X-ray or gamma ray systems or devices – Electronic circuit – With switching means
Reexamination Certificate
1998-12-22
2001-04-10
Kim, Robert H. (Department: 2862)
X-ray or gamma ray systems or devices
Electronic circuit
With switching means
C378S101000, C378S111000
Reexamination Certificate
active
06215850
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to x-ray tubes used in imaging systems and more particularly, to a switching unit to control the duration and magnitude of x-ray beams transmitted from an x-ray tube.
In at least one known imaging system configuration, an x-ray source projects an x-ray beam. The x-ray beam passes through an object being imaged and after being attenuated by the object, impinges upon a radiation detector. The intensity of the attenuated beam radiation received at the detector is dependent upon the attenuation of the x-ray beam by the object. The detector produces an electrical signal that is a measurement of the beam attenuation. A plurality of attenuation measurements are acquired to produce an image of the object.
The x-ray source, sometimes referred to as an x-ray tube, typically includes an evacuated glass x-ray envelope containing an anode, a control grid and a cathode. X-rays are produced by applying a high voltage across the anode and cathode and accelerating electrons from the cathode against a focal spot on the anode by applying a high voltage to the x-ray tube control grid.
At least one known imaging system includes a costly grid control power supply as a means of turning on and off the control grid voltage for controlling x-rays from the x-ray source.
It would be desirable to provide a switching unit, or circuit, which adjusts the signals applied to the x-ray source so that the magnitude and duration of the x-ray beams emitted from the x-ray tube are altered. It would also be desirable to provide a switching unit which includes any number of modular switching elements which may be combined to provide incremental control of the tube signals as required by the application while minimizing cost of the switching unit. Additionally, it would also be desirable to provide such a unit which utilizes a beam or beams of light to control the switching elements to provide isolation from the high voltage tube signals.
BRIEF SUMMARY OF THE INVENTION
These and other objects may be attained, in one embodiment, by a switching unit for altering the signals supplied to an x-ray tube to control the duration and magnitude of an x-ray beam emitted from the x-ray tube. More specifically, and in one embodiment, the switching unit controls a grid voltage of the x-ray tube so that the x-ray dosage to the patient is altered.
More particularly, and in an exemplary embodiment, the switching unit includes any number of switch elements for altering a grid bias voltage supplied to the x-ray tube, an insulating support structure for securing the modular switch elements together, and an electrostatic shield for eliminating corona discharge from the switch elements. Each switch element utilizes a beam of light excitation signal to alternate between two different modes, or states, of operation. These states of operation are sometimes referred to herein as the conduction state and the steady state. In the conduction state, if an excitation signal is received by the switch element, a switch element voltage drop across the element becomes approximately zero and a maximum signal is applied to the x-ray tube so that a maximum number of x-rays are emitted from the x-ray source. The steady state refers to the condition when an excitation signal is not received by a switch element. In the steady state, a voltage drop is generated by the switch element so that the signal applied to the x-ray tube is decreased by an amount determined by a voltage drop element.
In operation, the duration and magnitude of the x-ray beam emitted from the x-ray tube is altered by configuring each switch element in a steady state or conduction state. Specifically, by transmitting a light excitation signal to selected switch elements, the grid bias voltage supplied to the x-ray tube is altered. More specifically, by transitioning individual switch elements between the steady state and conduction state, the magnitude of the x-ray beams emitted from the x-ray tube may be incrementally altered. Particularly, and in one embodiment, the grid bias voltage is incrementally reduced so that the magnitude of the emitted x-ray beam is incrementally reduced.
In one embodiment, as a result of the modular configuration of the switching elements, the desired incremental change in the grid control voltage may be determined by combining a selected number of selected voltage drop configuration switching elements. More specifically, a switching unit is fabricated by combining any number of a switching elements, each having a specific voltage drop, in order to reduce cost and provide the proper incremental grid voltage change.
The above described switching unit controls x-ray tube signals so that the magnitude and duration of the x-ray beams emitted from the x-ray tube are altered. In addition, the switching unit includes a selectable number of switching elements to incrementally control the signals of the x-ray tube as required by the application while reducing cost of the switching unit. Further, the switching unit provides isolation from the x-ray tube high voltage signals.
REFERENCES:
patent: 5077771 (1991-12-01), Skillcorn et al.
patent: 5495165 (1996-02-01), Beland
Blake James A.
Blok Alexander M.
Schmidt Jonathan R.
Armstrong Teasdale LLP
Cabou Christian G.
Dunn Drew A.
General Electric Company
Kim Robert H.
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