JP2008142389A - X-ray ct system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an X-ray CT system which effectively carries out fluoroscopy for biopsy along with effective scout scanning for scanning plan. <P>SOLUTION: The X-ray CT system has a photographing part which reconstructs images based on projection data acquired by scanning a subject with X rays and a control part which controls the operation involved. The control part alters X-ray energy per scanning during the operation of plural times of continuous scanning pertaining to the same site. The control part works to form a differential image between tomographic images with the X-ray energies different from each other. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an X-ray CT (Computed Tomography) apparatus, and in particular, an imaging unit that performs image reconstruction based on projection data (data) obtained by scanning a subject with X-rays and controls the imaging unit. The present invention relates to an X-ray CT apparatus having a control unit.

In the X-ray CT apparatus, a subject is scanned with X-rays, and an image is reconstructed based on the obtained projection data. Fluoroscopy is performed using an X-ray CT apparatus that is accelerated in scanning and image reconstruction. Fluoroscopy is used to perform biopsy of a subject while monitoring real time tomograms. (For example, refer to Patent Document 1).
JP-A-10-118057

  Since a metal puncture needle is used for biopsy, the fluoroscopy image has many metal artifacts. For this reason, it is difficult for the surgeon to correctly grasp the tip position of the puncture needle.

  Therefore, an object of the present invention is to realize an X-ray CT apparatus capable of effectively performing fluoroscopy for biopsy. Another object of the present invention is to realize an X-ray CT apparatus capable of performing effective scout scanning for scan planning.

  An invention for solving the problem is an X-ray CT apparatus having an imaging unit that performs image reconstruction based on projection data obtained by scanning a subject with X-rays and a control unit that controls the imaging unit. The control unit is an X-ray CT apparatus that changes X-ray energy for each scan while performing a plurality of continuous scans for the same part.

The scan is preferably an axial scan from the viewpoint of performing fluoroscopy.
Regarding the same part, it is preferable to reconstruct a tomographic image based on projection data obtained by an axial scan that is repeatedly performed a plurality of times in terms of obtaining tomographic images having different X-ray energies.

It is preferable to form a difference image between the tomographic images having different X-ray energies from the viewpoint of obtaining a tomographic image related to a specific substance.
The scan is preferably a scout scan from the viewpoint of facilitating scan planning.

It is preferable to reconstruct a fluoroscopic image based on the projection data obtained by the scout scan from the viewpoint of obtaining fluoroscopic images having different X-ray energies.
It is preferable to form a difference image between the fluoroscopic images having different X-ray energies from the viewpoint of obtaining a fluoroscopic image relating to the specific substance.

  According to the present invention, the X-ray CT apparatus includes an imaging unit that performs image reconstruction based on projection data obtained by scanning a subject with X-rays, and a control unit that controls the imaging unit. Since the X-ray energy is changed for each scan during the execution of a plurality of continuous scans for the same part, an X-ray CT apparatus capable of effectively performing biopsy fluoroscopy can be realized. Further, it is possible to realize an X-ray CT apparatus that can perform an effective scout scan for scan planning.

  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 projection data of a plurality of views, and inputs it to the operator console 300.

  The operator console 300 performs image reconstruction based on the projection data input from the gantry 100 and displays the reconstructed image on a display 302. Image reconstruction is performed by a dedicated computer in the operator 300. The computer for image reconstruction, the gantry 100, and the table 200 are examples of the photographing unit in the present invention.

  The operator console 300 also controls the operation of the gantry 100 and the table 200. Control is performed by a dedicated computer in the operator 300. This computer is an example of a control unit in the present invention. The control unit also controls image reconstruction.

  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 adjusting the height of the top plate 202 and the horizontal movement distance of the cradle 204 on the top plate by a built-in position adjustment mechanism.

  An axial scan can be performed by scanning with the cradle 204 stopped. A cine scan can be performed by repeatedly performing an axial scan a plurality of times. Fluoroscopy is performed by using a cine scan to obtain a plurality of tomographic images of the same portion that are continuous in time.

 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. By continuously moving the cradle 204 with the rotation of the X-ray irradiation / detection device 110 stopped, a scout scan can be performed.

  The height adjustment of the top plate 202 is performed by swinging the support column 206 around the attachment portion to the base 208. The top plate 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 top plate 202 to cancel the horizontal displacement of the top plate 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.

  As shown in FIG. 2, the table 200 may be of a type in which the top plate 202 moves up and down vertically with respect to the base 208. The top plate 202 is moved up and down by a built-in lifting mechanism. In this table 200, the horizontal movement of the top plate 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 becomes a 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 x, y, and z axes are three axes in a 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. As a result, the X-ray detector 150 becomes a multi-channel X-ray detector. The detection cell 154 is configured by, for example, a combination of a scintillator and a photodiode.

  FIG. 5 shows a block diagram of the tube voltage supply system of the X-ray tube 130. As shown in FIG. 5, the X-ray tube 130 is supplied with a tube voltage from a high voltage generator 140. The high voltage generator 140 includes a high voltage inverter & insulation unit 142 and a tube voltage control unit 144.

 The high voltage inverter & insulation unit 142 applies a high voltage to the X-ray tube 130 under the control of the tube voltage control unit 144. Tube voltage control by the tube voltage control unit 144 is performed by feedback control. The tube voltage control unit 144 is constituted by, for example, firmware.

 Tube voltage control by the tube voltage control unit 144 is performed based on control information given from the operator console 300. Control information is determined by a system software scan plan.

  FIG. 6 shows a flowchart of the operation of the present apparatus. This operation is performed under the control of the operator console 300. As shown in FIG. 6, in step 601 a scout scan is performed. Scout scanning is performed by continuously moving the cradle 204 while irradiating X-rays while the rotation of the X-ray irradiation / detection device 110 is stopped.

 The cradle 204 moves in a reciprocating manner, and the X-ray energy is different between forward and backward. The same reciprocating operation may be repeated twice. The X-ray energy is changed by changing the tube voltage of the X-ray tube 130.

 For example, as shown in FIG. 7, the tube voltage is changed in two stages of Low kV and High kV. Scan 1 is performed at low kV, and scan 2 is performed at high kV. Low kV is, for example, 80 kV, and High kV is, for example, 140 kV. As a result, a dual energy scout scan is performed. Note that the tube voltage change may be performed in a plurality of stages of three or more stages. Hereinafter, an example of two stages will be described, but the same applies to three or more stages.

 Each of the perspective images is reconstructed from two types of projection data obtained by the dual energy scout scan. As a result, two types of fluoroscopic images having different X-ray energies are obtained.

 For two types of fluoroscopic images, a difference image is obtained. As a result, a fluoroscopic image depicting a specific substance is obtained. The substance to be drawn is determined according to the combination of Low kV and High kV values. Such substances are, for example, fat, iron (Fe), calcium (Ca) and the like.

 In this way, two types of fluoroscopic images having different X-ray energies and a fluoroscopic image showing the distribution of the specific substance are obtained. In addition, when such a fluoroscopic image is not required, a single energy scout scan with a single tube voltage may be performed.

 In step 602, localization is performed. Localization is performed by the operator through the operator console 300. Thereby, for example, a slice position a as shown in FIG. 8 is set.

 The dual energy scout scan provides two types of fluoroscopic images with different X-ray energies and a fluoroscopic image showing the distribution of specific substances, so localization is more abundant than the fluoroscopic images obtained by a single energy scout scan. Can be done on the basis. Thus, effective localization can be performed.

In step 603, fluoroscopy is performed. Fluoroscopy is also performed with dual energy. That is, fluoroscopy is performed by changing the tube voltage in two stages.
FIG. 9 shows an example of a scan for fluoroscopy and a tube voltage pattern. As shown in FIG. 9 (a), fluoroscopy is performed by repeating two successive scans 1 and 2. That is, a cine scan in which scans 1 and 2 are paired is performed.

 Scans 1 and 2 are both half scans. The rotation angle of the half scan is 180 degrees + γ. γ is a fan angle of the X-ray beam 134. There is an inter scan delay ISD between which the two scans are not irradiated with X-rays. ISD is the time required for the rotation angle to change by 360 ° − (180 ° + γ).

 As shown in FIG. 9B, scan 1 is performed at low kV and scan 2 is performed at high kV. Low kV is, for example, 80 kV, and High kV is, for example, 140 kV. Note that the tube voltage change may be performed in a plurality of stages of three or more stages. Hereinafter, an example of two stages will be described, but the same applies to three or more stages.

 FIG. 10 shows another example of a scan for fluoroscopy and a tube voltage pattern. As shown in FIG. 10A, the fluoroscopy is performed by repeating two consecutive scans 1 and 2. That is, a cine scan in which scans 1 and 2 are paired is performed.

 Scans 1 and 2 are both half scans. There is no interscan delay between the two scans, and there is only a transition period for switching the tube voltage. As shown in FIG. 10B, scan 1 is performed at low kV and scan 2 is performed at high kV. Low kV is, for example, 80 kV, and High kV is, for example, 140 kV.

 A tomogram is reconstructed from each of two types of projection data obtained by the dual energy cine scan. Thereby, two types of tomographic images having different X-ray energies are obtained.

 A difference image is obtained for these two types of tomographic images. As a result, a tomographic image depicting a specific substance is obtained. The substance to be drawn is determined according to the combination of Low kV and High kV values. Such substances are, for example, fat, iron (Fe), calcium (Ca) and the like.

 When biopsy is performed, it is a combination of Low kV and High kV that can depict iron. Thereby, a tomographic image in which the puncture needle is depicted is obtained. This tomographic image is superimposed on one of the two types of tomographic images before the difference. Thereby, a fluoroscopic image with a clear position of the puncture needle is obtained. Alternatively, an image close to that can be obtained by alternately displaying two types of tomographic images before the difference. Using such a fluoroscopic image, an operator can perform biopsy accurately and easily.

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 block diagram which shows a tube voltage supply system. 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. It is a time chart of the tube voltage at the time of a scout scan. It is a figure which shows an example of localization. It is a figure which shows an example of the scan for fluoroscopy, and a tube voltage pattern. It is a figure which shows an example of the scan for fluoroscopy, and a tube voltage pattern.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10: Subject 100: Gantry 110: X-ray irradiation and 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: Top plate 204: Cradle 206: Supporting column 208: Base 300: Operator console 302: Display 140: High voltage generator 142: High voltage inverter & insulation unit 144: Tube voltage control unit

Claims (7)

An X-ray CT apparatus having an imaging unit that performs image reconstruction based on projection data obtained by scanning a subject with X-rays and a control unit that controls the imaging unit,
The controller is
An X-ray CT apparatus, wherein X-ray energy is changed for each scan while performing a plurality of continuous scans for the same part. The X-ray CT apparatus according to claim 1, wherein the scan is an axial scan. The controller is
The X-ray CT apparatus according to claim 2, wherein a tomographic image is reconstructed based on projection data obtained by an axial scan repeatedly performed a plurality of times for the same part. The controller is
The X-ray CT apparatus according to claim 3, wherein a difference image between the tomograms having different X-ray energies is formed. The X-ray CT apparatus according to claim 1, wherein the scan is a scout scan. The controller is
The X-ray CT apparatus according to claim 5, wherein a fluoroscopic image is reconstructed based on projection data obtained by the scout scan. The controller is
The X-ray CT apparatus according to claim 6, wherein a difference image between the fluoroscopic images having different X-ray energies is formed.

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