X-ray CT apparatus Number:7,522,697 from the United States Patent and Trademark Office (PTO) owispatent

Title: X-ray CT apparatus

Abstract: The present invention is to easily associate X-ray projection data and scanning table z-direction coordinate information with each other. Using set parameters of the operations of a scanning gantry and a scanning table, the association of the X-ray projection data and scanning table z-direction coordinate information with each other is executed. Thereafter, image reconstruction is carried out based on the X-ray projection data to obtain a tomographic image. The operation set parameters are stored as part of the X-ray projection data. Alternatively, they are collectively stored even in the case of files separate from the X-ray projection data.

Patent Number: 7,522,697 Issued on 04/21/2009 to Satta,   et al.

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Inventors:	Satta; Yusuke (Tokyo, JP), Sato; Kazuhiko (Tokyo, JP), Nishide; Akihiko (Tokyo, JP), Hagiwara; Akira (Tokyo, JP)
Assignee:	GE Medical Systems Global Technology Company, LLC (Waukesha, WI)
Appl. No.:	11/680,404
Filed:	February 28, 2007

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Foreign Application Priority Data

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Mar 01, 2006 [JP]			2006-055417

Current U.S. Class:	378/15 ; 378/19; 378/20
Current International Class:	G21K 1/12 (20060101)
Field of Search:	378/4,15,19,20,62,162,208,209

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References Cited [Referenced By]

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U.S. Patent Documents

5768336	June 1998	Khutoryansky et al.
5787886	August 1998	Kelly et al.
6580777	June 2003	Ueki et al.
6816567	November 2004	Drummond et al.
6977984	December 2005	Hsieh et al.
7173997	February 2007	Hagiwara
7426255	September 2008	Miyazaki et al.
2003/0161435	August 2003	Ozaki

Primary Examiner: Kiknadze; Irakli
Attorney, Agent or Firm: Armstrong Teasdale LLP

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Claims

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The invention claimed is:

1. An X-ray CT apparatus comprising: a scanning table configured to support a subject thereon and to move the subject within the X-ray CT apparatus; a scanning gantry comprising: an X-ray generator; an X-ray detector configured to detect X-rays generated by the X-ray generator, the X-ray detector positioned in opposition to the X-ray generator; and a rotation device configured to rotate the X-ray generator and the X-ray detector, the X-ray generator configured to expose the X-rays to the subject moved by the scanning table while the X-ray generator and the X-ray detector are rotated about the subject, the scanning gantry configured to perform a scan including detecting the X-rays transmitted through the subject at the X-ray detector to acquire X-ray projection data; a scanning condition setting device configured to set parameters for controlling a movement of the scanning table along a moving direction during the scan, the parameters including an acceleration and a deceleration of the movement of the scanning table; a predicting device configured to predict a plurality of positions of the scanning table along the moving direction for each view of the scan by calculating the plurality of positions of the scanning table using the parameters set by the scanning condition setting device; and an image reconstructing device configured to reconstruct a plurality of tomographic images within a range scanned during the acceleration and the deceleration of the movement of the scanning table along the moving direction by reconstructing the X-ray projection data, wherein the X-ray projection data is correlated to the plurality of predicted positions.

2. The X-ray CT apparatus according to claim 1, wherein the parameters comprise at least one of a scanning table acceleration, a scanning table deceleration, a scanning table constant velocity, a scanning table initial position, a scanning table stop position, a scanning table acceleration end position, and a scanning table deceleration start position.

3. The X-ray CT apparatus according to claim 1, wherein the predicting device is further configured to add the parameters to the X-ray projection data as a part of header information of the X-ray projection data.

4. The X-ray CT apparatus according to claim 1, wherein the predicting device is further configured to record the parameters to a file associated with the X-ray projection data.

5. The X-ray CT apparatus according to claim 1, wherein the scanning condition setting device is further configured to set as one of the parameters a tilt parameter for controlling a tilt angle of the scanning gantry during the scan, and wherein the predicting device is configured to calculate the plurality of positions by using the parameters and the tilt parameter.

6. The X-ray CT apparatus according to claim 1, wherein the scan is a helical shuttle scan.

7. The X-ray CT apparatus according to claim 1, wherein the image reconstructing device is configured to perform a three-dimensional image reconstruction.

8. A method for producing an X-ray CT image by reconstructing projection data, said method comprising: obtaining the projection data during a scan including an acceleration and a deceleration of a movement of a scanning table using an X-ray CT apparatus, wherein the X-ray CT apparatus comprises the scanning table configured to support a subject thereon and to move the subject within the X-ray CT apparatus, and a scanning gantry comprising an X-ray generator, an X-ray detector configured to detect X-rays generated by the X-ray generator, the X-ray detector positioned in opposition to the X-ray generator, and a rotation device configured to rotate the X-ray generator and the X-ray detector, the X-ray generator configured to expose the X-rays to the subject moved by the scanning table while the X-ray generator and the X-ray detector are rotated about the subject, the scanning gantry configured to perform the scan including detecting the X-rays transmitted through the subject at the X-ray detector to acquire the projection data; predicting a plurality of positions of the scanning table along a moving direction for each view of the scan by calculating the plurality of positions of the scanning table using parameters for controlling movement of the scanning table along the moving direction; and reconstructing a plurality of tomographic images within a range scanned during the acceleration and the deceleration of the movement of the scanning table by reconstructing the projection data, wherein the projection data are correlated to the plurality of predicted positions.

9. The method for producing X-ray CT image according to claim 8, wherein predicting a plurality of positions further comprises calculating the plurality of positions of the scanning table using parameters comprising at least one of a scanning table acceleration, a scanning table deceleration, a scanning table constant velocity, a scanning table initial position, a scanning table stop position, a scanning table acceleration end position, and a scanning table deceleration start position.

10. The method for producing X-ray CT image according to claim 8 further comprising adding the parameters to the projection data as a part of header information of the projection data.

11. The method for producing X-ray CT image according to claim 8 further comprising recording the parameters to a file associated with the projection data.

12. The method for producing X-ray CT image according to claim 8, wherein predicting a plurality of positions of the scanning table further comprises using the parameters and a tilt parameter for controlling a tilt angle of the scanning gantry during, the scan to predict the plurality of positions.

13. The method for producing X-ray CT image according to claim 8, wherein obtaining the projection data during a scan further comprises performing a helical shuttle scan.

14. The method for producing X-ray CT image according to claim 8, wherein reconstructing a plurality of tomographic images further comprises performing a three-dimensional image reconstruction.

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Description

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CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Application No. 2006-055417 filed Mar. 1, 2006.

BACKGROUND OF THE INVENTION

The present invention relates to an X-ray CT apparatus which is a medical X-ray CT (Computed Tomography) apparatus or an industrial X-ray CT apparatus and which holds operations of an X-ray data acquisition system or information for imaging conditions and performs image reconstruction based on the same, upon a conventional scan (axial scan), a cine scan, a helical scan, a variable-pitch helical scan or a helical shuttle scan.

An X-ray CT apparatus acquires X-ray projection data by scanning a subject with X rays and image-reconstructs a tomographic image of the subject, based on the X-ray projection data (refer to, for example, Japanese Unexamined Patent Publication No. 2004-173756).

Such an X-ray CT apparatus has a two-dimensional X-ray area detector of a matrix structure typified by, for example, a multi-row X-ray detector or a flat panel. Upon data acquisition by a conventional scan (axial scan), a cine scan or a helical scan, a scanning table is changed in a z direction by the operation of an X-ray data acquisition system during scan to perform X-ray data acquisition. In the case of a variable-pitch helical scan and a helical shuttle scan, an absolute coordinate position or a relative coordinate position of a z-direction coordinate of the scanning table is recorded for each view or at several views as position information of the scanning table. Described specifically, when a scanning table velocity changes like v(t) as shown in FIG. 16, a scanning table position changes like z(t) and a data acquisition view number linearly increases like N(i). Therefore, for example, data of a scanning table position z(t1) is recorded so as to correspond to an N(t1) view. Incidentally, the data of the scanning table position z(t1) may be recorded with being added to X-ray projection data.

Here, an encoder for detecting a position is installed in the scanning table as in the case of a rotary encoder, a linear encoder or the like, and the installed encoder is used to obtain data about each position of the scanning table in real time during scan. For example, X-ray projection data and position data of the scanning table at the time that the X-ray projection data is obtained, are stored in association with each other. For example, as file data different from the X-ray projection data, the position data of the scanning table is stored in association with it each other. Thereafter, image reconstruction is carried out using the X-ray projection data and the position data of the scanning table both associated with each other, thereby to obtain a tomographic image of the subject.

Therefore, there is a case in which the addition of the X-ray projection data to each view is not easy. Further, there was a case where when z-direction coordinate information of the scanning table corresponding to each view was contained as another file, it was not easy to associate the z-direction coordinate information of the scanning table and each view for the X-ray projection data with each other upon image reconstruction.

Thus, there was a case in which a problem arose in that the association of the X-ray projection data and the scanning table z-direction coordinate information with each other upon the X-ray projection data acquisition or image reconstruction was not easy.

In an X-ray CT apparatus having a multi-row X-ray detector or an X-ray CT apparatus having a two-dimensional X-ray area detector typified by a flat panel, there is a tendency to increase the number of channels of an X-ray detector and increase the number of views for X-ray projection data as the resolution in a row direction rises. Further, there is a tendency to make the rotational velocity of the gantry fast. That is, the number of views per unit time trends to increase. A z-direction position of a scanning table or cradle is measured by the scanning table. Its z-direction position data is added to X-ray projection data obtained by a data acquisition system (DAS) of a scanning gantry rotating section at a scanning gantry fixing section. Therefore, this control becomes difficult due to the increase in the number of views per unit time.

Thus, an object of the present invention is to provide an X-ray CT apparatus capable of efficiently describing and storing position information and photography information of an X-ray data acquisition system by less parameters.

SUMMARY OF THE INVENTION

When an operator sets an imaging condition, the operations of an X-ray data acquisition system and a scanning table or cradle are determined. The scanning table or cradle will be explained below as the scanning table. That is, as the operations of the X-ray data acquisition system and the scanning table with a subject placed thereon, a scanning table z-direction coordinate position, a scanning table x-direction coordinate position, a scanning table y-direction coordinate position, a scanning gantry rotating section rotation-angle position, a scanning gantry tilt angle position, a scanning gantry x-direction coordinate position, a scanning gantry y-direction coordinate position, and a scanning gantry z-direction coordinate position are predicted upon setting of the imaging condition. Since the X-ray data acquisition system and the scanning table are normally feedback-controlled with an accuracy of 0.1 mm or less, they do not deviate vastly from their predicted values. Therefore, if the predicted operations of X-ray data acquisition system and scanning table can be described by several parameters, then the operations of the X-ray data acquisition system and the scanning table can be reproduced if the parameters are recorded.

FIG. 17 describes the manner of traveling of the scanning table (or cradle) in the z direction. If parameters for cradle acceleration, cradle deceleration, a cradle stationary velocity, a cradle initial position, a cradle stop position, a cradle acceleration end position and a cradle deceleration start position exist, then the operation of the scanning table or cradle can be described.

If the scanning gantry and the scanning table corresponding to the X-ray data acquisition system can be moved with sufficient accuracy as predicted based on the parameters, it is then unnecessary to subject information about a scanning table z-direction coordinate position, a scanning table x-direction coordinate position, a scanning table y-direction coordinate position, a scanning gantry rotating section rotation-angle position, a scanning gantry tilt angle position, a scanning gantry x-direction coordinate position, a scanning gantry y-direction coordinate position, and a scanning gantry z-direction coordinate position set for each view to measurement, data acquisition and addition to X-ray projection data.

Therefore, in the present invention, the operation of a scanning gantry corresponding to an X-ray data acquisition system, and the operation of a scanning table or cradle are predicted when an operator sets an imaging condition, and described with operation parameters. When the parameters are added to X-ray projection data upon X-ray data acquisition to perform image reconstruction, the image reconstruction is carried out using the operation parameters. Alternatively, the operation parameters are inserted into another file and associated with the X-ray projection data. Upon execution of image reconstruction, the image reconstruction is carried out using the operation parameters.

In order to solve the above problems, there is provided an X-ray CT apparatus according to a first aspect, comprising a scanning table for placing a subject thereon and moving the subject placed thereon;

a scanning gantry comprising an X-ray generator, an X-ray detector for detecting the X rays in opposition to the X-ray generator, and a rotation device for rotating the X-ray generator and the X-ray detector, for causing the X-ray generator to expose X rays to the subject moved by the scanning table while the X-ray generator and the X-ray detector are being rotated about the subject, and performing a scan for causing the X-ray detector to detect the X rays transmitted through the subject thereby to acquire X-ray projection data;

image reconstructing device for image-reconstructing the X-ray projection data acquired by the scanning gantry;

image display device for displaying a tomographic image reconstructed by the image reconstructing device; and

imaging condition setting device for setting an imaging condition including a parameter for operating the scanning gantry and/or a parameter for causing the scanning table to move the subject upon execution of the scan,

wherein the image reconstructing device reconstructs the X-ray projection data using the parameter for operating the scanning gantry and/or the parameter for causing the scanning table to move the subject set by the imaging condition setting device as the imaging condition.

In the X-ray CT apparatus according to the first aspect, the operations of an X-ray data acquisition system comprising the X-ray data acquisition device and the scanning table are recognized in advance by operation parameters. Since the position of an X-ray beam passing through each pixel on an image reconstruction plane can be predicted properly upon image reconstruction, the image reconstruction can be carried out with a high degree of accuracy.

In order to solve the above problems, there is provided an X-ray CT apparatus according to a second aspect, wherein in the X-ray CT apparatus according to the first aspect, the X-ray data acquisition device adds the parameters set as the imaging condition by the imaging condition setting device to the X-ray projection data and records the result of addition therein.

In the X-ray CT apparatus according to the second aspect, the operations of an X-ray data acquisition system comprising the X-ray data acquisition device and scanning table are recognized in advance by operation parameters, and the operation parameters are added to X-ray projection data. Since the position of an X-ray beam passing through each pixel on an image reconstruction plane can be predicted properly based on the operation parameters added to the X-ray projection data upon image reconstruction, the image reconstruction can be performed accurately.

In order to solve the above problems, there is provided an X-ray CT apparatus according to a third aspect, wherein the X-ray data acquisition device records, as parameters for the operations of the X-ray data acquisition device and the scanning table, data containing at least one of a scanning table z-direction coordinate position, a scanning table x-direction coordinate position, a scanning table y-direction coordinate position, a scanning gantry rotating section rotation-angle position, a scanning gantry tilt angle position, a scanning gantry x-direction coordinate position, a scanning gantry y-direction coordinate position, and a scanning gantry z-direction coordinate position.

In the X-ray CT apparatus according to the third aspect, even when the scanning gantry, and the X-ray data acquisition device and scanning table lying thereinside are allowed to perform photography and diagnoses by various applications or various operations, the operations of the X-ray data acquisition system comprising the X-ray data acquisition device and scanning table lying in the scanning gantry are recognized more by respective operation parameters. If the scanning gantry and the X-ray data acquisition device and scanning table lying thereinside can be moved with satisfactory accuracy as recognized, then an X-ray beam passing through each pixel on an image reconstruction plane can be predicted properly upon image reconstruction. Therefore, the image reconstruction can be carried out accurately.

There is provided an X-ray CT apparatus according to a fourth aspect, wherein in the X-ray CT apparatus according to any of the first to third aspects, an X-ray data acquisition system has X-ray data acquisition device which records at least one of at least one absolute coordinate value or relative coordinate value of a scanning table z-direction coordinate position, a scanning table x-direction coordinate position, a scanning table y-direction coordinate position, a scanning gantry rotating section rotation-angle position, a scanning gantry tilt angle position, a scanning gantry x-direction coordinate position, a scanning gantry y-direction coordinate position, and a scanning gantry z-direction coordinate position.

In order to solve the above problems, in the X-ray CT apparatus according to the fourth aspect, the operation parameters set by the scanning gantry, and the X-ray data acquisition device and scanning table lying thereinside are recorded using the absolute coordinate value and the relative coordinate value when the operation parameters are recorded in the third aspect. Since the position of an X-ray beam passing through each pixel on an image reconstruction plane can be properly predicted absolutely or relatively upon image reconstruction, the image reconstruction can be carried out accurately.

In order to solve the above problems, there is provided an X-ray CT apparatus according to a fifth aspect, wherein in the X-ray CT apparatus according to any of the first to fourth aspects, an X-ray data acquisition system has X-ray data acquisition device which records at least one of at least one absolute coordinate value or relative coordinate value of a scanning table z-direction coordinate position, a scanning table x-direction coordinate position, a scanning table y-direction coordinate position, a scanning gantry rotating section rotation-angle position, a scanning gantry tilt angle position, a scanning gantry x-direction coordinate position, a scanning gantry y-direction coordinate position, and a scanning gantry z-direction coordinate position and adds the same to X-ray projection data.

In the X-ray CT apparatus according to the fifth aspect, when the operation parameters set by the scanning gantry, and the X-ray data acquisition device and scanning table lying thereinside are recorded in the third or fourth aspect, they are recoded with being added to X-ray projection data. It is thus unnecessary to associate the operation parameters with another file where they are set as another file. Therefore, the operation of the X-ray data acquisition device can be predicted on software of an image reconstruction device according to a simpler file operation upon image reconstruction. Further, the position of an X-ray beam passing through each pixel on an image reconstruction plane can properly be predicted upon image reconstruction. It is therefore possible to carry out the image reconstruction accurately.

In order to solve the above problems, there is provided an X-ray CT apparatus according to a sixth aspect, wherein in the X-ray CT apparatus according to any of the first to fifth aspects, the X-ray data acquisition device records at least one of accelerations or decelerations about operations in a scanning table z direction, a scanning table x direction, a scanning table y direction, a scanning gantry rotating section rotation-angle direction, a scanning gantry tilt angle direction, a scanning gantry x-direction angle direction, a scanning gantry y-direction angle direction and a scanning gantry z-direction angle direction of an X-ray data acquisition system.

In the X-ray CT apparatus according to the sixth aspect, the acceleration and deceleration at each time are contained in the operation parameters set by the scanning gantry corresponding to the X-ray data acquisition device, and the X-ray data acquisition device thereinside and scanning table lying in the first to fifth aspects. Since the velocities and travel distances for the operations are known from this point, the prediction of the operations can be carried out properly. Thus, since the position of an X-ray beam passing through each pixel on an image reconstruction plane can be properly predicted upon image reconstruction, the image reconstruction can be carried out accurately.

In order to solve the above problems, there is provided an X-ray CT apparatus according to a seventh aspect, wherein in the X-ray CT apparatus according to any of the first to sixth aspects, the X-ray data acquisition device records at least one of initial positions, stop positions, acceleration end positions or deceleration start positions about operations in a scanning table z direction, a scanning table x direction, a scanning table y direction, a scanning gantry rotating section rotation-angle direction, a scanning gantry tilt angle direction, a scanning gantry x-direction angle direction, a scanning gantry y-direction angle direction and a scanning gantry z-direction angle direction of an X-ray data acquisition system.

In the X-ray CT apparatus according to the seventh aspect, the initial positions, stop positions, acceleration end positions or deceleration start positions about the operations are contained in the operation parameters set by the scanning gantry corresponding to the X-ray data acquisition device, and the X-ray data acquisition device and scanning table lying thereinside in the first to sixth aspects. From this point, the position of the X-ray data acquisition system is known in combination with the acceleration and deceleration, so the prediction of the operations can be carried out properly. Thus, since the position of an X-ray beam passing through each pixel on an image reconstruction plane can be predicted properly upon image reconstruction, the image reconstruction can be carried out accurately.

In order to solve the above problems, there is provided an X-ray CT apparatus according to an eighth aspect, wherein in the X-ray CT apparatus according to any of the first to seventh aspects, the X-ray data acquisition device records stationary velocities about operations in a scanning table z direction, a scanning table x direction, a scanning table y direction, a scanning gantry rotating section rotation-angle direction, a scanning gantry tilt angle direction, a scanning gantry x-direction angle direction, a scanning gantry y-direction angle direction and a scanning gantry z-direction angle direction of an X-ray data acquisition system.

In the X-ray CT apparatus according to the eighth aspect, the steady-state or stationary velocities are contained in the operation parameters set by the scanning gantry corresponding to the X-ray data acquisition device, and the X-ray data acquisition device and scanning table lying thereinside in the first to seventh aspects. From this point, the position of the X-ray data acquisition system can be reconfirmed, and the prediction of each operation reduced in error can be carried out properly. Thus, since the position of an X-ray beam passing through each pixel on an image reconstruction plane can be predicted properly upon image reconstruction, the image reconstruction can be carried out accurately.

In order to solve the above problems, there is provided an X-ray CT apparatus according to a ninth aspect, wherein in the X-ray CT apparatus according to any of the first to eighth aspects, when X-ray projection data corresponding to respective views are image-reconstructed, the image reconstructing device reproduces position information of an X-ray data acquisition system to perform image reconstruction.

In the X-ray CT apparatus according to the ninth aspect, there is a need to reproduce the position information of the X-ray data acquisition system by the operation parameters upon image reconstruction in the first to eighth aspects. Thus, since the position of an X-ray beam passing through each pixel on an image reconstruction plane can be predicted properly upon image reconstruction, the image reconstruction can be performed accurately.

In order to solve the above problems, there is provided an X-ray CT apparatus according to a tenth aspect, wherein in the X-ray CT apparatus according to any of the first to ninth aspects, the operations of an X-ray data acquisition system about a scanning table z direction, a scanning table x direction, a scanning table y direction, a scanning gantry rotating section rotation-angle direction, a scanning gantry tilt angle direction, a scanning gantry x-direction angle direction, a scanning gantry y-direction angle direction and a scanning gantry z-direction angle direction of an X-ray data acquisition system are linear control.

In the X-ray CT apparatus according to the tenth aspect, the operations of the scanning gantry corresponding to the X-ray data acquisition device, and the X-ray data acquisition device and scanning table lying thereinside are linearly-controlled. Consequently, the prediction of the operations becomes simple and hence the burden on a control system is reduced. Thus, since the position of an X-ray beam passing through each pixel on an image reconstruction plane can be predicted properly upon image reconstruction, the image reconstruction can be carried out accurately.

In order to solve the above problem, there is provided an X-ray CT apparatus according to an eleventh aspect, wherein in the X-ray CT apparatus according to any of the first to ninth aspects, the operations of an X-ray data acquisition system about a scanning table z direction, a scanning table x direction, a scanning table y direction, a scanning gantry rotating section rotation-angle direction, a scanning gantry tilt angle direction, a scanning gantry x-direction angle direction, a scanning gantry y-direction angle direction and a scanning gantry z-direction angle direction of an X-ray data acquisition system are nonlinear control.

In the X-ray CT apparatus according to the eleventh aspect, the operations of the scanning gantry corresponding to the X-ray data acquisition device, and the X-ray data acquisition device and scanning table lying thereinside are nonlinearly-controlled. Consequently, the discontinuity of acceleration can be eliminated and hence smoother operations can be taken. In particular, it is preferable to use the scanning table because it gives a softer operation to a subject placed thereon. Since the position of an X-ray beam passing through each pixel on an image reconstruction plane can properly be predicted upon image reconstruction even in this case, the proper image reconstruction can be carried out.

In order to solve the above problems, there is provided an X-ray CT apparatus according to a twelfth aspect, wherein in the X-ray CT apparatus according to any of the first to eleventh aspects, the image reconstructing device performs three-dimensional image reconstruction as image reconstruction.

In the X-ray CT apparatus according to the twelfth aspect, the three-dimensional image reconstruction is used to perform image reconstruction properly after the X-ray beam passing through each pixel on the image reconstruction plane is properly predicted upon image reconstruction in the first to eleventh aspects. Consequently, each X-ray projection data is backprojected on its corresponding proper position as viewed in the z direction and hence the photography or imaging of a tomographic image reduced in artifact and good in image quality can be realized.

In order to solve the above problems, there is provided an X-ray CT apparatus according to a thirteenth aspect, wherein in the X-ray CT apparatus according to any of the first to twelfth aspects, the X-ray data acquisition device records at least one of an initial value, a completion value, an acceleration value, a deceleration value and a constant value with respect to at least one imaging condition of an X-ray tube voltage, an X-ray tube current, a scan velocity, an X-ray collimator aperture or open width and an X-ray collimator open position.

In the X-ray CT apparatus according to the thirteenth aspect, even at executing portions of continuous operations, operations and changes, of an X-ray data acquisition system related to a mechanism system or an analog electric circuit, such as the X-ray tube voltage, X-ray tube current, scan velocity, X-ray collimator open width and X-ray collimator open position, the operations of the portions can be predicted and described with operation parameters when operated in X-ray data acquisition during photography in a manner similar to the prediction of the z-direction position of the scanning table, the prediction of the scanning gantry tilt angle and the like. Executing image reconstruction in consideration of the operations upon image reconstruction at this time enables proper image reconstruction.

In order to solve the above problems, there is provided an X-ray CT apparatus according to a fourteenth aspect, wherein in the X-ray CT apparatus according to any of the first to thirteenth aspects, the X-ray data acquisition device adds at least one of an initial value, a completion value, an acceleration value, a deceleration value and a constant value to X-ray projection data and records the result of addition therein, with respect to at least one imaging condition of an X-ray tube voltage, an X-ray tube current, a scan velocity, a view data acquisition sampling frequency, the number of data acquisition channels and the number of data acquisition rows.

In the X-ray CT apparatus according to the fourteenth aspect, the continuous operations, operations and changes of the X-ray data acquisition system can be described with their corresponding operation parameters, and the operation parameters can be recorded with being added to the X-ray projection data in the thirteenth aspect. Thus, image reconstruction can be executed properly by performing the image reconstruction in consideration of the operations upon the image reconstruction.

According to the present invention, an X-ray CT apparatus can be realized which is capable of efficiently storing position information and photography or imaging information of an X-ray data acquisition system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an X-ray CT apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an X-ray generator (X-ray tube) and a multi-row X-ray detector as viewed in an xy plane.

FIG. 3 is an explanatory diagram illustrating the X-ray generator (X-ray tube) and the multi-row X-ray detector as viewed in a yz plane.

FIG. 4 is a flow chart depicting the flow of subject imaging.

FIG. 5 is a flow chart showing a schematic operation for image reconstruction, of the X-ray CT apparatus according to the first embodiment of the present invention.

FIG. 6 is a flow chart illustrating the details of a pre-process.

FIG. 7 is a flow chart depicting the details of a three-dimensional image reconstructing process.

FIGS. 8a and 8b are conceptual diagrams showing a state in which lines on a reconstruction area are projected in an X-ray penetration direction.

FIG. 9 is a conceptual diagram illustrating lines projected onto an X-ray detector plane.

FIG. 10 is a conceptual diagram showing a state in which projection data Dr (view, x, y) are projected onto a reconstruction area.

FIG. 11 is a conceptual diagram showing backprojection pixel data D2 corresponding to respective pixels on a reconstruction area.

FIG. 12 is an explanatory diagram showing a state in which backprojection pixel data D2 are added together corresponding to pixels over all views to obtain backprojection data D3.

FIGS. 13a and 13b are conceptual diagrams illustrating a state in which lines on a circular reconstruction area are projected in an X-ray penetration direction.

FIG. 14 is a diagram showing an imaging condition input screen of the X-ray CT apparatus.

FIG. 15 is a diagram showing an example illustrative of a three-dimensional MPR display and a three-dimensional display.

FIG. 16 is a diagram showing a relationship between scanning table position information and data acquisition view numbers.

FIG. 17 is a diagram showing operations of a scanning table (cradle) at a helical shuttle scan.

FIG. 18 is a diagram illustrating operation parameters of the scanning table (cradle) and z-direction coordinates at the helical shuttle scan.

FIG. 19 is a diagram depicting operation parameters of the scanning table (cradle) at the helical shuttle scan.

FIG. 20 is a diagram showing operation parameters of the scanning table (cradle) and z-direction coordinates at a variable-pitch helical scan.

FIG. 21 is a diagram showing a scan reduced in X-ray needless exposure at the time that X-ray data acquiring device is tilted during a helical scan.

FIG. 22 is a diagram illustrating tilt operation parameters and data acquisition tilt angles of a data acquisition system at a scan reduced in X-ray needless exposure when the X-ray data acquiring device is tilted during the helical scan.

FIG. 23 is a diagram depicting a case in which operation parameters are added to X-ray projection data.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will hereinafter be explained in further detail by embodiments illustrated in the figures. Incidentally, the present invention is not limited to or by the embodiments.

[Apparatus Construction]

FIG. 1 is a block diagram of an X-ray CT apparatus according to a first embodiment of the present invention.

As shown in FIG. 1, the X-ray CT apparatus 100 according to the present embodiment is equipped with an operation console 1, an imaging or scanning table 10 and a scanning gantry 20.

As shown in FIG. 1, the operation console 1 includes an input device 2 which receives an input from an operator, a central processing unit 3 which executes data processing such as a pre-process, an image reconstructing process, a post-process, etc. a data acquisition buffer 5 which acquires or collects X-ray detector data acquired by the scanning gantry 20, a monitor 6 which displays a tomographic image image-reconstructed from projection data obtained by pre-processing the X-ray detector data, and a memory or storage device 7 which stores programs, X-ray detector data, projection data and X-ray tomographic images therein. In the present embodiment, an input for imaging or photographing conditions is inputted from the input device 2 and stored in the storage device 7. An example of an imaging condition input screen is shown in FIG. 14.

As shown in FIG. 1, the scanning table 10 includes a cradle 12 which inserts and draws a subject into and from a bore or aperture of the scanning gantry 20 with the subject placed thereon. Although not shown in the figure in particular, the cradle 12 is elevated and moved linearly on the scanning table 10 by a motor built in the scanning table 10.

As shown in FIG. 1, the scanning gantry 20 includes an X-ray tube 21, an X-ray controller 22, a collimator 23, a beam forming X-ray filter 28, a multi-row X-ray detector 24, a DAS (Data Acquisition System) 25, a rotating section controller 26 which controls the X-ray tube 21 or the like that are mounted on a rotating section 15 so as to be rotated about a body axis of the subject, and a control controller 29 which swaps control signals or the like with the operation console 1 and the scanning table 10. Here, the beam forming X-ray filter 28 is configured so as to be thinnest in thickness as viewed in the direction of X rays directed to the center of rotation corresponding to the center of imaging, to increase in thickness toward its peripheral portion and to be able to further absorb the X rays as shown in FIG. 2. Therefore, in the present embodiment, the body surface of a subject whose sectional shape is nearly circular or elliptic can be less exposed to radiation. The scanning gantry 20 can be tiled about .+-.30.degree. or so forward and rearward as viewed in the z direction by a scanning gantry tilt controller 27.

The X-ray tube 21 and the multi-row X-ray detector 24 are rotated about the center of rotation IC as shown in FIG. 2. Assuming that the vertical direction is a y direction, the horizontal direction is an x direction and the travel direction of the table and cradle orthogonal to these is a z direction, the plane at which the X-ray tube 21 and the multi-row X-ray detector 24 are rotated, is an xy plane. The direction in which the cradle 12 is moved, corresponds to the z direction.

FIGS. 2 and 3 are explanatory diagrams showing a geometrical arrangement or layout of the X-ray tube 21 and the multi-row X-ray detector 24 as viewed from the xy plane or yz plane.

As shown in FIG. 2, the X-ray tube 21 generates an X-ray beam called a cone beam CB. Incidentally, when the direction of a central axis of the cone beam CB is parallel to the y direction, this is defined as a view angle 0.degree..

As shown in FIG. 2, the multi-row X-ray detector 24 has X-ray detector rows arranged in plural form in the z direction and has, for example, X-ray detector rows corresponding to 256 rows. Each of the X-ray detector rows has X-ray detector channels corresponding to, for example, 1024 channels as viewed in a channel direction.

As shown in FIG. 2, the X-ray beam emitted from an X-ray focal point of the X-ray tube 21 is spatially controlled in X-ray dosage by the beam forming X-ray filter 28 in such a manner that more X rays are radiated in the center of a reconstruction area or plane P and less X rays are radiated at a peripheral portion of the reconstruction area P. Thereafter, the X rays are absorbed by the subject that exists inside the reconstruction area P, and the X rays transmitted through the subject are acquired by the multi-row X-ray detector 24 as X-ray detector data.

As shown in FIG. 3, the X-ray beam emitted from the X-ray focal point of the X-ray tube 21 is controlled in the direction of a slice thickness of a tomographic image by the X-ray collimator 23. That is, the X-ray beam is controlled in such a manner that the width of the X-ray beam becomes D at a central axis of rotation IC. Then, the X rays are absorbed into the subject existing in the vicinity of the central axis of rotation IC, and the X rays transmitted through the subject are acquired by the multi-row X-ray detector 24 as X-ray detector data.

Thus, the projection data acquired by application of the X rays are outputted from the multi-row X-ray detector 24 to the DAS 25 and A/D converted by the DAS 25. Then, the data are inputted to the data acquisition buffer 5 via a slip ring 30. Thereafter, the data inputted to the data acquisition buffer 5 are processed by the central processing unit 3 in accordance with the corresponding program stored in the storage device 7, so that the data are image-reconstructed as a tomographic image. Afterwards, the tomographic image is displayed on a display screen of the monitor 6.

Outline of Operations

The outline of each operation of the X-ray CT apparatus 100 is shown below.

FIG. 4 is a flow chart showing the outline of the operations of the X-ray CT apparatus according to the present embodiment.

At Step P1, as shown in FIG. 4, the subject is first placed on the cradle 12 and its alignment is made.

Here, a slice light center position of the scanning gantry 20 is aligned with a reference point of each region of the subject placed on the cradle 12.

Next, at Step P2, scout image acquisition is performed as shown in FIG. 4.

Here, a scout image is normally photographed at view angles of 0.degree. and 90.degree.. Incidentally, only a 90.degree. scout image may be photographed or imaged as in the case of, for example, the head, depending upon each region. The details of the photographing of the scout image will be described later.

Next, at Step P3, an imaging or photographing condition is set as shown in FIG. 4.

Here, the imaging condition is normally set while the position and size of a tomographic image to be photographed are being displayed on a scout image. In this case, the whole X-ray dosage information corresponding to one helical scan, variable-pitch helical scan, helical shuttle scan, conventional scan (axial scan) or cine scan is displayed. When the number of rotations of a scanning gantry rotating section (an X-ray data acquisition system) or the set value of imaging (X-ray application) time is inputted upon the cine scan, X-ray dosage information corresponding to the inputted number of rotations in the area of interest of the subject or the time inputted is displayed.

Upon setting of an imaging condition for the helical shuttle scan or the variable-pitch helical scan, operation parameters for performing z-direction operation control can be defined at the scanning table. These operation parameters are determined upon the setting of the imaging condition and sent to a scanning table control section to actually operate the scanning table. Then, these operation parameters are added to X-ray projection data. Upon image reconstruction, the position of an X-ray beam passing through each pixel on an image reconstruction plane is properly predicted in consideration of such an operation to perform proper three-dimensional image reconstruction. This image reconstruction will be explained in detail in FIG. 5 shown below. The three-dimensional image reconstruction will be described in detail in FIG. 7 shown below.

The details of the operation parameters for the helical shuttle scan or the variable-pitch helical scan will also be explained later.

Next, at Step P4, tomographic image photography is performed as shown in FIG. 4.

The details of the tomographic image photography and the image reconstruction will be described later.

Next, at Step P5, an image-reconstructed tomographic image is displayed as shown in FIG. 4.

Next, at Step P6, a three-dimensional image display is performed as shown in FIG. 4.

Here, a tomographic image photographed continuously in a z direction is used as a three-dimensional image and three-dimensionally image-displayed as shown in FIG. 15.

As methods for the three-dimensional image display, may be mentioned, a volume rendering three-dimensional image display method, an MIP (Maximum Intensity Projection) image display method, an MPR (Multi Plain Reformat) image display method, a three-dimensional reprojection image display method, etc. They are used properly according to diagnostic applications.

[Outline of Operations at Tomographic Image Photography and scout Image Photography]

The outline of operations of the X-ray CT apparatus 100 at the execution of tomographic image photography (Step P4 in FIG. 4) and scout image photography (Step P2 in FIG. 4) upon will be shown below.

FIG. 5 is a flow chart showing the outline of the operations for the tomographic image photography and scout image photography, of the X-ray CT apparatus 100 of the embodiment according to the present invention.

At Step S1, data acquisition is first performed as shown in FIG. 5.

When the data acquisition is carried out by a helical scan upon executing the tomographic image photography, the operation of rotating the X-ray tube 21 and the multi-row X-ray detector 24 about the subject and carrying out data acquisition of X-ray detector data while the cradle 12 placed on the imaging or scanning table 10 is being linearly moved, is performed. Upon the helical scan for acquiring or collecting the X-ray detector data, data acquisition in a constant-speed range is performed.

Upon a variable-pitch helical scan or a helical shuttle scan, data acquisition is performed even at acceleration and deceleration in addition to the data acquisition in the constant-speed range. In this case, scanning table z-direction operation parameters predicted by the central processing unit 3 including imaging condition setting device are added to X-ray detector data D0 (view, j, i) indicated by a view angle view, a detector row number j and a channel number i.

FIG. 17 is a diagram showing operations of the scanning table (cradle) at the helical shuttle scan.

FIG. 17 describes the manner in which the scanning table is moved in the z direction. If parameters like, for example, cradle acceleration, cradle deceleration, a cradle stationary speed or velocity, a cradle initial position, a cradle stop position, a cradle acceleration end position and a cradle deceleration start position exist as shown in FIG. 17 here, then the operations of the scanning table can be described.

If the scanning gantry and the scanning table corresponding to the X-ray data acquisition system can be moved with sufficient accuracy as predicted based on the parameters, it is then unnecessary to subject information about a scanning table z-direction coordinate position, a scanning table x-direction coordinate position, a scanning table y-direction coordinate position, a scanning gantry rotating section rotation-angle position, a scanning gantry tilt angle position, a scanning gantry x-direction coordinate position, a scanning gantry y-direction coordinate position, and a scanning gantry z-direction coordinate position set for each view to measurement, data acquisition and addition to X-ray projection data.

Upon the conventional scan (axial scan) or the cine scan, the data acquisition system is rotated once or plural times while the cradle 12 placed on the scanning table 10 is being fixed to a given z-direction position, thereby to perform data acquisition of X-ray detector data. The cradle 12 is moved to the next z-direction position as needed and thereafter the data acquisition system is rotated once or plural times again to perform data acquisition of X-ray detector data.

On the other hand, upon execution of the scout image photography, the operation of fixing the X-ray tube 21 and the multi-row X-ray detector 24 and performing data acquisition of X-ray detector data while the cradle 12 placed on the scanning table 10 is being linearly moved, is performed.

Next, at Step S2, a pre-process is performed as shown in FIG. 5.

Here, the pre-process is performed on the X-ray detector data D0 (view, j, i) to convert it into projection data. As shown in FIG. 6, the pre-process comprises an offset correction of Step S21, logarithmic translation of Step S22, an X-ray dosage correction of Step S23 and a sensitivity correction of Step S24.

Upon the scout image photography, the pre-processed X-ray detector data is displayed with each of a pixel size in the channel direction and a pixel size in the z direction corresponding to the cradle linear moving direction being made coincident with a display pixel size of the monitor 6.

Next, at Step S3, a beam hardening correction is performed as shown in FIG. 5.

Here, the beam hardening correction is effected on the pre-processed projection data D1 (view, j, i). Assuming that upon the beam hardening correction of Step S3, projection data subjected to the sensitivity correction S24 at the pre-process S2 is defined as D1 (view, j, i) and data subsequent to the beam hardening correction of Step S3 is defined as D11 (view, j, i), the beam hardening correction is expressed in the form of, for example, a polynomial as given by the following expression (1).

[1] D11(view,j,i)=D1(view,j,i)(B.sub.0(j,i)+B.sub.1(j,i)D1(view,j,i)+B.sub- .2(j,i)D1(view,j,i).sup.2) Expression (1)

Since, at this time, the independent beam hardening corrections can be carried out for every j row of the detectors, the difference between X-ray energy characteristics of the detectors placed for every row can be corrected if tube voltages of respective data acquisition systems are different on the imaging condition.

Next, at Step S4, a z-filter convolution process is performed as shown in FIG. 5.

Here, the z-filter convolution process for applying filters in the z direction (row direction) is effected on the projection data D11 (view, j, i) subjected to the beam hardening correction.

That is, after the pre-process at each view angle and each data acquisition system, projection data of the multi-row X-ray detector D11 (view, j, i) (where i=1 to CH and j=1 to ROW) subjected to the beam hardening correction is multiplied in the row direction by filters in which such row-direction filter sizes as expressed in the following expressions (2) and (3) are five rows, for example. However, (the expression 3) is satisfied. (w.sub.1(i), w.sub.2(i), w.sub.3(i), w.sub.4(i), w.sub.5(i)) (Expression 2)

.times..function..times..times. ##EQU00001##

The corrected detector data D12 (view, j, i) is given as expressed in the following expression (4):

.times..times..times..times..times..times..times..times..times..times..fun- ction..times..times. ##EQU00002##

Incidentally, assuming that the maximum value of the channel is CH and the maximum value of the row is ROW, the following expressions (5) and (6) are established.

[4] D11(view,-1,i)=D11(view,0,i)=D11(view,1,i) (Expression 5)

[5] D11(viw,ROW,i)=D11(view,ROW+1,i)=D11(view,ROW+2,i) (Expression 6)

When row-direction filter coefficients are changed for every channel, slice thicknesses can be controlled depending upon the distance from an image reconstruction center. In a tomographic image, its peripheral portion generally becomes thicker in slice thickness than the reconstruction center thereof. Therefore, the row-direction filter coefficients are changed at the central and peripheral portions, and the row-direction filter coefficients are widely changed in width in the neighborhood of a central channel and narrowly changed in width in the neighborhood of a peripheral channel, thereby making it possible to make the slice thickness uniform at both the peripheral portion and the image reconstruction center.

Controlling the row-direction filter coefficients at the central and peripheral channels of the multi-row X-ray detector 24 in this way makes it possible to control the slice thickness at the central and peripheral portions. Thickening the slice thickness slightly by each row-direction filter yields extensive improvements in both artifact and noise. Thus, the degree of the improvement in artifact and the degree of the improvement in noise can also be controlled. That is, it is possible to control the quality of a three-dimensionally image-reconstructed tomographic image in the xy plane. In addition to above, a tomographic image having a thin slice thickness can also be realized by setting row-direction (z-direction) filter coefficients to deconvolution filters.

Next, at Step S5, a reconstruction function convolution process is performed as shown in FIG. 5.

That is, X-ray projection data subjected to the processes up to the (Expression 6) is subjected to Fourier transformation and multiplied by a reconstruction function, followed by being subjected to inverse Fourier transformation. Assuming that upon the reconstruction function convolution process S5, data subsequent to the z filter convolution process is defined as D12, data subsequent to the reconstruction function convolution process is defined as D13, and the convoluting reconstruction function is defined as Kernel(j), the reconstruction function convolution process is expressed as given by the following expression (7):

[6] D13(view,j,i)=D12(view,j,i)*Kernel(j) (Expression 7)

That is, since the independent reconstruction function convolution process can be performed for every j row of the detectors, the reconstruction function Kernel (j) can correct differences in noise characteristic and resolution characteristic for every row.

Next, at Step S6, a three-dimensional backprojection process is performed as shown in FIG. 5.

Here, the three-dimensional backprojection process is effected on the projection data D13 (view, j, i) subjected to the reconstruction function convolution process to determine backprojection data D3 (x, y, z). An image-reconstructed image is three-dimensionally image-reconstructed on an xy plane corresponding to a plane orthogonal to the z axis. A reconstruction area or plane P to be shown below is assumed to be parallel to the xy plane. The three-dimensional backprojection process will be explained later referring to FIG. 5.

Next, at Step S7, a post-process is performed as shown in FIG. 5.

Here, the post-process including image filter convolution, CT value conversion and the like is effected on the backprojection data D3 (x, y, z) to obtain a CT or tomographic image D31 (x, y).

Assuming that upon the image filter convolution process in the post-process, a tomographic image subsequent to the three-dimensional backprojection is defined as D31 (x, y, z), data subsequent to the image filter convolution is defined as D32 (x, y, z), and a two-dimensional image filter convolved on the xy plane corresponding to a tomographic image plane is defined as Filter(z), the following expression (8) is established.

[7] D32(x,y,z)=D31(x,y,z)*Filter(z) (Expression 8)

That is, since the independent image filter convolution process can be performed for every j row of the detectors, it is possible to correct differences in noise characteristic and resolution characteristic for every row.

An image space z-direction filter convolution process shown below may be performed after the two-dimensional image filter convolution process. The image space z-direction filter convolution process may be performed before the two-dimensional image filter convolution process. Further, a three-dimensional image filter convolution process may be performed to bring about such an effect as to share both the two-dimensional image filter convolution process and the image space z-direction filter convolution process.

Assuming that upon the image space z-direction filter convolution process, a tomographic image subjected to the image space z-direction filter convolution process is defined as D33 (x, y, z), and a tomographic image subjected to the two-dimensional image filter convolution process is defined as D32 (x, y, z), the following relation (expression 9) is established. However, v(i) becomes such a coefficient row as expressed below (in expression 10) in the form of image space z-direction filter coefficients at which the width in the z direction is 21+1.

.times..times..times..times..times..times..times..times..times..times..fun- ction..times..times..function..function..times..times..function..function.- .function..times..times..function..function..times..times. ##EQU00003##

Upon the helical scan, the image space filter coefficient v(i) may be an image space z-direction filter coefficient independent on a z-direction position. However, when the two-dimensional X-ray area detector 24 or the multi-row X-ray detector 24 broad in detector width as viewed in the z direction is used in particular, the image space z-direction filter coefficient v(i) can be subjected to detailed adjustments dependent on row positions of respective tomographic images upon execution of the conventional scan (axial scan) or the cine scan if the image space z-direction filter coefficient v(i) is given as each of image space z-direction filter coefficients dependent on the positions of the rows of the X-ray detector in the z direction. Therefore, this is further effective.

The so-obtained tomographic images are displayed on the monitor 6.

[Three-Dimensional Backprojection Process]

The outline of the operation at the time that the three-dimensional backprojection process is carried out (S6 in FIG. 5) at the operations of the X-ray CT apparatus 100, is shown below.

FIG. 7 is a flow chart showing the details of the three-dimensional backprojection process.

In the present embodiment, an image to be image-reconstructed is three-dimensionally image-reconstructed on an xy plane corresponding to a plane orthogonal to the z axis. That is, the reconstruction area P is assumed to be parallel to the xy plane.

At Step S61, attention is first given to one of all views (i.e., views corresponding to 360.degree. or views corresponding to "180.degree.+fan angles") necessary for image reconstruction of a tomographic image as shown in FIG. 7. Projecti