Patent Publication Number: US-11380510-B2

Title: X-ray tube and a controller thereof

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an X-ray tube and a controller thereof. 
     Description of Related Art 
     Conventional X-ray tubes generally use a filament as a cathode and, in this case, use thermoelectrons extracted from the filament as an electron source. An electron beam emitted from the electron source passes through a target disposed on the surface (hereinafter, referred to as “anode surface”) of an anode that faces the cathode and then passes through the anode to be absorbed by a power supply. Hereinafter, an area in the anode surface with which the electron beam collides is referred to as “focal point area”. 
     There is known a technology that moves the focal point area on the anode surface by controlling the trajectory of an electron beam emitted from an electron source. Examples of such a technology are disclosed in, for example, U.S. Pat. Nos. 6,292,538, 7,257,194, 8,588,372, and U.S. Patent Application Publication No. 2012/0128122. Being capable of moving the focal point area on the anode surface means being capable of moving a heating point on the anode surface, which, for example, can raise the upper limit of power supply to a fixed anode type X-ray tube. Further, in an X-ray tube for X-ray CT, photographing resolution can be increased by moving the focal point area (Flying Focus) (see Proceedings of SPIE, Volume 7622 (1), Apr. 1, 2010, A super resolution technique for clinical multi slice CT (Xin Liu, et al.)). 
     SUMMARY 
     However, conventional focal point area moving technology involves on/off control of thermoelectrons at high voltages and beam control using an electromagnetic field, thus disadvantageously complicating the structure of an X-ray tube. 
     The object of the present invention is to provide a cathode structure and a focusing structure of a cold cathode X-ray tube for avoiding the above problem and a drive method therefor and to achieve focal point area movement in the X-ray tube with a simple structure. 
     An X-ray tube according to the present invention includes: an electron emission part including an electron emission element using a cold cathode; an anode part having an anode surface with which an electron emitted from the electron emission part collides; and a focusing structure disposed between the electron emission part and a target part disposed on the anode surface. The focusing structure has a plurality of focal point areas that are applied with a voltage in a mutually independent manner. The electron emission part has first and second electron beam emission areas that are on/off controlled in a mutually independent manner. The X-ray tube is designed in such a way that a collision area of the electron beam emitted from each of the first and second electron beam emission areas on the anode surface moves in response to a voltage applied to the focusing structure. 
     An X-ray tube controller according to a first aspect of the present invention is a controller for an X-ray tube, wherein the X-ray tube including an electron emission part including an electron emission element using a cold cathode; an anode part having an anode surface with which an electron emitted from the electron emission part collides; and a focusing structure disposed between the electron emission part and a target part disposed on the anode surface, the focusing structure having a plurality of focusing areas that are applied with a voltage in a mutually independent manner, the electron emission part having first and second electron beam emission areas that are on/off controlled in a mutually independent manner, and the X-ray tube being designed in such a way that a collision area of the electron beam emitted from each of the first and second electron beam emission areas on the anode surface moves in response to a voltage applied to each of the plurality of focusing areas. The controller alternately turns on/off the first and second electron beam emission areas in sync with the voltage applied to each of the plurality of focusing areas. 
     An X-ray tube controller according to a second aspect of the present invention is a controller for an X-ray tube, wherein the X-ray tube including an electron emission part including an electron emission element using a cold cathode; an anode part having an anode surface with which an electron emitted from the electron emission part collides; and a focusing structure disposed between the electron emission part and a target part disposed on the anode surface, the focusing structure having two focusing areas that are applied with a voltage in a mutually independent manner, the electron emission part having first and second electron beam emission areas that are on/off controlled in a mutually independent manner, and the X-ray tube being designed in such a way that a collision area of the electron beam emitted from each of the first and second electron beam emission areas on the anode surface is moves in response to a voltage applied to each of the two focusing areas. The controller alternately applies a voltage to the two focusing areas during driving of the electron emission part to move the collision area. 
     An X-ray tube controller according to a third aspect of the present invention is a controller for an X-ray tube, the X-ray tube including an electron emission part including an electron emission element using a cold cathode; an anode part having an anode surface with which an electron emitted from the electron emission part collides; and a focusing structure disposed between the electron emission part and a target part disposed on the anode surface, the focusing structure having a plurality of focusing areas that are applied with a voltage in a mutually independent manner, the electron emission part having first and second electron beam emission areas that are on/off controlled in a mutually independent manner, and the X-ray tube being designed in such a way that a collision area of the electron beam emitted from each of the first and second electron beam emission areas on the anode surface is moves in response to a voltage applied to each of the plurality of focusing areas. The controller changes stepwise a voltage to be applied to the each of the plurality of focusing areas during driving of the electron emission part to dynamically move the collision area. 
     An X-ray tube controller according to a fourth aspect of the present invention is a controller for an X-ray tube, the X-ray tube including a plurality of electron emission parts each including an electron emission element using a cold cathode; an anode part having an anode surface with which an electron emitted from each of the plurality of electron emission parts collides; and a plurality of focusing structures each disposed between each of the plurality of electron emission parts and a target part disposed on the anode surface, the plurality of focusing structures each having a plurality of focusing areas that are applied with a voltage in a mutually independent manner, the plurality of electron emission parts each having first and second electron beam emission areas that are on/off controlled in a mutually independent manner, and the X-ray tube being designed in such a way that a collision area of the electron beam emitted from each of the first and second electron beam emission areas belonging to each of the plurality of electronic emission parts on the anode surface moves in response to a voltage applied to each of the plurality of corresponding focusing areas. The controller sequentially controls the plurality of electron beam emission parts to sequentially emit an X-ray from a plurality of different areas on the anode surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above features and advantages of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which: 
         FIG. 1A  is a schematic cross-sectional view of an X-ray tube  1  according to the first embodiment of the present invention; 
         FIG. 1B  is a schematic cross-sectional view of the electron emission part  10  shown in  FIG. 1A ; 
         FIG. 2  is a view schematically illustrating the configuration of a part of the X-ray tube  1  shown in  FIG. 1A  between the electron emission part  10  and the anode surface  11   a;    
         FIG. 3  is a view illustrating changes in the position and shape of the focal point area FS when the voltages VfL and VfR shown in  FIG. 2  are changed; 
         FIG. 4  is a view illustrating the relationship between the voltage VfR shown in  FIG. 2  and the beam centroid position; 
         FIG. 5  is a view schematically illustrating the configuration of a part of the X-ray tube  1  according to the second embodiment of the present invention between the electron emission part  10  and the anode surface  11   a;    
         FIG. 6A  is a view schematically illustrating the configuration of a part of the X-ray tube  1  according to the third embodiment of the present invention between the electron emission part  10  and the anode surface  11   a;    
         FIG. 6B  a schematic plan view of the electron emission part  10  and focusing structure  13  of the X-ray tube  1  according the third embodiment of the present invention; 
         FIG. 7  is a view illustrating the temporal relationship between the on/off states of the respective first and second electron beam emission areas C 1  and C 2  shown in  FIG. 6B  and the voltages VfL and VfR shown in  FIG. 6B ; and 
         FIG. 8  is a view schematically illustrating the configuration of the X-ray tube  1  according to the fourth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Preferred embodiments of the present invention will be explained below in detail with reference to the accompanying drawings. 
     The present invention moves the focal point area on the anode surface of a cold cathode electronic tube with a simple method. Specifically, the present invention has a plurality of electron beam emission parts that can be controlled independently of one another and a plurality of focusing areas surrounding the electronic emission areas, and changes the position of the focal point area on the anode surface by electrostatically changing a voltage to be applied to each focusing area. 
     Using the cold cathode and electrostatic focusing structure allows a comparatively large movement of the focal point area with a simple structure. The cold cathode has a higher degree of freedom in design than a filament, so that focus control is facilitated only with the electrostatic focusing structure. The present invention utilizes this advantage. 
     Hereinafter, first to fourth embodiments of the present invention will be described sequentially. 
     First Embodiment 
       FIG. 1A  is a schematic cross-sectional view of an X-ray tube  1  according to the first embodiment of the present invention. As illustrated in  FIG. 1A , the X-ray tube  1  has a structure in which an electron emission part  10 , an anode part  11 , a target part  12 , and a focusing structure  13  are disposed in a vacuum area surrounded by a glass outer wall  14 .  FIG. 1A  also illustrates a controller  2  for the X-ray tube  1 . 
       FIG. 1B  is a schematic cross-sectional view of the electron emission part  10 . As illustrated in  FIG. 1B , the electron emission part  10  includes a cathode part  20 , a plurality of electron emission elements  21  disposed on the upper surface of the cathode part  20 , and a gate electrode  22  having a plurality of openings  22   h  which are arranged in a matrix. The plurality of electron emission elements  21  are each a Spindt-type cold cathode element and disposed in the openings  22   h  one by one. The upper end of each electron emission element  21  is positioned in the openings  22   h . The cathode part  20  is connected to the ground end through a transistor T and is grounded when the transistor T is ON. 
     The anode part  11  has an anode surface  11   a  with which an electron emitted from the electron emission part  10  collides. The anode surface  11   a  is the surface of the anode part  11  that faces the electron emission part  10 . The anode part  11  is connected with a power supply P, so that when the transistor T is ON, current flows from the power supply P to the anode part  11 , electron emission part  10 , and cathode part  20 , sequentially. At this time, a plurality of electrons are emitted from each of the electron emission elements  21  illustrated in  FIG. 1B . The anode surface  11   a  constitutes a collision surface of these electrons and the electrons colliding with the anode surface  11   a  pass through the inside of the anode part  11  and are then absorbed by the power supply P. As illustrated in  FIG. 1A , the anode surface  11   a  is formed so as to be inclined with respect to the moving direction of the electrons (in  FIG. 1A , the direction from left to right). 
     The target part  12  is a member made of a material that generates an X-ray by receiving electrons and disposed on the anode surface  11   a . Since the target part  12  is disposed on the anode surface  11   a , some or all of the plurality of electrons that collide with the anode surface  11   a  pass through the target part  12 , and an X-ray is generated in the target part  12  during the passage. The thus generated X-ray is radiated downward in  FIG. 1A  due to inclination of the anode surface  11   a.    
     The focusing structure  13  is a structure having a function of correcting the trajectory of the electron emitted from the electron emission part  10  and is disposed between the electron emission part  10  and the target part  12  disposed on the anode surface  11   a . The focusing structure  13  has a window  13   h . The electrons emitted from the electron emission part  10  are directed to the target part  12  through the window  13   h.    
       FIG. 2  is a view schematically illustrating the configuration of a part of the X-ray tube  1  between the electron emission part  10  and the anode surface  11   a . As illustrated in  FIG. 2 , the focusing structure  13  according to the present embodiment has a disk-like outer shape having an ellipsoidal window  13   h  at the center thereof. Further, the focusing structure  13  is divided into two focusing areas  13   a  and  13   b  by a line forming the diameter of the outer shape. The focusing areas  13   a  and  13   b  are electrically independent of each other and can be applied with mutually different voltages VfL and VfR, respectively. 
     Referring back to  FIG. 1A , the controller  2  controls a connection state between the cathode part  20  and the ground end by performing on/off control of the transistor T and applies the mutually different voltages VfL and VfR to the focusing areas  13   a  and  13   b.    
     Referring again to  FIG. 2 , an area C illustrated in  FIG. 2  is an emission area of an electron beam emitted from the electron emission part  10 . When the controller  2  turns ON the transistor T to connect the cathode part  20  to the ground end, an electron beam is emitted from the electron beam emission area C toward the anode surface  11   a . A focal point area FS which is a collision area of the electron beam on the anode surface  11   a  moves within the anode surface  11   a  in response to a change in the values of voltages VfL and VfR applied to the focusing areas  13   a  and  13   b . A focal point area FS′ and a focal point area FS″ denoted by dashed lines in  FIG. 2  each illustrate an example of the position of the focal point area FS after thusly moving. The reason why the focal point area FS moves in this manner is that a magnetic field generated from the focusing areas  13   a  and  13   b  is changed in response to the change in the voltages VfL and VfR to correct the trajectory of the electron beam. Thus, the controller  2  according to the present embodiment is configured to move the focal point area FS intentionally by changing the values of the voltages VfL and VfR by design. Although not illustrated in  FIG. 2 , the change in the values of the voltages VfL and VfR under the control of the controller  2  can also change the shape of the focal point area FS. 
       FIG. 3  is a view illustrating changes in the position and shape of the focal point area FS when the voltages VfL and VfR are changed. More specifically,  FIG. 3  illustrates simulation results of the focal point area FS when the voltages VfL and VfR are each changed stepwise from 1200 V to 2000 V by 200 V in a state where the power supply P of 50 KV is used, 0 V is applied to the cathode part  20 , and 35 V is applied to the gate electrode  22 . In  FIG. 3  a black area in each section view represents the focal point area FS. It can be understood from the results of  FIG. 3  that the position and shape of the focal point area FS can be changed by changing the voltages VfL and VfR. 
       FIG. 4  is a view illustrating the relationship between the voltage VfR and the beam centroid position (position at which the density of the electron beam takes the highest value). More specifically,  FIG. 4  illustrates simulation results of the beam centroid position when the potential VfL is fixed to 1600 V while the voltage VfR is changed stepwise from 1200 V to 2000 V by 200 V. It can be understood from the results of  FIG. 4  that the beam centroid position can be moved by 0.8 mm from the −0.4 mm position to +0.4 mm position by changing the value of the voltage VfR. 
     As described above, according to the present embodiment, it becomes possible to move the focal point area FS by changing the voltages VfL and VfR under control of the controller  2 . Thus, it can be said that it becomes possible to achieve the movement of the focal point area FS on the anode surface  11   a  of the X-ray tube  1  with a comparatively simple structure by using the electron emission elements  21  which are cold cathode elements. Also, as a result of that, it becomes possible to easily realize X-ray imaging utilizing the plurality of focal point areas FS, X-ray imaging requiring dynamic movement of the focal point area FS, and tomosynthesis imaging. 
     Second Embodiment 
       FIG. 5  is a view illustrating the configuration of the X-ray tube  1  according to the second embodiment of the present invention. The X-ray tube  1  according to the present embodiment differs from the X-ray tube  1  according to the first embodiment in that the electron beam emission area C illustrated in  FIG. 2  is divided into a plurality of areas. Further, the concrete configuration of the focusing structure  13  also differs from that of the X-ray tube  1  according to the first embodiment. Other configurations are the same as those of the X-ray tube  1  according to the first embodiment, so the same reference numerals are given to the same elements, and the different points from the first embodiment will mainly be described. 
     The electron emission part  10  according to the present embodiment includes first and second electron beam emission areas C 1  and C 2 . The first and second electron beam emission areas C 1  and C 2  are each an emission area of an electron beam emitted from the electron emission part  10  and can be on/off controlled independently of each other under the control of the controller  2 . This configuration is achieved by providing, in place of the transistor T of  FIG. 1 , a first transistor (not illustrated) connected between the cathode part  20  of the first electron beam emission area C 1  and the ground end and a second transistor (not illustrated) connected between the cathode part  20  of the second electron beam emission area C 2  and the ground end and by performing on/off control of the first and second transistors independently under the control of the controller  2 . 
     As illustrated in  FIG. 5 , the first and second electron beam emission areas C 1  and C 2  are each a rectangular area elongated in the illustrated Y-direction and are arranged in the Y-direction. 
     The focusing structure  13  according to the present embodiment is divided into five focusing areas  13   a  to  13   e  that can be applied with voltage in a mutually independent manner. The controller  2  applies a voltage VfL to the focusing area  13   a , a voltage VfR to the focusing area  13   b , and a voltage VfV to the focusing areas  13   c  to  13   e.    
     The focusing areas  13   c  to  13   e  are each a rectangular area elongated in the illustrated X-direction (the direction perpendicular to the Y-direction) and are arranged in this order in the Y-direction at an equal interval. The first electron beam emission area C 1  is disposed between the focusing areas  13   c  and  13   d , and the second electron beam emission area C 2  is disposed between the focusing areas  13   d  and  13   e . The focusing areas  13   a  and  13   b  are each a rectangular area elongated in the illustrated Y-direction and are arranged in the X-direction. The focusing areas  13   c  to  13   e  and first and second electron beam emission areas C 1  and C 2  are disposed between the focusing areas  13   a  and  13   b.    
     When the controller  2  changes the voltage VfR from 1200 V to 2000 V in a state where the first electron beam emission area C 1  is ON and where both the voltages VfV and VfL are fixed to 1600 V, the focal point area of the electron beam emitted from the first electron beam emission area C 1  moves from a focal point area FS 1  to a focal point area FS 1 ′ as illustrated in  FIG. 5 . Similarly, when the controller  2  changes the voltage VfR from 1200 V to 2000 V in a state where the second electron beam emission area C 2  is ON and where both the voltages VfV and VfL are fixed to 1600 V, the focal point area of the electron beam emitted from the second electron beam emission area C 2  moves from a focal point area FS 2  to a focal point area FS 2 ′ as illustrated in  FIG. 5 . 
     As described above, according to the present embodiment, if becomes possible to move each of the focal point area of the electron beam emitted from the first electron beam emission area C 1  and the focal point area of the electron beam emitted from the second electron beam emission area C 2  largely as illustrated in  FIG. 5 . 
     Third Embodiment 
       FIG. 6A  is a view schematically illustrating the configuration of a part of the X-ray tube  1  according to the third embodiment of the present invention between the electron emission part  10  and the anode surface  11   a .  FIG. 6B  is a schematic plan view of the electron emission part  10  and focusing structure  13  of the X-ray tube  1  according to the present embodiment. The X-ray tube  1  according to the present embodiment differs from the X-ray tube  1  according to the second embodiment in planar arrangement of the first and second electron beam emission areas C 1  and C 2  and the concrete configuration of the focusing structure  13 . Further, control contents performed by the controller  2  also differ from those of the X-ray tube  1  according to the second embodiment. Other configurations are the same as those of the X-ray tube  1  according to the second embodiment, so the same reference numerals are given to the same elements, and the different points from the second embodiment will mainly be described. 
     The first and second electron beam emission areas C 1  and C 2  according to the present embodiment are each a rectangular area elongated in the illustrated Y-direction and are arranged in the X-direction perpendicular to the Y-direction. 
     The focusing structure  13  according to the present embodiment has a disk-like outer shape having a circular window  13   h  at the center thereof and is divided into two focusing areas  13   a  and  13   b  by a line forming the diameter of the outer shape. The first and second electron beam emission areas C 1  and C 2  are disposed at the center of the window  13   h  in a plan view. The electrical configuration of the focusing areas  13   a  and  13   b  is the same as that in the first embodiment, and the controller  2  applies the voltages VfL and VfR to the focusing areas  13   a  and  13   b , respectively. 
     The controller  2  according to the present embodiment alternately turns on/off the first and second electron beam emission areas C 1  and C 2  in sync with the voltage applied to each of the focusing areas  13   a  and  13   b . In another viewpoint, the controller  2  alternately applies a voltage to the two focusing areas  13   a  and  13   b  during driving of the electron emission part  10 . According to the control performed by the controller  2 , the movable range of the focusing area becomes wider than those in the first and second embodiments. Hereinafter, details will be described with reference to  FIG. 6A  and  FIG. 7 . 
       FIG. 7  are views illustrating the temporal relationship between the on/off states of the respective first and second electron beam emission areas C 1  and C 2  and the voltages VfL and VfR according to the present embodiment.  FIG. 7( a )  illustrates the on/off states of the respective first and second electron beam emission areas C 1  and C 2 ,  FIG. 7( b )  illustrates an example of changes in the respective voltages VfL and VfR, and  FIG. 7( c )  illustrates another example of changes in the respective voltages VfL and VfR. 
     As illustrated in  FIGS. 7( a ) and 7( b ) , the controller  2  according to the present embodiment changes the voltage VfL and voltage VfR from High to Low and Low to High, respectively, while the second electron beam emission area C 2  is ON. As a result, the focal point area of the electron beam emitted from the second electron beam emission area C 2  moves from the focal point area FS 2  to the focal point area FS 2 ′ as illustrated in  FIG. 6A . Then, the controller  2  turns OFF the second electron beam emission area C 2 , turns ON the first electron beam emission area C 1 , and changes the voltage VfL and voltage VfR from Low to High and High to Low, respectively. As a result, the focal point area of the electron beam emitted from the first electron beam emission area C 1  moves from the focal point area FS 1  to the focal point area FS 1 ′ as illustrated in  FIG. 6A . 
     As described above, according to the present embodiment, it becomes possible to move the focal point area largely from the area FS 2  shown in  FIG. 6A  to the area FS 1 ′ shown in  FIG. 6A  in a continuous manner. Therefore, it can be said that the movable range of the focal point area becomes wider than those in the first and second embodiments. 
     As illustrated in  FIG. 7C , only one of the voltages VfL and VfR may be changed with the other one thereof set to a fixed potential. In this case, the fixed potential is preferably set to an intermediate potential between High and Low. Even in this case, the relative magnitude correlation between the voltages VfL and VfR are the same as that in the example of  FIG. 7B , so that the movable range of the focal point area can be widened as in the example of  FIG. 7B . 
     Fourth Embodiment 
       FIG. 8  is a view schematically illustrating the configuration of the X-ray tube  1  according to the fourth embodiment of the present invention. The X-ray tube  1  according to the present embodiment differs from the X-ray tube  1  according to the third embodiment in that it is a multi-source X-ray tube  1  having a plurality of electron emission parts  10 . Further, control contents performed by the controller  2  also differs from those of the X-ray tube  1  according to the third embodiment. Other configurations are the same as those of the X-ray tube  1  according to the third embodiment, so the same reference numerals are given to the same elements, and the different points from the third embodiment will mainly be described. 
     The X-ray tube  1  according to the present embodiment includes five electron emission parts  10 . The individual electron emission part  10  has the same configuration as that in the third embodiment and includes two electron beam emission areas C 1  and C 2 . In  FIG. 8 , the electron beam emission areas C 1  and C 2  of the first electron emission part  10  are referred to respectively as electron beam emission areas CA 1  and CA 2 , the electron beam emission areas C 1  and C 2  of the second electron emission part  10  are referred to respectively as electron beam emission areas CB 1  and CB 2 , the electron beam emission areas C 1  and C 2  of the third electron emission part  10  are referred to respectively as electron beam emission areas CC 1  and CC 2 , the electron beam emission areas C 1  and C 2  of the fourth electron emission part  10  are referred to respectively as electron beam emission areas CD 1  and CD 2 , and the electron beam emission areas C 1  and C 2  of the fifth electron emission part  10  are referred to respectively as electron beam emission areas CE 1  and CE 2 . 
     Five focusing structures  13  are prepared corresponding to the five electron emission part  10 . The individual focusing structure  13  has the same configuration as that in the third embodiment and includes two focusing areas  13   a  and  13   b  which are arranged so as to surround their corresponding electron beam emission areas C 1  and C 2 , respectively, in a plan view. In  FIG. 8 , the focusing areas  13   a  and  13   b  corresponding respectively to the electron beam emission areas CA 1  and CA 2  are referred to respectively as focusing areas  13 Aa and  13 Ab, the focusing areas  13   a  and  13   b  corresponding respectively to the electron beam emission areas CB 1  and CB 2  are referred to respectively as focusing areas  13 Ba and  13 Bb, the focusing areas  13   a  and  13   b  corresponding respectively to the electron beam emission areas CC 1  and CC 2  are referred to respectively as focusing areas  13 Ca and  13 Cb, the focusing areas  13   a  and  13   b  corresponding respectively to the electron beam emission areas CD 1  and CD 2  are referred to respectively as focusing areas  13 Da and  13 Db, and the focusing areas  13   a  and  13   b  corresponding respectively to the electron beam emission areas CE 1  and CE 2  are referred to respectively as focusing areas  13 Ea and  13 Eb. 
     The controller  2  according to the present embodiment performs the same control for the individual electron emission part  10  and individual focusing structure  13  as that in the third embodiment. The focal point areas FSA and FSA′ illustrated in  FIG. 8  correspond respectively to the focal point areas FS 2  and FS 1 ′ illustrated in  FIG. 6A  in the correspondence relation to the electron beam emission areas CA 1  and CA 2  and focusing areas  13 Aa and  13 Ab. The same can be said for the focal point areas FSB and FSB′, focal point areas FSC and FSC′, focal point areas FSD and FSD′, and focal point areas FSE and FSE′. 
     Further, the controller  2  according to the present embodiment controls the five electron emission parts  10  and their corresponding focusing structures  13  in a time series manner. As a result, an X-ray is emitted from different areas (sequentially from the focal point areas FSA, FSA′, FSB, FSB′, FSC, FSC′, FSD, FSD′, FSE, and FSE′) on the anode surface  11   a.    
     As described above, according to the present embodiment, it becomes possible to emit an X-ray sequentially from different areas on the anode surface  11   a . Thus, it becomes possible to obtain many pieces of image information without increasing the number of the electron emission parts  10  and complicating the structure of the X-ray tube, and this makes it possible to obtain a high definition tomosynthesis image. 
     While the preferred embodiments of the present invention have been described, the present invention is not limited to the above embodiments but may be variously modified within the scope thereof. 
     For example, the controller  2  according to the respective embodiments may change stepwise a voltage to be applied to the plurality of focusing areas during driving of the electronic emission part  10  to dynamically move the focal point area. With this configuration, it becomes possible to move the focal point area in stages.