Patent Publication Number: US-7722252-B2

Title: Apparatus and method of use of a high-voltage diagnostic tool for x-ray systems

Description:
BACKGROUND OF THE INVENTION 
     The invention relates generally to systems having a high-voltage energy source and, more particularly, to a method and apparatus of providing a high-voltage diagnostic tool for x-ray imaging systems. 
     Typically, in an x-ray imaging system such as a computed tomography (CT) imaging system, an x-ray source emits a fan-shaped beam toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image. 
     The x-ray source, or x-ray tube, is connected to a high-voltage (HV) generator or tank via high-voltage cables or lines, wherein the HV generator provides the x-ray tube with voltage sufficient to emit an x-ray beam toward the subject. On occasion, x-ray tubes fail when in use in the imaging system due to high-voltage instability, thereby necessitating service to the imaging system by a trained technician. This high-voltage instability results in a high-voltage discharge or arcing between the electrodes of the x-ray tube or between an electrode and ground, where these high-voltage discharges are commonly referred to in the art as “spits.” The “spits” can cause not only failure of the x-ray tube itself, but also failure of attached electrical components. 
     Typically, the technician will perform a no-load test using a “dummy plug” in place of an x-ray tube. The dummy plug is designed to maintain the insulation integrity of the system, which is generally done by leaving the pins of the dummy plug open or shorted to provide adequate insulation for the system, yet not provide the load characteristics of an x-ray tube. The use of a dummy plug in this manner allows the technician to distinguish whether the system failure is attributable to a faulty x-ray tube or high-voltage instability in the HV generator and/or high-voltage cables. Based on the results of this test, the technician typically decides whether it is desired to either simply replace the x-ray tube or to perform a more in-depth analysis of the HV generator using, for instance, another x-ray tube. 
     However, while the no-load test using a dummy plug may distinguish whether the failure is attributable to the x-ray tube or the HV generator, the test typically does not allow the technician to diagnose or detect specific problems that may be related to the x-ray tube, HV generator, or high-voltage cables. For instance, kV regulation errors related to the HV generator would not be detectable when using the dummy plug, as the dummy plug does not mimic the load characteristics of an x-ray tube. As such, a technician typically cannot diagnose specific issues related to the HV generator while in the field. Thus, by using a dummy plug, solutions proposed by the technician in correcting the HV generator or x-ray tube issues may not address the actual failure mode of the system. 
     In order to diagnose a system problem, a technician may use a second known-good x-ray tube which may be connected to the generator to test the system. However, if the problem being diagnosed is in the high-voltage generator, then the technician may unknowingly put the second x-ray tube at risk. Thus, if the second x-ray tube is damaged in the process, it may cost additional time, money, and inconvenience to both the technician and the owner of the system before the problem can be properly diagnosed. 
     Therefore, it would be desirable to design an apparatus and method of providing a high-voltage diagnostic tool for x-ray imaging systems that is capable of providing load conditions for an HV generator during troubleshooting, and is further capable of allowing a technician to diagnose specific problems related to HV generator and/or tank/generator integration issues. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The invention is a directed method and apparatus for simulating or mimicking load conditions of an x-ray tube for an HV generator during troubleshooting, and is further capable of allowing a technician to diagnose specific problems related to HV generator and/or generator/tube integrated functional issues. 
     According to one aspect of the present invention, a diagnostic tool for an x-ray imaging system includes a first test device configured to simulate a first load condition of an x-ray tube, and a first connector electrically coupled to the first test device and configured to couple the first test device to a high-voltage generator in the x-ray imaging system. 
     In accordance with another aspect of the invention, a method of manufacturing a diagnostic tool for an x-ray imaging system includes forming an x-ray tube mimicking device comprising one or more capacitors and resistors. The method further includes attaching a plug interface to the x-ray tube mimicking device, the plug interface configured to connect to a receptacle in the x-ray imaging system, and providing a plurality of leads connecting the plug interface to the one or more capacitors and resistors of the x-ray tube mimicking device. 
     Yet another aspect of the present invention includes a method of diagnosing high-voltage problems for an x-ray imaging system that includes connecting a testing device to a high-voltage generator, the testing device configured to mimic a load condition of an x-ray tube, applying power to the testing device, and identifying a source of a high-voltage instability in the x-ray imaging system using the connected device. 
     Various other features and advantages of the invention will be made apparent from the following detailed description and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate one preferred embodiment presently contemplated for carrying out the invention. 
       In the drawings: 
         FIG. 1  is a block diagram of an imaging system that can benefit from incorporation of an embodiment of the invention. 
         FIG. 2  is a schematic diagram of a testing device for testing major or minor insulation on the cathode side of a high-voltage generator, according to an embodiment of the invention. 
         FIG. 3  is a schematic diagram of a testing device for testing major or minor insulation on the cathode side of a high-voltage generator, according to another embodiment of the invention. 
         FIG. 4  is a schematic diagram of a testing device for testing major or minor insulation on the cathode side of a high-voltage generator, according to another embodiment of the invention. 
         FIG. 5  is a schematic diagram of a testing device for testing major insulation on the anode side of a high-voltage generator, according to another embodiment of the invention. 
         FIG. 6  is a schematic diagram of a testing device for testing minor insulation on the anode side of a high-voltage generator, according to another embodiment of the invention. 
         FIG. 7  is a schematic diagram of a testing device for testing electrode electrical supplies in a wobble-capable high-voltage generator according to another embodiment of the invention. 
         FIG. 8  is a pictorial view of an x-ray system for use with a non-invasive package inspection system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a block diagram of an embodiment of an imaging system  10  designed to acquire original image data and to process the image data for display and/or analysis. It will be appreciated by those skilled in the art that embodiments of the invention are applicable to numerous medical imaging systems implementing an x-ray tube, such as x-ray or mammography systems. Other imaging systems or modalities such as computed tomography (CT) systems and digital radiography systems, which acquire image three dimensional data for a volume, also benefit from embodiments of the invention. The following discussion of x-ray system  10  is merely an example of one such implementation and is not intended to be limiting in terms of modality. 
     As shown in  FIG. 1 , x-ray system  10  includes an x-ray source  12  configured to project a beam of x-rays  14  through an object  16 . Object  16  may include a human subject, pieces of baggage, or other objects desired to be scanned. X-ray source  12  may be a conventional x-ray tube producing x-rays having a spectrum of energies that range, typically, from 30 keV to 200 keV. The x-rays  14  pass through object  16  and, after being attenuated by the object, impinge upon a detector  18 . Each detector in detector  18  produces an analog electrical signal that represents the intensity of an impinging x-ray beam, and hence the attenuated beam, as it passes through the object  16 . In one embodiment, detector  18  is a scintillation based detector; however, it is also envisioned that direct-conversion type detectors (e.g., CZT detectors, etc.) may also be implemented. 
     Referring still to  FIG. 1 , a processor  20  receives the analog electrical signals from the detector  18  and generates an image corresponding to the object  16  being scanned. A computer  22  communicates with processor  20  to enable an operator, using operator console  24 , to control the scanning parameters and to view the generated image. That is, operator console  24  includes some form of operator interface, such as a keyboard, mouse, voice activated controller, or any other suitable input apparatus that allows an operator to control the x-ray system  10  and view the reconstructed image or other data from computer  22  on a display unit  26 . Additionally, console  24  allows an operator to store the generated image in a storage device  28  which may include hard drives, floppy discs, compact discs, etc. The operator may also use console  24  to provide commands and instructions to computer  22  for controlling a high-voltage generator  30  that provides power and timing signals to x-ray source  12 . 
     Typically, x-ray source  12  is an x-ray tube connected to a high-voltage generator, such as the high-voltage generator  30  illustrated in  FIG. 1 , which supplies the high-voltage for operating the x-ray tube. In one arrangement, the x-ray tube includes one or more filaments positioned within a cathode that emit electrons toward an anode when the high-voltage is applied thereto, and when a current is driven through the one or more filaments. In another arrangement, the x-ray tube includes, typically, a single filament having bias tabs positioned proximately thereto. In such an arrangement, bias voltages may be applied to the bias tabs in a rapidly alternating fashion in order to redirect the electron beam emitted from the filament, in order to “wobble” the beam as it is directed toward the anode. As is known in the art, such arrangements typically may include a lead for controlling length of the focal spot, a focus electrode, right and left deflection bias tabs, and a common. In an alternate known arrangement, the beam may be “wobbled” via electromagnetic deflection. 
     As mentioned above, x-ray tubes may experience a failure when in use in an imaging system due to high-voltage instability. Previously, the source of such high-voltage instability was not easily determined by technicians working in the field. However, embodiments of the invention provide a diagnostic tool connectable to the high-voltage generator that is capable of mimicking operation of an x-ray tube and enabling a technician to determine the source of high-voltage instability, thereby allowing technicians to effectively and efficiently resolve issues pertaining to the x-ray tube, the high-voltage generator, or the high-voltage cable connected therebetween. 
     High-voltage systems like those discussed above may either be monopolar systems or bipolar systems. In monopolar systems, the high-voltage generator comprises a single high-voltage receptacle to which an x-ray tube or other device is connected. The single receptacle is designed to provide a negative high-voltage to the cathode side of, for example, an x-ray tube, while the anode side of the x-ray tube is grounded. Conversely, a bipolar system comprises two high-voltage receptacles, one of which provides negative high-voltage to, for example, the cathode side of the x-ray tube and another that provides positive high-voltage to, for example, the anode side of the x-ray tube. 
     As will be set forth below, embodiments of the invention provide for the testing of devices for both monopolar systems and bipolar systems.  FIGS. 2-4 , which will be discussed in further detail below, show devices according to embodiments of the invention that are capable of being used alone in a monopolar system to test for high-voltage instability on the cathode side of a system.  FIGS. 5-6 , on the other hand, include devices according to embodiments of the invention used in bipolar systems. The embodiments shown in  FIGS. 5-6  are input into the anode side of the high-voltage generator and are designed to be used in conjunction with a device similar to that shown in any of  FIGS. 2-4 , which would be input into the cathode side of the high-voltage generator. 
     The testing devices of  FIGS. 2-6  are designed to test major and/or minor insulation in an x-ray system. Major insulation is known as high-voltage insulation, e.g., from 140 kV to ground. Minor insulation, on the other hand, is insulation typically between lines carrying voltages ranging from 20 V to 2 kV. The cathode-side testing devices shown with regard to  FIGS. 2-4  are capable of testing both major and minor insulation on the cathode side of either a monopolar or a bipolar device, while the testing devices shown in  FIGS. 5-6  are designed to test, respectively, major insulation or minor insulation on the anode side of a bipolar device. The specific details of the testing devices according to embodiments of the invention are set forth herebelow. 
     Referring now to  FIG. 2 , testing device or diagnostic tool  50  comprises a connector or plug interface  51  connected to a device  52  for testing major or minor insulation on the cathode side of a high-voltage generator, according to an embodiment of the invention. Plug interface  51  serves to seal and connect the components of device  52  directly with a high-voltage generator  53  having a receptacle  56  configured to mate with plug interface  51 . In one embodiment, a high-voltage cable  54  is positioned between the plug interface  51  and the receptacle  56 . Plug interface  51  is shown to have three leads: a large filament lead  60 ; a common lead  62 ; and a small filament lead  64 . Device  50  may be designed having leads  60 - 64  selected based on the type of x-ray tube being mimicked. Thus, when the testing device is connected to the high-voltage generator  53 , application of high-voltage by the high-voltage generator  53  may allow testing the major insulation thereof, and application of a current to the large filament lead  60  may allow testing the minor insulation thereof. 
     As illustrated in  FIG. 2 , device  52  contains a circuit configuration comprising a resistor  68 , a high-voltage resistor  70 , and a high-voltage capacitor  72  configured to simulate or mimic the load of an x-ray tube. Resistor  68  provides electrical resistance to simulate or mimic the load of filament operation in an x-ray tube and typically has a resistance value that includes resistances ranging from 0.4 ohms to 1.3 ohms. Resistor  70  and capacitor  72  together mimic the load of the high-voltage between cathode and ground of a typical monopolar x-ray tube. Thus, the specific values of the resistors  68 ,  70 , as well as the capacitance of capacitor  72 , may be selected based on the tube being mimicked under its desired operating conditions (e.g., kV, mA, and filament current). Further, while small filament lead  64  is shown to be open in  FIG. 2 , small filament lead  64  may alternatively be connected to a circuit configuration similar to that shown with regard to large filament lead  60 . Thus, diagnostic tool  50  can additionally be configured to test a load through small filament lead  64 , thus testing the minor insulation associated with the small filament and the major insulation associated therewith. In this way, diagnostic tool  50  is capable of testing various load levels so as to mimic different types of x-ray tubes under different operating conditions (e.g., kV, mA, and filament current). 
     In an example where high-voltage instability is observed, a tool, such as tool  50 , may be used to diagnose the source of the problem in place of an x-ray tube or dummy plug. Thus, when diagnostic tool  50  is connected to high-voltage generator  53  via plug interface  51 , the diagnostic tool  50  mimics the full load characteristics of an x-ray tube, thereby simulating the x-ray tube under operation. When diagnostic tool  50  is connected and power from high-voltage generator  53  is applied to tool  50 , the technician can observe whether or not high-voltage discharges (or “spits”) occur, or whether other symptoms of high-voltage instability are present, as is understood within the art. If symptoms occur when the diagnostic tool  50  is connected directly to the high-voltage generator  53 , the technician can ascertain that, for instance, high-voltage instability may be attributable to the high-voltage generator  53  and not a faulty x-ray tube or high-voltage cable. However, if minimal or no high-voltage discharges are observed when the diagnostic tool  50  is connected to high-voltage generator  53 , the technician may deduce that the cause of high-voltage instability in the system lies in either the high-voltage cable or the x-ray tube itself. In such an instance, a test using a high-voltage cable to connect the diagnostic tool  50  to the high-voltage generator  53  can also be performed, where the technician is able to observe whether symptoms occur. Thus, in this instance, if significant discharges are observed, then the technician may further deduce that the problem may be caused by a faulty high-voltage cable. However, if minimal or no high-voltage discharges are observed in this scenario, then a faulty x-ray tube may be deduced to be the cause of the high-voltage instability in the system. 
     In this way, the diagnostic tool  50  enables a technician to deduce whether a failure is caused by the x-ray tube itself, by the high-voltage generator, or by the connection therebetween. If it is determined that the x-ray tube is not at the root of the failure, diagnostic tool  50  is further capable of pinpointing the source of high-voltage instability in the system, be it the high-voltage generator  53  or the high-voltage cable, thereby greatly improving the technician&#39;s understanding of the reasons behind the failure. Further, based on the resistances of resistors  68  and  70 , the capacitance of capacitor  72 , and the type of testing conducted (e.g., kV, mA, and filament current applied) the diagnostic tool  50  may be used as described above to test either the major insulation or the minor insulation of the system. 
     Referring now to  FIG. 3 , a diagnostic tool  80  according to another embodiment of the invention is shown. Diagnostic tool  80  includes a plug interface  81  and device  82 . Plug interface  81  is shown to have three leads: a large filament lead  84 ; a common lead  86 ; and a small filament lead  88 , similar to that which is shown in  FIG. 2 . Diagnostic tool  80  comprises two separate circuit configurations: a small load  87  configured to mimic a small filament, and a large load  89  configured to mimic a large filament, each of which are selectable by way of a switch  90 . Corresponding resistors  92  and  94  provide filament resistance to switch between large and small filaments and to draw the desired current when their respective loads  87 ,  89  are selected via switch  90 . Thus, when switch  90  is connected to the “small” load side  87 , resistor  96  and capacitor  98  together mimic loading of the high-voltage anode/cathode of an x-ray tube, and the small filament is mimicked via the resistor  94 . Conversely, when switch  90  is connected to the “large” load side  89 , resistor  100  and capacitor  98  mimic loading of the high-voltage anode/cathode of an x-ray tube, and the large filament is mimicked via the resistor  92 . Thus, through the use of switch  90 , diagnostic tool  80  is capable of testing both the small and large filament circuits of a system (i.e., minor insulation), which may be done using variable load parameters (kV, mA, and A), as well as testing the major insulation of the system. As such, the diagnostic tool  80  can be used to test for high-voltage instability and deduce the source of instability for a plurality of mimicked scan techniques, and is thus capable of testing both major insulation and minor insulation. 
     Referring now to  FIG. 4 , yet another embodiment of the invention is shown.  FIG. 4  illustrates a diagnostic tool  110  having four circuit configurations  112 ,  114 ,  116 , and  118 . The diagnostic tool further includes a common lead  122 , a large filament lead  123 , and a small filament lead  128 . Switch  120  may select either line  111  or  113  to connect common lead  122  to circuit configurations  112 ,  114  representing, for example, “large” load circuit configurations or to circuit configurations  116 ,  118  representing, for example, “small” load circuit configurations. For example,  FIG. 4  shows that switch  120  connects common lead  122  to the “small” load side circuit configuration  116  at pole  121  and via switch  124 . 
     Further, circuit configurations  112 ,  114  are connected to switch  127  via contact points  1 ,  2 , respectively, for coupling to large filament lead  123 . Circuit configurations  116 ,  118  are likewise connected to switch  126  via contact points  3 ,  4 , respectively, for coupling to small filament lead  128 . Circuit configurations  112 - 118  are designed, like that described above with respect to circuit configurations  87 ,  89  of  FIG. 3 , such that each circuit configuration  112 - 118  represents a respective set of load parameters (kV, mA, and A) corresponding to desired x-ray tube and scan parameter characteristics. 
     Thus, as an example, with switch  120  at pole  121 , and using switches  124  and  126 , the diagnostic tool  110  can be used to choose loads for a desired scan technique using the small filament lead  128 . In like fashion, switch  120  may be switched instead to pole  125 , thus enabling selection of the large load circuits  112 ,  114  via switches  119  and  127 . Furthermore, it can be easily understood that alternate configurations for coupling circuit configurations  112 - 118  to leads  122 ,  123 , and  128  are possible and are deemed to be within the scope of embodiments of the invention. While four circuits  112 - 118  are illustrated, embodiments of the invention are not limited as such, and one skilled in the art will recognize that less or more circuit configurations than those illustrated may be implemented in a single diagnostic tool  110 . 
     In providing these multiple load settings within one device, diagnostic tool  110  enables a technician to test a high-voltage system using a variety of different scan techniques and using a variety of large or small filament resistances, without the need for multiple diagnostic tool devices. Thus, a technician is capable of testing both major insulation and minor insulation in a system using multiple settings embodied in a single device and deducing the source of high-voltage instability in the manner described above. 
     When subjected to high load tests, diagnostic tools  50 ,  80 ,  110  of  FIGS. 2-4  may generate heat that is desirable to be removed therefrom. Accordingly,  FIG. 4  shows a heat pipe  129  or similar device thermally coupled to each circuit configuration  114 ,  118  for cooling the diagnostic tool  110 . Heat pipes  129  are operable to dissipate heat from the circuits thermally coupled thereto and protect the components within diagnostic tool  110 , and heat pipes  129  may be sunk to a cooling device (not shown) that is external to the diagnostic tool  110 . While shown in  FIG. 4 , one skilled in the art will recognize that heat pipe  129  may be thermally coupled to any of the embodiments described herein. One skilled in the art will also recognize that other mechanisms, such as forced convection cooling using gases (such as air), or liquids (such as glycol, dielectric oil, or water, as examples) may be used to cool the diagnostic tool  110   
       FIGS. 2-4  above illustrate embodiments of the invention in relation to monopolar systems, wherein the high-voltage generator  53  has a single receptacle in which the diagnostic tool (or x-ray tube) is connected, and wherein the cathode is at potential while the anode is grounded. However, the embodiments illustrated in  FIGS. 2-4  may be used for testing the cathode side of a bipolar device as well, if used in conjunction with a device configured to test the anode side.  FIGS. 5 and 6  illustrate embodiments of the invention pertaining to a bipolar system, wherein a device may be included to mimic operation of the anode side of a system and diagnose a source of high-voltage instability in a bipolar system, for testing major insulation ( FIG. 5 ) or minor insulation ( FIG. 6 ). 
     Referring to  FIG. 5 , a testing device  130  according to an embodiment of the invention is shown for input into an anode receptacle  152  of the high-voltage generator  150  in a bipolar device, for testing major insulation thereof. The testing device  130  comprises a device  134  and a plug interface  132 , wherein the plug interface  132  includes three leads  135 ,  136 , and  138 . As  FIG. 5  shows, the leads  135 ,  136 , and  138  are open, thus allowing high-voltage to be applied thereto in order to test the major insulation. Thus, in a bipolar system, testing device  130  may be used on an anode side of a high-voltage generator, in conjunction with the cathode side testing devices  50 ,  80 ,  110 . As such, the major insulation on the anode side of a bipolar system may be tested and the source of high-voltage instability therein may be accordingly deduced. 
       FIG. 6  illustrates a testing device  140  usable on the anode receptacle  162  of high-voltage generator  150  for testing minor insulation thereof according to an embodiment of the invention. Testing device  140  includes a device  144  and plug interface  142 , which is designed to be connected with anode receptacle  162  of high-voltage generator  150 . Plug interface  142  has three leads  145 ,  146 , and  148  that are connected to a stator configuration  165  and positioned in device  144  that acts to mimic the load condition of an anode of an x-ray tube for use in a bipolar system. While the configuration is shown in a “delta” configuration, the device is not meant to be limited as such, and one skilled in the art will recognize that other configurations, such as a “wye” configuration, are also within the scope of embodiments of the invention. When inserted into the anode receptacle  162  of the high-voltage generator  150 , testing device  140  may be used to test the minor insulation of the anode side by applying voltage thereto and observing high-voltage instability therein. 
     Thus, when used in conjunction with the testing devices  50 ,  80 ,  110 , both the major and minor insulation of the anode side of a bipolar system can be tested by using, respectively, device  130  of  FIG. 5  and device  140  of  FIG. 6 . Sources of high-voltage instability in the system may accordingly be diagnosed. 
     Referring to  FIG. 7 , yet another embodiment of the invention is shown. The diagnostic tool  180  is designed for troubleshooting high-voltage systems having bias supplies  201  positioned in the high-voltage generator  200 . The bias supplies  201  provide bias voltages to either bias or focus tabs (not shown) within an x-ray tube in order to wobble the electron beam therein. In an alternate embodiment, bias supplies  201  are positioned as supplies that are separate from the high-voltage generator  200 . In such an embodiment the high-voltage generator is configured to bring only the high voltage to the components, and bias voltages are provided via supplies that may be positioned external to the generator  200 , and having minor insulation associated with each lead. 
     In such a system, the diagnostic tool  180  simulates or mimics the capacitive load of the bias or focus tabs within an x-ray tube. As  FIG. 7  illustrates, diagnostic tool  180  comprises a device  184  and a plug interface  182 . Plug interface  182  comprises five electrodes  185 ,  186 ,  187 ,  188 , and  189  connectable to the bias supplies  201  of the high-voltage generator  200  via receptacle  202 . Each electrode  185 - 189  corresponds, in this example, to length, focus, deflection left, deflection right, and common, respectively, of a wobble-capable x-ray tube which enable control of a wobbled spot therein. Each of electrodes  185 - 189  are attached to leads  190 ,  191 ,  192 ,  193 , and  194 , respectively, which are in turn connected to capacitors  210 ,  212 ,  214 ,  216 , and  218  positioned in device  184 . Capacitors  210 - 218  have a capacitive value typically between 100-500 pf. In this case, diagnostic tool  180  acts to mimic the capacitance characteristics of the bias electrodes an x-ray tube having wobble capability, and is operable to allow diagnosis of high-voltage instability attributable to generator bias supplies and/or tube electrodes. In the alternate embodiment where bias supplies  201  are positioned separate from the high-voltage generator  200 , leads bringing electrical supply to the electrodes  185 - 189  may have their minor insulation tested in accordance with the techniques described herein. 
     One skilled in the art will recognize that embodiments of the invention may be combined herein. For instance, the embodiment illustrated in  FIG. 7  is directed toward testing the capacitance characteristics of electrodes in a wobble-capable tube. Because the electrodes are on the cathode side of the wobble-capable tube, such capacitance testing functionality may be combined in a single device with other aspects of the invention having leads that connect to and mimic loading of the small and large filaments. Thus, as an example, in a monopolar device having focal spot wobble capability, the embodiment of  FIG. 7  may be combined with one of the embodiments illustrated in  FIGS. 2-4  to enable mimicking loading of the filaments and the electrodes and, in the manners described above, may be capable of mimicking operation of the cathode in order to test major or minor insulation, as well as the bias tabs and their supplies. Likewise, such a combined device may be further used in conjunction with one of the devices described with respect to  FIGS. 5-6  in order to mimic, test, and diagnose loading and/or operation of a bipolar x-ray tube system having wobble capability. Furthermore, in combining embodiments of the invention, one skilled in the art will recognize that a high-voltage cable may be positioned between the test devices described herein and the high-voltage generator or tank to which they are attached. In such a fashion, a test configuration may include the effects of the high-voltage cable, thus allowing troubleshooting of the high-voltage cable to determine its effect on poor system performance. 
       FIG. 8  is a pictorial view of an x-ray imaging system  500  for use with a non-invasive package inspection system. The x-ray system  500  includes a gantry  502  having an opening  504  therein through which packages or pieces of baggage may pass. The gantry  502  houses a high frequency electromagnetic energy source, such as an x-ray tube  506 , and a detector assembly  508 . A conveyor system  510  is also provided and includes a conveyor belt  512  supported by structure  514  to automatically and continuously pass packages or baggage pieces  516  through opening  504  to be scanned. Objects  516  are fed through opening  504  by conveyor belt  512 , imaging data is then acquired, and the conveyor belt  512  removes the packages  516  from opening  504  in a controlled and continuous manner. As a result, postal inspectors, baggage handlers, and other security personnel may non-invasively inspect the contents of packages  516  for explosives, knives, guns, contraband, etc. One skilled in the art will recognize that gantry  502  may be stationary or rotatable. In the case of a rotatable gantry  502 , system  500  may be configured to operate as a CT system for baggage scanning or other industrial or medical applications. 
     According to one embodiment of the present invention, a diagnostic tool for an x-ray imaging system includes a first test device configured to simulate a first load condition of an x-ray tube, and a first connector electrically coupled to the first test device and configured to couple the first test device to a high-voltage generator in the x-ray imaging system. 
     In accordance with another embodiment of the invention, a method of manufacturing a diagnostic tool for an x-ray imaging system includes forming an x-ray tube mimicking device comprising one or more capacitors and resistors. The method further includes attaching a plug interface to the x-ray tube mimicking device, the plug interface configured to connect to a receptacle in the x-ray imaging system, and providing a plurality of leads connecting the plug interface to the one or more capacitors and resistors of the x-ray tube mimicking device. 
     Yet another embodiment of the present invention includes a method of diagnosing high-voltage problems for an x-ray imaging system that includes connecting a testing device to a high-voltage generator, the testing device configured to mimic a load condition of an x-ray tube, applying power to the testing device, and identifying a source of a high-voltage instability in the x-ray imaging system using the connected device. 
     The invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.