JP4665055B2 - X-ray CT system - Google Patents

Description

  The present invention irradiates a subject with X-rays from a rotating anode X-ray tube, and detects the transmitted X-rays with a detector having a plurality of detector rows arranged in the body axis direction of the subject. Thus, the present invention relates to an X-ray CT apparatus that simultaneously reconstructs a plurality of tomographic images in the body axis direction of a subject.

  In general, a rotary anode X-ray tube is used as an X-ray irradiation source of an X-ray CT apparatus. The rotary anode X-ray tube mainly includes a filament that emits thermoelectrons and a focusing groove that is disposed around the filament and focuses the thermoelectrons emitted from the filament to form a focal point on the anode target. A focusing portion having a cathode, a target having an umbrella-like facing surface disposed opposite to the cathode, a rotating mechanism for supporting and rotating the target, and the rotating mechanism An anode part composed of a fixed part that rotatably supports the part, and an envelope that insulates and supports the cathode part and the anode part and seals them in a vacuum-tight manner.

  The rotary anode X-ray tube is configured to emit X-rays from the focal point on the target when a high voltage is applied between the cathode portion and the anode portion, and at this time, a large amount of heat is emitted from the anode portion. Therefore, it is used by being enclosed in an X-ray tube container (hereinafter abbreviated as a tube container). More specifically, in this tube container, the rotary anode X-ray tube is insulated and supported and immersed in insulating oil. This tube container is provided with an X-ray emission window in the vicinity of the target of the rotary anode X-ray tube, and a cable receptacle for introducing a high voltage in the vicinity of the cathode portion and the anode portion. The cathode side high voltage cable is connected to the cathode side cable receptacle, and a negative high voltage and a filament heating voltage for heating the filament are introduced. Also, the anode side cable receptacle is connected to the anode side high voltage cable, and a positive high voltage is introduced (in recent years, however, there is an anode grounding type in which the anode side cable receptacle is grounded). A stator for rotating the anode part is attached around the rotation mechanism part of the anode part.

  In the rotating anode X-ray tube, as described above, a high voltage (a few hundred kV) is applied between the cathode part and the anode part, and the thermoelectrons emitted from the cathode part filament are applied to the anode part target. X-rays are generated by collision. The filament has a structure in which a thin wire made of an electron emitting material such as tungsten is wound in a coil shape, and is heated to a high temperature by passing a filament heating current. The heated filament emits thermoelectrons in an amount corresponding to the temperature and is accelerated toward the anode as an electron beam by an electric field formed by a high voltage applied between the cathode and anode. . At this time, the electron beam is focused by the electric field formed by the focusing groove of the focusing electrode so as to be a focal point having a desired size on the target of the anode part.

  The flow of this electron beam is the X-ray tube current, and the high voltage applied between the cathode part and the anode part is the X-ray tube voltage. The dose of X-rays generated at the target increases as the values of the X-ray tube current and the X-ray tube voltage increase. The dose of X-rays also depends on the material of the target, and increases as the atomic number of the target material increases. However, since the generation efficiency of X-rays in the X-ray tube voltage region used for X-ray imaging is very low and less than 1%, most of the energy input by the electron beam colliding with the target focal point. Is converted into thermal energy. For this reason, the target of the anode part is rotated at a high speed by the rotation mechanism part in order to prevent local overheating of the focal point by the electron beam.

  In addition, as described above, the target has an umbrella-like facing surface, and X-rays generated at the target are inclined angles of the facing surface (more specifically, a surface orthogonal to the rotation axis of the target). In the direction corresponding to the target angle). Then, the X-ray transmitted through the X-ray emission window is irradiated to the subject. In addition, the shape of this target is disclosed by Unexamined-Japanese-Patent No. 2001-76657, for example (for example, refer patent document 1).

  By the way, this rotary anode X-ray tube is used in a multi-slice X-ray CT apparatus capable of reconstructing a plurality of tomographic images in the body axis direction of a subject. In this multi-slice X-ray CT apparatus, in order to reconstruct a plurality of tomographic images, in order to simultaneously collect transmitted X-ray doses corresponding to each of them, the body axis direction of the subject (hereinafter also referred to as the slice direction). ) Includes a detector having a plurality of detector rows, specifically, a multi-row detector or a flat detector.

  However, in such a detector, the difference in the position of each detector row in the slice direction with respect to the rotating anode X-ray tube is large, so as shown in FIG. 9, depending on the position of each detector row in the slice direction. Thus, a difference occurs in the apparent focal spot size, dose, and radiation quality of the X-rays irradiated thereto (hereinafter, these are referred to as changes in X-ray radiation quality sensitivity). In particular, in a recent multi-slice X-ray CT apparatus, the number of detector rows reaches an enormous number of 128 to 256. Accordingly, the position difference in the slice direction of each detector row is also very large. Therefore, there is a current situation where the sensitivity change of the X-ray quality cannot be ignored. Incidentally, in the conventional multi-slice X-ray CT apparatus, the number of detector rows is about 4 to 16, and the position difference in the slice direction of each detector row is not so large. The sensitivity change of the radiation quality could be ignored.

  On the other hand, recent multi-slice X-ray CT apparatuses are required to collect more accurate projection data in order to reconstruct a tomographic image with higher resolution. In order to realize this, it is necessary to irradiate the subject with X-rays having an accurate and uniform X-ray dose distribution and collect projection data by each detector array.

JP 2001-76657 A (paragraphs [0016]-[0019], FIGS. 1 and 2)

  However, as described above, the dose distribution of the X-rays emitted from the rotary anode X-ray tube is substantially uniform in the body width direction of the subject, but each detector row in the body axis direction. Since the distribution has a difference according to the position in the slice direction, specifically, the distribution has a gentle slope, the image quality of the tomographic image reconstructed based on the projection data detected by each detector row is There is a problem that the difference in the X-ray dose distribution resulting from the difference in the position of the detector row becomes non-uniform.

  The present invention has been made in view of the above circumstances, and an object thereof is a rotating anode X-ray tube generated by using a detector having a plurality of detector rows in the body axis direction of a subject. By reducing the difference in the dose distribution of the X-rays irradiated from each detector row of the detector, the difference in image quality of the tomographic images reconstructed based on the projection data from each detector row can be reduced. An object of the present invention is to provide an X-ray CT apparatus that can be suppressed.

  In order to solve the above-mentioned problem, the invention according to claim 1 is a detection in which an X-ray tube and a plurality of detector rows are arranged in the body axis direction of the subject to detect X-rays transmitted through the subject. An X-ray tube and the detector that rotates around the body axis of the subject and reconstructs a tomographic image of the subject based on the X-ray dose detected by the detector In the X-ray CT apparatus, the X-ray tube includes a cathode that emits an electron beam, and an inclined surface formed at a position facing the cathode, and the emitted electron beam collides with the inclined surface, thereby A disk-shaped target that emits X-rays in a direction corresponding to the inclination angle of the surface, and the inclined surface of the target is composed of a plurality of regions equally divided in the circumferential direction, and the inclination in the plurality of regions The angle is different from the adjacent areas, and the adjacent areas Boundary is an X-ray CT apparatus characterized by being smoothly connected.

  In order to solve the above-mentioned problem, the invention according to claim 2 is the X-ray CT apparatus according to claim 1, wherein the detector detects the X-ray dose for each of the plurality of detector rows. A period deriving unit for deriving a detection period until completion, and based on the derived detection period, the stator coil causes the disk-shaped target to be detected so that the detection period is an integral multiple of the target rotation period. And a rotation control unit that performs control for adjusting the number of rotations.

  In order to solve the above-mentioned problem, the invention described in claim 3 is the X-ray CT apparatus according to claim 2, wherein the period deriving means is configured to detect X-rays for each of the plurality of detector rows in the detector. And start / end detection means for detecting, as the detection cycle, the time from the start of dose detection to the end of dose detection.

  In order to solve the above-mentioned problems, the invention according to claim 4 is the X-ray CT apparatus according to claim 1 or 2, wherein the position detection means for detecting the rotational position of the target, and the cathode Based on the detected rotational position, the electron beam emission suppressing means that suppresses the emission of the electron beam from the cathode by generating a magnetic field in a direction that hinders the progress of the emitted electron beam. An electron beam that controls the adjustment of the timing of emitting the electron beam from the cathode by the electron beam emission suppressing means so that the boundary part of a plurality of regions is identified and the electron beam collides avoiding the boundary part And a release control means.

  In order to solve the above-mentioned problem, the invention described in claim 5 is the X-ray CT apparatus according to any one of claims 1 to 4, wherein a plurality of the inclined surfaces of the target are equally divided. The number and the inclination angle of the region are determined so that the region is a point object based on the rotation axis of the target.

  According to the X-ray CT apparatus according to the first aspect of the present invention, the inclined surface of the target that emits X-rays is composed of a plurality of regions equally divided in the circumferential direction, and the inclination angle in the plurality of regions is Since it has an angle different from the areas adjacent to each other, the irradiation direction of the X-rays emitted from the target can be switched over several times to reduce the difference in dose distribution. Therefore, in each detector array arranged in the body axis direction of the subject, the difference in the X-ray dose distribution is reduced, and a plurality of tomograms reconstructed based on the projection data from each detector array Differences in image quality can be suppressed. In addition, since the boundary portion between adjacent regions is smoothly connected, the X-ray dose distribution can be smoothly continued.

  Further, according to the X-ray CT apparatus according to claim 2 and claim 3 of the present invention, within the detection cycle until the detection of the X-ray dose for each of the plurality of detector rows is completed in the detector. Since the irradiation direction of the X-rays emitted from the target can be switched over a plurality of times, the difference in the X-ray dose distribution in each detector row can be reduced appropriately.

  According to the X-ray CT apparatus of the present invention, the rotational position of the target is detected to identify the boundary portions of the plurality of regions on the inclined surface of the target and emitted from the cathode. Since the timing can be adjusted so that the electron beam collides with avoiding the boundary portion, X-rays can be appropriately emitted from the target.

  According to the X-ray CT apparatus of the present invention, the number of the plurality of regions that equally divide the inclined surface of the target is a point object based on the rotation axis of the target. And the tilt angle are provided, the stability during rotation of the target can be ensured.

It is a block diagram showing the whole structure in one Embodiment of the X-ray CT apparatus concerning this invention. It is sectional drawing showing the whole structure of the rotating anode X-ray tube shown in FIG. It is explanatory drawing for demonstrating the detailed structure of the X-ray detector array shown in FIG. 4A is a side view showing the overall configuration of the target shown in FIG. 2, and FIG. 4B is a front view showing the overall configuration of the target shown in FIG. FIG. 5A shows that the difference in X-ray dose distribution irradiated to each detector row of the X-ray detector array is reduced by the targets shown in FIGS. 4A and 4B. FIG. 5B is an explanatory diagram for explanation, and FIG. 5B shows the X-ray dose irradiated to each detector row of the X-ray detector array by the target shown in FIGS. 4A and 4B. It is explanatory drawing for demonstrating that the difference of distribution is reduced. 4A and 4B are explanatory diagrams for explaining that a difference in dose distribution of X-rays irradiated to each detector row of the X-ray detector array is reduced by the targets shown in FIGS. is there. FIG. 2 is a block diagram showing a control configuration for performing control to adjust the rotation period of the target to 1 / integer of the data collection period of the X-ray detector array in the X-ray CT apparatus shown in FIG. 1. In the X-ray CT apparatus shown in FIG. 1, a control configuration for controlling the output of the thermoelectrons generated from the filament so that the thermoelectrons from the filament collide avoiding the boundary portions of the plurality of inclined surfaces of the target is shown. It is a block diagram. It is explanatory drawing for demonstrating that a difference arises in the dose distribution of the X-ray irradiated to each detector row | line | column which comprises a multi-row detector by the target of the rotary anode X-ray tube used for the conventional X-ray CT apparatus. is there.

  Hereinafter, an example of a preferred embodiment of an X-ray CT apparatus according to the present invention will be specifically described with reference to the drawings.

[X-ray CT system]
<Configuration of X-ray CT apparatus>
First, the overall configuration of the X-ray CT apparatus in the present embodiment will be described with reference to FIG. As shown in FIG. 1, the X-ray CT apparatus mainly includes a scanning gantry 10 that performs an axial / heric scan of a subject P using X-rays that spread in a fan shape in the body width direction of the subject P, and a subject P. And an operation console 40 for the user to perform these operations.

  The scanning gantry 10 includes a rotary anode X-ray tube 11, an X-ray control unit 12 that controls the tube voltage, tube current, exposure time, and the like of the rotary anode X-ray tube 11, the X-ray body width direction and the body axis. A collimator 13 that limits the exposure range in the direction, a collimator controller 14 that controls the position of the collimator 13, and an X-ray detector array 16 that is a multi-row detector in which a number of X-ray detection elements are arranged in a matrix. And a data collection unit (DAS) 17 that collects detection data of the X-ray detector array 16, that is, projection data, and a rotation mechanism unit 15 that rotates these around the body axis of the subject P. Has been.

  As shown in FIG. 2, the X-ray detector array 16 has a configuration in which a large number of X-ray detection elements are arranged in a matrix in the body axis direction and the body width direction of the subject P, and are arranged in the slice direction. Projection data is collected for each detected detector row.

  The operation console 40 includes a central processing unit 41 (the CPU 41a and a main memory (MEM) 41b used by the CPU 41a) that performs main control processing (scan control, tomographic image reconstruction processing, etc.) of the X-ray CT apparatus. ), An input device 42 composed of a keyboard, a mass screen, etc., imaging parameters for imaging planning (tube voltage, tube current, scanning time, slice thickness in the subject body axis direction, etc.), tomographic images of imaging results, etc. A display device (CRT) 43, a control interface 44 for exchanging various control signals and monitor signals between the CPU 41 a, the scanning gantry 10 and the imaging table 19, and projection data from the data collection unit 17 are accumulated. Data collection buffer 45 and various data and application programs necessary for the operation of the X-ray CT apparatus That a secondary storage device (disk) 46 is constituted comprising a common bus 47 of the CPU 41a, the.

  In this configuration, the X-ray imaging operation performed in the X-ray CT apparatus will be described. The X-rays irradiated from the rotary anode X-ray tube 11 pass through the subject P and the X-ray detector array 16. Are simultaneously incident on each detector row. The data collection unit 17 collects projection data of the subject P from each detector row of the X-ray detector array 16 (at this time, scanning for sequentially collecting projection data is performed in each detector row arranged in the slice direction). And stored in the data collection buffer 45. Further, at the position where the scanning gantry 10 is slightly rotated, the above-described imaging is performed again, and the projection data is collected and accumulated. Thereafter, similarly, the projection data for one rotation of the scanning gantry 10 is collected and accumulated, and the imaging table 19 is moved intermittently / continuously in the body axis direction of the subject P according to the Axial / Hericl scan method. All projection data for the required imaging region of the subject P is collected and accumulated. Then, the CPU 41 a reconstructs a plurality of CT tomographic images of the subject P based on the obtained all projection data, and displays them on the display device 43.

<Configuration of rotating anode X-ray tube>
Next, the overall configuration of the rotary anode X-ray tube 11 shown in FIG. 1 will be described with reference to FIG. As shown in FIG. 3, the rotary anode X-ray tube 11 includes an envelope 61 that keeps the inside of the tube in a vacuum, a filament 62 that generates thermoelectrons, and a focused thermoelectron generated from the filament 62. A focusing electrode 63, a cathode sleeve 64 that supports the filament 62 and the focusing electrode 63, an umbrella-shaped tungsten disk or the like, and a target 65 that generates X-rays when thermoelectrons collide with the target 65 and rotate the target 65. The rotary anode 67 is supported, a bearing 68 that pivotally supports the rotary anode 67, and an anode shaft 69 that supports the anode side of the rotary anode X-ray tube 11. The rotating anode 67 rotates at a high speed by a magnetic field (rotating magnetic field or the like) applied from a stator coil (not shown) provided around the envelope 61. Further, the inclination angle of the umbrella-shaped portion of the target 65 is set such that X-rays emitted from the target 65 are incident on the detector rows of the X-ray detector array 16 all at once. Further, since a large amount of heat is generated from the rotary anode X-ray tube 11, the periphery of the rotary anode X-ray tube 11 is covered with a housing 70 made of aluminum or the like, and cooling oil is circulated from outside to rotate the rotary anode X-ray tube 11. The forced cooling is performed.

  In such a configuration, the thermoelectrons generated in the filament 62 are accelerated by a high voltage applied between the cathode sleeve 64 and the rotary anode 67, and are focused by the focusing electrode 63 as an electron beam, and on the target 65. Collide with a small focal point 66. Thereby, X-rays are generated at the focal point 66 of the target 65. In general, the conversion efficiency of thermoelectrons to X-rays is as low as 1% or less. Therefore, most of the energy is converted into heat, and high heat is generated at the focal point 66. Therefore, the rotary anode 67 (target 65) is attached to the anode shaft 69. Is rotated at a high speed (about 130 to 160 Hz) to increase the effective area of the focal point 66 to obtain a required X-ray output and to prevent overheating leading to failure or breakage of the X-ray tube 11. Is called.

<Target configuration>
Here, the overall configuration of the target 65 of the rotary anode X-ray tube 11 which is a characteristic part of the present invention will be described with reference to FIGS. 4 (A) and 4 (B). As shown in FIGS. 4 (A) and 4 (B), the target 65 has an inclined surface divided into a plurality of regions in the circumferential direction, for example, at an angle of rotation of 90 degrees. It has a plurality of inclined surfaces in which corners (hereinafter referred to as target angles) are alternately switched between 6 degrees and 10 degrees. That is, every time the target 65 is rotated 90 degrees by the rotating magnetic field from the stator coil, the target angle is switched between 6 degrees and 10 degrees, and the X-rays generated from the target 65 correspond to the target angle. In this configuration, each detector row in the slice direction of the X-ray detector array 16 is irradiated so as to have a uniform dose distribution. Incidentally, the boundary portions of the inclined surfaces adjacent to each other of the target 65 are smoothly connected to prevent the energy of the thermal electrons from being extremely lost by the edges.

  The number of the plurality of inclined surfaces of the target 65 and the target angle are determined so that the rotational center of gravity of the target 65 is positioned on the rotation axis of the target 65 in consideration of the stability when the target 65 rotates. In addition, it is provided as much as possible as a point object with the rotation axis of the target 65 as a reference. Specifically, the number of the plurality of inclined surfaces is preferably determined to be 4 or 8, and the target angles are preferably alternately repeated by the same number of different angles. Here, the target angle is determined according to the distance between the target 65 and the X-ray detector array 16 and the incident angle of the thermoelectrons from the filament 62 that collides with the target 64. In view of the fact that the target angle of the target of the multi-slice X-ray CT apparatus is generally 7 degrees or 9 degrees, in order to switch the X-ray irradiation direction within the range covering this, the angle is 6 degrees and 10 degrees. Alternatively, it is preferably determined to be an angle in the vicinity thereof.

  With such a configuration, the X-rays emitted from the target 65 are irradiated in directions corresponding to a target angle of 6 degrees and a target angle of 10 degrees, as shown in FIGS. 5 (A) and 5 (B). Then, each detector row in the slice direction of the X-ray detector array 16 is irradiated, and the dose distribution obtained by adding up these doses is the conventional case as shown in FIG. 6 (see FIG. 9). And the difference is reduced (however, the X-rays irradiated from the target 65 have a target angle of 6 degrees and a target angle of 10 degrees for one rotation of the target 65). Since the irradiation is repeated twice with the irradiation direction corresponding to, the total dose is shown in FIGS. 6 (A) and 6 (B). Note that, as described later, the X-ray irradiated from the target 65 has a rotation period of the target 65 that is the data collection period of the X-ray detector array 16 (until a series of data collection in each detector row is completed. The period is adjusted to 1 / integer, and the irradiation is repeated by the integer number of times, and the dose is an integral multiple of the values shown in FIGS. 6 (A) and 6 (B). It becomes. With this, the dose is equivalent to the conventional case shown in FIG.

  Accordingly, by switching the irradiation direction of the X-rays emitted from the target 65 a plurality of times in this way, the difference in dose distribution is reduced in each detector row in the slice direction of the X-ray detector array 16. Therefore, it is possible to suppress a difference in image quality between tomographic images reconstructed based on the projection data detected by each detector row.

  In the X-ray CT apparatus, the rotation period of the target 65 is the data collection period of the X-ray detector array 16 (the period until a series of data collection in each detector row is completed) and the target. In order to prevent non-uniformity in the distribution of the dose of X-rays irradiated to each detector row within the data acquisition period of the X-ray detector array 16 due to the difference in the rotation period of 65, X-ray detection It is assumed that control is performed so as to adjust to 1 / integer of the data collection period of the array 16. That is, the rotation period of the target 65 is set so that the irradiation direction of the X-rays irradiated to each detector row is repeated within the data collection period of the X-ray detector array 16 and is switched just an integer number of times. Control is performed to adjust the data collection period of the array 16 to 1 / integer.

  FIG. 7 is a block diagram showing a control configuration for controlling the rotation period of the target 65 to be an integral number of the data collection period of the X-ray detector array 16. As shown in FIG. 7, a position detector 110 such as a rotary encoder that detects the rotation position is provided on the rotation shaft of the target 65. In addition, the X-ray detector array 16 has a synchronization signal (for synchronizing the data collection period and a period obtained by multiplying the rotation period of the target 65 by an integer) in accordance with the data collection period of the X-ray detector array 16. A synchronization signal generator 120 is provided that generates a signal for notifying when data collection is started and when data collection is completed in each detector row of the X-ray detector array 16. In such a configuration, the rotation control unit 130 (which may be configured by the X-ray control unit 12 described above) and a position signal related to the rotation position of the target 65 output from the position detector 110 and the synchronization signal generator 120. The data collection period of the X-ray detector array 16 is calculated on the basis of the synchronization signal generated from (specifically, the synchronization signal for notifying when the data collection is started and the time when the data collection is completed) Is generated by the stator coil so as to adjust the rotation speed of the target 65 so that the rotation period of the target 65 becomes an integral number of the data collection period. Control the strength of the rotating magnetic field.

  As a result, the irradiation direction of the X-rays irradiated from the target 65 is repeatedly switched by an integer number of times within the data acquisition period of the X-ray detector array 16, and therefore within the data acquisition period of the X-ray detector array 16. It is possible to prevent non-uniformity in the distribution of the X-ray dose irradiated to each detector row in FIG.

  Further, in the X-ray CT apparatus, as described above, the thermal electrons from the filament 62 collide with the boundary portions of the plurality of inclined surfaces of the target 65, and the generated X-ray dose is nonuniform. In order to prevent this, the rotation control unit 130 controls the output of the thermoelectrons generated from the filament 62 so that the thermoelectrons from the filament 62 collide with each other while avoiding the boundary portions of the plurality of inclined surfaces of the target 65. I will do it.

  FIG. 8 is a block diagram showing a control configuration for performing output control of the thermoelectrons generated from the filament 62. As shown in FIG. 8, a position detector 110 such as a rotary encoder for detecting the rotation position is provided on the rotation shaft of the target 65. The X-ray detector array 16 includes a synchronization signal for synchronizing the rotation period of the target 65 according to the data acquisition period of the X-ray detector array 16 (each detector row of the X-ray detector array 16). A synchronization signal generator 120 is provided which generates a signal for notifying when data collection is started and when data collection is completed. Furthermore, a grid 71 is provided on the front surface of the filament 62 and generates a magnetic field in a direction to block the thermoelectrons emitted from the filament 62 when a negative bias voltage is applied thereto. There is provided a grid control device 140 that controls the emission of thermoelectrons (control of the timing of emitting thermoelectrons) by applying the negative bias voltage described above at the timing. In such a configuration, the rotation control unit 130 (which may be configured by the X-ray control unit 12 described above) and a position signal related to the rotation position of the target 65 output from the position detector 110 and the synchronization signal generator 120. The data collection period of the X-ray detector array 16 is calculated on the basis of the synchronization signal generated from (specifically, the synchronization signal for notifying when the data collection is started and the time when the data collection is completed) Is generated by the stator coil so as to adjust the rotation speed of the target 65 so that the rotation period of the target 65 becomes an integral number of the data collection period. Control the strength of the rotating magnetic field. Further, the grid control device 140 specifies the positions of the boundary portions of the plurality of inclined surfaces of the target 65 based on the position signal regarding the rotational position of the target 65 output from the position detector 110 (that is, the rotational position of the target 65). And the positions of the boundary portions of the plurality of inclined surfaces are associated with each other in advance) so that the thermoelectrons from the filament 62 collide with each other so as to avoid the boundary positions. The timing of thermionic emission from the filament 62 is adjusted by applying the negative bias voltage described above, and at the same time, the data of the X-ray detector array 16 is based on the synchronization signal generated from the synchronization signal generator 120. In order to irradiate X-rays from the target 65 only within the collection period, the grid 71 is described above at a predetermined timing. Thermionic performs control to adjust the timing emitted from the filament 62 by applying a negative bias voltage.

  Note that the X-ray CT apparatus in the present embodiment described above exemplifies a preferred embodiment of the present invention, and does not exclude other embodiments.

  For example, in the X-ray CT apparatus according to the present embodiment, the number of the plurality of inclined surfaces of the target 65 is four and the target angles are alternately switched between 6 degrees and 10 degrees. As described above, in consideration of the stability during rotation of the target 65, if the rotational center of gravity of the target 65 is positioned on the rotation axis of the target 65, the target 65 should be provided as a point target based on the rotation axis of the target 65. As long as this condition is satisfied, other numbers and angles may be set. The target angle is determined according to the distance between the target 65 and the X-ray detector array 16 and the incident angle of the thermoelectrons from the filament 62 that collides with the target 64, and is a range corresponding to this condition. Other angles may be set within the range.

  In the X-ray CT apparatus according to the present embodiment, the X-ray detector array 16 in which a plurality of detector arrays are arranged in an array is described as an example of the X-ray detector. A planar detector in which a plurality of detector rows are formed by dividing the detection elements arranged in a matrix may be used.

DESCRIPTION OF SYMBOLS 10 Scanning gantry 11 Rotating anode X-ray tube 12 X-ray control part 13 Collimator 14 Collimator control part 15 Rotation mechanism part 16 X-ray detector array 17 Data acquisition part (DAS) 19 Imaging table 40 Operation console 41 Central processing unit 41a CPU
41b Main memory (MEM) 42 Input device 43 Display device (CRT)
44 Control interface 45 Data collection buffer 46 Secondary storage device (disk etc.) 47 Common bus
61 Envelope 62 Filament 63 Focusing electrode 64 Cathode sleeve 65 Target 66 Focus 67 Rotating anode 68 Bearing 69 Anode shaft 70 Housing 71 Grid 110 Position detector 120 Synchronization signal generator 130 Rotation controller 140 Grid controller P Subject

Claims (5)

An X-ray tube, and a detector configured by arranging a plurality of detector rows in the body axis direction of the subject and detecting X-rays transmitted through the subject, the X-ray tube and the detector being the subject In an X-ray CT apparatus for reconstructing a tomographic image of the subject based on the X-ray dose detected by the detector while rotating around the body axis of
The X-ray tube is
A cathode that emits an electron beam;
An inclined surface is formed at a position facing the cathode, and the emitted electron beam collides with the inclined surface, whereby a disk-shaped target that emits X-rays in a direction according to the inclination angle of the inclined surface; With
The inclined surface of the target is composed of a plurality of regions equally divided in the circumferential direction, and the inclination angles in the plurality of regions are different from regions adjacent to each other,
An X-ray CT apparatus characterized in that a boundary portion between the adjacent regions is smoothly connected. A period deriving means for deriving a detection period until the detection of the X-ray dose for each of the plurality of detector rows is completed in the detector;
A rotation control unit that performs control to adjust the number of rotations of the disk-shaped target so that the detection period is an integer multiple of the rotation period of the target based on the derived detection period; The X-ray CT apparatus according to claim 1, wherein:   The period deriving means includes a start / end detection means for detecting, as the detection period, a time from when the detection of the X-ray dose for each of the plurality of detector rows is started to the end time at the detector. The X-ray CT apparatus according to claim 2, wherein: Position detecting means for detecting the rotational position of the target;
An electron beam emission suppressing means for suppressing the emission of the electron beam from the cathode by generating a magnetic field in a direction that obstructs the progress of the electron beam emitted from the cathode;
Based on the detected rotational position, a boundary portion of the plurality of regions is specified, and the electron beam is suppressed from the cathode by the electron beam emission suppression means so that the electron beam collides avoiding the boundary portion. The X-ray CT apparatus according to claim 1, further comprising: an electron beam emission control unit that performs control for adjusting the emission timing.   The number and the inclination angle of the plurality of regions equally dividing the inclined surface of the target are provided so as to be point-symmetric with respect to the rotation axis of the target. The X-ray CT apparatus according to any one of 4.

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