Constant discharge current bleeder

Patent metadata

Field	Value
Publication number	US-2022406555-A1
Application number	US-202017776407-A
Country	US
Kind code	A1
Filing date	Nov 6, 2020
Priority date	Nov 14, 2019
Publication date	Dec 22, 2022
Grant date	—

Abstract

The present invention relates to a rotary anode X-ray source. In addition to a primary cathode of a rotary anode X-ray tube, an auxiliary cathode is provided in the rotary anode X-ray tube. Electrons from the auxiliary cathode are focused into an area on the anode, from which X-rays cannot enter the used X-ray beam generated by the primary cathode. An emission current controlling device is used to control the electron emission of the auxiliary cathode. Thus, the voltage down-ramp for dual energy scanning is kept constant even though the primary X-ray output changes for the sake of dose modulation or during a transient of the primary electron current.

First claim

1 . An X-ray tube for generating an X-ray beam, comprising:
a primary cathode; an auxiliary cathode; a rotatable anode; and an electron current controller; wherein the primary cathode is configured to emit first electrons establishing a flow of primary electron current, the first electrons being focused on a first area on the rotatable anode for generating the X-ray beam; wherein the auxiliary cathode is configured to emit second electrons establishing a flow of auxiliary electron current, the second electrons being directed to a second area, which is different from the first area, on the rotatable anode for generating X-rays, wherein the generated X-rays are configured to be directed to a direction different from that of the X-ray beam, such that the X-rays do not enter the X-ray beam; and wherein the electron current controller is configured to adjust the auxiliary electron current in response to a change of the primary electron current, such that a sum of the primary electron current and the auxiliary electron current remains constant.

2 . The X-ray tube according to claim 1 , wherein the electron current controller comprises an emission control grid arranged between the auxiliary cathode and the anode; and wherein the emission control grid is configured to control the flow of the auxiliary electron current between the auxiliary cathode and the anode.

3 . The X-ray tube according to claim 2 , wherein the emission control grid has a grid control voltage that is configured to sufficiently reduce the auxiliary electron current, such that the X-ray beam is generated with a maximum X-ray intensity.

4 . The X-ray tube according to claim 1 , wherein the electron current controller comprises
at least one heating supply configured to supply the primary and the auxiliary cathodes with different heating powers, such that the sum of the primary electron current and the auxiliary electron current remains constant.

5 . The X-ray tube according to claim 4 , wherein the at least one heating supply comprises
an alternating current AC heating circuit with a variable frequency; wherein the AC heating circuit is configured to supply the primary and the auxiliary cathodes with different heating powers using at least one of a inductor and a capacitor.

6 . The X-ray tube according to claim 4 , wherein the at least one heating supply comprises:
a primary heating supply associated with the primary cathode; and an auxiliary heating supply associated with the auxiliary cathode, wherein the auxiliary heating supply is configured to change a heating current of the auxiliary cathode to adjust the auxiliary electron current in response to a change of the primary electron current, such that a sum of the primary electron current and the auxiliary electron current remains constant.

7 . The X-ray tube according to claim 1 , further comprising an emission control grid arranged between the primary cathode and the anode, and wherein the emission control grid is configured to control a shape of the first electrons to adjust a focal spot on the first area on the rotatable anode.

8 . The X-ray tube according to claim 7 , wherein the emission control grid is configured as a focusing electrode or a set of focusing electrodes to keep a size of the focal spot constant when the tube voltage changes.

9 . The X-ray tube according to claim 1 , wherein the primary cathode and the auxiliary cathode are connected in series or in parallel.

10 . The X-ray tube according to claim 9 , wherein, when connected in series with the primary cathode, the auxiliary cathode is configured to produce a sufficiently high auxiliary electron current at a lower heating power compared with a heating power required for the primary cathode to keep the sum of the primary electron current and the auxiliary electron current constant for the case that the primary cathode carries only a minimal primary electron current close to zero.

11 . The X-ray tube according to claim 10 , wherein the auxiliary cathode is configured to have a slew rate for rise and/or fall of the auxiliary electron current upon a change of the heating current, which is configured to be equal or higher than that of the primary cathode.

12 . The X-ray tube according to claim 11 , wherein the auxiliary cathode is configured to have:
a higher heat conduction from a wire of the auxiliary cathode to a surrounding than that of the primary cathode; and/or a higher heat radiation from a wire of the auxiliary cathode to a surrounding than that of the primary cathode.

13 . The X-ray tube according to claim 1 , wherein the auxiliary cathode comprises a field emission cathode.

14 . An X-ray imaging system, comprising:
an X-ray tube comprising:
a primary cathode;
an auxiliary cathode;
a rotatable anode; and
an electron current controller;
wherein the primary cathode is configured to emit first electrons establishing a flow of primary electron current, the first electrons being focused on a first area on the rotatable anode for generating the X-ray beam;
wherein the auxiliary cathode is configured to emit second electrons establishing a flow of auxiliary electron current, the second electrons being directed to a second area, which is different from the first area, on the rotatable anode for generating X-rays, wherein the generated X-rays are configured to be directed to a direction different from that of the X-ray beam, such that the X-rays do not enter the X-ray beam; and
wherein the electron current controller is configured to adjust the auxiliary electron current in response to a change of the primary electron current, such that a sum of the primary electron current and the auxiliary electron current remains constant; and
an X-ray detector arranged to be opposite to the X-ray tube, wherein the X-ray tube is configured to generate an X-ray beam towards an object of interest; and wherein the X-ray detector is configured to detect attenuated X-rays passing through the object of interest.

15 . A method of controlling an X-ray tube control, comprising:
emitting, by a primary cathode of an X-ray tube claim 1 , first electrons establishing a flow of primary electron current, the first electrons being focused on a first area on a rotatable anode of the X-ray tube for generating an X-ray beam; emitting, by an auxiliary cathode of the X-ray tube, second electrons establishing a flow of auxiliary electron current, the second electrons being directed to a second area, which is different from the first area, on the rotatable anode for generating X-rays, wherein the generated X-rays are configured to be directed to a direction different from that of the X-ray beam such that the X-rays do not enter the X-ray beam; and adjusting, by an electron current controller, the auxiliary electron current in response to a change of the primary electron current such that a sum of the primary electron current and the auxiliary electron current remains constant.

Assignees

• Koninklijke Philips Nv

Inventors

• Behling Rolf Karl Otto
• Proksa Roland
• Gleich Bernhard
• David Bernd Rudi
• Bontus Claas
• Reusch Tobias
• Thran Axel

Classifications

• H01J2235/068

  Multi-cathode assembly · CPC title

• H01J35/06 Primary

  Cathodes · CPC title

• H01J35/10

  Rotary anodes; Arrangements for rotating anodes; Cooling rotary anodes · CPC title

• H05G1/34

  Anode current, heater current or heater voltage of X-ray tube · CPC title

• H01J2235/086

  Target geometry · CPC title