Calibration system and method for CT detectors using a wire phantom

Abstract

This invention provides a system and method for calibrating a CT system using a wire phantom connected to the CT system. [Solution] During the calibration of a CT system, when performing a rotational scan using the CT system, the position of the detector elements of the CT system's detector array is measured using the wires of a wire phantom. In subsequent scans, the measured positions of the detector elements are applied during image reconstruction from projection data acquired via the CT system. This method relies on the linearity of the wires within the wire phantom, which is maintained by the spherical swaged ends of the wires when tension is applied to the wires. The phantom holder for the wire phantom may include clamps and handles for positioning the wire phantom on a table.

Description

TECHNICAL FIELD

[0001] Embodiments of the subject matter disclosed in the present specification relate to computed tomography (CT) imaging systems, and more particularly to calibration of CT imaging systems using wire phantoms.

BACKGROUND ART

[0002] In a computed tomography (CT) imaging system, an electron beam generated by a cathode is directed toward a target in an X-ray tube. A fan-shaped or cone-shaped X-ray beam generated by collision of electrons with the target is directed toward an object such as a patient. X-rays attenuated by the object reach an array of radiation detector elements. An electrical signal is generated at each detector element, and an image of the object is reconstructed using the electrical signals generated at the detector elements. Here, each electrical signal corresponds to a voxel / pixel of the image.

[0003] Image quality in terms of resolution, contrast-to-noise ratio, and other factors may depend on the alignment of each detector element in the detector array. Misalignment of detector elements may lead to increased artifacts in the image and degraded image quality. This misalignment can be measured and corrected using mechanical alignment techniques. Mechanical alignment techniques employ multiple measurement methods, such as contact-type and / or laser-type positioning tools. Based on the measurement data, a series of machine tools can be used to realign the detector elements. However, current alignment techniques may be difficult to apply to new CT systems equipped with small-sized detector elements that require positional accuracy of less than 10 μm.

SUMMARY OF THE INVENTION

[0004] This disclosure solves, at least in part, one or more of the problems identified above by a computed tomography (CT) system comprising a processor and a non-temporary memory containing a command to cause the processor to perform a first rotational scanning series to determine the linearity of a wire phantom at runtime. A second rotational scanning series is performed to determine the tilt angle of the wire phantom. When the linearity of the wire is within a first threshold deviation and the tilt angle of the wire is within a second threshold deviation, the position of each detector element in the detector array of the CT system is measured relative to the position of the wire during a calibration scan performed using the CT system. The measured positions of each detector element are then applied to the image reconstruction from projection data acquired via the CT system during a subsequent scan performed using the CT system. The reconstructed image is then displayed on the display device of the CT system. The linearity of the wire is maintained within a first threshold deviation by applying tension to the wire when a first spherical swaged end of the wire is fitted to a free-floating end which is connected via a spring to a first end cap at the first end of the wire phantom tube. Furthermore, by applying tension to the wire between the second spherical swage end portion, which is fitted into the hollow threaded portion of a bolt fastened with a bolt to the center point of the inner circumferential surface of the tube at the second end face, which is the second end of the wire phantom, the linearity of the wire is maintained within the first threshold deviation.

[0005] The advantages and other benefits described above, as well as the features of this specification, will be readily apparent from the following detailed description, either alone or in conjunction with the accompanying drawings. It should be understood that the above summary is provided to introduce in a simplified form some of the concepts that will be further elaborated in the detailed description. It is not intended to identify any essential or important features of the subject matter covered by the claims, which are the sole scope defined by the claims that follow the detailed description. Furthermore, the scope of the claims is not limited to embodiments that resolve any of the defects described above or in any part of this specification. [Brief explanation of the drawing]

[0006] Various aspects of this disclosure will be better understood by reading the detailed description below and referring to the drawings. [Figure 1] A schematic diagram of a CT imaging system according to one or more embodiments of this disclosure is shown. [Figure 2] A schematic block diagram of an exemplary CT imaging system according to one or more embodiments of the present disclosure is shown. [Figure 3A] One or more embodiments of this disclosure show a wire phantom for calibrating a CT imaging system. [Figure 3B] Figure 3A shows the wire phantom aligned with the table of a CT system, according to one or more embodiments of the present disclosure; [Figure 3C] Figure 3A shows the alignment of the wire phantom with the detector array of the CT system according to one or more embodiments of this disclosure. [Figure 4] This is a schematic diagram of an exemplary detector array of a CT system according to one or more embodiments of the present disclosure. [Figure 5A] This flowchart illustrates an exemplary method for improving the accuracy of CT images using calibration data, according to one or more embodiments of the present disclosure. [Figure 5B] This flowchart shows an example of a method for calibrating a CT system using a wire phantom, according to one or more embodiments of the present disclosure. [Figure 6] This is a schematic diagram illustrating an exemplary arrangement for aligning a linear phantom with respect to an X-ray source and an X-ray detector array, according to one or more embodiments of the present disclosure. [Figure 7] A graph of a synogram generated using a wire phantom according to one or more embodiments of the present disclosure. [Figure 8] One or more embodiments of this disclosure describe a method for determining the position of a detector element by fitting a parabolic function to the output of a detector array. [Figure 9]Exemplary projection geometry used to calculate the positions of detector elements of a detector array relative to a wire phantom, according to one or more embodiments of this disclosure, is shown. [Figure 10] An exemplary embodiment of a wire phantom including a self-centered wire termination is shown. [Figure 11] Figure 10 shows a perspective view of the first self-centered wire termination in the embodiment. [Figure 12] The spherical swaged termination of the first self-centered termination is shown. [Figure 13] This shows an enlarged view of the end portion of a spherical swage. [Figure 14] The end cap of the first self-centering terminal is shown. [Figure 15] Figure 10 shows a perspective view of the second self-centered wire termination in the embodiment. [Figure 16] This shows the base-side joint of the second self-centered wire termination. [Figure 17] This shows a phantom holder for a wire phantom, including a clamp. [Figure 18] Figure 17 shows the first set of components of the clamp. [Figure 19] Figure 17 shows the second set of components of the clamp. [Figure 20] Figure 17 shows the handle of the phantom holder.

[0007] The drawings illustrate specific aspects of the systems and methods described herein. Together with the following description, the drawings demonstrate and illustrate the structures, methods, and principles described herein. In the drawings, the sizes of components may be exaggerated or altered for clarity. Well-known structures, materials, or operations are not shown or described in detail so as not to obscure aspects of the components, systems, and methods described herein. [Modes for carrying out the invention]

[0008] This description and embodiments relating to the subject matter disclosed herein relate to methods and systems for improving the quality of images acquired through computed tomography (CT) systems. Typically, in a computed tomography (CT) imaging system, an X-ray source emits a fan-shaped or conical beam toward a subject, such as a patient. The X-rays emitted from the X-ray source are attenuated to varying degrees by the subject before being detected by radiation detector elements arranged in one or more detector arrays. In a CT system, the X-ray source and detector arrays typically rotate around the gantry in the imaging plane and around the patient, and an image is generated from projection data of multiple views at different viewing angles. For example, a CT system may generate 1000 views while the X-ray source rotates once. The beam attenuated by the patient is irradiated onto a radiation detector element array. The detector array typically includes a collimator that collimates the X-ray beam to be received by the detector, a collimator-adjacent scintillator that converts the X-rays into light energy, and a photodiode that receives light energy from the adjacent scintillator and generates an electrical signal. The intensity of the attenuated beam radiation received by the detector array typically depends on the attenuation of the X-ray beam by the patient. Each detector element in the detector array generates a separate electrical signal indicating the attenuated beam it received. These electrical signals are transmitted to a data processing system for analysis. The data processing system processes the electrical signals to facilitate image generation.

[0009] The detector array may be curved, and by aligning the detector elements on the array toward the X-ray source, X-rays emitted from the X-ray source can be detected more accurately and efficiently. Detector elements may be arranged in clusters. For example, a detector array may include multiple detector modules, each detector module may include multiple groups of detector elements called "chiclets," and each chiclet may include multiple detector elements.

[0010] The quality of images reconstructed from projection data collected by detector elements may depend on the alignment between each detector element and the X-ray source. Due to the limited capabilities of mechanical alignment tools, some detector elements may not be accurately aligned during assembly, or misalignment may occur over time or with the use of the CT system. For example, a detector module of a detector array may be damaged and replaced with a new detector module. Since high-precision alignment tools are not available at the customer site, the new detector module may not be accurately aligned. In the first place, the detector modules may not be assembled accurately within the detector array, the tiles within the detector module may be misaligned, and / or the detector elements within the tiles may be misaligned.

[0011] Misalignment in a plurality of detector elements may lead to increased noise artifacts in the image and degraded image quality. It is possible to improve image quality by correcting the misalignment. To correct misalignment, CT systems are periodically calibrated to mechanically adjust the positions of detector modules, tiles, or detector elements. However, current misalignment measurement and correction are performed using alignment techniques, which may be difficult to apply to new types of CT systems having smaller detector elements and pixel sizes.

[0012] To address the issues of calibrating CT systems including small detector elements and correcting misalignment of detector elements, the present specification proposes a method for directly measuring the positions of detector elements, which does not rely on mechanical alignment techniques and generates detector positions from projection data collected using a wire phantom. By generating a calibration vector from the measured detector positions and applying it to projection data acquired in subsequent scans during image reconstruction, the misaligned detector positions can be corrected. In some embodiments, instead of correcting the misaligned detector positions, the measured detector positions can be directly applied during image reconstruction as a substitute for the target design detector positions.

[0013] Examples of CT systems are shown in Figures 1 and 2. Figure 3A shows an example of a wire phantom that can be used for calibrating a CT system. The wire phantom is placed on the table of the CT system, as shown in Figure 3B. Figure 3C shows the position of the wires of the wire phantom relative to the X-ray source and detector array of the CT system during the calibration process described herein. The detector array may include multiple detector elements organized into modules, as shown in Figure 4. A method for calibrating the CT system to correct for misalignment of the detector elements is shown in Figure 5B, and a method for applying the measured detector positions generated during the calibration process to image reconstruction to improve the quality of the resulting image is shown in Figure 5A. Figure 6 shows the arrangement of the wire phantom in the imaging plane of the CT system during calibration. During calibration, projection data is collected at the detector elements as the gantry holding the detector array and X-ray source rotates around the wire phantom. Due to this rotation, the projection data collected during calibration is graphically represented as a synogram, as shown in Figure 7, showing the detector elements that detect X-ray attenuation by the wire at a specific field of view or frame. The attenuation may be maximum at the detector element represented by a parabolic function fitted to the detector output data, as shown in Figure 8. The position of the detector element relative to the wire is measured based on the projection geometry shown in Figure 9.

[0014] Figures 3A, 3B, 4, and 6 are examples of configurations showing the relative positional relationships of various components. Where elements are shown as being in direct contact or directly joined, in at least one instance, such elements are described as being in direct contact or directly joined. Similarly, elements shown as adjacent or close to each other can be said to be adjacent or close to each other in at least one instance. For example, components that share a surface in contact with each other can be said to be in surface-sharing contact. Another example is elements that are spaced apart from each other, with only space between them and no other components present, can be said to be so in at least one instance. Yet another example is elements located above / below / left / right / opposite sides of each other, or to the left / right of each other, which may be referred to in relation to each other. Furthermore, as shown in the figures, in at least one instance, the uppermost element or vertex of an element may be called the "top" of a component, and the lowermost element or bottom point of an element may be called the "bottom" of a component. In this specification, up / down, upper / lower, and upper / lower are used relative to the vertical axis of the drawing and are used to describe the relative positional relationships of elements within the drawing. Therefore, an element shown above another element is, for example, located vertically above the other element. As yet another example, the shape of an element depicted in a figure may be described as having that shape (e.g., circular, linear, planar, curved, rounded, chamfered, angled, etc.). Furthermore, as at least one example, elements shown intersecting each other may be described as intersecting elements or intersecting each other. Finally, as yet another example, an element shown within another element, or outside of another element, may be described in that way.

[0015] Figure 1 shows an example of a CT system 100 configured for CT imaging. In particular, the CT system 100 is configured to image a subject 112 such as a patient, an inanimate object, one or more manufactured parts, and / or a foreign body present in the body, such as a dental implant, stent, and / or contrast agent. In one embodiment, the CT system 100 includes a gantry 102, which may further include at least one X-ray source 104 configured to emit an X-ray emission beam 106 (see Figure 2) used for imaging the subject 112 lying on a table 114. Specifically, the X-ray source 104 is configured to emit the X-ray emission beam 106 toward a detector array 108 located on the opposite side of the gantry 102. Although Figure 1 shows a single X-ray source 104, in certain embodiments, it is possible to use multiple X-ray sources and detectors to emit multiple X-ray emission beams and obtain projection data at different energy levels corresponding to the patient. In some embodiments, the X-ray source 104 allows for rapid switching of peak kilovolts (kVp). In the embodiments described herein, the X-ray detector employed is a photon counting detector capable of distinguishing X-ray photons of different energies.

[0016] In certain embodiments, the CT system 100 further includes an image processing unit 110 configured to reconstruct images of a target region of a subject 112 using iterative or analytical image reconstruction methods. For example, the image processing unit 110 can reconstruct images of a target region of a patient using analytical image reconstruction techniques such as filtered back projection (FBP). As another example, the image processing unit 110 can reconstruct images of a target region of a subject 112 using iterative image reconstruction techniques such as advanced statistical iterative reconstruction (ASIR), conjugate gradient (CG), maximum likelihood expectation maximization (MLEM), and model-based iterative reconstruction (MBIR). As will be further described herein, in some examples, the image processing unit 110 can use both iterative image reconstruction techniques and analytical image reconstruction techniques such as FBP.

[0017] In some CT imaging system configurations, an X-ray source projects a cone-shaped X-ray beam, which is collimated within the XYZ plane of the Cartesian coordinate system (commonly called the "imaging plane"). The X-ray beam passes through the object being imaged, such as a patient or subject. The X-ray beam, attenuated by the object, reaches the detector array. The intensity of the attenuated X-ray beam received by the detector array depends on the degree of attenuation of the X-ray beam by the object. Each detector element in the array generates a separate electrical signal, which is a measurement of the X-ray beam attenuation at the detector position. The attenuation measurements from all detector elements are acquired individually to generate a transmission profile.

[0018] In some CT systems, the X-ray source and detector array rotate with the gantry within the imaging plane and around the object being scanned. This constantly changes the angle at which the X-ray beam intersects the object. A set of X-ray attenuation measurements from the detector array at a given gantry angle (e.g., projection data) is called a "view." A "scan" of an object refers to a set of views acquired at different gantry angles (or view angles) during one rotation of the X-ray source and detector.

[0019] Figure 2 shows an exemplary imaging system 200 similar to the CT system 100 in Figure 1. According to aspects of this disclosure, the imaging system 200 is configured to image a subject 204 (e.g., subject 112 in Figure 1). In one embodiment, the imaging system 200 includes a detector array 108 (see Figure 1). The detector array 108 further includes a plurality of detector elements 202 that jointly sense an X-ray emission beam 106 (see Figure 2) passing through the subject 204 (e.g., a patient) and acquire corresponding projection data. In some embodiments, the detector array 108 may be manufactured in a multislice configuration including a plurality of cells or rows of detector elements 202. In this configuration, one or more additional rows of detector elements 202 are arranged in parallel to acquire projection data. Typical detector array configurations are described later with reference to Figure 4.

[0020] In certain embodiments, the imaging system 200 is configured to move to different angular positions around the subject 204 to acquire desired projection data. Thus, the gantry 102 and its mounted components may be configured to rotate around a rotation center 206, for example, to acquire projection data at different energy levels. Alternatively, in embodiments where the projection angle relative to the subject 204 changes as a function of time, the mounted components may be configured to move along a general curve rather than part of a circular arc.

[0021] As the X-ray source 104 and detector array 108 rotate, the detector array 108 collects data of the attenuated X-ray beam. The data collected by the detector array 108 undergoes preprocessing and calibration to adjust the data to represent the line integral of the attenuation coefficient of the canned subject 204. The processed data is generally called projection data. In some examples, individual detectors or detector elements 202 of the detector array 108 may include photon counting detectors that register the interaction of individual photons in one or more energy bins.

[0022] The acquired projection dataset may be used for substrate decomposition (BMD). In BMD, the measured projections are converted into a set of material density projections. The material density projections are reconstructed to form pairs or sets of material density maps or images corresponding to each substrate, such as bone, soft tissue, and contrast agent maps. These density maps or images are further correlated to form a 3D volumetric image of the substrates (e.g., bone, soft tissue, contrast agent) within the imaging area.

[0023] After reconstruction, the substrate image generated by the imaging system 200 reveals the internal features of the subject 204 represented by the density of the two substrates. The density image is displayed to show these features. In conventional approaches to diagnosing pathological conditions such as disease states, or more generally, medical events, radiologists or physicians consider hard copies or displays of density images to identify characteristic features of interest. These features include lesions, the size and shape of specific anatomical structures or organs, and other features that can be identified from the image based on the skills and knowledge of the individual healthcare professional.

[0024] In one embodiment, the imaging system 200 includes a control mechanism 208 that controls the operation of components such as the rotation of the gantry 102 and the operation of the X-ray source 104. In a particular embodiment, the control mechanism 208 further includes an X-ray controller 210 configured to supply power and timing signals to the X-ray source 104. Furthermore, the control mechanism 208 includes a gantry motor controller 212 configured to control the rotational speed and / or position of the gantry 102 based on imaging requirements.

[0025] In certain embodiments, the control mechanism 208 further includes a data acquisition system (DAS) 214 configured to sample analog data received from the detector elements 202 and convert the analog data into digital signals for subsequent processing. The DAS 214 may be further configured to selectively aggregate analog data from a subset of the detector elements 202 into a so-called macrodetector, as described later. The data sampled and digitized by the DAS 214 is transmitted to a computer or computing device (arithmetic unit) 216. Note that in at least one example, the computing device 216 may be the same as or similar to the image processing unit 110. In one example, the computing device 216 stores the data in a storage device or mass storage device 218. The storage device 218 may be, for example, any kind of non-temporary storage device and may include a hard disk drive, a floppy disk drive, a compact disc read / write (CD-R / W) drive, a digital versatile disc (DVD) drive, a flash drive, and / or a solid-state storage device drive.

[0026] Furthermore, the computing device 216 provides commands and parameters to one or more DAS 214s, X-ray controllers 210, and gantry motor controllers 212 to control system operations such as data acquisition and / or processing. In certain embodiments, the computing device 216 controls system operations based on operator input. The computing device 216 receives operator input, including commands and / or scanning parameters, for example, via an operator console 220 operationally connected to the computing device 216. The operator console 220 may include a keyboard (not shown) or a touchscreen to allow the operator to specify commands and / or scanning parameters.

[0027] Figure 2 shows one operator console 220, but multiple operator consoles may be connected to the imaging system 200 for purposes such as inputting or outputting system parameters, requesting examinations, plotting data, and / or displaying images. Furthermore, in certain embodiments, the imaging system 200 may be located in a facility or hospital, or in a completely different location via one or more configurable wired and / or wireless networks, such as the Internet, a virtual private network, a wireless telephone network, a wireless LAN, a wired LAN, a wireless WAN, or a wired WAN.

[0028] In one embodiment, for example, the image system 200 includes or is connected to an image archive communication system (PACS) 224. In an exemplary embodiment, the PACS 224 is further connected to remote systems such as a radiology department information system, a hospital information system, and / or internal or external networks (not shown) to allow operators in different locations to supply commands and parameters or access image data.

[0029] The computing device 216 operates the table motor controller 226 using operator-provided and / or system-defined commands and parameters, thereby controlling the table 114, which may be an electric table. Specifically, the table motor controller 226 can move the table 114 to properly position the subject 204 within the gantry 102 in order to acquire projection data corresponding to the target volume of the subject 204.

[0030] As described above, the DAS214 samples and digitizes the projection data acquired by the detector element 202. The image reconstruction device 230 then performs high-speed reconstruction using the sampled and digitized X-ray data. Although Figure 2 shows the image reconstruction device 230 as an independent component, in certain embodiments, the image reconstruction device 230 may form part of the computing device 216. Alternatively, the image reconstruction device 230 may not be present in the imaging system 200, and instead, the computing device 216 may perform one or more functions of the image reconstruction device 230. Furthermore, the image reconstruction device 230 may be located locally or remotely and operably connected to the imaging system 200 using a wired or wireless network. In particular, in one embodiment, the image reconstruction device 230 may use computing resources in a “cloud” network cluster.

[0031] In one embodiment, the image reconstruction device 230 stores the reconstructed image in a storage device 218. Alternatively, the image reconstruction device 230 may transmit the reconstructed image to a computing device 216 to generate useful patient information for diagnosis and evaluation. In certain embodiments, the computing device 216 can transmit the reconstructed image and / or patient information to a display or display device 232 that is communicatively connected to the computing device 216 and / or the image reconstruction device 230. In some embodiments, the reconstructed image may be transmitted from the computing device 216 or the image reconstruction device 230 to the storage device 218 for short-term or long-term storage.

[0032] The detector array 108 may include multiple detector modules. Each detector module may include multiple chiclets, where a chiclet is a collection of individual sensors or detector elements.

[0033] A simplified view of Figure 4 shows an exemplary detector array 400. It should be understood that the detector array 400 may consist of different sizes and / or shapes, such as square, rectangular, circular, or other shapes. The actual field of view (FOV) of the detector array 400 is directly proportional to the size and shape of the detector array 400. In the illustrated embodiment, the detector array 400 has curvature, and the detector elements of the detector array 400 are aligned toward an X-ray source located at a fixed distance above the center point 404 of the detector array 400, as indicated by the dashed line 420 and the reference axis 450.

[0034] The detector array 400 includes rails 440 having collimating blades or plates 406 positioned between them. The plates 406 are positioned to collimate the X-ray beam 425 before it irradiates the plurality of detector modules 402 of the detector array 400. The detector modules 402 may be positioned between the plates 406. Each detector module 402 includes a plurality of chiclets, and each chiclet includes a plurality of detector elements or pixels. For example, the detector array 400 may include 25 detector modules 402, each detector module 402 may include 16 chiclets, and each chiclet may include 12 detector elements. Thus, each detector module 402 includes 192 detector elements, and the detector array 400 contains a total of 4,800 detector elements. As an example, the width of the chiclets is 8.74 mm, each detector element has 100 pixels, and each pixel has a width of 365 μm in the X direction and a pitch of 765 μm in the Z direction. The minute pixel size of 365 μm requires precise mechanical alignment, and even if the positioning of the detection elements within each chiclet can be controlled by robotic placement, achieving this can be difficult.

[0035] Returning to Figure 2, since the reconstructed image is generated from the electrical signals produced by each detector element 202, the accuracy and / or image quality of the reconstructed image may depend on whether the detector elements 202 are aligned within the detector array. Each detector element 202 has a corresponding position within the detector array. Not all detector elements 202 are perfectly aligned. If the actual position of the detector element 202 deviates from the design target position (for example, if the detector element is misaligned), the accuracy of the reconstructed image may be reduced.

[0036] The detector element 202 is very small, and alignment can be difficult. For example, to achieve threshold image quality, alignment errors of less than 10% (e.g., less than 36.5 microns) may be desirable. If any part of the detector element 202 is misaligned by more than 10% with respect to either the x-axis or z-axis, or both, the quality of the reconstructed image may be degraded.

[0037] Due to the manufacturing process or as a result of the CT imaging system 200 being transported from the factory to the hospital, some of the detector elements 202 may become misaligned. Misalignment of some of the detector elements 202 may also occur if the detector module of the detector array 108 is damaged or replaced with a new one. Misalignment can occur between detector modules (e.g., inter-module alignment), between parts of a detector module (e.g., inter-chicklet alignment), or between sensors within a chiclet.

[0038] To ensure threshold image quality, one or more detector arrays 108 of the CT imaging system 200 may be calibrated periodically. For example, calibration may be performed when the CT imaging system 200 is first installed in a medical facility, after replacing a damaged module, after a predetermined period of time, or at different times. During calibration, the position of each detector element 202 is measured relative to a reference position provided by a wire phantom. Slight variations in the position of the detector elements relative to the reference position are detected and collected and used to generate a calibration vector for each detector array 108. The calibration vector may include correction values ​​for the measured position of the detector elements, or for the measured position of each detector element 202 in the detector array. This calibration vector is used to perform mechanical alignment of the various detector elements of the detector array. Furthermore, or alternatively, during image reconstruction, the calibration vector can be applied to projection data acquired from the detector elements 202 to correct for positional variations of the detector elements 202. Correcting these variations can improve image quality.

[0039] Figure 3A shows a typical wire phantom assembly 300 used to calibrate one or more detector arrays 108. The wire phantom assembly 300 includes a wire phantom 302 and a table mount 320. The table mount 320 can be used to mount the wire phantom 302 to a table (e.g., table 114) of a CT imaging system, such as the CT imaging system 200 in Figure 2.

[0040] The table mount 320 includes a mounting surface 334 that can be coupled to the surface of the table and a phantom holder 323 to which the wire phantom 302 can be coupled at a desired position. The phantom holder 323 allows the wire phantom 302 to be positioned downward by a distance 325 from the underside of the table. For example, the distance 325 can be adjusted by bolting the phantom holder 323 to the table mount 320 at different positions 327 (e.g., holes in the phantom holder 323). The table mount 320 includes one or more rubber shims 322 coupled to the phantom holder 323, which can be aligned in surface-sharing contact with the edge of the table. The rubber shims 322 provide a tighter and more secure bond between the table mount 320 and the table. The base plate 336 of the wire phantom 302 is coupled to the phantom holder 323 via one or more bolts, such as a first bolt 324 and a second bolt 330.

[0041] Referring briefly to Figure 3B, the table mounting diagram 340 shows the alignment of the wire phantom 302 and the table mount 320 with respect to the table 342 of the CT imaging system. The mounting surface 334 is aligned with the lower surface 348 of the table 342. For example, the mounting surface 334 is clamped to the lower surface 348. The alignment of the phantom holder 323 with respect to the lower surface 348 of the table 342 is adjustable along the X-axis of the CT imaging system (for example, according to the reference axis 341) via the first tilt screw 347. The alignment of the phantom holder 323 with respect to the lower surface 348 of the table 342 along the Y-axis of the CT imaging system can be adjusted via the second tilt screw 349.

[0042] Figure 17 is a perspective view 1700 showing an example of a phantom holder 323 equipped with a clamp 1701 for clamping a mounting surface 334 to the lower surface 348 of the table 342 of Figure 3B. The clamp 1701 includes a knob 1702 and a threaded portion 1704. The knob 1702 has a diameter 1720, which may be larger than the diameter of the threaded portion 1704. The outer surface of the knob 1702 may be textured so that the user of the wire phantom assembly 300 can grasp and rotate the knob 1702 by hand.

[0043] On the upper surface 1750 of the clamp 1701, the threaded portion 1704 passes through a hole in the bearing plate 1708, which is securely fixed to the upper end of the phantom holder 323, as shown in Figure 19. The threaded portion 1704 extends through this hole to the cradle 1706 on the lower surface 1752 of the clamp 1701. The cradle 1706 may include a lower section 1730 that extends outward from the back surface 1722 of the phantom holder 323 toward the table 342, in the direction indicated by arrow 1790. Since the lower section 1730 extends outward beyond the vertical position of the threaded portion 1704 of the clamp 1701, the bottom end 1734 of the threaded portion 1704 can be inserted into the lower section 1730, as shown in enlarged view 1760. The bottom end 1734 of the threaded portion 1704 may extend into a nut 1762 located in a cavity in the lower part 1730, which is held in place by one or more walls 1766 of the cavity. The cradle 1706 is coupled to the back surface 1722 of the phantom holder 323. The cradle 1706 may also have a flange portion 1732 extending upward along the back surface 1722, thereby allowing the cradle 1706 to be secured to the phantom holder 323 (back surface 1722) via one or more fasteners 1736. For example, the fasteners 1736 may be bolts, screws, or other types of fasteners.

[0044] The cradle 1706 may be manufactured from a plastic or similar material that is flexibly deformable under pressure. The cradle 1706 may be positioned on the phantom holder 323 so that the phantom holder 323 can be mounted on the table 342. Specifically, the mounting surface 334 is inserted into the accessory slot of the table 342 so that the bottom surface 1738 of the lower part 1730 makes surface-sharing contact with the upper edge of the table 342. The position of the cradle 1706 on the phantom holder 323 may be configured such that the table 342 has a tight or interfering fit between the bottom surface 1738 and the mounting surface 334. After the mounting surface 334 is inserted into the accessory slot of the table 342, the clamp 1701 can be actuated to increase the pressure between the bottom surface 1738 of the lower part 1730 and the upper edge of the table 342 by rotating the knob 1702 of the clamp 1701 clockwise as indicated by arrow 1712. The inner circumference of the hole in the bearing plate 1708 into which the threaded portion 1704 is inserted may be threaded. When the knob 1702 is rotated clockwise, the bottom end 1734 of the threaded portion 1704 engages with the threads of the nut 1762, generating a downward force on the lower part 1730. This force presses the lower part 1730 against the upper surface of the table 342 in the direction indicated by arrow 1742. As can be seen in the enlarged view 1760 of the lower part 1730, one or more pads 1764 are provided on the bottom surface 1738 to protect the upper surface of the table 342 from damage and to improve the grip between the lower part 1730 and the table 342. Therefore, by rotating the knob 1702, the phantom holder 323 can be securely fixed to the table 342. To remove the phantom holder 323 from the table 342, the knob 1702 is rotated in the reverse direction (counterclockwise) to engage the nut 1762 in the reverse direction, releasing the pressure acting on the table 342 by force, and allowing the phantom holder 323 to slide away from the table 342.

[0045] Figure 18 shows an exploded view 1800 of the cradle 1706. The rear surface 1722 may have one or more holes, such as holes 1802 and 1804, for bolting the cradle 1706. The flange portion 1732 of the cradle 1706 is provided with holes 1806 and 1808, which are larger and more elliptical than holes 1802 and 1804, allowing the cradle 1706 to be adjusted vertically on the rear surface 1722 after preliminary mounting. The flange portion 1732 of the cradle 1706 can be bolted to the rear surface 1722 via first bolts 1814 inserted along the axis 1820 into holes 1806 and 1802. Second bolts 1816 are inserted along the axis 1822 into holes 1808 and 1804. A first guide 1810 is provided between the first bolt 1814 and the hole 1806, and a second guide 1812 is provided between the second bolt 1816 and the hole 1808. In some embodiments, a recess 1824 is provided on the upper surface 1740 of the lower part 1730, and when the clamp 1701 applies force to the lower part 1730, the bottom end 1734 of the threaded portion 1704 of the clamp 1701 fits into the recess 1824.

[0046] Figure 19 is a perspective view 1900 showing an example of attaching a bearing plate 1708 to the upper end 1925 of a phantom holder 323. In the illustrated example, the bearing plate 1708 is joined to the upper end 1925 via several screws, including screws 1901, 1902, and 1903. Screws 1901, 1902, and 1903 pass through holes 1911, 1912, and 1913 (hidden by the knob 1702 in Figure 19) in the support plate 1708, and further pass through holes 1921, 1922, and 1923 in the upper end 1925 of the phantom holder 323, respectively. The threaded portion 1704 of the clamp 1701 may have an extending core 1930 that extends through the hole 1908 in the bearing plate 1708 to the center of the knob 1702 of the clamp 1701. The first bushing 1906 is provided between the knob 1702 and the hole 1908, and the second bushing 1907 is provided between the hole 1908 and the threaded portion 1704.

[0047] As another example, Figure 20 shows an embodiment 2000 of a phantom holder 323 that includes a handle portion 2002 configured to allow the wire phantom assembly 300 to be manually moved, carried, or inserted into a desired position on a table 342, with the bearing plate 1708 being extended. The handle portion 2002 includes a hole 2004 into which a person's hand can be inserted to carry the phantom holder 323, and an encircling portion 2003 is provided around the hole 2004. By providing the handle portion 2002 on the support plate 1708, the risks associated with handling and manipulating the wire phantom assembly 300 by the tube 1001 can be reduced. Furthermore, the hole 2004 can be positioned on the wire phantom assembly 300 side opposite the clamp 1701 and cradle 1706, which brings the lifting point of the wire phantom assembly 300 closer to its center of gravity, allowing the wire phantom assembly 300 to remain horizontal even when lifted by the handle portion 2002.

[0048] Returning to Figure 3A, the wire phantom 302 includes a wire 304 positioned along the central axis of the tube 306. This central axis coincides with the z-axis of the CT imaging system. The tube 306 protects the wire 304 and provides a structure that maintains the linearity of the wire 304 and protects the wire 302. The wire phantom 302 has a first end cap 308 on a first side 314 (e.g., the gantry side) and a second end cap 312 on a second side 316 (e.g., the table side). The wire 304 extends from the first inner surface of the first end cap 308 to the second inner surface of the second end cap 312. The first end cap 308, the second end cap 312, and the tube 306 have a diameter 307. For example, the diameter 307 may be 20 cm or a different number.

[0049] The wire 304 has a length 305, which is long enough to cover the entire detector array. For example, the length 305 may be 150 mm or more. The wire 304 contains or is made of a high-attenuation material such as steel or tungsten, which may attenuate X-rays and leave a characteristic signal in the readout of the CT imaging system during scanning. During calibration, the position of each detector element can be measured relative to the position of the wire 304. Scanning can be performed on the wire phantom 302. As the detector array rotates around the table via the gantry (e.g., gantry 102), the attenuation of X-rays by the wire 304 is detected at different viewing angles for each detector element.

[0050] The thickness or diameter of the wire 304 may depend on the transverse dimension of the detector element (e.g., a pixel). To measure each pixel position reproducibly and reliably, a suitable diameter is desirable to be 2 to 4 times the transverse pixel dimension. In various embodiments, a suitable diameter is at least 3 times the transverse dimension. In one embodiment, the transverse dimension is 356 micrometers, and the diameter of the wire 304 is 1 mm (approximately 3 pixels wide). Therefore, if the diameter of the wire 304 is approximately 3 pixels wide, the X-ray attenuation by the wire 304 during calibration may be detected by three or more pixels at a given viewing angle.

[0051] The wire 304 is a multithread and / or braided wire, or a braided stainless steel cable, which may be more likely to achieve a threshold straightness than a single-wire wire. For example, the threshold straightness may have an allowable deviation of 30 microns from a perfect straight line. In various embodiments, the threshold straightness may be maintained by placing the wire 304 under the tension of a spring 309. The spring 309 may be located on the first side 314 of the wire phantom 302 (e.g., the first end cap 308) or on the second side 316 of the wire phantom 302 (e.g., the second end cap 312). Furthermore, the wire 304 can be molded from a plastic resin, which further ensures that threshold straightness is achieved. The positional accuracy of the detector element measured during calibration may depend on the precise angular alignment of the wire 304 relative to the table and gantry. As an example, precise angular alignment is desirable to be within a threshold of 3 milliradians (mrad) in parallelism with respect to the central axis of the gantry. This precise angular adjustment is controlled and / or adjusted via one or more tilt adjustment screws located on the phantom holder 323. Specifically, the alignment of the wire 304 with the table mount 320 is adjusted via a first wire phantom tilt adjustment screw 326 and / or a second wire phantom tilt adjustment screw 332. The first wire phantom tilt adjustment screw 326 adjusts the vertical angle of the wire phantom 302 (e.g., the y-direction indicated by the reference axis 301), and the second wire phantom tilt adjustment screw 332 adjusts the horizontal angle (e.g., the x-direction). The wire 304 is aligned or realigned to be parallel to the central axis of the gantry before and after each calibration and / or data analysis. Residual uncertainty resulting from alignment accuracy of 3 milliradians or less can be corrected in the final calibration step, which involves adjusting and fitting the wire itself.

[0052] When the spring 309 is positioned on the end cap 308, the end 303 of the wire 304 is located outside the spring 309. As the spring 309 is subjected to tension, a tilting force acts on the end cap 308, potentially causing bending of the wire 304. Excessive tightening of the wire 304 (e.g., by technicians or users) can compress the spring 309, and after the end cap 308 bottoms out, the tension of the wire 304 may increase rapidly. This could cause the soldered end of the wire 304 to be pulled away from the end 303. To prevent excessive tightening while maintaining the linearity and / or tension of the wire 304, the wire 304 is provided with a swaged end having a spherical end. The spherical end allows the wire 304 to self-center within the tube 306, thereby eliminating bending forces. Details of the self-centered end will be described later with reference to Figures 10-17.

[0053] Referring to Figure 10, an embodiment 1000 of the wire phantom 302 is shown. This embodiment 1000 includes a wire or cable 1002 (e.g., wire 304) with a swaged end having a spherical end. The spherical end self-centers the cable 1002 within a tube 1001 (e.g., tube 306) and prevents bending of the cable 1002 that may occur due to tightening of the cable 1002.

[0054] Tube 1001 has a first end cap 1004 at the first end 1050 of tube 306 and a second end cap 1006 at the second end 1052. The first end cap 1004 is secured to tube 1001 via a first set of fasteners 1008 (e.g., screws, bolts, etc.), and the second end cap 1006 is secured to tube 1001 via a second set of fasteners 1010. Cable 1002 is connected to the first end cap 1004 via a first spherical swaged end 1012, which fits into the end 1015 of the first end cap 1004. Cable 1002 may be connected to the second end cap 1006 via a second spherical swaged end 1014. Although hidden in Figure 10, it can be fitted onto a bolt 1014 connected to a second end cap 1006. Spherical swage ends such as the first spherical swage end 1012 and the second spherical swage end 1014 are shown in Figure 13. The bolt 1014 and the second spherical swage end are shown in detail in Figures 15-17.

[0055] The end portion 1015 is connected to the first end cap 1004 via a spring 1016. The end portion 1015 is fixed to the first end of the spring 1016, and the second end of the spring 1016 is fixed to the first end cap 1004 via a pin 1018. The configuration of the first spherical swage end portion 1012, the end portion 1015, and the first end cap 1004 is shown in detail in Figures 11 and 12.

[0056] Referring to Figure 13, a spherical swaged end 1300 of wire 1301 is shown. This is a non-limiting example of a first spherical swaged end 1012 and / or a second spherical swaged end 1014 of wire 1002. In the illustrated example, wire 1301 is a braided stainless steel cable. In other examples, wire 1301 may be made of a different material or have a different configuration, such as a non-braided configuration. The spherical swaged end 1300 has a shank 1302 at the first end 1350 of the spherical swaged end 1300 and a spherical portion 1303 at the second end 1352 of the spherical swaged end 1300. Wire 1301 is inserted into the shank 1302 and the spherical portion 1303. In some embodiments, wire 1301 protrudes from the second end 1352 by a distance of 1312. The first diameter 1306 of the spherical portion 1303 is larger than the second diameter 1308 of the shank 1302. Because the first diameter 1306 is larger than the second diameter 1308, when tension is applied to the wire 1301, as shown in Figure 11, the spherical portion 1303 fits into the end of the wire phantom's end cap (e.g., the end 1015 of the first end cap 1004). The advantage of the swaged end is that it can support tension up to the full strength of the wire 1301 (e.g., 160 pounds for a 19-strand braided 300 series stainless steel cable).

[0057] Referring to Figure 11, a perspective view 1100 of the first end 1050 is shown, and enlarged views of the first spherical swage end 1012, end 1015, spring 1016, and pin 1018 are shown. In the illustrated example, the end 1015 has a cylindrical shape. In other examples, the end 1015 may have a different shape. The end 1015 may have a slot 1120 on one side so that the first spherical swage end 1012 can be fitted into the end 1015. The slot 1120 may include a wider portion 1122 at the end of the end 1015 closest to the first end 1050. The first width 1130 of the wider portion 1122 may be longer than the diameter of the first spherical swage end 1012 (e.g., the first diameter 1306). The second width 1132 of slot 1120 may be longer than the diameter of shank 1013 (e.g., second diameter 1308) and shorter than the diameter of the first spherical swage end 1012. As a result, when there is no tension on the wire 1002, it is possible to insert the first spherical swage end 1012 into the wider section 1122 and simultaneously insert the wire 1002 and shank 1013 into slot 1120. The spherical portion of the first spherical swage end 1012 (e.g., spherical portion 1303) is located at the center of the end 1015 and abuts against a lip 1140 that prevents the first spherical swage end 1012 from moving in direction 1190.

[0058] After the first spherical swage end portion 1012 is fitted into the end portion 1015, the first end coil 1104 of the spring 1016 can be inserted from the first end 1050 into the wider portion 1122. Then, the roll pin 1102 can be inserted into the hole 1134 of the end portion 1015 and passed through the first end coil 1104 to connect the spring 1016 to the end portion 1015. In some embodiments, the hole 1134 may penetrate the end portion 1015 completely. In other embodiments, the hole 1134 may not penetrate the end portion 1015 completely. The roll pin 1102 may be held in place by interference fitting or a locking screw. Then, the pin 1018 can be inserted into the second end coil 1106 of the spring 1016, thereby securing the spring 1016 to the first end cap 1004. The second end coil 1106 is fitted onto the concave periphery 1150 of the pin 1018, preventing the spring 1016 from sliding up and down on the pin 1018 in the direction indicated by the bidirectional arrow 1192. Once the pin 1018 is secured to the first end cap 1004, the spring 1016 generates tension in the wire 1002. The material, dimensions, and strength of the spring 1016 are set to generate the tension necessary to hold the wire 1002 straight and centered within the tube 1001.

[0059] Figure 12 shows a side view 1200 of the first spherical swage end 1012 fitted to the end 1015, highlighting the self-centering characteristics of the wire 1002. The shank 1013 extends outward (to the left in Figure 12) from the end 1015 in direction 1190. The end 1015 is free-floating, i.e., coupled to the spring 1016 via the roll pin 1102 and not directly coupled to the tube 1001 (not via the first end cap 1004), so the end 1015 is movable, thereby aligning the wire 1002 linearly and perpendicularly with the pin 1018 along the central axis 1202 of the tube 1001. The tube 1001 may be fixed to the first end cap 1004 as shown in Figure 14. As a result, the tension acting on the wire 1002 via the spring 1016 (for example, when the pin 1018 is fixed to the first end cap 1004, and / or when the first end cap 1004 is fixed to the tube 1001) does not cause bending of the wire 1002.

[0060] The terminal portion 1015 may include a first portion 1204 and a second portion 1206. The first portion 1204 may be a cylindrical portion having a diameter of 1212 and a length of 1208. The second portion 1206 is a substantially cylindrical portion having a length of 1210 and a diameter of 1212, but having a first concave surface 1220 on the upper side of the terminal portion 1015 (see Figure 12) and a second concave surface 1222 on the bottom side of the terminal portion 1015, with a hole 1134 extending from the first concave surface 1220 (see Figure 12) and a second concave surface 1222 on the bottom surface of the terminal portion 1015, with a hole 1134 extending from the first concave surface 1220 to the second concave surface 1222. The roll pin 1102 is insertable into the hole 1134. The length 1213 of the roll pin 1102 is shorter than its diameter 1212 and thicker than the thickness 1214 of the second portion 1206, measured between the first concave 1220 and the second concave 1222. When the first spherical swage end 1012 is fitted onto the end 1015 and tension is applied to the spring 1016, the spherical portion 1230 of the first spherical swage end 1012 rests on the rib 1140, and the shank 1013 and cable 1002 extend from the first portion 1204 of the end 1015.

[0061] Figure 14 shows a second perspective view 1400 of the first end 1050 of embodiment 1000 of the wire phantom 302. The second perspective view 1400 shows the positional relationship of the first end cap 1004 at the first end 1050. The first end cap 1004 has a cylindrical shape and may include a first, flatter cylindrical portion 1450 (which seals the first end cap 1004 to the tube 1001) and a second cylindrical portion 1454 extending outward from the tube 1001 in the direction indicated by arrow 1457, i.e., toward the first end 1050. The first cylindrical portion 1450 may have a diameter 1462 equal to or greater than the diameter of the tube 1001 and may have a structurally sufficient height or thickness 1451 to withstand the desired tension of the wire 1002 without deformation or damage. The desired tension may be, for example, 15 pounds (lbf). The second cylindrical portion 1454 has a height 1456 and may be configured to house the spring 1016 when engaged to provide the desired tension to the wire 1002. The diameter 1460 of the second cylindrical portion 1454 is smaller by a distance 1452 than the diameter 1462, and the first cylindrical portion 1450 is configured to extend circumferentially outward from the second cylindrical portion 1454 by a distance 1452. The second perspective view 1400 shows the cap 1404. This cap 1404 has a height approximately equal to the height 1456 of the second cylindrical portion 1454 and an inner diameter equal to the diameter 1460 of the second cylindrical portion 1454, so that the cap 1404 is slidably inserted onto the second cylindrical portion 1454, covering and protecting the connection between the wire 1002 and the first end cap 1004, and providing a neat appearance. In various embodiments, the cap 1404 can be made of plastic.

[0062] The first end cap 1004 is provided with notches 1406 and 1408 on opposing sides of the end portion 1015, thereby allowing the spring 1016 to be held or manipulated when the first end cap 1004 is secured to the tube 1001 (for example, via the fastener 1008). The notches 1406 and 1408 also form saddle portions 1410 and 1412 between the notches 1406 and 1408. These support the pin 1018 when tension is applied to the spring 1016. The pin 1018 has a first circumferential end portion 1420 with a reduced diameter, which can be fitted into a recess 1430 on the outer surface 1440 of the saddle portion 1410. It also has a second circumferential end 1422 with a reduced diameter, which fits into a recess 1432 on the outer surface 1441 of the saddle portion 1412, preventing the pin 1018 from moving laterally along the outer surfaces 1440 and 1441 of the saddle portions 1410 and 1412, respectively.

[0063] Referring to Figure 15, perspective view 1500 shows the second end 1052 of embodiment 1000 of the wire phantom 302. Second perspective view 1500 shows the position of the second end cap 1006 at the second end 1052 (e.g., base-end fitting). The diameter of the second end cap 1006 is greater than or equal to the diameter 1462 of the tube 1001, so that the second end cap 1006 seals the tube 1001 at the second end 1052. The second end cap 1006 may be coupled to a base plate 336. The base plate 336 may be coupled to the second end cap 1006 with a phantom holder 323, as described above in Figure 3A. The wire 1002 may be coupled to the second end cap 1006 via a bolt 1040. Here, the second spherical swage end 1014 can be fitted onto the bolt 1040 in the same manner as described above with respect to the first end cap 1004. The bolt 1040 is bolted to the circular inner surface 1502 at its center point. The spherical bolt 1520 allows the base plate 336 to pivot in the x / y direction as indicated by the reference axis 301.

[0064] Figure 16 shows a perspective view 1600 of bolt 1040, showing the second spherical swage end 1014 fitted onto bolt 1040. Bolt 1040 comprises a head 1601 and a threaded portion 1602 having a diameter 1620. The threaded portion 1602 is hollow and may include a first cylindrical chamber 1630 positioned coaxially with the central axis 1690 of bolt 1040. The first cylindrical chamber 1630 may have a diameter 1622 (for example, smaller than diameter 1620). The diameter 1622 may be larger than the diameter of the spherical portion 1604 of the second spherical swage end 1014. The threaded portion 1602 may include a second cylindrical chamber 1632 positioned coaxially with the central axis 1690 and extending from the first cylindrical chamber 1630 toward the head 1601. The second cylindrical chamber 1632 has a diameter of 1624, which may be larger than the diameter of the shank portion 1614 of the second spherical swage end portion 1014 and smaller than the diameter of the spherical portion 1604 of the second spherical swage end portion 1014. Both the head 1601 and the threaded portion 1602 may be provided with a slot 1612 that extends to the center of the bolt 1040 and opens into the first cylindrical chamber 1630 and the second cylindrical chamber 1632, thereby allowing the wire 1002 to be inserted laterally into the bolt 1040 when the spherical portion 1604 at the end 1660 of the threaded portion 1602 is inserted into the first cylindrical chamber 1630. After the spherical portion 1604 is inserted into the first cylindrical chamber 1630, the wire 1002 is pulled in the direction indicated by arrow 1680 (via the spring 1016 located at the first end 1050 of the tube 1001), and as the shank 1614 slides into the second cylindrical chamber 1632, the second spherical swage end 1014 seats within the threaded portion 1602. Once the second spherical swage end 1014 is fitted into the threaded portion 1602, the spherical portion 1604 abuts against the lip 1634 between the first cylindrical chamber 1630 and the second cylindrical chamber 1632, securing the wire 1002 within the bolt 1040. As shown in Figure 15, the bolt 1040 is then coupled to the second end cap 1006.

[0065] Figure 3C shows a detector array diagram illustrating the typical positional relationship of the wire 304 to the detector array 360 during calibration using the wire phantom 302. The detector array diagram 360 includes the X-ray source 362 and the detector array 364. The X-ray source 362 and the detector array 364 are fixedly mounted on the gantry (e.g., gantry 102). The center point 363 of the X-ray source 362 and the detector array 364 may be aligned along the Y-axis of the CT imaging system, and the detector array 364 and the X-ray source 362 rotate around the isocenter 380 of the gantry. The gantry may rotate in the direction indicated by the arrow 382.

[0066] The detector array 364 may be arc-shaped in a first dimension along the X-axis of the CT imaging system and flat in a second dimension along the Z-axis of the CT system. During calibration scanning, the table of the CT system (not shown in Figure 3C) is positioned along the z-axis, and the wire 304 is connected to one end of the table and positioned so that the wire 304 extends between the detector array 364 and the X-ray source 362. Therefore, as the gantry rotates, the position of the wire 304 relative to the detector array 364 and the X-ray source 362 changes.

[0067] At the position shown in detector array figure 360, X-rays 372 directed towards detector element 368 may be attenuated when they collide with wire 304 at point 370, reducing the amount of X-rays 372 detected by detector element 368. However, other X-rays emitted by X-ray source 362 at the same x-position (e.g., along the x-direction indicated by arrow 384) may be detected by other detector elements positioned at the same x-position on detector array 364. Therefore, the attenuation of X-rays 372 by wire 304 can be used to establish a linear relationship between detector element 368, point 370 on wire 304, and X-ray source 362. Once this linear relationship is established, projection geometry can be used to measure the position of detector element 368 on detector array 364 and the alignment angles of detector element 368 in the X and Z axes relative to wire 304. The calculation of the position of the detector element 368 based on the attenuation of the X-rays 372 will be described later with reference to Figures 7, 8, and 9.

[0068] Referring to Figure 7, the wire position graph 700 shows exemplary lines 702 across multiple field angles indicating the position of wires in a wire phantom (e.g., wire 304 of wire phantom 302 in Figure 3A) as detected by multiple detector elements of the detector array during one rotation of the gantry while scanning by the CT imaging system. The x-axis of the wire position graph 700 displays frames corresponding to different field angles, and the y-axis displays the pixel (e.g., detector element) position in the x-dimension.

[0069] As described above, line 702 has the shape of a synogram because the gantry rotates around the wire. During calibration, the wire phantom may be connected to a table in a fixed position relative to the gantry. The fixed position may be set outside the field of view (FOV) of the detector array so that all detector elements of the detector array are calibrated. For example, the fixed position may be set 50 cm outside the FOV. In other words, if the fixed position is within the FOV, some elements of the detector array between the fixed position and the edge of the FOV will not detect the wire and will not be calibrated. As a result of the fixed position being outside the FOV, the upper region 750 and the lower region 751 of line 702 may be excluded from the wire position graph 700.

[0070] For example, the first point 704 on line 702 indicates that, in the field of view corresponding to the 200th frame, the first attenuation of X-rays due to the wire (referred to herein as wire attenuation) was detected to the greatest extent by the first detector element located at x-position 350 in the detector array, which includes the detector element. The first wire attenuation may indicate the x-coordinate (e.g., 350) of the detector element in the detector array.

[0071] As a second example, a second point 705 on line 702 may indicate that the second wire attenuation is detected to the maximum extent by the first detector element located at x-coordinate 350 in the detector array at the field of view corresponding to the 1350th frame. The second wire attenuation can be identified by the x-position (e.g., 350) of the detector element in the detector array. Each detector element in the detector array can detect the wire in two different frames of the full rotation.

[0072] Because the wire's diameter is larger than the cross-sectional diameter of the detector elements in the detector array, the X-ray attenuation caused by the wire may be detected by multiple adjacent detector elements. For example, if the wire diameter is 1 pixel and the cross-sectional diameter of the detector element is 356 micrometers, 3 to 5 adjacent detector elements may record the attenuation. The attenuation may be strongest at the central pixels of the 3 to 5 adjacent detector elements, and line 702 corresponds to the central pixel that records the line attenuation during gantry rotation. The line attenuation is weaker at adjacent detector elements, which may generate wire shading 709 around line 702.

[0073] In the line position graph 700, the wire shading 709 around line 702 may have a horizontal spread 710, which is based on multiple viewing angles in which attenuation is recorded by a single detector element. The wire shading 709 may also have a vertical spread 720, which is based on the number of pixels in which attenuation is recorded at a given viewing angle.

[0074] For example, the first dashed line 706 indicates that in the 200th frame, the greatest attenuation of X-rays due to the wire occurs at the detector element located at x position 350 on the y axis, corresponding to the first point 704. However, the X-rays are attenuated to a lesser extent by adjacent detector elements in the X direction (on the Y axis), such as the detector elements corresponding to the first adjacent point 711 and the second adjacent point 713.

[0075] Similarly, the second dashed line 712 indicates the possibility that a single detector element may detect wire attenuation across multiple adjacent frames / fields of view. As the position of the detector element relative to the wire changes due to the rotation of the gantry, the detector element may detect attenuation that increases to maximum attenuation and then decreases to zero. For example, the second dashed line 712 shows that the detector element at x position 1050 (on the y axis) records a first low attenuation in the 1650th frame corresponding to point 718, a second maximum attenuation detected in the 1700th frame corresponding to point 714 (e.g., on line 702), and a third low attenuation detected in the 1750th frame corresponding to point 719.

[0076] Figure 8 shows a fitting diagram 800 illustrating how the precise x-position of a detector element in a detector array is precisely determined from line 702 by fitting a function to the measurements taken at the detector element. For example, this function could be a Gaussian function, a parabolic function, or some other kind of function. Fitting diagram 800 includes a wire position graph 802 similar to wire position graph 700, where exemplary line 803 shows the wire position of a synogram-shaped wire phantom generated by wire attenuation measurements recorded at multiple detector elements / pixels. The x-position of pixels in the detector array is shown along the y-axis of graph 802, and multiple frames with the gantry rotated are shown on the x-axis as in Figure 7. A portion 812 of line 803 is shown in magnified diagram 804, and portion 812 shows the wire shading around line 803.

[0077] Graph 806 shows a plot 820 of measurements 822 collected at multiple pixels corresponding to a region 812 (indicated by a dashed line 805) centered on a pixel located at x-coordinate 300 on the detector array. The y-axis of graph 806 shows the signal intensity generated at the pixel, and the x-axis shows the x-coordinate of the pixel. Thus, each measurement shown in graph 806 represents the normalized signal intensity of 0.0 to 1.0 recorded at the corresponding pixel. At the pixel at x-position 300, the lowest signal intensity 824 (e.g., 0.3) is recorded because the X-rays are most attenuated by the wire. The low signal intensity measurements at positions 828 and 829 (e.g., 0.4) indicate wire shading, where the X-rays may be partially attenuated by the wire. Other adjacent pixels show less shading, but the shading does not exceed two pixels on either side of the pixel at x-coordinate 300.

[0078] To precisely identify the pixel position where X-ray attenuation due to the wire is maximum, the parabolic function 826 can be fitted to the measured value 822. Since the wire thickness (e.g., diameter) may exceed the transverse dimension of the detector element (e.g., several times greater), multiple detector elements may record high levels of wire attenuation. Using the parabolic function 826, a single detector element (e.g., pixel position) with maximum wire attenuation can be selected. Using a wire thicker than the transverse dimension of the detector element can improve the accuracy of pixel positioning compared to other wire phantoms containing thinner wires. For example, alternative wire phantoms using thinner wires may produce mismatched or missing signals as the X-ray beam scans the detector array. Conversely, using a wire that is too thick can lead to excessive shielding of the detector element, reducing the accuracy of pixel positioning. In various embodiments, the wire thickness is selected based on the dimensions and characteristics of the CT system being calibrated. For example, in one embodiment, the selected thickness may be a function of a first distance between adjacent detector elements (e.g., detector pitch), the size of the focal spot of the CT system, and a second distance between the focal spot and the detector elements. In other embodiments, other or different variables may be considered.

[0079] Attenuated signal-weighted averaging may not provide the necessary accuracy for the centroid of the wire position due to measurement variability resulting from limitations in X-ray count statistics. Exemplary graph 806 shows parabolic function fitting to reduce statistical variability or inter-measurement variability. Exemplary graph 806 shows pixel centroid calculation by fitting to the pixel direction, but depending on the final fitting model, it is possible to obtain the frame by fitting to the frame direction.

[0080] After selecting a single detector element that maximizes wire attenuation, the position of the single detector element relative to the wire (e.g., a known position) can be measured using projection geometry. The measurement of the single detector position will be described later with reference to Figures 5A, 5B, and 9.

[0081] Figure 5A is a flowchart illustrating an exemplary method 500 for using calibration data to improve the quality of images reconstructed using a CT system, such as the CT imaging systems 100 and 200 described above. As previously stated, during the calibration of the CT system, a calibration vector is generated that includes the measurement position (or correction value) for each detector element of each detector array of the CT imaging system (e.g., detector arrays 108 and 400). Subsequently, when scanning a subject (e.g., a patient) using the CT system, the misalignment of the detector elements can be corrected by applying this calibration vector during image reconstruction. Specifically, projection data processing during image reconstruction depends on the precise position of each detector element. However, the design target position of the detector elements, provided by, for example, a detector design drawing based on the physical dimensions and characteristics of the CT imaging system, may differ from the actual measurement position of the detector elements. The measurement position is used for image reconstruction, not the design target position. By correcting for misalignment, the accuracy and image quality of the reconstructed image can be improved. Method 500 is stored as an instruction in non-temporary memory and executed by one or more processors in the computing device of the CT imaging system, such as the computing device 216 of the imaging system 200 in Figure 2.

[0082] Method 500 begins in 502 and includes performing calibration of one or more detector arrays of a CT imaging system using a wire phantom. Performing calibration of one or more detector arrays using a wire phantom will be described in more detail with reference to Figure 5B.

[0083] In step 504, method 500 includes storing the calibration vector generated during the calibration of the CT imaging system in the memory of the CT imaging system (e.g., the memory of the computing device 216 in Figure 2). This calibration vector is acquired and applied during the processing of projection data acquired through the CT imaging system until a new calibration vector is generated in a subsequent calibration.

[0084] In step 506, method 500 includes performing a scan on the subject. During the scan, projection data is acquired by the CT imaging system. However, the projection data may contain pixel-level inaccuracies due to misalignment of detector elements (e.g., detector element 202) positioned on the detector array of the CT imaging system.

[0085] In step 508, method 500 includes applying a calibration vector during processing of acquired projection data during image reconstruction. The calibration vector may include the measured position of each detector element in the detector array. During image reconstruction, the signal generated by each detector element is processed based on the design target position of that detector element in the detector array. If the actual (e.g., measured) position of a detector element in the detector array differs from the design target position, the quality of the resulting image may be degraded. Therefore, the measured position of the detector element stored in the calibration vector can be used instead of the design target position.

[0086] Alternatively, in some embodiments, the calibration vector may include position correction values ​​to compensate for misalignment of the detector elements, and each position of each detector element in the projection data is adjusted by applying the corresponding position correction value of the calibration vector. It should be noted that the calibration vector referred to herein should not be confused with other different calibration vectors that may be applied additionally, for example, to compensate for signal variations from (correctly aligned) detector elements.

[0087] In step 510, method 500 includes displaying the reconstructed image on a display device of the CT imaging system (e.g., display device 232 in Figure 2) and / or storing the reconstructed image in the memory of the CT imaging system, and method 500 ends.

[0088] Figure 5B shows Method 550, which illustrates an exemplary procedure for calibrating the detector array of a CT imaging system using a wire phantom. The various steps of Method 550 are stored as instructions in non-temporary memory and can be executed by one or more processors of the computing devices of the CT imaging system, such as the computing device 216 of the imaging system 200 in Figure 2. Some steps of Method 550 may not be executed by a computing device and may be performed manually, as described later.

[0089] Method 550 begins in 552 and includes setting a wire phantom in a fixed position on the table of the CT imaging system (e.g., table 114). The wire phantom can be set up manually, for example, by the operator of the CT imaging system. The wire phantom may be set up as described in relation to Figure 3B, that is, the wire phantom is attached to the edge or border of the table, and the wire of the wire phantom (e.g., wire 304) extends into the space between the detector array and the X-ray source, as described above in relation to Figure 3C. The fixed position of the wire may be set outside the field of view of the detector array. As an example, the wire phantom is set up on the table using a gantry horizontal / vertical laser so that the wire is 180 degrees and 27 cm below the gantry isocenter. A spirit level is used on the wire tube to adjust it to be as horizontal as possible with respect to the Z-axis of the CT imaging system. The center of the wire may be indicated as the 0 mm reference position on the Z-axis.

[0090] In some embodiments, Method 550 may include instructing an operator to move the table to a predetermined height and / or to a predetermined position along the Z-axis of the CT imaging system. For example, after the operator has attached the wire phantom to the end or edge of the table, the instructions may be provided via a display device of the CT imaging system (e.g., display device 232).

[0091] In step 554, method 550 includes determining whether the wire is verified to be straight (e.g., within the tolerance range for linearity). In various embodiments, the wire is verified to be straight based on input from the operator. If there is variability in linearity, the wire is not used to calibrate the detector array. For example, if the tolerance threshold is 30 micrometers, and any portion of the wire deviates from linearity by more than 30 micrometers, the wire is not considered straight and is not used to calibrate the detector array. If the wire does not deviate from linearity by more than 30 micrometers, the wire is confirmed to be straight and is used to calibrate the detector array. If the wire phantom is new or has not been recently tested, the linearity of the wire may be checked before proceeding with the calibration. For example, the linearity of the wire may be checked periodically, such as every six months or after a predetermined number of scans (e.g., 600 scans).

[0092] If it is determined in step 554 that the linearity of the wire has not been confirmed, method 550 proceeds to step 556. In 556, method 550 performs a linearity analysis of the wire. During the linearity analysis, the wire phantom is positioned at different locations along the z-axis and rotational scanning is performed. That is, between each rotational scan, the position of the wire phantom in the z-axis direction is adjusted in small increments, such as 5 mm. During each rotational scan, data may be collected from a few columns near the center of the detector array (e.g., 2-4 columns) and not from other columns of the detector array. The data collected from the few columns near the center is used to determine whether the wire is within the acceptable range of linearity.

[0093] For example, with the wire phantom placed on the table, the position of the table in the z-axis direction can be adjusted so that the rotation plane (e.g., imaging plane) in the x and y dimensions of the gantry intersects at a first point on the wire of the wire phantom. The rotation plane may include a line along the Y-axis of the CT imaging system between the X-ray source of the CT imaging system and the center point of the detector array (e.g., X-ray source 362 and center point 363 in Figure 3C) (e.g., dashed line 420 in Figure 4), and this line is perpendicular to the Z-axis. A first rotational scan can be performed to collect a first wire attenuation dataset from the central 2-4 columns of the detector array. Then, the table position can be adjusted by an increment to move to a second specific position, and a second rotational scan can be performed to collect a second wire attenuation dataset from the central 2-4 columns of the detector array. Then, the table position can be adjusted by an increment to move to a third specific point, and a third rotational scan can be performed to collect a third wire attenuation dataset. This operation is repeated until data is collected at multiple desired wire positions along the z-axis.

[0094] For example, by adjusting the table so that the gantry's imaging plane intersects the wire at a position -55 mm relative to the wire's center (the 0 position), a total of 23 scans can be performed by adjusting the table along the z-axis in 5 mm increments until the position reaches 55 mm relative to the 0 position. 55 mm may be sufficient to cover the imaging field along the z-axis.

[0095] Referring briefly to Figure 6, a wire phantom positioning diagram 600 is shown, which illustrates the position of the wire phantom 605 at three different time points during wire attenuation data acquisition according to one embodiment. The wire phantom 605 is connected to a table mount 606 (e.g., table mount 320) which is connected to a table 608 (e.g., table 114).

[0096] At the first time point 601, the wire phantom 605 is positioned such that the XY rotation plane of the gantry, indicated by the dotted line 607, intersects with the first point 614 of the wire 604 of the wire phantom 605. The imaging plane of the gantry is perpendicular to the z-axis, indicated by the arrow 650 and the reference axis 690, and includes the X-ray source 620 located on the first side of the gantry, the center point 612 of the detector array 610 located on the second side (opposite side) of the gantry, and the isocenter point 611 on which the gantry rotates. The wire phantom 605 is offset from the isocenter point 611, and as the X-ray source 620 and the detector array 610 rotate around the isocenter point 611, the distance 615 between the wire 604 and the detector array 610 changes. The first point 614 is the center point of the wire 604 and may be set as a landmark as the 0 mm reference point of the wire 604. At the first time point 601, wire 604 is located within the field of view (FOV) of the detector array 610.

[0097] At the second time point 602, the position of the wire phantom 605 in the z-axis direction is shifted in the first positive direction indicated by the first arrow 622. The wire phantom 605 is positioned such that the imaging plane, indicated by the dotted line 607, intersects with the wire 604 at a second point 616 on the wire 604 of the wire phantom 605. The second point 616 may be at the 55 mm reference point of the wire 604 (for example, 55 mm in the positive direction from the first point 614 (0 mm)). At the second time point 602, the wire 604 is located partially outside the FOV (field of view) of the detector array 610.

[0098] At the third time point 603, the position of the wire phantom 605 in the z-axis direction is shifted in the second negative direction indicated by the second arrow 624. The wire phantom 605 is positioned such that the imaging plane, indicated by the dotted line 607, intersects wire 604 at a third point 618 on wire 604 of the wire phantom 605. The third point 618 may be at the -55 mm reference point of wire 604 (for example, 55 mm in the negative direction from the first point 614). At the third time point 603, wire 604 is located partially outside the FOV (field of view) of the detector array 610.

[0099] To determine the linearity of wire 604, data is collected in multiple steps, such as 5 mm intervals, between the first point 614 and the third point 618, as described above. By collecting and comparing data at multiple steps, the linearity of wire 604 can be precisely determined. For example, if the first wire attenuation dataset collected at the second time point 602 indicates the first position of the first part of wire 604, and the second wire attenuation dataset collected at the third time point 603 indicates the second position of the second part of wire 604, the deviation between the first and second positions indicates that the first part is not aligned with the second part, and thus it can be inferred that wire 604 is not straight. If this deviation is less than a threshold deviation (e.g., 30 micrometers), wire 604 is considered straight.

[0100] Returning to method 550, in step 558, method 550 includes determining whether the wire is straight, following the procedure described above with respect to Figure 6. If it is determined in step 558 that the wire is not straight, method 550 proceeds to step 560. In step 560, method 550 includes displaying instructions for fixing or replacing the wire on a display device for the operator, and method 550 returns to step 556. If it is determined in step 558 that the wire is straight, method 550 proceeds to step 562.

[0101] In step 562, method 550 performs an angle alignment analysis of the wire to determine the alignment of the wire with respect to the z-axis of the CT imaging system on which the table is aligned. For example, the wire is considered aligned with the z-axis if it deviates from parallelism with the z-axis by less than a threshold deviation. For example, the threshold deviation can be 3 milliradians (3 mrad). That is, if the wire deviates from parallelism with the z-axis by more than 3 milliradians, the wire can be adjusted using adjustment tilt screws (for example, tilt screws 326 and 332 in Figure 3A), and the collection and analysis of alignment data can be repeated until less than 3 milliradians is achieved, as described in the next section.

[0102] A second set of rotational scans can be performed to perform wire alignment analysis. The second set of rotational scans can be performed in the same manner as described above in relation to Figure 6, except that fewer scans can be performed because the wire is known to be straight. In one embodiment, two wire alignment scans may be performed. A first alignment scan of the wire phantom can be performed by positioning the wire phantom so that the image plane intersects the wire at a first distance (e.g., 0 mm) in a first direction (e.g., arrow 622 in Figure 6) from the wire's central reference point. A second wire alignment scan of the wire phantom can be performed by positioning the wire phantom so that the imaging plane intersects the wire at a second distance from the wire's central reference point in a second opposite direction (e.g., arrow 624). The second distance may be equal to the first distance. The first and second distances may be separated by a threshold distance. For example, the threshold distance may be 80 mm.

[0103] For example, both the first and second distances may be 40 mm. The table may initially be adjusted to position the wire so that the imaging plane intersects the wire at a position 40 mm from the wire's central reference point in order to perform the first rotational scan. The table is then adjusted to position the wire so that the imaging plane intersects the wire at a position -40 mm from the wire's central reference point, and the second rotational scan is performed. In each of the first and second rotational scans, wire attenuation data is acquired in the 2nd to 4th columns from the center of the detector elements of the detector array. Since the wire has already been confirmed to be straight, performing the angle adjustment analysis may be faster than performing the linearity analysis.

[0104] By collecting and comparing data from a first rotational scan and a second rotational scan, the angular alignment of wire 604 with respect to the z-axis can be precisely determined. For example, if a first wire attenuation dataset collected during the first rotational scan indicates a first position of wire 604, and a second wire attenuation dataset collected during the second rotational scan indicates a second position of wire 604, the deviation between the first and second positions may indicate that the wire is not aligned. If the deviation is less than a threshold deviation (e.g., 3 mrad), the wire is considered aligned with the Z-axis.

[0105] In step 564, method 550 determines whether the wire is aligned with the z-axis according to the procedure described above. If it is determined that the wire is not aligned with the z-axis (for example, if the deviation exceeds a threshold deviation), method 550 proceeds to step 566. In step 566, method 550 includes displaying instructions on a display device for readjusting the wire. In various embodiments, readjusting the wire may be performed by an operator by adjusting one or more inclined screws on the wire phantom. For example, a vertical inclined screw located in the phantom holder of the wire phantom (e.g., inclined screw 326 on phantom holder 323) adjusts the position of the wire relative to the Y-axis, and a horizontal inclined screw (e.g., inclined screw 332 on phantom holder 323) adjusts the position of the wire relative to the X-axis. After readjusting the wire, method 550 returns to 562 and runs the wire angle adjustment analysis again. In some cases, the wire is readjusted and the wire angle adjustment analysis is run multiple times to ensure that the wire is properly aligned with the Z-axis.

[0106] If it is determined in step 564 that the wire is aligned with the z-axis, method 550 proceeds to 568. In step 568, method 550 includes performing a calibration scan to measure the precise position of each individual detector element (detector element 202) of the detector array relative to the wire. Since the position of the wire is known and fixed, a full rotation can be performed, similar to the methods described above with reference to Figures 7 and 8, a function can be fitted to the synogram generated by the projection data, and the precise position of each individual detector element can be measured using projection geometry based on the physical properties of the CT system.

[0107] Referring to Figure 9, projection geometry figure 900 shows a plurality of variables used to calculate the position of the wire. Projection geometry figure 900 shows an exemplary CT system 902 (e.g., CT system 100 or imaging system 200) including an X-ray source 904 and a detector array 906 (which may be a non-limiting example of the detector array 400 in Figure 4). The X-ray source 904 and the detector array 906 may be connected to a gantry (e.g., gantry 102). The gantry may be connected to a gantry (e.g., gantry 102) that rotates along direction 901 about an isocenter (point) 914, where the isocenter 914 is located midway between the center point 907 of the X-ray source 904 and the detector array 906 along the isocenter line 905. The detector array 906 includes a plurality of detector modules 908, each detector module 908 containing a plurality of pixels 912. The pixels 912 may be organized into slices or chiclets 910. Each pixel 912 in the detector array 906 is referenced by the distance 909 from the center point 907 along the detector array 906 in the x direction, and by the row number of the pixel 912 in the z direction, based on the reference axis 990. The wires of the wire phantom are positioned at wire positions 916 in the CT system 902.

[0108] Figure 9 shows the CT system at a point when the gantry has rotated from its initial position (indicated by line 926) by a rotation angle 922(β) of the gantry relative to line 926. The wire position 916 (relative to the X-ray source 904 and / or detector array 906) is measured based on the distance R (indicated by line 917) between the wire position 916 and the isocenter 914 and the angle 918(φ) between line 917 and line 926.

[0109] At the time shown in Figure 9, the X-ray beam emitted from the X-ray source 904 is detected by the detector array 906. However, pixel 920 may not detect the X-ray beam in the trajectory indicated by line 919, and this beam collides with the wire at wire position 916. Line 919 makes an angle 924(γ) with respect to the equicenter line 905. Therefore, the angular position γ of pixel 920 can be expressed as a function of its position relative to the equicenter line 905 based on the gantry rotation angle β. Here, R and φ are the wire positions measured in the wire alignment step described above. R is the wire distance from the isocenter, and φ is the wire angle from the isocenter line 905. SID is the distance from source 904 to isocenter 914, which is known by design. β922 is the gantry rotation angle with respect to the gantry vertical Y-axis 926.

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[0110] In step 570, method 500 optionally includes generating alignment correction values ​​from the measurement position of the detector element. Here, the alignment correction values ​​are calculated based on the difference between the measurement position of the detector element and the design target position.

[0111] In step 572, method 500 includes saving the measured positions (or alignment correction values) of the detector elements in a calibration vector for use in subsequent scans of the subject. This completes method 550. In other words, a calibration vector is generated that includes the measured positions of each detector element, or correction values ​​indicating adjustments to be made to the positions of the detector elements to compensate for detected and quantified misalignments. This calibration vector is used by method 500 in Figure 5A to improve the quality of the reconstructed image of the subject in subsequent scans, as described above.

[0112] Therefore, a method is provided for correcting misalignment of detector elements in a CT system's detector array. This method can be used when mechanical calibration techniques are not applicable due to the size of the detector elements. Unlike other wire phantoms, this method relies on a wire phantom containing wires thicker than the detector elements, which can lead to discrepancies in detector readings. In the first step, the wire phantom is placed on the table of the CT system, and the linearity and tilt angle of the wires are verified according to the procedure described herein. After the linearity and correct alignment of the wires are confirmed, the position of each detector element in the detector array is measured relative to the wires. The measured positions are stored in a calibration vector and applied to correct misalignment during subsequent scans of the subject and during image reconstruction.

[0113] By using the measured positions of the detector elements rather than the target positions based on the detector array design model, positional displacement of the detector elements during scanning of the subject can be corrected, resulting in improved image quality of the resulting reconstructed images. The advantage of using measured detector element positions is that there is no need to rely on mechanical alignment techniques for adjusting the position of the detector elements. As a result, this method can be applied to detector arrays containing detector elements smaller than those that can be adjusted by mechanical alignment techniques. Furthermore, it can reduce the calibration time, resource allocation, and cost of the CT system, thereby improving the efficiency of the CT system. This improves the operability of the CT system, reduces downtime, and improves processing speed and accuracy during calibration using the CT system. In addition, applying the calibration method described herein can enable the generation of high-quality images by the CT system, potentially leading to improved diagnostic success rates and better patient outcomes.

[0114] The technical benefit of using a wire phantom to calibrate the position of detector elements within the detector array of a CT system is that it can improve the quality of images reconstructed using the CT system.

[0115] This disclosure also provides a means for supporting a wire phantom assembly for calibrating a computed tomography (CT) system. The wire phantom assembly includes a wire phantom containing a wire mounted in a tube, and a phantom holder configured to support the wire phantom. The phantom holder is mountable to a table of the CT system, and the linearity of the wire in the tube is maintained by applying tension to the wire between a first spherical swage end connected to a first end of the wire phantom and a second spherical swage end connected to a second end (opposite side) of the wire phantom. In a first embodiment of the system, the first spherical swage end is fitted to a free-floating end connected via a spring to a first end cap of the tube at the first end, the spring generating tension. In a second embodiment of the system (optionally including the first embodiment), the first end coil of the spring is connected to the end via a first pin passing through a hole in the end. In a third embodiment of the system, which optionally includes either one or both of the first and second embodiments, the first end cap comprises a first cylindrical portion having a first diameter equal to or greater than the diameter of the tube that seals the first end cap to the tube, a second cylindrical portion having a second diameter, and notches provided on opposing sides of the second cylindrical portion, with a saddle portion of the second cylindrical portion formed between the notches. In a fourth embodiment of the system, which optionally includes one or more or all of the first to third embodiments, the opposing end coils of the spring are coupled to the first end cap via a second pin, the first side of the second pin fitted into a first recess on the first outer surface of the first saddle portion of the first end cap, and the second side of the second pin fitted into a second recess on the second outer surface of the second saddle portion of the first end cap. In the fifth embodiment of the system, which optionally includes one or more or all of the first to fourth embodiments, the second pin has a first circumferential end with a reduced diameter that fits into the first recess and a second circumferential end with a reduced diameter that fits into the second recess.In the sixth embodiment of the system, which optionally includes one or more or all of the first to fifth embodiments, the system further includes: a cylindrical cap having an inner diameter equal to that of the second cylindrical portion, which is slidably inserted onto the second cylindrical portion to cover and protect the joint between the wire and the first end cap. In the seventh embodiment of the system, which optionally includes one or more or all of the first to sixth embodiments, the second spherical swage end is fitted into the hollow threaded portion of a bolt that is bolted to the center point of the inner circumferential surface of the second end cap of the tube at the second end of the tube. In the eighth embodiment of the system, which optionally includes one or more or all of the first to seventh embodiments, the hollow threaded portion of the bolt is provided with a first cylindrical chamber coaxially positioned along the central axis of the bolt, the diameter of which is greater than the diameter of the spherical portion of the second spherical swage end, and also has a second cylindrical chamber coaxially positioned along the central axis of the bolt and extending from the first cylindrical chamber toward the bolt head, the diameter of which is greater than the shank diameter of the second spherical swage end but smaller than the diameter of the spherical portion. In the ninth embodiment of the system, which optionally includes one or more or all of the first to eighth embodiments, the bolt head and hollow threaded portion are provided with slots that extend to the center of the bolt and open into the first cylindrical chamber and the second cylindrical chamber. This secures the wire within the bolt such that the spherical portion of the second spherical swage end is inserted into the first cylindrical chamber, where the end end is at the end of the threaded portion, while the shank is inserted into the second cylindrical chamber. This causes the second spherical swage end to contact the lip between the first and second cylindrical chambers when tension is applied to the wire. In the tenth embodiment of the system, one or more or all of the first to ninth embodiments are optionally included, and the wire is a braided stainless steel cable. In the eleventh embodiment of the system, one or more or all of the first to tenth embodiments are optionally included, and the phantom holder is configured to be secured to a table via a clamp connected to a cradle mounted on the back of the phantom holder.The clamp includes a knob and a threaded portion that is inserted into a hole in a bearing plate connected to the upper end of the phantom holder. When rotated by the knob, it applies force to the lower part of the cradle, increasing the pressure between the lower bottom surface and the upper end of the table. In a twelfth embodiment of the system, which optionally includes one or more or all of the first to eleventh embodiments, the flange portion of the cradle is attached to the rear via a plurality of bolts, and the bearing plate is attached to the upper end of the phantom holder via a plurality of screws. In a thirteenth embodiment of the system, which optionally includes one or more or all of the first to twelfth embodiments, the cradle is manufactured from a material that deforms flexibly under pressure, and the pressure between the lower bottom surface and the upper end surface of the table results from the flexible deformation of the cradle due to the force of the threaded portion of the clamp. In a fourteenth embodiment of the system, which optionally includes one or more or all of the first to thirteenth embodiments, the support plate is extended to include a handle portion having a hole into which a human hand can be inserted, and the handle portion is configured to allow the wire phantom assembly to be moved, transported, or placed on the table manually. This hole is located on the opposite side of the wire phantom assembly's clamp and cradle, and because the lifting point of the wire phantom assembly is close to its center of gravity, the wire phantom assembly remains horizontal even when lifted by the handle.

[0116] The Disclosure further provides support for a computed tomography (CT) system comprising a processor and non-temporary memory containing instructions that cause the processor to perform the following actions at runtime: perform a first rotational scanning series of the wire phantom to determine the linearity of the wires of the wire phantom; perform a second rotational scanning series of the wire phantom to determine the inclination angle of the wires; if the linearity of the wires is within a first threshold deviation and the inclination angle of the wires is within a second threshold deviation, measure the position of each detector element of the detector array of the CT system relative to the position of the wires during a calibration scan performed using the CT system; and during subsequent scans performed using the CT system, apply the measured positions of each detector element when reconstructing images from projection data acquired through the CT system, and display the reconstructed image on the display device of the CT system. Here, the linearity of the wires is maintained within a first threshold deviation by the first spherical swage end of the wire being connected via a spring to a free end cap at the first end of the tube of the wire phantom, and the second spherical swage end being fitted into the hollow thread of a bolt, which is bolted to the center of the tube of the wire phantom. The wire is maintained by applying tension between a first floating end portion, which is connected via a spring to a first end cap at the first end of the wire phantom, and a second spherical swaged end portion, which is fitted into the hollow threaded portion of a bolt fastened with a bolt to the center point of the inner circumferential surface of the second end cap at the opposing second end of the wire phantom. In the first embodiment of this system, the phantom holder is configured to be fixed to the table via a clamp connected to a cradle mounted on the back of the phantom holder. This clamp has a knob and a threaded portion that is inserted into a hole in a bearing plate connected to the upper end of the phantom holder, and by rotating the knob, force is applied to the lower part of the cradle, increasing the pressure between the lower bottom surface and the upper end of the table. This pressure is generated by the elastic deformation of the cradle due to the force from the threaded portion of the clamp. In the second embodiment of this system (optionally including the first embodiment), the bearing plate is extended and includes a handle portion with a hole into which a human hand can be inserted.This handle section is configured to allow the wire phantom assembly to be moved, transported, or placed on a table manually. The hole is located on the opposite side of the wire phantom assembly's clamp and cradle, and the lifting point of the wire phantom assembly is close to its center of gravity, so the wire phantom assembly remains horizontal even when lifted by the handle section.

[0117] This disclosure further provides support for a method for computed tomography (CT) systems. The method includes: during calibration of a CT system: measuring the position of detector elements of the detector array of the CT system using the wire of a wire phantom connected to the table of the CT system. during rotational scanning performed using the CT system, and during subsequent scanning performed on a subject using the CT system: when reconstructing an image from projection data acquired via the CT system, applying the measured position rather than the design target position of the detector elements, and displaying the reconstructed image on the display device of the CT system. The wire is held linear and centrally within the tube of the wire phantom by a first spherical swaged end of the wire connected to a free-floating end connected to a first end cap of the tube via a tension-providing spring, and a second spherical swaged end fitted to a hollow bolt connected to the center point of a second opposing end cap of the tube. In a first embodiment of this method, the wire phantom is clamped to a table via a clamp connected to a cradle mounted on a phantom holder of the wire phantom. The clamp includes a knob and a threaded portion that is inserted into a hole in the bearing plate of the phantom holder. When rotated by the knob, it applies force to the cradle, increasing the pressure between the bottom surface of the cradle and the top edge of the table.

[0118] When introducing elements of the various embodiments described herein, the articles "a," "an," and "the" indicate the presence of one or more elements. Furthermore, terms such as "first," "second," etc., are used simply to distinguish elements, not to indicate order, quantity, or importance. Terms such as "include," "contain," and "have" are comprehensive, meaning that additional elements may exist beyond those described. Where terms such as "connected" and "combined" are used herein, the connection or combination of one object (e.g., material, element, structure, member, etc.) to another object does not depend on whether the object is directly connected or combined with the other object, or whether there are one or more intervening objects between them. Moreover, references to "one embodiment" or "embodiment" in this specification should not be interpreted as excluding the existence of additional embodiments incorporating the described features.

[0119] Further aspects of the present invention are provided by the subject matter of the following clauses. [Embodiment 1] A wire phantom assembly for calibrating a computed tomography (CT) system, A wire phantom including a wire mounted in a tube, A phantom holder configured to support the wire phantom, the phantom holder mountable on a table of the CT system, A wire phantom assembly, including, wherein the straightness of the wire in the tube is maintained by a tension on the wire between a first spherical swage-end termination of the wire coupled to a first end of the wire phantom, and a second spherical swage-end termination coupled to a second, opposite end of the wire phantom. [Embodiment 2] The wire phantom assembly according to any of the preceding embodiments, wherein the first spherical swage-end termination is fitted into a free-floating termination part that is coupled to a first end cap of the tube at the first end via a spring, the spring generating the tension. [Embodiment 3] A wire phantom assembly according to any of the preceding embodiments, wherein a first end coil of the spring is coupled to the termination part via a first pin extending through a hole in the termination part. [Embodiment 4] The wire phantom assembly according to any prior embodiment, wherein the first end cap includes a first cylindrical portion having a first diameter equal to or greater than the diameter of the tube that seals the first end cap against the tube, and a second cylindrical portion having a second diameter and cutaway sections on opposing sides of the second cylindrical portion that create saddle portions between the cutaway sections. [Embodiment 5] A wire phantom assembly according to any of the preceding embodiments, wherein a second, opposing end coil of the spring is coupled to the first end cap via a second pin, a first side of the second pin seated in a first recessed portion of a first outer surface of a first saddle portion of the first end cap, and a second side of the second pin seated in a second recessed portion of a second outer surface of a second saddle portion of the first end cap. [Embodiment 6] The wire phantom assembly according to any of the preceding embodiments, wherein the second pin has a first circumferential end portion with a reduced diameter that is seated in the first recessed portion, and a second circumferential end portion with a reduced diameter that is seated in the second recessed portion. [Embodiment 7] Furthermore, the wire phantom assembly according to any of the preceding embodiments includes a cylindrical cap having the same inner diameter as the second cylindrical portion, the cylindrical cap being slidably inserted over the second cylindrical portion to cover and protect the coupling of the wire to the first end cap. [Embodiment 8] The wire phantom assembly according to any of the preceding embodiments, wherein the second spherical swage-end termination is fitted in a hollow threaded portion of a bolt that is bolted to a center point of an inner circular surface of a second end cap of the tube at the second end of the tube. [Embodiment 9] The hollow threaded portion of the bolt includes a first cylindrical chamber coaxially aligned around the central axis of the bolt with a first diameter greater than the diameter of a spherical portion of the second spherical swage-end termination, and a second cylindrical chamber coaxially aligned around the central axis that extends from the first cylindrical chamber toward a head portion of the bolt, the second cylindrical chamber having a second diameter greater than the shank diameter of the second spherical swage-end termination, but less than the diameter of the spherical portion, as described in any of the preceding embodiments. [Embodiment 10] Both the head portion and the hollow threaded portion of the bolt have a slot that extends into the center of the bolt, opening into the first cylindrical chamber and the second cylindrical chamber, which allows the wire to be inserted laterally into the bolt as the spherical portion of the second spherical swage-end termination is inserted into the first cylindrical chamber at an end of the threaded portion, with the shank inserting into the second cylindrical chamber, so that when tension is applied to the wire, the second spherical swage-end termination abuts against a rib between the first cylindrical chamber and the second cylindrical chamber, fixing the wire inside the bolt. A wire phantom assembly as described in any of the preceding embodiments, between the first cylindrical chamber and the second cylindrical chamber to secure the wire within the bolt when tension is applied to the wire. [Embodiment 11] The wire is a braided stainless steel cable, as described in any of the preceding embodiments of the wire phantom assembly. [Embodiment 12] The phantom holder is configured to be secured to the table via a clamp coupled to a cradle attached to a back surface of the phantom holder, the clamp including a knob and a threaded portion that is inserted through a hole in a bearing plate coupled to a top edge of the phantom holder that, when rotated via the knob, exerts a force on a lower portion of the cradle that increases a pressure between a bottom surface of the lower portion and an upper edge of the table, as described in any prior embodiment of the wire phantom assembly. [Embodiment 13] A wire phantom assembly according to any of the preceding embodiments, wherein a flange portion of the cradle is bolted to the back surface via a plurality of bolts, and the bearing plate is attached to the top edge of the phantom holder via a plurality of screws. [Embodiment 14] The wire phantom assembly according to any of the preceding embodiments, wherein the cradle is manufactured from a material that is flexibly deformed under pressure, and the pressure between the bottom surface of the lower portion and the upper edge of the table is generated as a result of the force exerted by the threaded portion of the clamp acting on the cradle and causing it to deform flexibly. [Embodiment 15] The wire phantom assembly according to any of the preceding embodiments, wherein the bearing plate is extended to include a handle portion having a hole into which a person's hand may be inserted, the handle portion configured to allow wire phantom assembly to be manually moved, carried, or mounted on the table, the hole positioned on an opposite side of the wire phantom assembly from the clamp and the cradle with a lift point of the wire phantom assembly close to a center of gravity of the wire phantom assembly, and the wire phantom assembly remains level when lifted by the handle portion. [Embodiment 16] A computed tomography (CT) system comprising a processor and a non-transitory memory including instructions that, when executed, cause the processor to perform multiple operations. The aforementioned multiple operations are, The steps include performing a first series of rotational scans of a wire phantom to determine the straightness of a wire of the wire phantom, The steps include performing a second series of rotational scans of the wire phantom to determine an angle of inclination of the wire, In response to the linearity of the wire being within a first threshold deviation and the angle of inclination of the wire being within a second threshold deviation, During a calibration scan performed using the CT system, The steps include: measuring the position of each detector element of the detector array of the CT system with respect to the position of the wire; During a subsequent scan performed using the CT system, The steps include: applying the measured position of each detector element during image reconstruction of projection data acquired via the CT system; The steps include: displaying the reconstructed image on a display device of the CT system; Includes, The straightness of the wire is maintained within the first threshold deviation by applying tension to the wire between a first spherical swage-end termination of the wire seated in a free-floating termination part coupled to a first end cap at a first end of a tube of the wire phantom via a spring, and a second spherical swage-end termination seated in a hollow threaded portion of a bolt bolted to the center point of an inner circular surface of a second end cap of the tube at a second, opposite end of the wire phantom. Phantom), wire phantom assembly. [Embodiment 17] The phantom holder is configured to be secured to the table via a clamp coupled to a cradle attached to the back surface of the phantom holder, the clamp including a knob and a threaded portion that is inserted through a hole in a bearing plate coupled to the top edge of the phantom holder, and when rotated by the knob, exerts a force on a lower portion of the cradle that increases a pressure between the lower portion and the top edge of the table, the pressure generated as a result of the cradle elastically deforming due to the force exerted by the threaded portion of the clamp A wire phantom assembly (clamp) as described in any of the preceding embodiments. [Embodiment 18] The wire phantom assembly according to any of the preceding embodiments, wherein the bearing plate is extended to include a handle portion having a hole into which a person's hand may be inserted, the handle portion configured to allow wire phantom assembly to be manually moved, carried, or mounted on the table, the hole positioned on an opposite side of the wire phantom assembly from the clamp and the cradle with a lift point of the wire phantom assembly close to a center of gravity of the wire phantom assembly such that the wire phantom assembly remains level when lifted by the handle portion. [Embodiment 19] A method for a computed tomography (CT) system, During the calibration of the CT system, The procedure involves measuring the position of a detector element of a detector array of the CT system using a wire of a wire phantom coupled to a table of the CT system, during a rotational scan performed using the CT system. During a subsequent scan performed on a subject using the CT system, In the image reconstruction of projection data acquired by the CT system, the step of applying the measured position of the detector element rather than the design target position of the detector element is performed. The steps include: displaying the reconstructed image on a display device of the CT system; Includes, The wire is maintained straight and centered within the tube of the wire phantom by a first spherical swage-end termination of the wire connected to a free-floating termination part connected to a first end cap of the tube via a spring that provides tension, and a second spherical swage-end termination fitted in a hollow bolt connected to a center point of a second, opposing end cap of the tube, in a method. [Embodiment 20] The wire phantom is clamped to the table via a clamp coupled to a cradle attached to a phantom holder of the wire phantom, the clamp including a knob and a threaded portion that is inserted through a hole in a bearing plate of the phantom holder that, when rotated via the knob, exerts a force on the cradle that increases a pressure between a bottom surface of the cradle and an upper edge of the table, the method according to any prior embodiment.

[0120] In addition to the modifications described herein, a person skilled in the art could devise numerous other variations and alternative configurations without departing from the spirit and scope of this specification, and the invention described in the claims is intended to encompass such variations and configurations. Therefore, although the information described above is detailed in relation to what is currently considered the most practical and preferred aspect, it will be apparent to a person skilled in the art that numerous modifications are possible, including but not limited to form, function, method of operation and method of use, without departing from the principles and concepts described herein. Furthermore, the examples and embodiments used herein are for illustrative purposes only and should not be construed as restrictive in any sense. [Explanation of Symbols]

[0121] 100: Computed Tomography (CT) System 102: Gantry 104: X-ray Source 106: X-ray Beam 108: Detector Array 110: Image Processing Unit 112: Subject 114: Table 200: Imaging System 202: Detector Element 204: Subject 206: Rotation Center 208: Control Mechanism 210: X-ray Controller 212: Gantry Motor Controller 214: Data Acquisition System (DAS) 216: Computing Device 218: Mass Storage Device 220: Operator Console 224: Picture Archiving and Communication System (PACS) 226: Table Motor Controller 230: Image Reconstruction Device 232: Display / Display Device 300: Wire Phantom Assembly 301: Reference Axis 302: Wire Phantom 303: Termination 304: Wire 305: Length 306: Tube 307: Diameter 308: First end cap 309: Spring 312: Second end cap 314: First side 316: Second side 320: Table mount 322: Rubber shim 323: Phantom holder 324: First bolt 325: Distance 326: First wire phantom tilt adjustment screw 327: Different position 330: Second bolt 332: Second wire phantom tilt adjustment screw 334: Mounting surface 336: Base plate 340: Table mounting diagram 341: Reference axis 342: Table 347: First tilt screw 348: Bottom surface 349: Second tilt screw 362: X-ray source 363: Center point 364: Detector array 368: Detector element 370: Point 372: X-ray 380: Isocenter 382, 384: Arrows 400: Detector array 402: Detector module 404: Center point 406: Collimating blade / collimating plate 420: Dashed line 425: X-ray 440: Rail 450: Reference axis 600: Wire phantom positioning diagram 601: First time point 602: Second time point 603: Third time point 604: Wire 605: Wire phantom 606: Table mount 607: Dotted line 608: Table 611: Isocenter point 612: Center point 614: First point 615: Distance 616: Second point 618: Third point 620: X-ray source 622: First arrow 624: Second arrow 650: Arrow 700: Wire position graph702: Line 704: First point 705: Second point 706: First dashed line 709: Line shading 710: Horizontal spread 711: First adjacent point 712: Second dashed line 713: Second adjacent point 714, 718, 719: Point 720: Vertical spread 750: Upper region 751: Lower region 800: Fitting diagram 802: Wire position graph 803: Line 804: Magnified view 805: Dashed line 806: Graph 812: Part / region 820: Plot 822: Measurement 824: Lowest signal intensity 826: Parabola function 828, 829: Low signal intensity measurement 900: Projection geometry diagram 901: Direction 902: CT system 904: X-ray source 905: Isocenter line 906: Detector array 907: Center point 908: Detector module 910: Chiclet 912: Pixel 914: Isocenter 916: Wire position 917: Line 918: Angle 919: Line 920: Pixel 922: Gantry rotation angle β 924: Angle 926: Y-axis 990: Reference axis 1001: Tube 1002: Cable 1004: First end cap 1006: Second end cap 1008: First multiple fasteners 1010: Second multiple fasteners 1012: First spherical swage end 1013: Shank 1014: Second spherical swage end 1015: End 1016: Spring 1018: Pin 1040: Bolt 1050: First end 1052: Second end 1100: Perspective view 1102: Roll pin 1104: First end coil 1106: Second end coil 1120: Slot 1122: Wide section 1130: First width 1132: Second width 1134: Hole 1150: Concave periphery 1190: Direction 1192: Bidirectional arrow 1200: Side view 1202: Central axis 1204: First section 1206: Second section 1208, 1210: Length 1212: Diameter 1213: Length 1214: Thickness 1220: First concave surface 1222: Second concave surface 1230: Spherical section 1300: Spherical swage end 1301: Wire 1302: Shank 1303: Spherical part 1306: First diameter 1308: Second diameter 1312: Distance 1350: First end 1352: Second end 1400: Second perspective view 1404: Cap 1406, 1408: Notches1410, 1412: Saddle portion 1420: First circumferential end 1422: Second circumferential end 1430, 1432: Recess 1440, 1441: Outer surface 1450: First cylindrical portion 1451: Thickness 1452: Distance 1454: Second cylindrical portion 1456: Height 1457: Arrow 1460, 1462: Diameter 1500: Second perspective view 1502: Circular inner surface 1520: Spherical bolt 1601: Head 1602: Threaded portion 1604: Spherical portion 1612: Slot 1614: Shank portion 1620, 1622, 1624: Diameter 1630: First cylindrical chamber 1632: Second cylindrical chamber 1634: Lip 1660: End 1680: Arrow 1690: Center axis 1700: Perspective view 1701: Clamp 1702: Knob 1704: Threaded section 1706: Cradle 1708: Bearing plate 1712: Arrow 1720: Diameter 1722: Back view 1730: Bottom 1732: Flange section 1734: Bottom end 1736: Fastener / bolt 1738: Bottom surface 1740: Top surface 1742: Arrow 1750: Top surface 1752: Bottom surface 1760: Extended view 1762: Nut 1764: Pad 1766: Wall 1790: Arrow 1800: Split view 1802, 1804, 1806, 1808: Hole 1810: First guide 1812: Second guide 1814: First bolt 1816: Second bolt 1820, 1822: Shaft 1824: Recess 1900: Perspective view 1901, 1902, 1903: Screw 1906: First bushing 1907: Second bushing 1908, 1911, 1912, 1913, 1921, 1922, 1923: Hole 1925: Top end 1930: Extension core 2002: Handle section 2003: Enclosure section 2004: Hole

Claims

1. A wire phantom assembly (300) for calibrating a computed tomography (CT) system (100), A wire phantom (302) including a wire (304) attached inside a tube (306), A phantom holder (323) configured to support the wire phantom (302), wherein the phantom holder (323) is attachable to the table of the CT system (100), and the phantom holder (323) A wire phantom assembly (300) including, wherein the linearity of the wire (304) within the tube (306) is maintained by the tension between a first spherical swaged end (1012) of the wire (304) connected to a first end of the wire phantom and a second spherical swaged end (1014) connected to the second end on the opposite side of the wire phantom (302).

2. The wire phantom assembly (300) according to claim 1, wherein the first spherical swage end portion (1012) is fitted into a free-floating end portion (1015) which is connected via a spring (309) to a first end cap (308) of the tube (306) at the first end, and the spring (309) generates the tension.

3. The wire phantom assembly (300) according to claim 2, wherein the first end coil (1014) of the spring (309) is connected to the end portion (1015) via a first pin that passes through a hole in the end portion (1015).

4. The wire phantom assembly (300) according to claim 2, wherein the first end cap (308) includes a first cylindrical portion (1450) having a first diameter greater than or equal to the diameter of the tube (306) that seals the first end cap (308) to the tube (306), a second cylindrical portion (1454) having a second diameter, and the notches (1406) provided on opposing sides of the second cylindrical portion (1454) that form a plurality of saddle portions (1410) between the notches (1406) of the second cylindrical portion (1454).

5. The wire phantom assembly (300) according to claim 4, wherein the second opposing end coil of the spring (309) is connected to the first end cap (308) via a second pin, the first side of the second pin is fitted into a first recess on the first outer surface of the first saddle of the first end cap (308), and the second side of the second pin is fitted into a second recess on the second outer surface of the second saddle of the first end cap.

6. The wire phantom assembly (300) according to claim 5, wherein the second pin has a first circumferential end (1420) with a reduced diameter that fits into the first recess, and a second circumferential end (1422) with a reduced diameter that fits into the second recess.

7. The wire phantom assembly (300) according to claim 4, further comprising a cylindrical cap (1404) having the same inner diameter as the second cylindrical portion (1454), wherein the cylindrical cap (1404) is slidably inserted onto the second cylindrical portion (1454) to cover and protect the joint between the wire (304) and the first end cap (308).

8. The wire phantom assembly (300) according to claim 1, wherein the second spherical swage end portion (1014) is fitted onto the hollow threaded portion (1602) of a bolt (1040) which is fixed by the bolt (1040) to the center point of the inner circumferential surface of the second end cap (312) of the tube at the second end of the tube (306).

9. The wire phantom assembly (300) according to claim 8, wherein the hollow threaded portion (1602) of the bolt (1040) includes a first cylindrical chamber (1630) positioned coaxially with the central axis (1690) of the bolt (1040) and having a first diameter larger than the diameter of the spherical portion of the second spherical swage end (1014), and a second cylindrical chamber (1632) positioned coaxially with the central axis (1690) and extending from the first cylindrical chamber (1630) toward the head of the bolt (1040), wherein the second cylindrical chamber (1632) has a second diameter larger than the shank diameter of the second spherical swage end (1014) and smaller than the diameter of the spherical portion (1604).

10. Both the head (1601) and the hollow threaded portion (1602) of the bolt (1014) have slots that extend to the center of the bolt (1014) and open into the first cylindrical chamber (1630) and the second cylindrical chamber (1632), so that the spherical portion (1604) of the second spherical swage end (1014) is inserted into the first cylindrical chamber (1630) at the end of the threaded portion (1602). The wire phantom assembly (300) according to claim 9, wherein at times the wire (304) is inserted laterally into the bolt (1014), and thereby, when tension is applied to the wire (304), the second spherical swage end (1014) abuts against the lip (1140) between the first cylindrical chamber (1630) and the second cylindrical chamber (1632), thereby fixing the wire (304) inside the bolt (1014).

11. The wire phantom assembly (300) according to claim 1, wherein the wire (304) is a braided stainless steel cable.

12. The wire phantom assembly (300) according to claim 1, wherein the phantom holder (323) is configured to be fixed to the table via a clamp (1701) connected to a cradle (1706) attached to the back surface (1722) of the phantom holder (323), the clamp (1701) includes a knob (1702) and a threaded portion (1704) inserted into a hole in a bearing plate (1708) connected to the upper end of the phantom holder (323), and when rotated by the knob (1702), it applies force to the lower part (1730) of the cradle (1706), increasing the pressure between the bottom surface (1738) of the lower part (1730) and the upper end of the table.

13. The wire phantom assembly (300) according to claim 12, wherein the flange portion (1732) of the cradle (1706) is attached to the back surface (1722) via a plurality of bolts, and the bearing plate (1708) is attached to the upper end of the phantom holder (323) via a plurality of screws (1901, 1902, 1903).

14. The wire phantom assembly (300) according to claim 13, wherein the cradle (1706) is manufactured from a material that deforms flexibly under pressure, and the pressure between the lower bottom surface and the upper end of the table is generated as a result of the force from the threaded portion (1704) of the clamp (1701) acting on the cradle (1706) causing it to deform flexibly.

15. The wire phantom assembly (300) according to claim 12, wherein the bearing plate (1708) is extended to include a handle portion (2002) having a hole (2004) into which a human hand can be inserted, the handle portion (2002) is configured to allow the wire phantom assembly (300) to be moved, transported or placed on the table by hand, the hole (2004) is located on the opposite side of the wire phantom assembly (300) from the clamp (1701) and the cradle (1706), the lifting point of the wire phantom assembly (300) is positioned close to the center of gravity of the wire phantom assembly (300), and the wire phantom assembly (300) is configured to remain horizontal when lifted by the handle portion (2002).

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