone angle of the cone beam increases. In other words, the size of the X-ray detector data and projection data collected by the data collection system in one rotation is in a direction to become larger.

  Therefore, an object of the present invention is to provide a conventional scan (axial scan) of an X-ray CT apparatus having a two-dimensional area X-ray detector having a matrix structure represented by a multi-row X-ray detector or a flat panel X-ray detector. Or, compress the size of the X-ray detector data or projection data without degrading the density resolution and spatial resolution image quality of the area of interest in the cine scan or helical scan tomography, shorten the imaging time or image of the X-ray CT system An object of the present invention is to provide an X-ray CT apparatus that can shorten the reconstruction time.

  The present invention divides X-ray detector data or projection data of an X-ray CT apparatus into a region of interest and a non-interest region, and compresses the X-ray detector data or projection data of the non-region of interest to reduce the size of the data. The transfer time input / output to / from the storage device during X-ray detector data acquisition and image reconstruction is shortened. This provides an X-ray CT apparatus or an X-ray CT imaging method characterized in that the imaging time and image reconstruction time of the X-ray CT apparatus can be shortened.

  In a first aspect, the present invention lies between an X-ray generator and a multi-row X-ray detector that detects X-rays relative to each other while rotating around a rotation center therebetween. X-ray data collection means for collecting X-ray projection data transmitted through the subject, image reconstruction means for reconstructing the projection data collected from the X-ray data collection means, and displaying an image reconstructed tomographic image In an X-ray CT apparatus comprising image display means and imaging condition setting means for setting various imaging conditions for tomographic imaging, projection data and tomographic imaging of a region of interest that is an area where a subject to be tomographically imaged exists Provided is an X-ray CT apparatus characterized by having X-ray data collection means for collecting projection data by changing the data format of projection data of a non-interest area, which is an area where there is no subject to be examined.

  In the X-ray CT apparatus according to the first aspect described above, an area where the density resolution and spatial resolution of the tomographic image of the X-ray CT apparatus should not be deteriorated is a region of interest, and the density resolution and spatial resolution of the tomographic image of the X-ray CT apparatus. A region that can be degraded is set as a non-interesting region. At this time, the size of the projection data can be reduced by reducing the amount of each data of the projection data of the non-interest region compared to the projection data of the region of interest.

  In a second aspect, the present invention relates to a two-dimensional X-ray area detector having a matrix structure typified by a flat panel X-ray detector that detects X-rays relative to an X-ray generator, and a rotation between them. X-ray data collection means for collecting X-ray projection data transmitted through a subject in between while rotating around the center, and image reconstruction for reconstructing the projection data collected from the X-ray data collection means There is an object to be tomographically imaged in an X-ray CT apparatus comprising: a configuration unit, an image display unit that displays a tomographic image that has been reconstructed, and an imaging condition setting unit that sets various imaging conditions for tomography It has X-ray data collection means for collecting projection data by differentiating the data format of the projection data of the region of interest that is the target region and the projection data of the non-region of interest that is the region where the subject to be tomographically imaged does not exist. An X-ray CT apparatus characterized by:

  In the X-ray CT apparatus in the second aspect, the X-ray CT is also used in the two-dimensional X-ray area detector having a matrix structure represented by the flat panel X-ray detector that detects X-rays as in the first aspect. A region where the density resolution and spatial resolution of the tomographic image of the apparatus should not be degraded is set as a region of interest, and a region where the density resolution and spatial resolution of the tomographic image of the X-ray CT apparatus can be degraded is set as a non-interesting region. At this time, the size of the projection data can be reduced by reducing the amount of each data of the projection data of the non-interest region compared to the projection data of the region of interest.

  In a third aspect, the present invention provides an X-ray CT apparatus according to the first aspect, wherein X-ray data collection means having different spatial resolutions of projection data for the projection data of the region of interest and the projection data of the non-region of interest. An X-ray CT apparatus characterized by having it is provided.

  In the X-ray CT apparatus in the third aspect, the density resolution and spatial resolution of the tomographic image of the X-ray CT apparatus are defined as regions of interest where the density resolution and spatial resolution of the tomographic image of the X-ray CT apparatus should not be degraded. A region that can be degraded is set as a non-interesting region. At this time, the size of the projection data can be reduced by reducing the spatial resolution of each data of the projection data of the non-interest area as compared with the projection data of the area of interest.

  In a fourth aspect, the present invention provides an X-ray CT apparatus according to the third aspect, wherein when performing image reconstruction from projection data of the region of interest and projection data of the non-region of interest having different spatial resolutions, Provided is an X-ray CT apparatus characterized by having image reconstruction means for performing image reconstruction after performing processing for compensating spatial resolution on projection data of a region of interest.

  In the X-ray CT apparatus according to the fourth aspect described above, when reconstructing a tomographic image of the X-ray CT apparatus, it is easier to process if the spatial resolution is entirely uniform. It is possible to perform image reconstruction by performing processing to compensate for the spatial resolution of the projection data.

  In a fifth aspect, the present invention provides an X-ray CT apparatus according to any one of the first to fourth aspects, wherein the projection data of the region of interest and the projection data of the non-region of interest have a gradation resolution of the projection data. Provides an X-ray CT apparatus characterized by having different X-ray data collection means.

  In the X-ray CT apparatus in the fifth aspect, the density resolution and spatial resolution of the tomographic image of the X-ray CT apparatus are defined as regions of interest where the density resolution and spatial resolution of the tomographic image of the X-ray CT apparatus should not be degraded. A region that can be degraded is set as a non-interesting region. In this case, the size of the projection data can be reduced by lowering the gradation resolution of each data of the projection data of the non-interest area as compared with the projection data of the area of interest.

  In a sixth aspect, the present invention provides the X-ray CT apparatus according to the fifth aspect, when performing image reconstruction from the projection data of the region of interest and the projection data of the non-region of interest with different gradation resolutions. Provided is an X-ray CT apparatus characterized by having image reconstruction means for performing image reconstruction after performing processing for compensating gradation resolution for projection data of a non-interest area.

  In the X-ray CT apparatus according to the sixth aspect, when the tomographic image of the X-ray CT apparatus is reconstructed, it is easier to process with the same gradation resolution as a whole. It is possible to perform image reconstruction by performing processing that compensates for the gradation resolution of the projection data of the region of interest.

  In a seventh aspect, the present invention provides the X-ray CT apparatus according to any one of the first to sixth aspects, wherein the setting of the region of interest and the non-region of interest of the projection data is manually set by a user interface. X-ray characterized in that it has X-ray data collection means that collects projection data in different data formats while distinguishing projection data of the region of interest and projection data of the non-interest region. Provide CT equipment.

  In the X-ray CT apparatus according to the seventh aspect, the area where the density resolution and spatial resolution in the tomographic image of the X-ray CT apparatus should not be degraded is largely determined by visual judgment by the operator. It may be better to manually define the region of interest and the non-region of interest. For this reason, the region setting can be performed more appropriately by manually determining the region of interest and the non-region of interest.

  In an eighth aspect, the present invention provides the X-ray CT apparatus according to the seventh aspect, wherein the region of interest and the region of non-interest in the projection data are set on a scout image by manually setting the region of interest. An X-ray CT apparatus characterized by having X-ray data collection means for collecting projection data in different data formats while distinguishing between projection data of a region of interest and projection data of a non-region of interest, which is determined based on information I will provide a.

  In the X-ray CT apparatus according to the eighth aspect described above, the area where the density resolution and spatial resolution in the tomographic image of the X-ray CT apparatus should not be degraded is largely determined by visual judgment by the operator. It may be better to manually define the region of interest and the non-region of interest. For this reason, in scout image photographing performed for setting photographing conditions, it is possible to perform region setting more appropriately by determining the region of interest and the region of non-interest by the operator's visual judgment and manual operation.

  In a ninth aspect, the present invention provides the X-ray CT apparatus according to the eighth aspect, wherein the region of interest and the non-region of interest of the projection data are manually set on the scout images in two directions. It is determined based on the set area information, and has X-ray data collection means for collecting projection data in different data formats while distinguishing between projection data of the region of interest and projection data of the non-region of interest. An X-ray CT apparatus is provided.

  In the X-ray CT apparatus according to the ninth aspect described above, the area where the density resolution and spatial resolution in the tomographic image of the X-ray CT apparatus should not be deteriorated largely depends on the visual judgment of the operator. It may be better to manually define the region of interest and the non-region of interest. For this reason, in scout image capturing performed to set the imaging conditions, for example, the scout image of the subject in the AP direction (y direction) (0 degree direction) and the LR direction (x direction) (90 degree direction) of the subject As in the case of a scout image, the region setting can be performed more appropriately by determining the region of interest and the region of non-interest by the operator's visual judgment and manual operation while viewing the scout image in two directions.

In a tenth aspect, the present invention provides the X-ray CT apparatus according to the seventh aspect, wherein the region of interest and the non-region of interest of the projection data are set on the tomographic image of the region of interest manually set. An X-ray CT apparatus characterized by having X-ray data collection means for collecting projection data in different data formats while distinguishing between projection data of a region of interest and projection data of a non-region of interest, which is determined based on information I will provide a.

  In the X-ray CT apparatus according to the tenth aspect described above, the area where the density resolution and spatial resolution in the tomographic image of the X-ray CT apparatus should not be deteriorated largely depends on the visual judgment of the operator. It may be better to manually define the region of interest and the non-region of interest. For this reason, in the tomographic images taken in advance, it is more appropriate to set the region of interest by determining the region of interest especially required for diagnosis by visual judgment and manual operation of the operator and determining the region of interest and the region of non-interest. It can be carried out.

  In an eleventh aspect, the present invention provides the X-ray CT apparatus according to any one of the seventh to tenth aspects, wherein the shape of the region of interest set manually is an elliptical shape or a circular shape. X-ray data collecting means for collecting projection data in different data formats while distinguishing the projection data of the region of interest from the projection data of the non-region of interest is defined as X A line CT system is provided.

  In the X-ray CT apparatus according to the eleventh aspect, the area where the density resolution and spatial resolution in the tomographic image of the X-ray CT apparatus should not be degraded is largely determined by visual judgment by the operator. It may be better to manually define the region of interest and the non-region of interest. For this reason, the region of interest especially required for diagnosis is determined by the operator's visual judgment and manual operation so that the shape of the region of interest on the tomographic image becomes an ellipse or a circle. It is possible to set the area more appropriately by determining the area.

  In a twelfth aspect, the present invention provides the X-ray CT apparatus according to any one of the seventh to tenth aspects, wherein the shape of the region of interest set manually in the tomographic image is a rectangular shape. An X-ray CT apparatus comprising X-ray data collecting means for collecting projection data in different data formats while distinguishing between projection data of the region of interest and projection data of the non-region of interest I will provide a.

  In the X-ray CT apparatus according to the twelfth aspect, the area where the density resolution and spatial resolution in the tomographic image of the X-ray CT apparatus should not be deteriorated is largely determined by visual judgment by the operator. It may be better to manually define the region of interest and the non-region of interest. For this reason, the region of interest especially required for diagnosis is determined by the operator's visual judgment and manual operation so that the region of interest is rectangular on the tomographic image, and the region of interest and non-region of interest are defined. The area can be set more appropriately.

  In a thirteenth aspect, the present invention provides the X-ray CT apparatus according to any one of the first to sixth aspects, wherein the setting of the region of interest and the non-region of interest in the projection data is a data value of each of the projection data X-ray data collection means for automatically collecting projection data in different data formats while distinguishing between projection data of a region of interest and projection data of a non-region of interest. A line CT system is provided.

  In the X-ray CT apparatus according to the thirteenth aspect, for example, an air portion is determined based on each data value of projection data, and is automatically determined as a region that is not often used for diagnosis, and determined as a non-interest region. Sometimes you can. In this way, the region setting can be performed more appropriately by determining the region of interest and the non-region of interest.

  In a fourteenth aspect, the present invention provides the X-ray CT apparatus according to the thirteenth aspect, wherein the region of interest and the non-region of interest in the projection data are set on the scout image by automatically setting the region of interest. An X-ray CT apparatus characterized by having an X-ray data collection means for collecting projection data in different data formats while distinguishing between projection data of a region of interest and projection data of a non-region of interest. provide.

  In the X-ray CT apparatus according to the fourteenth aspect described above, binarization is performed with several types of binarization threshold values on the scout image, and the reference point of the subject is extracted, or the reference point of the subject is extracted from the correlation calculation using a plurality of patterns The region of interest can be set based on the point.

  In a fifteenth aspect, the present invention provides the X-ray CT apparatus according to the thirteenth aspect, wherein the setting of the region of interest and the non-region of interest in the projection data is information on a region in which the region of interest is automatically set on the tomographic image. An X-ray CT apparatus characterized by having an X-ray data collection means for collecting projection data in different data formats while distinguishing between projection data of a region of interest and projection data of a non-region of interest. provide.

  In the X-ray CT apparatus according to the fifteenth aspect, binarization is performed on a tomographic image by using several types of binarization threshold values, and the reference point of the subject is extracted, or the reference point of the subject is extracted from a correlation calculation using a plurality of patterns The region of interest can be set based on the point.

  In a sixteenth aspect, the present invention provides the X-ray CT apparatus according to any one of the fourteenth and fifteenth aspects, wherein the region of interest automatically set on a scout image or a tomographic image has an elliptical shape or It is determined to have a circular shape or a rectangular shape, and has X-ray data collection means for collecting projection data in different data formats while distinguishing between projection data of a region of interest and projection data of a non-region of interest. An X-ray CT apparatus is provided.

  In the X-ray CT apparatus according to the sixteenth aspect, when a region of interest is set on a scout image or a tomographic image, if it is obtained based on image processing and image measurement, it may be an indefinite region and difficult to handle. In order to avoid this, the region of interest can be set in an elliptical shape, a circular shape or a rectangular shape including the region of interest obtained by image processing and image measurement.

  In a seventeenth aspect, the present invention provides the X-ray CT apparatus according to any one of the first to sixteenth aspects, wherein the region of interest and the non-region of interest in the projection data are set in a tomographic image on an xy plane. It has X-ray data collection means that collects projection data in different data formats while distinguishing projection data of the region of interest and projection data of the non-interest region while changing depending on the vertical z-axis direction position The characteristic X-ray CT apparatus is provided.

  In the X-ray CT apparatus according to the seventeenth aspect, the shape of the subject changes depending on the z direction perpendicular to the tomographic image that is the xy plane and the z direction that is the traveling direction of the imaging table. For this reason, it is efficient to change the setting of the region of interest and the non-region of interest on the data depending on the z direction. In this way, the region setting can be performed more appropriately by determining the region of interest and the non-region of interest.

  In an eighteenth aspect, the present invention relates to an X-ray CT apparatus according to any one of the first to seventeenth aspects, in the case of conventional scan (axial scan) or cine scan, when collecting data at a certain z-direction position. Depending on the detector row or at least one of the positions of each pixel of the tomographic image, the setting of the region of interest and the non-region of interest in the projection data is a z-direction position perpendicular to the tomographic image on the xy plane. X-ray CT characterized by having X-ray data collection means that collects projection data in different data formats while distinguishing between projection data of the region of interest and projection data of the non-region of interest while changing depending on Providing equipment.

  In the X-ray CT apparatus according to the eighteenth aspect, in the case of a conventional scan (axial scan) or a cine scan, data is collected for one rotation or a plurality of rotations while staying at the position in the z direction. Therefore, if you try to change the setting of the region of interest and non-interest region depending on the z direction, depending on each detector row of the two-dimensional X-ray area detector or multi-row X-ray detector, or 3 In the case of dimensional image reconstruction, the region of interest and the non-region of interest are set depending on the position of each pixel of each tomographic image. In this way, the region setting can be performed more appropriately by determining the region of interest and the non-region of interest.

  In a nineteenth aspect, the present invention provides an X-ray CT apparatus according to any one of the first to seventeenth aspects, in the case of a helical scan, when the data acquisition system moves in the z direction, Depending on at least one of the z position or the position of each pixel of the tomographic image, the setting of the region of interest and the non-interesting region in the projection data is performed at a position in the z direction perpendicular to the tomographic image on the xy plane. X-ray CT apparatus characterized by having X-ray data collecting means for collecting projection data in different data formats while distinguishing between projection data of a region of interest and projection data of a non-interest region while changing depending on I will provide a.

  In the X-ray CT apparatus according to the nineteenth aspect, in the case of helical scanning, each pixel of each tomographic image for each view when the data acquisition system moves in the z direction or in the case of three-dimensional image reconstruction And the detector row used for each view are different. For this reason, the region of interest and the non-region of interest are set depending on the z-direction position of each detector row or depending on the position of each pixel of the tomographic image. In this way, the region setting can be performed more appropriately by determining the region of interest and the non-region of interest.

  In a twentieth aspect, the present invention relates to the X-ray CT apparatus according to any one of the first to nineteenth aspects, and collects projection data while having a plurality of regions of interest in one tomographic image. Provided is an X-ray CT apparatus characterized by having an X-ray data collecting means.

  In the X-ray CT apparatus according to the twentieth aspect, even if there are a plurality of regions of interest, the section of the region of interest on the projection data only increases to a plurality, and the present invention provides the sixteenth from the first point of view. It can be similarly realized from the viewpoint.

  According to the X-ray CT apparatus or X-ray CT image reconstruction method of the present invention, a multi-row X-ray detector or a two-dimensional area X-ray detector having a matrix structure represented by a flat panel X-ray detector is provided. The size of X-ray detector data or projection data is compressed without degrading the density resolution and spatial resolution image quality of conventional scans (axial scans) or cine scans or helical scans of X-ray CT systems. This has the effect of shortening the imaging time or the image reconstruction time of the line CT apparatus.

Hereinafter, the present invention will be described in more detail with reference to embodiments shown in the drawings. Note that the present invention is not limited thereby.
FIG. 1 is a configuration block diagram of an X-ray CT apparatus according to an embodiment of the present invention. The X-ray CT apparatus 100 includes an operation console 1, an imaging table 10, and a scanning gantry 20.

  The operation console 1 collects X-ray detector data collected by the scanning device gantry 20 and an input device 2 that receives input from the operator, a central processing device 3 that performs preprocessing, image reconstruction processing, post-processing, and the like. Data acquisition buffer 5, monitor 6 that displays tomograms reconstructed from projection data obtained by preprocessing X-ray detector data, program, X-ray detector data, projection data, and X-ray tomogram And a storage device 7 for storing.

  The imaging table 10 includes a cradle 12 on which a subject is placed and put into and out of the opening of the scanning gantry 20. The cradle 12 is moved up and down and linearly moved by the motor built in the imaging table 10.

  The scanning gantry 20 rotates around an X-ray tube 21, an X-ray controller 22, a collimator 23, a multi-row X-ray detector 24, a DAS (Data Acquisition System) 25, and the body axis of the subject. A rotation controller 26 for controlling the X-ray tube 21 and the like, and a controller 29 for exchanging control signals and the like with the operation console 1 and the imaging table 10. The scanning gantry tilt controller 27 can tilt the scanning gantry 20 forward and backward in the z direction by about ± 30 degrees.

FIG. 2 is an explanatory diagram of the geometric arrangement of the X-ray tube 21 and the multi-row X-ray detector 24. FIG.
The X-ray tube 21 and the multi-row X-ray detector 24 rotate around the rotation center IC. When the vertical direction is the y direction, the horizontal direction is the x direction, and the table traveling direction perpendicular thereto is the z direction, the rotation plane of the X-ray tube 21 and the multi-row X-ray detector 24 is the xy plane. The moving direction of the cradle 12 is the z direction.

The X-ray tube 21 generates an X-ray beam called a cone beam CB. When the direction of the central axis of the cone beam CB is parallel to the y direction, the view angle is 0 degree.
The multi-row X-ray detector 24 has, for example, 256 X-ray detector rows. Each X-ray detector array has, for example, 1024 channels of X-ray detector channels.

  Projection data collected by irradiation with X-rays is A / D converted from the multi-row X-ray detector 24 by the DAS 25 and input to the data collection buffer 5 via the slip ring 30. The data input to the data collection buffer 5 is processed by the central processing unit 3 according to the program in the storage device 7, reconstructed into a tomographic image, and displayed on the monitor 6.

FIG. 3 is a flowchart showing an outline of operations of tomographic imaging and scout imaging of the X-ray CT apparatus 100 of the present invention.
In step S1, in the helical scan, the X-ray detector data is obtained by rotating the X-ray tube 21 and the multi-row X-ray detector 24 around the subject and moving the cradle 12 on the imaging table 10 linearly on the table. The X-ray detector data D0 (view, j, i) represented by the view angle view, detector row number j, and channel number i is moved to the table linear movement z direction position Ztable (view) To collect X-ray detector data. In conventional scan (axial scan) or cine scan, X-ray detector data is collected by rotating the data acquisition system one or more times while the cradle 12 on the imaging table 10 is fixed at a certain z-direction position. Do. If necessary, after moving to the next position in the z direction, the data acquisition system is rotated once or a plurality of times again to repeatedly collect data of X-ray detector data.

  In scout imaging, the X-ray tube 21 and the multi-row X-ray detector 24 are fixed, and the data collection operation of the X-ray detector data is performed while the cradle 12 on the imaging table 10 is moved linearly. .

  The X-ray detector data collected by the conventional scan (axial scan), cine scan, or helical scan data collection is stored in the storage device 7 as necessary, and is read out at the time of image reconstruction. When this data collection is performed, the data collection is performed by controlling the spatial resolution and gradation resolution of the X-ray detector data separately for the set region of interest and non-region of interest. This control method will be described later.

  In step S2, the X-ray detector data D0 (view, j, i) is preprocessed and converted into projection data. As shown in FIG. 4, the preprocessing includes step S21 offset correction, step S22 logarithmic conversion, step S23 X-ray dose correction, and step S24 sensitivity correction.

  In the case of scout image capture, the preprocessed X-ray detector data can be displayed as a scout image by displaying the pixel size in the channel direction and the pixel size in the z direction, which is the cradle linear movement direction, in accordance with the display pixel size of the monitor 6. Completion.

The preprocessed projection data is stored in the storage device 7 as necessary, and is read out at the time of image reconstruction.
In step S3, beam hardening correction is performed on the preprocessed projection data D1 (view, j, i). In the beam hardening correction S3, if the projection data subjected to the sensitivity correction S24 in the preprocessing S2 is D1 (view, j, i), and the data after the beam hardening correction S3 is D11 (view, j, i) The beam hardening correction S3 is expressed, for example, in a polynomial form as follows.

  At this time, since independent beam hardening correction can be performed for each j column of the detector, if the tube voltage of each data acquisition system differs depending on the imaging conditions, the X-ray energy characteristics of the detector for each column Differences can be corrected.

In step S4, z-filter convolution processing for applying a filter in the z-direction (column direction) to the projection data D11 (view, j, i) subjected to beam hardening correction is performed.
In step S4, z-filter convolution processing for applying a filter in the z-direction (column direction) to the projection data D11 (view, j, i) subjected to beam hardening correction is performed.

  That is, the projection of the multi-row X-ray detector D11 (view, j, i) (i = 1 to CH, j = 1 to ROW) subjected to beam hardening correction after preprocessing in each view angle and each data acquisition system For example, a filter with a column direction filter size of 5 columns as shown below is applied to the data in the column direction.

(W ₁ (i), w ₂ (i), w ₃ (i), w ₄ (i), w ₅ (i)),

  The corrected detector data D12 (view, j, i) is as follows.

  It becomes. If the maximum value of the channel is CH and the maximum value of the column is ROW,

And
Further, when the column direction filter coefficient is changed for each channel, the slice thickness can be controlled in accordance with the distance from the image reconstruction center. In general, in slice images, the slice thickness is thicker in the periphery than in the reconstruction center, so the column direction filter coefficient is changed between the center and the periphery, and the column direction filter coefficient is changed in the column direction near the center channel If the width of the filter coefficient is changed widely, the slice thickness can be made close to the periphery and the center of the image reconstruction uniformly by changing the width of the column direction filter coefficient in the vicinity of the peripheral channel. Further, depending on the value of the column direction filter coefficient, a tomographic image having a thin slice thickness can be realized. In this way, the slice thickness can be controlled by the column direction filter coefficient.

  In this way, by controlling the column direction filter coefficients of the central channel and the peripheral channel of the multi-row X-ray detector 24, the slice thickness can also be controlled at the central portion and the peripheral portion. When the slice thickness is slightly reduced with the row direction filter, both artifacts and noise are greatly improved. Thereby, artifact improvement and noise improvement can also be controlled. That is, it is possible to control the tomographic image reconstructed, that is, the image quality in the xy plane. As another embodiment, a thin slice thickness tomogram can be realized by using a deconvolution filter with column direction (z direction) filter coefficients.

  In step S5, reconstruction function superimposition processing is performed. That is, the Fourier transform is performed, the reconstruction function is multiplied, and the inverse Fourier transform is performed. In reconstruction function superimposition processing S5, assuming that the data after z filter convolution processing is D12, the data after reconstruction function convolution processing is D13, and the reconstruction function to be superimposed is Kernel (j), the reconstruction function convolution processing is as follows: It is expressed as

In other words, since the reconstruction function kernel (j) can perform the reconstruction function superimposing process independently for each j column of the detector, the difference in noise characteristics and resolution characteristics for each column can be corrected.
In step S6, three-dimensional backprojection processing is performed on the projection data D13 (view, j, i) subjected to reconstruction function superimposition processing to obtain backprojection data D3 (x, y). The image to be reconstructed is a three-dimensional image reconstructed on a plane perpendicular to the z axis and on the xy plane. The following reconstruction area P is assumed to be parallel to the xy plane. This three-dimensional backprojection process will be described later with reference to FIG.

In step S7, post-processing such as image filter superimposition and CT value conversion is performed on the backprojection data D3 (x, y, z) to obtain a tomographic image D31 (x, y).
In post-processing image filter superimposition processing, the tomographic image after three-dimensional backprojection is D31 (x, y, z), the data after image filter superimposition is D32 (x, y, z), and the image filter is Filter (z )

That is, since independent image filter convolution processing can be performed for each j column of the detector, the difference in noise characteristics and resolution characteristics for each column can be corrected.
The obtained tomographic image is displayed on the monitor 6.

FIG. 5 is a flowchart showing details of the three-dimensional backprojection process (step S6 in FIG. 4).
In this embodiment, the image to be reconstructed is reconstructed into a three-dimensional image on a plane perpendicular to the z axis and on the xy plane. The following reconstruction area P is assumed to be parallel to the xy plane.

  In step S61, attention is paid to one view in all views necessary for image reconstruction of the tomogram (that is, a view of 360 degrees or a view of “180 degrees + fan angle”). Projection data Dr corresponding to each pixel is extracted.

  As shown in FIGS. 6A and 6B, a square region of 512 × 512 pixels parallel to the xy plane is set as a reconstruction region P, and a pixel row L0 parallel to the x axis where y = 0, y = 63 Pixel column L63, pixel column L127 of y = 127, pixel column L191 of y = 191, pixel column L255 of y = 255, pixel column L319 of y = 319, pixel column L383 of y = 383, pixel of y = 447 When the pixel column L511 of column L447, y = 511 is taken as a column, these pixel columns L0 to L511 are projected on the surface of the multi-row X-ray detector 24 in the X-ray transmission direction, and lines T0 to T511 as shown in FIG. If the upper projection data is extracted, they become projection data Dr (view, x, y) of the pixel columns L0 to L511. However, x and y correspond to each pixel (x, y) of the tomographic image.

  The X-ray transmission direction is determined by the X-ray focal point of the X-ray tube 21 and the geometric position of each pixel and the multi-row X-ray detector 24, but z of the X-ray detector data D0 (view, j, i). Since the coordinate z (view) is attached to the X-ray detector data as the table linear movement z-direction position Ztable (view), the X-ray detector data D0 (view, j, i) during acceleration / deceleration is also known. The X-ray transmission direction can be accurately determined in the data acquisition geometric system of the X-ray focus and multi-row X-ray detector.

  For example, a part of the line goes out of the channel direction of the multi-row X-ray detector 24, such as a line T0 in which the pixel row L0 is projected on the surface of the multi-row X-ray detector 24 in the X-ray transmission direction. In this case, the corresponding projection data Dr (view, x, y) is set to “0”. Further, if the projection is out of the z direction, the projection data Dr (view, x, y) is extrapolated.

Thus, as shown in FIG. 8, projection data Dr (view, x, y) corresponding to each pixel in the reconstruction area P can be extracted.
Returning to FIG. 5, in step S62, the projection data Dr (view, x, y) is multiplied by the cone beam reconstruction weighting coefficient to create projection data D2 (view, x, y) as shown in FIG.

  Here, the cone beam reconstruction weighting coefficient w (i, j) is as follows. In the case of fan beam image reconstruction, in general, when view = βa, a straight line connecting the focus of the X-ray tube 21 and the pixel g (x, y) on the reconstruction area P (on the xy plane) is the center of the X-ray beam. When the angle formed with respect to the axis Bc is γ and the opposite view is view = βb,

It is.
If the angles between the X-ray beam passing through the pixel g (x, y) on the reconstruction area P and the opposite X-ray beam and the reconstruction plane P are αa and αb, the cone beam reconstruction weighting coefficient depending on them Multiply and multiply by ωa and ωb to obtain backprojection pixel data D2 (0, x, y).

  In addition, the sum of the opposite beams of the cone beam reconstruction weighting coefficient is

It is.
Cone angle artifacts can be reduced by multiplying and adding cone beam reconstruction weighting coefficients ωa and ωb.

  For example, the cone beam reconstruction weighting coefficients ωa and ωb can be obtained by the following equations. Note that ga is a weighting coefficient of a certain X-ray beam, and gb is a weighting coefficient of an opposing X-ray beam.

  When 1/2 of the fan beam angle is γmax,

(For example, q = 1)
For example, as an example of ga and gb, if max [] is a function that takes the larger value,

In the case of fan beam image reconstruction, each pixel on the reconstruction area P is further multiplied by a distance coefficient. For the distance coefficient, the distance from the focus of the X-ray tube 21 to the detector row j and channel i of the multi-row X-ray detector 24 corresponding to the projection data Dr is r0, and the distance from the focus of the X-ray tube 21 corresponds to the projection data Dr. When the distance to the pixel on the reconstruction area P to be set is r1, (r1 / r0) ² .

In the case of parallel beam image reconstruction, each pixel on the reconstruction area P may be multiplied by only the cone beam reconstruction weight coefficient w (i, j).
In step S63, as shown in FIG. 10, the projection data D2 (view, x, y) is added in correspondence with the pixels to the backprojection data D3 (x, y) cleared in advance.

  In step S64, steps S61 to S63 are repeated for all the views necessary for image reconstruction of the tomographic image (that is, views for 360 degrees or views for "180 degrees + fan angle"), as shown in FIG. Then, back projection data D3 (x, y) is obtained.

Note that the reconstruction area P may not be a square area of 512 × 512 pixels, but may be a circular area having a diameter of 512 pixels as shown in FIGS.
A method for compressing X-ray detector data or projection data will be described below based on the following three embodiments.

Example 1: An example in which projection data is compressed for a portion where air is present around a subject.
Example 2: Example in which a portion to be diagnosed is photographed in a tomographic image of a subject. In particular, only the heart part in the lung field is photographed. Or only the liver in the chest is photographed. The case is considered.

  Example 3: An example in which the region of interest of the subject changes depending on the z direction during helical scanning, or during conventional scanning (axial scanning) or cine scanning that continues in the z direction.

The first embodiment is an embodiment in which the X-ray detector data and the projection data are compressed for a portion where there is air around the subject.
In general, a CT apparatus performs imaging as shown in FIG.

In step P1, the subject is set.
In step P2, scout image shooting is performed.
In step P3, shooting conditions are set.

In step P4, imaging by conventional scanning (axial scan), cine scan or helical scan, and data collection are performed.
In step P5, X-ray detector data and projection data are stored in a storage device.

In step P6, image reconstruction is performed.
In step P7, a tomographic image is displayed.
In this case, in the setting of imaging conditions after scout imaging, the region of interest at the time of diagnosis can be set on the scout image. Alternatively, the region of interest can be automatically set and confirmed by the operator.

  As shown in FIG. 14, the region of interest can be set in the scout image of the head. This region of interest is a region where a subject to be tomographically imaged exists, and does not mean a region where imaging is performed. In FIG. 14, in the scout image in the LR direction (x direction) (90-degree direction), lz in the z-direction and ly in the y-direction with respect to the 90-degree direction scout image of the head of the subject set in the head holder It shows how the length of interest is set. Here, a rectangular region of interest is set with the head of the subject to be diagnosed as the region of interest. In addition to the region of interest, a tomographic image position for imaging is set. In FIG. 15, in the scout image in the AP direction (y direction) (0 degree direction), the region of interest of lx in the x direction and ly length in the y direction is set in the scout image of the head in the 0 degree direction. It shows a state. Similarly, a rectangular region of interest is set with the head of the subject to be diagnosed as the region of interest. In addition to the region of interest, a tomographic image position for imaging is set.

  The region of interest set in FIG. 14 is ly in the y direction, lz in the z direction, and the region of interest set in FIG. 15 is lx in the x direction and lz in the z direction. However, since both are scout images, the length of the region of interest changes on the X-ray tube 21 side and the multi-row X-ray detector 24 side, but lx, ly are x, y, The length is in the z direction. Based on the information lx, ly set on the scout image, the region of interest on the tomographic image is obtained. FIG. 16 shows a method for setting a region of interest in a tomographic image. In FIG. 16, a rectangular region of interest having lx in the x direction and ly in the y direction is set in the tomographic image of the head. Alternatively, an elliptical region of interest having an x-direction diameter of lx and a y-direction diameter of ly may be set. Similarly, FIG. 17 shows a region of interest setting in the case of the lower limb. In the case of the lower limbs, there are a plurality of tomographic image regions, usually two tomographic image regions (two lower limbs) due to the morphological characteristics. In this case, efficient data compression can be performed by setting the tomographic image region of each lower limb as the region of interest. FIG. 18 shows the setting of the region of interest in the case of the heart. If the lung field usually exists outside the heart, but the purpose of the examination is the heart only and it is not necessary to see the lung field, set the region of interest only in the heart and capture the field of view only in the heart region. It is possible to compress the projection data in the lung field region by reducing the spatial resolution and density resolution.

  In this way, when the set region of interest is developed on the projection data, it is as shown in FIG. On the projection data, the space between the axis in the channel direction and the axis in the view direction is considered. FIG. 19 shows how the region of interest is set on the projection data. Thereby, the start channel Sch (view) and the end channel Ech (view) of the region of interest are known for each view on the projection data. For this reason, the projection data between the start channel Sch (view) and the end channel Ech (view), which are the regions of interest for each view, may be left uncompressed, and data compression may be performed for portions outside this range. Also, as shown in FIG. 20, even if there are a plurality of regions of interest, the same data compression process can be performed only in cases where there are a plurality of regions of interest regions of each view on the projection data.

  In particular, in the case of the head, since the head holder is used instead of the cradle 12, the non-interesting area in the periphery of the imaging area is almost air, so there is almost no information related to diagnosis. That is, there is almost no necessary projection data. For this reason, it is considered that the compression rate of the data compression in the non-interest area may be considerably reduced.

For example, the following compression can be considered.
(1) In the non-interested area portion, n channels of data are substituted with one average value, and 1 / n data compression is performed. (Spatial resolution data compression)
(2) The non-interested area is set to a constant value. (Spatial resolution data compression)
(3) When the gradation resolution of the data of the region of interest is 16 bits, the gradation resolution of the data of the non-region of interest is reduced to 12 bits, 10 bits, or 8 bits. (Data compression with gradation resolution)
For example, in a CT apparatus with a maximum field of view diameter of 50 cm, the compression rate when a head with a diameter of 20 cm is imaged is assumed to be 1000 channels with n = 10.

  Thus, the projection data can be compressed to 43%. Similarly, in the case of method (2),

As described above, the projection data can be compressed to about 40%.
In the case of method (3), if the gradation resolution of the non-interest area is set to 8 bits,

As described above, the projection data can be compressed to 70%.
Further, the effect becomes more remarkable when the compression of the spatial resolution and the compression of the gradation resolution are combined as in (1) and (3), (2) and (3).

Such data compression can be performed on the X-ray detector data or the preprocessed projection data by the following method.
(1) Data collection is performed in the data collection device (DAS) 25 during data collection.

(2) At the time of data collection, it is performed in the data collection buffer 5 or the central processing unit 3 before the preprocessing in step S1.
(3) Performed in the central processing unit 3 after the preprocessing in step S2 or after the beam hardening correction in step S3.

Further, the spatial resolution and gradation resolution can be supplemented by the following method at the time of image reconstruction for these compressions.
For the spatial resolution data compression method of (1), as shown in FIG. 21, for example, the data averaged every n channels is approximated by a polynomial to obtain the data of each channel, and even the original data is a little You can also get closer. In FIG. 21, the horizontal axis represents the channel direction and the vertical axis represents the X-ray detector data value or the projection data value, and the change in the X-ray detector data value or the projection data data value of each channel is shown. The portion indicated by the dotted line shows the average of the data values for every three channels. When compressing data, the data is compressed to the average of the data values for each of these three channels. When restoring data, the data values for each of these three channels are approximated by a polynomial, and are indicated by the original “x” in FIG. It can be made close to the original data.

  For the spatial resolution data compression method (2), as shown in FIG. 22, data is restored by putting a constant value in all channels of the non-interest region. In FIG. 22, in the original data, the channel range included in the region of interest and the channel range included in the non-region of interest exist in the channel direction when the horizontal axis is the channel direction and the vertical axis is the data value. ing. When data compression is performed, the data value of each channel in the channel range included in the region of interest is left without being compressed, but the data value of each channel in the channel range included in the non-region of interest is, for example, The data value is compressed to the average value of the data value of each channel of the region of interest. At the time of data restoration, the value of each channel included in the non-region of interest is restored by putting the average value data as a constant value in each channel of the non-region of interest.

  For the data compression method with the gradation resolution of (3), as shown in FIG. 23, the data with the data value “0” in the lower 8 bits is compared to the data compressed from 16 bits to 8 bits. The data is processed again after being restored to 16 bits.

In this way, the processing flow of the present invention is as shown in FIG.
In step P11, the subject is set.
In step P12, scout image shooting is performed.

In step P13, shooting conditions are set and a region of interest is set.
In step P14, imaging, data collection, and data compression in a non-interest area are performed.
In step P15, the X-ray detector data and the projection data are stored in the storage device.

In step P16, data decompression of the non-interest area is performed.
In step P17, image reconstruction is performed.
In step P18, a tomographic image is displayed.

  In Example 2, the projection data area necessary for diagnosing a part of one organ, such as the heart inside the lung field and the liver in the abdomen, the X-ray detector data and projection data of the part of interest By using as the region of interest, the X-ray detector data and projection data in the non-region of interest can be compressed, and the data transfer and data storage processing time in image reconstruction can be shortened.

  Set the region of interest in the scout image, convert the region of interest information into a rectangular or elliptical region of interest on the tomographic image, and finally expand the region of interest on the projection data and X-ray detector data The point is the same as in the first embodiment.

  For example, FIG. 25 shows the setting of the region of interest of the heart in the lung field and the liver in the abdomen in the scout image in the RL direction. Similarly, FIG. 26 shows the setting of the region of interest of the heart in the lung field and the liver in the abdomen in the AP direction scout image.

  FIG. 27 shows a region of interest on a tomographic image based on the region of interest information set in this scout image. In FIG. 27, the original image in the upper left is an image displayed by setting the window width and window level in accordance with the CT value level of the lung field in the imaging region 40 cm. The original image on the lower left is also an image displayed with the window width and window level set according to the CT value level of the soft tissue in the imaging region 40 cm. The upper right image and the lower right image show a case where the region of interest (red circular portion) is limited to the portion of the imaging region 30 cm. The upper right image and the tomographic image of the lower right image have been reconstructed by the processing shown in FIG.

  The upper right image shows the window width and the window level according to the CT value level of the lung field, and the lower right image shows the window width and the window level according to the CT value level of the soft tissue. Is an image displayed together. It can be seen that even in the CT value level of the upper right image, the image quality is the same as that of the upper left original image in the region of interest. It can also be seen that the image quality is the same in the region of interest as the lower left original image at the CT value level of the lower right image.

  That is, FIG. 27 shows a tomographic image restored from the profile area sum of the data of the region of interest and the projection data in each view direction (projection data direction) by the method (4). The image quality in the peripheral non-interest area displayed in blue is degraded due to data compression, but the image quality in the red interest area is not affected by the image degradation in the peripheral non-interest area. Recognize.

  In the case of Example 1, in the tomogram of the X-ray CT apparatus, which is a non-interest area, for example, the data of the air portion is compressed, and in the data restoration, restoration from only the compressed data was considered, In the second embodiment, the data of a part of the subject that is not the region of interest is also compressed, and when restoring at the time of image reconstruction, the data restoration may not be performed only from the compressed projection data of the non-region of interest. In addition, the projection data of the non-interest region is attempted to be restored using the projection data of the region of interest.

  That is, for example, when it is desired to examine only the heart portion, the region of interest may be set only to the heart portion, and the lung field portion reflected outside the region may be subjected to data compression. If the data in the lung field outside the region of interest is restored and the image is reconstructed at the time of image reconstruction, the image of the heart portion that is the region of interest does not deteriorate and can be used without clinical problems. In this case, in the data restoration of the lung field portion, a profile area value S (z0), which is an integrated value in the channel direction of projection data at a certain z-direction coordinate position z0, which is a tomographic imaging position in a scout image, is obtained.

Here, D1 (view, j, i) is the preprocessed projection data, view is a certain view position, j is the column number of the multi-row X-ray detector 24, i is the channel number, and CH is the maximum channel. Number.
If the profile area value S (z ₀ ) of all channels, the profile area value SR (z ₀ ) of the region of interest, and the profile area value S0 (z ₀ ) of the non-region of interest

When the projection data of the non-interesting area is compressed and restored, the profile area value S0 (z ₀ ) of the non-interesting area must be shifted, so the data should be S0 (z ₀ ) above. If the profile area value S0 (z ₀ ) of the non-interesting region when restored is shifted, correction is performed.

Original profile area value S0 (z ₀ )
If the profile area value at the time of data compression and data restoration is S01 (z ₀ ), the projection data value of the non-interest region may be corrected by multiplying it by S0 (z ₀ ) / S01 (z ₀ ).

  Specifically, based on the region-of-interest information set on the scout image as in Example 1, the region of interest on the tomographic image is, for example, a lx rectangle in the x direction, a ly rectangle in the y direction, or a diameter in the x direction. The corresponding region of interest on the projection data is defined as shown in Fig. 19 and Fig. 20, such that is an ellipse with lx in the y direction and the region of interest in each view of the projection data. A region of interest and a non-region of interest are defined such that the start channel is Sch (view) and the end channel is Ech (view).

Data compression is performed on this non-interesting area. For example, there are the following compression methods.
(1) For the non-interested region, the data for n channels is substituted with one average value, and 1 / n compression is performed. (Spatial resolution data compression)
(2) When the gradation resolution of the data of the region of interest is 16 bits, the gradation resolution of the data of the non-interest region is reduced to 12 bits, 10 bits, or 8 bits. (Data compression with gradation resolution)
(3) Data compression on spatial resolution and gradation resolution is performed using reversible data compression and lossy data compression of conventionally known data compression techniques.

(4) Remember only the profile area sum of the region of interest data and the projection data of each view, and perform data compression.
For example, in a CT device with a maximum field of view diameter of 50 cm, the compression ratio when a heart with a diameter of 12 cm is imaged is compressed with n = 20 by the method of (1),

As described above, the projection data can be compressed to about 28%.
In contrast to these data compression methods, spatial resolution and gradation resolution can be supplemented for data compressed by the following method at the time of image reconstruction.

  For the data compression method (1), as shown in FIG. 21, for example, the data averaged every n channels is approximated by a polynomial to obtain the data of each channel, and the data is restored close to the original original data. You can also.

For the data compression method of (2), as shown in Fig. 23, for the data compressed from 16 bits to 8 bits, data is processed by restoring 0 to the lower 8 bits and restoring it to 16 bits again. Do.
For the data compression method of (3), a decompression method corresponding to each compression method is used.

For the data compression method (4), the projection data of the non-interest region is predicted from the profile area sum of the projection data of each view, and image reconstruction is performed.
Furthermore, in the method (4), when the X-ray collimator in the channel direction or the beam forming X-ray filter movable in the channel direction is used to reduce the X-ray exposure of the subject, the imaging time can be shortened and the image can be reproduced. In addition to the effect of shortening the construction time, the effect of reducing X-ray exposure can also be achieved.

  Details of the processing performed in FIG. 27 will be described in the following embodiment. In the overall flow shown in FIG. 28, the projection data of the non-region of interest that has been compressed and restored in the following flow is supplemented, and the region of interest can be imaged with good image quality.

In step P1, scout image data is first collected.
In step P2, a region to be photographed and a region of interest are set on the scout image.
In step P3, the profile area of each z position to be photographed is obtained from the scout image or the projection data of the scout image.

In Step P4, shooting is performed and data is collected.
In step P5, the projection data is preprocessed, and the profile area information at each z position of the scout image or the projection data of the scout image is obtained to predict and correct the projection data portion missing in the data-compressed peripheral portion. To do. Details of this correction will be described later in the description of FIG. 29 below.

In Step P6, image reconstruction processing is performed using the projection data to which the missing part is added.
In step P7, a tomographic image is displayed.

A description will be given of correction for reconstructing projection data by predicting a portion outside a region of interest that has been lost when data compression is performed in step P5, with reference to FIG.
In FIG. 29, a case where projection data lacking due to data compression is added is described.

  First, why the projection data outside the region of interest influences the image reconstruction within the region of interest in the image reconstruction of the X-ray CT apparatus will be described. In the image reconstruction flow of FIG. 3, there is reconstruction function superimposition processing in step S5. In this process, as shown in FIG. 32, the reconstruction function k (x) is superimposed on the projection data d (x) in the projection data space, and the projection data d1 (x )

  However, “*” indicates a superposition calculation. Note that this is an explanation of step S5 in FIG. 3 in the previous embodiment.

  Is simply expressed in an equivalent expression that expresses the same content as. In an ordinary X-ray CT apparatus, the Fourier transform of d1 (x) and k (x) is used to multiply in the frequency space as shown below. This is shown in FIG. 32 as a real space process. .

  In the case of processing in real space, it is as follows.

  Since the reconstruction function k (x) is a function in the range of (−∞, ∞), the value of the region of interest in the projection data d1 (x) on which the reconstruction function is superimposed includes the projection data d (x ) Is the value of the non-interest area range. For this reason, if there is a non-negligible amount of projection data d (x) in the non-interested area, it is necessary to predict and restore the non-interested area projection data correctly to some extent after compressing the non-interested area projection data. There is. The profile area distribution obtained from the scout image is used for prediction at this time. FIG. 30 shows an elliptic approximated profile obtained from a scout image. This is an approximate ellipse obtained by rounding the fine fluctuations of the profile area obtained from the scout image for each channel to some extent, resulting in a rough profile area in the channel direction. The range of the region of interest and the range of the non-interest region are made to correspond to the profile areas ei (x) and ej (x) approximated by the ellipse.

  Note that ei (x) is the elliptical approximate profile area distribution of the i-th slice, and ej (x) is the elliptical approximate profile area distribution of the j-th slice. Among these, ei (x) and ej (x) of the non-interesting region are extracted and merged with the region of interest of the actual projection data di (x) and dj (x). Here, di (x) is the actual projection data of the i-th slice, and dj (x) is the actual projection data of the j-th slice.

That is, assuming that the region of interest is (xs, xe), the restored projection data dri (x) of the i-th slice and the restored projection data drj (x) of the j-th slice are as follows.
However, CH is the maximum channel number.

  In this way, by correctly predicting projection data outside the region of interest to some extent at the time of data restoration, a tomographic image in the region of interest is correctly reconstructed as shown in the upper right and lower right diagrams of FIG.

  As shown in the figure on the right side of FIG. 31, the same effect can be obtained by using the triangle approximation instead of the ellipse approximation when restoring the projection data of the non-interest region, as shown in the upper right and lower right figures of FIG. In addition, a tomographic image in the region of interest is correctly reconstructed.

The feedforward control of the channel direction X-ray collimator will be described with reference to the flowchart of FIG.
In step C1, as shown in FIG. 34, the angle β (view angle β) of the X-ray data acquisition system composed of the X-ray tube 21, the multi-row X-ray detector 24, and the DAS 25, and the imaging region of interest (for example, the center) (Xo, yo), a circular region of interest with a radius R) and the angular range on the multi-row X-ray detector 24 to be irradiated with X-rays (from the minimum irradiation channel γmin to the maximum irradiation channel γmax) or channel Calculate the range.

  Note that the relationship between the minimum irradiation channel γmin, the maximum irradiation channel γmax, the X-ray tube 21, the multi-row X-ray detector 24, and the DAS 25 in the above and the channel direction collimator is as shown in FIG.

  here,

,
In Step C2, the channel direction collimator (which may be an eccentric cylindrical collimator or a shielded sheet collimator) is opened from the minimum irradiation channel γmin to the maximum irradiation channel γmax.

In step C3, it is confirmed whether the channel direction collimator control and data collection for all the views of the planned imaging scan are completed.
Further, as shown in FIG. 35, the relationship between the imaging region of interest, the minimum irradiation channel, and the maximum irradiation channel when the view angle is 0 degree is as follows.

  here,

  For example, when the position of the circular imaging region of interest is (xo, yo), the radius is R, and the view angle is 0 degree, that is, the X-ray focal point is at (0, FCD), the following is obtained. (However, FCD: Focus Center Distance X-ray focus rotation center distance)

Further, as shown in FIG. 36, the relationship between the imaging region of interest at the view angle β, the minimum irradiation channel, and the maximum irradiation channel is as follows.
here,

  For example, when the position of the circular imaging region of interest is (xo, yo) and the radius is R, and the view angle is 0 degree, that is, the X-ray focal point is at (FCD · sinβ, FCD · cosβ), the following results. (However, FCD: Focus Center Distance X-ray focus rotation center distance)

Next, feedback control of the channel direction X-ray collimator is shown in FIG.
In Step C1, as in Step C1 of FIG. 33, the angle β (view angle β) of the X-ray data acquisition system including the X-ray tube 21, the multi-row X-ray detector 24, and the DAS 25, and the imaging region of interest ( For example, the angle range on the multi-row X-ray detector 24 to be irradiated with X-rays (from the minimum irradiation channel γmin to the maximum irradiation channel γmax) according to the size and position of the center (xo, yo) radius R). Or calculate the channel range.

  In Step C2, as in Step C2 of FIG. 33, the channel direction collimator (which may be an eccentric cylindrical collimator or a shielded collimator) is opened from the minimum irradiation channel γmin to the maximum irradiation channel γmax.

  In step C3, the range of data irradiated with X-rays is obtained by looking at the data of DAS25. Assuming that Chmin to Chmax are the data input range irradiated with X-rays, it is confirmed whether this corresponds to the minimum irradiation channel γmin and the maximum irradiation channel γmax obtained in step C1.

If it is within a minute error range of ± ε, it is acceptable, but if this error range is exceeded, go to Step C4.
In Step C4, γmin−Chmin · Chang = Δγmin, γmax−Chmax · Chang = Δγmax
Correction amounts Δγmin and Δγmax are added to the control amount. After this, go to step C5.

  In step C5, data is input to the DAS 25, and the channel direction range Chmin to Chmax, that is, the channel angle range γmin to γmax is set as the region of interest, and data is collected while compressing the projection data of the non-region of interest.

In step C6, the data is restored and the image is reconstructed while correcting the projection data lacking the data-compressed projection data.
In step C7, it is confirmed whether or not the data collection of all views is completed. If not completed, the process returns to step C1 to continue the channel direction collimator control and the data collection.

  In this case, elliptical approximation is performed from the profile area and the width of the profile in the channel direction. As shown in FIG. 29, from the positional relationship between the profile approximated to an ellipse and the region to be imaged, the projection data Sil, I understand Sir. By reconstructing an image by attaching Sil and Sir to the left and right of the projection data, a tomographic image with better image quality can be obtained.

Next, FIG. 38, FIG. 39, and FIG. 40 introduce an example in which the beam forming X-ray filter 32 is used.
In the second embodiment, the channel direction X-ray collimator 31 has been described. However, the same effect can be obtained by using the beam forming X-ray filter 32 as shown in FIGS. 38, 39, and 40. .

FIG. 38 shows the normal position of the beam forming X-ray filter, that is, when the movement amount in the channel direction is zero.
39 and 40 show cases where the movement amounts of the beam forming X-ray filter are Δd ₁ and Δd ₂ . In this case, the straight line connecting the center of the region of interest and the X-ray focal point may be controlled so that the X-ray transmission path of the beam forming X-ray filter 32 overlaps the shortest straight line.

  To overlay this, (Formula 4) (Formula 5)

  If the distance between the X-ray focal point and the beam forming filter is D as shown in FIG.

  In the first and second embodiments, the data compression method for the region of interest, the non-region of interest, and the non-region of interest for one tomographic image on the xy plane has been described. Actually, as shown in FIG. 41 and FIG. In the helical scan by changing the region of interest, or the conventional scan (axial scan) or cine scan continuous in the z direction, manually setting the region of interest one by one according to each tomographic image position in the z direction Alternatively, a more optimal region of interest can be automatically set on the scout image by image processing and image measurement. In this case, the projection data of the non-interest region other than the region of interest can be compressed, and the imaging time and the image reconstruction time can be reduced by optimization as in the first and second embodiments.

  Furthermore, in this case, if X-rays can be controlled only in the region of interest, a very good effect can be realized from the viewpoint of reducing exposure. For example, when the projection data of the non-interesting area is not used as much as (4) of the second embodiment, it is preferable from the viewpoint of reducing the exposure to make the X-ray irradiation area substantially equal to the interest area. In this case, the movement in the channel direction may be controlled so that the X-rays that have passed through the channel direction collimator 31 do not irradiate the non-interest region with the X-rays.

Similarly, even when an X-ray beam forming filter that can move in the channel direction is used, the movement in the channel direction may be controlled so that more non-interested regions are not irradiated with more X-rays.
In this way, when performing helical scanning, conventional scanning in the z direction (axial scanning), or cine scanning, it is difficult to set the region of interest at each z coordinate position. It is realistic to automatically set the region by image processing and measurement. FIG. 43 shows a flowchart for automatically setting a region of interest by image processing and measurement of a scout image.

In Step P21, scout image photographing in the 0 degree and 90 degree directions is performed.
In Step P22, the scout image in the 0 degree and 90 degree directions is binarized, and the area of the cradle and the subject or the head holder and the subject head is obtained. Depending on the region, the threshold value for extracting the lung field and the threshold value for extracting the vertebral body are further binarized.

  In step P23, the position and size of the subject are measured, and the position and size of the subject are obtained from the binarization threshold value for obtaining the cradle and the subject or the head holder and the subject head. From the threshold value for extracting the lung field part, the position and size of the lung field part are obtained. A reference position of the vertebral body is obtained from the threshold value for extracting the vertebral body.

In step P24, a region of interest for tomographic imaging is set. The region of interest at this time is determined from the size and position of the subject, the size and position of the lung field, the reference position of the vertebral body, and the like.
In step P25, tomographic imaging is performed. When tomographic imaging is performed, data is collected by compressing projection data of a non-interest area, and in the image reconstruction process, the compressed projection data is restored and image reconstruction is performed.

In step P26, a tomographic image is displayed.
In the above X-ray CT apparatus 100, according to the X-ray CT apparatus or the X-ray CT imaging method of the present invention, a two-dimensional matrix structure represented by a multi-row X-ray detector or a flat panel X-ray detector X-ray detector data or projection data without degrading the density resolution and spatial resolution of tomographic images of conventional scans (axial scans) or cine scans or helical scans of X-ray CT devices with area X-ray detectors By reducing the size of the X-ray CT, it is possible to reduce the imaging time or the image reconstruction time of the X-ray CT apparatus.

  Note that the image reconstruction method may be a three-dimensional image reconstruction method by a conventionally known Feldkamp method. Furthermore, other three-dimensional image reconstruction methods may be used. The same effect can be obtained by the two-dimensional image reconstruction method.

  In this embodiment, column direction (z direction) filters having different coefficients are superimposed for each column, thereby adjusting image quality variation and realizing uniform slice thickness, artifact, and noise image quality. However, various filter coefficients can be considered for this, and any of them can produce the same effect.

In this embodiment, the medical X-ray CT apparatus is written based on the X-ray CT-PET apparatus, the X-ray CT-SPECT apparatus, etc. combined with the industrial X-ray CT apparatus or other apparatuses. Available.
In this embodiment, X-ray detector data is divided into a set region of interest and a non-region of interest at the time of data collection, and the data format is changed. However, the same applies to the preprocessed projection data. The same effect can be obtained by changing the data format separately for the region of interest and the region of non-interest.

  In this embodiment, the data size is controlled by reducing the spatial resolution of the data of the non-interesting area by the data collecting means, but a conventionally known data compression method is used to control the data size of the non-interesting area. But you can get the same effect.

  In this embodiment, the data collection unit controls the data size by reducing the gradation resolution of the data of the non-interesting area. However, a conventionally known data compression method is used to control the data size of the non-interesting area. Even if used, the same effect can be produced.

  In this embodiment, the spatial resolution is compensated by interpolation as a method of compensating the spatial resolution of the data of the non-interest area by image reconstruction. However, the same effect can be obtained by using a conventionally known data decompression method instead. I can put it out.

  Further, in this embodiment, the gradation resolution is compensated by interpolation as a method for compensating the gradation resolution of the data of the non-interest area by image reconstruction. Can produce an effect.

It is a block diagram which shows the X-ray CT apparatus concerning one Embodiment of this invention. It is explanatory drawing which shows rotation of a X-ray generator (X-ray tube) and a multi-row X-ray detector. It is a flowchart which shows schematic operation | movement of the X-ray CT apparatus which concerns on one Embodiment of this invention. It is a flowchart which shows the detail of pre-processing. It is a flowchart which shows the detail of a three-dimensional image reconstruction process. It is a conceptual diagram which shows the state which projects the line on a reconstruction area | region to a X-ray transmissive direction. It is a conceptual diagram which shows the line projected on the detector surface. It is a conceptual diagram which shows the state which projected the projection data Dr (view, x, y) on the reconstruction area. It is a conceptual diagram which shows the backprojection pixel data D2 of each pixel on a reconstruction area. It is explanatory drawing which shows the state which obtains backprojection data D3 by adding all the views to backprojection pixel data D2 corresponding to a pixel. It is a conceptual diagram which shows the state which projects the line on a circular reconstruction area | region to a X-ray transmissive direction. It is a figure which shows the data structure of X-ray detector data and projection data. It is a figure which shows imaging | photography of an X-ray CT apparatus. It is a figure which shows the scout image of LR direction (x direction). It is a figure which shows the scout image of AP direction (y direction). It is a figure which shows the relationship (in the case of a head) between the subject and the region of interest on a tomographic image. It is a figure which shows the region of interest setting in the case of a leg. It is a figure which shows the region of interest setting in the case of the heart. It is a figure which shows the setting of the region of interest on projection data. It is a figure which shows the case where there are two or more regions of interest. FIG. 6 is a diagram illustrating a first example of restoration of data with compressed spatial resolution. FIG. 10 is a diagram illustrating a second example of restoration of data with compressed spatial resolution. FIG. 6 is a diagram illustrating an example 1 of restoration of data with compressed gradation resolution. It is a flowchart which shows the flow of a process of this invention. It is a figure which shows the setting of the region of interest in the scout image of RL direction (x direction). It is a figure which shows the setting of the region of interest in the scout image of AP direction (y direction). It is a figure which shows the region of interest which restricted the imaging region of the imaging region 30 cm with a halftone photograph. It is a figure which shows the flow of a process of the algorithm which decompress | restores projection data from a profile area sum. It is a figure which shows the case where the projection data lacked by data compression are added. It is a figure which shows the prediction of the missing projection data. It is a figure which shows addition of the projection data lacked by data compression. It is a figure which shows the superimposition of projection data and a reconstruction function. It is a figure which shows the feedforward control of a channel direction collimator. It is a figure which shows explanatory drawing of the imaging | photography region of interest and irradiation channel range at the time of view angle = 0 degree | times. It is explanatory drawing of the imaging | photography region of interest at the time of view angle = 0 degree | times, an irradiation minimum channel, and an irradiation maximum channel. It is explanatory drawing of the imaging | photography region of interest at the time of view angle (beta), the irradiation minimum channel, and the irradiation maximum channel. It is a figure which shows the feedback control of a channel direction collimator. FIG. 3 is a diagram showing a normal position of a beam forming X-ray filter 32. It is a figure which shows beam forming X-ray filter 32 position control (the 1). It is a figure which shows beam forming X-ray filter 32 position control (the 2). It is a figure which shows the setting of the region of interest in the scout image of RL direction (x direction) when a region of interest changes to az direction. It is a figure which shows the setting of the region of interest in the scout image of AP direction (y direction) when a region of interest changes to az direction. It is a flowchart which sets a region of interest automatically by image processing and measurement of a scout image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Operation console 2 Input device 3 Central processing unit 5 Data collection buffer 6 Monitor 7 Storage device 10 Imaging table 12 Cradle 15 Rotating part 20 Scanning gantry 21 X-ray tube 22 X-ray controller 23 Collimator 24 Multi-row X-ray detector 25 DAS ( Data collection device)
26 Rotation unit controller 27 Scanning gantry tilt controller 29 Control controller 30 Slip ring dP X-ray detector plane P Reconstruction area PP Projection plane
IC rotation center (ISO)

Claims (20)

X-ray projection data transmitted through the subject between the X-ray generator and the multi-row X-ray detector that detects X-rays relative to each other while rotating around the center of rotation. X-ray data collection means to collect,
Image reconstruction means for reconstructing an image of the projection data collected from the X-ray data collection means;
Image display means for displaying the reconstructed tomographic image;
Imaging condition setting means for setting various imaging conditions for tomographic imaging,
In the X-ray CT system consisting of
Projection data is collected by changing the data format of the projection data of the region of interest, which is the region where the subject to be tomographically imaged, and the projection data of the non-interesting region, which is the region where the subject to be tomographically imaged does not exist. X-ray CT apparatus characterized by having X-ray data collection means to do. While making a two-dimensional X-ray area detector with a matrix structure typified by a flat panel X-ray detector that detects X-rays relative to the X-ray generator while rotating around the center of rotation, X-ray data collection means for collecting X-ray projection data transmitted through the subject in between,
Image reconstruction means for reconstructing an image of the projection data collected from the X-ray data collection means;
Image display means for displaying the reconstructed tomographic image;
Imaging condition setting means for setting various imaging conditions for tomographic imaging,
In the X-ray CT system consisting of
Projection data is collected by changing the data format of the projection data of the region of interest, which is the region where the subject to be tomographically imaged, and the projection data of the non-interesting region, which is the region where the subject to be tomographically imaged does not exist. X-ray CT apparatus characterized by having X-ray data collection means to do. In the X-ray CT apparatus of claim 1,
An X-ray CT apparatus comprising: X-ray data acquisition means having different spatial resolution of projection data for projection data of the region of interest and projection data of the non-region of interest. In the X-ray CT apparatus of claim 3,
When reconstructing an image from the projection data of the region of interest and the projection data of the non-interest region having different spatial resolutions, the image reconstruction is performed after performing a process for compensating the spatial resolution on the projection data of the non-interest region. An X-ray CT apparatus characterized by having an image reconstruction means to perform. In the X-ray CT apparatus according to any one of claims 1 to 4,
An X-ray CT apparatus comprising: X-ray data collection means for projecting data of the region of interest and projection data of the non-region of interest having different gradation resolutions of the projection data. In the X-ray CT apparatus of claim 5,
When reconstructing an image from the projection data of the region of interest and the projection data of the non-interest region having different gradation resolutions, the image reconstruction is performed after performing a process for compensating the gradation resolution on the projection data of the non-interest region. An X-ray CT apparatus having an image reconstruction means for performing configuration. In the X-ray CT apparatus according to any one of claims 1 to 6,
The setting of the region of interest and the non-interest region of the projection data is determined based on region information manually set by the user interface, and is different while distinguishing the projection data of the region of interest from the projection data of the non-region of interest. An X-ray CT apparatus having X-ray data collection means for collecting projection data in a data format. In the X-ray CT apparatus of claim 7,
The setting of the region of interest and the region of non-interest in the projection data is determined on the scout image based on the information of the region set in the region of interest manually, and distinguishes the projection data of the region of interest from the projection data of the non-region of interest. However, an X-ray CT apparatus having X-ray data collection means for collecting projection data in different data formats. In the X-ray CT apparatus of claim 8,
The setting of the region of interest and the non-region of interest of the projection data is determined based on information on the region of interest set manually on each scout image in two directions. An X-ray CT apparatus characterized by having X-ray data collection means for collecting projection data in different data formats while distinguishing projection data. In the X-ray CT apparatus of claim 7,
The setting of the region of interest and the non-region of interest in the projection data is determined on the tomographic image based on the information of the region in which the region of interest is manually set, and the projection data of the region of interest and the projection data of the non-region of interest are distinguished. However, an X-ray CT apparatus having X-ray data collection means for collecting projection data in different data formats. In the X-ray CT apparatus according to any one of claims 7 to 10,
The manually set shape of the region of interest on the tomographic image is determined to be an elliptical shape or a circular shape, and is different while distinguishing the projection data of the region of interest from the projection data of the non-region of interest. An X-ray CT apparatus characterized by having X-ray data collection means for collecting projection data in a data format. In the X-ray CT apparatus according to any one of claims 7 to 10,
The manually set shape of the region of interest on the tomographic image is determined to be a rectangular shape, and distinguishes between the projection data of the region of interest and the projection data of the non-region of interest while different data formats are used. An X-ray CT apparatus characterized by having an X-ray data collection means for collecting projection data. In the X-ray CT apparatus according to any one of claims 1 to 6,
The setting of the region of interest and the non-region of interest in the projection data is automatically determined according to each data value of the projection data, and is different while distinguishing the projection data of the region of interest from the projection data of the non-region of interest. An X-ray CT apparatus characterized by having X-ray data collection means for collecting projection data in a data format. In the X-ray CT apparatus of claim 13,
The setting of the region of interest and the non-region of interest in the projection data is determined based on the information on the region of interest automatically set on the scout image, and distinguishes between the projection data of the region of interest and the projection data of the non-region of interest. However, an X-ray CT apparatus having X-ray data collection means for collecting projection data in different data formats. In the X-ray CT apparatus of claim 13,
The setting of the region of interest and the non-region of interest in the projection data is determined based on the information of the region of interest set automatically on the tomographic image, and distinguishes between the projection data of the region of interest and the projection data of the non-region of interest. However, an X-ray CT apparatus having X-ray data collection means for collecting projection data in different data formats. In the X-ray CT apparatus according to claim 14 or 15,
The shape of the region of interest automatically set on the scout image or tomographic image is determined to be an elliptical shape, a circular shape, or a rectangular shape, and distinguishes the projection data of the region of interest from the projection data of the non-region of interest. However, an X-ray CT apparatus having X-ray data collection means for collecting projection data in different data formats. In the X-ray CT apparatus according to any one of claims 1 to 16,
The setting of the region of interest and the non-region of interest in the projection data changes depending on the z-axis direction position perpendicular to the tomographic image on the xy plane, distinguishing the projection data of the region of interest from the projection data of the non-region of interest However, an X-ray CT apparatus having X-ray data collection means for collecting projection data in different data formats. In the X-ray CT apparatus according to any one of claims 1 to 17,
In the case of conventional scan (axial scan) or cine scan, the interest in the projection data depends on at least one of the positions of each detector row or each pixel of the tomogram when collecting data at a certain z-direction position. The setting of the region and the non-interesting region varies depending on the z-direction position perpendicular to the tomographic image on the xy plane, while distinguishing the projection data of the region of interest from the projection data of the non-interesting region. An X-ray CT apparatus characterized by having X-ray data collection means for collecting projection data in a format. In the X-ray CT apparatus according to any one of claims 1 to 17,
In the case of helical scan, when the data acquisition system moves in the z direction, the region of interest in the projection data depends on at least one of the z position of each detector row or the position of each pixel of the tomographic image. And the setting of the non-interesting region varies depending on the z-direction position perpendicular to the tomographic image on the xy plane, while distinguishing the projection data of the region of interest from the projection data of the non-interesting region, and different data formats An X-ray CT apparatus characterized by having an X-ray data collection means for collecting projection data. In the X-ray CT apparatus according to any one of claims 1 to 19,
An X-ray CT apparatus comprising X-ray data collection means for collecting projection data while having a plurality of regions of interest in one tomogram.