X-ray tube and X-ray CT apparatus

1. An X-ray tube, comprising:

a Wehnelt electrode having a dent inside;

a filament arranged in the dent of the Wehnelt electrode and configured to emit an electron beam when electricity is passed therethrough;

an anode configured to emit an X-ray in response to the incident electron beam;

an electrode part configured by at least one pair of electrode members, the electrode members facing each other across a path of the electron beam, a voltage being applied to each of the electrode members;

a voltage controller configured to control the voltage applied to the electrode part; and

a shield member arranged in contact with the Wehnelt electrode and configured to cover part of the dent by a projecting part.

2. The X-ray tube according to claim 1 , wherein:

the dent is a groove formed on the Wehnelt electrode, and the filament is arranged along the groove;

the electrode part has a pair of first electrode members and a pair of second electrode members;

the first electrode members are arranged facing each other, the second electrode members are arranged facing each other, a direction along which the first electrode members face is orthogonal to a direction along which the second electrode members face, and voltages are applied to the respective electrode members; and

the voltage controller is configured to:

by controlling the voltages applied to the first electrode members, control change of a size in a first direction of a radiation range of the electron beam on the anode and movement of the electron beam in the first direction; and

by controlling the voltages applied to the second electrode members, control change of a size in a second direction orthogonal to the first direction of the radiation range of the electron beam on the anode and movement of the electron beam in the second direction.

3. The X-ray tube according to claim 2 , wherein both the first electrode members and the second electrode members are arranged on a same plane perpendicular to a radiation direction of the electron beam.

4. The X-ray tube according to claim 2 , wherein the filament is a coil filament, the filament is arranged so that a plane including a diameter direction of a coil includes the second direction, and a length of the first direction of the coil is longer than the diameter of the coil.

5. The X-ray tube according to claim 3 , wherein the voltage controller is configured to, in a state of already applying voltages to the first electrode members and the second electrode members:

by changing a voltage applied in a same electric potential state to each of the first electrode members, change the size of the radiation range of the electron beam on the anode in the first direction; and

by changing a voltage applied in a same electric potential state to each of the second electrode members, change the size of the radiation range of the electron beam on the anode in the second direction.

6. The X-ray tube according to claim 3 , wherein the voltage controller is configured to, in a state of already applying voltages to the first electrode members and the second electrode members:

by raising a voltage applied to one of the first electrode members from a voltage applied thereto at present and lowering a voltage applied to the other from a voltage applied thereto at present, move the electron beam toward one or the other of the first electrode members; and

by raising a voltage applied to one of the second electrode members from a voltage applied thereto at present and lowering a voltage applied to the other from a voltage applied thereto at present, move a focal point of the electron beam toward one or the other of the second electrode members.

7. The X-ray tube according to claim 1 , wherein:

the Wehnelt electrode and the shield member are configured so that voltages can be applied thereto; and

the voltage controller is configured to apply a lower voltage than a voltage applied to the filament to the Wehnelt electrode and the shield member to thereby cut off entrance of the electron beam emitted from the filament to the anode.

8. The X-ray tube according to claim 1 , further comprising, between the electrode part and the anode on the path of the electron beam, an electromagnetic deflector configured to deflect the path of the electron beam arranged so as to surround the path of the electrode beam.

9. An X-ray CT apparatus, comprising an X-ray tube configured to radiate an X-ray, a detector configured to detect the X-ray radiated from the X-ray tube, a reconstruction part configured to reconstruct an image from projection data based on detection by the detector, and a controller configured to control a scan by detection of the X-ray including control of the X-ray tube, wherein the X-ray tube includes:

a Wehnelt electrode having a dent inside;

a filament arranged in the dent of the Wehnelt electrode and configured to emit an electron beam when electricity is passed therethrough;

an anode configured to emit an X-ray in response to the incident electron beam;

an electrode part configured by at least one pair of electrode members, the electrode members facing each other across a path of the electron beam, a voltage being applied to each of the electrode members;

a voltage controller configured to control the voltage applied to the electrode part; and

a shield member arranged in contact with the Wehnelt electrode and configured to cover part of the dent by a projecting part.