JP2008142387A - X-ray ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus that appropriately carries out a helical scan even during acceleration and deceleration periods of a table. <P>SOLUTION: The X-ray CT apparatus carries out a helical scan even during acceleration and deceleration periods of the linear movement of the table mounting a subject, and regenerates a tomographic image on the basis of the acquired data. The apparatus is equipped with a control means to control the linear movement of the table on the basis of a speed profile with an adjustable characteristic. The speed profile is characterized by that at least one of the acceleration part and the deceleration part is linear, and that at least one of the acceleration part and the deceleration part is curved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an X-ray CT (Computed Tomography) apparatus, and in particular, performs a helical scan including an acceleration / deceleration period of linear movement of a table on which a subject is placed, and based on the obtained data The present invention relates to an X-ray CT apparatus for reconstructing a tomographic image.

The X-ray CT apparatus scans a subject with X-rays, and reconstructs a tomographic image based on the obtained data (data). Helical scanning can be performed by performing continuous scanning while continuously moving the table on which the subject is placed in a straight line. The helical scan may be performed including not only the constant speed movement period of the table but also the acceleration period and deceleration period before and after that period (see, for example, Patent Document 1).
Japanese Patent Laying-Open No. 2005-40582

  The acceleration of the table from the stop state to the constant speed state and the deceleration of the table from the constant speed state to the stop state are performed with predetermined acceleration characteristics and deceleration characteristics. These acceleration / deceleration characteristics are fixed depending on the table feed mechanism, but depending on the purpose of imaging and the state of the subject, there are cases where the acceleration / deceleration characteristics are not fixed.

  Accordingly, an object of the present invention is to realize an X-ray CT apparatus that appropriately performs a helical scan including a table acceleration / deceleration period.

  An invention for solving the problem is an X-ray CT apparatus that performs a helical scan including an acceleration / deceleration period of linear movement of a table on which a subject is placed, and reconstructs a tomographic image based on the obtained data. An X-ray CT apparatus comprising control means for controlling linear movement of the table based on a velocity profile having variable characteristics.

In the speed profile, it is preferable that at least one of the acceleration portion and the deceleration portion is linear in terms of simplifying the control.
In the speed profile, it is preferable that at least one of the acceleration portion and the deceleration portion is curved in terms of smooth acceleration / deceleration.

In the curved portion of the speed profile, it is preferable that the acceleration changes continuously from the viewpoint of smooth acceleration / deceleration.
The continuous change in acceleration is preferably a continuous change from 0 and a continuous change to 0 from the viewpoint of reducing impact at the start and stop of movement.

It is preferable that the speed profile includes a waiting period until the start of acceleration in terms of adjusting the timing from the start of scanning to the start of table movement.
The speed profile preferably includes a stop period after the end of deceleration in terms of adjusting the timing from the table stop to the end of scanning.

The control means preferably stores the speed profile from the viewpoint of effectively performing table movement control.
The stored speed profiles are preferably a plurality of speed profiles, from the viewpoint of a plurality of table control patterns.

  It is preferable that the plurality of velocity profiles respectively correspond to a plurality of imaging protocols from the viewpoint of appropriately performing a helical scan.

  According to the present invention, an X-ray CT apparatus that performs a helical scan including an acceleration / deceleration period of linear movement of a table on which a subject is placed and reconstructs a tomogram based on the obtained data is a linear line of the table. Since the control means for controlling the movement based on the speed profile with variable characteristics is provided, an X-ray CT apparatus that appropriately performs a helical scan including the acceleration / deceleration period of the table can be realized.

  The best mode for carrying out the invention will be described below with reference to the drawings. Note that the present invention is not limited to the best mode for carrying out the invention. FIG. 1 shows a schematic configuration of an X-ray CT apparatus. This apparatus is an example of the best mode for carrying out the present invention. An example of the best mode for carrying out the invention related to the X-ray CT apparatus is shown by the configuration of the apparatus.

  The apparatus has a gantry 100, a table 200, and an operator console 300. The gantry 100 scans the subject 10 carried by the table 200 with the X-ray irradiation / detection device 110, collects transmission X-ray signals (scan data) of a plurality of views, and inputs them to the operator console 300. . The operator console 300 performs image reconstruction based on the scan data input from the gantry 100 and displays the reconstructed image on a display 302.

  The operator console 300 also displays on the display 302 a user interface for enabling an interactive operation of the apparatus by the user. The display for displaying the user interface may be different from the display for displaying the reconstructed image.

  The operator console 300 also controls the operation of the gantry 100 and the table 200. Under the control of the operator console 300, the gantry 100 scans under a predetermined scan condition, and the table 200 positions the subject 10 so that a predetermined part is scanned. Positioning is performed by controlling the height of the table top 202 and the horizontal movement distance of the cradle 204 on the table top 202 by a built-in position control mechanism.

 A helical scan can be performed by continuously performing a plurality of scans while continuously moving the cradle 204. A cluster scan can be performed by scanning each cradle 204 while intermittently moving the cradle 204.

  An axial scan can be performed by scanning with the cradle 204 stopped. A cine scan can be performed by continuously performing a plurality of scans while the cradle 204 is stopped.

  The height of the table top 202 is controlled by swinging the support column 206 around the attachment portion to the base 208. The table top 202 is displaced in the vertical direction and the horizontal direction by the swing of the column 206. The cradle 204 moves in the horizontal direction on the table top 202 to cancel the horizontal displacement of the table top 202. Depending on the scan conditions, the scan is performed with the gantry 100 tilted. The gantry 100 is tilted by a built-in tilt mechanism.

  The table 200 may be of a type in which the table top 202 moves up and down vertically with respect to the base 208 as shown in FIG. The table top 202 is raised and lowered by a built-in lifting mechanism. In this table 200, the horizontal movement of the table top 202 accompanying the raising and lowering does not occur.

  FIG. 3 schematically shows the configuration of the X-ray irradiation / detection device 110. The X-ray irradiation / detection device 110 detects an X-ray 134 emitted from the focal point 132 of the X-ray tube 130 with an X-ray detector 150.

  The X-ray 134 is shaped by a collimator (not shown) and is a symmetrical cone beam or fan beam X-ray. The X-ray detector 150 has an X-ray incident surface 152 that expands two-dimensionally corresponding to the spread of X-rays. The X-ray incident surface 152 is curved so as to constitute a part of a cylinder. The central axis of the cylinder passes through the focal point 132.

  The X-ray irradiation / detection device 110 rotates around a central axis passing through an imaging center, that is, an isocenter O. The central axis is parallel to the central axis of the partial cylinder formed by the X-ray detector 150.

  The direction of the center axis of rotation is the z direction, the direction connecting the isocenter O and the focal point 132 is the y direction, and the direction perpendicular to the z direction and the y direction is the x direction. These three axes in the x, y, and z directions are the three axes of the rotating coordinate system with the z axis as the central axis.

  FIG. 4 schematically shows a plan view of the X-ray incident surface 152 of the X-ray detector 150. The X-ray incident surface 152 has detection cells 154 arranged two-dimensionally in the x direction and the z direction. That is, the X-ray incident surface 152 is a two-dimensional array of detection cells 154. In the case of using fan beam X-rays, the X-ray incident surface 152 may be a one-dimensional array of detection cells 154.

  Each detection cell 154 constitutes a detection channel of the X-ray detector 150. As a result, the X-ray detector 150 becomes a multi-channel X-ray detector. The detection cell 154 includes, for example, a combination of a scintillator and a photodiode.

  FIG. 5 shows a speed profile for linear movement of the cradle 204 during helical scanning. As shown in FIG. 5, the velocity profile is represented by a diagram in a two-dimensional coordinate space. The vertical axis and the horizontal axis of the two-dimensional coordinate space are speed and time, respectively. In such a two-dimensional coordinate space, the speed profile represents a speed change during the imaging period from time t1 to time t6.

  The speed profile includes a stop (speed 0) state from time t1 to t2, an acceleration state from time t2 to t3, a constant speed maintenance state from time t3 to t4, a deceleration state from time t4 to t5, and from time t5. This represents a stop (speed 0) state up to t6.

 Hereinafter, the period from time t1 to t2 is referred to as a standby period T1, the period from time t2 to time t3 is referred to as an acceleration period, the period from time t3 to t4 is referred to as a constant speed period, and the period from time t4 to t5 is referred to as a deceleration period. The period from t5 to t6 is referred to as a stop period T2.

  The speed profile can be arbitrarily set or adjusted by the user. Setting or adjusting the speed profile is performed using a user interface. Accordingly, the standby period T1, the acceleration period, the constant speed period, the deceleration period, and the stop period T2 are set to desired values, and the acceleration characteristics during the acceleration period, the speed during the constant speed period, and the deceleration period are set. A speed profile in which the deceleration characteristics are set as desired can be obtained.

 The waiting period T1, for example, delays the time until the start of the cradle movement by an amount corresponding to a half rotation of the X-ray irradiation / detection device 110 in order to obtain an image at the imaging start position, and monitors the degree of staining of the contrast agent. The cradle movement is started at an appropriate timing. The waiting period T1 can be set from 0.

  The acceleration (deceleration) period and acceleration (deceleration) characteristics include, for example, taking a region of interest in a short time with high acceleration, imaging with a low acceleration and less body movement due to acceleration of the imaging region, It is set in consideration of reducing the patient's body movement and burden by the S-shaped acceleration (decrease) speed at which the acceleration at the start and end of acceleration becomes small.

  The stop period T2 is used, for example, to shorten the time until the next operation start as much as possible and restart imaging in a short time, or to lengthen the time until the next operation start to reduce the burden on the patient. The The stop period T2 can be set from 0.

  FIG. 6 shows an example of adjusting acceleration / deceleration characteristics. As shown in FIG. 6, the acceleration / deceleration characteristics are set so as to obtain desired acceleration / deceleration. Here, the acceleration / deceleration characteristics are S-shaped acceleration / deceleration. As a result, the acceleration changes continuously, and the acceleration at the start of acceleration (deceleration) and at the end of acceleration (deceleration) becomes zero, so that the patient's body movement and burden are reduced.

  FIG. 7 shows another example of acceleration / deceleration characteristic adjustment. As shown in FIG. 7, the acceleration / deceleration characteristics are set so as to achieve desired acceleration / deceleration. Here, the acceleration / deceleration characteristics are linear acceleration (deceleration) speeds. That is, the acceleration during the acceleration (deceleration) period is constant. Such acceleration / deceleration can be realized by simple control.

  FIG. 8 shows a flowchart of the operation of this apparatus. As shown in FIG. 8, in step 801, scout imaging is performed. Thereby, a fluoroscopic image of the subject 10 is obtained.

In step 802, localization is performed. For localization, a perspective image obtained by scout photography is used. Thereby, the photographing range is set.
In step 803, a speed profile is set. The speed profile is set by the user. The user sets a desired speed profile using the user interface.

  When setting the speed profile, the protocol (protocol) such as adaptation site and examination method, image quality, imaging time, priority for exposure dose, patient information such as weight and age, information obtained by scout imaging such as fat and built-in configuration, or An optimum speed profile is set in consideration of various input information such as information obtained from an electrocardiograph.

 The speed pull file may be automatically set by the operator console 300 based on input information. Alternatively, a plurality of speed profiles may be stored in a memory in advance, and an optimum one may be selected according to the input information. If the speed profile is stored corresponding to the imaging protocol, the optimum speed profile can be selected efficiently.

 In step 804, a helical scan is performed. The cradle feed at this time is performed based on the speed profile set as described above under the control of the operator console 300. Thereby, the helical scan including the acceleration / deceleration period of the table can be optimally performed. The operator console 300 is an example of a control unit in the present invention.

 In step 805, image reconstruction is performed. The image reconstruction is performed by the operator console 300 based on the data obtained by the helical scan.

It is a figure which shows the structure of the X-ray CT apparatus of an example of the best form for implementing this invention. It is a figure which shows the structure of the X-ray CT apparatus of an example of the best form for implementing this invention. It is a figure which shows the structure of a X-ray irradiation / detection apparatus. It is a figure which shows the structure of the X-ray entrance plane of an X-ray detector. It is a figure which shows a speed profile. It is a figure which shows a speed profile. It is a figure which shows a speed profile. It is a flowchart which shows operation | movement of the X-ray CT apparatus of an example of the best form for implementing this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10: Subject 100: Gantry 110: X-ray irradiation / detection apparatus 130: X-ray tube 132: Focus 134: X-ray 150: X-ray detector 152: X-ray incident surface 154: Detection cell 200: Table 202: Table top 204: Cradle 206: Prop 208: Base 300: Operator console 302: Display

Claims (10)

An X-ray CT apparatus that performs a helical scan including an acceleration / deceleration period of linear movement of a table on which a subject is placed, and reconstructs a tomogram based on the obtained data,
An X-ray CT apparatus comprising control means for controlling linear movement of the table based on a speed profile having variable characteristics. The X-ray CT apparatus according to claim 1, wherein at least one of the acceleration portion and the deceleration portion is linear in the velocity profile. The X-ray CT apparatus according to claim 1, wherein at least one of the acceleration portion and the deceleration portion is curved in the velocity profile. The X-ray CT apparatus according to claim 3, wherein the acceleration continuously changes in a curved portion of the velocity profile. The X-ray CT apparatus according to claim 4, wherein the continuous change in acceleration is a continuous change from 0 and a continuous change to 0. The X-ray CT apparatus according to claim 1, wherein the velocity profile includes a waiting period until acceleration starts. The X-ray CT apparatus according to claim 1, wherein the speed profile includes a stop period after completion of deceleration. The X-ray CT apparatus according to claim 1, wherein the control unit stores the velocity profile. The X-ray CT apparatus according to claim 8, wherein the stored velocity profile is a plurality of velocity profiles. The X-ray CT apparatus according to claim 9, wherein the plurality of velocity profiles respectively correspond to a plurality of imaging protocols.

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