Patent Grant
7123689
The present invention relates generally to generating X-rays, and specifically to an improved method and system for generating X-rays using a field emitter X-ray source.
X-ray systems are generally utilized in various applications, such as for imaging in the medical and non-medical fields. For example, X-ray systems, such as radiographic systems, computed tomography (CT) systems, and tomosynthesis systems, are used to create images or views of tissues of a patient based on the attenuation of X-ray beams passing through the patient. X-ray systems and sources may also be utilized to in non-medical applications, such as detecting minute flaws in equipment or structures, and scanning baggage, crystallography, to mention only a few.
Typically, a X-ray system includes an X-ray source that generates X-ray beams that are directed towards a detector or film. Conventional X-ray tubes generate a beam of X-rays by bombarding a rotating anode with a stream of electrons in vacuum tube. More recent developments have provided a design in which an electron source, such as an array of field emitters, and an anode assembly, are housed inside an evacuated tube. The field emitters include sharp tips that are subjected to high electric currents to emit electrons by a phenomenon called field emission. The electrons thus emitted, travel across an open space at very high speeds and collide with the anode assembly to produce the X-ray beams.
In field emitter X-ray sources, the tips of the field emitters can become degraded by deposition of oxides and other contaminations. A low level of contamination in field emitters may be tolerated in applications such as flat panel displays. However, these contaminations can significantly affect the performance of the field emitters that are subjected to very high electric currents in applications such as X-ray systems.
Thus, there exists a need for an improved field emitter X-ray source for generating X-rays. There is a particular need in the art for techniques that will limit or correct the deposition of contaminates in field emitter arrays, thereby permitting the arrays to be more effective over a longer useful life.
Briefly, in accordance with one embodiment, the present technique provides an X-ray source. The X-ray source includes a field emitter array having a plurality of field emitter elements disposed in a vacuum chamber and configured to emit electrons in the vacuum chamber towards an anode assembly. The X-ray source also includes an anode disposed in the vacuum chamber for receiving the electrons emitted by the field emitter array, and configured to thereby generate X-ray radiation. The X-ray source further includes a source of cleaning gas coupled to the vacuum chamber, wherein the source of cleaning gas is configured to provide cleaning gas to the vacuum chamber towards the field emitter array to reduce deposition of contaminants on or to clean contaminates from the field emitter array.
In accordance with another aspect of the present technique, a method of generating X-rays is provided. The method includes creating a vacuum in a vacuum chamber. The method also includes applying an electric current to a field emitter array disposed in the vacuum chamber to emit electrons. The method also includes receiving the emitted electrons on an anode to produce X-ray radiation that is emitted from the vacuum chamber, operation of the field emitter array and anode resulting in deposition of contaminants on the field emitter array. The method further includes introducing a cleaning gas into the vacuum chamber to contact the field emitter array to remove contaminants from the field emitter array.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
The present technique is generally directed towards an X-ray source, which may be used for medical and non-medical applications, and likewise for imaging and non-imaging applications. Such applications may include, without limitation, patient evaluation, and passenger and/or baggage screening, and generally to provide useful two-dimensional and three-dimensional data and context. To facilitate explanation of the present techniques, however, medical implementations will be generally discussed herein, though it is to be understood that non-medical implementations are also within the scope of the present techniques.
Turning now to the drawings, and referring first to
The X-ray source system 10 also includes an anode 18, which is also disposed inside the vacuum chamber 16. The anode 18 acts as a positive electrode. The anode 18 emits X-rays 20 upon collision of electrons emitted by the field emitter elements 14. The anode 18 generally includes different components that are utilized to produce X-rays 20. For instance, the anode 18 may include an anode disk 22 that is configured to rotate about a longitudinal axis 24 of the X-ray source system 10. The anode disk 22 may be constructed from tungsten alloy or other suitable material. The rotation of the anode disk 22 facilitates improving thermal conditions of the anode disk 22, i.e. dissipating heat due to operations. The anode 18 also includes other components, such as a stem 26 for supporting the anode disk 22 and a rotor with bearings (not shown) to facilitate rotation of the anode disk 22. In certain embodiments, the X-ray source system 10 may include more than one anode 18 to generate X-rays 20.
The vacuum chamber 16 of the X-ray source system 10 may be made of glass or metallic material. The vacuum chamber 16 is coupled to a vacuum system to create a vacuum or partial pressure inside the vacuum chamber 16 on the order of about 10−4 to 10−9 Torr. In the present embodiment, the vacuum system includes a vacuum pump 28.
As described above, the tips of the field emitter elements 14 can become degraded by deposition of oxides and other contaminations, which adversely affect the performance of the X-ray source system 10. Hence, the X-ray source system 10 includes a cleaning gas source 30. The cleaning gas source 30 is coupled to the vacuum chamber 16. The cleaning gas source 30 provides a cleaning gas to the vacuum chamber that may be directed towards or generally into contact with the field emitter array 12 to reduce the deposition of contaminants on or to clean contaminates from the field emitter array 12. In certain embodiments, the cleaning gas source 30 provides the cleaning gas into the vacuum chamber 16 intermittently when there is no emission of electrons by the field emitter elements 14 of the field emitter array 12. In another embodiment, the cleaning gas source provides the cleaning gas to deposit active sites on the field emitter array, which in turn enhances the performance of the field emitter array. In the present embodiment, the X-ray source system uses hydrogen as the cleaning gas. In another embodiment, water vapor may be used as the cleaning gas. Alternatively, the cleaning gas may also include inert gases, such as nitrogen (N2), argon (Ar). Other gases may be suitable for removal of contaminants as well.
The X-ray source system 10 may be controlled by an X-ray controller 32. A power supply 34 provides electric current to the field emitter array 12 and the anode through the X-ray controller 32. An operator may control and operate the X-ray source system 10 through an operator workstation 36. The operator workstation 36 may include input devices such as a keyboard, a mouse, and other user interaction devices (not shown).
Turning briefly to
In a typical application, the X-ray source would be utilized in its normal mode of operation to produce X-rays. During such operation, the chamber in which the emitter array or arrays are disposed will be evacuated as described above. Periodically, then, the cleaning gas is introduced to remove deposited contaminants. This may be done by simply releasing a supply of gas (e.g., by opening a valve), or by pumping the gas into the chamber for circulation over the emitter arrays. The cleaning operation effectively removes the contaminants from the emitters, and also evacuates them from the chamber. Following the cleaning operation, then, the cleaning gas source is once again isolated from the chamber (e.g., by closing the valve), and the chamber is once again evacuated for normal operation of the X-ray source. In presently contemplated embodiments, the cleaning operation may simply be performed periodically. However, the operation may also be planned based on the actual use of the source, or may be performed as a maintenance operation based upon sensed changes in emission intensity, or other sensed parameters.
The system further includes an X-ray controller 66, a table controller 68 and a data acquisition controller 70, which may all function under the direction of a system controller 72. The X-ray controller 72 regulates timing for discharges of X-ray radiation, which is directed from points around the scanner 58 toward a detector segment on an opposite side thereof. The detector 62 is provided with apertures through which the source can emit radiation. The arrangement permits for additional data to be collected between the locations where the distributed source emits through the detector. Data acquisition controller 70, coupled to detector elements receives signals from the detector elements and processes the signals for storage and later image reconstruction.
The various circuitry described herein, may be defined by hardware circuitry, firmware or software. The particular protocols for imaging sequences, for example, will generally be defined by code executed by the system controllers. Moreover, initial processing, conditioning, filtering, and other operations required on the transmitted X-ray intensity data acquired by the scanner may be performed in one or more of the components depicted in
System controller 72 is also coupled to an operator interface 74 and to one or more memory devices 76. The operator interface 74 may be integral with the system controller 72, and will generally include an operator workstation for initiating imaging sequences, controlling such sequences, and manipulating data acquired during imaging sequences. The memory devices 76 may be local to the CT imaging system 56, or may be partially or completely remote from the system. Moreover, the memory devices 76 may be configured to receive raw, partially processed or fully processed data for reconstruction.
The positioner 84 also supports an X-ray detector 88. The X-ray detector 88 may be an analog detector or a digital detector. The X-ray source 86 emits the X-rays 90 through a patient 92 towards the X-ray detector 88. The X-ray detector 88 receives this X-rays 90 and is configured to generate signals in response to the X-rays. The X-ray detector 88 may be stationary or may move in coordination with or independent from the X-ray source 86 and/or support 84.
The operation of the X-ray source 86 may be controlled by a system controller 94. The motion of the X-ray source 86 and/or the X-ray detector 88 may also be controlled by the system controller 94, such as by the motor controller 98, to move independently of one another or to move in synchrony. The system controller 94 may employ positioner 84 to facilitate the acquisition of radiographic projections at various angles through the patient.
The system controller 94 may also control the operation and readout of the X-ray detector 88, such as through detector acquisition circuitry 100. Processing circuitry 102 is typically present to process and reconstruct the data read out from the X-ray detector 88 by the detector acquisition circuitry 100. In particular, projection data or projection images are typically generated by the detector acquisition circuitry 100 in response to the X-rays emitted by the X-ray source 86.
Processing circuitry 102 may also include memory circuitry to store the processed and to be processed data. The memory circuitry may also store processing parameters, and/or computer programs.
The processing circuitry 102 may be connected to an operator workstation 104. The images generated by the processing circuitry 102 may be sent to the operator workstation 104 for display, such as on the display 106. The processing circuitry 102 may be configured to receive commands or processing parameters related to the processing or images or image data from the operator workstation 104, which may include input devices such as a keyboard, a mouse, and other user interaction devices (not shown). The operator workstation 104 may also be connected to the system controller 94 to allow an operator to provide commands and scanning parameters related to the operation of the X-ray source 86 and/or the X-ray detector 88 to the system controller 94. Hence an operator may control the operation of all or part of the tomosynthesis system 82 via the operator workstation 104.
The operator workstation 104 may be coupled to a picture archiving and communication systems (PACS) 110. The PACS 110 may be utilized to archive the captured X-ray images. Accordingly, the operator workstation 104 may access images or data accessible via the PACS 110 for processing by the processing circuitry 102, for displaying on the display 106, or for printing on the printer 108. Also, the PACS 110 may be coupled to a remote workstation 112 to provide remote access to the X-ray images.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
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