X-RAY SOURCE

Abstract

The invention relates to an X-ray source (2) for an imaging device comprising at least three electrodes; a power supply configured to provide a primary gap voltage between a first (13) and a second (12) electrode among said at least three electrodes, said primary gap voltage having an AC component, causing a transport of electrons from the first electrode toward the second electrode; and a controller configured to supply a variable potential on a third electrode (14) among said at least three electrodes, wherein the X-ray source is configured to generate an X-ray beam with an energy spectrum based on the voltage difference between the first electrode and the second electrode, and wherein the controller is configured to set the variable potential on the third electrode to a value causing at least a partial blocking of said transport of electrons, whenever a predetermined condition is met.

Claims

1. X-ray source for an imaging device comprising: at least three electrodes, a power supply configured to provide a primary gap voltage between a first and a second electrode among said at least three electrodes, said primary gap voltage having an AC component and having a DC component, causing a transport of electrons from the first electrode toward the second electrode and part of the energy of the electrons is absorbed by the second electrode, and a small part of it is restituted by emitting X-ray radiation, and a controller configured to supply a variable potential on a third electrode among said at least three electrodes, wherein the X-ray source is configured to generate an X-ray beam with an energy spectrum based on the voltage difference between the first electrode and the second electrode, and wherein the controller is configured to set the variable potential on the third electrode being set to the value causing at least a partial blocking of said transport of electrons, impeding the electrons emitted by the first electrode to reach the second electrode, whenever the primary gap voltage is comprised between a minimum extinction value (N2) and a maximum extinction value (n1).

2. (canceled)

3. X-Ray source according to claim 1, the minimum extinction value being comprised between 30 kVp and 80 kVp .

4. X-Ray source according to claim 3, the maximum extinction value being comprised between 80 kVp and 160 kVp.

5. (canceled)

6. X-Ray source according to claim 1, said offset DC component being comprised between 80 kilovolts and 150 kilovolts, preferably between 90 kilovolts and 120 kilovolts, more preferably of 100 kilovolts.

7. X-Ray source according to claim 6, the variable potential on the third electrode being set to the value causing at least the partial blocking of said transport of electrons at regular intervals, said intervals corresponding to a given first frequency.

8. X-Ray source according to claim 7 said first frequency matching the frequency of the AC component of the primary gap voltage.

9. X-Ray source according to claim 6, the variable potential on the third electrode having a crenel-shaped voltage curve.

10. X-Ray source according to claim 6, the AC component of the primary gap voltage having a frequency comprised between 10 Hz and 20 kHz , preferably close to the readout frequency of the detector.

11. X-Ray source according to claim 10, the X-ray source further comprising a transformer.

12. X-Ray source according to claim 11, the transformer being configured to adapt an impedance of the at least three electrodes to the tube in order to obtain a resonating circuit.

13. Imaging device comprising an X-Ray source according to claim 1.

14. Imaging device according to the claim 13, being a Computed Tomography device.

15. Method of controlling an energy level of an X-ray beam in an X-ray source comprising: generating a primary gap voltage causing a transport of electrons from a first electrode toward a second electrode, the electrons hitting said second electrode generating an X-Ray beam, setting a potential on a third electrode being set to the value causing at least a partial blocking of said transport of electrons, impeding the electrons emitted by the first electrode to reach the second electrode, whenever the primary gap voltage is comprised between a minimum extinction value (N2) and a maximum extinction value (n1).

16. X-Ray source according to claim 1, wherein the controller is configured to set the variable potential on the third electrode being set to the value causing said transport of electrons whenever the primary gap voltage is comprised between a minimum value n1 and a maximum value N1, n1 and N1 defining an interval comprising the maximum values of the primary gap voltage PV.

17. X-Ray source according to claim 1, wherein the controller is configured to set the variable potential on the third electrode being set to the value causing said transport of electrons whenever the primary gap voltage is comprised between a minimum value n2 and a maximum value N2, n2 and N2 defining an interval comprising the minimum values of the primary gap voltage PV.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0039] The invention shall be better understood by reading the following detailed description of an embodiment of the invention and by examining the annexed drawing, on which:

[0040] FIG. 1 is schematically represents a general layout of a device according to the invention,

[0041] FIG. 2 represents instant X-Ray spectra corresponding to different kVp-values applied to a standard X-Ray source,

[0042] FIG. 3 is a diagram showing the different voltages applied to the electrodes of a device according to the invention over time, and the resulting X-ray.

[0043] In order to implement the main embodiment of the invention, a grid switch 11 is set up.

[0044] FIG. 1 represents a device 1 according to the invention. An X-ray tube 2, comprises a first electrode, the cathode 13, and another electrode, the anode 12.

[0045] X-ray are produced in a usual way by sending high energy electrons from the cathode 13, toward the anode 12. Part of the energy of the electrons is absorbed by the anode 12, and a small part of it is restituted by emitting X-ray radiation 20. In order to induce the transportation of electrons from the cathode 13 to the anode 12, a primary gap voltage PV is applied between the cathode 13 and the anode 12.

[0046] The resulting emitted X-ray spectrum depends on the energy of the transported electrons, and thus on said primary gap voltage PV. In order to have different energetic contributions to the output spectrum, the primary gap voltage PV has both a high-voltage DC component, or offset, produced by a high voltage generator 15, and an AC component produced by an AC generator 16. The AC component and the DC component are summed up together by a transformer 17. The generator 16, the transformer 17 and tube can be designed as a resonating circuit.

[0047] Between the anode 12 and the cathode 13, a grid-shaped electrode 14 is inserted. The grid-shaped electrode 14 is part of a grid switch system 11, which further comprises a controller which enables to apply a certain grid potential GV, a crenel voltage, to the electrode 14. Said grid potential GV allows to stop the X-ray emission 20 very quickly when desired.

[0048] The terms grid switch refer to a X-ray tube internal layout known in the art allowing for a very fast extinction of the resulting X-ray beam.

[0049] Due to capacitive effects, the X-ray emission does not stop instantly when the primary gap voltage PV is set to zero. The grid switch allows to solve this issue.

[0050] The grid switch 11 has two positions: an on position and an off position. When the switch is on, the switch interferes as little as possible with the electrons travelling from the cathode 13 toward the anode 12. Therefore, the potential of the electrode 14 is set to a highly positive value V. When the switch is off, the switch impedes the electrons emitted by the cathode 13 to reach the anode 12. Therefore, the potential is set to a highly negative value v.

[0051] The transition between the on and off positions is controlled by a controller, not represented on the drawing, which sets the potential GV on the electrode 14 accordingly. The transition may be made in any way, but the most convenient way to switch between two constant voltage values is to use a voltage with a crenel-shaped voltage curve.

[0052] The grid potential GV is chosen in order to allow only certain values of the primary gap voltage PV to contribute to the average output X-ray spectrum. FIG. 2 illustrates two possible grid potentials GV and the resulting output X-ray spectra. In a first embodiment, corresponding to the plain gray area of the diagram, the grid switch is set to its on position when the primary gap voltage PV is comprised between a minimum value n1 and a maximum value N1; n1 and N1 defining an interval comprising the maximum values of the primary gap voltage PV. When the primary gap voltage PV does not lie between these values, the grid switch is set to its off position. Because of this configuration, the resulting X-ray spectrum, the diagram plotted on the left-high corner of FIG. 2, has energetic contributions comprised only between n1 and N1: it allows to have a spectrum with a high energy tail, which may be useful to image thick patients for instance. In a second embodiment, corresponding to the hatched area of the diagram, the grid switch is set to its on position when the primary gap voltage PV is comprised between a minimum value n2 and a maximum value N2; n2 and N2 defining an interval comprising the minimum values of the primary gap voltage PV. When the primary gap voltage PV is not comprised between these values, the grid switch is set to its off position. Because of this configuration, the resulting X-ray spectrum, the diagram plotted on the right-high corner of FIG. 2, has energetic contributions comprised only between n2 and N2, which allows for low kVp spectrum which allows for better contrast images.

[0053] Both these embodiments imply that the grid potential GV is a periodic potential with a frequency identical to the primary gap voltage PV, in order to always cut the same values of the voltage.

[0054] The invention also allows to combine several energy ranges, as illustrated in FIG. 3. In FIG. 3, the grid switch is set to its on position each time the primary gap voltage is either between n1 and N1 or between n2 and N2, and set to its off position otherwise. This allows to shape the output spectrum. FIG. 3b represents three different output X-ray spectra. The first spectrum, plotted with a grey thin line 31, corresponds to the X-ray spectrum detected if the only energetic contributions to the spectrum are low-kVp, such as the one comprised between n2 and N2. The second spectrum, plotted with a plain thick line 32, corresponds to the X-ray spectrum detected if the only energetic contributions to the spectrum are high-kVp, such as the one comprised between n1 and N1. Eventually, the third spectrum, plotted with a dotted line 33, corresponds to a spectrum with both contributions. The latter has a high energy tail which allows to image effectively thicker patients but also have an increased low-energy part, which allows for better contrasts.

[0055] By adapting the combination, the one skilled in the art obtains a lot of freedom to many ways of increasing the contributions according to the needs, for instance according to the physiology of the patient who is to be imaged.

[0056] The one skilled in the art could also use a different grid potential GV. As a matter of fact, a crenel-shaped voltage only allows two positions of the grid switch system, and thus only permits to shut down certain radiations. By using a shaped voltage, it is possible to give a weight to each value and thus control the beam energy more finely.

[0057] Controlling the beam energy allows to minimize the dose of X-ray radiation effectively received by the patient imaged.

[0058] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the discussed embodiments.

[0059] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.