SYSTEM AND METHOD FOR AN INTEGRATED FILTER ASSEMBLY HAVING TWO CARRIAGES - Patent application

Abstract

To provide various systems and methods for an integrated filter assembly including at least one bowtie filter and at least one beam hardening filter that are mounted on a carriage.SOLUTION: An imaging system may include a first carriage 54 including at least one beam hardening filter 64 and at least one bowtie filter 58, a second carriage 56 including at least two additional bowtie filters, and a carriage driving system for moving the carriages to selectively position the at least one beam hardening filter and one of the bowtie filters in a path of an X-ray beam. The at least one beam hardening filter may overlap with at least one of the bowtie filters.SELECTED DRAWING: Figure 7B

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE Embodiments of the subject matter disclosed herein relate to diagnostic imaging systems and methods, and more particularly, to computed tomography (CT) imaging systems having an integrated filter assembly. [Background technology]

[0002] A non-invasive imaging modality can transmit energy in the form of X-ray radiation to an imaging subject. Based on the transmitted energy, an image can be generated that shows structural or functional information inside the imaging subject. In a computed tomography (CT) imaging system, an X-ray source generates X-rays, which are emitted toward an X-ray detector and pass through the imaging subject (such as a patient). A bowtie filter can be placed between the X-ray source and the imaging subject to adjust the spatial distribution of the X-ray energy based on the anatomy of the imaging subject. The bowtie filter can be designed to emit high X-ray energy to a specific imaging region of the subject. As a result, the quality of the amplitude of the signal received by the X-ray detector is improved in the central region and the X-ray dose is reduced in the peripheral parts of the subject. Different bowtie filters may be required for different anatomy of the subject. For example, bowtie filters of different materials, shapes, and sizes can be designed to image separate regions of the subject's body (such as the head, chest, and abdomen).

[0003] Additionally, a radiation hardening filter can be placed between the x-ray source and the imaged subject to absorb or block low energy x-rays, thereby attenuating and "hardening" the x-ray beam. Conditioning the x-ray beam using a radiation hardening filter may be particularly desirable during calibration or during diagnostic patient scans or scout scans (scans performed prior to diagnostic scans that may include the subject's internal structure and provide projection views along the subject's longitudinal axis). Thus, there is a need for a system and method that integrates at least one radiation hardening filter with one or more bowtie filters. Summary of the Invention

[0004] One aspect is a system including at least one carriage including at least one radiation hardening filter and at least one bowtie filter, and a carriage drive system for moving the at least one carriage such that the at least one radiation hardening filter and the at least one bowtie filter are selectively positioned in and out of the path of the X-ray beam between an X-ray tube and a subject, the at least one radiation hardening filter can be positioned in and out of the path of the X-ray beam, and the at least one radiation hardening filter can be positioned in and out of the path of the X-ray beam in combination with at least one bowtie filter of the one or more bowtie filters.

[0005] One aspect is an imaging system including a collimator assembly disposed adjacent to an x-ray source generating an x-ray beam that passes through the collimator assembly, the collimator assembly including at least one carriage including at least one beam hardening filter and at least one bowtie filter, the beam hardening filter coupled to an edge of the carriage and extending away from the at least one bowtie filter.

[0006] One aspect is a method of an imaging system that includes moving a first carriage during a first acquisition such that a beam hardening filter coupled to the first carriage is positioned on a path of an x-ray beam, moving a second carriage during a first acquisition such that a second bowtie filter housed in a second carriage is positioned on the path of the x-ray beam, and moving the first carriage during the second acquisition such that the beam hardening filter is moved out of the path of the x-ray beam.

[0007] One embodiment is a computed tomography (CT) imaging system including a gantry, an X-ray source disposed on the gantry and emitting X-rays, an X-ray detector disposed on the gantry and facing the X-ray source, a first carriage including a first bowtie filter and a first radiation hardening filter, a second carriage including a second bowtie filter and a third bowtie filter, the second radiation hardening filter being disposed between the second bowtie filter and the third bowtie filter, and a carriage drive system for switching filters by moving one or more of the first bowtie filter, the second bowtie filter, the third bowtie filter, and the first radiation hardening filter, the second radiation hardening filter into or out of an X-ray beam.

[0008] One aspect is a pre-collimator assembly for a computed tomography (CT) imaging system. The pre-collimator assembly includes a first carriage including a beam hardening filter and a first bowtie filter, a first carriage drive system coupled to the first carriage for moving the first carriage, and thus the beam hardening filter and the first bowtie filter, into and out of the X-ray beam path, a second carriage including a second bowtie filter and a third bowtie filter, and a second carriage drive system coupled to the second carriage for moving the second carriage, and thus the second bowtie filter and the third bowtie filter, into and out of the X-ray beam path, the beam hardening filter being disposed along and coupled to an outer edge of the first carriage, and the beam hardening filter may be positioned on the X-ray beam path alone or in combination with one of the second bowtie filter and the third bowtie filter.

[0009] 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. The above summary is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims set forth after the detailed description. Moreover, the claimed subject matter is not limited to implementations that solve the disadvantages discussed above or in any part of this disclosure.

[0010] The subject matter of the present disclosure will be better understood from the following description of non-limiting embodiments, taken in conjunction with the accompanying drawings, in which: [Brief description of the drawings]

[0011] [Figure 1]FIG. 1 is a diagram of a computed tomography (CT) imaging system. [Diagram 2] 1 is a block schematic diagram of a CT imaging system. [Diagram 3] FIG. 2 is a perspective view of an example of an integrated filter assembly including a carriage, a beam hardening filter, and a bowtie filter. [Figure 4] 4 is a first partially exploded view of the exemplary integrated filter assembly of FIG. 3. [Diagram 5] FIG. 1 is a partially exploded view of an example of an integrated filter assembly including a carriage and at least two bowtie filters. [Figure 6] FIG. 1 illustrates a partially exploded view of an example of an integrated filter assembly including a carriage and at least two bowtie filters. [Figure 7A] 6 is a cross-sectional view of an exemplary collimator assembly including the integrated filter assembly of FIGS. 3-4 and the integrated filter assembly of FIG. 5 at different positions within the collimator assembly. [Figure 7B] 6 is a cross-sectional view of an exemplary collimator assembly including the integrated filter assembly of FIGS. 3-4 and the integrated filter assembly of FIG. 5 at different positions within the collimator assembly. [Figure 8] 7 is a cross-sectional view of an alternative embodiment collimator assembly including the integrated filter assembly of FIGS. 3-4 and the integrated filter assembly of FIG. 6. FIG. [Figure 9] 13 is a cross-sectional view of another alternative embodiment collimator assembly including an alternative embodiment integrated filter assembly. [Figure 10] 13 is a cross-sectional view of another alternative embodiment collimator assembly including an alternative embodiment integrated filter assembly. [Figure 11A] FIG. 2 shows a filter assembly with three bowtie filters and one beam hardening filter in a first position. [Figure 11B] FIG. 11B shows the filter assembly of FIG. 11A in a second position. [Figure 11C] FIG. 11B illustrates the filter assembly of FIG. 11A in a third position. [Figure 11D] FIG. 11B shows the filter assembly of FIG. 11A in a fourth position. [Figure 11E] FIG. 11B shows the filter assembly of FIG. 11A in a fifth position. [Figure 11F] FIG. 11B shows the filter assembly of FIG. 11A in a sixth position. [Figure 12A] FIG. 11B is a schematic diagram showing the components of a scan when using an exemplary filter assembly in any one of the second, third, or sixth positions shown in FIGS. 11B, 11C, and 11F. [Figure 12B] FIG. 11F is a schematic diagram showing the components of a scan when using the exemplary filter assembly in the fifth position shown in FIG. 11E. [Figure 12C] FIG. 11E is a schematic diagram showing the components of a scan when using the exemplary filter assembly in the fourth position shown in FIG. [Figure 13] 4 shows examples of energy spectrum curves of different radiation hardening filters that can be used with the exemplary filter assemblies described herein. [Figure 14] FIG. 1 compares the energy spectra of unfiltered and filtered X-rays. [Figure 15] 1 shows a flow chart of an example of a calibration method using an integrated filter assembly. [Figure 16] 1 is a flow chart illustrating an example of a method for scout and diagnostic scanning using an integrated filter assembly. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] One or more specific embodiments are described below. These embodiments are an attempt to be concise, and not all features of an actual implementation are described herein. It should be understood that the development of any actual implementation, like any engineering or design project, requires numerous implementation-specific decisions to be made to achieve the developer's particular goals (such as compliance with system-related and business-related constraints, which may vary from implementation to implementation). Moreover, it should be understood that such a development effort may be complex and time-consuming, but would be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill in the art having the benefit of this disclosure.

[0013] When introducing elements of various embodiments of the disclosure, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the element. The terms "including," "comprising," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. Furthermore, the numerical examples in the following description are intended to be non-limiting, and thus, additional numerical values, ranges, and percentages are within the scope of the disclosed embodiments.

[0014] The following description relates to various embodiments of x-ray imaging systems and methods. In particular, systems and methods are provided for a computed tomography (CT) imaging system that uses at least one radiation hardening filter and at least one bowtie filter. FIGS. 1-2 show an exemplary embodiment of a computed tomography (CT) imaging system, where one or more filters are placed between an x-ray source (e.g., an x-ray tube) and an imaged subject. Different filters can be selected based on the anatomy of the imaged subject or for calibration. FIGS. 3-4 show an example of an integrated filter assembly including a carriage, a radiation hardening filter, and a bowtie filter, which can be positioned to adjust the spatial distribution and to adjust the beam reaching the subject. As an example, in a single carriage, the bowtie filter can be positioned adjacent to a radiation hardening filter coupled to one edge of the carriage. By moving the carriage along an axis perpendicular to the beam, the bowtie filter or radiation hardening filter can be positioned on the path of the beam. FIG. 5 shows an exemplary second carriage including two bowtie filters that can be used in conjunction with the first carriage. FIG. 6 shows an exemplary second carriage including two bowtie filters and an optional radiation hardening filter that can be used in conjunction with the first carriage. The second carriage can be positioned such that the filter of the second carriage is positioned on the path of the beam simultaneously with the radiation hardening filter of the first carriage. FIGS. 7A and 7B show cross-sectional views of exemplary first and second carriages in different positions. FIGS. 8-10 show first and second carriages in different positions, with different positions of the radiation hardening filter. For example, the radiation hardening filter can be coupled to the second carriage (e.g., a carriage with two bowtie filters). FIGS. 11A-11F show various positions of an exemplary filter assembly with three bowtie filters and one radiation hardening filter.12A-12C are schematic diagrams illustrating various components of a scan that can be performed using an exemplary filter assembly. For example, a radiation hardening filter can be used to perform a low-dose scan and / or a calibration of a CT imaging system. FIGS. 13 and 14 graphically represent energy spectra with reduced dose when using an exemplary filter assembly. FIG. 15 illustrates an exemplary method for calibrating an imaging system using one or more filters included in an integrated filter assembly. FIG. 16 illustrates an exemplary method for imaging a subject using one or more filters included in an integrated filter assembly.

[0015] Although a CT imaging system is described as an example, it will be understood that the present technique is usefully applied to images acquired using other imaging modalities, such as x-ray imaging systems, fluoroscopic imaging systems, interventional imaging systems, mammography imaging systems, surgical imaging systems, etc. The CT imaging modality of this description is provided merely as one example of a suitable imaging modality.

[0016] Various embodiments can be implemented in different types of imaging systems. For example, various embodiments can be implemented in a CT imaging system, where an x-ray source projects a fan- or cone-shaped beam that is collimated to lie in an xy plane of a Cartesian coordinate system, commonly referred to as an "image plane." The x-ray beam passes through an object being imaged (such as a patient). After being attenuated by the patient, the x-ray beam impinges on an x-ray detector. The intensity of the attenuated x-rays received by the x-ray detector depends on the attenuation of the x-ray beam by the imaged object. Each detector element of the x-ray detector produces a separate electrical signal that is a measurement of the x-ray intensity at the location of each detector element. The x-ray intensity measurements from all detector elements are taken separately to create a transmission profile.

[0017] In a typical rotational CT imaging system, the x-ray source and x-ray detector rotate in a gantry around the object being imaged such that the angle at which the x-ray beam intersects the object being imaged changes continuously. A full 360 degree rotation of the gantry results in a complete rotation of the gantry. A group of x-ray attenuation measurements (e.g., projection data) of the x-ray detector at one gantry angle is called a "view." Thus, a view is each incremental position of the gantry. A "scan" of the object consists of a set of views acquired at different gantry angles (or view angles) during one revolution of the x-ray source and x-ray detector. In an axial diagnostic scan, the projection data is processed to construct an image corresponding to a two-dimensional slice across the object. In a scout scan (also referred to herein as a localizer scan), projection views are acquired along the longitudinal axis of the object being imaged, typically resulting in multiple aggregations, each aggregation including the object's internal structure. One method for reconstructing an image from a set of projection data is known in the art as filtered backprojection, which converts the attenuation measurements obtained from a scan into an integer number called a "CT number" or "Hounsfield Unit (HU)," which is used to control the brightness of the corresponding pixel on a display.

[0018] Scout scans (also referred to herein as localizer scans) and diagnostic scans may have different x-ray beam characteristics (e.g., size, shape, energy, etc.). During certain scout and diagnostic scans, it is desirable to use higher x-ray power. Higher x-ray power improves diagnostic scan image quality and improves the thermal stability of the x-ray source. However, increased x-ray power can increase the patient's x-ray exposure or dose. Therefore, a beam hardening filter can be used in the path of the x-ray beam to attenuate the x-rays before they enter the patient and reduce the amount of low energy x-ray beam (Figure 14). A beam hardening filter can be used in conjunction with a bowtie filter when a higher energy x-ray beam is desired for the patient scan (e.g., large patients). The beam hardening filter and bowtie filter can be mounted on separate carriages that can be moved in and out of the x-ray beam as needed. However, the use of multiple carriages increases the cost and complexity of the pre-collimator assembly. Also, moving the carriage in and out of the x-ray beam between sections of the scan may increase the time to complete the scan. Therefore, according to embodiments disclosed herein, the carriage, multiple radiation hardening filters, and multiple bowtie filters may be incorporated into a single integrated filter assembly. Based on the scan setup, one or more filters of the carriage may be positioned in the path of the x-ray beam. Including multiple bowtie filters and multiple radiation hardening filters in a single integrated filter assembly may increase the reliability of the scan setup and reduce the cost and complexity of the scan setup.

[0019] FIG. 1 illustrates an exemplary computed tomography (CT) imaging system 10, and FIG. 2 illustrates an exemplary block diagram of an exemplary CT imaging system according to one embodiment. The CT imaging system includes a gantry 12. The gantry 12 has an X-ray source 14 that generates and projects an X-ray beam 16 toward an X-ray detector assembly 15 located on the opposite side of the gantry 12. The X-ray source 14 projects the X-ray beam 16. The X-ray beam 16 passes through a pre-collimator assembly 13 that conditions the X-ray beam 16, for example, using one or more filters. The X-ray detector assembly 15 includes a collimator assembly 18 (or a post-collimator assembly), multiple detector modules 20 (e.g., detector elements or sensors), and a data acquisition system (DAS) 32. The multiple detector modules 20 detect the projected X-rays that pass through a subject 22, i.e., a subject being imaged, and the DAS 32 converts the data into digital signals for further processing. Each detector module 20 in a conventional system produces an analog electrical signal that represents the intensity of an incident x-ray beam and hence the intensity of the beam attenuated as it passes through the subject 22. During a scan to acquire x-ray projection data, the gantry 12 and the components mounted on the gantry 12 rotate about a center of rotation 25 (e.g., an isocenter) such that attenuation data is collected from multiple view angles relative to the imaging volume.

[0020] Rotation of the gantry 12 and operation of the x-ray source 14 are governed by a control system 26 of the CT imaging system 10. The control system 26 includes an x-ray controller 28, which provides power and timing signals to the x-ray source 14, a collimator controller 29, which controls the aperture length and width of the pre-collimator assembly 13 (and thus the size and shape of the x-ray beam (e.g., x-ray beam) 16), and a gantry motor controller 30, which controls the rotational speed and position of the gantry 12. An image reconstructor 34 receives sampled and digitized x-ray data from the DAS 32 and performs high speed image reconstruction. The reconstructed image is used as an input to a computer 36, which stores the image in a storage device 38. The computer 36 receives commands and scanning parameters from an operator via an operator console 40. An associated display 42 allows the operator to observe the reconstructed image and other data from the computer 36. The operator supplied commands and parameters are used by computer 36 to provide control signals and information to DAS 32, x-ray controller 28, collimator controller 29, and gantry motor controller 30. Computer 36 also operates a table motor controller 44, which controls a motorized table 46 to position subject 22 and gantry 12. In particular, table 46 moves subject 22 so that a portion of the subject passes through an opening or bore 48 in the gantry.

[0021] According to aspects of the present disclosure, the CT imaging system 10 is configured to perform automatic exposure control in response to user input. Exposure control can be achieved using one or more filter assemblies (e.g., filter assemblies 50 and 52 of FIGS. 3-6) that can be mounted in the gantry 12 between the x-ray source 14 and the subject 22. The filter assemblies 50, 52 can move in the z-direction to move in and out of the beam 16 when the beam 16 is substantially in the y-direction. In the embodiments described herein, the filter assemblies 50, 52 include multiple bowtie filters and at least one radiation hardening filter. The filter assemblies 50, 52 can be positioned such that two or more filters are located on the path of the x-ray beam 16 during a scan.

[0022] 3-6 show exemplary filter assemblies 50, 52 that can be used with the exemplary CT imaging system 10 described herein. The two filter assemblies 50, 52 can each include a carriage 54, 56, and each carriage 54, 56 can include at least one bowtie filter. When combined, the filter assemblies 50, 52 include multiple bowtie filters that are different from each other. In particular, the first filter assembly 50 shown in FIGS. 3-4 includes a first carriage 54 having a first bowtie filter 58. The second filter assembly 52 shown in FIGS. 5-6 includes a second carriage 56 with a second bowtie filter 60 and a third bowtie filter 62. Additionally, the exemplary carriages 54, 56 can include a radiation hardening filter. In the embodiment shown in Figures 3, 4 and 6, the first carriage 54 includes a first radiation hardening filter 64 extending from an upper edge 66 of the carriage 54, and the second carriage 56 includes a second radiation hardening filter 96 disposed between the second bowtie filter 60 and the third bowtie filter 62 as shown in Figure 6. However, the radiation hardening filters 64, 96 may be disposed differently (e.g., as shown in alternative configurations in Figures 8-10). Here, as an example, the bowtie filters 58, 60, 62 are shown as rectangular in shape. Each bowtie filter 58, 60, 62 may be rigid and non-deformable. Alternatively, the bowtie filters 58, 60, 62 may have different shapes and different material compositions to provide suitable x-ray spectra for imaging various types of anatomical structures. The bowtie filters 58, 60, 62 can modify the spatial distribution of the x-ray beam (i.e., tune the x-ray beam) in the axial plane of the object 22 (e.g., a patient). For example, the modified spatial distribution of the x-ray beam 16 can have high energy at the center of the object 22 and low energy at the periphery of the object 22.Each of the bowtie filters 58, 60, 62 can be designed to image a particular anatomical structure or a particular region of the human body, such as the head, chest, and abdomen. During imaging, one of the bowtie filters 58, 60, 62 can be selected based on the anatomy of the subject 22 being scanned, and the selected filter can be placed on the x-ray beam path 16. As the anatomy changes, the filter can be changed to another filter. Based on the nature of the scan, the carriage can be positioned so that the radiation hardening filter is placed on the x-ray beam path 16, or the carriage can be positioned so that the radiation hardening filter is not placed on the x-ray beam path 16. The radiation hardening filters 64, 96 attenuate the x-ray beam 16 and remove low energy components, thereby adjusting the x-ray beam 16 for a particular scan, such as a patient scan or a calibration scan.

[0023] The first filter assembly 50 is shown in Figures 3-4. The first filter assembly 50 may include a first carriage 54. The first carriage 54 may include a first slot 70 formed within a cavity of the first carriage 54. In one embodiment, the first slot 70 may extend the entire length of the first carriage 54. In another embodiment, the first slot 70 may extend a portion of the length of the first carriage 54.

[0024] The first bowtie filter 58 may be received in the first slot 70. The first bowtie filter 58 may be in the shape of a "bowtie" having a first long side that is straight and a second long side that is parallel to the first long side and includes a central depression. The first bowtie filter 58 may be formed of graphite. The bowtie filter 58 may be used to adjust the spatial distribution of the X-ray beam 51 passing through the first bowtie filter 58, and the size of the bowtie filter controls the level of spatial distribution adjustment performed on the X-ray beam 16 passing through the first bowtie filter 58. The carriage 54 may include a cutout portion 72 in a side wall through which the bowtie filter 58 is visible. The first carriage 54 may move along a direction perpendicular to the X-ray beam 51, as indicated by arrow 53, to position the X-ray beam at the bowtie filter 58 or the beam hardening filter 64.

[0025] The beam hardening filter 64 may be coupled to the carriage 54 at an edge 66 of a top surface 76 of the carriage 54. The beam hardening filter 64 may be positioned adjacent to the first bowtie filter 58 and extends away from the edge 66 of the carriage 54 and the first bowtie filter 58. The physical size of the beam hardening filter 64 may vary, but since the beam hardening filter 64 is closer to the x-ray source 14 than the filter 58, the physical size of the beam hardening filter 64 may be the same as or smaller than the physical size of the first bowtie filter 58. Since the beam hardening filter 64 is positioned to extend from the top surface 76 of the first carriage 54, the first carriage 54 and the second carriage 56 may be positioned such that the beam hardening filter 64 overlaps (e.g., extends over) a bowtie filter in the second carriage 56 (e.g., the second bowtie filter 60 or the third bowtie filter 62).

[0026] The beam hardening filter 64 may include a support structure 78 and one or more metal sheets 80 sandwiched between the support structure 78. In this embodiment, the support structure 78 includes an upper window frame member 78A and a lower support member 78B on either side of the one or more metal sheets 80. Each metal sheet 80 and the support structure 78 may be laminated together and secured to the edge 66 of the carriage 54 by a plurality of fasteners 74. In this embodiment, the metal sheets 80 and the support structure 78 may have a plurality of concentric holes 82 formed therein, and each fastener 74 (used to attach a layer of the beam hardening filter 64 to the carriage 54) may pass through each of the concentric holes 82 present in each layer. In one embodiment, the support structure 78 may be made of a metal (such as aluminum), and the metal sheets 80 may be made of the same metal or a different metal. Examples of highly attenuating or heavy element materials for the metal sheets 80 include copper, lead, tin, molybdenum, tungsten, titanium, zirconium, and the like. The metal sheet 80 filters out low energy x-rays and passes high energy x-rays, as shown in FIG. 14. Alternatively, if a specific energy threshold is required for the x-ray detector, the radiation hardening filter 64 can be tungsten and the radiation hardening filter 64 can be used primarily for calibrating the x-ray detector. This is especially true for photon counting x-ray detectors in photon counting CT imaging systems that have multiple energy thresholds for assigning each captured x-ray to multiple energy bins (e.g., multiple low energy bins, medium energy bins, and high energy bins). Energy binning allows material discrimination in the patient images that improves CT diagnostic capabilities. The energy threshold of the x-ray detector can be calibrated with a monoenergetic x-ray source. Thin tungsten films (<50um) can function as a typical radiation hardening filter, but thicker tungsten between 200um and 600um absorbs most of the power of a multi-energy x-ray source and emits tungsten-specific 69.5keV K-edge x-rays (FIG. 13). Other heavy element materials, such as lead, emit K-edge x-ray energies that are specific to those other heavy element materials and can also be used as single energy sources.The 300 μm thick tungsten prevents over 99% of the x-ray beam from passing through the filter, resulting in the emission of monoenergetic x-rays at a specific energy of 69.5 keV (Figure 13). The specific energy emitted by a tungsten beam hardening filter is ideal for calibrating the energy threshold of the photon counting x-ray detector in a photon counting CT imaging system.

[0027] The beam hardening filter 64 can be used to block low energy x-rays, thereby attenuating and "hardening" the x-ray beam 51 passing through the beam hardening filter 64. How much the x-ray beam is attenuated depends on one or more of the number of attenuating layers (such as metal sheets), the thickness of each attenuating layer, the material used for the attenuating layers, and the overall size of the attenuating layers in the beam hardening filter.

[0028] As an example, if a thinner sheet of radiation hardening material is used for the metal sheet 80, the support structure 78 can be used to inhibit deflection of the radiation hardening filter 64 due to gantry rotation forces that may act to bend the middle of the radiation hardening material. In this embodiment, the support structure 78 is positioned outside the cross-sectional area of ​​the hardened x-ray beam 51 used for imaging. In this manner, the radiation hardening filter 64 can independently harden the x-ray beam 51 while being mechanically strengthened by the support structure 78 near the area where the x-ray beam 51 passes through the radiation hardening filter 64. Additionally, the support structure 78 can be fabricated from a stiff, yet lightweight material (such as aluminum) to minimize excess x-ray scattering near the radiation hardening filter 64. The first filter assembly 50 alone can be used in the exemplary CT imaging system 10, or the first filter assembly 50 can be used in conjunction with additional filter assemblies (such as the second filter assembly 52 of FIGS. 5-6).

[0029] The second filter assembly 52 is shown in Figures 5-6. The second filter assembly 52 can include a second carriage 56. The second carriage 56 can include a first slot 86 and a second slot 88 formed in a cavity of the carriage 56. The first slot 86 can be separated from the second slot 88 by a tab 90. In one embodiment, each of the two slots 86 and 88 can extend through the second carriage 56 the entire length of the second carriage 56. In another embodiment, each of the two slots 86 and 88 can extend partially through the length of the carriage 56.

[0030] The second bowtie filter 60 may be received in the first slot 86 and the third bowtie filter 62 may be received in the second slot 88. In one embodiment, the second bowtie filter 60 and the third bowtie filter 62 may be disposed adjacent to each other but not in contact with each other. In another embodiment, the second bowtie filter 60 and the third bowtie filter 62 may be disposed adjacent to each other with their faces in contact with each other. Each of the second bowtie filter 60 and the third bowtie filter 62 may be formed as a "bowtie" having a first long side that is straight and a second long side that is parallel to the first long side and includes a central depression. In one embodiment, the second bowtie filter 60 and the third bowtie filter 62 may be filters of the same size (width, length, thickness, etc.). In another embodiment, the second bowtie filter 60 and the third bowtie filter 62 may be filters of different sizes (width, length, thickness, etc.). Each of the second bowtie filter 60 and the third bowtie filter 62 may be formed of graphite or other x-ray attenuating material. The bowtie filters may be used to adjust the spatial distribution of the x-ray beam 51 passing through the filter, and the size of the bowtie filter controls the level of spatial distribution adjustment performed on the x-ray beam 51 passing through the filter. The carriage 56 may include a cutout portion 92 in a side wall through which the bowtie filters 60, 62 are visible. As shown in this embodiment, the third bowtie filter 62 may be flush with the side wall and cutout portion 92 of the carriage 56. In FIG. 5, the bowtie filters 60, 62 may be secured within the respective slots 86, 88 by a support structure 100 and fasteners 106. The support structure 100 may be recessed in the recess 98 between the second bowtie filter 60 and the third bowtie filter 62 and secured to the carriage 56 by a number of fasteners 106 at each end of the support structure 100.In this embodiment, a number of openings 108 are formed in two ends of the support structure 100, and each fastener 106 (used to attach the support structure 100 to the carriage 56) can pass through each of the openings 108. As an example, one end of the support structure 100 can be attached to a tab 90 on the carriage 56. The second carriage 56 can move in a direction perpendicular to the x-ray beam 51, as indicated by arrow 53, to position the x-ray beam on one of the bowtie filters 60, 62.

[0031] FIG. 6 differs from FIG. 5 in the presence of a radiation hardening filter 96 that can be coupled to the carriage 56 between the second bowtie filter 60 and the third bowtie filter 62. The radiation hardening filter 96 can be recessed in a recess 98 between the second bowtie filter 60 and the third bowtie filter 62. The length of the radiation hardening filter 96 can be equal to or greater than the length of each of the second bowtie filter 60 and the third bowtie filter 62. However, the width of the radiation hardening filter 96 can be narrower than the width of each of the second bowtie filter 60 and the third bowtie filter 62. Since the radiation hardening filter 96 is disposed between the second bowtie filter 60 and the third bowtie filter 62, the radiation hardening filter 96 can at least partially overlap each of the second bowtie filter 60 and the third bowtie filter 62, and the surface of the radiation hardening filter 96 can contact the top / side surface of the bowtie filter.

[0032] The radiation hardening filter 96 may include one or more metal strips 102, 104 below the support structure 101. In this embodiment, a first metal strip 102 and a second metal strip 104 are disposed below the support structure 101. The first metal strip 102, the second metal strip 104, and the support structure 101 are stacked together, and each of the first metal strip 102, the second metal strip 104, and the support structure 101 may be secured to the carriage 56 at each end by a plurality of fasteners 106. In this embodiment, a plurality of concentric openings 108 are formed at two ends of each of the first metal strip 102, the second metal strip 104, and the support structure 101, and each fastener 106 (used to attach a layer of the radiation hardening filter 96 to the carriage 56) may pass through each of the concentric openings 108 present in each layer. In one embodiment, one end of the radiation hardening filter 96 can be attached to a tab 90 of the carriage 56. In one embodiment, the support structure 101 can be made of a metal (such as aluminum), and the first metal strip 102 and the second metal strip 104 can be made of the same metal or different metals. Examples of highly attenuating or heavy element materials for the metal strips 102, 104 include copper, lead, tin, molybdenum, tungsten, titanium, zirconium, etc.

[0033] The beam hardening filter 96 can absorb low energy x-rays and thereby attenuate the low energy x-rays to "harden" the x-ray beam 51 passing through the beam hardening filter 96. The amount of beam attenuation depends on one or more of the number of attenuating layers (such as metal strips), the thickness of each attenuating layer, the material used in the attenuating layers, and the overall size of the attenuating layers. The amount of beam attenuation is much greater with heavy element materials (highly attenuating materials). Heavy element materials (such as tungsten) absorb incident x-rays and emit monoenergetic K-edge x-rays that are characteristic of the material. Monoenergetic x-ray beams are primarily intended to calibrate the energy thresholds of x-ray detectors.

[0034] As an example, if thin strips of radiation hardening material are used for the metal strips 102, 104, the support structure 101 can be used to suppress deflection due to gantry rotation forces that may act to bend intermediate portions of the radiation hardening material. In this embodiment, the support structure 101 is positioned outside the cross-sectional area of ​​the hardened x-ray beam 51 used for imaging. In this manner, the radiation hardening filter 96 can independently harden the x-ray beam 51 while being mechanically strengthened by the support structure 101 near the area where the x-ray beam 51 passes through the radiation hardening filter 96. Additionally, the support structure 101 can be fabricated from a stiff, yet lightweight material (such as aluminum) to minimize excess x-ray scattering near the radiation hardening filter.

[0035] 7A and 7B show cross-sectional views of the first integrated filter assembly 50 of FIGS. 3-4 and the second integrated filter assembly 52 of FIG. 5 positioned in the exemplary CT imaging system 10 of FIG. 1. As shown in FIGS. 7A and 7B, the filter assemblies 50, 52 can be positioned such that the first radiation hardening filter 64 of the first filter assembly 50 is positioned on the path of the x-ray beam 16. In this position, the radiation hardening filter 64 is the only filter located on the path of the x-ray beam 16. This position of the filter may be suitable for a particular imaging operation (such as calibration of the imaging system). In another exemplary position of the first filter assembly 50 and the second filter assembly 52, both the radiation hardening filter 64 of the first filter assembly 50 and the bowtie filter (e.g., the second bowtie filter 60) of the second filter assembly 52 can be positioned on the path of the x-ray beam 16. In this illustrated position, the radiation hardening filter 64 overlaps the second bowtie filter 60.

[0036] 8-10 show cross-sectional views of alternative configurations of the first integrated filter assembly 50 of FIGS. 3-4 and the second integrated filter assembly 52 of FIGS. 5-6 disposed within the exemplary CT imaging system 10 of FIG. 1. In the exemplary configuration shown in FIG. 8, the first filter assembly 50 is the same as the exemplary first filter assembly 50 shown in FIGS. 3-4. However, the second filter assembly 52 includes a beam-hardening filter 96 disposed between the second bowtie filter 60 and the third bowtie filter 62. FIG. 9 shows an alternative configuration in which the first filter assembly 50 does not include a beam-hardening filter, and the second filter assembly 52 includes a beam-hardening filter 112 coupled to an edge 114 of the top surface 116 of the second carriage 56. The exemplary beam-hardening filter 112 can be similar to the beam-hardening filter 64 described with reference to FIGS. 3-4. In Figure 10, the alternative configurations shown include a first filter assembly 50 that does not include a radiation hardening filter, and a second filter assembly 52 that includes a radiation hardening filter 112 coupled to an edge 114 of a top surface 116 of the carriage 56, and a radiation hardening filter 96 disposed between the second bowtie filter 60 and the third bowtie filter 62. Although three alternative configurations are shown in Figures 8-10, various configurations of filter assemblies can be used with radiation hardening filters (e.g., radiation hardening filters 64, 96) coupled to an edge of the top surface of the carriage, as described herein.

[0037] As shown in Figures 7A, 7B and 8-10, an additional filter 110, 111 may be coupled to the underside of the carriage 56, 54 and extend along the entire underside of the carriage 56, 54. This filter may further condition the x-ray beam 16 after it has passed through one or more of the beam hardening and bowtie filters.

[0038] During a calibration or imaging scan, the X-ray beam 16 may first pass through the beam hardening filter 64 or 112, followed by the bowtie filter (e.g., bowtie filter 58, 60, or 62). The carriage 54, 56 may move along a direction perpendicular to the X-ray beam 16 (indicated by arrow 53 in FIG. 7A ) so that the X-ray beam passes through the bowtie filter 58, 60, 62 and / or the beam hardening filter 64 or 112. By selecting the beam hardening filter 64 or 112 and / or the bowtie filter 58, 60, 62, the level of beam attenuation and spatial distribution may be adjusted. In one embodiment, the carriage 54, 56 may be positioned so that the X-ray beam passes through the beam hardening filter 64 and the second bowtie filter 60, and the beam hardening filter 64 overlaps the second bowtie filter 60. In another embodiment, the carriages 54, 56 can be positioned such that the x-ray beam passes through the first bowtie filter 58, the second bowtie filter 60, or the third bowtie filter 62. In yet another embodiment, the carriages 54, 56 can be positioned such that the x-ray beam passes through the beam hardening filter 64 or 112. After passing through one of the second bowtie filter 60 and the third bowtie filter 62, the x-ray beam also passes through the additional filter 110 before being incident on the subject. In some embodiments, the second carriage 56 can be positioned such that the x-ray beam passes through the beam hardening filter 96 of the second carriage 56 and one of the second bowtie filter 60 and the third bowtie filter 62. In some embodiments, the second carriage 56 can be positioned such that the x-ray beam passes through the beam hardening filter 96 of the second carriage 56.

[0039] It may be particularly desirable to attenuate the x-ray beam with a radiation hardening filter during a scout scan that precedes a diagnostic scan. During a diagnostic scan, a diagnostic scan may be performed using a bowtie filter without a radiation hardening filter. Typically, a scout scan may use a smaller beam size (coverage) than that used for the diagnostic scan. The smaller beam may pass through a radiation hardening filter 96 that is narrower than the bowtie filter. The radiation hardening filter 64, 96 may also allow the use of a higher power x-ray source with increased x-ray tube temperature during the scan without increasing the x-ray exposure or dose to the subject. The higher power may improve image quality in the scout scan and / or subsequent diagnostic scans and may improve the thermal stability of the x-ray tube, including the target. The higher x-ray tube target temperature contributes to the long term reliability of the device as the target is maintained closer to its optimum operating temperature and reduces temperature cycling of internal components, contributing to improved reliability.

[0040] 11A-11F illustrate various exemplary positions for the filter assemblies 50, 52. In particular, FIGS. 11A-11F illustrate the three bowtie filters 58, 60, 62 in the carriages 54, 56 and the beam hardening filter 64 in the first filter assembly 50. In this example, the first bowtie filter 58 and the beam hardening filter 64 are positioned together in the first filter assembly 50, and the second bowtie filter 60 and the third bowtie filter 62 are positioned within the second filter assembly 52.

[0041] The first carriage 54 of the first filter assembly 50 can be coupled to a first shaft 120, and a first motor 122 can rotate the first shaft 120 to move the carriage 54 along the first shaft 120. The first shaft 120 can be a screw, ball screw, or other similar design for converting rotational motion into linear motion of the first carriage 54. The second carriage 56 of the second filter assembly 52 can be coupled to a second shaft 126, and a second motor 128 can rotate the second shaft 126 to move the second carriage 56 along the second shaft 126. The second shaft 126 can be a screw, ball screw, or other similar design for converting rotational motion into linear motion of the second carriage 56. A local clearance (not shown) exists on the second carriage 56 to avoid interference between the first shaft 120 and the second carriage 56 as it moves along the second shaft 126. The position of the X-ray beam passing through the collimator assembly is represented by 103 in FIG. 11A, with the center of the X-ray beam indicated by the horizontal line 16. By rotating one or both shafts 120, 126 by motors 122, 128, respectively, one of the three bowtie filters 58, 60, 62 in addition to the radiation hardening filter 64 can be selectively moved onto the beam path of the X-ray beam 16. The first shaft 120 and the second shaft 126 can be aligned and spaced apart from each other by a gap. The X-ray beam 16 can transmit through the gap. The motors (such as motors 122, 128), the shafts (such as shafts 120, 126) coupled to the motors 122, 128, and the filter assemblies (such as filter assemblies 50, 52) coupled to the shafts 120, 126 can form a carriage drive system 130, 132, such as a motor, for moving the filters in and out of the x-ray beam. The filter assemblies 50, 52 may include one or more carriage drive systems 130, 132.

[0042] 11A shows the filter assemblies 50, 52 in a first position 134. The x-ray beam 16 transmits through the collimator housing 136 as shown at 103 without passing through any filters. The first carriage 54 can be positioned near the first motor 122 and the second carriage 56 can be positioned near the second motor 128.

[0043] 11B shows a second position 138 of the filter assemblies 50, 52. The x-ray beam 16 is transmitted through the third bowtie filter 62 of the second carriage 56. The second filter assembly 52 can be moved from the first position 134 to the second position 138 by actuating the second motor 128 and moving the third bowtie filter 62 of the carriage 56 into the x-ray beam path 16.

[0044] 11C illustrates a third position 140 of the filter assemblies 50, 52. The x-ray beam 16 is transmitted only through the second bowtie filter 60 of the second carriage 56. The second carriage 56 can be moved from the first position 134 or the second position 138 to the third position 140 by actuating the second motor 128 to move the second bowtie filter 60 onto the x-ray beam path 16.

[0045] 11D illustrates a fourth position 142 of the filter assemblies 50, 52. The x-ray beam 16 is transmitted through the radiation hardening filter 64. The filter assembly 50 can be moved from any one of the first position 134, second position 138, and third position 140 described above to the fourth position 142 by actuating the first motor 122 to move the first carriage 54 further away from the first motor 122 and, if desired, subsequently or simultaneously actuating the second motor 128 to move the second carriage 56 out of the x-ray beam path 16.

[0046] 11E illustrates a fifth position 144 of the filter assemblies 50, 52. The X-ray beam 16 is transmitted through the radiation hardening filter 64 and the second bowtie filter 60. The filter assemblies 50, 52 can be moved from any one of the first position 134, the second position 138, the third position 140, and the fourth position 142 to the fifth position 144 by actuating the first motor 122 as needed to move the first carriage 54 relative to the first motor 122, and then or simultaneously actuating the second motor 128 as needed to move the second bowtie filter 60 of the second carriage 56 into the X-ray beam path 16.

[0047] 11F illustrates a sixth position 146 of the filter assemblies 50, 52. The x-ray beam 16 is transmitted through the first bowtie filter 58. The filter assembly 50 can be moved from any one of the first position 134, second position 138, third position 140, fourth position 142, and fifth position 144 described above to the sixth position 146 by actuating the first motor 122 to move the first carriage 54 further away from the first motor 122 and, if desired, subsequently or simultaneously actuating the second motor 128 to move the second carriage 56 out of the x-ray beam path 16.

[0048] Based on instructions stored in the non-transitory memory, a computing device (such as the computer 36 in FIG. 2) can move the filter assembly 50, 52 from one of the above positions to another by actuating one or more of the two motors 122, 128. In one embodiment, one filter and a radiation hardening filter are disposed on one carriage and two filters are disposed on the other carriage. As an example, two filters can be coupled to one shaft and driven by one motor. In another embodiment, four or more filters and multiple radiation hardening filters can be disposed in the collimator housing 136. For example, when the total number of filters in the housing is an even number, the number of filters coupled to each shaft is the same. When the total number of filters in the housing is an odd number, the number of filters coupled to each shaft is different.

[0049] In yet another embodiment, the arrangement of the filters in the collimator housing 136 can be determined based on the type of filter. Here, the type of filter can be determined based on which part of the subject the filter is designed to image. For example, a first bowtie filter 58 used to image a first part of the subject 22 and a second bowtie filter 60 used to image a second part of the subject 22 can be positioned next to each other when the first and second parts are connected. Also, the first bowtie filter 58 and the second bowtie filter 60 can be positioned away from each other (e.g., separated by another filter) when the first and second parts are not connected. As an example, a filter for imaging the abdomen can be positioned next to a filter for imaging the chest but away from a filter for imaging the head. In this way, when imaging the chest after imaging the abdomen, the filter can be switched more easily with less movement of the entire carriage. The beam hardening filter can be coupled between the two filters that can be used for the scout scan. By placing the beam hardening filter in this position, switching from a scout scan to a diagnostic scan can be achieved with less movement of the entire carriage.

[0050] In other embodiments, instead of a shaft, any one of a rack and pinion, belt, and cable drive system can be used to move the carriage containing the filter.

[0051] 12A-12C are schematic diagrams illustrating components of a scan using the exemplary filter assemblies in various positions described with respect to FIGS. 11A-11F. For example, FIG. 12A illustrates an exemplary schematic diagram of a scan using a CT imaging system 10 in which the filter assemblies 50, 52 are positioned such that the bowtie filters are located on the path of the x-ray beam 16. For example, FIG. 12A illustrates the filter assemblies 50, 52 in one of the second position 138, the third position 140, and the sixth position 146 in which one of the bowtie filters 58, 60, 62 is in the path of the x-ray beam 16. FIG. 12B illustrates an exemplary schematic diagram of a scan using a CT imaging system 10 in which the filter assemblies 50, 52 are positioned such that the bowtie filter and the beam hardening filter are located on the path of the x-ray beam 16. For example, FIG. 12B illustrates the filter assemblies 50, 52 in the fifth position 144 in which the second bowtie filter 60 and the beam hardening filter 64 are in the path of the x-ray beam 16. 12C illustrates an exemplary schematic diagram of a scan with the CT imaging system 10 in which the filter assemblies 50, 52 are positioned such that the radiation hardening filter 64 is located on the path of the x-ray beam 16. For example, FIG. 12C illustrates the filter assemblies 50, 52 in a fourth position 142 in which the radiation hardening filter 64 is on the path of the x-ray beam 16.

[0052] Thus, FIGS. 1 to 12C show a CT imaging system having a gantry for receiving a subject to be imaged, an X-ray source disposed within the gantry and emitting X-rays, an X-ray detector disposed in the gantry at a position opposite the X-ray source, a motorized table for moving the subject to be imaged or patient into and out of an opening in the gantry, a computing device having instructions stored in a non-transitory memory, a carriage mounted to the gantry, one or more bowtie filters disposed on one of the plurality of filter carriages, at least one radiation hardening filter disposed on one of the plurality of filter carriages, and a carriage drive system for switching filters by moving one of the plurality of bowtie filters and / or one of the plurality of hardening filters into or out of the X-ray beam.

[0053] 13 and 14 are graphs of energy spectrum curves showing the effect of the radiation hardening filter 64 of FIG. 3 depending on the material (e.g., tungsten). The use of a radiation hardening filter of tungsten results in a monoenergetic X-ray beam of a specific energy (e.g., 69.5 keV, FIG. 13). This monoenergetic X-ray beam is used to calibrate the energy of a photon counting X-ray detector. The monoenergetic X-ray beam can also be used for scanning to improve image quality, since it is an ideal X-ray source for various imaging applications if high X-ray intensity can be obtained. The radiation hardening filter absorbs low energy X-rays and passes high energy X-rays (FIG. 14) used to image the patient. This filter is called a radiation hardening filter because it increases the average energy of the X-rays. The low energy X-rays are also expected to be absorbed by the patient, so they do not contribute to the image quality of the patient image, but the patient dose increases. Although FIG. 13 and FIG. 14 show different filter characteristics, in this specification, both cases are radiation hardening filters.

[0054] 15 illustrates an exemplary method 200 for performing a calibration scan using a radiation hardening filter of an integrated filter assembly (such as integrated filter assemblies 50, 52 described herein). Method 200 provides for calibration of an x-ray detector of an imaging system (such as CT imaging system 10) by using a radiation hardening filter (such as radiation hardening filter 64) disposed in the filter assembly. Additionally, a phantom may be used during calibration, or the calibration may be performed as an air scan. Method 200 and all methods described herein may be performed according to instructions stored in a non-transitory memory in a computing device (such as computer 36 of FIG. 2) of CT imaging system 10.

[0055] At 202, a subject for a calibration scan (e.g., subject 22 of FIG. 2, a phantom, or nothing) can be placed on a motorized table (such as table 46 of FIG. 1). A table motor controller 44 can move table 46 so that the appropriate portion of subject 22 is positioned within gantry 12 for imaging.

[0056] At 204, the routine includes determining whether a calibration scan is desired. A calibration scan can be used to calibrate one or more components of the imaging system (e.g., the x-ray detector, the x-ray source, the x-ray dose, the weight balance of the gantry, and / or software or firmware used to process data collected by the imaging system). A calibration scan can also be used to detect misalignment of the imaging system.

[0057] If it is determined that a calibration scan is desired, then at 206, scan parameters for performing the calibration scan may be set. For example, a user may enter or select scan parameters according to a scan protocol or menu. Scan parameters may include the type and order of filters to be used during the scan. As an example, a calibration scan may use a radiation hardening filter to adjust the x-ray beam used to image the subject. Scan parameters may also include scan timing settings. As an example, scan timing may include a start time and duration for imaging each site.

[0058] At 208, a beam hardening filter (such as beam hardening filter 64 of FIG. 3) can be positioned on the path of the x-ray beam by actuating a motor coupled to a carriage containing the beam hardening filter. The carriage can move along a shaft in a plane perpendicular to the plane of the x-ray beam such that the beam hardening filter is positioned in the x-ray beam. A controller can actuate the motor to move the shaft and carriage to a desired position. The beam hardening filter can block low energy x-rays, thereby attenuating and "hardening" the x-ray beam.

[0059] At 210, the method 200 may begin acquiring a data set for a calibration scan. For example, an x-ray source (such as 14 in FIG. 2) may be activated and begin exposing the subject to x-rays using a radiation hardening filter.

[0060] A data set is acquired from an x-ray detector (such as 15 in FIG. 2) upon receiving attenuated x-rays from the subject being imaged. As an example, the acquired data set can be analyzed to ascertain the subject's anatomical structure or location. The current image position can be calculated based on the scan start position and the motorized table travel distance. In an embodiment, the subject's anatomical structure or location can be grouped into different typologies. As another example, the collected data can be analyzed, for example, by a K-edge search to locate the 69.5 keV in the electronics and generate a result. The result can be used to determine whether to terminate the calibration or to repeat the calibration.

[0061] At 212, the routine includes determining whether the calibration scan is finished, which may be determined based on the protocol set in step 206. If it is determined that the calibration scan is not finished, the scout scan may continue to acquire data at 214. If it is determined that the calibration scan is finished, the calibration is complete.

[0062] 16 illustrates an exemplary method 300 for performing an image scan using multiple filters included in an integrated filter assembly (such as integrated filter assemblies 50, 52). Method 300 provides image acquisition of an imaged subject by changing filters between successive scans. Method 300, and all methods described herein, may be performed according to instructions stored in a non-transitory memory of a computing device (such as computer 36 of FIG. 2) of a CT imaging system.

[0063] At 302, a subject for an imaging scan (such as subject 22 in FIG. 2) can be placed on a motorized table (such as table 46 in FIG. 2). A table motor controller 44 can move the table so that the appropriate portion of the subject is positioned within the gantry to be imaged.

[0064] At 304, the routine includes determining whether a scout scan is desired. A scout scan obtains projection views along a longitudinal axis of an imaging subject, typically resulting in multiple aggregations, each aggregation including the subject's internal structure. During a scout scan, all components of the imaging system may be maintained in a stationary position, but the subject is moved through the imaging system as a scan of the subject is performed. The scout scan may be used to identify regions of interest in the subject for subsequent diagnostic scans.

[0065] If it is determined that a scout scan is desired, scan parameters for performing a scout scan can be set at 306. For example, a user can enter or select scan parameters according to a scan protocol or menu. Scan parameters can include the type and order of filters to be used during the scan. As an example, a scout scan can use a bowtie filter in conjunction with a beam hardening filter to adjust the x-ray beam used to image the subject. Scan parameters can also include setting scan timing. As an example, scan timing can include a start time and duration for imaging each region.

[0066] At 308, the bowtie filter and the radiation hardening filter can be positioned in the path of the x-ray beam by actuating a motor coupled to a carriage that includes the bowtie filter (such as bowtie filter 60 of FIG. 6) and the radiation hardening filter (such as radiation hardening filter 64 of FIG. 3). The carriage can move along a shaft in a plane perpendicular to the plane of the x-ray beam such that the bowtie filter and the radiation hardening filter are positioned in the x-ray beam. A controller can actuate the motor to move the shaft and the carriage to a desired position. The bowtie filter can change the spatial distribution of the x-ray beam in an axial plane of an object (such as a patient). For example, the changed spatial distribution x-ray beam can have a higher energy at the center of the object and a lower energy at the periphery of the object. The radiation hardening filter can block lower energy x-rays, thereby attenuating and "hardening" the beam. The radiation hardening filter can at least partially overlap the bowtie filter such that the beam first passes through the radiation hardening filter and then is incident on the bowtie filter.

[0067] At 310, the method 300 can begin acquiring a data set of the subject. For example, an x-ray source (such as 14 in FIG. 2) can be activated and begin x-ray exposing the subject with a bowtie filter and a radiation hardening filter. A smallest permissible beam can be used for a scout scan. In one example, the beam can be 5 mm. By using a radiation hardening filter to attenuate the beam that reaches the subject, a higher power x-ray source with a higher x-ray tube temperature can be used during the scout scan without increasing the x-ray exposure of the subject. The higher power improves the quality of the diagnostic scan and improves the thermal stability of the x-ray tube, including the target. As an example, a 50 kW x-ray power scanning technique (100 kV, 500 mA) can be used.

[0068] A data set is acquired from an X-ray detector (such as 15 in FIG. 2) upon receiving transmitted radiation signals from the subject. As an example, the acquired data set can be analyzed to ascertain the subject's anatomical structure. As another example, the subject's anatomical structure can be estimated by the currently imaged position. The currently imaged position can be calculated based on the start position of the scan and the travel distance of the motorized table. In one embodiment, the subject's anatomical structure can be classified into different types. For example, the human body anatomical structures can be classified based on size, type (such as head, chest, and abdomen).

[0069] At 312, the routine includes determining whether the scout scan is finished, which may be determined based on the protocol set in step 306. If it is determined that the scout scan is not finished, at 314, the scout scan may continue and data may be acquired.

[0070] If it is determined that the scout scan is completed, then at 316 the routine includes determining whether a diagnostic scan is desired. As an example, the decision to perform a diagnostic scan may be made based on an image reconstructed from data acquired during the scout scan. The image obtained from the scout scan may be a two-dimensional image or a three-dimensional image. Based on the scout scan, a particular anatomical structure may be selected for a diagnostic scan. A diagnostic scan may provide detailed images of particular anatomical structures that may not be available in a scout scan.

[0071] If, at 304, it is determined that a scout scan is not desired, the routine proceeds directly to step 316 to determine whether a diagnostic scan is desired. A scout scan does not have to be performed prior to a diagnostic scan.

[0072] If it is determined that a diagnostic scan is not desired and the scout scan is complete, the data sets acquired from the scout scan are displayed and stored at 318. In one embodiment, data sets acquired from different parts of the subject may be reconstructed to form an image. The acquired data sets, as well as the processed images, may be saved in the imaging system's storage device so that no other scans are performed. The routine may then end.

[0073] If it is determined that a diagnostic scan is desired, the routine proceeds to step 320. In step 320, scan parameters for performing a diagnostic scan may be set. A user may enter or select scan parameters according to a scan protocol or menu. Scan parameters may include the type and order of filters to be used during the scan. The type of filters may be selected based on the anatomical structure of the subject to be imaged to be imaged. The parameters may also include setting scan timing. As an example, the scan timing may include a start time and a duration time for imaging each part. Anatomical information of the subject to be imaged may be loaded into the memory of the computing device. The anatomical information may be obtained from a pre-scan. The anatomical information may be obtained from a previously performed scout scan or from a scan of the specific part. This step may include moving the subject to be imaged by a motorized table so that the desired part of the subject is positioned within the gantry for imaging.

[0074] At 322, a contrast agent may be injected into the imaging subject. The contrast agent may enhance the contrast of images, particularly of certain anatomical structures. This step is optional, and diagnostic scans may be performed without the use of a contrast agent.

[0075] At 324, a bowtie filter can be positioned on the path of the x-ray beam by actuating a motor coupled to a carriage that includes the bowtie filter. The type of filter can be determined based on the anatomy of the current imaging region of the subject. The carriage can move along a shaft in a plane perpendicular to the plane of the x-ray beam to position the bowtie filter in the beam. In one example, the bowtie filter used in the diagnostic scan can be the same as the bowtie filter used in the scout scan. In another example, the bowtie filter used in the diagnostic scan can be different than the bowtie filter used in the scout scan. In this manner, a single carriage that includes one or more bowtie filters and / or beam hardening filters can be used for both scout and diagnostic scans without the need for additional parts. Additionally, multiple filter carriages can be used together to position bowtie filters, with or without beam hardening filters, on the x-ray beam.

[0076] At 326, a data set of the subject may be acquired. For example, the x-ray source may be activated to begin exposing the subject to x-rays using the selected bowtie filter. For diagnostic scans, a beam size of about 25 mm to about 160 mm may be used in the filter assembly. When the transmitted radiation signal from the imaged subject is received by the x-ray detector, a data set is acquired from the x-ray detector. As an example, the acquired data set may be analyzed to ascertain the anatomical structure of the imaged subject. As another example, the anatomical structure of the imaged subject may be estimated based on the currently imaged position. The currently imaged position may be calculated based on the start position of the scan and the travel distance of the motorized table. In one embodiment, the anatomical structure of the subject may be classified into different types. For example, the anatomical structures of the human body may be classified based on size, type (e.g., head, chest, and abdomen).

[0077] At 328, the routine includes determining whether the diagnostic scan is complete, which may be determined based on the protocol set in step 320. If it is determined that the diagnostic scan is not complete, at 330, the diagnostic scan may continue and data may be acquired.

[0078] When it is determined that the diagnostic scan is complete, the data sets acquired from the diagnostic scan are displayed and stored. In one embodiment, data sets acquired from different locations on the subject may be reconstructed to form an image. The acquired data sets and processed images may be saved in a storage device of the imaging system and no further scans may be performed. The routine may then terminate.

[0079] In this way, for a first imaging session (such as a scout scan), the carriage can be moved to position the radiation hardening filter and the first bowtie filter housed in the carriage on the path of the X-ray beam between the X-ray source and the subject being imaged, and for a second imaging session (such as a diagnostic scan), the carriage can be moved to remove the radiation hardening filter and the first bowtie filter from the X-ray path and position the second bowtie filter housed in the carriage on the X-ray path.

[0080] The technical effect of attenuating the beam reaching the subject by using a beam hardening filter is that a higher power X-ray source can be used during the scan, increasing the X-ray tube temperature, without increasing the X-ray exposure of the subject, which in turn improves the quality of the diagnostic scan and the thermal stability of the X-ray tube, including the target.

[0081] In one embodiment, the imaging system includes a carriage with one or more radiation hardening filters and one or more bowtie filters. A carriage drive system moves the carriage to selectively position the one or more radiation hardening filters and one of the one or more bowtie filters on a path of the x-ray beam between the x-ray source and the subject. The one or more radiation hardening filters may extend from an edge of the carriage and overlap a bowtie filter of a second carriage. The one or more radiation hardening filters extending from the carriage may be coupled to the carriage using a support structure. In the method of the previous example, additionally or optionally, the one or more radiation hardening filters may overlap the one or more bowtie filters. In any or all of the previous examples, additionally or optionally, the one or more bowtie filters include a first bowtie filter and a second bowtie filter disposed adjacent to each other in the carriage. In any or all of the above examples, additionally or optionally, a radiation hardening filter is disposed between the first bowtie filter and the second bowtie filter, the radiation hardening filter overlapping each of the first bowtie filter and the second bowtie filter. In any or all of the above examples, additionally or optionally, the first bowtie filter is received within a first slot formed in a cavity of the carriage, the second bowtie filter is received within a second slot formed in the cavity of the carriage, the first slot being separated from the second slot by a tab. In any or all of the above examples, additionally or optionally, the radiation hardening filter is recessed between the first bowtie filter and the second bowtie filter, and one or more of the radiation hardening filters are coupled to the tab. In any or all of the above examples, additionally or optionally, each radiation hardening filter includes a support structure and one or more metal sheets, the support structure and the one or more metal sheets being stacked and coupled to the tabs by a plurality of fasteners.In any or all of the above examples, additionally or optionally, the support structure and the one or more metal sheets can be the same dimensions and the support structure can be made of a material different from the material of the one or more metal sheets.

[0082] In any or all of the above examples, additionally or optionally, the X-ray beam passes through one or more radiation hardening filters, a bowtie filter of the one or more bowtie filters, and an aluminum filter before being incident on the subject. In any or all of the above examples, additionally or optionally, the carriage drive system includes a motor coupled to the carriage via a shaft, the motor operable to drive the shaft to position the one or more radiation hardening filters and the bowtie filter of the one or more bowtie filters on the path.

[0083] Another exemplary method of the imaging system includes: for a first image acquisition, moving the carriage to position the radiation hardening filter and the first bowtie filter housed in the carriage on the path of the x-rays between the x-ray source and the imaged subject; and for a second image acquisition, moving the carriage to move the radiation hardening filter and the first bowtie filter out of the path of the x-rays and positioning the first bowtie filter or the second bowtie filter housed in the carriage on the path of the x-rays. In the exemplary method described above, additionally or optionally, the first image acquisition is a scout scan and the second image acquisition is a diagnostic scan of an anatomical structure of the imaged subject, and the beam size used in the first image acquisition is smaller than the beam size used in the second image acquisition. In any or all of the above examples, moving the carriage may additionally or optionally include actuating a motor coupled to the carriage via a shaft, the shaft driving the carriage in a direction perpendicular to the direction of the path of the x-rays such that one or more of the beam hardening filter, the first bowtie filter, and the second bowtie filter are positioned on the path of the x-rays. In any or all of the above examples, additionally or optionally, each of the first bowtie filter and the second bowtie filter is disposed in a corresponding one of adjacent slots in the carriage, and the beam hardening filter is coupled to the carriage between the first bowtie filter and the second bowtie filter. In any or all of the above examples, additionally or optionally, the beam hardening filter overlaps each of the first bowtie filter and the second bowtie filter, and as used herein, in the first imaging, the x-ray beam first passes through the beam hardening filter and then through the first bowtie filter. In any or all of the above examples, additionally or optionally, one or more beam hardening filters extend from the first carriage, and the one or more beam hardening filters can be moved to overlap a bowtie filter disposed in the second carriage.

[0084] In yet another embodiment, a system for an imaging system includes a gantry for receiving an imaged subject, an X-ray source disposed in the gantry for emitting X-rays, an X-ray detector disposed on an opposite side of the gantry relative to the X-ray source, a motorized table for moving the imaged subject within the gantry, a computing device having instructions stored in a non-transitory memory, one or more bowtie filters, and one or more radiation hardening filters disposed within a filter carriage. The one or more radiation hardening filters can extend from the carriage. In some examples, the one or more radiation hardening filters may overlap a bowtie filter of a second carriage. Additionally or alternatively, the one or more radiation hardening filters can be mounted between a first bowtie filter of the one or more bowtie filters and a second bowtie filter of the one or more filters such that the one or more radiation hardening filters overlap each of the first bowtie filter and the second bowtie filter. The carriage drive system switches the filters by moving the one or more bowtie filters and / or the one or more radiation hardening filters into or out of the X-ray beam. In any of the exemplary systems described above, each bowtie filter may additionally or optionally have a first long side that is straight and a second long side that is parallel to the first long side and includes a central depression. Each bowtie filter may be made of graphite. In any or all of the exemplary systems described above, the beam hardening filter may additionally or optionally include a support structure and one or more metal sheets layered below the support structure. In any or all of the exemplary systems described above, the rectangular support structure may additionally or optionally be made of aluminum and the one or more metal sheets may be made of copper, each of the one or more metal sheets having a different thickness from the other.

[0085] 3-12C show exemplary arrangements depicting the relative positional relationships of various components. When elements are shown as being in direct contact with or directly connected to one another, these elements can, in at least one embodiment, be referred to as directly contacting or directly connected elements, respectively. Similarly, elements shown as being contiguous or adjacent to one another can, in at least one embodiment, be referred to as being contiguous or adjacent to one another, respectively. As an example, elements sharing a surface with one another can be referred to as surface sharing elements. As another example, elements positioned apart from one another can, in at least one embodiment, be referred to as being separated from one another if there is a space between the elements but no other elements are present. Also, as another example, elements shown above and below one another, opposite one another, or left and right from one another can be referred to as above and below, opposite one another, or left and right elements. Additionally, as shown in the figures, in at least one embodiment, the topmost element or the topmost point of an element can be referred to as the "top" of the element, and the bottommost element or the bottommost point of an element can be referred to as the "bottom" of the element. As used herein, top / bottom, upper / lower, above / below are relative to the vertical axis of the figure and are used to describe the location of elements of the figure relative to one another. Thus, elements shown on top of other elements are, by way of example, vertically positioned on top of the other elements. As yet another example, the shapes of elements shown in the figures can be referred to as having their shapes (e.g., circular, rectilinear, flat, curvilinear, rounded, chamfered, angled, etc.). Additionally, elements shown intersecting one another can, at least in one example, be referred to as intersecting elements or elements intersecting one another. Additionally, elements shown within or outside of another element can, in one example, be referred to as elements shown within or outside of another element.

[0086] In this specification, an element or step described in the singular and preceded by the word "a" or "an" should be understood as not excluding a plurality of elements or steps, unless the exclusion is expressly stated. Furthermore, references to "one embodiment" are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Furthermore, unless expressly stated to the contrary, an embodiment "comprising," "including," or "having" an element or elements having a particular characteristic can include additional elements that do not have that characteristic. The terms "including" and "in which" are used as the plain-language equivalents of the respective terms "comprising" and "wherein." Furthermore, the terms "first," "second," "third," etc. are used merely as labels and are not intended to impose numerical requirements or a specific positional order on the objects.

[0087] The description set forth herein uses examples to disclose the subject matter of the present disclosure, including the best mode, and also enables any person skilled in the art to practice the subject matter of the present disclosure, including making and using any devices or systems, and performing any methods incorporating the same. The patentable scope of the subject matter of the present disclosure 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 contain structural elements that do not differ from the literal language of the claims, or if they contain equivalent structural elements that do not differ insubstantially from the literal language of the claims. [Explanation of symbols]

[0088] 10 CT Imaging System 12 Gantry 13 Precollimator assembly 14 X-ray source 15 X-ray detector assembly 16 X-ray beam 18 Collimator Assembly 20 Detector Module 22 Subject 25 Rotation Center 26 Control System 28 X-ray Controller 29 Collimator Controller 30 Gantry motor controller 32 Data Collection System 34 Image Reconstructor 36 Computer 38 Storage device 40 Operator Console 44 Table motor controller 46 Table 48 Bore

Claims

1. 1. An imaging system comprising: a collimator assembly disposed adjacent to an X-ray source, the X-ray source including a collimator assembly that generates an X-ray beam that passes through the collimator assembly, the collimator assembly comprising:

1. An imaging system comprising: at least one carriage including at least one radiation hardening filter and at least one bowtie filter, the radiation hardening filter coupled to an edge of the carriage and extending away from the at least one bowtie filter, the radiation hardening filter including one or more metal sheets and a support structure having a window frame member and a lower support member, the one or more metal sheets being positioned between the window frame member and the lower support member.

2. 2. The imaging system of claim 1, further comprising a carriage drive system that moves the at least one carriage such that one of the at least one radiation hardening filter and the at least one bowtie filter is selectively positioned in and out of the path of the x-ray beam.

3. 3. The imaging system of claim 2, wherein the carriage drive system includes a motor coupled to the carriage via a shaft, and actuating the motor to drive the shaft such that one of the at least one radiation hardening filter and the at least one bowtie filter is positioned in or out of the path of the X-ray beam.

4. 2. The imaging system of claim 1, wherein the at least one carriage is a first carriage, the imaging system further comprising a second carriage, the second carriage including one or more bowtie filters, and the at least one beam hardening filter of the first carriage is movable to a position overlapping one of the one or more bowtie filters of the second carriage.

5. The imaging system of claim 1 , wherein the at least one radiation hardening filter is a heavy element material that emits monoenergetic x-rays for energy calibration of an x-ray detector.

6. 5. The imaging system of claim 4, wherein the at least one bowtie filter of the first carriage is a first bowtie filter, and the one or more bowtie filters of the second carriage include a second bowtie filter and a third bowtie filter positioned adjacent to one another within the second carriage.

7. 7. The imaging system of claim 6, wherein the first bowtie filter is disposed in a first slot formed in the first carriage, the second bowtie filter is disposed in a second slot formed in the second carriage, and the third bowtie filter is disposed in a third slot formed in the second carriage, the second slot being separated from the third slot by a tab.

8. 5. The imaging system of claim 4, wherein the at least one radiation hardening filter is coupled to an upper surface of an edge of the first carriage, and the radiation hardening filter can be moved to a position above a bowtie filter of the one or more bowtie filters of the second carriage to overlap the bowtie filter of the one or more bowtie filters of the second carriage.

9. 5. The imaging system of claim 4, wherein the at least one radiation hardening filter of the first carriage is movable to a position where the x-ray beam passes through the at least one radiation hardening filter.

10. The imaging system of claim 1, wherein the support structure and the one or more metal sheets are laminated and attached to the at least one radiation hardening filter by a plurality of fasteners.

11. The imaging system of claim 1 , wherein the support structure and the one or more metal sheets are of the same dimensions, and the support structure is made of a material different than a material of the one or more metal sheets.

12. 1. A pre-collimator assembly for a computed tomography (CT) imaging system, the pre-collimator assembly comprising: a first carriage including a beam hardening filter and a first bowtie filter; a first carriage drive system coupled to the first carriage, the first carriage drive system configured to move the first carriage, and thus the radiation hardening filter and the first bowtie filter, into and out of the x-ray beam path; a second carriage including a second bowtie filter and a third bowtie filter; and a second carriage drive system coupled to the second carriage, the second carriage drive system configured to move the second carriage, and thus the second bowtie filter and the third bowtie filter, into and out of the X-ray beam path. Including, the beam hardening filter is disposed along an outer edge of the first carriage and coupled to the outer edge using a support structure, the support structure including a window frame member and a lower support member; The radiation hardening filter may be positioned on the X-ray beam path alone or in combination with one of the second bowtie filter and the third bowtie filter.

Images