System and method for three-dimensional printing of collimator

Abstract

To provide a method for producing a metallic grid structure collimator by means of three-dimensional (3D) printing.SOLUTION: A method for producing a metallic grid structure includes utilizing 3D printing for printing a first layer of a first wall section 112 of the metallic grid structure in a first direction along a first vector 122 offset from a center line of the first wall section 112 by half of a first distance of a first width of the first wall section that is orthogonal to the center line. The method also includes printing a second layer of the first wall section 112 on the first layer in a second direction along a second vector 126 offset from the first line of the first wall section 112 by half of the first distance of the first width of the first wall section 112, where the second direction is opposite the first direction, and the first vector 122 and the second vector 126 are disposed on opposite sides of the center line.SELECTED DRAWING: Figure 6

Description

[Background technology]

[0001] The subject matter disclosed herein relates to three-dimensional (3D) printing of collimators.

[0002] Various mechanical and micromechanical systems can use gratings or grids that include some form of trench or other opening at least partially defined by sidewalls (e.g., vertical sidewalls or partitions). Such gratings or grids can be used to restrict or collimate the passage of energy or matter from one side of the grating or grid to the other, or the trench or other sidewall structure can perform other functions to facilitate the functioning of the overall system.

[0003] Additive manufacturing techniques are becoming more commonplace in industrial environments. It is well established that they can be manufactured in multiple materials (e.g., 316L, J13 Iconel 718, 625, AlSi10Mg, etc.). However, refractory materials remain an issue, especially with laser powder bed fusion (LPBF) technology. At the same time, tungsten printing is niche, with limited industry investment. For example, manufacturing computed tomography (CT) collimators using 3D printing is challenging due to the thin walls, tight manufacturing tolerances, and the use of tungsten material. Manufacturing 3D printed collimators using LPDF requires multiple layers (to achieve thickness) and currently produces articles with lower than acceptable density and rough surfaces, creating quality issues. Summary of the Invention

[0004] Certain embodiments commensurate in scope with the originally claimed subject matter are summarized below. These embodiments are not intended to limit the scope of the claimed subject matter, but rather are intended only to provide a brief summary of possible embodiments. Indeed, the disclosed subject matter may encompass a variety of forms that may be similar to or different from the embodiments set forth below.

[0005] In one embodiment, a method of forming a metal grid structure is provided, the method including printing a first layer of first walls of the metal grid structure using three-dimensional (3D) printing, the first layer being printed in a first direction along a first vector offset from a first centerline of the first wall by half a first distance of a first width of the first wall perpendicular to the first centerline, and printing a second layer of first walls using three-dimensional (3D) printing on the first layer in a second direction along a second vector offset from the first centerline of the first wall by half the first distance of the first width of the first wall, the second direction being opposite the first direction, the first vector and the second vector being disposed on opposite sides of the first centerline.

[0006] In an additional embodiment, a method of forming a collimator configured for use with an x-ray detector of an x-ray imaging system is provided, the method including: utilizing three-dimensional (3D) printing to print alternating layers of a first set of partitions of the collimator extending in a first direction by utilizing alternating first and second vectors in printing the layers of the first set of partitions, the first and second vectors pointing in opposite directions along the first direction and positioned on opposite sides of a first centerline of each partition of the first set of partitions and offset from the first centerline by a first distance half of a first width of each partition of the first set of partitions. The method also includes using three-dimensional (3D) printing to alternately print layers of a second set of partitions of the collimator extending in a second direction by alternatingly using a third vector and a fourth vector when printing the layers of the second set of partitions, wherein the third vector and the fourth vector point in opposite directions along the second direction and are disposed on opposite sides of a second centerline of each partition in the second set of partitions and are offset from the second centerline by a second distance of half a second width of each partition in the second set of partitions, and the first direction is perpendicular to the second direction.

[0007] In another embodiment, a system is provided for forming a collimator configured for use with an x-ray detector of an x-ray imaging system. The system includes a memory encoding a processor-executable routine. The system also includes a processing circuit configured to access the memory and execute the processor-executable routine. The routine, when executed by the processing circuit, causes the processing circuit to perform an action. The action includes printing alternating layers of a first set of partitions of the collimator extending in a first direction by utilizing alternating first and second vectors in printing the layers of the first set of partitions using three-dimensional (3D) printing, the first and second vectors pointing in opposite directions along the first direction, positioned on opposite sides of a first centerline of each partition of the first set of partitions, and offset from the first centerline by a first distance of one-half of a first width of each partition of the first set of partitions. The action also includes using three-dimensional (3D) printing to alternately print layers of a second set of partitions of the collimator extending in a second direction by alternatingly using a third vector and a fourth vector when printing the layers of the second set of partitions, wherein the third vector and the fourth vector point in opposite directions along the second direction and are positioned on opposite sides of a second centerline of each partition in the second set of partitions and are offset from the second centerline by half a second distance of a second width of each partition in the second set of partitions, and the first direction is perpendicular to the second direction. [Brief description of the drawings]

[0008] These and other features, aspects, and advantages of the present subject matter will become better understood when the following detailed description is read in conjunction with the drawings, in which like reference numbers represent like elements throughout. [Figure 1]1 illustrates components of a computed tomography imaging system according to certain aspects of the present disclosure. [Diagram 2] 1A and 1B are schematic diagrams illustrating a side view of a detector channel with collimator blades disposed therein, in accordance with certain aspects of the present disclosure; [Diagram 3] FIG. 2 is a top view of a portion of a collimator, in accordance with certain aspects of the present disclosure. [Figure 4] 1 shows a schematic diagram of a conventional printing method (e.g., using a single vector) for printing the walls or partitions of a collimator. [Diagram 5] 1 shows a schematic diagram of a conventional printing method (e.g., using a two-vector method) for printing the walls or partitions of a collimator. [Figure 6] 1A-1C are schematic diagrams illustrating a zigzag printing method for printing collimator walls or septa (eg, zigzag printing using a single vector printing method) according to an aspect of the present disclosure. [Figure 7] FIG. 6 is a top view of a portion of a collimator printed using the conventional printing method of FIG. [Figure 8] 7 shows a top view of a portion of a collimator printed using the zigzag printing method of FIG. 6 according to an embodiment of the present disclosure. [Figure 9] FIG. 13 is a schematic diagram illustrating a zigzag printing method (e.g., zigzag printing using alternating vector printing) for printing collimator walls or partitions, according to an aspect of the present disclosure. [Figure 10] 1A-1C are schematic diagrams illustrating a general zigzag printing method for forming joints between intersecting walls or partitions of a collimator according to an aspect of the present disclosure. [Figure 11] 11A and 11B are schematic diagrams illustrating a top view of a printing method for printing an initial layer of the wall or partition of FIG. 10 according to an embodiment of the present disclosure. [Figure 12] 11A and 11B are schematic diagrams illustrating a top view of a printing method for printing the next layer of the walls or partitions of FIG. 10 according to an embodiment of the present disclosure. [Figure 13] 11A and 11B are schematic diagrams illustrating a top view of a printing method for overprinting a first layer and a next layer of the wall or partition of FIG. 10 according to an embodiment of the present disclosure. [Figure 14] 1 illustrates a schematic diagram of a laser powder bed fusion system for printing collimator walls or bulkheads in accordance with an aspect of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] One or more specific embodiments are described below. While an attempt is made to describe these embodiments concisely, it is not possible to describe all features of an actual implementation herein. It should be understood that in developing such an actual implementation, as with any engineering or design project, numerous implementation-specific decisions must 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, while such a development effort may be complex and time-consuming, it should be understood that to those skilled in the art having the benefit of this disclosure, such an effort would be considered a routine undertaking of design, fabrication, and manufacture.

[0010] When introducing elements of various embodiments of the present subject matter, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the element in question. The words "comprising," "including," "having," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, 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.

[0011] Although the following aspects are described in the context of medical imaging, it should be understood that the techniques of the present invention are not limited to such medical contexts. Indeed, the examples and description of such medical contexts are provided merely to facilitate explanation by providing examples of real-world implementations and applications. However, the techniques can also be utilized in other contexts, such as tomographic image reconstruction for industrial computed tomography (CT) used in non-destructive testing of manufactured parts or goods (i.e., quality control or quality inspection applications) and / or non-invasive inspection of packages, boxes, luggage, and the like (i.e., security or screening applications). In general, the techniques are useful in imaging or screening contexts that utilize X-ray imaging gratings (such as collimators or anti-scatter grids). Also, although the techniques are described in the context of CT imaging, the methods can be utilized in imaging systems that utilize collimators or anti-scatter grids (e.g., conventional X-ray imaging systems, positron emission tomography imaging, etc.).

[0012] The present technology relates to various aspects of additive manufacturing (e.g., three-dimensional (3D) printing) of x-ray grating or metal grid structures (e.g., collimators or x-ray grids). The present technology provides a customized single vector zigzag printing method (i.e., printing method that utilizes a single vector for each layer of a given wall or wall portion) that utilizes alternating vectors offset by half the vector distance in opposite directions from the center of the partition (e.g., wall). For example, 3D printing can be utilized to print a collimator (e.g., a collimator made from multiple layers) for use with an x-ray detector of an x-ray imaging system, where 3D printing can be utilized to alternately print a first set of layers of partitions that extend in a first direction of the collimator, and to alternate between a first vector and a second vector when printing the first set of layers of partitions. The first and second vectors are oriented in opposite directions along a first direction, are positioned on opposite sides of a first centerline of each of the partitions in the first set of partitions, and are offset from the first centerline by a first distance (e.g., vector distance) of a first width of each of the partitions in the first set of partitions. 3D printing can also be used to alternately print layers of the second set of partitions extending in a second direction of the collimator, and alternately use a third and fourth vector when printing layers of the second set of partitions. The third and fourth vectors are oriented in opposite directions along a second direction, are positioned on opposite sides of a second centerline of each of the partitions in the second set of partitions, and are offset from the second centerline by a second distance of a second width of each of the partitions in the second set of partitions. The first direction is orthogonal to the second direction. This results in an article (i.e., a collimator) with a smooth finish and high density (whereas conventional processes require a multi-vector approach for a given thickness (i.e., a given thickness greater than 100 micrometers)). The disclosed technique also improves productivity, produces uniform partition wall properties, and prints symmetrical walls. Additionally, the disclosed technique uses backlighting and improves metrology performance when using collimators, as the smooth finish aids in edge detection.Additionally, the disclosed techniques reduce cleaning time and reduce / remove residual particles on the partition surface.

[0013] In light of the foregoing, Figure 1 illustrates one embodiment of an imaging system 10 for acquiring and processing image data in accordance with the structures and techniques described herein. That is, the type of imaging system 10 illustrated is an example of one type of imaging system that can benefit from or utilize components (e.g., multi-layer x-ray gratings such as anti-scatter grids or collimators) made in accordance with the techniques described herein. However, as noted herein, other types of systems (e.g., non-imaging systems, non-medical systems, etc.) can also utilize components manufactured in accordance with the techniques described herein.

[0014] In the illustrated embodiment, system 10 is a computed tomography (CT) system designed to acquire x-ray projection data and reconstruct the projection data into volumetric reconstructions for display and analysis. CT imaging system 10 includes one or more x-ray sources 12 (such as one or more x-ray tubes or solid state emission structures) capable of generating x-rays of one or more energy spectra during an imaging session.

[0015] In certain embodiments, the source 12 may be located in proximity to a pre-collimator and / or filter assembly 22 that may be used to condition the x-ray beam 20 to define the shape of the x-ray beam 20 (e.g., by limiting off-angle radiation) and / or to define the extent of high intensity regions of the x-ray beam 20, to control or define the energy profile of the x-ray beam 20, and / or to limit x-ray exposure to portions of the patient 24 that are not within the region of interest. In practice, the filter assembly or beam shaper 22 may be located in the gantry between the source 12 and the imaging volume.

[0016] The X-ray beam 20 passes through a region in which a subject (e.g., a patient 24) or object of interest (e.g., a manufactured part, luggage, packaging, etc.) is located. The subject attenuates at least a portion of the X-ray photons 20, resulting in attenuated X-ray photons 26 impinging on a pixelated detector array 28 formed by a plurality of detector elements (e.g., pixels) arranged in an array. In the illustrated example, the attenuated X-ray photons 26 pass through a collimator 18 (e.g., an anti-scatter grid) to the detector array 28. As described herein, the collimator 18 may be comprised of a plurality of blades or other elements aligned substantially perpendicular to a surface of the detector array 28 and formed from an attenuating material that limits or prevents X-ray photons 26 traveling at an off-angle (e.g., scattered X-rays) from reaching the detector array 28. Electrical signals reaching the detector array 28 are detected and processed to generate one or more projection data sets. In the illustrated embodiment, detector 28 is coupled to a system controller 30 , which directs acquisition of the digital signal produced by detector 28 .

[0017] The system controller 30 may command operation of the imaging system 10 and process acquired data such that filtering, examination protocols and / or calibration protocols are performed. With respect to the x-ray source 12, the system controller 30 provides power, focal spot position, control signals, etc. for x-ray examination sequences. In certain embodiments, the system controller 30 may control the operation of the filter assembly 22, the CT gantry (or other structural support to which the x-ray source 12 and detector 28 are mounted), and / or the movement and / or tilt of the patient support during an examination.

[0018] Additionally, the system controller 30 may control, via a motor controller 36, the operation of a linear positioning subsystem 32 and / or a rotational subsystem 34 used to move the subject 24 and / or components of the imaging system 10, respectively. For example, in a CT system, the radiation source 12 and detector 28 rotate around the object (e.g., patient 24) so ​​that x-ray transmission data is acquired over a range of angular views. Thus, in an actual implementation, the imaging system 10 is configured to generate x-ray transmission data corresponding to each of a number of angular positions (e.g., 360°, 180°+fan beam angle (α), etc.) covering the entire scan region of interest.

[0019] The system controller 30 may include signal processing circuitry and associated memory circuitry. In such an embodiment, the memory circuitry may store programs, routines, and / or encoded algorithms executed by the system controller 30 to operate the imaging system 10, including the x-ray source 12 and / or filter assembly 22, and to process digital measurements acquired by the detector 28. In one embodiment, the system controller 30 may be implemented as all or part of a processor-based system.

[0020] The source 12 may be controlled by an X-ray controller 38 included within the system controller 30. The X-ray controller 38 may be configured to provide power, timing signals, and / or focal spot size and position to the source 12. Additionally, in some embodiments, the X-ray controller 38 may be configured to selectively operate the source 12 such that multiple X-ray tubes or multiple emitters at different locations within the system 10 operate synchronously or independently of one another, or to switch the source between different energy profiles during an imaging session.

[0021] The system controller 30 may include a data acquisition system (DAS) 40. The DAS 40 receives data collected by the readout electronics of the detector 28 (e.g., digital signals from the detector 28). The DAS 40 then converts and / or processes the data for subsequent processing by a processor-based system (e.g., computer 42). In certain implementations described herein, circuitry within the detector 28 may convert the detector's analog signals to digital signals before transmitting them to the data acquisition system 40. The computer 42 may include or communicate with one or more non-transitory memory devices 46, which may store data to be processed by the computer 42, data to be processed by the computer 42, or instructions to be executed by the image processing circuitry 44 of the computer 42. For example, the processor of the computer 42 may execute one or more sets of instructions stored in the memory 46, which may be the memory of the computer 42, the memory of the processor, firmware, or similar embodiments. As an example, the image processing circuitry 44 of the computer 42 may be configured to generate diagnostic images.

[0022] The computer 42 may also be adapted to control functions executable by the system controller 30 (i.e., scanning operations and data acquisition) in response to commands and scanning parameters provided by an operator through, for example, an operator workstation 48. The system 10 may also include a display 50 coupled to the operator workstation 48 that allows the operator to view relevant system data, image parameters, raw image data, reconstructed data or images, and the like. The system 10 may also include a printer 52 coupled to the operator workstation 48 that is configured to print desired measurements. The display 50 and printer 52 may be directly connected to the computer 42 (as shown in FIG. 1 ) or may be connected through the operator workstation 48. The operator workstation 48 may also include or be coupled to a picture archiving and communication system (PACS) 54. The PACS 54 may be coupled to a remote system or client 56, a radiology information system (RIS), a hospital information system (HIS), or an internal or external network to allow others at different locations to access the image data.

[0023] With the above description of the overall imaging system 10 in mind, and referring now to FIG. 2, a side cross-sectional view of an example arrangement of a detector 28 and collimator 18 is shown. In this example, the detector 28 is shown as including an array of pixels 58, each pixel corresponding to a readout channel. A set of collimator blades 60 of the collimator 18 is shown associated with the array of pixels 58, each pixel being collimated separately. The blades 60 are shown positioned at the pixel junctions such that any shadow cast by the blades 60 is primarily at the pixel junctions, with the majority of the active area of ​​the pixels 58 being relatively free of the shadow cast by the blades. In this manner, each pixel 58 is affected by the collimator blades 60 in a relatively consistent and uniform manner.

[0024] FIG. 3 illustrates a top view of a portion of a collimator 18 (e.g., a metal grid structure). As illustrated, the collimator 18 includes a first set 62 of partitions 64 (e.g., walls) that extend in a first direction 66. The collimator 18 also includes a second set 68 of partitions 64 (e.g., walls) that extend in a second direction 70 that is orthogonal to the first direction 66. Each partition 64 of both the first set 62 of partitions 64 and the second set 68 of partitions 64 has a width 72 (e.g., thickness) that extends in the second direction 70 and the first direction 66, respectively. In certain embodiments, the width 72 is greater than 100 micrometers. The first set 62 of partitions 64 and the second set 68 of partitions 64 intersect or meet to form a junction or intersection 74. In certain embodiments, the collimator 18 of FIGS. 2 and 3 can be 3D printed and formed in multiple layers, as described in more detail below. In a particular embodiment, the collimator 18 of Figures 2 and 3 may be made from tungsten.

[0025] FIG. 4 illustrates a schematic of a conventional printing strategy (e.g., a strategy utilizing a single vector) for printing the walls or partitions of a collimator. As shown in FIG. 4, a vertical box 76 represents a collimator wall or partition extending in a direction 80 (e.g., Y direction). The wall or partition 76 includes a centerline 78. The wall or partition 76 is 3D printed in multiple layers 82, each layer 82 printed as a laser patch on top of the other layers 82, such that the wall or partition 76 extends in a direction 84 (e.g., Z direction). Each layer 82 has a layer thickness 86 (e.g., L t ). The walls or partitions 76 have a width 88 (e.g., wall thickness) that extends in a direction 90 (e.g., X-direction) perpendicular to direction 80. Width 88 is 100 micrometers or less. Centerline 78 is located in the middle of width 88. Individual layers 82 of walls or partitions 76 are printed as a single vector exposure 92 in direction 80 (e.g., with a thickness of 100 micrometers or less).

[0026] If the collimator walls or partitions have a wall thickness of more than 100 micrometers, a different strategy must be used. Figure 5 shows a schematic of a conventional printing strategy (e.g., using a two-vector strategy) for printing collimator walls or partitions. As shown in Figure 5, a vertical box 94 represents a portion of a collimator wall or partition 96 extending in a direction 80 (e.g., Y direction) printed using a first vector exposure 98 (e.g., with a thickness of 100 micrometers or less). A vertical box 100 represents a portion of a wall or partition 96 printed using a second vector exposure 102 (e.g., with a thickness of more than 100 micrometers). The wall or partition 96 includes a centerline 104. The wall or partition 96 is 3D printed in multiple layers 82, each layer 82 printed as a laser patch (of the same vector exposure) on top of the other layers 82, and the wall or partition 96 extends in a direction 84 (e.g., Z direction). Each layer 82 has a layer thickness 86 (e.g., L t ). The wall or partition 96 has a width 106 (e.g., wall thickness) that extends in a direction 90 (e.g., X-direction) perpendicular to the direction 80. The width 106 is greater than 140 micrometers. The centerline 78 is centered within the width 106. Each layer 82 of the wall or partition 96 is printed using two adjacent vectors (a first vector exposure 98 in the direction 80 and a second vector exposure 102 in a direction 108 opposite the direction 80). A portion 94 of the wall or partition 96 is formed by printing the multiple layers 82 as laser patches on each layer using the first vector exposure 98 to form portion 94. A portion 100 of the wall or partition 96 is formed by printing the multiple layers 82 as laser patches on each layer using the second vector exposure 102 to form portion 100. In particular, each layer of the wall 96 is printed using the first vector exposure 98 and the second vector exposure 102. Vector distance 110 (e.g., L Dxy ) represents the distance in direction 90 between a first vector exposure 98 and a second vector exposure 102.

[0027] The printing strategy of FIG. 4 works well when printing collimator walls or partitions smaller than 100 micrometers. However, when the collimator walls or partitions are larger than 100 micrometers, a multi-vector strategy (a strategy for printing individual layers) as shown in FIG. 5 is utilized, which has the following problems. These problems include increased surface roughness and reduced wall density relative to the designed (desired) wall density. These problems also include asymmetric wall characteristics (e.g., more roughness and less density in the second vector patch). These problems also include the measured wall thickness not representing the designed wall thickness. In particular, residual particles and porosity on the surface of the partitions usually result in thicker walls but less dense, which reduces the collimator performance. These problems also include time-consuming post-processing (e.g., ultrasonic cleaning to remove loosely bound particles on the partition surface).

[0028] In the following, a zigzag printing strategy using a single vector printing strategy is provided that can be used in 3D printing (e.g., by LPBF) of collimators (e.g., tungsten collimators) having walls or partitions with a wall thickness of more than 100 micrometers. FIG. 6 shows a schematic of a zigzag printing strategy (e.g., using a single vector printing strategy) for printing a collimator wall or partition 112 or printing a portion of a wall or partition 112. As shown in FIG. 6, the collimator wall or partition 112 extends in a direction 80 (e.g., Y direction). The wall or partition 112 includes a centerline 114. The wall or partition 112 is 3D printed in multiple layers 116, each layer 116 printed as a laser patch on top of the other layers 116, and the wall or partition 112 extends in a direction 84 (e.g., Z direction). Each layer 116 has a layer thickness 86 (e.g., Lt) in the direction 84. The walls or partitions 112 have a width 118 (e.g., wall thickness) that extends in a direction 90 (e.g., X-direction) perpendicular to the direction 80. The width 118 is greater than 100 micrometers. The centerline 114 is centered within the width 118. The individual layers 116 of the walls or partitions 112 are alternately printed using two different vectors (e.g., using a single vector per layer 116). As shown, an initial layer 120 (layer n) is printed in a first direction (i.e., Y-direction 80) along a first vector 122 (V1) using exposure of the first vector. The first vector 122 is offset from the centerline 114 by half the distance of the width 118 (or vector distance 136). The next layer 124 (layer n+1) is printed as a laser patch on the initial layer 120 along a second vector 126 (V2) in a second direction 128 opposite the first direction 80 using a second vector exposure. The second vector 126 is offset from the centerline 114 by half the distance of the width 118 (or vector distance 136). The first vector 122 and the second vector 126 are located on opposite sides 130, 132, respectively, relative to the centerline 114. The layer 124 has the same thickness as the initial layer 120. The layers 120, 124 together have a layer thickness 134 (2xL t) The vector distance is 136 (for example, L Dxy ) represents the distance in direction 90 between the first vector 122 and the second vector 126. The vector distance 136 represents the distance of travel between the first vector 122 and the second vector 126 to print each layer 116. The vector distance 136 is determined based on a combination of laser power and laser speed to achieve the expected printing result. In this case, the vector distance 136 is the same as the width 118 of the wall 112. In certain embodiments, when printing a partition or layer of a wall, vectors of different directions can be utilized to improve the density and surface finish of the printed collimator. In certain embodiments, different vectors can be utilized for different (and adjacent) portions of the wall or partition of the same layer, with a single vector utilized for each portion of the wall or partition.

[0029] As shown in FIG. 6, the layers 116 are alternately printed by alternating between the first vector 122 and the second vector 126, with each layer 116 being printed. The alternating between the first vector 122 and the second vector forms a zigzag pattern 138 in the direction 84. The zigzag strategy improves productivity, improves the surface finish of the collimator, and improves the wall density to 99.9 percent (excluding cracks). The zigzag strategy also improves the partition wall characteristics and prints symmetrical walls. The zigzag strategy also improves measurement capabilities (e.g., using backlight and smooth surface finish aids in edge detection). The zigzag strategy further reduces cleaning time and reduces or removes residual particles on the partition wall surface. In summary, the zigzag strategy allows faster printing with better quality that meets the quality criteria.

[0030] 7 and 8 show the difference between a collimator printed with a conventional zigzag printing strategy and a collimator printed with a customized zigzag printing strategy. FIG. 7 shows an image 140 of a top view of a portion of a collimator 142 printed using a conventional printing strategy (e.g., the two-vector strategy of FIG. 5). FIG. 8 shows an image 144 of a top view of a portion of a collimator 146 printed using the zigzag printing strategy of FIG. 6 (and / or FIG. 9 and / or FIG. 10). As shown in image 140, the wall 148 of collimator 142 is clearly asymmetric. Furthermore, the wall 148 of collimator 142 is rough and has density problems. In contrast, as shown in image 144, the wall 150 of collimator 146 is more symmetric. Furthermore, the wall 150 is denser and smoother. Furthermore, the wall 150 has less residual particles. The target wall thickness for both collimators 142, 146 was 150 micrometers.

[0031] As described above, 3D printing (e.g., by LPBF) of collimators having partitions or walls with a wall thickness of more than 100 micrometers (e.g., tungsten collimators) can utilize multiple vectors. FIG. 9 shows a schematic of a zigzag printing strategy (e.g., a strategy utilizing an alternating vector printing strategy) for printing the walls or partitions of the collimator. As shown in FIG. 9, the walls or partitions 112 of the collimator extend in a direction 80 (e.g., the Y direction). In particular, the walls or partitions 112 are printed in two parts (sections) 152 and 154. The parts 152 and 154 are printed adjacent to each other and aligned in the direction 80. The printing of the part 152 utilizes a zigzag printing strategy in which two vectors alternate when printing the layers of the part 152. The printing of portion 154 utilizes a zigzag printing strategy in which the same two vectors (utilized in printing portion 152) are alternated when printing the layers of portion 154, but the two vectors are utilized in a different order.

[0032] The wall or partition 112 includes a centerline 114 of both the portion 152 and the portion 154. The portion 152 has multiple layers 116 3D printed therein, each layer 116 printed as a laser patch on top of the other layers 116, and the portion 152 extends in a direction 84 (e.g., Z direction). Each layer 116 has a layer thickness 86 (e.g., Lt) in the direction 84. The portion 152 has a width 118 (e.g., wall thickness) extending in a direction 90 (e.g., X direction) perpendicular to the direction 80. The width 118 is greater than 100 micrometers. The centerline 114 is centrally located within the width 118. The individual layers 116 of the portion 152 are alternately printed using two different vectors (e.g., a single vector is used for each portion of the layer 116). As shown, the initial layer 120 (layer n) of the portion 152 is printed along a first vector 122 (V1) in a first direction (i.e., Y-direction 80) using an exposure of a first vector. The first vector 122 is offset from the centerline 114 by half the distance of the width 118 (or vector distance 136). The next layer 124 (layer n+1) of the portion 152 is printed as a laser patch on the initial layer 120 along a second vector 126 (V2) in a second direction 128 opposite the first direction 80 using an exposure of a second vector. The second vector 126 is offset from the centerline 114 by half the distance of the width 118 (or vector distance 136). The first vector 122 and the second vector 126 are positioned on opposite sides 130, 132, respectively, of the centerline 114 when printing the portion 152. The layer 124 has the same thickness as the initial layer 120. The layers 120, 124 of portion 152 together form a layer thickness 134 (2xL t ) The vector distance is 136 (for example, L Dxy ) represents the distance in direction 90 between first vector 122 and second vector 126. Vector distance 136 represents the shift distance between first vector 122 and second vector 126 to print each layer 116 of portion 152. Vector distance 136 is determined based on a combination of laser power and laser speed to achieve the expected printing result. In this case, vector distance 136 is the same as width 118 of wall 112.

[0033] The portion 154 is 3D printed with multiple layers 116 (layers corresponding to the same layers 116 of the portion 152), each layer 116 printed as a laser patch on top of the other layers 116, and the portion 154 extends in a direction 84 (e.g., Z direction). Also, each layer 116 of the portion 154 has the same layer thickness 86 (e.g., Lt) in the direction 84. The portion 154 has the same width 118 (e.g., wall thickness) as the portion 152 extending in a direction 90 (e.g., X direction) perpendicular to the direction 80. The individual layers 116 of the portion 154 are alternately printed using the same two different vectors used in printing the portion 152 (e.g., a single vector is used for each portion of the layer 116). As shown, the initial layer 120 (layer n) of the portion 154 is printed along a second vector 126 (V2) in a second direction 128 opposite the first direction 80 using exposure of the second vector. The second vector 126 is offset from the centerline 114 by half the distance of the width 118 (or vector distance 136). The next layer 124 (layer n+1) of portion 154 is printed as a laser patch on the initial layer 120 along the first vector 122 (V1) in the first direction 80 using the exposure of the first vector. The first vector 122 is offset from the centerline 114 by half the distance of the width 118 (or vector distance 136). The first vector 122 and the second vector 126 are positioned on opposite sides 130, 132, respectively, with respect to the centerline 114 when printing portion 154. Layer 124 has the same thickness as the initial layer 120. The layers 120, 124 of portion 154 together have the same layer thickness 134 (2xL t ) vector distance 136 (e.g., L Dxy) represents the distance in direction 90 between first vector 122 and second vector 126. Vector distance 136 represents the shift distance between first vector 122 and second vector 126 to print each layer 116 of portion 152. Vector distance 136 is determined based on a combination of laser power and laser speed to achieve the expected printing result. In this case, vector distance 136 is the same as width 118 of wall 112. This printing strategy utilizing alternating vectors in printing adjacent portions of wall 112 reduces residual stress and improves the quality of wall 112.

[0034] As mentioned above, partial vectors can be used in 3D printing (e.g., using LPBF) of collimators (e.g., tungsten collimators) having partitions or walls with wall thicknesses of more than 100 micrometers, and partial vectors can form joints or intersections between intersecting or orthogonal walls of the collimator. FIG. 10 shows a schematic of an overall zigzag printing strategy for forming joints between intersecting walls or partitions 156 and 158 of a collimator. FIG. 11 shows a schematic of a top view of a printing strategy for printing an initial layer 160 (layer n) of the walls or partitions 156 and 158 of FIG. 10. FIG. 12 shows a schematic of a top view of a printing strategy for printing a next layer 162 (layer n+1) of the walls or partitions 156 and 158 of FIG. 10. FIG. 13 shows a schematic top view of a printing strategy for printing an initial layer 160 and a next layer 162 of the walls or partitions 156 and 158 of FIG. 10 in an overlapping manner.

[0035] As shown in Figures 10-13, the collimator walls or partitions 156 extend in a direction 80 (e.g., the Y direction). The walls or partitions 156 include a centerline 164. As shown in Figures 11-13, the collimator walls or partitions 158 extend in a direction 90 (e.g., the X direction). The walls or partitions 158 include a centerline 166. Both the walls 156 and the walls 158 are 3D printed with multiple layers 116, each layer 116 printed as a laser patch on top of the other layers 116, and the walls or partitions 156 and 158 extend in a direction 84 (e.g., the Z direction). Each layer 116 of the walls 156 and 158 has a layer thickness 86 (e.g., Lt) in the direction 84. Walls 156 and 158 each have a width 118 (e.g., wall thickness) that extends in direction 90 (e.g., X-direction) and direction 80, which are perpendicular to one another. Width 118 is greater than 100 micrometers. Centerlines 164 and 166 are centered within their respective widths 118.

[0036] The individual layers 116 of each wall 156 and 158 are alternately printed using different vectors (a single vector is used for each portion of a particular layer 116). As shown in Figures 10, 11 and 13, an initial layer 160 (layer n) of the wall 156 is printed along a first vector 168 in a first direction (i.e., Y direction 80) for one portion of the wall 156, and then switches to a second vector 170 in the first direction 80 for another portion of the wall 156. Both the first vector 168 and the second vector 170 are offset from the centerline 164 by half the distance of the width 118 (or the vector distance 136 between the first vector 168 and the second vector 170). The first vector 168 and the second vector 170 are located on opposite sides 130, 132 of the centerline 164, respectively. In certain embodiments, gaps occur in the printing of the wall 156 where the printing switches between the first vector 168 and the second vector 170. Where the printing switches between the first vector 168 and the second vector 170 is where the walls 156 and 158 form a junction 171. The switch between the first vector 168 and the second vector 170 can occur multiple times in the first direction 80 where the wall 156 forms a junction with another wall. Each region of the initial layer 160 of the wall 156 having the first vector 168 and the second vector 170 can be considered to be a contiguous distinct portion of the wall 156 (and thus have a single vector per layer of the wall).

[0037] As shown in Figures 10, 11 and 13, an initial layer 160 (layer n) of the wall 158 is printed along a third vector 172 in a second direction 174 (i.e., opposite the X-direction 90) for a portion of the wall 158, and then switches to a fourth vector 176 in the second direction 174 for another portion of the wall 158. Both the third vector 172 and the fourth vector 176 are offset from the centerline 166 by half the distance of the width 118 (or the vector distance 136 between the third vector 172 and the fourth vector 176). The third vector 172 and the fourth vector 176 are positioned on opposite sides 178, 180, respectively, with respect to the centerline 166. In certain embodiments, gaps occur in the printing of the wall 158 where the printing switches between the third vector 172 and the fourth vector 176. The location where printing switches between third vector 172 and fourth vector 176 is where walls 156 and 158 form junction 171. The switch between third vector 172 and fourth vector 176 can occur multiple times in second direction 174 where wall 158 forms a junction with another wall. Each region of initial layer 160 of wall 158 having third vector 172 and fourth vector 176 can be considered to be a different adjacent portion of wall 156 (and thus have a single vector per layer of wall).

[0038] The printing of the initial layer 160 of the wall 156 with the first vector 168 and the second vector 170 and the printing of the initial layer 160 of the wall 158 with the third vector 172 and the fourth vector 176 intersect where a junction 171 is formed. In particular, the printing of the initial layers 160 of the walls 156 and 158 intersect where the respective vectors utilized to print the respective walls 156 and 158 intersect. In certain embodiments, to form the junction 171, the printing of the initial layer 160 of the wall 156 fills in the gap where the printing of the wall 158 switches between the third vector 172 and the fourth vector 176, and the printing of the initial layer 160 of the wall 158 fills in the gap where the printing of the wall 156 switches between the first vector 168 and the second vector 170.

[0039] As shown in Figures 10, 12 and 13, the next layer 162 (layer n+1) of the wall 156 is printed along a fifth vector 182 in a third direction 184 (i.e., opposite the Y direction 80) for a portion of the wall 156, and then switches to a sixth vector 186 in the third direction 184 for another portion of the wall 156. Both the fifth vector 182 and the sixth vector 186 are offset from the centerline 164 by half the distance of the width 118 (or the vector distance 136 between the fifth vector 182 and the sixth vector 186). The fifth vector 182 and the sixth vector 186 are positioned on opposite sides 130, 132, respectively, with respect to the centerline 164. In certain embodiments, gaps occur in the printing of the wall 156 where the printing switches between the fifth vector 182 and the sixth vector 186. The location where the printing switches between the fifth vector 182 and the sixth vector 186 is where the walls 156 and 158 form the junction 171. The switch between the fifth vector 182 and the sixth vector 186 can occur multiple times in the third direction 184 where the wall 156 forms a junction with another wall. Each area of ​​the next layer 162 of the wall 158 having the fifth vector 182 and the sixth vector 186 can be considered to be a different adjacent portion of the wall 158 (and thus have a single vector per layer of the wall).

[0040] As shown in Figures 10, 12 and 13, the next layer 162 (layer n+1) of the wall 158 is printed along a seventh vector 188 in the fourth direction (i.e., the X-direction 90) for a portion of the wall 158, and then switches to an eighth vector 190 in the fourth direction 90 for another portion of the wall 158. Both the seventh vector 188 and the eighth vector 190 are offset from the centerline 166 by half the distance of the width 118 (or the vector distance 136 between the seventh vector 188 and the eighth vector 190). The seventh vector 188 and the eighth vector 190 are located on opposite sides 180, 178, respectively, with respect to the centerline 166. In certain embodiments, gaps occur in the printing of the wall 158 where the printing switches between the seventh vector 188 and the eighth vector 190. The location where the printing switches between the seventh vector 188 and the eighth vector 190 is where the walls 156 and 158 form the junction 171. The switch between the seventh vector 188 and the eighth vector 190 can occur multiple times in the fourth direction 90 where the wall 158 forms a junction with another wall. Each area of ​​the next layer 162 of the wall 158 having the seventh vector 188 and the eighth vector 190 can be considered to be a different adjacent portion of the wall 158 (and thus have a single vector per layer of the wall).

[0041] The printing of the next layer 162 of the wall 156 with the fifth vector 182 and the sixth vector 186 and the printing of the initial layer 160 of the wall 158 with the seventh vector 188 and the eighth vector 190 intersect where the junction 171 is formed. In particular, the printing of the next layer 162 of the walls 156 and 158 intersect where the respective vectors utilized in printing the respective walls 156 and 158 intersect. In certain embodiments, to form the junction 171, the printing of the next layer 162 of the wall 156 fills in the gap where the printing of the wall 158 switches between the seventh vector 188 and the eighth vector 190, and the printing of the initial layer 160 of the wall 158 fills in the gap where the printing of the wall 156 switches between the fifth vector 182 and the sixth vector 186.

[0042] As mentioned above, the collimator can be 3D printed using LPBF. LPBF is also known as direct metal laser sintering (DMLS), selective laser melting (SLM) or direct metal printing (DMP). FIG. 14 shows a schematic of an LPBF system 192 for printing the walls or bulkheads of the collimator. The LPBF system 192 includes a stock of metal powder 194 (e.g., tungsten powder) disposed on a powder platform 196 coupled to a piston 198. The LPBF system 192 also includes a powder bed 200 (e.g., a bed having tungsten powder) located on a build platform 202 coupled to a piston 204. The LPBF system 192 further includes a powder roller 206 for transferring (e.g., spreading) powder from the powder stock 194 to the powder bed 200 during the formation of a layer of the collimator walls or bulkheads 207. The LPBF system 192 further includes a laser 208 that can be directed through a mirror 210 or directly onto the powder bed 200 to form the layers of the wall or bulkhead 207 .

[0043] The LPBF system 192 further includes a controller 212 coupled to the laser 208. The controller 212 includes a processor 214 (e.g., processing circuitry) and a memory 216 (e.g., memory circuitry). The processor 214 may include multiple microprocessors, one or more “general purpose” microprocessors, one or more special purpose microprocessors, and / or one or more application specific integrated circuits (ASICS), system on a chip (SoC) devices, or some other processor configuration. For example, the processor 214 may include one or more reduced instruction set (RISC) processors or complex instruction set (CISC) processors. The processor 214 may execute instructions to perform various zigzag printing strategies as described above to form the walls or septa of the collimator. These instructions may be encoded in a program or code stored in a tangible, non-transitory computer readable medium such as the memory 216 (e.g., optical disk, solid state device, chip, firmware, etc.). The controller 212 controls the operation of the laser 208 and the LPBF system 192.

[0044] To form the collimator walls or partitions 207, a layer of powder (e.g., tungsten powder) is spread (e.g., by powder roller 206) on the build platform 202. A laser 208 melts this first layer of the walls or partitions 207. A new layer of powder is then spread (e.g., by powder roller 206) on top of the previous layer, and another layer is melted and added on top of the initial layer. This process is repeated until the entire walls or partitions 207 are formed (i.e., until the walls or partitions reach the desired height). The loose and unmelted powder is then removed during post-processing.

[0045] Technical effects of the disclosed embodiments include providing a customized single vector zigzag printing strategy (i.e., utilizing a single vector for each layer of a given wall) for 3D printing of collimators that utilizes alternating vectors offset from the center of the septum (e.g., wall) in opposite directions by half the vector distance. Technical effects of the disclosed embodiments also include creating articles (i.e., collimators) with smooth finishes and high density, where for a given thickness (i.e., thickness greater than 100 micrometers), conventional processes would require a multi-vector strategy. Technical effects of the disclosed embodiments further include improved productivity, uniform septum properties, and the ability to print symmetrical walls. Technical effects of the disclosed embodiments further include improved metrology capabilities when using collimators with backlighting, as the smooth finish aids in edge detection. Technical effects of the disclosed embodiments further include reduced cleaning time and reduced / removed residual particles on the septum surface.

[0046] The technology presented and claimed herein has been referred to and applied to specific examples and tangible objects that have practical properties that clearly improve the art, and as such are not abstract, intangible, or purely theoretical. Moreover, where a claim contains one or more elements specified as "means for [performing] ... a [function]" or "steps for [performing] ... a [function]," it is intended that such elements be construed under 35 USC 112(f). However, for claims that contain elements specified in other ways, such elements are not to be construed under 35 USC 112(f).

[0047] The description herein uses examples to disclose the subject matter (including the best mode) and also enables one skilled in the art to practice the subject matter (such as making and using any devices or systems and performing any methods incorporating the same). The patentable scope of the subject matter is defined in 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 that do not differ insubstantially from the literal language of the claims. [Explanation of symbols]

[0048] 10 CT Imaging System 12 X-ray source 18 Collimator 26 X-ray photons 28 Detector Array 30 System Controller 32 Linear Positioning Subsystem 34 Rotation Subsystem 36 Motor Controller 38 X-ray controller 40 Data Collection System 42 Computers 44 Image processing circuit 48 Operator Workstation 50 Display 52 Printer 56 clients 58 pixels 60 Blades 66 First Direction 70 Second Direction 72 Width 74 Intersection 78 Center line 82 layers 84 directions 86 layer thickness 88 Width 94 Vertical Box 96 Wall 100 Vertical Box 100 pieces 102 Second Vector Exposure 104 Center line 106 Width 108 opposite direction 110 Vector Distance 114 Center line 116 layers 118 Width 122 First Vector 124 layers 126 Second Vector 128 Second Direction 130 opposite side 134 layer thickness 136 Vector Distance 138 Zigzag Pattern 140 images 142 Collimator 144 images 146 Collimator 148 Wall 150 Wall 154 parts 156 Wall 158 Wall 160 Initial layer 162 layers 164 Center line 166 Center line 168 First Vector 170 Second Vector 171 Joint 172 The Third Vector 174 Second Direction 176 The Fourth Vector 178 opposite side 180 opposite side 182 The Fifth Vector 184 The Third Direction 186 The Sixth Vector 188 The Seventh Vector 190 The 8th Vector 192 LPBF system 194 Powder Stock 196 Powder Platform 198 Piston 200 Powder Bed 202 Build Platform 204 Piston 206 Powder Roller 207 Bulkhead 208 Laser 210 Mirror 212 Controller 214 processor 216 Memory

Claims

1. 1. A method of forming a metal grid structure, the method comprising: Using three-dimensional (3D) printing, printing a first layer of a first wall of the metal grid structure, printing the first layer in a first direction along a first vector offset from a first centerline of the first wall by half a first distance of a first width of the first wall perpendicular to the first centerline; printing the second layer of the first wall on the first layer in a second direction along a second vector offset from the first centerline of the first wall by half the first distance of the first width of the first wall, the second direction being opposite the first direction, and the first vector and the second vector being disposed on opposite sides of the first centerline. A method comprising:

2. 2. The method of claim 1, further comprising printing alternating layers of the first wall in the first direction along the first vector and in the second direction along the second vector until the first wall reaches a desired height.

3. 3. The method of claim 2, further comprising: printing respective layers of a plurality of walls of the metal grid structure, alternating printing respective layers of the plurality of walls in the first direction along the first vector and the second direction along the second vector until each wall of the plurality of walls reaches a desired height, wherein the first and second vectors utilized in printing each wall are offset from and positioned on opposite sides of a respective first centerline of each wall.

4. Using 3D printing, printing a first layer of second walls of the metal grid structure in a third direction along a third vector offset from a second centerline of the second walls by half a second distance of a second width of the second walls perpendicular to the second centerline; and 2. The method of claim 1, further comprising: printing a second layer of the second wall on the first layer, the second layer of the second wall in a fourth direction along a fourth vector offset from a second centerline of the second wall by half the second distance of the second width of the second wall, the fourth direction being opposite to the third direction, the third vector and the fourth vector being disposed on opposite sides of the second centerline, and both the third direction and the fourth direction being perpendicular to both the first direction and the second direction.

5. 5. The method of claim 4, further comprising printing alternating layers of the second wall in the third direction along the third vector and in the fourth direction along the fourth vector until the second wall reaches a desired height.

6. The method of claim 4 , wherein the first wall and the second wall are joined at an intersection.

7. Using 3D printing, printing a first layer of second walls of the metal grid structure in a second direction along the second vector; and printing the second layer of the second wall on the first layer in the first direction along the first vector, the first wall and the second wall being adjacent to each other and aligned in the first direction; The method of claim 1 further comprising:

8. 2. The method of claim 1, wherein the first vector and the second vector constitute unique vectors along the first direction and the second direction, respectively, for printing the first wall portion.

9. The method of claim 1 , wherein the metal grid structure comprises an anti-scatter grid or collimator configured for use with an X-ray detector of an X-ray imaging system.

10. The method of claim 9 , wherein the metal grid structure comprises tungsten.

11. The method of claim 1 , wherein the 3D printing comprises laser powder bed fusion.

12. The method of claim 1 , wherein the first distance of the first width of the first wall is greater than 100 micrometers.

13. 1. A method of forming a collimator configured for use with an x-ray detector of an x-ray imaging system, comprising: Using three-dimensional (3D) printing, printing alternating layers of a first set of partitions of the collimator extending in a first direction by alternately utilizing a first vector and a second vector when printing the layers of the first set of partitions, the first vector and the second vector pointing in opposite directions along the first direction, disposed on opposite sides of a first centerline of each partition of the first set of partitions, and offset from the first centerline by a first distance of one-half of a first width of each partition of the first set of partitions; printing alternating layers of a second set of partitions extending in a second direction of the collimator by alternately utilizing a third vector and a fourth vector when printing the layers of the second set of partitions, the third vector and the fourth vector pointing in opposite directions along the second direction, disposed on opposite sides of a second centerline of each partition of the second set of partitions, and offset from the second centerline by a second distance half of a second width of each partition of the second set of partitions, the first direction being orthogonal to the second direction. A method comprising:

14. 14. The method of claim 13, further comprising printing alternating layers of both the first set of partitions and the second set of partitions until both the first set of partitions and the second set of partitions reach a desired height.

15. The method of claim 13 , wherein the first set of septa and the second set of septa are joined at an intersection.

16. The method of claim 13 , wherein the collimator comprises tungsten.

17. The method of claim 13 , wherein each of the first distance and the second distance is greater than 100 micrometers.

18. 1. A system for forming a collimator configured for use with an x-ray detector of an x-ray imaging system, comprising: a memory encoding routines executable by the processor; and a processing circuit configured to access the memory and execute a processor-executable routine that, when executed by the processing circuit, causes the processing circuit to: Using three-dimensional (3D) printing, printing alternating layers of a first set of partitions of the collimator extending in a first direction by alternately utilizing a first vector and a second vector when printing the layers of the first set of partitions, the first vector and the second vector pointing in opposite directions along the first direction, disposed on opposite sides of a first centerline of each partition of the first set of partitions, and offset from the first centerline by a first distance of one-half of a first width of each partition of the first set of partitions; printing alternating layers of a second set of partitions extending in a second direction of the collimator by alternately utilizing a third vector and a fourth vector when printing the layers of the second set of partitions, the third vector and the fourth vector pointing in opposite directions along the second direction, disposed on opposite sides of a second centerline of each partition of the second set of partitions, and offset from the second centerline by a second distance half of a second width of each partition of the second set of partitions, the first direction being orthogonal to the second direction. A system that executes the above.

19. 20. The system of claim 18, wherein each of the first distance and the second distance is greater than 100 micrometers.

20. 20. The system of claim 19, wherein the first set of septa and the second set of septa are joined at an intersection.

Images