Patent Publication Number: US-2023152245-A1

Title: Scanning spectral x-ray imaging using an alternating high voltage x-ray source

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of priority under 35 U.S.C. 120 to and U.S. Provisional Patent Application Ser. No. 63/279,371, entitled “SCANNING SPECTRAL X-RAY IMAGING USING VARIABLE HIGH VOLTAGE X-RAY SOURCE”, filed on Nov. 15, 2021, the contents of which are incorporated by reference. 
    
    
     BACKGROUND 
     1. Field 
     This specification relates to a system for executing a high-speed tomographic X-ray examination of objects using scanning single or multiple X-ray beams with different spectra. 
     2. Description of the Related Art 
     X-ray imaging is typically performed by producing X-ray radiation, directing it onto the object of examination and capturing the X-ray radiation that passes through the object using various detection technologies. The generation of X-rays has traditionally been performed with a high voltage placed across an anode-cathode vacuum gap, which accelerates electrons from the cathode into the anode. The electrons decelerate in the anode material and produce Bremsstrahlung (“braking radiation”) X-rays, which form a continuous spectrum that is distributed across a range of energies, an example of which is shown in  FIG.  1   .  FIG.  1    shows the typical Bremsstrahlung X-ray spectrum when 70 kVp is applied to the X-ray source. The continuous Bremsstrahlung spectrum may also carry additional peaks of characteristic emission of the anode material. The high voltage that is applied to the anode-cathode gap may be altered to change the range of X-ray photon energies, an effect that is used to optimize the energy dependent attenuation of X-rays in the object under examination. 
     Some technologies use a technique called “spectral imaging.” Spectral imaging measures the energy of the individual X-ray photons captured by the X-ray detector. With information about the photon energies, analysis of the materials through which the X-ray photons have passed may be obtained, which may be used to increase the diagnostic capability of various X-ray imaging modalities. For example, in Computed Tomography (CT), this additional information can be used for facilitating differentiation of tumors and other diseases from healthy tissue by using contrast agents with specific attenuation properties. 
     The challenges of combining spectral X-ray imaging with 3D imaging are significant and are currently resolved at premium cost only by spectral CT machines. However, the spectral CT modality is limited in its applicability to multiple X-ray medical applications—breast cancer screening, orthopedics, pediatric and neonatal X-ray imaging, cardiology, and so on. For example, spectral CT is not suited to the specific patient positioning requirements of breast cancer screening. Spectral CT is also not applicable to real-time X-ray imaging applications, like fluoroscopy, minimally invasive surgery, and others, which require access to the patient during the imaging session. At this time, there are no technologies available for performing spectral 3D X-ray imaging for a majority of traditional medical diagnostic modalities. 
     Systems that employ spectral X-ray detectors may carry a significant cost premium, which impedes widespread adoption of spectral X-ray imaging. The complexity and the additional cost come from the X-ray image acquisition subsystem, which needs to be capable of clinically acceptable spectrometric performance. These acquisition systems may employ photon counting X-ray detectors that exploit the direct detection principle of capturing the X-rays, which drives up the inherent costs. Charge sharing is an additional challenge of the direct detection photon counting systems. Charge sharing is the activation of multiple adjacent pixels by a signal produced by one detected X-ray photon, which reduces the resolution of the resulting image. 
     Some designs use kV switching to perform spectral imaging at different energies. For example, kV switching adjusts the applied high voltage to generate different energy exposures from the same X-ray source, as illustrated in  FIG.  2   .  FIG.  2    shows typical X-ray spectra generated by kV switching between 50 kVp and 70 kVp. kV switching, however, limits the selection of high voltage levels based on the complexity of the high voltage switching hardware and the time required to switch voltage levels, which can introduce motion artifacts in the image. As a result, kV switching may be limited to the imaging of static objects. 
     All CT systems, including the kV switching CT systems described above, are also systems which employ scanning of the X-ray source with respect to the object. CT systems are unique in the sense that the X-ray source and detector relationship is fixed while this assembly is rotated about the patient at a high speed. The cost and geometry of this type of scanning system makes it impractical for standard X-ray diagnostic imaging or industrial applications. However, the use of scanning X-ray sources in diagnostic imaging is well established in the prior art, these systems generate tomographic images for applications such as lung nodule detection and skeletal anomalies. Diagnostic radiography systems can also perform dual spectrum imaging through kV switching although the switching speed, similar to CT, limits the application of this technology in rapid acquisition modalities like tomography. The resolution requirements of diagnostic imaging also prohibit the use of lower resolution CT spectral detectors. 
     Accordingly, there is a need for a system, apparatus, and/or method for scanning spectral X-ray imaging technology suitable for performing high resolution, 3D capture and visualization of dynamic objects and processes. 
     SUMMARY 
     In general, one aspect of the subject matter described in this application is embodied in a scanning imaging system. The scanning imaging system includes a power source. The power source is configured to provide an alternating high voltage. The scanning imaging system includes a single or distributed X-ray source coupled to the power source. The distributed X-ray source includes an array of X-ray emitters. The distributed X-ray sources is configured to generate an X-ray beam with an energy spectrum based on the alternating high voltage. The scanning imaging system includes a controller coupled to the power source and the distributed X-ray source. The controller is configured to sense and control the alternating high voltage. The controller is configured to control a timing of when to engage an X-ray emitter of the array of X-ray emitters of the distributed X-ray source based on a predefined firing pattern. The controller is also configured to drive a scanning mechanism that physically moves the X-ray source through a pre-planned trajectory around the object. 
     These and other embodiments may optionally include one or more of the following features. The controller may be configured to synchronize the timing of when to engage the X-ray emitter with the alternating high voltage. The timing may be adjusted based on a feedback signal from the distributed X-ray source. The timing of when to engage each X-ray emitter of the array of X-ray emitters may be different from the other X-ray emitters and may be based on a change of the alternating high voltage. 
     The power source may be an Alternating Current (AC) generator. The alternating high voltage source may be a combination of direct current and alternating current. The scanning imaging system may include a step-up transformer. The step-up transformer may be coupled to the power source and the distributed X-ray source. The step-up transformer may be configured to receive the alternating high voltage and output a second voltage that is greater than the alternating high voltage. The alternating high voltage may use an alternating current (AC) power line frequency. 
     The scanning imaging system may include multiple X-ray filters. The multiple X-ray filters may be configured to receive the X-ray beam with the energy spectrum as produced by the array of X-ray emitters. The multiple X-ray filters may reduce or eliminate lower energy X-ray photons within the energy spectrum so that an amount of energy delivered is reduced without affecting image quality. The multiple X-ray filters may be configured to use K-edge absorption phenomenon for spectral adjustments. 
     The scanning imaging system may include means to scan multiple X-ray filters. The controller may be configured to select a specific X-ray filter for an X-ray exposure and engage a physical scanning mechanism to position the X-ray emitter such that the X-ray radiation produced by the emitter passes through the selected X-ray filter when the exposure is made. 
     The scanning imaging system may include means to scan X-ray filters with a spatially variant density (gradient filters). The controller may be configured to select a position on a specific gradient X-ray filter for an X-ray exposure and engage a physical scanning mechanism to position the X-ray emitter such that the X-ray radiation produced by the emitter passes through the selected gradient X-ray filter at a position corresponding to a defined X-ray spectrum when the exposure is made. 
     In another aspect, the subject matter is embodied in a method of performing spectral tomographic reconstruction of an object. The method includes providing, by a power source, an adjustable or alternating voltage to the X-ray emitter of a scanning X-ray source. The method includes selecting an X-ray emitter with an energy spectrum from the adjustable or alternating voltage when the adjustable or alternating voltage is within a specific range. The method includes generating, by the X-ray source, a plurality of X-ray beams with multiple energy spectra. 
     The method also includes scanning a single or multiple emitter X-ray source in a pre-planned trajectory around the object to obtain multi-spectral and multiple views of the object for reconstruction into a spectral tomographic image. The pre-planned trajectory may be linear or may incorporate multi-dimensional motion around the object. 
     The method also includes scanning an object in a pre-planned trajectory through the X-ray beam created by the X-ray source(s) to obtain multi-spectral and multiple views of the object for reconstruction into a spectral tomographic image. The pre-planned trajectory may be linear or may incorporate multi-dimensional motion of the object. 
     These and other embodiments may optionally include one or more of the following features. The method may include filtering, using one or more filters, the X-ray beam energy spectrum to remove lower energy photons or to emphasize specific energy spectrum characteristics. The method may include detecting, using an X-ray detector, the multiple X-ray beams created by the scanning X-ray source in rapid succession to form images. The multiple X-ray filters may use K-edge absorption phenomenon for spectrum adjustments. The scanning imaging system may position the X-ray source with respect to the multiple filters to generate a specific X-ray spectrum. The method may include reconstructing the image into a tomographic image. The method may include providing the tomographic image data to a user. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other systems, methods, features, and advantages of the present invention will be apparent to one skilled in the art upon examination of the following figures and detailed description. Component parts shown in the drawings are not necessarily to scale, and may be exaggerated to better illustrate the important features of the present invention. 
         FIG.  1    shows an example graph of a typical Bremsstrahlung X-ray spectrum when 70 kVp is applied to the X-ray source. 
         FIG.  2    shows an example graph of a typical X-ray spectra generated using kV switching between 50 kVp and 70 kVp. 
         FIG.  3    shows a spectral imaging system using a single X-ray source according to an aspect of the invention. 
         FIG.  4    shows an X-ray source with a third electrode for controlling electron flow between the anode and the cathode to shape the X-ray beam according to an aspect of the invention. 
         FIG.  5 A  shows an example graph of spectra designed to identify iodine content in an object using a spectral imaging system according to an aspect of the invention. 
         FIG.  5 B  shows an example graph of spectra designed to identify gadolinium content in the object using a spectral imaging system according to an aspect of the invention. 
         FIG.  5 C  shows an example graph of spectra designed to enable three energy imaging for material decomposition and identification using a spectral imaging system according to an aspect of the invention. 
         FIG.  5 D  shows an example graph of spectra designed to enable four energy imaging for material decomposition and identification using a spectral imaging system according to an aspect of the invention. 
         FIG.  6    shows an example schematic of a scanning spectral imaging system that employs an X-ray source according to an aspect of the invention. 
         FIG.  7    shows an example of different configurations of a distributed X-ray source array of a spectral imaging system according to an aspect of the invention. 
         FIG.  8    shows an example control process to generate multiple different X-ray spectra using the spectral imaging system of  FIG.  6    according to an aspect of the invention. 
         FIG.  9    shows an example of a scanning spectral imaging system that is designed for dual-energy 3D spectral examinations according to an aspect of the invention. 
         FIG.  10    is an example flow diagram of a process to perform a spectral 3D examination using the scanning imaging system  200 ,  300  according to an aspect of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed herein are scanning systems, X-ray sources, filters, detectors, and methods for creating 3D tomographic images. Particular embodiments of the subject matter described in this specification may be implemented to realize one or more of the following advantages. The scanning imaging system has an X-ray source that may drive rapid pulses at a selected time period corresponding to a specific voltage on an alternating high voltage waveform. In this manner, multiple shots may be generated at the same high voltage, or a series of different spectra may be generated by selecting different time periods corresponding to different high voltages. Moreover, the amplitude and the frequency of the alternating voltage may be selected to control the rate and spectral separation of the pulsed X-ray source. This allows the generation of images using different energy spectra without the complexity of multiple power supplies or fast kV switching and may allow the scanning imaging system to operate in spectral imaging mode. Thus, as used herein, the alternating high voltage may refer to alternating current switching or adjustable voltage. 
     Moreover, an array of X-ray emitters may be used and controlled by an array of synchronized spectral selection triggers. Using the array of synchronized spectral selection triggers and/or the array of X-ray emitters, either cold cathode or thermionic, makes it possible to select which emitter will be turned on at which time to control the X-ray spectrum produced by a given X-ray emitter. This allows the generation of spectral angular tomographic information of the object of examination in a very short period of time. Active pixel CMOS X-ray detectors are capable of capturing the X-ray images at required speeds. The spectral angular tomographic information of the object generated by the multiple X-ray emitters coupled with the spectral angular tomographic information obtained by scanning the X-ray source may be computationally processed to create a 3D model of the object which may be further subjected to various analytical processing methods that are dependent on the imaging application. 
       FIG.  3    shows a typical ‘kV switching’ spectral imaging system  100 . The imaging system  100  includes a high voltage (HV) power source  102 , two-electrode X-ray source  106  with an X-ray emitter  106   a , a controller  108 , an X-ray filter  126 , an X-ray detector  120  and/or a computing device  122 . In an example embodiment, the computing device  122  may drive the controller  108  with suitable “user-defined” configurations. An imaging system  100  that uses kV switching may not generate significantly different X-ray spectra with a change of HV only. The imaging system  100  emits X-rays during the time when the HV is applied to the X-ray source  106 , which may affect the quality of the X-ray beam during the rising and falling edges of the HV pulse. 
     As shown in  FIG.  4   , the imaging system  100  may control the production of X-ray radiation through the addition of a third electrode placed between the cathode  118  and the anode  116 , which works as a switching mechanism for the electron current between the cathode and the anode. This third electrode may be called a “grid”  115 . When a first voltage is placed on the grid  115 , the flow of electrons from the cathode  118  to the anode  116  may be stopped, preventing the production of X-ray radiation. When a second voltage is applied to the grid  115 , the electrons accelerate through the grid  115  and the X-ray source  106  produces X-ray beam  114 . The imaging system  100  may operate to produce the X-ray beam based on the timing of the HV voltage and grid control. Therefore, the imaging system  100  is capable of rapid “ON” and “OFF” switching of the X-ray beam. 
     The imaging system  100  may produce short X-ray pulses and may comprise X-ray sources, which employ non-thermionic or “cold” cathodes. These types of devices by design employ the three-electrode X-ray emitter structure. Advanced non-thermionic electron emitting technology, e.g., Carbon Nano Tubes, also enables practical multi-emitter X-ray sources for 3D X-ray imaging due to reduced mechanical and thermal constraints compared to standard thermionic technology. Sources of this type have the capability to switch rapidly, facilitating the concept of selecting a time period where the alternating high voltage would be of a specific value and triggering the source “ON” and “OFF” during these time periods to create multiple spectra in rapid succession. This may allow a scanning imaging system to produce rapidly changing X-ray spectra. If coupled with a detector of sufficiently high frame rate, the result may be a fast spectral imaging system with a single image chain and a single alternating high voltage power supply. 
     The electrons flowing from the cathode  118  to the anode  116  may impact the anode  116  in a defined area with a specific geometry. This impact area geometry may generate an X-ray beam  114  for a particular application. The imaging system  100  may employ a passive, fixed, or variable device or component  119  to focus the electron beam onto the impact area of the anode  116 , creating an X-ray beam  114 , for the particular application. 
     The imaging system  100  may have one or more X-ray filters  126 . The X-ray source  106  may emit the X-ray beam  114  through X-ray filter(s)  126  that have a controlled thickness and/or composition, which may change the spectrum of the X-ray beam. This may provide additional control over the X-ray spectrum produced by the X-ray source  106 . 
     The X-ray filter(s)  126  may be made out of aluminum as this metal exhibits monotonous dependence of attenuation vs. X-ray photon energy in the diagnostic range of X-ray beam energies. X-ray filters of this type are called ‘absorption’ X-ray filters. As X-ray imaging applications vary with respect to the optimal X-ray spectrum to achieve the best X-ray contrast, it is desirable to use different X-ray beam filtration for different X-ray imaging applications. When the thickness of absorption X-ray filter  126  is increased, the low energy X-ray photons are attenuated more than the high energy X-ray photons which results in average energy of the X-ray spectrum shifting towards higher values. This spectral “hardening” reduces the soft energies in the X-ray spectrum which are highly likely to be absorbed by the object and may not reach the X-ray detector  120 . In medical imaging, reducing, or eliminating the lower energy X-ray photons reduces the overall dose to a patient without affecting the image quality. 
     Some materials with high atomic numbers may be used in X-ray filtering to modify the high energy content of the X-ray spectrum. For example, the materials may be a metal, such as tungsten, tin, silver, and others, which have an increased absorption above specific X-ray energies. If X-ray filter(s)  126  made out of this material are inserted into the X-ray beam, a sharp cut-off of the high energy part of the spectrum may be achieved. The rearrangement of the structure of electron shells in the metal atom when the excitation energy of the X-ray photons exceeds the binding energies of the electrons in different electron shells of the atom results in a sharp X-ray absorption increase at energy of X-ray photons which is unique for a specific element. The transition from L-shell to K-shell may have a characteristic energy which falls into the X-ray energy range of interest, which may be referred to as ‘K-edge absorption.’ K-edge absorption X-ray filters also provide filtering for the soft X-rays in the spectrum of the X-ray beam and may provide more control of the X-ray spectrum as compared to absorption filters only. 
     The imaging system  100  may include an X-ray detector  120  and/or a computing device  122 . The X-ray detector  120  may be used to capture X-ray images. The X-ray detector  120  may provide the captured X-ray images to the computing device  122  to analyze and/or process. The computing device  122  may include one or more processors, such as the processor  123  of the computing device  122 . The one or more processors may execute instructions stored in one or more memory, such as the memory  125  of the computing device  122 , to control the power source  102  or to construct the X-ray image. 
     The computing device  122  may include a user interface  124 . The user interface  124  may include an input/output device that receives user input, such as a user interface element, a button, a dial, a microphone, a keyboard, or a touch screen, and/or provides output, such as a display, a speaker, an audio and/or visual indicator. The user interface  124  may receive user input that may include configuration settings. The display of the user interface  124  may present or provide information to the operator, such as the composition of the material of the object. 
       FIGS.  5 A- 5 D  show graphical representations of the X-ray spectra that may be produced by the imaging system  100  using a K-edge absorption filter(s). In  FIG.  5 A , the X-ray filter used for the 70 kVp exposure is 0.5 mm gadolinium, while the X-ray filter for the 40 kVp exposure is 0.2 mm tin. These voltage and X-ray filter combinations will produce X-ray energy spectra with an average energy of approximately 43.9 keV and 25.6 keV, respectively.  FIG.  5 A  also shows an iodine absorption curve. Using these two spectra, two images may be created with iodine emphasized in one and not in the other. The difference between these images is then the iodine alone.  FIG.  5 B  shows the HV values applied to the X-ray source and K-edge absorption filter design which may be used to identify gadolinium using the same principle. Iodine and gadolinium are common contrast agents used in medical imaging. The ability to identify the location of these contrast agents in the body provides clinical data for the radiologist. While these HV and X-ray filter combinations may be capable of discriminating these materials in clinical practice, using them with a single X-ray source  106  requires means to switch the filters between exposures. The X-ray filter switching time delay between the exposures, however, may generate motion artifacts between the exposures and lengthens the examination. 
     The imaging system  100  may vary the high voltage applied to the X-ray source  106  and select one or more K-edge absorption filters to produce X-ray beams that exhibit minimal spectral overlap and may be used effectively for spectral imaging.  FIG.  5 C  shows a non-overlapping X-ray spectra produced using the X-ray source  106  if the X-ray beams produced at 40 kVp, 70 kVp, and 90 kVp are filtered with a 0.2 mm tin filter, a 0.5 mm gadolinium filter, and a 0.3 mm tungsten filter, respectively. This provides for improved material identification based on analysis of the object&#39;s attenuation of the three non-overlapping X-ray spectra. 
       FIG.  5 D  shows one of the possible techniques to increase the number of energy spectra above three. In  FIG.  5 D , the imaging system  100  may use four different HV and additional filtration combinations: 40 kVp, 70 kVp, 90 kVp, and 120 kVp and the X-ray filters respectively are 0.2 mm tin, 0.5 mm gadolinium, 0.3 mm tungsten, and 38 mm aluminum. The difference between the imaging results produced with 120 kVp and a 35 mm aluminum X-ray filter and 90 kVp with a 0.3 mm tungsten X-ray filter may be representative of the exposure produced by a separate X-ray beam with the fourth non-overlapping spectrum starting at approximately 70 keV. Other HV and X-ray filtration combinations using K-edge absorption X-ray filters and absorption X-ray filters may be also designed to address specific needs of various X-ray imaging applications. 
     A scanning imaging system  200  that has a single scanning X-ray source  206 , as shown in  FIG.  6   , for example, may provide switching between different X-ray spectra in generated X-ray beams. For this, the scanning imaging system  200  employs a scanning X-ray source  206  and X-ray filters  230 . The scanning imaging system  200  may utilize scanning to position the X-ray source with respect to specific X-ray filters  230   a  and  230   b  to generate a specific X-ray spectrum. The scanning imaging system  200  may also utilize scanning to move the X-ray source with respect to the object (or vice versa) to obtain different angular views of the object for tomographic imaging. 
     The single scanning X-ray source  206  may be positioned to scan linearly or in a multi-dimensional trajectory. The X-ray source  206  may be positioned at a different location or position surrounding the object and/or may be positioned or moved using an actuator to be directed at the same or different location or position surrounding the object. This allows generating spectral angular tomographic information of the object under examination. 
     The scanning imaging system  200  may be used for dual energy 3D X-ray imaging or for multi-energy 3D X-ray imaging. The scanning imaging system  200  may include an alternating high voltage power source  202 , a X-ray source  206  having a grid-controlled X-ray emitter  206   a , and an X-ray filter(s)  230  that is comprised of different X-ray filters  230   a  and  230   b , which are aligned with or scanned by the X-ray emitter  206   a  of the X-ray source  206  and use absorption filtering and/or K-edge filtering. The scanning imaging system  200  may include a controller  208 , a detector  220  and/or a computing device  222 . Typically, X-ray emitters with grid control of X-ray emission may be operated with sub-millisecond timing resolution, which is at least an order of magnitude faster than the high voltage switching times of the current X-ray high voltage power supplies. Because of this, the speed of switching between the different X-ray spectra for imaging system  200  is determined by the speed of high voltage adjustments of the high voltage power source  202 . 
     The scanning imaging system  200  includes the power source  202 . The power source  202  may be an Alternating Current (AC) generator. The controller  208  may be coupled to the power source  202  and may monitor, control, and/or adjust the adjustable voltage so that different energy spectrums may be produced. The AC generator may provide the voltage in the form of various waveforms, frequencies, and/or amplitudes based on application needs for the imaging system  200 . 
     The AC generator may include or be coupled to a step-up high voltage transformer  204  operated at standard AC power line frequencies, in this case the output high voltage of the power source  202  may be a sine wave with the standard frequency of the AC power line. The diagnostic X-rays in medical imaging may use a high voltage in the range of 40 kV-150 kV. This voltage range may be used for other applications, e.g., in security, food processing, or non-destructive testing. The scanning imaging system  200  may be configured to facilitate rapid high voltage change at the X-ray source  206 , which may enable 3D spectral X-ray imaging. 
     The step-up transformer  204  may provide an alternating high voltage that may be approximately a 70 kVp sine wave  502  running at standard AC line frequency, as shown in  FIG.  8    for example. The controller  208  may be synchronized with the AC line frequency and may select and/or trigger an X-ray emitter at different time intervals  504   a - d . For example, a first X-ray emitter is turned “ON” when the cathode of the first X-ray emitter is enabled during the time interval  504   a  by the control pulse CTRL1, which corresponds to approximately 40 kVp applied to the X-ray source. The controller  208  may adjust the timing based on a feedback signal  250  and  250   a  to ensure that the time interval delivers the desired variable HV to the X-ray emitter. Feedback signal  250  may provide feedback to the controller on the anode voltage at source  206 , and feedback signal  250   a  may provide feedback to the controller on the cathode voltage at source  206 . Furthermore, a feedback signal  250   b  may facilitate coarse alignment. The X-ray filters  230   a  and  230   b  associated with this emitter may be designed to achieve specific filtration of the X-ray beam. The X-ray filters  230   a  and  230   b  may be associated with the X-ray emitter by physically placing the X-ray filters  230   a  or  230   b  in the path of the X-ray beam or the X-ray filters  230   a  or  230   b  may be selected by positioning the X-ray beam of the X-ray source via an actuator so that the X-ray beam passes through the selected X-ray filters  230   a  or  230   b . Therefore, during time interval  504   a , a first X-ray beam with a first energy spectrum may be produced. Subsequently, controller  208  may trigger the X-ray emitter during time interval  504   b , which corresponds to approximately 70 kVp applied at the X-ray source. Additionally, the controller  208  may actuate the scanning mechanism to position the X-ray source with respect to a X-ray filters  230   a  or  230   b  designed to produce a different X-ray spectrum filtration compared to the first X-ray beam, therefore, a second generated X-ray beam may have a different X-ray spectrum. 
     Further, the X-ray filters  230   a  and  230   b  may not be composed of uniform materials, but may be composed of a composite materials which generate a gradient in the filter&#39;s attenuative characteristics. In the scanning imaging system  200 , the controller  208  may position the X-ray source via an actuator at a specific point with respect to the X-ray filters  230   a  and  230   b  that corresponds to specific filtering characteristics not available with a filter of uniform material. 
     In some implementations, the high voltage may not be constant during time intervals  504   a  and  504   b . As previously mentioned, the K-edge filtering technique may alter the spectrum according to the individual properties of the X-ray filter material and therefore the K-edge X-ray filter may also reduce the impact on the X-ray beam spectrum from the varying HV during the time interval that the X-ray emitter is ‘ON’. 
     Further, the controller  208  may operate the actuator to position the X-ray emitter  206   a  in the scanning X-ray source  206  according to the time intervals  504   a  and  504   b  until the last position of the X-ray source is achieved and control pulses CTRL(N−1)  504   c  and CTRL(N)  504   d  are executed. Therefore, with a single emitter, the system is configured to scan with the N variable achieved through scanning at different voltage levels and/or at different physical locations. As a result, the scanning imaging system  200  may produce two sets of X-ray exposures with alternating X-ray spectra between the exposures, each pair taken at different incident angles with respect to the object of examination. This set of X-ray exposures may be used to reconstruct a 3D spectral tomographic image of the object. 
     The scanning imaging system  200  may include a fast X-ray detector (or “detector”)  220 . The detector  220  may capture X-ray images at a high frame rate. The detector  220  may be an active pixel CMOS X-ray detector capable of capturing the X-ray images at the desired speeds. With the detector  220 , the scanning imaging system  200  may reduce the time required to generate a set of spectral tomographic images of the object. 
     The detector  220  may capture images that are produced in a standard mode of operation for the detector  220 . The resolution of the captured X-ray images may be dependent on the geometry of the scanning imaging system  200  and the design of the detector  220 . Therefore, the scanning imaging system  200  may be deployed in imaging applications that require a higher or increased X-ray resolution, e.g., Digital Breast Tomosynthesis. 
     The scanning imaging system  200  may include a computing device  222  and/or a controller  208 . The computing device  222  may include the controller  208  and/or be separate from the controller  208 . The computing device  222  and/or the controller  208  may include one or more processors, such as the processor  223  of the computing device  222 . The one or more processors may execute instructions stored in one or more memory, such as the memory  225  of the computing device  222 , to control the amount of the high voltage that is applied, select the position of the X-ray source  206  to capture the exposure of the one or more images, control a timing of the capture of the exposure and reconstruct the composition of the object to display or provide to an operator. Moreover, in various example embodiments, the controller can be a single controller or a distributed controller. 
     The computing device  222  may include a user interface  224 . The user interface  224  may include an input/output device that receives user input, such as a user interface element, a button, a dial, a microphone, a keyboard, or a touch screen, and/or provides output, such as a display, a speaker, an audio and/or visual indicator. The user interface  224  may receive user input that may include configuration settings. The display of the user interface  224  may present or provide information to the operator, such as the composition of the material of the object. 
       FIG.  9    shows a scanning imaging system  300 . The scanning imaging system  300  may have a high voltage source  302  that may be adjustable or alternating and have or be coupled to a step-up transformer  304 , a controller  308  that is synchronized with the variation of high voltage source  302 , a distributed X-ray source  306  with multiple X-ray emitters  306   a -N, multiple X-ray filters (e.g., filters  330   a -N), and a fast X-ray detector  320  connected to a computing device  322 . The computing device  322  may include a processor  323  and/or a memory  325 . The processor and/or the memory  325  may have similar structure and/or functionality as the processor  123 ,  223  and/or the memory  125 ,  225 . 
     In the scanning imaging system  300 , the multiple emitters in the distributed X-ray source  306  may be arranged or positioned in a two-dimensional (2D) array  242  or in a line array  240 , as shown in  FIG.  7   , for example. 
     The multiple X-ray emitters  306   a -N of the distributed X-ray source  306  may be scanned or positioned around or located at different locations or positions surrounding the object  307 , which is being examined. Alternatively, the object may be positioned via an actuator with respect to the distributed X-ray source  306 . The distributed X-ray source  306  may have or use multiple X-ray filters  330   a ,  330   b - 330 N. The multiple X-ray filters  330   a -N may include multiple types or kinds, such as a first type of X-ray filter  330   a  and/or a second type of X-ray filter  330   b  (up to and including N X-ray filters), which are aligned to corresponding X-ray emitters  306   a -N to filter the X-ray spectra generated by the X-ray emitters  306   a -N. The first type of X-ray filter  330   a  may be designed to output a low energy X-ray beam by a combination of absorption and K-edge absorption materials, whereas the second type of X-ray filter  330   b  may be designed to output a high energy X-ray beam by a combination of absorption and K-edge absorption materials. The multiple X-ray filters  330   a -N may be uniformly distributed across the corresponding X-ray emitters  306   a -N. 
     The controller  308  may select time intervals from the alternating high voltage where the high voltage amplitude in combination with the multiple X-ray filters  330   a -N may produce X-ray beams with the required spectral characteristics. The controller  308  may turn the X-ray emitters “ON” and “OFF” during these time intervals. The timing of the selection of the time intervals may be similar to the timing diagram shown in  FIG.  8   . The controller  308  may select one or more of the X-ray emitters  306   a -N based on configuration data to image the object with enough spectral and angular variation to perform spectral tomographic imaging. The controller may further receive feedback, via feedback signals (not shown), providing feedback with respect to the anode and cathode voltage level for each emitter  306   a -N. 
     The controller  308  may also scan or position the distributed X-ray source  306  via an actuator to different locations or positions surrounding the object  307 , which is being examined. Conversely, the controller may scan or position the object with respect to the distributed X-ray source  306 . In either case, the scanning imaging system  300  may generate a set of spectral angular views of the object through physical scanning of the source or object and/or through the angular separation of the X-ray emitters  306   a -N within the distributed X-ray source  306 . This set of spectral angular views may be reconstructed by the computing device  322  to form a 3D tomographic image of the object. 
       FIG.  10    is a flow diagram of the process  400  to perform a spectral 3D examination using the scanning imaging system  200 ,  300 . One or more computers or one or more data processing apparatuses, for example, the controller  208 ,  308  and/or the processor  223 ,  323  of the computing devices  222 ,  322  of the scanning imaging system  200 ,  300 , appropriately programmed, may implement the process  400 . 
     The scanning imaging system  200 ,  300  receives user input ( 402 ). The user input may include one or more configuration settings for the one or more controllers  208 ,  308  and/or the one or more computing devices  222 ,  322 . The user input may be received from an operator or a user and/or may be pre-loaded, pre-configured or otherwise pre-determined. Different configuration settings may be used for different imaging sequences. The user input may also include a power on signal that powers on the scanning imaging system  200 ,  300 . The user input may indicate the number of X-ray emitter(s)  206   a ,  306   a -N to be selected, used and/or fired. The scanning imaging system  200 ,  300  may turn on when the power on signal is received and configure the controller  208 ,  308  and/or the detector  220 ,  320  based on the one or more configuration settings. 
     The scanning imaging system  200 ,  300  configures the controller  208 ,  308  and/or the detector  220 ,  320  ( 404 ). The imaging system  200 ,  300  may configure the controller  208 ,  308  and/or the detector  220 ,  320  based on the one or more configuration settings. The one or more configuration settings may have been stored in the memory  225 ,  325 . The imaging system  200 ,  300  may configure the power of the X-ray and the spectrum. The imaging system  200 ,  300  may configure X-ray emitter(s)  206   a ,  306   a -N used. 
     The scanning imaging system  200 ,  300  receives a start command ( 406 ). The scanning imaging system  200 ,  300  may receive the start command from the user interface  224 ,  324 . The start command may initialize the power source  202 ,  302  to power on the power source  202 ,  302  to provide the high voltage. 
     The scanning imaging system  200 ,  300  enable or provides the high voltage ( 408 ). The power source  202 ,  302  turns on and provides a variable high-voltage, such as an alternating or adjustable high-voltage. The scanning imaging system  200 ,  300  determines whether the variable high voltage is an alternating or adjustable voltage ( 410 ). When the variable high voltage is an alternating high voltage, the controller  208 ,  308  synchronizes the controller  208 ,  308  to the variable high voltage ( 412 ). The controller  208 ,  308  may be a slave and obtain the high voltage value from the power source  202 ,  302  and follow the high voltage value to synchronize with the variable high voltage. Whereas, when the variable high voltage is an adjustable high voltage, the controller  208 ,  308  sets the high voltage to a required value ( 414 ). The controller  208 ,  308  may be a master and may set or adjust the power source  202 ,  302  to provide the high voltage at the required value. 
     Once the controller  208 ,  308  is synchronized and/or the high voltage is adjusted to the required value, the imaging system  200 ,  300  calculates an exposure timing. The controller  208 ,  308  calculates the exposure timing to control the X-ray emitter(s)  206   a ,  306   a -N from among the one or more X-ray emitters  206   a ,  306   a -N to produce the exposure ( 416 ). The scanning imaging system  300  may determine or select the X-ray emitters,  306   a -N based on the exposure timing to energize or fire the electrode of the X-ray emitters  306   a -N( 418 ). 
     The controller  208 ,  308  may be configured to determine the positioning of the X-ray source  206 ,  306  with respect to the object based on configuration data provided by the user input. The controller  208 ,  308  may be configured to determine if the X-ray source  206 ,  306  is in the correct position in trajectory ( 417 ). If it is not in the correct position, the controller  208 ,  308  may issue the commands to the actuator to drive the actuator to position the X-ray source  206 ,  306  at the pre-determined position (i.e. correct position) for the exposure ( 419 ). In accordance with various example embodiments, the actuator is controlled by computer  322 . Moreover, the computer  222 / 322  may be configured to control one or more of the actuator, the controller  208 ,  308 , and the X-ray filter  230   a  or  230   b ,  330   a -N. 
     The controller  208 ,  308  may also determine the X-ray filter  230   a  or  230   b ,  330   a -N required for the exposure. In other words, the system may be configured to determine if the correct X-ray filter has been selected ( 421 ). If not, the controller  208 ,  308  may position the X-ray source  206 ,  306  through an actuator to align the X-ray beam with the selected X-ray filter  230   a  or  230   b ,  330   a -N( 423 ). 
     The scanning imaging system  200 ,  300  may fire the selected or determined X-ray emitter  206   a ,  306   a -N( 420 ). The variable high voltage is provided through the selected or determined X-ray emitter  206   a ,  306   a -N so that the detector  220 ,  320  may capture an exposure of the image from the selected or determined X-ray emitter  206   a ,  306   a -N. 
     The scanning imaging system  200 ,  300  may capture the X-ray image ( 422 ). The detector  220 ,  320  may capture the X-ray image from the selected or determined X-ray emitter  206   a ,  306   a -N. The detector  220 ,  320  may capture or detect the X-ray beam from each of the one or more X-ray emitters  206   a ,  306   a -N of the X-ray source  206 ,  306 . 
     The scanning imaging system  200 ,  300  determines whether all the spectral images at the position of the X-ray emitter  206   a  or the position and number of the X-ray emitters  306   a -N have been engaged ( 424 ). The scanning imaging system  200 ,  300  may determine whether the position and/or number of X-ray emitters  206   a ,  306   a -N that have been fired is equivalent to the position and/or number of X-ray emitters  206   a ,  306   a -N that were expected to be used. The scanning imaging system  200 ,  300  compares the position and/or number of X-ray emitters  206   a ,  306   a -N used to the number of X-ray emitters  206   a ,  306   a -N specified by the user input. 
     When the positions and/or number of X-ray emitters  206   a ,  306   a -N used is less than the position and/or number of X-ray emitters  206   a ,  306   a -N specified by the user input, the scanning imaging system  200 ,  300  selects or determines a different position and/or number of the X-ray emitter  206   a ,  306   a -N from among the one or more X-ray emitters  206   a ,  306   a -N ( 423 ). The controller  208 ,  308  may cycle, either sequentially or non-sequentially, through each of the one or more positions and/or number of the X-ray emitters  206   a ,  306   a -N until a threshold position and/or number of X-ray emitters  206   a ,  306   a -N have been selected to emit a corresponding X-ray beam so that the detector  220 ,  320  captures or detects the corresponding X-ray image. The threshold position and/or number may be equivalent to the position and/or number of X-ray emitters  206   a ,  306   a -N to be used as indicated in the user input. 
     When the position and/or number of X-ray emitters  206   a ,  306   a -N used matches the position and/or number of X-ray emitters  206   a ,  306   a -N specified by the user input, the imaging system  200 ,  300  may process the X-ray images ( 426 ). The scanning imaging system  200 ,  300  may reconstruct the tomographic image from the captured images and provide the tomographic image to a user or operator. 
     The scanning imaging system  200 ,  300  determines whether another imaging sessions is needed ( 428 ). The scanning imaging system  200 ,  300  may determine whether another imaging session is needed based on the user input. The user input may indicate a number of imaging sessions and/or applications. When the there is no other imaging session needed, the scanning imaging system  200 ,  300  may power down or power off ( 430 ). The scanning imaging system  200 ,  300  may discontinue the delivery of power. Otherwise, the scanning imaging system  200 ,  300  may reconfigure the controller and/or detector for the next or subsequent scanning imaging system  200 ,  300  ( 404 ) session. 
     The implementations of the scanning imaging system  200 ,  300  may have a similar or like components and/or structure, which may have the same or similar functionality. For example, the computing devices  222 ,  322 , the power sources  202 ,  302 , the user interfaces  224 ,  324 , the X-ray sources  206 ,  306 , the controllers  208 ,  308  the X-ray emitters  206   a ,  306   a -N, and/or the X-ray filters  230   a - e ,  330   a -N may have the same or similar structure and/or functionality across the different implementations of the scanning imaging system  200 ,  300 . Other components, such as the step-up transformer  204  may also be interchanged or included in any or all of the different implementations of the scanning imaging system  200 ,  300  to perform the same or similar functionality, as described above. 
     Exemplary embodiments of the methods/systems have been disclosed in an illustrative style. Accordingly, the terminology employed throughout should be read in a non-limiting manner. Although minor modifications to the teachings herein will occur to those well versed in the art, it shall be understood that what is intended to be circumscribed within the scope of the patent warranted hereon are all such embodiments that reasonably fall within the scope of the advancement to the art hereby contributed, and that that scope shall not be restricted, except in light of the appended claims and their equivalents.