Systems and methods for computed tomography - Patents.com

Abstract

To increase the quality of computed tomography (CT) images generated by a CT system by altering a shape of a focal spot of an X-ray emitter of the CT system.SOLUTION: A method comprises: controlling (904, 914) a CT system to focus a beam of electrons generated by a cathode of the CT system on a plurality of focal spots on a surface of a target of the CT system; generating a composite focal spot from the plurality of focal spots; and obtaining (920) projection data of the CT system with the composite focal spot. For example, two focuses may be combined to generate the composite focus. By combining the focal spots to generate the composite focal spots, the quality of view is increased.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE Embodiments of the subject matter disclosed herein relate to medical imaging, and more particularly, to computed tomography imaging systems. [Background technology]

[0002] In a computed tomography (CT) imaging system, an electron beam generated by a cathode is directed at a target in an x-ray tube. In some embodiments, the target may be an anode, and in other embodiments, the x-ray tube may include an anode separate from the target. A fan- or cone-shaped x-ray beam generated by the electrons colliding with the target is directed at an object, such as a patient. After being attenuated by the object, the x-rays impinge on an array of radiation detectors to generate an image. The focal region in the image may depend on the focus of the electron beam on the target, which is created by focusing the electron beam using focusing electrodes and / or magnets. Images generated using a larger focal spot may have a lower spatial resolution, and images generated using a smaller focal spot may have a higher spatial resolution. Thus, to generate images with a desired focal region and a desired spatial resolution, the CT system may be configured to generate a focal spot of a desired size and / or shape. Additionally, in some embodiments, the CT system may be configured to dynamically adjust the position of the focal spot from a first position to a second position alternating between views acquired by the CT system. By alternating the position of the focal spot between successive views, the focal region of the image can be increased, improving image quality.

[0003] However, the inventors herein recognize potential problems with sizing and shaping of focal spots in CT systems. In particular, CT systems may not support alternating two or more focal spots of different sizes and / or shapes, which may combine the advantages of having a smaller focal spot with the advantages of having a larger focal spot. In other words, both a large focal area and high spatial resolution in a portion of an image may be desired, which may not be supported by current CT systems. Furthermore, by generating different focal spots within a view rather than between successive views, the noise distribution resulting from using different focal spots in alternating views may be reduced, and the quality of the image may be increased. Summary of the Invention

[0004] The present disclosure addresses at least in part one or more of the problems identified above by a method for a computed tomography (CT) system that includes controlling the CT system to focus an electron beam generated by a cathode of the CT system to a plurality of focal spots on a surface of a target of the CT system, generating a composite focal spot from the plurality of focal spots, and acquiring projection data of the CT system using the composite focal spot. For example, two foci can be combined to generate a composite focal spot. Combining the two foci can include combining various characteristics of the focal profiles of the two foci, including the positions, shapes, dwell times, and / or transitions of the two foci. Combining the focal spots to generate a composite focal spot can enhance the quality of the resulting view generated by the CT system.

[0005] The above and other advantages and features of the present specification will become readily apparent from the following detailed description, taken alone or in conjunction with the accompanying drawings. It should be understood that the above summary is provided to introduce in a simplified form a selection of concepts that are further described in the detailed description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims that follow the detailed description. Moreover, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. [Brief description of the drawings]

[0006] The various aspects of the disclosure may be better understood upon reading the following detailed description and upon reference to the drawings, in which: [Figure 1] 1 shows a pictorial diagram of an imaging system in accordance with one or more embodiments of the present disclosure. [Diagram 2] FIG. 1 is a block schematic diagram of an exemplary imaging system in accordance with one or more embodiments of the present disclosure. [Diagram 3] 3A and 3B are schematic diagrams of an exemplary X-ray tube and a composite focal spot on a target, in accordance with one or more embodiments of the present disclosure; [Figure 4] 1A-1C are electron distribution diagrams illustrating distribution of electrons of an electron beam into a single focal spot and a composite focal spot in accordance with one or more embodiments of the present disclosure. [Diagram 5]FIG. 5A illustrates a first composite focal spot generated from the first and second focal spots based on a first dwell time, position, and transition of the first and second focal spots, in accordance with one or more embodiments of the present disclosure. FIG. 5B illustrates a second composite focal spot generated from the first and second focal spots based on a second dwell time, position, and transition of the first and second focal spots, in accordance with one or more embodiments of the present disclosure. FIG. 5C illustrates a third composite focal spot generated from the first and second focal spots based on a third dwell time, position, and transition of the first and second focal spots, in accordance with one or more embodiments of the present disclosure. FIG. 5D illustrates a fourth composite focal spot generated from the first and second focal spots based on a fourth dwell time, position, and transition of the first and second focal spots, in accordance with one or more embodiments of the present disclosure. [Figure 6] 6A is a diagram illustrating a first composite focal spot generated from a first focal spot and a second focal spot at the same location based on a dwell time, shape / size, and transition of the first focal spot and the second focal spot of a first dwell time, in accordance with one or more embodiments of the present disclosure; FIG. 6B is a diagram illustrating a second composite focal spot generated from a first focal spot and a second focal spot at the same location based on a second dwell time, shape / size, and transition of the first focal spot and the second focal spot of a second dwell time, in accordance with one or more embodiments of the present disclosure; and FIG. 6C is a diagram illustrating a third composite focal spot generated from a first focal spot and a second focal spot at the same location based on a third dwell time, shape / size, and transition of the first focal spot and the second focal spot of a third dwell time, shape / size, and transition of the first focal spot and the second focal spot of a third dwell time, in accordance with one or more embodiments of the present disclosure. [Figure 7A]FIG. 13 illustrates a first composite focal spot generated from a first focal spot of a first size and first shape at a first location and a second focal spot of a second size and second shape at a second location based on a first dwell time and a transition of the first focal spot and the second focal spot in accordance with one or more embodiments of the present disclosure. [Figure 7B] FIG. 7B illustrates a second composite focal spot generated from the first and second focal spots of FIG. 7A based on a second dwell time and a transition of the first and second focal spots in accordance with one or more embodiments of the present disclosure. [Figure 7C] A figure showing a third composite focal spot generated from the first and second focal spots of FIG. 7A based on a third dwell time and a transition of the first and second focal spots in accordance with one or more embodiments of the present disclosure. [Figure 7D] A figure showing a fourth composite focal spot generated from the first and second focal spots of Figure 7A based on a fourth dwell time and a transition of the first and second focal spots in accordance with one or more embodiments of the present disclosure. [Figure 7E] FIG. 13 illustrates a fifth composite focal spot generated from a first focal spot of a first size and first shape at a first location and a second focal spot of a second size and second shape at a second location based on dwell times and transitions of the first and second focal spots in accordance with one or more embodiments of the present disclosure. [Figure 8] 1 illustrates a plot of a Gaussian electron distribution at a focal point including side lobes in accordance with one or more embodiments of the present disclosure. [Figure 9] 1 is a flowchart illustrating an example method for generating a composite focal spot including a first focal spot and a second focal spot in accordance with one or more embodiments.

[0007] The drawings show certain aspects of the described systems and methods. Together with the following description, the drawings demonstrate and explain the structures, methods, and principles described herein. In the drawings, sizes of components may be exaggerated or otherwise modified for clarity. Well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the described components, systems, and methods. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] This description and embodiments of the subject matter disclosed herein relate to methods and systems for computed tomography (CT) systems. Typically, in a computed tomography (CT) imaging system, an x-ray source emits a fan or cone beam toward an object, such as a patient. Typically, in a CT system, an x-ray source and a detector array are rotated about a gantry within an imaging plane and around the patient, and an image is generated from projection data in multiple views at different viewing angles. For example, for one rotation of the x-ray source, 984 views may be generated by the CT system. The beam, after being attenuated by the patient, impinges on an array of radiation detectors. The x-ray detector or detector array typically includes a collimator for collimating the x-ray beam received at the detector, a scintillator disposed adjacent the collimator for converting x-rays to light energy, and a photodiode for receiving the light energy from the adjacent scintillator and generating an electrical signal therefrom. The intensity of the attenuated beam radiation received at the detector array typically depends on the attenuation of the x-ray beam by the patient. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element, which is transmitted to a data processing system for analysis, which processes the electrical signals to facilitate generating an image.

[0009] The x-ray source includes an x-ray tube, where the cathode emits an electron beam that is directed toward the anode of the x-ray source to strike a target of the x-ray source. The size and shape of the focal spot may depend in part on the angle of the surface of the target relative to the electron beam directed toward the anode. The size and shape of the focal spot on the target may be adjusted by focusing the electron beam via electrostatic controls, electromagnetic controls, or a combination of electrostatic and electromagnetic controls. The x-rays emitted as a result of the electrons striking the target are focused on the patient at an effective focal spot based on the focal spot.

[0010] On the target, the focal spot may have a height corresponding to the patient's Z dimension and a width corresponding to the patient's X dimension. For example, the Z dimension may be aligned with the length of the patient's body (e.g., from the patient's head to the patient's toes) and the X dimension may be aligned with the width of the patient's body (e.g., from the patient's left side to the patient's right side). The height and width of the focal spot may be controlled by electrostatic and electromagnetic controls used to focus the electron beam. In addition, the distribution of electrons in the electron beam impinging on the target may be controlled by electrostatic and electromagnetic controls. For example, the electrostatic and electromagnetic controls may be adjusted to generate a first focal spot having a first distribution of electrons having a first height and a first width, or the electrostatic and electromagnetic controls may be adjusted to generate a second focal spot having a second distribution of electrons having a second height and a second width, one or more of the second distribution, the second height, and the second width being different from the first distribution, the first height, and the first width, respectively.

[0011] The quality of the image produced by the X-ray detector array may depend on the size of the focal spot. If the focal spot is larger, more X-ray flux can be delivered to the patient, which allows thicker or more absorbing anatomical structures to be imaged in a shorter time. When using an X-ray tube where the thermal properties of the target may limit the tube current, less X-ray flux is delivered to the patient when the focal spot is smaller. However, a smaller focal spot results in a higher spatial resolution of the image, and a larger focal spot size results in a lower spatial resolution of the image. Thus, there may be a trade-off between power (e.g., number of electrons striking the target) and spatial resolution. For some clinical tasks, higher power (e.g., larger signal with lower spatial resolution) may be desirable, while for other clinical tasks, high spatial resolution may be desirable.

[0012] The position of the focal spot on the target can also be adjusted via electrostatic and electromagnetic control. In other words, the focal spot can be deflected from a first position on the target to a second position on the target by either or both electrostatic and electromagnetic control. For example, the focal spot can be deflected in the X dimension, where the first position is at a first X position and the second position is at a second X position, or the focal spot can be deflected in the Z dimension, where the first position is at a first Z position and the second position is at a second Z position, or the focal spot can be deflected in both the X and Z dimensions. Additionally, the CT system can provide a “2-point”, “wobble” or “flying focal spot” mode, where the focal spot can alternate between a first position and a second position in successive views acquired by the CT system. For example, a first image of an image sequence can be generated from a first view in which the focal spot is at the first position. A second image of the sequence can be generated from a second view in which the focal spot is at the second position. A third image of the sequence can be generated from a third view with focus at the first position, a fourth image of the sequence can be generated from a fourth view with focus at the second position, and so on. By deflecting the focal spot to alternate between the first and second positions, the quality of the images generated can be increased by increasing the overall focal area of ​​the image. A combination of more than two positions can be used, for example two positions in X and two positions in Z, resulting in a total of four different positions.

[0013] However, the modes supported by the CT system may not support alternating between two or more focal spots of different sizes and / or shapes, which may allow for the advantages of having a larger focal spot (e.g., more power) and the advantages of having a smaller focal spot (e.g., higher spatial resolution), as described in more detail herein. In addition, while a CT system may support alternating between focal spots at different locations between views, the CT system may not support generating more than one focal spot within a view. Because noise is generated each time a signal is sampled, generating more than one focal spot within a view reduces the amount and / or distribution of noise in the generated image, thereby improving the quality of the image without increasing the dose of radiation to which the patient is exposed.

[0014] Thus, methods and systems are proposed herein for generating a composite focal spot including a first focal spot of a first size and shape at a first location and a second focal spot of a second size and shape at a second location, where the second size and shape may be different from the first size and shape. The image generated using the composite focal spot may include both a wide focal region and a portion of the image with high spatial resolution, thereby combining the advantages of using a smaller focal spot with the advantages of using a larger focal spot. The size and shape of the first focal spot and the size and shape of the second focal spot may be individually configured based on the desired profile of the composite focal spot. Furthermore, the composite focal spot may be generated by focusing an electron beam to a first focal spot and a second focal spot within a view acquired by the CT system, or by alternately focusing the electron beam between views acquired by the CT system. A further advantage of the systems and methods described herein is that the composite focal spot may be configured using software while relying on the existing hardware configuration of the X-ray tube of the CT system.

[0015] Examples of CT systems that may be used to perform contrast scans in accordance with the present technique are provided in Figures 1 and 2. Figure 3A shows an exemplary X-ray tube, where an electron beam is focused on a target with a composite focal spot, such as the composite focal spot shown in Figure 3B. Figure 4 shows how a composite focal spot consisting of two discrete focal spots can be generated, where the overall size of the composite focal spot can be increased without increasing the power of the electron beam. The two discrete focal spots can be depicted as a distribution of electrons impinging on a target of the X-ray tube, as shown in Figures 5A-8. Figures 5A-7E show various electron distributions of different sizes, shapes, and positions corresponding to various composite focal spots. Figure 5A shows a first composite focal spot generated from a first focal spot and a second focal spot of the same size based on a first dwell time, position, and transition of the first focal spot and the second focal spot. FIG. 5B illustrates a second composite focal spot generated from the first and second focal spots of FIG. 5A based on a second dwell time, location, and transition of the first and second focal spots. FIG. 5C illustrates a third composite focal spot generated from the first and second focal spots of FIG. 5A based on a third dwell time, location, and transition of the first and second focal spots. FIG. 5D illustrates a fourth composite focal spot generated from the first and second focal spots of FIG. 5A based on a fourth dwell time, location, and transition of the first and second focal spots. FIG. 6A illustrates a first composite focal spot generated from the first and second focal spots at the same locations based on a first dwell time, shape / size, and transition of the first and second focal spots. FIG. 6B illustrates a second composite focal spot generated from the first and second focal spots of FIG. 6A and based on a second dwell time, shape / size, and transition of the first and second focal spots.FIG. 6C illustrates a third composite focal spot generated from the first and second focal spots of FIG. 6A based on a third dwell time, shape / size, and transition of the first and second focal spots. FIG. 7A illustrates a first composite focal spot generated from a first focal spot of a first size and shape at a first location and a second focal spot of a second size and shape at a second location based on a first dwell time and transition of the first and second focal spots. FIG. 7B illustrates a second composite focal spot generated from the first and second focal spots of FIG. 7A based on a second dwell time and transition of the first and second focal spots. FIG. 7C illustrates a third composite focal spot generated from the first and second focal spots of FIG. 7A based on a third dwell time and transition of the first and second focal spots. 7D illustrates a fourth composite focal spot generated from the first and second focal spots of FIG. 7A based on a fourth dwell time and transition of the first and second focal spots. FIG. 7E illustrates a fifth composite focal spot generated from a first focal spot of a first size and shape at a first location and a second focal spot of a second size and shape at a second location based on a dwell time and transition of the first and second focal spots. The fifth composite focal spot of FIG. 7E may include side lobes, such as the side lobes depicted in FIG. 8. The composite focal spot may be generated by following one or more steps of the method described with reference to FIG. 9.

[0016] FIG. 1 illustrates an exemplary CT system 100 configured for CT imaging. In particular, the CT system 100 is configured to image a subject 112, such as a patient, an inanimate object, one or more manufactured parts, and / or a foreign object present in a body, such as a dental implant, a stent, and / or a contrast agent. In one embodiment, the CT system 100 includes a gantry 102, which may further include at least one X-ray source 104 configured to project a beam of X-ray radiation 106 (see FIG. 2) for use in imaging the subject 112 lying on a table 114. In particular, the X-ray source 104 is configured to project the beam of X-ray radiation 106 toward a detector array 108 disposed on the opposite side of the gantry 102. Although FIG. 1 illustrates a single X-ray source 104, in certain embodiments, multiple X-ray sources and detectors may be used to project multiple beams of X-ray radiation to obtain projection data at different energy levels corresponding to the patient. In some embodiments, the X-ray source 104 can enable dual-energy gemstone spectral imaging (GSI) with fast peak kilovoltage (kVp) switching. In some embodiments, the X-ray detectors used are photon-counting detectors that can distinguish between X-ray photons of different energies. In other embodiments, two sets of X-ray sources and detectors, one set at a low kVp and the other at a high kVp, are used to generate dual-energy projections. Thus, it should be appreciated that the methods described herein can be implemented using single-energy acquisition techniques as well as dual-energy acquisition techniques.

[0017] In certain embodiments, the CT system 100 further includes an image processor unit 110 configured to reconstruct an image of the target volume of the object 112 using an iterative or analytical image reconstruction method. For example, the image processor unit 110 can use an analytical image reconstruction approach, such as filtered back projection (FBP), to reconstruct an image of the target volume of the patient. As another example, the image processor unit 110 can reconstruct an image of the target volume of the object 112 using an iterative image reconstruction approach, such as advanced statistical iterative reconstruction (ASIR), conjugate gradient (CG), maximum likelihood expectation maximization (MLEM), model-based iterative reconstruction (MBIR), etc. As described further herein, in some implementations, the image processor unit 110 can use both an analytical image reconstruction approach, such as FBP, in addition to an iterative image reconstruction approach.

[0018] In some CT imaging system configurations, an X-ray source projects a cone-shaped X-ray radiation beam that is collimated to lie within an XYZ plane of a Cartesian coordinate system, commonly referred to as the "imaging plane." The X-ray radiation beam passes through an object being imaged, such as a patient or subject. The X-ray radiation beam is attenuated by the object and then impinges on an array of detector elements. The intensity of the attenuated X-ray radiation beam received at the detector array depends on the attenuation of the X-ray radiation beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the X-ray beam attenuation at the detector location. The attenuation measurements from all the detector elements are acquired separately to produce a transmission profile.

[0019] In some CT systems, the x-ray source and detector array are rotated with a gantry around the object being imaged in the imaging plane such that the angle at which the x-ray beam intersects the object is constantly changing. A group of x-ray radiation attenuation measurements, e.g., projection data, from the detector array at one gantry angle is called a "view." A "scan" of an object includes the set of views made at different gantry angles, or field of view angles, during one revolution of the x-ray source and detector.

[0020] The X-ray source 104 includes an anode and a cathode. Electrons emitted by the cathode (e.g., resulting from energizing the cathode) may be intercepted by a target disposed at or near the anode. The electrons intercepted by the target may emit energy in the form of X-rays, which are directed to the detector array 108. The area of ​​the target surface that receives the electrons from the cathode and forms the emitted X-rays may be referred to herein as a "focal spot." The emitted X-rays may be focused on a portion of the scanned object 204 at an "effective focal spot." The size of the effective focal spot may depend on the angle of the actual focal spot (e.g., on the target surface). For example, a small effective focal spot may be desirable when scanning a small area, while a large effective focal spot may be desirable when scanning a larger area.

[0021] In some embodiments, the X-ray generating system, including the X-ray source 104, can move and / or shape the focal spot. For example, the X-ray generating system can increase or decrease the size of the focal spot. Additionally, in some embodiments, the X-ray generating system can generate a composite focal spot, which is a combination of two or more separate focal spots. For example, two separate focal spots located apart from each other can be combined to generate a single composite focal spot. Composite focal spots are described in more detail below with reference to FIGS. 3-9.

[0022] An exemplary imaging system 200 similar to the CT system 100 of FIG. 1 is shown. According to aspects of the present disclosure, the imaging system 200 is configured to image an object 204 (e.g., the subject 112 of FIG. 1). In one embodiment, the imaging system 200 includes a detector array 108 (see FIG. 1). The detector array 108 further includes a plurality of detector elements 202 that together sense an x-ray radiation beam 106 (see FIG. 2) passing through the object 204 (e.g., a patient) to obtain corresponding projection data. In some embodiments, the detector array 108 can be fabricated in a multi-slice configuration that includes multiple rows of cells or detector elements 202, with one or more additional rows of detector elements 202 arranged in a parallel configuration to obtain projection data.

[0023] In certain embodiments, the imaging system 200 is configured to traverse different angular positions around the object 204 to acquire desired projection data. Thus, the gantry 102 and the components mounted thereon may be configured to rotate about a center of rotation 206 to acquire projection data at different energy levels, for example. Alternatively, in embodiments in which the projection angle relative to the object 204 changes as a function of time, the mounted components may be configured to move along a general curve rather than along a segment of a circle.

[0024] As the X-ray source 104 and detector array 108 rotate, the detector array 108 collects data of the attenuated X-ray beam. The data collected by the detector array 108 undergoes pre-processing and calibration to condition the data to represent the line integral of the attenuation coefficient of the scanned object 204. The processed data is commonly referred to as a projection. In some embodiments, the individual detectors or detector elements 202 of the detector array 108 may include photon-counting detectors that register individual photon interactions into one or more energy bins. It should be understood that the methods described herein may also be implemented using energy-integrating detectors.

[0025] The acquired projection data set may be used for basis material decomposition (BMD). During BMD, the measured projections are transformed into a set of material density projections. The material density projections may be reconstructed to form a pair or set of material density maps or images of each respective basis material, such as bone, soft tissue, and / or contrast agent maps. The density maps or images may be related to form a 3D volumetric image of the basis materials, e.g., bone, soft tissue, and / or contrast agent, within the imaged volume.

[0026] Once reconstructed, the basis material images produced by the imaging system 200 reveal internal features of the object 204, represented by the density of the basis materials. Density images may be displayed to show these features. In a traditional approach to the diagnosis of medical conditions, such as disease states, or more generally medical events, a radiologist or physician considers a hard copy or display of the density image to identify features of interest. Such features may include lesions, sizes and shapes of particular anatomical structures or organs, as well as other features identifiable within the image based on the skill and knowledge of the individual practitioner.

[0027] In one embodiment, the imaging system 200 includes a control mechanism 208 for controlling movement of components such as the rotation of the gantry 102 and the operation of the X-ray source 104. In certain embodiments, the control mechanism 208 further includes an X-ray controller 210 configured to provide power and timing signals to the X-ray source 104. Additionally, the control mechanism 208 includes a gantry motor controller 212 configured to control the rotational speed and / or position of the gantry 102 based on imaging requirements.

[0028] In certain embodiments, the control mechanism 208 further includes a data acquisition system (DAS) 214 configured to sample analog data received from the detector elements 202 and convert the analog data to a digital signal for subsequent processing. The DAS 214 may be further configured to selectively aggregate analog data from a subset of the detector elements 202 into a so-called macro-detector, as further described herein. The data sampled and digitized by the DAS 214 is transmitted to a computer or computing device 216. In one example, the computing device 216 stores the data in a storage device or mass storage 218. The storage device 218 may be any type of non-transitory memory and may include, for example, a hard disk drive, a floppy disk drive, a compact disk read / write (CD-R / W) drive, a digital versatile disk (DVD) drive, a flash drive, and / or a solid-state storage drive.

[0029] Additionally, the computing device 216 provides commands and parameters to one or more of the DAS 214, the X-ray controller 210, and the gantry motor controller 212 to control system operations, such as data acquisition and / or processing. In certain embodiments, the computing device 216 controls system operations based on operator input. The computing device 216 receives operator input, including, for example, commands and / or scanning parameters, via an operator console 220 operably coupled to the computing device 216. The operator console 220 may include a keyboard (not shown) or a touch screen that allows an operator to specify the commands and / or scanning parameters.

[0030] 2 illustrates an operator console 220, multiple operator consoles may be coupled to the imaging system 200, for example, for inputting or outputting system parameters, requesting examinations, plotting data, and / or viewing images. Additionally, in certain embodiments, the imaging system 200 may be coupled to multiple displays, printers, workstations, and / or similar devices, either locally or remotely, e.g., located within a facility or hospital, or at entirely different locations, via one or more configurable wired and / or wireless networks, such as the Internet and / or a virtual private network, a wireless telephone network, a wireless local area network, a wired local area network, a wireless wide area network, a wired wide area network, etc.

[0031] In one embodiment, for example, imaging system 200 includes or is coupled to a picture archiving and communications system (PACS) 224. In an exemplary implementation, PACS 224 is further coupled to remote systems, such as a radiology department information system, a hospital information system, and / or an internal or external network (not shown), allowing operators at different locations to provide commands and parameters and / or gain access to image data.

[0032] The computing device 216 may use operator-supplied and / or system-defined commands and parameters to operate a table motor controller 226, which may control the table 114, which may be a motorized table. In particular, the table motor controller 226 may move the table 114 to properly position the subject 204 within the gantry 102 to acquire projection data corresponding to a target volume of the subject 204.

[0033] As mentioned above, the DAS 214 samples and digitizes the projection data acquired by the detector elements 202. The image reconstructor 230 then performs high-speed reconstruction using the sampled and digitized x-ray data. Although FIG. 2 illustrates the image reconstructor 230 as a separate entity, in certain embodiments, the image reconstructor 230 may form part of the computing device 216. Alternatively, the image reconstructor 230 may not be present in the imaging system 200, and instead, the computing device 216 may perform one or more functions of the image reconstructor 230. Furthermore, the image reconstructor 230 may be located locally or remotely and may be operably connected to the imaging system 200 using a wired or wireless network. In particular, an exemplary embodiment may use computing resources in a "cloud" network cluster for the image reconstructor 230.

[0034] In one embodiment, the image reconstructor 230 stores the reconstructed image in the storage device 218. Alternatively, the image reconstructor 230 may transmit the reconstructed image to the computing device 216 for generating patient information useful for diagnosis and evaluation. In certain embodiments, the computing device 216 may transmit the reconstructed image and / or patient information to a display or display device 232 communicatively coupled to the computing device 216 and / or the image reconstructor 230. In some embodiments, the reconstructed image may be transmitted from the computing device 216 or the image reconstructor 230 to the storage device 218 for short-term or long-term storage.

[0035] Referring to FIG. 3A, an exemplary X-ray tube 300 is shown. In one embodiment, the X-ray tube 300 may be the X-ray source 104 (see FIG. 1). In the illustrated embodiment, the X-ray tube 300 includes an exemplary cathode 302 and an anode 303 disposed within a tube casing 306. The cathode may include one or more emitters 308. The one or more emitters 308 may be flat emitters or curved emitters with a concave curvature providing pre-focusing of the electron beam. In other embodiments, emitters with shapes such as square, rectangular, elliptical, or circular may be used. It should be noted that emitters of different shapes or sizes may be used based on application requirements. For example, in some embodiments, two emitters 308 may be used, with a first emitter 308 generating a first focal spot on the target 304 and a second emitter 308 generating a second focal spot on the target 304, as described in more detail below.

[0036] In this example, the cathode 302, and in particular the one or more emitters 308, may be directly heated by passing a current through the one or more emitters 308, which may be supplied by a voltage source 310. In one embodiment, a current of about 10 amps (A) may be passed through the one or more emitters 308. The one or more emitters 308 may emit an electron beam 312 as a result of being heated by the current supplied by the voltage source 310. As used herein, the term "electron beam" may be used to refer to a stream of electrons having substantially similar velocities.

[0037] The electron beam 312 may be directed toward the target 304 to generate x-rays 314. More specifically, the electron beam 312 may be accelerated from the emitter 308 toward the target 304 by applying a potential difference between the one or more emitters 308 and the anode 303. In one embodiment, a high voltage in the range of about 40 kV to about 450 kV may be applied to set a potential difference between the one or more emitters 308 and the anode 303, thereby generating one or more electric fields 320 within the x-ray tube 300. In one embodiment, a high voltage difference of about 140 kV may be applied between the one or more emitters 308 and the anode 303 to accelerate the electrons in the electron beam 312 toward the target 304. For example, the one or more emitters 308 may be at a potential of about -140 kV, and the anode 303 and the target 304 may be at ground potential or about 0 volts.

[0038] When the electron beam 312 strikes the target 304, heat may be generated within the target 304, which may be large enough to melt the target 304. In various embodiments, a rotating target may be used to avoid the problem of heat generation in the target 304. For example, the target 304 may be configured to rotate such that the electron beam 312 striking the target 304 does not strike the target 304 at the same location, thereby preventing the target 304 from melting. In various embodiments, the target 304 may include materials such as, but not limited to, tungsten or molybdenum. The size of the focal spot on the target 304 may also be adjusted to reduce the amount of heat generated within the target 304, with a smaller focal spot allowing a greater amount of heat to be generated at a particular location. An electron collector 329 held at the same potential as the target 304 acts as a sink for electrons that bounce off the surface of the target 304 during the initial strike, which reduces the chances that those same electrons will re-strike the target. By collecting the backscattered electrons in this manner, target heating is further reduced.

[0039] The X-ray tube 300 may include one or more focusing electrodes 316 that may be positioned adjacent to the emitter 308 such that the one or more focusing electrodes 316 focus the electron beam 312 toward the target 304. As used herein, the term "adjacent" means close in space or position. To focus the electron beam 312, a voltage may be applied to the one or more focusing electrodes 316 to generate one or more electric fields 321. The voltage may be different for each of the one or more focusing electrodes 316. For example, a first voltage may be applied to a first focusing electrode 316, a second voltage may be applied to a second focusing electrode 316, a third voltage may be applied to a third focusing electrode 316, and so on. For some focusing electrodes 316, the voltage may be zero, and no voltage may be applied to the focusing electrodes 316. In some embodiments, a first portion of the focusing electrodes 316 can be used to deflect the electron beam 312 and a second portion of the focusing electrodes 316 can be used to focus the electron beam 312. In this manner, voltages can be selectively applied by a controller in the control electronics module 322 to generate one or more particular electric fields that focus the electron beam 312 into a desired shape and deflect the electron beam 312 to a desired location.

[0040] In some embodiments, the one or more focusing electrodes 316 may each be maintained at a lower potential than the one or more emitters 308. The potential difference between the one or more emitters 308 and the one or more focusing electrodes 316 may prevent electrons generated from the one or more emitters 308 from traveling toward the one or more focusing electrodes 316. In some embodiments, the one or more focusing electrodes 316 may be maintained at a negative potential relative to the potential of the one or more emitters 308. The negative potential of the one or more focusing electrodes 316 relative to the one or more emitters 308 may focus the electron beam 312 away from the one or more focusing electrodes 316, thereby facilitating focusing of the electron beam 312 onto the target 304.

[0041] In other embodiments, the one or more focusing electrodes 316 may be maintained at a potential equal to or substantially similar to that of the one or more emitters 308. Similar voltage potentials of the one or more focusing electrodes 316 relative to the voltage potentials of the one or more emitters 308 may generate a collimated electron beam by shaping the electrostatic field due to the shape of the one or more focusing electrodes 316. The one or more focusing electrodes 316 may be maintained at a potential equal to or substantially similar to that of the one or more emitters 308 through the use of leads coupling the emitter 308 and the one or more focusing electrodes 316.

[0042] Additionally, the x-ray tube 300 may include one or more extraction electrodes 318 that may be used to additionally control and focus the electron beam 312 toward the anode 303. The one or more extraction electrodes 318 may be located between the anode 303 and the one or more emitters 308. In some embodiments, the one or more extraction electrodes 318 may be positively biased by supplying a desired voltage to the one or more extraction electrodes 318.

[0043] The energy of the electron beam 312 can be controlled in a variety of ways. For example, the energy of the electron beam 312 can be controlled by varying the potential difference (e.g., acceleration voltage) between the cathode 302 and the anode 303. As used herein, the term "electron beam current" refers to the flow of electrons per second between the cathode 302 and the anode 303. The current of the electron beam 312 can be controlled by adjusting the emitter voltage 310 to vary the temperature of the emitter 308. The electron beam current can be controlled by changing the voltage applied to the extraction electrode 318. It should be noted that one or more emitters 308 may be treated as an infinite source of electrons.

[0044] One or more electric fields 321 are generated between the one or more extraction electrodes 318 and the one or more focusing electrodes 316 by a potential difference between the one or more focusing electrodes 316 and the one or more extraction electrodes 318. The strength of the one or more electric fields 320 can be used to control the strength of the electron beam 312 generated by the one or more emitters 308 towards the anode 303. More specifically, the electric field 320 can accelerate the electrons emitted by the emitters 308 towards the anode 303. The stronger the one or more electric fields 320, the stronger the acceleration of the electrons from the one or more emitters 308 towards the anode 303. Alternatively, the weaker the one or more electric fields 320, the weaker the acceleration of the electrons from the one or more emitters 308 towards the anode 303. Thus, the strength of the electron beam 312 impinging on the target 304 can be controlled by the one or more electric fields 320 and 321.

[0045] Additionally, voltage shifts of up to 8 kV may be applied to one or more of the extraction electrodes 318 to control the intensity of the electron beam 312. In certain embodiments, these voltage shifts may be applied to one or more of the extraction electrodes 318 through the use of a control electronics module 322, which may be a non-limiting embodiment or may be part of the x-ray controller 210 of FIG.

[0046] In some embodiments, a compound focal spot can be generated as a result of electrostatic focusing by selectively applying voltages to the focusing electrodes 316. When the electron beam 312 is focused onto the target 304, the electrons can form a Gaussian distribution. For purposes of this disclosure, a Gaussian distribution may be an approximately Gaussian distribution.

[0047] The Gaussian distribution of electrons in the electron beam 312 can be narrowed or collimated, and electrons colliding with the target 304 on either side of the Gaussian distribution can be directed toward the center of the Gaussian distribution. In other words, the distribution of electrons on either side of the Gaussian distribution can be inverted. As a result of the narrowing or collimation of the Gaussian distribution, the intensity of the electron beam 312 can be greater at the sides (e.g., outer edges) of the Gaussian distribution than the intensity of the electron beam 312 at the center of the Gaussian distribution. When the intensity of the electron beam 312 is greater on either side of the Gaussian distribution than at the center, this can be visually depicted as "side lobes" formed at the edges of a plot of the Gaussian distribution. A voltage can be applied to the focusing electrodes 316 to generate side lobes on either side of the Gaussian distribution (e.g., in a dimension such as the X or Y dimension as shown by coordinate axes 349 and 352), or a voltage can be applied to the focusing electrodes 316 to generate a side lobe on one side of the Gaussian distribution.

[0048] When Gaussian distribution of electrons with side lobes collide with the target 304 to generate a focal spot, the portion of the focal spot corresponding to the side lobes may receive a greater number of electron collisions than the central portion of the focal spot, generating a composite focal spot. As a result, an image generated using the composite focal spot generated by electrostatic focusing may include a large focal region (e.g., corresponding to the overall size of the composite focal spot) and smaller regions (e.g., corresponding to the side lobes) with high spatial resolution within the large focal region. Thus, by controlling the voltages applied to the focusing electrodes 316, the shape and size of the composite focal spot includes the shapes and sizes of the first component focus (e.g., corresponding to the overall distribution of electrons) and additional component foci (e.g., corresponding to the electron distribution of the side lobes). The generation of a composite focal spot including component focal spots with side lobes is described in more detail below with reference to FIG. 7E.

[0049] Additionally, the x-ray tube 300 may also include one or more magnets 324 for focusing and / or positioning and deflecting the electron beam 312 on the target 304. In various embodiments, the magnet 324 may be disposed between the cathode 302 and the target 304. In some embodiments, the one or more magnets 324 may include one or more multi-pole magnets that affect the focusing of the electron beam 312 by generating one or more magnetic fields 323 that shape the electron beam 312 on the target 304. The one or more multi-pole magnets may include one or more quadrupole magnets, one or more dipole magnets, or a combination thereof. For example, a dipole magnet may be used to deflect the electron beam 312 and position the electron beam 312 in one dimension, while a quadrupole magnet may be used to focus the electron beam 312 in two dimensions (e.g., the length and width of the electron beam 312). For example, in a first step, the electron beam generated by one or more emitters 308 may be deflected and focused by electrostatic focusing. In a second step, the electron beam may be further deflected by one or more dipole magnets to adjust the position of the focal point of the electron beam on the target 304. In a third step, which may be performed before or after the second step, the electron beam may be focused to produce a desired electron distribution (e.g., a desired shape of the focal spot) on the target.

[0050] As the electron beam current and voltage characteristics change, the electrostatic focusing of the electron beam 312 changes accordingly. To maintain a stable size, shape, and other characteristics of the focal spot, or to rapidly modify the focal spot size and / or shape according to system requirements, one or more magnets 324 may provide a magnetic field with controllable performance from steady state to sub-30 microsecond time scale for a wide range of focal spot sizes and shapes. Once the electron beam 312 is focused and positioned, it impacts the target 304 to generate x-rays 314. The x-rays 314 generated by the impact of the electron beam 312 with the target 304 may be directed from the x-ray tube 300 through an opening in the tube casing 306 toward the object 328 at the x-ray window 337.

[0051] As described in more detail in FIG. 8, in various embodiments, the electron beam 312 can be electrostatically and / or magnetically controlled and focused to generate a composite focal spot including two distinct focal spots. More specifically, the electron beam 312 can be electrostatically and / or magnetically controlled and focused to alternate between a first electron beam 325 and a second electron beam 326 that generate a composite focal spot 331 including a first focal spot 332 and a second focal spot 334, respectively, on the target 304. That is, the first electron beam 325 generates a first focal spot 332 and the second electron beam 326 generates a second focal spot 334. The first focal spot 332 and the second focal spot 334 can be separated by a space 335 that represents a portion of the target 304 where the number of electrons of the first electron beam 325 and the second electron beam 326 that collide with the target 304 is minimized. In other words, the electrons of the first electron beam 325 impinge on the target at the first focal point 332 with a first distribution, the electrons of the second electron beam 326 impinge on the target at the second focal point 334 with a second distribution, and at the intersection of the first and second distributions at space 335, a smaller number of electrons impinge on the target 304.

[0052] Further, in some embodiments, the first electron beam 325 is focused on the target 304 for a first duration, the second electron beam 326 is focused on the target 304 for a second duration, and is not focused on the target 304 for a third duration between the first and second durations. That is, during the transition from the first electron beam 325 to the second electron beam 326, the electron beam from one or more emitters 308 can be inhibited or "gridded" by the electrodes 318, such that no electron beam is generated. In some embodiments, one or more emitters 308 can be gridded in response to the duration of the transition exceeding a threshold transition time. In other words, if the transition time is fast (e.g., less than the threshold transition time), one or more emitters 308 may not be gridded, and if the transition time is slow (e.g., greater than the threshold transition time), one or more emitters 308 may be gridded.

[0053] As a result of no electron beam being generated during the transition, the number of electrons impinging on the target 304 in the space 335 may be minimized. Switching off the emitter 308 between the first and second durations may be referred to as beam blanking or blanking. As a result of blanking, the power of the first electron beam 325 and the second electron beam 326 may be maximized (e.g., by minimizing electron collisions on the target 304 between the first and second focal spots).

[0054] When the first electron beam portion 325 impacts the target 304 at the first focal point 332, a first set of x-rays 336 is generated and directed out of the x-ray window 337 toward the object 328. The first set of x-rays 336 may intersect the object 328 at a first effective focal point 340. When the second electron beam portion 326 impacts the target 304 at the second focal point 334, a second set of x-rays 338 is generated and directed out of the x-ray window 337 toward the object 328. The second set of x-rays 338 intersect the object 328 at a second effective focal point 342 that overlaps with the first effective focal point 340. Thus, the first set of x-rays 336 and the second set of x-rays 338 generated from the composite focal spot 331 may be focused to a composite effective focal spot 344 on the object 328. The composite effective focal spot can have a width (in the X dimension, as shown by coordinate axis 348) and a length (in the Z dimension, as shown by coordinate axis 348).

[0055] The size of the first focus 332 may be different from the size of the second focus 334. For example, the first focus 332 may be larger than the second focus 334, and the first focus 332 may be smaller than the second focus 334. Furthermore, the shape of the first focus 332 may be different from the shape of the second focus 334. For example, the first focus 332 may have a first shape with a first width (in the X dimension as shown by coordinate axis 349) and a first height (in the Y dimension as shown by coordinate axis 349), and the second focus 334 may have a second shape with a second width and a second height, and the first height and the first width may be different from the second height and the second width, respectively. The size and shape of the space 335 may also vary. For example, the distance (e.g., the spacing 335) between the first focus 332 and the second focus 334 may be large, or the distance between the first focus 332 and the second focus 334 may be small.

[0056] For example, a front view of a target 304 is shown including a first focal spot 332 and a second focal spot 334. The first focal spot 332 is shown as having a similar width as the second focal spot 334 (in the X dimension, as shown by coordinate axis 352), but a higher height than the second focal spot 334 (in the Y dimension, as shown by coordinate axis 352). The first focal spot 332 is also shown as having a square shape, and the second focal spot 334 is also shown as having a rectangular shape. A space 335 between the first focal spot 332 and the second focal spot 334 has a width equal to the first focal spot 332 and the second focal spot 334, and a height less than the height of the first focal spot 332 and the second focal spot 334. As discussed above, the target 304 may be a rotating circular target such that the first focal spot 332 and the second focal spot 334 are generated at different locations on the surface of the target 304 as the target 304 rotates. By creating the first focal point 332 and the second focal point 334 at different locations on the surface of the target 304, the amount of heat absorbed at the location of the target 304 can be minimized.

[0057] 4, an electron distribution diagram 400 illustrates an initial distribution of electrons of an electron beam of a CT system to a single focal spot 402 that may be split into a compound focal spot 416 including a first distribution of electrons to a first focal spot 404 and a second distribution of electrons to a second focal spot 406 as a result of electrostatic and / or magnetic focusing. The compound focal spot 416 may be the same as or similar to the compound focal spot 331. That is, the single focal spot 402 is generated by the electron beam 312, the first focal spot 404 is the same as or similar to the first focal spot 332 generated by focusing the first electron beam 325 on the target 304, and the second focal spot 406 is the same as or similar to the second focal spot 334 generated by focusing the second electron beam 326 on the target 304.

[0058] The size and shape of the single focal spot 402 may depend on one or more electric fields (e.g., one or more electric fields 321) generated by one or more focusing electrodes (e.g., one or more focusing electrodes 316) and one or more magnetic fields (e.g., magnetic field 323) generated by one or more magnets (e.g., one or more magnets 324). For example, the one or more electric fields may perform a first focusing of an electron beam (e.g., electron beam 312, 325, or 326) to generate an initial focal spot of a first size and shape and deflect the electron beam to a desired location on a target of the CT system, the first size and shape of the initial focal spot may be further refined to a second size and shape by the magnetic field of a quadrupole magnet of one or more magnets, and the resulting focal spot may be further deflected by a dipole magnet of one or more magnets to adjust the position of the focal spot to a desired location.

[0059] The distribution of electrons producing the focal spot in Figure 4 (e.g., single focal spot 402, first focal spot 404, and second focal spot 406) is shown as having a rectangular shape. Although a rectangular shape may be approximated on the target as a result of the configuration of the electric field(s), magnetic field(s), and various shields or barriers of the CT system, it should be appreciated that the distribution of electrons throughout the focal spot is not uniform, but rather may be based on a combination of Gaussian distributions produced by the configuration of the electric field(s) and / or magnetic field(s). Different possible shapes of Gaussian distributions are further described below with reference to Figures 5A-8.

[0060] The single focal spot 402 may have a length 407 and a width 408 as measured along the X-axis of the first focal spot 402. Thus, the single focal spot 402 may have a first size based on the height 407 and the width 408. The first focal spot 404 and the second focal spot 406, together or combined, may have a size equivalent to the first size of the single focal spot 402. In other words, the first focal spot 404 and the second focal spot 406 may have the same length 407 as the single focal spot 402. The first focal spot 404 may have a width 410 and the second focal spot 406 may have a width 412, and the sum of the width 410 and the width 412 may be equal to the width 408. Thus, the total area occupied by the first focal spot 404 and the second focal spot 406 may be equivalent to the total area occupied by the single focal spot 402.

[0061] The first focal spot 404 and the second focal spot 406 of the composite focal spot 416 may be separated by a space 415 (e.g., space 335 in FIG. 3A). The space 415 may have a width 414 that may vary depending on the desired size of the composite focal spot 416. If a larger size of the composite focal spot 416 is desired, the width 414 of the space 415 may be increased. If a smaller size of the composite focal spot 416 is desired, the width 414 of the space 415 may be decreased. Thus, by separating the first focal spot 404 and the second focal spot 406 by the space 415, the size of the composite focal spot 416 may be increased to a size larger than the size of the single focal spot 402, which is indicated by the dashed rectangle 418 in the composite focal spot 416. In other words, the width 420 of the dashed rectangle 418 may be equal to the width 408 of the single focal spot 402, which may be less than the sum 422 of the composite focal spot 416.

[0062] For example, a CT system may have the capability to generate a single focal spot with a maximum width of 2.5 mm, and the width 408 of the first focal spot 402 may be 2.5 mm. To image a particular anatomical structure of a patient, a focal spot with a larger width of 4.5 mm may be desired. To generate a focal spot with a larger width of 4.5 mm, a composite focal spot 416 may be generated and the single focal spot 402 may be split into two focal spots, the first focal spot 404 and the second focal spot 406. In one embodiment, the width 410 of the first focal spot 404 is 2.0 mm, which corresponds to 80% of the width 408 of the single focal spot 402, and the width 412 of the third focal spot 404 is 0.5 mm, which corresponds to 20% of the width 408 of the single focal spot 402. The width 408 (2.5 mm) of the single focal spot 402 may be the sum of the width 410 (2.0 mm) of the first focal spot 404 and the width 412 (0.5 mm) of the second focal spot 406. The first focal spot 404 may then be separated from the second focal spot 406 by 2.25 mm (e.g., width 414) such that the width 422 of the composite focal spot 416 is a desired width of 4.5 mm, which is greater than width 420 (2.5 mm).

[0063] The composite focal spot 416 may be generated in a variety of ways. In some embodiments, the composite focal spot 416 may be generated by controlling the activation of one or more emitters (e.g., one or more emitters 308) and the generation of electrostatic and / or magnetic fields. For example, a single emitter of the one or more emitters may be activated at a first lower power to generate the first focal spot 404, and a single emitter may be activated at a second higher power to generate the second focal spot 406. When the single emitter is activated at a first lower power, the amount of energy delivered to the one or more focusing electrodes and the amount of energy delivered to the one or more magnets (e.g., current) may be controlled to focus the electron beam on the target at the first focal spot 404. When the single emitter is activated at a second higher power, the amount of energy delivered to the one or more focusing electrodes and the amount of energy delivered to the one or more magnets may be controlled to focus the electron beam on the target at the second focal spot 406. A method of activating the emitters of the cathode to generate two or more focal spots is described in FIG.

[0064] Alternatively, in various embodiments, multiple different emitters may be used to generate the first focal spot 404 and the second focal spot 406. For example, a first electron beam (e.g., electron beam 325) may be generated by a first emitter (e.g., one or more of emitters 308 of FIG. 3A), and a second electron beam (e.g., electron beam 326) may be generated by a second emitter. The first emitter may generate the first focal spot 404, and the second electron beam may generate the second focal spot 406. In some embodiments, the first emitter and the second emitter may be configured to operate simultaneously such that the first focal spot 404 and the second focal spot 406 are generated simultaneously on the target (e.g., target 304). For example, a first emitter and a second emitter may be separated by a first distance, and one or more electric fields and one or more magnetic fields may generate a first focal spot 404 and a second focal spot 406 separated by a second distance, the second distance based on the first distance.

[0065] The emitter (e.g., the first emitter and / or the second emitter) may include a filament having a coil diameter. The amount of power generated by the emitter may depend on the coil diameter. For example, if the coil diameter is larger, a larger amount of power (e.g., a larger number of electrons) may be generated by the emitter. If the coil diameter is smaller, less power may be generated by the emitter. In addition, the shape of the focal spot (e.g., the first focal spot 404 and / or the second focal spot 406) may be based on the shape of the emitter. For example, the emitter may be flat and may generate a first electron distribution, or the emitter may be curved and may generate a second, different electron distribution. Different emitter shapes may result in different shapes of the focal spots.

[0066] As discussed above with respect to coil diameter, a flat emitter may generate a larger amount of power (e.g., a larger number of electrons) and a larger radiating area producing a larger (e.g., wider) focal spot, or a smaller amount of power (e.g., fewer electrons) and a smaller (e.g., narrower) focal spot.

[0067] The first emitter and the second emitter can be alternately operated to generate the first focal spot 404 and the second focal spot 406. In other words, the first electron beam is focused on the target for a first duration, and the second electron beam is focused on the target for a second duration. The one or more electric fields and the one or more magnetic fields are configured in a first configuration for a first duration to generate the first focal spot 404, and the one or more electric fields and the one or more magnetic fields are configured in a second configuration for a second duration to generate the second focal spot 406. Due to the amount of time it takes to switch from the first configuration to the second configuration, the composite focal spot 416 can be generated between two different views generated by the CT system when the composite focal spot 416 is generated by alternating the first focal spot 404 for a first duration and the second focal spot 406 for a second duration. For example, a first focal spot 404 is generated in a first view of the CT system, and a second focal spot 406 is generated in a second view of the CT system. An advantage of activating the first and second emitters simultaneously is that the composite focal spot 416 can have a higher average power when the focal spot power is target-limited.

[0068] For some types of anatomical features and / or clinical tasks, a compound focus within a view may be preferred. For other types of anatomical features and / or clinical tasks, a compound focus across two or more views may be preferred. For example, a first compound focus spot may be within a first view, the first view having a first noise distribution. A second compound focus is generated between a second view and a third view, the second view having a second noise distribution, and the third view having a third noise distribution. If the first noise distribution is preferred by the clinician, the CT system may be configured to acquire projection data, each view of the projection data including a compound focus within the view. Alternatively, if the second and / or third noise distributions are preferred by the clinician, the CT system may be configured to acquire projection data, in which a compound focus is generated across alternating views of the projection data.

[0069] Further, additional emitters can be used to generate a composite focal spot that includes additional focal spot components. In FIG. 1, it should be understood that the composite focal spot 416 in FIG. 4 includes two focal spot components (e.g., first focal spot 404 and second focal spot 406), and in other embodiments, additional focal spot components may be included. For example, the composite focal spot 416 can include a first focal spot 404, a second focal spot 406, and a third focal spot, where the first focal spot 404 and the second focal spot 406 are separated by a space 415, and the second focal spot 406 and the third focal spot are separated by a second space. The third focal spot can be generated by a third set of focusing voltages on 316 and focusing currents on 324. In yet other embodiments, a larger number of emitters may be used, such as 10 emitters, or 20 emitters, or a thermionic emitter array may be used, where a first set of emitters may be activated to generate a first focal spot, a second set of emitters may be activated to generate a second focal spot, a third set of emitters may be activated to generate a third focal spot, etc.

[0070] Thereby, the size and shape of the first focal spot 404 can be adjusted to a desired size and shape, and the size and shape of the second focal spot 406 can be adjusted to a desired size and shape. In addition, the shape of the composite focal spot 416 can be configured independent of the distribution of the composite focal spot 416. In other words, the width 410 of the first focal spot 404 can be adjusted based on a first configuration of electrostatic and / or magnetic control of the CT system, the width 412 of the second focal spot 406 can be adjusted based on a second configuration of electrostatic and / or magnetic control of the CT system, and the width 414 of the space 415 can be adjusted based on a third configuration of electrostatic and / or magnetic control of the CT system.

[0071] With respect to the single focal spot 402, the amount of x-ray power and x-ray spatial resolution generated by focusing the electron beam on the target may depend on the size of the single focal spot 402. For example, as the size of the single focal spot 402 decreases, the x-ray power decreases and the x-ray spatial resolution increases. As the size of the single focal spot 402 increases, the x-ray power increases and the x-ray spatial resolution may decrease. Thus, the size of the single focal spot 402 may be adjusted depending on the spatial resolution demands and / or power demands.

[0072] For example, a first type of anatomical feature and / or clinical task may require a higher spatial resolution, whereby the size of the single focal spot 402 may be adjusted to a smaller size. A second type of anatomical feature and / or clinical task may require a lower spatial resolution, whereby the size of the single focal spot 402 may be adjusted to a larger size. By adjusting the size of the single focal spot 402 to a larger size, a larger area of ​​the scanned object (e.g., object 328, such as an anatomical structure) may appear in focus, but with a lower spatial resolution, in a view of the scanned object generated by the CT system. By adjusting the size of the single focal spot 402 to a smaller size, a smaller area of ​​the scanned object may appear in focus, but with a higher spatial resolution.

[0073] Thus, with reference to the composite focal spot 416, the larger width 410 of the first focal spot 404 (e.g., with respect to the second focal spot 406) may correspond to a larger focal area of ​​the scanned object, while the smaller width 412 of the second focal spot 406 may correspond to a smaller high spatial resolution area of ​​the scanned object. By generating the composite focal spot 416 rather than the single focal spot 402, the area of ​​the scanned object that appears in focus may be increased due to the larger overall size of the width 422 of the composite focal spot 416 compared to the single focal spot 402. A first portion of the area of ​​the scanned object that appears in focus may be shown with a high X-ray flux (e.g., allowing small contrast differences between large objects to be more easily distinguished) corresponding to the larger first focal spot 404. A second portion of the area of ​​the scanned object may be shown with a high spatial resolution (e.g., features with large contrast differences may be easily distinguished and resolved) corresponding to the smaller second focal spot 406. Thus, an advantage of generating a composite focal spot 416, as opposed to a single focal spot 402, is that a larger area of ​​the scanned object may be brought into focus while still supporting high spatial resolution within a portion of the larger area. In other words, an image may be generated from a combination of projection data generated with a large focal spot and projection data generated with a small focal spot to balance and / or optimize both low contrast and high resolution throughout different portions of the image acquisition. In some embodiments, the configuration of the composite focal spot may be based on prior measurements of the patient's anatomy.

[0074] 5A-5D, 6A-6C, and 7A-7E show various exemplary distributions of electrons impinging on a target of a CT system, the electrons being generated by one or more emitters of the cathode of the CT system in an electron beam. The electron beam can be focused using the electric and / or magnetic fields of the CT system, such that the electrons impinge on the target at a composite focal spot having a distribution. The composite focal spot can include two or more component focal spots, where the electrons impinging on the target at each of the two or more component focal spots have an electron distribution, and the electron distribution of the composite focal spot is a combination of the electron distributions of the component focal spots. FIGS. 5A-5D, 6A-6C, and 7A-7E can be described with reference to the CT system 100 of FIG. 1 and / or the imaging system 200 of FIG. 2. Thus, the electron beam can be the same as or similar to the electron beams 325 and 326 generated in the x-ray tube 300 of FIG. 3A, and the composite focal spot can be a non-limiting embodiment of the composite focal spot 416. 5A-5D are shown as two-dimensional plots in the X dimension sharing the same X-axis 501. It should be understood that although the electron distributions in Figures 5A-5D are shown as two-dimensional plots in the X dimension, the electron distributions may also be plotted in the Y dimension of the target, with the width of the electron distribution corresponding to the distance along the Y axis.

[0075] The first exemplary electron distribution graph 500 shows a first composite distribution of electrons of two electron beams impinging on a target, the first composite distribution corresponding to a composite focal spot (e.g., composite focal spot 416). As described above with reference to FIG. 4, the composite focal spot can include a two component focal spot. The first line 504 shows a first electron distribution, corresponding to a first focal spot of two component focal spots (e.g., first focal spot 404 in FIG. 4), where the first focal spot is generated by the first electron beam (e.g., second electron beam 325). The second line 506 shows a second electron distribution, corresponding to a second focal spot of the two component focal spots (e.g., second focal spot 406), where the second focal spot is generated by the second electron beam (e.g., second electron beam 326). Lines 502, 504 and 506 share an X-axis 501 marked in millimeters (mm), with zero on the X-axis 501 indicating the central reference point on the target in the X dimension.

[0076] The center of the first electron distribution indicated by line 504 may correspond to the center of the first focal point indicated by dotted line 508. The center of the second electron distribution indicated by line 506 may correspond to the center of the second focal point indicated by dotted line 510. The center of the first electron distribution may be separated from the center of the second electron distribution by a distance 512. In FIG. 5A, the center of the first electron distribution is located at 0 mm on the X-axis 501 and the center of the second electron distribution is located at 1 mm on the X-axis 501, with the distance 512 equal to 1 mm.

[0077] In FIG. 5A, the first electron distribution is substantially similar to the second electron distribution, except that it is offset by a distance 512. As a result, the size and shape of the first focal spot may be identical to the size and shape of the second focal spot (e.g., different from the first focal spot 404 and the second focal spot 406 of FIG. 4). The first electron distribution is a result of deflecting the first electron beam a first distance, the second electron distribution is a result of deflecting the second electron beam a second distance, and the distance 512 may be the difference between the first distance and the second distance. For example, the first distance may be 0 and the second distance may be 1.

[0078] The first exemplary electron distribution graph 500 includes a dashed line 502 indicating a first compound effective focal point, which corresponds to a distribution of electrons of an x-ray (generated by a first electron beam and a second electron beam impinging on a target) on a subject, such as a patient. The first compound effective focal point may be generated by a first compound focal point on a target including a first focal point and a second focal point. The first compound focal point may be indicated by a line 516 on line 514 that intersects with the compound distribution 502. The line 516 may represent the "full width half max" intensity illustrated in FIG. 4.

[0079] The shape of the first compound effective focal spot indicated by line 502 may be adjusted based on a first position and dwell time at which the first electron beam is focused on the target at a first position (thereby generating a first electron distribution indicated by line 504), a second position and dwell time at which the second electron beam is focused on the target at a second position (thereby generating a second electron distribution indicated by line 506), and a transition time between generating the first and second electron beams. For example, in FIG. 5A, the first compound effective focal spot indicated by line 502 may be the result of a first dwell time equal to a second dwell time with a finite transition time between positions.

[0080] In FIG. 5B, a second exemplary electron distribution graph 530 shows a second composite distribution of electrons of the two electron beams of FIG. 5A, where the second composite distribution is based on the first electron distribution and location (indicated by line 504) and also the second electron distribution and location (indicated by line 506) of FIG. 5A. FIG. 5B shares the same X-axis 501 as FIG. 5A. In FIG. 5B, the second composite effective focal spot shown by line 532 has a transition time similar to that of FIG. 5A, but the first dwell time may be greater than the second dwell time. As a result of the first dwell time being greater than the second dwell time, the second composite effective focal spot shown by line 532 is positioned closer to the first electron distribution than the second electron distribution. Thus, by increasing the dwell time of the first electron distribution relative to the dwell time of the second electron distribution, the second composite effective focal spot may be shifted in a negative direction (e.g., leftward) on the X-axis 501.

[0081] In FIG. 5C, a third exemplary electron distribution graph 550 shows a third composite distribution of electrons of the two electron beams of FIGS. 5A and 5B, the third composite distribution being based on the first electron distribution and position (shown by line 504) and the second electron distribution and position (shown by line 506) of FIGS. 5A and 5B as well. FIG. 5C shares the same X-axis 501 as FIGS. 5A and 5B. In FIG. 5C, the third composite effective focal spot shown by line 552 may be the result of the same equal dwell time as FIG. 5A, except that the transition is blanked so that no electrons are emitted during the transition. The size of the third composite effective focal spot shown by line 552 may be larger than the first composite effective focal spot of FIG. 5A, because fewer electrons strike the target between the two positions, thus reducing the peak intensity at the center of the composite beam, effectively widening the beam.

[0082] In FIG. 5D, a fourth exemplary electron distribution graph 580 shows a fourth composite distribution of electrons of the two electron beams of FIGS. 5A, 5B, and 5C, where the fourth composite distribution is also based on the first electron distribution (indicated by line 504) and the second electron distribution (indicated by line 506) of FIGS. 5A, 5B, and 5C. FIG. 5D shares the same X-axis 501 as FIGS. 5A, 5B, and 5C. In FIG. 5D, a fourth composite effective focal spot indicated by line 582 may be the result when the first dwell time of the first electron distribution is greater than the second dwell time of the second electron distribution as in FIG. 5B, and there is a blank transition between the first and second electron distributions as in FIG. 5C. The fourth composite effective focal spot may have an electron distribution that is biased toward the first electron distribution as in line 504, but covers the full range of the second electron distribution as in line 506 along the X-axis 501.

[0083] 5A-5C show various exemplary distributions of electrons in a composite effective focal spot comprised of a first electron distribution and a second electron distribution of the same shape, where the first electron distribution and the second electron distribution are centered at different locations on the X-axis 501, whereas FIGS. 6A-6C show various exemplary distributions of electrons in a composite effective focal spot where the first electron distribution and the second electron distribution are centered at the same location 0 on the X-axis 501 but have different shapes and / or sizes.

[0084] 6A, a first exemplary electron distribution graph 600 illustrates a first composite distribution of electrons of two electron beams impinging on a target, the first composite distribution corresponding to a composite focal spot. The composite focal spot may be composed of two component focal spots, as described above with reference to FIG. 4. A first line 604 illustrates a first electron distribution corresponding to a first focal spot (e.g., first focal spot 404 of FIG. 4) of the two component focal spots, the first focal spot being generated by the first electron beam (e.g., second electron beam 325). A second line 606 illustrates a second electron distribution corresponding to a second focal spot (e.g., second focal spot 406 of FIG. 4) of the two component focal spot, the second focal spot being generated by the second electron beam (e.g., second electron beam 326).

[0085] 6A, a first electron distribution 604 is a result of focusing a first electron beam according to a first configuration of electrostatic and / or electromagnetic control of the CT system, and a second electron distribution 606 is a result of focusing a second electron beam according to a second configuration of electrostatic and / or electromagnetic control of the CT system. For example, the first configuration of the electrostatic and / or electromagnetic control may generate a wide electron distribution, and the second configuration of the electrostatic and / or electromagnetic control may generate a narrow electron distribution.

[0086] The first exemplary electron distribution graph 600 includes a dashed line 602 indicating a first compound effective focus, which corresponds to a distribution of electrons of an X-ray (generated by a first electron beam and a second electron beam impinging on a target) on a subject, such as a patient. The first compound effective focus may be generated by a first compound focus on a target including a first focus and a second focus. In FIG. 6A, the first compound focus may be indicated by a line 614 that intersects with the compound distribution 602 (indicated by a line 616). Both the first focus and the second focus may be centered on the same point 0 of the X-axis 501. The first focus indicated by the line 616 may be a large focus (e.g., wide in the X-dimension) and the second focus indicated by the line 618 may be a small focus (e.g., narrow in the X-dimension). Thus, the first focal spot may correspond to a larger focal area of ​​the image produced by the X-rays, and the second focal spot may correspond to a smaller area within the larger area (e.g., at the center of the area), and the smaller area may have a higher spatial resolution than the larger area.

[0087] The shape of the first compound effective focal spot indicated by line 602 may be adjusted based on a first dwell time during which the first electron beam is focused on the target (thereby generating a first electron distribution indicated by line 604), a second dwell time during which the second electron beam is focused on the target (thereby generating a second electron distribution indicated by line 606), and a transition time between generating the first and second electron beams. For example, the first compound effective focal spot indicated by line 602 in FIG. 6A may be the result of a first dwell time equal to a second dwell time, where the electron distribution of the first compound effective focal spot is centered between the first and second electron distributions.

[0088] In Fig. 6B, a second exemplary electron distribution graph 630 shows a second composite distribution of electrons of the two electron beams of Fig. 6A, which is also based on the first electron distribution (shown by line 604) and the second electron distribution (shown by line 606) of Fig. 6A. Fig. 6B shares the same x-axis 501 as Fig. 6A. In Fig. 6B, the second composite effective focal spot shown by line 632 is believed to be the result of the second dwell time being significantly greater than the first dwell time. As a result of the second dwell time being greater than the first dwell time, the second composite effective focal position shown by line 632 is closer to the second electron distribution than to the first electron distribution.

[0089] In FIG. 6C, a third exemplary electron distribution graph 650 shows a third composite distribution of electrons for the two electron beams of FIGS. 6A and 6B, where the third composite distribution is also based on the first electron distribution (shown by line 604) and the second electron distribution (shown by line 606) of FIG. 6A. FIG. 6C shares the same X-axis 501 as FIGS. 6A and 6B. In FIG. 6C, the third composite effective focal spot shown by line 652 is believed to be a result of blanking the beam during the transition time, with the second dwell time being greater than the first dwell time as in FIG. 6B. Thus, by both reducing the electrons during the transition from the wider focal spot to the smaller focal spot and increasing the dwell time of the second electron distribution relative to the dwell time of the first electron distribution, the shape of the second composite effective focal spot can be adjusted to more closely match the shape of the second electron distribution.

[0090] 7A-7D show various exemplary distributions of electrons in a composite effective focal spot consisting of a first electron distribution 704 and a second electron distribution 706. The first electron distribution 704 may be the result of focusing a first electron beam according to a first configuration of electrostatic and / or electromagnetic control of the CT system, and the second electron distribution 706 may be the result of focusing a second electron beam according to a second configuration of electrostatic and / or electromagnetic control of the CT system, as described above. In FIGS. 7A-7D, the first and second electron distributions are focused at different positions on the X-axis 501 (as in FIGS. 5A-5D) and further have different shapes and / or sizes (as in FIGS. 6A-6C). As a result of the first and second electron distributions focusing at different locations on the X-axis 501 and having different shapes and / or sizes, the composite effective focal spot depicted in Figures 7A-7D is based on a larger (e.g., wider) first focal spot produced by the first electron distribution and a smaller (e.g., narrower) second focal spot produced by the second electron distribution, where the second focal spot is offset from the first focal spot in the X dimension. Thus, the first and second focal spots may be similar to the first and second focal spots 404 and 406 of Figure 4. Additionally, the first focal spot may be separated from the second focal spot by a space (e.g., space 415 of Figure 4).

[0091] 7A, a first line 704 shows a first electron distribution and corresponds to a first focal spot. A second line 706 shows a second electron distribution corresponding to a second focal spot. Lines 704 and 706 share an X-axis 501, with 0 (zero) on the X-axis 501 indicating a central reference point on the target in the X-dimension.

[0092] The first exemplary electron distribution graph 700 includes a dashed line 702 indicating a first composite effective focal spot, which corresponds to a distribution of electrons of an x-ray (produced by a first electron beam and a second electron beam impinging on a target) on an object such as a patient. The first composite effective focal spot may be generated by a first composite focal spot on the target consisting of a first focal spot and a second focal spot. The first composite focal spot may be shown on a line 714 intersecting the composite distribution, the first focal spot shown by line 716 and the second focal spot shown by line 718. The composite focal spots shown by lines 716 and 718 may be separated by a spacing 720, similar to spacing 415 of composite focal spot 416 in FIG. 4. In FIG. 7A, the first focal spot shown by line 716 may be a large (e.g., wide in the X dimension) focal spot, and the second focal spot shown by line 718 may be a small (e.g., narrow in the X dimension) focal spot. Thus, the first focal spot corresponds to a large area of ​​focus in the image produced by the X-rays, and the second focal spot corresponds to a smaller area (offset in the X dimension from the larger area), where the smaller area can have higher spatial resolution than the larger area.

[0093] The shape of the first compound effective focal spot shown by line 702 can be adjusted based on the first dwell time during which the first electron beam is focused on the target (thereby generating a first electron distribution shown by line 704), the second dwell time during which the second electron beam is focused on the target (thereby generating a second electron distribution shown by line 706), and the transition time between generating the first and second electron beams. For example, the first compound effective focal spot shown by line 702 can be the result of equal dwell times and a finite transition period during which electrons strike the target between the first and second spots.

[0094] In Figure 7B, a second exemplary electron distribution graph 730 shows a second composite distribution of electrons for the two electron beams of Figure 7A, which is also based on the first electron distribution (shown by line 704) and the second electron distribution (shown by line 706) of Figure 7A. Figure 7B shares the same X-axis 501 as Figure 7A. In Figure 7B, the second composite effective focal spot shown by line 732 is believed to be the result of the second spot having a greater dwell time than the first spot. This results in a composite focal spot with a less pronounced first lobe.

[0095] In Figure 7C, a third exemplary electron distribution graph 750 shows a third composite distribution of electrons for the two electron beams of Figures 7A and 7B, where the third composite distribution is also based on the first electron distribution (shown by line 704) and the second electron distribution (shown by line 706) of Figures 7A and 7B. Figure 7C shares the same X-axis 501 as Figures 7A and 7B. In Figure 7C, the third composite effective focal spot shown by line 752 may be a result of the blanking of the beam during the transition, with a uniform dwell time as in Figure 7A. This creates a composite focal spot similar to the first and second, where no x-rays are generated during the transition.

[0096] In FIG. 7D, a fourth exemplary electron distribution graph 760 shows a fourth composite distribution of electrons of the two electron beams of FIG. 7A, 7B, and 7C, which is also based on the first electron distribution (shown by line 704) and the second electron distribution (shown by line 706) of FIG. 7A, 7B, and 7C. FIG. 7D shares the same X-axis 501 as FIG. 7A, 7B, and 7C. In FIG. 7D, the fourth composite effective focal spot shown by line 762 is believed to be the result of the second focal spot having a larger dwell time than the first as in FIG. 7B, followed by a blanking transition as in FIG. 7C. This results in a composite focal spot that underweights the wider portion relative to the narrow portion.

[0097] 7E, a fifth example electron distribution graph 770 illustrates a fifth composite distribution of electrons for the two electron beams of FIGS. 7A, 7B, 7C, and 7D, where the fifth composite distribution is based on a first electron distribution indicated by line 774 and a second electron distribution indicated by line 776. In FIG. 7E, the first electron distribution includes a first side lobe 778 at a first (e.g., left) edge 786 of the first electron distribution and a second side lobe 780 at a second (e.g., right) edge 788 of the first electron distribution. Similarly, the second electron distribution includes a first side lobe 782 at a first (e.g., left) edge 790 of the second electron distribution and a second side lobe 784 at a second (e.g., right) edge 792 of the second electron distribution. The side lobes 778, 780 of the first electron distribution may be the result of focusing the first electron beam via electrostatic and / or electromagnetic control of the CT system to narrow and parallelize a Gaussian distribution of electrons of the first electron beam. The side lobes 782, 784 of the second electron distribution may be the result of focusing the second electron beam via electrostatic and / or electromagnetic control to narrow and parallelize a Gaussian distribution of electrons of the second electron beam. The generation of side lobes is described in more detail with reference to FIG. 8.

[0098] Referring briefly to FIG. 8 , a side lobe diagram 800 shows a plot of a Gaussian electron distribution 802 at a focal spot, where the X-axis of the plot indicates the distribution of electrons impinging on a target along the X-dimension (e.g., along the width of the focal spot) and the Y-axis of the plot indicates the number of electrons impinging on the target at a corresponding point on the X-axis (e.g., the intensity of the focal spot). The Gaussian electron distribution 802 may be the result of applying electrostatic and / or electromagnetic control to focus the electron beam on a target (e.g., the electron beam 312 and the target 304). The electrostatic and / or electromagnetic control may generate one or more electric fields and / or one or more magnetic fields. The one or more electric fields and / or the one or more magnetic fields may exert a first force on the electrons of the electron beam toward the center of the Gaussian electron distribution 802 in a first direction indicated by arrow 820 and a second force on the electrons of the electron beam toward the center of the Gaussian electron distribution 802 in a second direction indicated by arrow 822. As a result of the first and second forces, electrons on the first and second edges 806, 808 of the Gaussian distribution may be redirected inwards towards a center of the Gaussian distribution. By redirecting the electrons on the first and second edges 806, 808 inwards towards the center, the shape of the Gaussian distribution may be changed, thereby inverting the sides of the Gaussian distribution 802 and causing the sides to approximate parallel lines.

[0099] As a result of the electrons being directed inward, more electrons may collide with the target at first edge 832 and second edge 834 of Gaussian distribution 802 than at the center of Gaussian distribution 802, as shown by a first side lobe 810 on the left side of Gaussian distribution 802 and a second side lobe 812 on the right side of Gaussian distribution 802. A compound focal spot 836 may result from the greater number of electrons colliding with the target at first edge 832 and second edge 834.

[0100] Returning now to FIG. 7E, a fifth composite effective focal spot, indicated by line 772, may be generated from a composite focal spot including a first focal spot based on a first electron distribution, indicated by line 774, and a second focal spot based on a second electron distribution, indicated by line 776. The fifth composite effective focal spot, indicated by line 772, may be the result of adjusting any of the dwell time, transition time, and transition blanking, as described in FIGS. 5A-5D, 6A-6C, and 7A-7D. Similar to FIGS. 5A-5D, 6A-6C, and 7A-7D, the fifth composite effective focal spot, indicated by line 772, may be generated by a fifth composite focal spot, indicated by line 796, on line 794 intersecting the composite distribution.

[0101] Referring to Figure 9, an exemplary method 900 is shown for generating an image from projection data acquired with a compound focal spot including a first focal spot and a second focal spot by alternately activating emitters of a cathode of a CT system. The method 900 is described with reference to the CT system 100 of Figure 1 and / or the imaging system 200 of Figure 2, where the cathode may be a non-limiting embodiment of the cathode 302 of the X-ray tube 300. The cathode may also be a non-limiting embodiment of the cathode 302 of the X-ray tube 300 of Figure 3A. The method 900 may be executed by a processor of a controller of the CT system, for example, a processor of the control electronics module 322 of Figure 3A, in response to instructions provided by an operator of the CT system and / or instructions stored in a memory of the CT system.

[0102] Method 900 begins at 902, where method 900 includes activating a cathode of a CT system to generate an electron beam 312 of Figure 3A. The electron beam is directed at a target (e.g., target 304) of the CT system, and electrons of the electron beam can collide with the target to generate x-rays that can be directed at an article (e.g., object 328).

[0103] At 904, the method 900 includes focusing the electron beam to a first focal spot on the target using electrostatic and / or electromagnetic control, the first focal spot being the same as or similar to, for example, first focal spot 404 of FIG.

[0104] At 906, focusing the electron beam to a first focal spot includes applying one or more voltages to one or more corresponding extraction and focusing electrodes of the x-ray tube (e.g., one or more focusing electrodes 316 of FIG. 3A). In various embodiments, a first set of one or more corresponding focusing electrodes may perform a first deflection of the electron beam and a second set of one or more corresponding focusing electrodes may perform a first focusing of the electron beam.

[0105] Performing a first deflection of the electron beam may include shifting the position of the electron beam in a dimension. For example, a first configuration of voltages applied to a first set of one or more corresponding focusing electrodes may generate an electric field that shifts the electron beam in the X dimension (e.g., to the left or right of the patient), and a second configuration of voltages applied to a first set of one or more corresponding focusing electrodes may generate an electric field (e.g., one or more electric fields 320 of FIG. 3A) that shifts the electron beam in the Z dimension (e.g., toward the patient's head or feet). The number of electric fields generated may correspond to the number of focusing electrodes receiving a voltage. For example, the first configuration may be a configuration in which a voltage is applied to the first focusing electrode and no voltage is applied to the second focusing electrode. The second configuration may include a configuration in which a voltage is applied to the second focusing electrode and no voltage is applied to the first focusing electrode. By applying voltages to select focusing electrodes of one or more focusing electrodes, a desired number of electric fields can be generated. Also, by adjusting each voltage, the magnitude of each electric field of the desired number of electric fields can be controlled. Each electric field exerts a force on the electrons of the electron beam, shifting the position of the electrons forming the electric beam in a desired direction. Thus, by deflecting the electron beam, the position of the focal spot created by the electron beam can be adjusted to a desired position.

[0106] Performing the first focusing of the electron beam may include changing the shape of the focal spot generated by the electron beam. For example, a first configuration of voltages applied to the second set of one or more corresponding focusing electrodes may generate an electric field that focuses the electron beam to generate a focal spot of a first shape, and a second configuration of voltages applied to the second set of one or more corresponding focusing electrodes may generate an electric field that focuses the electron beam to generate a focal spot of a second shape. For example, the first shape and the second shape may be rectangular shapes, the first shape having a width greater than the first and the second shape having a width less than the second (e.g., as described above with reference to the first focal spot 404 and the second focal spot 406 of FIG. 4). By applying different voltages to select focusing electrodes of the second set of one or more corresponding focusing electrodes, a desired number of electric fields that focus the electron beam to a desired shape and / or size may be generated.

[0107] At 908, focusing the electron beam to a first focal point using electrostatic and / or electromagnetic control further includes applying one or more currents to one or more respective dipole magnets of the X-ray tube (e.g., one or more magnets 324 of FIG. 3A) to perform a second deflection of the electron beam. In various embodiments, the one or more dipole magnets may be arranged in the X-ray tube to generate a force in the same dimension as the first deflection. More specifically, when one or more currents are applied to one or more respective dipole magnets, a respective number of magnetic fields (e.g., one or more magnetic fields 323 of FIG. 3A) may each generate a force on the electron beam to further adjust the deflection of the electron beam in the same dimension as the first deflection. The second deflection may be larger and / or more accurate than the first deflection due to the greater strength of the magnetic field relative to the electric field. In other words, a first deflection of the electron beam performed by the focusing electrodes may not be sufficient to deflect the first focal spot to a desired location (e.g., due to the length of the X-ray tube), whereby a second, additional deflection performed by the dipole magnet may be sufficient to deflect the first focal spot to a desired location.

[0108] At 910, focusing the electron beam to a first focal spot using electrostatic and / or electromagnetic control further includes applying one or more currents to one or more respective quadrupole magnets (e.g., one or more magnets 324 in FIG. 3A ) of the x-ray tube to perform a second focusing of the electron beam. When one or more currents are applied to one or more respective quadrupole magnets, each of the respective number of magnetic fields (e.g., one or more magnetic fields 323 in FIG. 3A ) can generate a force on the electron beam in two dimensions to focus the electron beam. The second focusing can be greater and / or more precise than the first focusing due to the greater strength of the magnetic field generated by the quadrupole magnets relative to the electric field. In other words, the first focusing of the electron beam performed by the focusing electrodes may not be sufficient to focus the first focal spot to the desired shape and / or size (e.g., due to the length of the X-ray tube), whereby the second, additional focusing performed by the quadrupole magnet may be sufficient to focus the first focal spot to the desired shape and / or size.

[0109] It should be appreciated that steps 906, 908, and 910 of method 900 may be applied simultaneously or in a different order than presented above.

[0110] At 912, the method 900 includes waiting for a first dwell time, which is a first period of time during which the electron beam is deflected and focused to generate a first focal spot at a desired location, shape, and size by a combination of one or more electric fields generated by the focusing electrodes and one or more magnetic fields generated by the dipole and quadrupole magnets.

[0111] At 914, the method 900 includes focusing the electron beam to a second focal spot via electrostatic and / or electromagnetic control. The second focal spot may be the same as or similar to, for example, second focal spot 406 of FIG. 4. Refocusing the electron beam to a second focal spot may include adjusting a configuration of the electrostatic and / or electromagnetic control. For example, focusing the electron beam to a first focal spot may include adjusting the electrostatic and / or electromagnetic control to a first configuration. Adjusting the electrostatic and / or electromagnetic control to the first configuration may include adjusting a first power delivered to a focusing electrode and / or adjusting a second power delivered to one or more dipole magnets and one or more quadrupole magnets of the x-ray tube. The first power may be greater than the second power, where the second power delivers a larger amount of energy to the focusing electrodes than the dipole magnets and the quadrupole magnets, or the second power may be greater than the first power, where the second power delivers a larger amount of energy to the dipole magnets and the quadrupole magnets than the focusing electrodes. Furthermore, the second power may be split and / or balanced between some magnets or poles of one or more magnets. For example, the second power may be distributed between the four poles of a quadrupole magnet to generate one or more magnetic fields having a desired strength and / or a desired direction. By adjusting the distribution of the second power between the four poles, the electrons may be deflected and / or focused to generate a first focus.

[0112] After expiration of the first time duration, the electrostatic and / or electromagnetic control can be adjusted from the first configuration to a second configuration, the second configuration focusing the electron beam to a second focal spot. Adjusting the electrostatic and / or electromagnetic control from the first configuration to the second configuration can include adjusting either or both of the second power and the first power, and / or adjusting a distribution of the second power between magnets or poles of the one or more dipole magnets and / or one or more quadrupole magnets.

[0113] At 916, refocusing the electron beam to a second focal spot via electrostatic and / or electromagnetic control may optionally include blanking the electron beam during a transition between focusing the electron beam to the first focal spot and refocusing the electron beam to the second focal spot. In various embodiments, blanking the electron beam may be accomplished by switching off an emitter of the cathode during the transition. For example, the emitter may be switched on for a first duration, the first duration being a first dwell time. At the end of the first duration, the emitter may be switched off for a second duration during which electrons are not directed at the target. At the end of the second duration, the emitter may be switched on for a third duration, the third duration being a second dwell time.

[0114] At 918, the method 900 includes waiting a second dwell time during which the electron beam is focused to a second focal spot. The second dwell time may be the same as the first dwell time, or the second dwell time may be different from the first dwell time. For example, in some embodiments, the first dwell time may be of a shorter duration and the second dwell time may be of a longer duration, while in other embodiments, the first dwell time may be of a longer duration and the second dwell time may be of a shorter duration. As discussed above with reference to FIGS. 5A-7E, the first dwell time and the second dwell time may be controlled to generate a compound focal spot of a desired shape, size, and location.

[0115] At 920, the method 900 includes generating an image from the projection data acquired using the compound focus, and the method 900 ends.

[0116] Thus, methods and systems are proposed herein for generating a composite focal spot including a first focal spot of a first size and shape at a first location and a second focal spot of a second size and shape at a second location, where the second size, shape and location may differ from the first size, shape and location. Images generated using the composite focal spot may include a large focal region where a portion of the image is of high spatial resolution, thereby combining the advantages of using a smaller focal spot with the advantages of using a larger focal spot. The sizes and shapes of the first and second focal spots may be individually configured based on the desired profile of the composite focal spot. The composite focal spot may be generated by alternately focusing the electron beam at the first and second focal points or by simultaneously activating multiple emitters of the cathode of the CT system. The composite focal spot may be generated within a view acquired by the CT system or between views acquired by the CT system. By using a compound focal spot, the overall size of the focal region in an image produced by the CT system can be increased, resulting in a higher quality image with a first portion of the focal region capable of distinguishing smaller contrast differences and a second portion of the focal region capable of distinguishing larger contrast differences. A further advantage of the systems and methods described herein is that the compound focal spot can be configured using software while relying on the existing hardware configuration of the CT system's x-ray tube.

[0117] A technical effect of creating a composite focal spot from two component focal spots is that the quality of an image produced using the composite focal spot may be improved relative to using a single focal spot.

[0118] The present disclosure also provides support for a method for a computed tomography (CT) system, the method including controlling the CT system to focus an electron beam generated by a cathode of the CT system to a plurality of focal spots on a surface of a target of the CT system, generating a composite focal spot from the plurality of focal spots, and acquiring projection data of the CT system using the composite focal spot. In a first embodiment of the method, generating the composite focal spot from the plurality of focal spots further includes generating the composite focal spot based on at least one of a shape of each of the plurality of focal spots, a position of each of the plurality of focal spots, a dwell time of each of the plurality of focal spots, and a transition time between each of the plurality of focal spots. In a second embodiment of the method, optionally including the first embodiment, a number of foci of the plurality of focal spots is two. In a third embodiment of the method, optionally including one or both of the first and second embodiments, a width of the composite focal spot in the X dimension is greater than a sum of a width of a first focal spot of the plurality of focal spots along the X dimension and a width of a second focal spot of the plurality of focal spots along the X dimension, and the width of the first focal spot is greater than a width of the second focal spot. In a fourth example, optionally including one or more or each of the first to third examples, controlling the CT system to focus the electron beam at two focal points further includes adjusting control of the CT system to focus the electron beam at the first focal point for a first dwell time, adjusting control of the CT system to focus the electron beam at the second focal point for a second dwell time starting after an end of the first dwell time, and switching off the electron beam between the first dwell time and the second dwell time in response to a transition time between focusing the electron beam at the first focal point and focusing the electron beam at the second focal point exceeding a threshold transition time.In a fifth embodiment of the method, optionally including one or more or each of the first to fourth embodiments, adjusting the control of the CT system further includes adjusting at least one of an electrostatic control and / or an electromagnetic control of the CT system, where adjusting the electrostatic control includes adjusting one or more voltages delivered at one or more electrodes of the CT system, and adjusting the electromagnetic control includes adjusting one or more currents delivered to one or more magnets of the CT system. In a sixth embodiment of the method, optionally including one or more or each of the first to fifth embodiments, a compound focal spot is generated within a view of the projection data of the CT system. In a seventh embodiment of the method, optionally including one or more or each of the first to sixth embodiments, a compound focal spot is generated between views of the projection data. In an eighth embodiment of the method, optionally including one or more or each of the first to seventh embodiments, the cathode includes a plurality of emitters, and a plurality of focal spots are generated by activating a respective number of emitters. In a ninth embodiment of the method, optionally including one or more or each of the first to eighth embodiments, the plurality of emitters further includes a first emitter having a first filament of a first size and a second emitter having a second filament of a second size, the first focal spot being generated by the first emitter and the second focal spot being generated by the second emitter. In a tenth embodiment of the method, optionally including one or more or each of the first to ninth embodiments, the composite focal spot includes a first focal spot at a first edge of the composite focal spot and a second focal spot at a second edge of the composite focal spot, the first focal spot and the second focal spot being generated by focusing the electron beam to adjust a distribution of electrons in the electron beam from a substantially Gaussian electron distribution to an electron distribution having side lobes.

[0119] The present disclosure also provides support for a computed tomography (CT) system comprising an X-ray tube including a cathode and a target, and an X-ray controller including one or more processors having executable instructions stored in a non-transitory memory of the CT system that, when executed, cause: a first electron beam generated by the cathode to be focused to a first focal spot on the target based on a first configuration of electrostatic and / or electromagnetic control of the X-ray controller; a second electron beam generated by the cathode to be focused to a second focal spot on the target based on a second configuration of electrostatic and / or electromagnetic control of the X-ray controller; and an image of an object from projection data acquired based on a composite focal spot including the first focal spot and the second focal spot. In a first embodiment of the system, focusing the first electron beam based on a first configuration of electrostatic and / or electromagnetic control further includes delivering a first set of voltages to one or more respective electrodes of the X-ray tube and / or one or more respective dipole magnets of the X-ray tube and / or one or more respective quadrupole magnets of the X-ray tube, and focusing the second electron beam based on a second configuration of electrostatic and electromagnetic control further includes delivering a second set of voltages to one or more respective electrodes of the X-ray tube and / or one or more respective dipole magnets of the X-ray tube and / or one or more respective quadrupole magnets of the X-ray tube. In a second embodiment of the system, optionally including the first embodiment, the first electron beam is generated by a first set of one or more emitters on the cathode, the first set of one or more emitters generating a first size and shape of the first focal spot, and the second electron beam is generated by a second different set of one or more emitters on the cathode, the second different set of one or more emitters generating a second size and shape of the second focal spot, the first size and shape being different from the second size and shape. In a third embodiment of the system, optionally including one or both of the first and second embodiments, the first electron beam is deflected to a first desired location on the target and focused for a first duration, and the second electron beam is deflected to a second desired location on the target and focused for a second duration, the second duration beginning after the end of the first duration.In a fourth embodiment of the system, optionally including one or more or each of the first to third embodiments, the first electron beam and the second electron beam are single electron beams, and the first focal spot is generated by directing electrons at a first edge of a Gaussian distribution of electrons of the single electron beam to a center of the Gaussian distribution based on a first configuration of electrostatic control and / or electromagnetic control, and the second focal spot is generated by directing electrons at a second edge of a Gaussian distribution of electrons of the single electron beam to a center of the Gaussian distribution based on a second configuration of electrostatic control and electromagnetic control.

[0120] The disclosure also provides support for a method for a computed tomography (CT) system, the method including focusing a first electron beam generated by a cathode of the CT system to a first focal spot on a surface of a target of the CT system, focusing a second electron beam generated by the cathode to a second focal spot on the surface of the target, generating a composite focal spot on the target including the first focal spot and the second focal spot, and generating an image from projection data of the CT system acquired using the composite focal spot, the image including a focal region corresponding to the composite focal spot, the focal region including a large X-ray flux region corresponding to the first focal spot where small contrast differences between large objects are better distinguished, and a small spatial resolution region corresponding to the second focal spot where large contrast differences between small objects are better distinguished. In a first embodiment of the method, generating the composite focal spot further includes generating the composite focal spot based on at least one of a first deflection of the first electron beam and a second deflection of the second electron beam, a first dwell time of the first electron beam at the first focal spot and a second dwell time of the second electron beam at the second focal spot, a first width of the first focal spot and a second width of the second focal spot in size (dimension), a first shape of the first electron distribution at the first focal spot and a second shape of the second electron distribution at the second focal spot, and a transition time between focusing of the first electron beam at the first focal spot and focusing of the second electron beam at the second focal spot. In a second embodiment of the method optionally including the first embodiment, the first electron beam is generated by a first set of one or more emitters of the cathode, and the second electron beam is generated by a second set of one or more emitters of the cathode, and the first electron beam is generated simultaneously with the second electron beam.In a third embodiment of the method, optionally including one or both of the first and second embodiments, generating the first beam of electrons simultaneously with the second beam of electrons further includes at least one of initiating the first beam of electrons before initiating the second beam of electrons, initiating the second beam of electrons before initiating the first beam of electrons, terminating the first beam of electrons before terminating the second beam of electrons, and terminating the second beam of electrons before terminating the first beam of electrons.

[0121] When introducing elements of various embodiments of the present disclosure, the articles "a," "an," and "the" are intended to mean that there are one or more of the elements. Terms such as "first," "second," and the like are used to distinguish one element from another without denoting any order, quantity, or importance. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. As used herein, the terms (e.g., materials, elements, structures, members, etc.) may be connected or coupled to one object, regardless of whether the one object is directly connected or coupled to the other object, or whether there are one or more intervening objects between the one object and the other object. In addition, it should be understood that references to "one embodiment" or "embodiments" in the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

[0122] In addition to any previously described modifications, numerous other variations and alternative configurations may be devised by those skilled in the art without departing from the spirit and scope of the present specification, and the appended claims are intended to cover such modifications and configurations. Thus, while the information has been described above with specificity and detail in connection with what are presently considered to be the most practical and preferred embodiments, it will be apparent to those skilled in the art that numerous modifications, including but not limited to form, function, mode of operation, and use, may be made without departing from the principles and concepts described herein. Moreover, the examples and embodiments, as used herein, are in all respects merely illustrative and should not be construed as limiting in any manner. [Embodiment 1] 1. A method for a computed tomography (CT) system, comprising: controlling the CT system to focus a plurality of beams of electrons generated by a cathode of the CT system to a plurality of focal spots on a surface of a target of the CT system; generating a composite focal spot from the plurality of focal spots; acquiring projection data of the CT system at the compound focus; The method includes: [Embodiment 2] generating the composite focal spot from the plurality of focal spots, a size of each focal spot of said plurality of focal spots; a shape of each focal spot of said plurality of focal spots; a position of each focal spot of the plurality of focal spots; a dwell time for each focal spot of said plurality of focal spots; a transition time between each focal spot of said plurality of focal spots; 2. The method of claim 1, further comprising generating the composite focal spot based on at least one of: [Embodiment 3] 3. The method of embodiment 2, wherein the plurality of focal spots includes a first focal spot having a first width in an X dimension and a second focal spot having a second width in the X dimension, the width of the composite focal spot in the X dimension being greater than a sum of the first width and the second width. [Embodiment 4] 4. The method of embodiment 3, wherein a position of the first focal spot in the X dimension is different from a position of the second focal spot in the X dimension. [Embodiment 5] 5. The method of embodiment 4, wherein controlling the CT system to focus the multiple electron beams to the multiple focal spots further comprises adjusting at least one of an electrostatic control and / or an electromagnetic control of the CT system, wherein adjusting the electrostatic control comprises adjusting one or more voltages delivered to one or more electrodes of the CT system, and adjusting the electromagnetic control comprises adjusting one or more currents delivered to one or more magnets of the CT system. [Embodiment 6] Adjusting at least one of the electrostatic and / or electromagnetic controls of the CT system further comprises: adjusting controls of the CT system to focus the electron beam at the first focal spot for a first dwell time; adjusting controls of the CT system to focus the electron beam to a second focal spot for a second dwell time beginning after the first dwell time has expired; 6. The method of embodiment 5, further comprising switching off the electron beam during the first dwell time and the second dwell time in response to a transition time between focusing the electron beam at the first focal spot and focusing the electron beam at the second focal spot exceeding a threshold transition time. [Embodiment 7] 7. A method according to any preceding embodiment, wherein the composite focal spot is generated within a view of the projection data of the CT system. [Embodiment 8] 8. A method according to any preceding embodiment, wherein the composite focal spot is generated between multiple views of the projection data. [Embodiment 9] 9. The method of any one of the preceding claims, wherein the cathode comprises a plurality of emitters and a plurality of focal spots are generated by activating a respective number of the emitters. [Embodiment 10] 10. The method of embodiment 9, wherein the plurality of emitters further includes a first emitter having a first filament with a first emission area and a second emitter having a second filament with a second emission area, the first emitter generating a first focal spot and the second emitter generating a second focal spot. [Embodiment 11] 3. The method of claim 2, wherein the composite focal spot includes a first focal spot at a first edge of the composite focal spot and a second focal spot at a second edge of the composite focal spot, and the first focal spot and the second focal spot are generated by adjusting a distribution of electrons in the electron beam from an approximately Gaussian electron distribution to an electron distribution having side lobes to focus the electron beam. [Embodiment 12] 1. A computed tomography (CT) system comprising: an x-ray tube including a cathode and a target; and an x-ray controller including one or more processors having executable instructions stored in a non-transitory memory of the CT system, the executable instructions, when executed, focusing a first electron beam generated by the cathode to a first focal spot on the target based on a first configuration of electrostatic and / or electromagnetic control of the x-ray controller; focusing a second electron beam generated by the cathode to a second focal spot on the target based on a second configuration of electrostatic and / or electromagnetic control of the x-ray controller; acquiring an image of the object from projection data acquired based on a composite focal spot including the first focal spot and the second focal spot; The system further comprises: [Embodiment 13] 13. The system of embodiment 12, wherein focusing the first electron beam based on electrostatic and / or electromagnetic control of the first configuration further comprises: supplying a first set of voltages to one or more respective electrodes of the X-ray tube, and / or one or more respective dipole magnets of the X-ray tube, and / or one or more respective quadrupole magnets of the X-ray tube; and focusing the second electron beam based on electrostatic and electromagnetic control of the second configuration further comprises supplying a second set of voltages to one or more respective electrodes of the X-ray tube, and / or one or more respective dipole magnets of the X-ray tube, and / or one or more respective quadrupole magnets of the X-ray tube. [Embodiment 14] 14. The system of embodiment 12 or 13, wherein the first electron beam is generated by a first set of one or more emitters on the cathode, the first set of one or more emitters generating a first size and shape of the first focal spot, and the second electron beam is generated by a second, different set of one or more emitters on the cathode, the second, different set of one or more emitters generating a second size and shape of the second focal spot, the first size and shape being different from the second size and shape. [Embodiment 15] 15. The system of any one of embodiments 12 to 14, wherein the first electron beam is deflected to a first desired position on the target and focused for a first duration, and the second electron beam is deflected to a second desired position on the target and focused for a second duration, the second duration starting after the end of the first duration. [Embodiment 16] A system as described in any of embodiments 12 to 15, wherein the first electron beam and the second electron beam are a single electron beam, the first focal spot is generated by directing electrons at a first edge of a Gaussian distribution of electrons of the single electron beam to a center of the Gaussian distribution based on the first configuration of the electrostatic control and / or electromagnetic control, and the second focal spot is generated by directing electrons at a second edge of a Gaussian distribution of electrons of the single electron beam to a center of the Gaussian distribution based on the second configuration of the electrostatic control and electromagnetic control. [Embodiment 17] 1. A method for a computed tomography (CT) system, comprising: focusing a first beam of electrons generated by a cathode of the CT system to a first focal spot on a surface of a target of the CT system; focusing a second beam of electrons produced by the cathode to a second focal spot on the surface of the target; generating a composite focal spot on the target including the first focal spot and the second focal spot; generating an image from projection data of the CT system acquired using the composite focal spot; Including, The method of claim 1, wherein the image includes a focal region corresponding to the composite focal spot, the focal region including a larger region of high x-ray flux corresponding to the first focal spot where small contrast differences between large objects are better distinguished, and a smaller region of high spatial resolution corresponding to the second focal spot where large contrast differences between small objects are better distinguished. [Embodiment 18] generating the composite focal spot comprises: a first deflection of the first electron beam and a second deflection of the second electron beam; a first dwell time of the first electron beam at the first focal spot and a second dwell time of the second electron beam at the second focal spot; a first width of the first focal spot and a second width of the second focal spot in one dimension; a first shape of a first distribution of electrons at the first focal spot and a second shape of a second distribution of electrons at the second focal spot; a transition time between focusing the first electron beam at the first focal spot and focusing the second electron beam at the second focal spot; 18. The method of embodiment 17, further comprising generating the composite focal spot by any one or more of the following: [Embodiment 19] 18. The method of embodiment 17, wherein the first electron beam is generated by a first set of one or more emitters of the cathode, and the second electron beam is generated by a second set of one or more emitters of the cathode, and the first electron beam is generated simultaneously with the second electron beam. [Embodiment 20] The step of generating the first electron beam simultaneously with the second electron beam includes: initiating the first electron beam before initiating the second electron beam; initiating the second electron beam before initiating the first electron beam; terminating the first electron beam before terminating the second electron beam; terminating the second electron beam before terminating the first electron beam; 20. The method of embodiment 19, comprising at least one of the following: [Explanation of symbols]

[0123] 100:CT system 102:Gantry 104:X-ray source 106:Beam of X-ray radiation 108:Detector array 110:Image processor unit 112:Object 114:Table 200:Imaging system 202:Detector element 204:Object 206:Center of rotation 208:Control mechanism 210:X-ray controller 212:Gantry motor controller 214:DAS 216:Computing device 218:Mass storage device 220:Operator console 224:PACS 226:Table motor controller 230:Image reconstructor 232:Display device 300:X-ray tube 302:Cathode 303:Anode 304:Target 306:Tube casing 308:Emitter 310:Voltage source 312:Electron beam 314:X-ray 316:Focusing electrode 318: Extraction electrode 320: Electric field 321: Electric field 322: Control electronics module 323: Magnetic field 324: Magnet 325: First electron beam 326: Second electron beam 328: Object 329: Electron collector 332: First focal spot 334: Second focal spot 335: Space 336: First set of X-rays 337: X-ray window 338: Second set of X-rays 340: First effective focal spot 342: Second effective focal spot 344: Composite effective focal spot 348, 349, 352: Coordinate axes 350: Composite focal spot 400: Electron distribution map 402: Single focal spot 404: First focal spot 406: Second focal spot 407: Length / height 408, 410, 412, 414: Width 415: Space 416: Compound focal spot 418: Rectangle 420: Width 422: Total 500, 530, 550, 580: Electron distribution graph 501: X-axis 502, 532, 552, 582: Dashed line 504: First line 506: Second line 508, 510: Dotted line 512: Distance 514, 516: Lines 600, 630, 650: Electron distribution graph 602, 632, 652: Compound distribution 604: First electron distribution 606: Second electron distribution 614, 616, 618: Lines 700, 730, 750, 760, 770: Electron distribution graph 702, 732, 752, 762, 772: dashed lines 704: first electron distribution 706: second electron distribution 714, 716, 718: lines 720: gaps 776, 794, 796: lines782: First side lobe 784: Second side lobe 786, 788: Edges 800: Side lobe diagram 802: Gaussian electron distribution 806: First edge 808: Second edge 810: First side lobe 812: Second side lobe 820, 822: Arrows 832: First edge 834: Second edge 836: Composite focal spot 900: Method

Claims

1. 1. A method for a computed tomography (CT) system, comprising: controlling (904, 914) an x-ray source of a CT system to generate a desired distribution of electrons impinging on a target of the CT system in each view of an object, the desired distribution forming a composite focal spot, the composite focal spot including a first focal spot having a first distribution of electrons impinging on the target and a second focal spot having a second distribution of electrons impinging on the target, the center of the first focal spot being separated from the center of the second focal spot; acquiring (920) projection data from x-rays produced by the desired distribution of electrons impinging on the target; reconstructing an image from the projection data; The method includes:

2. The first focal spot and the second focal spot are The size of each focal spot, The shape of each focal spot, The position of each focal spot, The dwell time of each focal spot, The transition time between each focal spot, The method of claim 1 , wherein at least one of:

3. The method of claim 2, wherein the first focal spot has a first width in the X dimension, the second focal spot has a second width in the X dimension, and a width of the composite focal spot in the X dimension is greater than a sum of the first width and the second width.

4. The method of claim 3, further comprising electrostatically and / or magnetically controlling the electron beam to alternate between a first electron beam impinging on the target at the first focal spot for a first dwell time and a second electron beam impinging on the target at the second focal spot for a second dwell time within a single view acquired by the CT system, the second dwell time beginning after the first dwell time has ended.

5. Electrostatically and / or magnetically controlling an electron beam to alternate between a first electron beam impinging on the target at the first focal spot for a first dwell time and a second electron beam impinging on the target at the second focal spot for a second dwell time, comprising: Switching off the electron beam during the first dwell time and the second dwell time. The method of claim 4 further comprising:

6. The method described in claim 1, wherein the desired distribution of electrons impinging on the target of the CT system forming the composite focal spot is generated within a view of projection data of the CT system and between successive views acquired by the CT system.

7. The method of claim 1 , wherein the cathode includes a plurality of emitters, and the plurality of focal spots are generated by activating a respective number of the emitters.

8. 8. The method of claim 7, wherein the plurality of emitters further comprises a first emitter having a first filament with a first emission area and a second emitter having a second filament with a second emission area, the first emitter generating the first focal spot and the second emitter generating the second focal spot.

9. the composite focal spot includes the first focal spot at a first edge of the composite focal spot and the second focal spot at a second edge of the composite focal spot; The method of claim 2 , wherein the desired distribution of electrons has side lobes.

10. 1. A computed tomography (CT) system comprising: an x-ray tube including a cathode and a target; and an x-ray controller including one or more processors having executable instructions stored in a non-transitory memory of the CT system; The executable instructions, when executed, cause one or more processors to generating a desired distribution of electrons impinging on a target of the CT system in each view of a subject, the desired distribution forming a composite focal spot, the composite focal spot including a first focal spot having a first distribution of electrons impinging on the target based on a first configuration of electrostatic and / or electromagnetic control of an x-ray controller, and a second focal spot having a second distribution of electrons impinging on the target based on a second configuration of electrostatic and / or electromagnetic control of an x-ray controller, a center of the first focal spot being separated from a center of the second focal spot; acquiring projection data from x-rays produced by the desired distribution of electrons impinging on the target; reconstructing an image from the projection data; A system that allows the user to:

11. Other instructions are stored in the memory, the other instructions, when executed, causing the one or more processors to: applying a first configuration of electrostatic and / or electromagnetic control to generate the first focal spot for a first dwell time; and applying a second configuration of electrostatic and / or electromagnetic control to generate said second focal spot for a second dwell time. Run the command, The system of claim 10 , wherein the second dwell time begins after the first dwell time ends.

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