System and method for built-in alignment mechanism for x-ray focus

Abstract

Systems and methods for maintaining an X-ray focal position at a desired location on an X-ray detector (15) of an X-ray imaging system include obtaining, via processing circuitry, a scanning scheme for performing an X-ray scan using the X-ray imaging system (10). The system and method also includes determining, via the processing circuitry, a curved magnet current value for maintaining an X-ray focal position of an X-ray beam emitted from an X-ray tube (14) of the X-ray imaging system (10) at a desired location on an X-ray detector (15) based on the plurality of acquisition parameters of the X-ray scan. The system and method also include maintaining, via the processing circuitry, the X-ray focal position at a desired location on the X-ray detector (15) using the curved magnet current value during the X-ray scan.

Description

Background Art

[0001] The subject matter disclosed herein relates to medical imaging systems, and more particularly, to systems and methods for a built-in alignment mechanism for an x-ray focal point.

[0002] In computed tomography (CT), X-ray radiation passes across an object or subject of interest being scanned (such as a human patient, luggage, or other object), and a portion of the radiation strikes a detector that collects image data. In a digital X-ray system, a photodetector produces a signal representing the amount or intensity of radiation striking a discrete pixel area of ​​the detector surface. The signal can then be processed to generate an image that can be displayed for viewing. In the images produced by such a system, it is possible to identify and examine internal structures and organs inside the subject's body. In a CT imaging system, as the gantry shifts around the subject or object being imaged, a detector array (comprising a series of detector elements or sensors) produces similar signals through various positions, thereby allowing a volumetric image reconstruction to be obtained.

[0003] Reconstructing images from acquired data is typically based on the assumption that X-ray photons have traveled in a straight path from the X-ray emission focus to the detector element at which the corresponding photon was detected. However, movement of the X-ray focus relative to one or more collimating elements or collimating plates (e.g., a post-patient anti-scatter grid) (e.g., X-ray focus drift) may result in image artifacts that are detrimental to the clinical use of imaging systems such as CT imaging systems. In addition, such X-ray focus drift may affect the accuracy of dose predictions. Multiple acquisition parameters (e.g., tube current (milliamperes (mA), tube voltage (kilovolts (kV)), focus size (of the electron beam impacting the anode), rotation speed, thermal state, etc.) may induce X-ray focus drift. Summary of the invention

[0004] Certain embodiments commensurate with the scope of the originally claimed subject matter are summarized below. These embodiments are not intended to limit the scope of the claimed subject matter, but rather, these embodiments are intended only to provide a brief overview of possible forms of the subject matter. In fact, the subject matter may include a variety of forms that may be similar to or different from the embodiments described below.

[0005] In one embodiment, a method for maintaining an X-ray focal position at a desired location on an X-ray detector of an X-ray imaging system is provided. The method includes obtaining, via a processing circuit system, a scanning scheme for performing an X-ray scan using the X-ray imaging system. The method also includes determining, via the processing circuit system, a bending magnet current value for maintaining an X-ray focal position of an X-ray beam emitted from an X-ray tube of the X-ray imaging system at a desired location on the X-ray detector based on a plurality of acquisition parameters of the X-ray scan. The method also includes maintaining the X-ray focal position at a desired location on the X-ray detector using the bending magnet current value during the X-ray scan via the processing circuit system.

[0006] In another embodiment, a system for maintaining an X-ray focal point position at a desired location on an X-ray detector of an X-ray imaging system is provided. The system includes a memory that encodes a processor executable routine. The system also includes a processing circuit system that is configured to access the memory and execute the processor executable routine, wherein these routines, when executed by the processing circuit system, cause the processing circuit system to perform an action. The action includes obtaining a scanning scheme for performing an X-ray scan using the X-ray imaging system. The action also includes determining a bending magnet current value for maintaining the X-ray focal point position of an X-ray beam emitted from an X-ray tube of the X-ray imaging system at a desired location on the X-ray detector based on multiple acquisition parameters of the X-ray scan. The action also includes maintaining the X-ray focal point position at a desired location on the X-ray detector using the bending magnet current value during the X-ray scan.

[0007] In yet another embodiment, a non-transitory computer readable medium includes processor executable code that, when executed by a processing circuit system, causes the processing circuit system to perform an action. The action includes obtaining a scanning scheme for performing a scan using a computed tomography (CT) imaging system. The action also includes determining a bending magnet current value according to a function graph for maintaining an X-ray focal position of an X-ray beam emitted from an X-ray tube of the CT imaging system at a desired location on an X-ray detector of the CT imaging system based on a plurality of acquisition parameters of the scan, wherein the function graph includes a plurality of bending magnet current values ​​and corresponding X-ray focal positions to be used for the plurality of acquisition parameters. The action also includes maintaining the X-ray focal position at a desired location on the X-ray detector using the bending magnet current value during the scan. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] These and other features, aspects, and advantages of the disclosed subject matter will be better understood when the following detailed description is read with reference to the accompanying drawings, in which like characters refer to like parts throughout the several views, and in which:

[0009] Figure 1 is a schematic diagram of the effect of X-ray tube current (mA) on X-ray focus drift;

[0010] Figure 2 is a schematic diagram of the effect of thermal state on X-ray focus drift;

[0011] Figure 3 is a pictorial representation of a CT imaging system according to aspects of the present disclosure;

[0012] Figure 4 According to various aspects of the present disclosure Figure 1 Block diagram of the CT imaging system in;

[0013] Figure 5 is a schematic diagram of a portion of an X-ray tube showing steering of an electron beam according to aspects of the present disclosure;

[0014] Figure 6 is a process flow of steps for integrating a built-in alignment mechanism for an X-ray focal point according to aspects of the present disclosure;

[0015] Figure 7 is a flow chart of a method for generating a function graph or a function lookup table according to aspects of the present disclosure;

[0016] Figure 8 is an example of a function graph according to aspects of the present disclosure;

[0017] Fig. 9 is a flow chart of a method for generating a function graph or a function lookup table according to aspects of the present disclosure;

[0018] Fig.10 is a flow chart of a method for utilizing a transfer function during scanning of a subject in accordance with aspects of the present disclosure;

[0019] Fig.11 is a schematic diagram showing application of a built-in alignment mechanism for an X-ray focal point for X-ray focal point variability due to different focal point sizes according to aspects of the present disclosure;

[0020] Fig.12 is a schematic diagram of a process flow showing steps for responding to a hardware change (eg, an X-ray tube replacement) in a CT imaging system according to aspects of the present disclosure; and

[0021] Fig.13 is a schematic diagram of a process flow showing steps for responding to a hardware change (eg, a bowtie filter replacement) in a CT imaging system in accordance with aspects of the present disclosure. DETAILED DESCRIPTION

[0022] One or more specific embodiments will be described below. In order to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be understood that in the development of any such actual implementation, as in any engineering or design project, many implementation-specific decisions must be made to achieve the developer's specific goals, such as complying with system-related and business-related constraints that may vary from implementation to implementation. In addition, it should be understood that such development efforts may be complex and time-consuming, but are still routine tasks for design, fabrication, and manufacturing for ordinary technicians who benefit from this disclosure.

[0023] When introducing elements of various embodiments of the present subject matter, the articles "a," "an," "the," and "said" are intended to indicate that there are one or more elements. The terms "comprising," "including," and "having" are intended to be inclusive, and mean that there may be additional elements in addition to the listed elements. Furthermore, any numerical examples in the following discussion are intended to be non-limiting, and thus the additional numerical values, ranges, and percentages are within the scope of the disclosed embodiments.

[0024] Although the various aspects discussed below may be provided in the context of medical imaging, it should be understood that the present technology is not limited to such medical contexts. In fact, examples and explanations are provided in such medical contexts only to facilitate explanation by providing examples of realistic implementation and application. However, the present method may also be used in other contexts, such as tomographic image reconstruction of industrial computed tomography (CT) used in non-destructive inspection of manufactured parts or manufactured products (i.e., quality control or quality audit applications) and / or non-invasive inspection of packages, boxes, luggage, etc. (i.e., security or screening applications). In general, the present method may be used in any imaging or screening context to provide a reconstructed image without artifacts caused by X-ray focus drift.

[0025] Movement of the X-ray focus relative to one or more collimating elements or collimating plates (e.g., a post-patient anti-scatter grid) (e.g., X-ray focus drift) may result in image artifacts that are detrimental to the clinical use of imaging systems such as CT imaging systems. In addition, such X-ray focus drift may affect the accuracy of dose prediction. Multiple acquisition parameters (e.g., tube current (milliamperes (mA), (kilovolts (kV)), focus size (of the electron beam impacting the anode), rotation speed, thermal conditions, etc.) may induce X-ray focus drift. Figure 1 It is a schematic diagram of the effect of X-ray tube current (mA) on X-ray focus drift.

[0026] Figure 1 and Figure 2Examples of acquisition parameters that induce X-ray focus drift are provided. Figure 1 A diagram 300 is included having a plot 302 showing a detector channel of an X-ray detector of an X-ray imaging system (e.g., a CT imaging system) in which an X-ray focus is positioned relative to a tube current applied to an X-ray tube of the X-ray imaging system. The Y-axis of the diagram 300 (represented by reference numeral 304) represents the detector channel. The X-axis of the diagram 300 (represented by reference numeral 306) represents the tube current (in mA). A dashed line 308 represents a detector center channel of the X-ray detector. Point 310 of the plot 302 represents an X-ray focus position positioned at the detector center channel 308 (e.g., at approximately 75 mA). Point 312 of the plot 302 represents an X-ray focus position positioned away from the detector center channel 308 (e.g., approximately 20 microns from the detector center channel 308 and at approximately 400 mA). Figure 1 Image 314 in FIG. 3 is an image of an object (eg, a phantom) obtained via a scan (eg, a CT scan) performed using a tube current of approximately 75 mA when the X-ray focus is positioned at the detector center channel 308 . Figure 1 316 is an image of the same object obtained via a scan (e.g., a CT scan) using a tube current of about 400 mA when the X-ray focus was positioned about 20 microns from the detector center channel 308. As shown in graph 300, the X-ray focus drift depends on the tube current. In addition, as shown in images 314 and 316, the X-ray focus drift induces artifacts in image 316.

[0027] Figure 2 Schematic diagram of the effect of thermal state on X-ray focus drift. Figure 2 Included are images 318, 320, and 322 of an object (e.g., a phantom) acquired at different thermal states of an X-ray tube of an X-ray imaging system (e.g., a CT imaging system) during a scan (e.g., a CT scan). Image 318 is associated with a lower temperature. Image 322 is associated with a highest temperature. Image 320 is associated with a temperature between the temperatures associated with image 318 and image 322. Image 318, image 320, and image 322 are associated with X-ray focus drifts of 0 microns, 42 microns, and 64 microns, respectively. As shown in images 318, 320, and 322, as the thermal state changes (e.g., the temperature increases), the X-ray focus drift increases. In addition, as shown in images 318, 320, and 322, the X-ray focus drift causes artifacts in images 320 and 322. As shown in images 318, 320, and 322, the X-ray focus drift causes artifacts in images 320 and 322. Figure 2 As shown, the X-ray focus drift depends on the thermal state of the X-ray tube.

[0028] The present disclosure provides systems and methods for maintaining an X-ray focus position at a desired position (e.g., a center detector channel position) on an X-ray detector of an X-ray imaging system (e.g., a CT imaging system) under different system operating conditions via a built-in alignment mechanism for the X-ray focus. Specifically, the technology disclosed in the present invention includes obtaining a scan plan (e.g., a calibration scan plan or a diagnostic scan plan) for performing an X-ray scan (e.g., a calibration scan or a diagnostic CT scan) using an X-ray imaging system (e.g., a CT imaging system). The technology disclosed in the present invention also includes determining a bending magnet current value for maintaining an X-ray focus position of an X-ray beam emitted from an X-ray tube of the X-ray imaging system at a desired position on the X-ray detector based on multiple acquisition parameters (or system operating parameters) of the X-ray scan (e.g., tube current, tube voltage, focus size, butterfly filter, rotation speed, gantry angle, thermal state, time of day, etc.). The technology disclosed in the present invention also includes maintaining the X-ray focus position at a desired position on the X-ray detector using the bending magnet current value during the X-ray scan. Bending magnet current values ​​may be applied to an electromagnet during an X-ray scan that maintains the X-ray focal point position at a desired location on an X-ray detector using electromagnetic deflection of an electron beam emitted from a cathode of an X-ray tube.

[0029] In some embodiments, prior to an X-ray scan, a function graph (or a function lookup table) may have been previously generated that relates bending magnet current values ​​to X-ray focus positions. The function graph includes a plurality of bending current values ​​and corresponding X-ray focus positions to be used for a plurality of acquisition parameters. In some embodiments, prior to an X-ray scan, a function graph (e.g., a function graph of a plurality of function graphs) is accessed and the function graph is used to determine bending magnet current values ​​based on a plurality of acquisition parameters for an X-ray scan. Access and use of the function graph acts as a built-in alignment mechanism for the X-ray focus, as the function graph may be stored locally with the X-ray imaging system for use with the X-ray tube.

[0030] The function graph is generated after an initial system staging of the X-ray imaging system. In certain embodiments, the function graph is regenerated or updated after hardware replacement or a planned maintenance period. The function graph may be generated by the following steps: obtaining air scan data and edge scan data using initial bending magnet current values ​​and initial acquisition parameters during an initial scan using the X-ray imaging system; determining an initial X-ray focal point position based on the air scan data and edge scan data; obtaining additional air scan data and additional edge scan data during subsequent scans using the X-ray imaging system using different bending magnet current values ​​used with the same initial acquisition parameters; and determining a different focal point position based on the additional air scan data and additional edge scan data (obtained using different bending magnet current values). This process may be repeated multiple times, wherein at least one of the acquisition parameters is different, to further generate the function graph or function lookup table.

[0031] The X-ray focal position utilized (e.g., maintained) during an X-ray scan is independent of a plurality of acquisition parameters (or system operating conditions). Due to the isolation of the correlation between the tube current (mA) and the X-ray focal position, the technology disclosed in the present invention improves both calibration robustness and image quality (e.g., by mitigating artifacts caused by X-ray focal position drift). The technology disclosed in the present invention also improves service availability by ensuring the desired X-ray focal position on the detector after replacing the hardware (e.g., of the X-ray tube or butterfly filter), thereby minimizing system downtime (e.g., by reducing calibration time). The technology disclosed in the present invention also improves dose delivery predictability by implementing assumptions related to the X-ray focal position (because accurate X-ray focal position on the detector is required to calculate and estimate the accurate dose for the patient). The technology disclosed in the present invention provides an overall method of combining system hardware with software for performing calculations and analysis to align the X-ray focal position to the desired detector position (i.e., to keep the X-ray focal position consistent at the desired position on the detector for all acquisition parameters).

[0032] Taking into account the foregoing and referring to Figure 3 and Figure 4 , a CT imaging system 10 is shown by way of example. Figure 3 and Figure 4The CT imaging system 10 can be used with a dual-modality imaging system (e.g., a positron emission tomography (PET) / CT imaging system). The CT imaging system 10 (e.g., a CT scanner) includes a coupled gantry 12 having a housing 13 (e.g., a gantry housing). The gantry 12 has a rotating component and a fixed component. The gantry 12 has an X-ray source or X-ray tube 14 that projects a beam of X-rays 16 toward an X-ray detector assembly or X-ray detector array 15 (e.g., having a plurality of detector modules) on an opposite side of the gantry 12. The X-ray source 14 and the X-ray detector assembly 15 are disposed on the rotating portion of the gantry 12. The X-ray detector assembly 15 is coupled to a data acquisition system (DAS) 33. The plurality of detector modules of the X-ray detector assembly 15 detect the projected X-rays that pass through the patient or subject 22, and the DAS 33 converts the data into digital signals for subsequent processing. Each detector module of the X-ray detector assembly 15 in a conventional system generates an analog electrical signal that represents the intensity of the incident X-ray beam and, therefore, the intensity of the attenuated beam as it passes through the patient 22. During a scan to acquire X-ray projection data, the gantry 12 and components mounted thereon rotate about a center of rotation 24 (e.g., isocenter) to collect attenuation data from multiple viewing angles relative to the imaging volume.

[0033] The rotation of the gantry 12 and the operation of the X-ray source 14 are controlled by a control mechanism 26 of the CT system 10. The control mechanism 26 includes an X-ray controller 28 that provides power and timing signals to the X-ray source 14 and a gantry motor controller 30 that controls the rotation speed and position of the gantry 12. An X-ray focusing controller 31 is communicatively coupled to the X-ray controller 28. The X-ray focusing controller 31 controls the positioning of the X-ray focal position of the X-ray beam 16 on the X-ray detector assembly 15. Specifically, the X-ray focusing controller 31 is configured to determine and utilize bending magnet current values ​​(e.g., obtained from a function table or a function lookup table) to maintain the X-ray focal position of the X-ray beam 16 at a desired position (e.g., detector center channel) of the X-ray detector assembly 15. A bending magnet current corresponding to the determined bending magnet current value is applied to the electromagnet to adjust the focus of the electron beam on the anode by electromagnetic deflection of the electron beam emitted from the cathode of the X-ray tube toward the anode to achieve the desired positioning of the X-ray beam 16 on the X-ray detector assembly 15.

[0034] A computer 42 (separate from or as part of the CT imaging system 10) includes a data correction unit 46 for processing or correcting CT scan data from the DAS 33. The computer 42 also includes an image reconstructor 48. The image reconstructor 48 receives sampled and digitized X-ray data from the DAS 33 and performs high-speed reconstruction. A reconstructed image 49 is applied as input to the computer 42, which stores the image in a mass storage device 50. The reconstructed image 49 (i.e., the air scan data and the edge scan data) is also used in conjunction with the X-ray focusing controller to generate a function table or function lookup table that can be stored in the mass storage device 50 and used to determine bending magnet current values ​​for maintaining the X-ray focus at a desired location on the X-ray detector assembly 15 during scanning for all acquisition parameters (or system operating conditions). The function map relates the bending magnet current value to the X-ray focus position. The function map includes a plurality of bending currents to be used for a set of acquisition parameters used with the X-ray imaging system to achieve a desired location of the X-ray focus.

[0035] The computer 42 also receives commands and scanning parameters from the operator via the console 52. An associated display 54 allows the operator to observe the reconstructed image 49 and other data from the computer 42. The computer 42 uses the commands and parameters provided by the operator to provide control signals and information to the DAS 33, the x-ray controller 28, the gantry motor controller 30, and the x-ray focusing controller 31. In addition, the computer 42 operates a table motor controller 56, which controls the motorized table 36 to position the patient 22 relative to the gantry 12. Specifically, the table 36 moves portions of the patient 22 through a gantry opening or aperture 58.

[0036] The computer 42 includes a processing circuit. The processing circuit may be one or more general or special purpose microprocessors. The processing circuit may be configured to execute instructions stored in a memory to perform various measures. For example, the processing circuit system may be used to generate an image from scan data (e.g., air scan data, edge scan data, diagnostic scan data, etc.). The processing circuit system may also be used to obtain a scanning scheme (e.g., a calibration scan scheme or a diagnostic scan scheme) for performing an X-ray scan (e.g., a calibration scan or a diagnostic CT scan) using an X-ray imaging system (e.g., a CT imaging system). The processing circuit system may also be used to determine a bending magnet current value for maintaining the X-ray focus position of an X-ray beam emitted from an X-ray tube of the X-ray imaging system at a desired location on an X-ray detector based on a plurality of acquisition parameters (or system operating parameters) of the X-ray scan (e.g., tube current, tube voltage, focal spot size, butterfly filter, rotation speed, gantry angle, thermal state, time of day, etc.). The processing circuit system may also be used to maintain the X-ray focus position at a desired location on an X-ray detector using the bending magnet current value during an X-ray scan. A bending magnet current corresponding to the bending magnet current value may be applied to an electromagnet during an X-ray scan that maintains the X-ray focal point position at a desired location on an X-ray detector using electromagnetic deflection of an electron beam emitted from a cathode of an X-ray tube.

[0037] Figure 5 is a schematic diagram showing a portion of an X-ray tube that steers an electron beam. The X-ray tube 14 includes an electron beam source 60, including a cathode 62, and an anode assembly 64, and a beam steering system 65 (e.g., including an electrode magnet or electromagnet 67). The cathode 62, the anode 66, and the beam steering mechanism 65 can be disposed in a housing (not shown) such as a glass or metal cladding. The X-ray tube 14 can be located in a case (not shown), which can be made of aluminum and lined with leads. In some embodiments, the anode assembly 64 can include a rotor and a stator (not shown) external to the X-ray tube 14, the stator at least partially surrounding the rotor for rotating the anode 66 during operation.

[0038] The cathode 62 is configured to receive an electrical signal via a series of electrical leads 68 (eg, coupled to a high voltage source) that causes emission of an electron beam 70. The anode 66 is configured to receive the electron beam 70 at a target surface 72 and to emit an electron beam 70 at a target surface 72. Figure 5, emits X-rays (e.g., an X-ray beam) when struck by an electron beam 70, as indicated by reference numeral 74. The electrical signal may be a timing / control signal (via a power supply 72 coupled to the X-ray controller 28 and the X-ray focusing controller 31) that causes the cathode 62 to emit an electron beam 70 of one or more energies. In addition, the electrical signal may at least partially control the electrical potential between the cathode 62 and the anode 66. The voltage difference between the cathode 62 and the anode 66 may range from tens of thousands of volts to over hundreds of thousands of volts. The anode 66 is coupled to a rotor (not shown) via a shaft (not shown). Rotating the anode 66 allows the electron beam 70 to continuously strike different points on the periphery of the anode. Within the housing of the X-ray tube 12, preferably maintained at about 10 -5 About 10 -9 A vacuum of the order of Torr is applied to allow undisturbed transmission of the electron beam 70 between the cathode 62 and the anode 66.

[0039] The power supply 72 is also coupled to the electromagnet 67 of the beam steering system 65. In response to control signals from the X-ray controller 28 and the X-ray focus controller, a bending magnet current from the power supply 72 can be applied to the electromagnet 67 to generate an electromagnetic field to steer the electron beam 70 between different focal positions (i.e., the focal positions in which the electron beam strikes the anode 66) such as the illustrated focal positions 76 and 78, which also changes the X-ray focal point (i.e., the location at which the X-ray beam 74 strikes the detector). The generated electromagnetic field can also change the size or shape of the focal point.

[0040] Figure 6 is a process flow for integrating a built-in alignment mechanism for an X-ray focus. The process flow begins at step 76. The process flow includes executing an X-ray imaging system (e.g., Figure 1 and Figure 2 System staging includes initially setting up the X-ray imaging system in a certain location (eg, unpacking components, running all cables, positioning the table and gantry, and installing components).

[0041] At step 80, a built-in alignment mechanism for an X-ray focus is generated. Specifically, during an initial scan using the X-ray imaging system, air scan data and edge scan data are obtained using initial bending magnet current values ​​and initial acquisition parameters. Then, an initial X-ray focus position is determined based on the air scan data and edge scan data. Subsequently, during subsequent scans using the X-ray imaging system, additional air scan data and additional edge scan data are obtained using different bending magnet current values ​​used with the same initial acquisition parameters, and different focus positions are determined based on the additional air scan data and additional edge scan data. Based on these calculation results, a function graph or a function lookup table is generated that relates the bending magnet current value to the X-ray focus position. The function graph includes a plurality of bending currents to be used for a set of acquisition parameters used with the X-ray imaging system to achieve a desired positioning of the X-ray focus. This process may be repeated multiple times, wherein at least one of the acquisition parameters is different, to further generate a function graph or a function lookup table.

[0042] At step 82, the function graph (or multiple function graphs) including the bending magnet current values ​​are saved for use with subsequent scans. For example, at step 84, a full system calibration can be performed using a bending current magnet from the function graph (based on the acquisition parameters of the calibration scan), which maintains the X-ray focus at a desired location on the X-ray detector. The calibration scan may include scanning a phantom with a known radiation density to check whether its measurement results (i.e., the CT imaging system) give an appropriate number of Hounsfield units (HU). For another example, at step 86, a patient scan (e.g., a diagnostic scan of a subject) can be performed using a bending current magnet from the function graph (based on the acquisition parameters of the patient scan), which maintains the X-ray focus at a desired location on the X-ray detector. After the scan, the processing flow ends at step 88.

[0043] Figure 7 is a flow chart of a method 90 for generating a function graph or a function lookup table. The method 90 may be Figure 3 and Figure 4 The method 90 may be performed by one or more components (e.g., processing circuitry) of the CT imaging system 10 in the embodiment of the present invention. The method 90 may be performed after grading the X-ray imaging system (e.g., the CT imaging system). The method 90 may also be performed after replacing the hardware (e.g., the butterfly filter, the X-ray tube, etc.) of the CT imaging system. The method 90 may also be performed after regular maintenance of the X-ray imaging system.

[0044] The method 90 includes performing an initial scan (e.g., an air scan without a subject in the gantry) using an X-ray imaging system (e.g., a CT imaging system) using an initial bending magnet current value and initial acquisition parameters (e.g., tube current (mA), tube voltage (kV), focal spot size (of the electron beam striking the anode), rotation speed, thermal conditions, etc.) (box 92). The method 90 also includes obtaining air scan data and edge scan data from the initial scan (box 94). The method 90 also includes determining an initial X-ray focal spot position (associated with the initial bending magnet current value and relative to a center channel of an X-ray detector) based on the air scan data and the edge scan data (box 96). The method 90 also includes performing subsequent scans (e.g., air scans) using different bending magnet current values ​​used with the same initial acquisition parameters (box 98). The method 90 even includes obtaining additional air scan data and additional edge scan data from each of the subsequent scans using the different bending magnet current values ​​(box 100). The method 90 further includes determining different X-ray focus positions (associated with different bending magnet current values ​​and relative to the center channel of the X-ray detector) based on the additional air scan data and the additional edge scan data (from the scans with different bending magnet current values) (box 102). The method 90 also includes calculating or generating a transfer function (e.g., a function map or a function lookup table) based on previous calculation results from the initial scan and the subsequent scan (box 104). The method 90 further includes storing the transfer function (e.g., locally using the X-ray imaging system) (box 105). This process can be repeated multiple times, wherein at least one of the acquisition parameters is different to further generate the function map or function lookup table.

[0045] Figure 8 is an example of a function graph 106. The Y-axis 108 of the function graph 106 represents the bending magnet current value. The X-axis 110 of the function graph 106 represents the X-ray focal point position (relative to the center channel of the X-ray detector). Points 112 represent data points obtained from the initial scan and the subsequent scan (such as Figure 7 106). Plotted line 114 represents the linear function obtained from point 112. Point 116 represents where linear function 114 intersects the desired position (e.g., center position) of the X-ray detector in function graph 106. Dashed line 118 represents the calculated bending magnet current value used to obtain the desired X-ray focus position (e.g., center position) on the X-ray detector.

[0046] Fig. 9 is a flow chart of a method 120 for generating a function graph or a function lookup table. The method 120 is similar to Figure 7 Method 90 in the embodiment of the present invention differs in that the specific examples of the acquisition parameters are used. Method 120 may be performed by Figure 3and Figure 4 Method 120 may be performed by one or more components (e.g., processing circuitry) of the CT imaging system 10 in the embodiment of the present invention. Method 120 may be performed after grading an X-ray imaging system (e.g., a CT imaging system). Method 120 may also be performed after replacing hardware (e.g., a butterfly filter, an X-ray tube, etc.) of the CT imaging system. Method 120 may also be performed after regular maintenance of the X-ray imaging system. Although method 120 depicts the use of tube voltage, focal spot size, and tube current, one or more different acquisition parameters or additional acquisition parameters (e.g., a butterfly filter, a rotation speed, a gantry angle, a thermal state, a time of day, etc.) may also be utilized. Although method 120 depicts the use of three acquisition parameters, more than three acquisition parameters may also be utilized.

[0047] After starting the method 120 (block 122), the method 120 includes setting the X-ray tube voltage (block 124). The method 120 also includes determining whether the current value i of the X-ray tube voltage is less than or equal to the set upper limit value m of the X-ray tube voltage (block 126). If the current value of the X-ray tube voltage is greater than the set upper limit value of the X-ray tube voltage, the method 120 ends (block 128). If the current value of the X-ray tube voltage is less than or equal to the set upper limit value of the X-ray tube voltage, the method 120 includes setting the focal spot size (i.e., the focal spot size of the electron beam that strikes the anode) (block 130). The method 120 also includes determining whether the current value j of the focal spot size is less than or equal to the set upper limit value n of the focal spot size (block 132). If the current value of the focal spot size is greater than the set upper limit value of the focal spot size, the method 120 ends (block 128). If the current value of the focal spot size is less than or equal to the set upper limit value of the focal spot size, the method 120 includes setting the X-ray tube current (block 134). The method 120 also includes determining whether the current value k of the X-ray tube current is less than or equal to the set upper limit value p of the X-ray tube current (block 136). If the current value of the X-ray tube current is greater than the set upper limit value of the X-ray tube current, the method 120 ends (block 128).

[0048] The method 120 also includes performing a transfer function calculation (block 138). Performing the transfer function calculation includes performing a scan (e.g., an air scan) for a given (and identical) setting (1, 2, etc.) of an X-ray tube voltage, a focal spot size, and an X-ray tube voltage using a plurality of different bending magnet current values. Performing the transfer function calculation also includes determining a corresponding X-ray focal spot position on an X-ray detector for each of the corresponding scans for the given setting of the X-ray tube voltage, the focal spot size, and the X-ray tube voltage (e.g., based on the corresponding air scan data and the edge scan data of the corresponding scan). Performing the transfer function calculation also includes generating a function graph based on the calculation results obtained from the scan for the given setting of the X-ray tube voltage, the focal spot size, and the X-ray tube voltage. The transfer function calculation is performed for each corresponding setting of the X-ray tube voltage, the focal spot size, and the X-ray tube voltage (block 138). The method 120 also includes storing a magnet current table (e.g., based on the transfer function) for all settings of the X-ray tube voltage, the focal spot size, and the X-ray tube voltage (block 140). After storing the magnet current table, the method 120 ends (block 128).

[0049] Fig.10 is a flow chart of a method 142 for utilizing a transfer function during scanning of a subject (eg, a patient). The method 142 may be performed by Figure 3 and Figure 4 The CT imaging system 10 may be implemented by one or more components (eg, processing circuitry) of the CT imaging system 10 .

[0050] After starting the method 142 (block 144), the method 142 includes obtaining (e.g., receiving) a scan plan (e.g., a calibration plan and / or a patient scan plan (e.g., a diagnostic scan plan)) for performing an X-ray scan (e.g., a calibration scan and / or a diagnostic scan) using an X-ray imaging system (e.g., a CT imaging system) (block 146). The method 142 also includes parsing the scan plan to determine specific acquisition parameters for the X-ray scan (block 148).

[0051] The method 142 also includes determining a bending magnet current value for maintaining (or setting) an X-ray focus position of an X-ray beam emitted from an X-ray tube of the X-ray imaging system at a desired position (e.g., a center position of the X-ray detector) on an X-ray detector of the X-ray imaging system based on acquisition parameters of the X-ray scan (e.g., obtained from a scanning plan) (block 150). Specifically, determining the bending magnet current value includes accessing a function map (e.g., of a plurality of function maps) based on the acquisition parameters, and then determining the bending magnet current value according to the function map.

[0052] The method 142 event also includes utilizing or using the determined bending current value to maintain (or cause the X-ray focal position to be positioned) at a desired location on the X-ray detector during an X-ray scan (e.g., a calibration scan and / or a diagnostic scan) (block 152). After the X-ray scan, the method 142 ends (block 154).

[0053] Fig.11 is a schematic diagram showing application of a built-in alignment mechanism for an X-ray focal point for X-ray focal point variability due to different focal point sizes; Fig.11 Three graphs 156, 158, and 160 are included that show X-ray focal spot positioning relative to X-ray tube current for different focal spot sizes (i.e., the electron beam of the X-ray tube striking the anode). Graph 160 is derived from data using an extra large focal spot size (which is larger than the focal spot size used for graph 156 and graph 158). Graph 158 is derived from data using a large focal spot size (which is smaller than the focal spot size used for graph 160). Graph 156 is derived from data using a small focal spot size (which is smaller than the focal spot size used for both graph 158 and graph 160). Graphs 156, 158, and 160 each include a Y-axis 162 representing the detector channel positioning of the X-ray detector and an X-axis 164 representing the X-ray tube current (mA). Plots 166, 168, and 170 represent the X-ray focus position or location relative to the X-ray tube current derived from data collected during a scan without utilizing the built-in alignment mechanism for the X-ray focus of graphs 156, 158, and 160 (as described above). Plots 172, 174, and 176 represent the X-ray focus position or location relative to the X-ray tube current derived from data collected during a scan with the built-in alignment mechanism for the X-ray focus of graphs 156, 158, and 160 (as described above). Dashed line 178 represents the desired X-ray focus position (e.g., the detector center channel of the X-ray detector). As depicted, the built-in alignment mechanism implements the desired X-ray focus position for both different focal spot sizes and different X-ray tube currents. The built-in alignment mechanism also implements the desired X-ray focus position for different values ​​of other acquisition parameters or system operating conditions.

[0054] Fig.121 is a schematic diagram showing a process flow of steps in response to a hardware change (e.g., an X-ray tube replacement) in a CT imaging system 10. Only a portion of the CT imaging system is shown. The process flow begins at step 180. The process flow includes performing an X-ray tube replacement at step 182, wherein an old X-ray tube 14 (i.e., tube 1) is replaced with a new X-ray tube 14 (i.e., tube 2). The old X-ray tube 14 may be replaced because it has reached the end of its life, has become damaged, or for other reasons.

[0055] At step 184, a built-in alignment mechanism for an X-ray focus is generated. Specifically, during an initial scan using the X-ray imaging system, air scan data and edge scan data are obtained using initial bending magnet current values ​​and initial acquisition parameters. Then, an initial X-ray focus position is determined based on the air scan data and edge scan data. Subsequently, during subsequent scans using the X-ray imaging system, additional air scan data and additional edge scan data are obtained using different bending magnet current values ​​used with the same initial acquisition parameters, and different focus positions are determined based on the additional air scan data and additional edge scan data. Based on these calculation results, a function graph or a function lookup table is generated that relates the bending magnet current value to the X-ray focus position. The function graph includes a plurality of bending currents to be used for a set of acquisition parameters used with the X-ray imaging system to achieve a desired positioning of the X-ray focus. This process may be repeated multiple times, wherein at least one of the acquisition parameters is different, to further generate a function graph or a function lookup table.

[0056] The function graph (or graphs) including the bending magnet current values ​​are saved for use with subsequent scans. For example, a scan may be performed using a bending current magnet from the function graph (based on the acquisition parameters of the calibration scan) so that the X-ray focus is at a desired location on the X-ray detector (e.g., the center of the X-ray detector). This is shown in Fig.1218. Graph 186 shows X-ray focus positioning relative to X-ray tube current. Graph 186 includes a Y-axis 188 representing the detector channel positioning of the X-ray detector and an X-axis 190 representing the X-ray tube current (mA). Plot 192 represents the X-ray focus positioning or position relative to the X-ray tube current derived from data collected during a scan before the built-in alignment mechanism was generated (but after the X-ray tube was replaced). Plot 194 represents the X-ray focus positioning or position relative to the X-ray tube current derived from data collected during a scan when the built-in alignment mechanism for X-ray focus positioning (for both the old and new X-ray tubes 14) is utilized. Dashed line 196 represents the desired X-ray focus positioning (e.g., the detector center channel of the X-ray detector). As depicted, the built-in alignment mechanism implements the desired X-ray focus positioning for the new X-ray tube 14 for a different X-ray tube current (which is the same as the X-ray tube current used with the old X-ray tube 14). The built-in alignment mechanism also implements the desired X-ray focus positioning for different values ​​of other acquisition parameters or system operating conditions. The process flow ends at step 198.

[0057] Fig.13 2 is a schematic diagram showing a process flow of steps in response to a hardware change (e.g., butterfly filter replacement) in a CT imaging system 10. Only a portion of the CT imaging system is shown. The process flow begins at step 200. The process flow includes performing a butterfly filter replacement at step 202, wherein an old butterfly filter 204 (i.e., butterfly 1) is replaced with a new butterfly filter 206 (i.e., butterfly 2). The old butterfly filter 204 may be replaced because it has reached the end of its life, has been damaged, or for other reasons.

[0058] At step 208, a built-in alignment mechanism for an X-ray focus is generated. Specifically, during an initial scan using the X-ray imaging system, air scan data and edge scan data are obtained using an initial bending magnet current value and initial acquisition parameters. Then, an initial X-ray focus position is determined based on the air scan data and the edge scan data. Subsequently, during subsequent scans using the X-ray imaging system, additional air scan data and additional edge scan data are obtained using different bending magnet current values ​​used with the same initial acquisition parameters, and different focus positions are determined based on the additional air scan data and the additional edge scan data. Based on these calculation results, a function graph or a function lookup table is generated that relates the bending magnet current value to the X-ray focus position. The function graph includes a plurality of bending currents to be used for a set of acquisition parameters used with the X-ray imaging system to achieve a desired positioning of the X-ray focus. This process may be repeated multiple times, wherein at least one of the acquisition parameters is different, to further generate a function graph or a function lookup table.

[0059] The function graph (or graphs) including the bending magnet current values ​​are saved for use with subsequent scans. For example, a scan may be performed using a bending current magnet from the function graph (based on the acquisition parameters of the calibration scan) so that the X-ray focus is at a desired location on the X-ray detector (e.g., the center of the X-ray detector). This is shown in Fig.13 204 and 206). Graph 210 shows X-ray focus positioning relative to X-ray tube current. Graph 210 includes a Y-axis 212 representing detector channel positioning of an X-ray detector and an X-axis 214 representing X-ray tube current (mA). Plot 216 represents the X-ray focus positioning or location relative to the X-ray tube current derived from data collected during a scan before the built-in alignment mechanism was generated (but after the butterfly filter was replaced). Plot 218 represents the X-ray focus positioning or location relative to the X-ray tube current derived from data collected during a scan using the built-in alignment mechanism for X-ray focus positioning (for both the old X-ray butterfly filter 204 and the new X-ray butterfly filter 206). Dashed line 220 represents the desired X-ray focus positioning (e.g., the detector center channel of the X-ray detector). As depicted, the built-in alignment mechanism implements the desired X-ray focus position for the new butterfly filter 206 for different X-ray tube currents that are the same as the X-ray tube currents used with the old butterfly filter 204. The built-in alignment mechanism also implements the desired X-ray focus position for different values ​​of other acquisition parameters or system operating conditions. The process flow ends at step 198.

[0060] The technical effects of the embodiments disclosed in the present invention include providing a system and method for maintaining the X-ray focus position at a desired position (e.g., center detector channel position) on an X-ray detector of an X-ray imaging system (e.g., CT imaging system) under different system operating conditions via a built-in alignment mechanism for the X-ray focus. The technical effects of the embodiments disclosed in the present invention also include improving both calibration robustness and image quality due to the isolation of the correlation between the tube current (mA) and the X-ray focus position (e.g., by reducing artifacts caused by X-ray focus position drift). The technical effects of the embodiments disclosed in the present invention also include improving service availability by ensuring the desired X-ray focus positioning on the detector after replacing hardware (e.g., X-ray tubes or butterfly filters), thereby minimizing system downtime (e.g., by reducing calibration time). The technical effects of the embodiments disclosed in the present invention also include improving dose delivery predictability by implementing assumptions related to the X-ray focus position (because an accurate X-ray focus position on the detector is required to calculate and estimate an accurate dose for a patient). The technical effects of the embodiments disclosed in the present invention also include providing an overall method of combining system hardware with software for performing calculations and analysis to align the X-ray focal position to the desired detector position (i.e., to keep the X-ray focal position consistent at the desired position on the detector for all acquisition parameters).

[0061] Reference is made to the technology presented and claimed herein and applied to physical and specific examples of a practical nature that clearly improves upon the present state of the art and, therefore, is not abstract, intangible, or purely theoretical. In addition, if any claim appended to the end of this specification contains one or more elements designated as "means for [performing] the function of ..." or "steps for [performing] the function of ...," it is intended that such elements be interpreted under 35 U.S.C. § 112(f). However, for any claim containing elements designated in any other manner, it is not intended that such elements be interpreted under 35 U.S.C. § 112(f).

[0062] This written description uses examples to disclose the subject matter, including the best mode, and also to enable those skilled in the art to practice the subject matter, including making and using any devices or systems and performing any included methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insignificant differences from the literal language of the claims.

Claims

1. A method for maintaining an X-ray focal point position at a desired location on an X-ray detector (15) of an X-ray imaging system (10), the method comprising: obtaining, via the processing circuit system, a scan plan for performing an X-ray scan using the X-ray imaging system (10); determining, via the processing circuitry, bending magnet current values ​​for maintaining the X-ray focal position of an X-ray beam emitted from an X-ray tube (14) of the X-ray imaging system (10) at the desired location on the X-ray detector (15) based on a plurality of acquisition parameters of the X-ray scan; as well as The bending magnet current values ​​are utilized via the processing circuitry to maintain the X-ray focal point position at the desired location on the X-ray detector (15) during the X-ray scan.

2. The method of claim 1 , wherein utilizing the bending magnet current value during the X-ray scan comprises applying a bending magnet current corresponding to the bending magnet current value to an electromagnet (67) to maintain the X-ray focal position of the X-ray beam emitted from the X-ray tube (14) by utilizing electromagnetic deflection of an electron beam emitted from a cathode (62) of the X-ray tube (14).

3. The method of claim 1 , further comprising accessing, via the processing circuit system, a function map prior to the X-ray scan, wherein the function map comprises a plurality of bending magnet current values ​​and corresponding X-ray focus positions to be used for the plurality of acquisition parameters.

4. The method of claim 3 , wherein determining the bending magnet current value for maintaining the X-ray focus position comprises determining the bending magnet current value according to the function graph based on the plurality of acquisition parameters of the X-ray scan to achieve the desired positioning of the X-ray focus.

5. The method of claim 4, further comprising generating the function graph via the processing circuit system prior to the X-ray scanning by the following steps: During an initial scan using the X-ray imaging system (10), obtaining air scan data and edge scan data using initial bending magnet current values ​​and initial acquisition parameters; determining an initial X-ray focus position based on the air scan data and the edge scan data; During subsequent scans using the X-ray imaging system (10), obtaining additional air scan data and additional edge scan data using different bending magnet current values ​​used with the initial acquisition parameters; and Different X-ray focus positions are determined based on the additional air scan data and the additional edge scan data.

6. The method of claim 5, further comprising storing the function map locally with the X-ray imaging system (10) via the processing circuitry for use with the X-ray tube (14).

7. The method according to claim 3 further comprises updating the function diagram via the processing circuit system in response to replacing the X-ray tube (14) with a different X-ray tube (14) or in response to replacing the butterfly filter (204) with a different butterfly filter (206).

8. The method of claim 1, wherein the scanning protocol comprises a calibration scanning protocol and the X-ray scan comprises a calibration scan.

9. The method of claim 1, wherein the scan protocol comprises a diagnostic scan protocol and the X-ray scan comprises a diagnostic scan.

10. The method of claim 1, wherein the X-ray imaging system (10) comprises a computed tomography imaging system.

11. The method of claim 1, wherein the X-ray focus position utilized during the X-ray scan is independent of the plurality of acquisition parameters.

12. The method of claim 1, wherein the plurality of acquisition parameters comprises three or more of tube current, tube voltage, focal spot size, butterfly filter (204, 206), rotation speed, gantry angle, thermal conditions, and time of day.

13. A system for maintaining an X-ray focal point position at a desired location on an X-ray detector (15) of an X-ray imaging system (10), the system comprising: a memory encoding a processor-executable routine; and a processing circuitry configured to access the memory and to execute the processor-executable routine, wherein the routine, when executed by the processing circuitry, causes the processing circuitry to perform: Obtaining a scanning plan for performing an X-ray scan using the X-ray imaging system (10); determining a bending magnet current value for maintaining the X-ray focal position of an X-ray beam emitted from an X-ray tube (14) of the X-ray imaging system (10) at the desired position on the X-ray detector (15) based on a plurality of acquisition parameters of the X-ray scan; and The bending magnet current value is used to maintain the X-ray focal point position at the desired location on the X-ray detector (15) during the X-ray scan.

14. The system of claim 13, wherein utilizing the bending magnet current value during the X-ray scan comprises applying a bending magnet current corresponding to the bending magnet current value to an electromagnet (67) to maintain the X-ray focal position of the X-ray beam emitted from the X-ray tube (14) utilizing electromagnetic deflection of an electron beam emitted from a cathode (62) of the X-ray tube (14).

15. The system of claim 13, wherein the routine, when executed by the processing circuitry, causes the processing circuitry to further access a function map prior to the X-ray scan, wherein the function map includes a plurality of bending magnet current values ​​and corresponding X-ray focus positions to be used for the plurality of acquisition parameters.

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