System and method for generating x-rays at multiple energy levels by a single device

Abstract

Systems and methods for generating X-rays at multiple energy levels by a single device are disclosed. The system comprises a vacuum tube, an anode target and multiple electron emitters. Each of the multiple switchable electron emitters are maintained at a different potential difference from the anode target. Each switchable electron emitter may be activated individually to produce X-rays with characteristic power levels as required.

Description

[0001] TITLE

[0002] SYSTEM AND METHOD FOR GENERATING X-RAYS AT MULTIPLE ENERGY LEVELS BY A SINGLE DEVICE

[0003] CROSS-REFERENCE TO RELATED APPLICATIONS

[0004] This application claims the benefit of priority from U.S. Provisional Patent Application No. 63 / 558,146, filed February 27, 2024, which is incorporated by reference in its entirety.

[0005] FIELD OF THE INVENTION

[0006] The disclosure herein relates to systems and methods for generating x-rays at multiple energy levels by a single device. In particular the disclosure relates to dual energy x-ray tubes in which two electron emitting constructs are each held at a distinct potential difference from a common anode target.

[0007] X-ray sources generally produce x-rays by accelerating a stream of electrons using a high voltage electric field towards an anode target. Typically, the electron emitters of x-ray sources are hot filament cathodes. Such x-ray sources are difficult to control as the accelerating field requires high voltage and high voltage supplies are not readily switchable. Furthermore, hot filament cathodes have slow response times.

[0008] As a result, typical x-ray sources may produce a steady stream of x-rays, but because of their long response times, they cannot produce x-ray pulses.

[0009] Furthermore, most x-ray sources use an electron emitting construct fixed at a single potential difference from the anode target such that all electrons accelerated towards the anode strike the target at a common speed resulting in the generation of x-rays having a single common energy level.

[0010] Thus, there is a need for controllable x-ray sources with fast response times and which may generate x-rays at multiple energy levels. The invention described herein addresses the above-described needs.

[0011] SUMMARY OF THE EMBODIMENTS

[0012] It is therefore an object of the invention to provide an X-ray emission system for generating X-rays at multiple energy levels.

[0013] According to an aspect of the presently disclosed subject matter, a multiple energy X-ray emission system configured to switch between generating X-rays having different energy levels is disclosed. The system comprises an anode target and a plurality of field emission type electron emitting constructs, wherein the electron emitting constructs are provided in a single X-ray tube. The system further comprises a low voltage driving circuit for each of the electron emitting constructs configured to generate gate voltage signals for activating the corresponding electron emitting construct. The system also comprises a high voltage supply for each of the electron emitting constructs configured to establish an electron accelerating potential between the corresponding electron emitting construct and the anode target. A digital switching unit for each of the electron emitting constructs is also provided operable to selectively connect and disconnect the corresponding low voltage driving circuit thereby selectively activating and deactivating the corresponding field emission type electron emitting construct such that when the corresponding field emission type electron emitting construct is activated electrons are accelerated towards the anode target and a pulse of x-rays is generated. The system further comprises a controller configured to generate activation signal for controlling the switching rate of each of the digital switching units in accordance with the corresponding gate voltage signals of the electron emitting construct.

[0014] As appropriate, each of the electron emitting constructs is maintained at a different potential difference from the anode target to enable different energy level X-ray transmission.

[0015] As appropriate, the field emission type electron emitting constructs comprise a Spindt type electron source, a carbon nanotube (CNT) type electron source, a metal-insulator-metal (MIM) type electron source, a metal-insulator-semiconductor (MIS) type electron source, or a combination thereof.

[0016] As appropriate, the electron emitting constructs are maintained at lower voltages than the anode target.

[0017] As appropriate, the electron emitting constructs are maintained at different negative voltages and the anode target is grounded.

[0018] As appropriate, the electron emitting constructs are either grounded or maintained at different positive or negative voltages and the anode target is maintained at a positive voltage higher than the voltages of the electron emitting constructs.

[0019] According to another aspect, the system further comprises one or more electron deflectors to direct the electrons emitted from the emitting constructs to a specific part of the anode target.

[0020] As appropriate, the activation signal comprises a series of gate pulses generated at regular intervals At and having a fixed gate-pulse duration 5t1 .

[0021] As appropriate, the system further comprising a timer for providing a fixed clock signal.

[0022] As appropriate, the electron emitting construct comprises a gated cone electron source and gate electrode.

[0023] As appropriate, the digital switching units of the electron emitting constructs are alternatively switched by the coordinated electrical activation of the activation signal generated by the controller and a clock signal.

[0024] In a further aspect, a multiple energy X-ray emission system configured to switch between generating X-rays having different energy levels is disclosed. The system comprises an X-ray tube and a discharge tube. The X-ray tube comprises an anode target, a first field emission type electron emitting construct, a first low voltage driving circuit configured to generate a first gate voltage signal for activating the first electron emitting construct and a first digital switching unit operable to selectively connect and disconnect the first low voltage driving circuit thereby selectively activating and deactivating the first electron emitting construct. The discharge tube comprises a discharge anode, a second field emission type electron emitting construct, a second low voltage driving circuit configured to generate a second gate voltage signal for activating the second electron emitting construct and a second digital switching unit operable to selectively connect and disconnect the second low voltage driving circuit thereby selectively activating and deactivating the second electron emitting construct.

[0025] In another aspect, the system further comprises a ladder of voltage multipliers configured to generate high voltage DC potential from an AC Driver, a voltage monitor configured to measure the voltage stored in the voltage multipliers and a controller configured to control the second gate voltage signal generated by the second low voltage driving circuit and monitor the voltage measured by the voltage monitor to switch from the second electron emitting construct to the first electron emitting construct when a required acceleration voltage is measured by the voltage monitor.

[0026] As appropriate, fast switching between the first electron emitting construct and the second electron emitting construct enables capturing multiple X-ray images of an object at different energy levels.

[0027] As appropriate, the AC driver is configured to charge a series of capacitors in the ladder of voltage multipliers to an initial voltage.

[0028] As appropriate, the controller is further configured to connect the second gate voltage to the second electron emitting construct such that the series of capacitors discharges via the discharge anode of the discharge tube until the required acceleration voltage is reached, disconnect the second gate voltage from the second electron emitting construct and connect the first gate voltage to the first electron emitting construct to activate the first electron emitting construct and generate X-rays at a particular energy level.

[0029] According to yet another aspect of the presently disclosed subject matter, a method for generating X-rays having different energy levels is disclosed. The method comprises providing a multiple energy X-ray emission system configured to switch between generating X-rays having different energy levels. The X-ray emission system comprising an anode target, a plurality of field emission type electron emitting constructs, wherein the electron emitting constructs are provided in a single X-ray tube, a low voltage driving circuit for each of the electron emitting constructs configured to generate gate voltage signals for activating the corresponding electron emitting construct, a high voltage supply for each of the electron emitting constructs configured to establish an electron accelerating potential between the corresponding electron emitting construct and the anode, a digital switching unit for each of the electron emitting constructs operable to selectively connect and disconnect the corresponding low voltage driving circuit thereby selectively activating and deactivating the corresponding field emission type electron emitting construct such that when the corresponding field emission type electron emitting construct is activated electrons are accelerated towards the anode target and a pulse of x-rays is generated and a controller configured to generate activation signal for controlling the switching rate of each of the digital switching units in accordance with the corresponding gate voltage signals of the electron emitting construct.

[0030] According to further aspect, the method comprises maintaining each of the electron emitting constructs at a different potential difference from the anode target, establishing, by a first high voltage supply, an electron accelerating potential between a first electron emitting construct and the anode target and generating, by the controller, an activation signal comprising at least one gate pulse to activate a first digital switching unit of the one of the digital switching units. The method further comprises sending, by the controller, the activation signal to the first digital switching unit, activating, by the first digital switching unit, a first low voltage driving circuit to generate first gate voltage signals for activating the first electron emitting construct for the duration of each gate pulse, emitting electrons from the first electron emitting construct, accelerating the electrons from the first electron emitting construct to the anode target and generating, by the anode target, X-rays at a first energy level for the duration of each gate pulse.

[0031] As appropriate, maintaining each of the electron emitting constructs at a different potential difference from the anode target comprises maintaining the electron emitting constructs at lower voltages than the anode target.

[0032] As appropriate, the method further comprises maintaining the electron emitting constructs at different negative voltages and grounding the anode target.

[0033] As appropriate, the method further comprises grounding or maintaining the electron emitting constructs at different positive or negative voltages and maintaining the anode target at a positive voltage higher than the voltages of the electron emitting constructs.

[0034] As appropriate, the method further comprises providing one or more electron deflectors in the multiple energy X-ray emission system to direct the electrons emitted from the emitting constructs to a specific part of the anode target.

[0035] As appropriate, generating the activation signal comprises generating a series of gate pulses at regular intervals At and having a fixed gate-pulse duration 5t1 .

[0036] As appropriate, the method further comprises providing a timer for providing a fixed clock signal.

[0037] According to a further aspect, the method comprises generating an activation signal comprising at least one gate pulse by the controller to activate a second digital switching unit of the one of the digital switching units, sending the activation signal to the second digital switching unit, activating a second low voltage driving circuit by the second digital switching unit to generate second gate voltage signals for activating a second emitting construct for the duration of each gate pulse, emitting electrons from the second electron emitting construct, accelerating the electrons from the second electron emitting construct to the anode target and generating X-rays at a second energy level by the anode target for the duration of each gate pulse.

[0038] As appropriate, the step of establishing, by the first high voltage supply, an electron accelerating potential between the first electron emitting construct and the anode target comprises varying the accelerating potential over time.

[0039] As appropriate, the step of generating, by the controller, an activation signal comprises selecting a required accelerating potential and selecting an activation time at which the first high voltage supply provides the required accelerating potential

[0040] As appropriate, the step of sending, by the controller, the activation signal to the first digital switching unit comprises sending gate pulse at the activation time.

[0041] BRIEF DESCRIPTION OF THE FIGURES

[0042] For a better understanding of the embodiments and to show how it may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings.

[0043] With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of selected embodiments only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects. In this regard, no attempt is made to show structural details in more detail than is necessary for a fundamental understanding; the description taken with the drawings making apparent to those skilled in the art how the various selected embodiments may be put into practice. In the accompanying drawings:

[0044] Fig. 1 is a block diagram representing selected elements of an embodiment of a switchable x-ray source;

[0045] Fig, 2 schematically represents a possible electron emitting construct for use in embodiments of the switchable x-ray source;

[0046] Fig 3 is a block diagram representing of another embodiment of a switchable x-ray source incorporating an synchronized optical imager;

[0047] Fig. 4A is a block diagram representing selected elements of a dual energy x-ray tube configured to switch between producing x-rays having two different energy levels;

[0048] Fig. 4B is another block diagram representing selected elements of a particular embodiment of the dual energy x-ray tube in which each of two electron emitter cathodes are each held at negative potentials at distinct high voltages relative to a common grounded anode target;

[0049] Fig. 4C is still another block diagram representing selected elements of another embodiment of the dual energy x-ray tube in which one electron emitter cathode is grounded and the other is held at a negative potential and the anode target is held at a positive potential;

[0050] Fig. 5A is a schematic illustration of an x-ray emission tube incorporating two cold cathode electron emission sources held at separate negative potential differences to a grounded anode according to one embodiment;

[0051] Fig. 5B is a schematic illustration of another embodiment of the x-ray emission tube incorporating two cold cathode electron emission sources held at separate negative potential differences to a grounded anode by a ladder of voltage multipliers; Figs. 6A schematically illustrates electrons accelerated towards the anode target from a higher voltage cathode emitter thereby generating high energy x-rays;

[0052] Figs. 6B schematically illustrates electrons accelerated towards the anode target from a lower voltage cathode emitter thereby generating high energy x-rays;

[0053] Fig. 7 is a schematic illustration indicating how two arrays, each including multiple cold cathode electron emitters, may all be directed towards a common extended anode target;

[0054] Fig. 8A is a schematic illustration of an x-ray emission tube incorporating two cold cathode electron emission sources in which the anode is held at a positive potential, a first cathode electron emission source is grounded, and the second cathode electron emission sources is held at a negative potential;

[0055] Fig. 8B is a schematic illustration of another embodiment of the x-ray emission tube in which the anode is held at a positive potential by a first ladder of voltage multipliers, the first cathode electron emission source is grounded, and the second cathode electron emission sources is held at a negative potential by a second ladder of voltage multipliers;

[0056] Fig. 8C is a schematic illustration of another embodiment of the x-ray emission tube in which the voltages at the anode and cathodes may be applied via a high-frequency high-voltage (HV / HF) transformer linked power converter;

[0057] Fig. 9 is a schematic illustration of an x-ray emission tube comprising electron deflecting plates for steering the electron beams towards specific part of the anode;

[0058] FIG. 9 shows an alternative embodiment for providing multiple energy levels in an x-ray tube having a single cathode;

[0059] Figs. 11 A and 11 B illustrate exemplary signal profiles of gate signals from the two emitters and the resulting anode current profiles generated at the anode; and

[0060] Fig. 12 illustrates exemplary gate signal profiles generated by alternatively switching the two emitters.

[0061] DETAILED DESCRIPTION OF THE EMBODIMENT

[0062] Aspects of the present disclosure relate to systems and methods for generating x-rays at multiple energy levels by a single device. In particular the disclosure relates to dual energy x-ray tubes in which two electron emitting constructs are each held at a distinct potential difference from a common anode target.

[0063] The system typically includes a vacuum tube, an anode target and multiple electron emitters. Each of the multiple switchable electron emitters may be maintained at a characteristic negative high voltage potential difference relative to the anode target.

[0064] Accordingly, each switchable electron emitters may be activated individually to produce x-rays with characteristic power levels as required.

[0065] As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely examples of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

[0066] As appropriate, in various embodiments of the disclosure, one or more tasks as described herein may be performed by a data processor, such as a computing platform or distributed computing system for executing a plurality of instructions. Optionally, the data processor includes or accesses a volatile memory for storing instructions, data or the like. Additionally or alternatively, the data processor may access a non-volatile storage, for example, a magnetic hard disk, flash-drive, removable media or the like, for storing instructions and / or data.

[0067] It is particularly noted that the systems and methods of the disclosure herein may not be limited in its application to the details of construction and the arrangement of the components or methods set forth in the description or illustrated in the drawings and examples. The systems and methods of the disclosure may be capable of other embodiments, or of being practiced and carried out in various ways and technologies.

[0068] Alternative methods and materials similar or equivalent to those described herein may be used in the practice or testing of embodiments of the disclosure. Nevertheless, particular methods and materials described herein for illustrative purposes only. The materials, methods, and examples not intended to be necessarily limiting. Accordingly, various embodiments may omit, substitute, or add various procedures or components as appropriate. For instance, the methods may be performed in an order different from described, and that various steps may be added, omitted or combined. In addition, aspects and components described with respect to certain embodiments may be combined in various other embodiments.

[0069] Fig. 1 is a block diagram representing selected elements of an embodiment of a switchable x-ray source 100. The digitally switchable x-ray emission system 100 includes an electron emitter 120, an anode target 140, a high voltage supply 145, a low voltage driver 125, a switching unit 160 a controller 180 and a timer 185.

[0070] The electron emitter 120 may be a cold cathode such as a low voltage activated field emission type electron emitting construct configured and operable to release electrons when stimulated by a low voltage. Accordingly, the low voltage driver 125 may include a low voltage driving circuit for activating the electron emitting construct.

[0071] The anode target 140 may comprise a metallic target selected such that x-rays 150 are generated when it is bombarded by accelerated electrons from the electron emitter 120. The anode 140 may be constructed of molybdenum, rhodium, tungsten, or the like or combinations thereof.

[0072] The high voltage supply 145 wired between said electron emitting construct 120 and the anode 140 is provided for establishing an electron accelerating potential between said electron emitting construct 120 and the anode 140.

[0073] It is a particular feature of the digitally switchable x-ray emission system 100 that the digital switching unit 160 is provided to selectively connect and disconnect the low voltage driving circuit 125 thereby selectively activating and deactivating the electron emitting construct 120. Accordingly, emission of the electrons may be controlled by the digital switching system 160.

[0074] When the emitting construct 120 is activated, electrons are accelerated towards said anode target 140 and a pulse of x-rays 150 is generated. As a result, x-ray emission from the anode 140 may be controlled digitally by the switching unit 160.

[0075] The controller 180 may be provided to generate an activation signal which can control the switching rate of the digital switching unit 160. It is particularly noted that in contrast to high voltage switching systems, because the activation signal is a low voltage signal, the response time of the electron emitter is much shorter than the response time of switching the high voltage accelerating potential.

[0076] As a result of the reduced response time of the low voltage switching unit, a timer 185 may be provided to generate a fixed clock signal and a high frequency activation signal may be provided consisting of a series of short duration gate pulses at regular intervals.

[0077] Referring now to Fig, 2, which schematically represents a possible electron emitting construct 220 for use in embodiments of the switchable x-ray source. A field emission type electron source 222 may be electrically connected to a driving circuit 225 via a signal line and further electrically connected to a gate electrode 224. The coordinated electrical activation of the driving circuit 225 and the gate electrode 224 connected to a field emission type electron source 222 results in its activation, i.e., electron emission 230. The field emission type electron source 222 performs the electron emission 230 by an electric field formed between the field emission type electron source 222 and the gate electrode 224.

[0078] The field emission type electron source 222 may be, e.g., a Spindt type electron source, a carbon nanotube (CNT) type electron source, a metal-insulator-metal (MIM) type electron source or a metal-insulator- semiconductor (MIS) type electron source. In a preferred embodiment, the electron source 222 may be a Spindt type electron source.

[0079] The activation signal AS may comprise a series of gate pulses GP generated at a regular intervals At and having a fixed gate-pulse duration 5t1 . Accordingly, the electron emission 230 may follow a similar regular pattern of emission.

[0080] With reference to the block diagram of Fig, 3 which represents another embodiment of a switchable x-ray source 300 incorporating a synchronized optical imager 390.

[0081] The x-rays 350 emitted by the x-ray source 340 may be directed towards a scintillator 370 such that the scintillator 370 fluoresces when a pulse of x-rays 350 is incident thereupon. The optical imager 390 is configured and operable to detect florescence 375 from the scintillator 370 when its shutter 392 is open.

[0082] A shutter controller 395 is provided to trigger the shutter 392 of the optical imager 390 when a shutter pulse is received.

[0083] It is noted that a synchronizer 310 may be provided to synchronize a shutter signal with the electron emission activation signal to further control the imaging duration of the system. Accordingly, the synchronizer 310 may be operable to coordinate a high voltage (HV) signal, a low voltage (LV) signal and an acquisition signal.

[0084] The high voltage signal may be a function overtime determining the characteristics of the high voltage amplitude of the electron accelerating potential produced by the high voltage supply 345. The signal profile of the HV signal may be controlled by the synchronizer 310 and coordinated with the LV signal and the acquisition signal to control the imaging rate of an x-ray device 300.

[0085] The low voltage signal may be a function over time determining the characteristics of the switching rate determined by the controller 380 of the digital switching unit 360. The digital switching unit 360 accordingly may activate the low voltage driver 325 for producing the low voltage activation potential provided to the electron emitting construct 320. The LV signal profile may be controlled by the synchronizer 310 and coordinated with the HV signal and the acquisition signal to control the imaging rate of an x-ray device.

[0086] The acquisition signal may be a function overtime determining the sampling rate of the optical imager 390. Accordingly, by controlling the acquisition signal and coordinating it with the HV signal and the LV signal the synchronizer 310 may control the imaging rate of an x-ray device 300.

[0087] Referring now to Fig. 4A which is a block diagram 400 representing selected elements of a dual energy x-ray generation system configured to switch between producing x-rays having two different energy levels. The dual energy system for generating x-rays at multiple energy levels includes an anode target 402 and at least two cold cathode electron emitters EMITTER I 404 and EMITTER II 404’. It is a feature of the current invention that each of the two cold cathode electron emitters is maintained at a different potential difference from the anode target 402.

[0088] Each cold cathode electron emitter includes a field emission type electron emitting construct and has an associated a low voltage driving circuit LVI DRIVER 406, LVII DRIVER 406’ and a high voltage supply HV1 408 and HV2 408’.

[0089] The field emission type electron emitting construct may be a Spindt type electron source, a carbon nanotube (CNT) type electron source, a metal-insulator-metal (MIM) type electron source or a metal-insulator- semiconductor (MIS) type electron source.

[0090] The low voltage driving circuits are provided to generate gate voltages in order to activate the field emission type electron emitting construct as required. Individual switching units, SWITCH UNIT I 410 AND SWITCH UNIT II 410’ may be provided to activate each low voltage driving circuit LVI DRIVER 406, LVII DRIVER 406’, such as digital switching unit configured to selectively connect and disconnect the associated low voltage driving circuit thereby selectively activating and deactivating the associated electron emitting construct. Accordingly, emission of the electrons from each emitter may be controlled by the digital switching system.

[0091] Although systems with only two power levels are described here for illustrative purposes, where required multiple further electron emitting constructs may be incorporated into the system each having a different high voltage potential difference to provide a multiple power level enabled x-ray source.

[0092] A controller 412 may be provided to generate activation signals which can control the switching rate of each digital switching unit in accordance with individual Low Voltage signals.

[0093] The high voltage supplies are provided to establish accelerating potentials between the associated field emission type electron emitting construct and the anode target. By way of example, the high voltage supplies may comprise a voltage multiplier such as a Villard cascade or the like configured to provide a high voltage DC output from a low voltage AC input.

[0094] It is noted that in order to accelerate electrons towards the anode target, the cathode must be maintained at a lower voltage than the anode. This is often referred to as the cathode being negative and the anode being positive, but it is the potential difference between the anode and the cathode which determines the nature of the accelerating electric field.

[0095] Therefore, there are at least two configurations which may be used to generate the accelerating electric field, cathode grounding connection and anode grounding connection.

[0096] In the cathode-ground connection, the cathode of the X-ray tube is connected to ground potential, and a positive output high-voltage power supply is connected to the anode side. In the anode-ground connection a high-voltage power supply with negative output is connected to the cathode side, while the anode is connected to ground.

[0097] Referring now to Fig. 4B another block diagram is shown representing selected elements of an anode grounded embodiment of the dual energy x-ray tube in which each of two electron emitter cathodes are each held at negative potentials at distinct high voltages relative to a common grounded anode target. In a particular embodiment, EMITTER I is held at a voltage of -120kV and EMITTER II is held at a voltage of -60kV.

[0098] It is a particular feature of the dual energy x-ray emission system that the anode 402 is grounded such that the negative high voltage potential of the first emitter 404 may be different from the negative high voltage potential of the second emitter 404’.

[0099] Reference is now made to the block diagram of Fig. 4C which represents selected elements of an alternative embodiment of the dual energy x-ray tube. In the alternative embodiment, the anode 402 is held at a positive voltage maintaining a positive potential difference between the anode 402 and the ground, for example using a voltage multiplier. The two electron emitter cathodes 404 and 404’ are again maintained at different potential difference to the common anode by grounding the first electron emitter cathode, EMITTER I 404, and maintaining a negative potential difference at the second electron emitter cathode, EMITTER II 404’.

[0100] Accordingly, the potential difference between the first electron emitter cathode EMITTER I 404 and the anode 402 is equal to the voltage of the anode 402 whereas the potential difference between the second electron emitter cathode EMITTER II 404’ and the anode 402 is equal to the sum of the absolute values of the voltages of the anode 402 and the second electron emitter 404’.

[0101] Fig. 5A is a schematic illustration 500 of a dual power x-ray emission tube incorporating two cold cathode electron emission sources held at separate negative potentials. Each cold cathode electron emission source of the embodiment comprises a Spindt type electron source. A Gate Voltage GV may be selectively applied between the gate electrode and the Spindt type electron sources so as to activate electron emission as required. The anode target 502 is connected to the ground and each of the two cold cathode electron emission sources are held at characteristic negative potentials. The first electron emission source 504 is maintained at a voltage of -120kV relative to the grounded anode 502 and the second electron emission source 504’ at a voltage of -60kV relative to the grounded anode 502.

[0102] Referring now to the embodiment of Fig. 5B illustrating another embodiment of the x-ray emission tube incorporating two cold cathode electron emission sources held at separate negative potential differences to a grounded anode. It is noted that a ladder of voltage multipliers 506 is provided to generate high voltage DC potential from an AC Driver 508. It is noted that by connecting the first electron emission source 504 to the end of the ladder of voltage multiplier 506 a voltage of -120kV may be generated, and by connecting the second electron emission source 504’ to the middle of the ladder of voltage multiplier 506 a voltage of -60kV may be generated.

[0103] Figs 6A and 6B schematically illustrate how electrons are accelerated towards the anode target when each of the electron emitters is activated. With particular reference to Fig. 6A, when the first switching unit 606 is closed and the second switching unit 606’ is open. An activating gate voltage is applied to the gate electrode releasing electrons from the first electron emitter 604 which are accelerated across an electric potential of -120kV towards the anode target 602 producing higher power x-rays 608.

[0104] Similarly, with reference to Fig. 6B, when the first switching unit 606 is open and the second switching unit 606’ is closed. An activating gate voltage is applied to the gate electrode releasing electrons from the second electron emitter 604’ which are accelerated across an electric potential of -60kV towards the anode target 602 producing lower power x-rays 608’.

[0105] It is further noted that, where appropriate, electron deflectors may be incorporated into the system to further shape the electron flow and to direct the electrons from the cathode to the anode. The electron deflector uses an electric field to precisely direct the stream of electrons towards a specific target on the anode, allowing for controlled manipulation of the X-ray beam produced. It essentially bends the electron beam to hit different areas of the target depending on the desired application, like selecting specific X-ray energies in a multi-target X-ray tube. The electrons are steered by deflection coils or plates 910 and 910’ as shown in Fig. 9. The deflection is carried out by applying a voltage across the two plates. The electron beam 908 is steered towards specific part of the anode 902 by varying the voltage difference across the plates.

[0106] Referring now to Fig. 7, a schematic illustration 700 is presented indicating how two arrays 704 and 704’, each including multiple cold cathode electron emitters, may all be directed towards a common extended anode target 702.

[0107] Fig. 8A is a schematic illustration 800 of another embodiment of the dual power x-ray emission tube incorporating two cold cathode electron emission sources. Here the anode 802 is held at a high voltage positive potential of +60kV. According to the embodiment, a first cold cathode electron emission source 804 and a second cold cathode electron emission source 804’ both comprise a Spindt type electron source. A Gate Voltage GV may be selectively applied between the gate electrode and the Spindt type electron sources so as to activate electron emission as required.

[0108] It is a feature of the embodiment that the first cold cathode electron emission source 804 is connected to the ground whereas the second cold cathode electron emission source 804’ is held at characteristic negative potential of -60kV.

[0109] Thus, when the first cold cathode electron emission source 804 of the embodiment is activated, the emitted electrons are accelerated towards the anode 802 through a potential difference of 60kV whereas when the second cold cathode electron emission source 804’ of the embodiment is activated the emitted electrons are accelerated towards the anode 802 through a total potential difference of 120kV.

[0110] Referring to Fig. 8B showing a schematic illustration of another embodiment of the x-ray emission tube in which the first cathode electron emission source 804 is grounded and the anode 802 is held at a positive potential by a first ladder of voltage multipliers 806, and the second cathode electron emission source 804’ is held at a negative potential by a second ladder of voltage multipliers 806’ both connected to a common AC driver 808.

[0111] In an alternative embodiment, the voltages at the anode and cathodes may be applied via high- frequency high-voltage (HV / HF) transformer linked power converter as shown in Fig. 8C. The first cathode electron emission source 804 is grounded and the anode 802 is held at a positive potential and the second cathode electron emission source 804’ is held at a negative potential by the power converter 810.

[0112] It should be noted that the potential difference between the anode and the cathode can be generated using any known technology.

[0113] FIG. 10 shows an alternative embodiment for providing multiple energy levels in an x-ray tube having a single cathode. A system 1000 is provided including an x-ray tube 1006 having a single cold cathode 1004 connected to a ladder of voltage multipliers 1008. A discharge tube 1006’ having a switchable cathode 1004’ is connected in parallel with the x-ray tube 1006.

[0114] A voltage monitor 1010 is provided to monitor the total voltage stored in the series of capacitors in the ladder 1008. A controller 1012 is provided to control the gate voltage of the cathode 1004’ of the discharge tube 1006’. The controller 1012 is further in communication with the voltage monitor 1010 such that the cathode 1004’ of the discharge tube 1006’ may be switched according to the monitored voltage.

[0115] The system 1000 may be used to provide the required acceleration voltage at the cathode 1004 of the x-ray tube 1006 through the following steps:

[0116] • The AC driver 1014 charges the series of capacitors in the ladder 1008 to an initial voltage;

[0117] • the voltage monitor 1010 monitors the voltage stored on the series of capacitors of the ladder circuit 1008;

[0118] • the controller 1012 connects the gate voltage to the cathode 1004’ of the discharge tube 1006’ such that the series of capacitors discharges via the discharge anode 1002’ of the discharge tube 1006’ until the voltage monitor 1010 indicates that the required voltage is reached;

[0119] • when the required acceleration voltage is reached, the controller 1012 disconnects the gate voltage to the cathode 1004’ of the discharge tube 1006’; and

[0120] • the gate voltage is connected to the cathode 1004 of the x-ray tube 1006.

[0121] It is noted that the fast response time of the switchable cathodes will allow multiple x-ray images to be produced of a single subject at multiple energy levels within a short span of time. The coordinated electrical activation of the driving circuit and the electron emitter results in its activation, i.e., electron emission. The activation signal may comprise a series of pulses generated at a regular intervals At and having a fixed pulse duration 5t1 . Accordingly, the electron emission may follow a similar regular pattern of emission as shown in Figs. 11 A and 11 B. In Fig. 11 A, the gate signal from the EMITTER I 404 is modulated by the activation signal to produce Pulse Width Modulated (PWM) gate signal 1102. The PWM gate signal 1102 comprise a series of gate pulses of a particular magnitude generated at a regular intervals At and having a fixed gate-pulse duration 5t1 . The plot of anode current la1104 corresponding to the gate signal from the EMITTER I 404 in time is shown. The X-ray dose is controlled by slicing the anode current la1104 in time using PWM of the gate voltage 1102. An effective anode current is given by (5t / At)*la. The effective anode current represents the current which effectively generated the X-ray pulses with the applied gate voltage overtime. The precise calculation of the effective anode current allows the X-ray dosage to be known with enough precision to enable X-ray detection by back scattering. The anode current in applications such as backscatter scanning is typically <100uA.

[0122] The plot of anode current la1104’ corresponding to the gate signal from the EMITTER II 404’ in time is shown in Fig. 10B. The gate signal from EMITTER II 404’ is modulated by the activation signal to produce Pulse Width Modulated (PWM) gate signal 1102’. The PWM gate signal 1102’ comprise a series of gate pulses of a magnitude higher than the magnitude of the pulses generated from EMITTER I, generated at a regular intervals At and having a fixed gate-pulse duration 5t1 .

[0123] In an alternative embodiment of the present invention, X-ray Pulse Code Modulation (PCM) may be used to encode signals into the sliced gate voltage signals. The gate signal is pulse coded modulated by NRZ-L modulation waveform to produce PCM gate signal. Any known PCM techniques such as Unipolar RZ, Bipolar RZ, RZ-AMI, Delay Modulation, etc. can be used to modulate the gate signal without limiting the scope of the invention. The X-ray dose is controlled by slicing the predetermined anode current in time using PCM gate voltage signal.

[0124] In an alternative embodiment, the gate signals generated by EMITTER I 404 and EMITTER II 404' may be alternatively switched by the coordinated electrical activation of the activation signal generated by the controller 412 and the clock signal. The controller 412 generates the activation signal which alternatively switches the SWITCH UNIT I and SWITCH UNIT II to generate gate signals from EMITTER I 404 and EMITTER II 404' as shown in Fig. 12.

[0125] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the disclosure. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

[0126] Although the invention has been described in conjunction with specific embodiments thereof, it is evident that other alternatives, modifications, variations and equivalents will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications, variations and equivalents that fall within the spirit of the invention and the broad scope of the appended claims. Additionally, the various embodiments set forth hereinabove are described in terms of exemplary block diagrams, flow charts and other illustrations. As will be apparent to those of ordinary skill in the art, the illustrated embodiments and their various alternatives may be implemented without confinement to the illustrated examples. For example, a block diagram and the accompanying description should not be construed as mandating a particular architecture, layout or configuration.

Claims

CLAIMS1. A multiple energy X-ray emission system configured to switch between generating X-rays having different energy levels, the system comprising: an anode target; a plurality of field emission type electron emitting constructs, wherein the electron emitting constructs are provided in a single X-ray tube; a low voltage driving circuit for each of the electron emitting constructs configured to generate gate voltage signals for activating the corresponding electron emitting construct; a high voltage supply for each of the electron emitting constructs configured to establish an electron accelerating potential between the corresponding electron emitting construct and the anode target; a digital switching unit for each of the electron emitting constructs operable to selectively connect and disconnect the corresponding low voltage driving circuit thereby selectively activating and deactivating the corresponding field emission type electron emitting construct such that when the corresponding field emission type electron emitting construct is activated electrons are accelerated towards the anode target and a pulse of x-rays is generated; and a controller configured to generate activation signal for controlling the switching rate of each of the digital switching units in accordance with the corresponding gate voltage signals of the electron emitting construct; wherein each of the electron emitting constructs is maintained at a distinct potential difference from the anode target to enable different energy level X-ray transmission.

2. The system of claim 1 , wherein the field emission type electron emitting constructs comprise a Spindt type electron source, a carbon nanotube (CNT) type electron source, a metal-insulator-metal (MIM) type electron source, a metal-insulator-semiconductor (MIS) type electron source, or a combination thereof.

3. The system of claim 1 , wherein the electron emitting constructs are maintained at lower voltages than the anode target.

4. The system of claim 3, wherein the electron emitting constructs are maintained at different negative voltages and the anode target is grounded.

5. The system of claim 3, wherein the electron emitting constructs are maintained at different voltages and the anode target is maintained at a positive voltage higher than the voltages of the electron emitting constructs.

6. The system of claim 1 further comprises one or more electron deflectors to direct the electrons emitted from the emitting constructs to a specific part of the anode target.

7. The system of claim 1, wherein the activation signal comprises a series of gate pulses generated at regular intervals At and having a fixed gate-pulse duration 5t1 .

8. The system of claim 1 further comprising a timer for providing a fixed clock signal.

9. The system of claim 1 , wherein the electron emitting construct comprises a gated cone electron source and gate electrode.

10. The system of claim 1 , wherein the digital switching units of the electron emitting constructs arealternatively switched by the coordinated electrical activation of the activation signal generated by the controller and a clock signal.

11. A multiple energy X-ray emission system configured to switch between generating X-rays having different energy levels, the system comprising: an X-ray tube comprising: an anode target; a first field emission type electron emitting construct; a first low voltage driving circuit configured to generate a first gate voltage signal for activating the first electron emitting construct; and a first digital switching unit operable to selectively connect and disconnect the first low voltage driving circuit thereby selectively activating and deactivating the first electron emitting construct; a discharge tube comprising: a discharge anode; a second field emission type electron emitting construct; a second low voltage driving circuit configured to generate a second gate voltage signal for activating the second electron emitting construct; and a second digital switching unit operable to selectively connect and disconnect the second low voltage driving circuit thereby selectively activating and deactivating the second electron emitting construct; a ladder of voltage multipliers configured to generate high voltage DC potential from an AC Driver; a voltage monitor configured to measure the voltage stored in the voltage multipliers; and a controller configured to control the second gate voltage signal generated by the second low voltage driving circuit and monitor the voltage measured by the voltage monitor to switch from the second electron emitting construct to the first electron emitting construct when a required acceleration voltage is measured by the voltage monitor, wherein fast switching between the first electron emitting construct and the second electron emitting construct enables capturing multiple X-ray images of an object at different energy levels.

12. The system of claim 11 , wherein the AC driver is configured to charge a series of capacitors in the ladder of voltage multipliers to an initial voltage.

13. The system of claim 12, wherein the controller is further configured to: connect the second gate voltage to the second electron emitting construct such that the series of capacitors discharges via the discharge anode of the discharge tube until the required acceleration voltage is reached; disconnect the second gate voltage from the second electron emitting construct; and connect the first gate voltage to the first electron emitting construct to activate the first electron emitting construct and generate X-rays at a particular energy level.

14. A method for generating X-rays having different energy levels, the method comprising: providing a multiple energy X-ray emission system configured to switch between generating X-rays having different energy levels comprising: an anode target;a plurality of field emission type electron emitting constructs, wherein the electron emitting constructs are provided in a single X-ray tube; a low voltage driving circuit for each of the electron emitting constructs configured to generate gate voltage signals for activating the corresponding electron emitting construct; a high voltage supply for each of the electron emitting constructs configured to establish an electron accelerating potential between the corresponding electron emitting construct and the anode; a digital switching unit for each of the electron emitting constructs operable to selectively connect and disconnect the corresponding low voltage driving circuit thereby selectively activating and deactivating the corresponding field emission type electron emitting construct such that when the corresponding field emission type electron emitting construct is activated electrons are accelerated towards the anode target and a pulse of x-rays is generated; and a controller configured to generate activation signal for controlling the switching rate of each of the digital switching units in accordance with the corresponding gate voltage signals of the electron emitting construct; maintaining each of the electron emitting constructs at a different potential difference from the anode target; establishing, by a first high voltage supply, an electron accelerating potential between a first electron emitting construct and the anode target; generating, by the controller, an activation signal comprising at least one gate pulse to activate a first digital switching unit of the one of the digital switching units; sending, by the controller, the activation signal to the first digital switching unit; activating, by the first digital switching unit, a first low voltage driving circuit to generate first gate voltage signals for activating the first electron emitting construct for the duration of each gate pulse; emitting electrons from the first electron emitting construct; accelerating the electrons from the first electron emitting construct to the anode target; and generating, by the anode target, X-rays at a first energy level for the duration of each gate pulse.

15. The method of claim 14, wherein maintaining each of the electron emitting constructs at a different potential difference from the anode target comprises maintaining the electron emitting constructs at lower voltages than the anode target.

16. The method of claim 15 further comprises maintaining the electron emitting constructs at different negative voltages and grounding the anode target.

17. The method of claim 15 further comprises grounding or maintaining the electron emitting constructs at different positive or negative voltages and maintaining the anode target at a positive voltage higher than the voltages of the electron emitting constructs.

18. The method of claim 14 further comprises providing one or more electron deflectors in the multiple energy X-ray emission system to direct the electrons emitted from the emitting constructs to a specific part of the anode target.

19. The method of claim 14, wherein generating the activation signal comprises generating a series of gate pulses at regular intervals At and having a fixed gate-pulse duration 5t1 .

20. The method of claim 14 further comprises providing a timer for providing a fixed clock signal.21 . The method of claim 14 further comprises: generating an activation signal comprising at least one gate pulse by the controller to activate a second digital switching unit of the one of the digital switching units; sending the activation signal to the second digital switching unit; activating a second low voltage driving circuit by the second digital switching unit to generate second gate voltage signals for activating a second emitting construct for the duration of each gate pulse; emitting electrons from the second electron emitting construct; accelerating the electrons from the second electron emitting construct to the anode target; and generating X-rays at a second energy level by the anode target for the duration of each gate pulse.

22. The method of claim 14, wherein: the step of establishing, by the first high voltage supply, an electron accelerating potential between the first electron emitting construct and the anode target comprises varying the accelerating potential over time; the step of generating, by the controller, an activation signal comprises: selecting a required accelerating potential; and selecting an activation time at which the first high voltage supply provides the required accelerating potential; and the step of sending, by the controller, the activation signal to the first digital switching unit comprises sending gate pulse at the activation time.

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