Collimator Assembly for X-ray Detectors

Abstract

To provide an X-ray imaging system and a collimator assembly on an X-ray path between an X-ray source and an X-ray detector.SOLUTION: The X-ray detector comprises a plurality of detector modules arranged side by side and oriented towards the X-ray source, the detector modules being arranged side by side along a direction substantially orthogonal to a direction of incoming X-rays. The collimator assembly is based on a plurality of spaced collimator plates 71 arranged side by side in a direction coinciding with the direction of the detector modules at intervals. The collimator assembly further comprises a physically stabilizing lateral support structure 72 arranged in a lateral plane extending in a direction substantially orthogonal to the direction of incoming X-rays.SELECTED DRAWING: Figure 15

Description

[Technical Field]

[0001] The proposed technique relates to X-ray technology and X-ray imaging, and in particular to X-ray imaging systems such as computed tomography (CT) imaging systems.

[0002] Radiation imaging modalities, such as computed tomography (CT) imaging systems, have been used for many years in medical applications such as medical diagnosis and treatment.

[0003] X-ray imaging systems, such as CT imaging systems, typically include an X-ray source and an X-ray detector, which has multiple detector modules containing one or more detector elements for independently measuring X-ray intensities. The X-ray source emits X-rays, which pass through the subject or object being imaged and are received by the X-ray detector. The X-ray source and X-ray detector are typically arranged on a rotating member in a gantry to rotate around the subject or object. As the emitted X-rays pass through the subject or object, they are attenuated by the subject or object, and the resulting transmitted X-rays are measured by the detector. The measured data is used to reconstruct an image of the subject or object.

[0004] It may be useful to provide a brief overview of an exemplary, typical X-ray imaging system of the prior art with reference to FIG. 1A. In this exemplary embodiment, the X-ray imaging system 100 includes an X-ray source 10, an X-ray detector 20, and a coupled image processing system 30. In general, the X-ray detector 20 is configured to store radiation from the X-ray source 10, which is optionally focused by X-ray optics or a collimator and passes through an object, subject, or portion of the object or subject. The X-ray detector 20 can be connected to the image processing system 30 through suitable analog readout electronics that are at least partially integrated into the X-ray detector 20, and the image processing system 30 can perform image processing and / or image reconstruction. Optionally, a collimator assembly 70 can be positioned in the X-ray path between the X-ray source 10 and the X-ray detector 20.

[0005] For example, a conventional CT imaging system includes an X-ray source and an X-ray detector positioned to acquire projection images of a subject or object at different viewing angles covering a range of at least 180 degrees. This is most commonly achieved by mounting the source and detector on a support (e.g., a rotating member of a gantry) that can rotate around the subject or object. An image containing projections recorded on different detector elements for different viewing angles is called a sinogram. In the following, even though the detector is two-dimensional, the collection of projections recorded on different detector elements for different viewing angles will be referred to as a sinogram, and the sinogram will be considered a three-dimensional image.

[0006] FIG. 1B is a schematic diagram showing an example of the layout of a prior art X-ray imaging system, illustrating a projection line from an X-ray source through an object to an X-ray detector.

[0007] A further development of X-ray imaging is energy-resolved X-ray imaging (also called spectral X-ray imaging), in which X-ray transmission is measured at multiple different energy levels. This can be achieved by rapidly switching the source between two different emission spectra, by using two or more X-ray sources emitting different X-ray spectra, or by using an energy-discriminating detector that measures incident radiation at two or more energy levels. An example of such a detector is a multi-bin photon-counting detector, in which each recorded photon generates a current pulse that is compared to a set of thresholds to count the number of photons incident in each of several energy bins.

[0008] Many X-ray imaging systems include a post-collimator positioned in the X-ray path between the X-ray source and the X-ray detector, primarily to remove scattered X-ray photons. Preferably, the collimator assembly provides sufficient scatter removal while allowing sufficient detection efficiency, and is easily manufacturable.

[0009] There is a general need for improvements in the design and / or construction of collimator assemblies (particularly post-collimators) in x-ray imaging systems (such as CT imaging systems). Summary of the Invention

[0010] This Summary introduces concepts that are described in more detail in the Detailed Description. This Summary is not intended to identify essential features of the claimed subject matter, nor should it be used to limit the scope of the claimed subject matter.

[0011] A general object is to provide an improved collimator assembly for an X-ray imaging system. A specific object is to provide an improved X-ray imaging system. These and other objects are achieved by one or more embodiments of the present invention as defined by the claims.

[0012] According to a first aspect, there is provided an X-ray imaging system including an X-ray source, an X-ray detector, and a collimator assembly coupled to the X-ray detector. The X-ray detector includes a plurality of detector modules arranged side by side and directed toward the X-ray source, the detector modules arranged side by side along a direction substantially perpendicular to the direction of incident X-rays. The collimator assembly includes a plurality of collimator plates arranged at intervals, the collimator plates arranged side by side in a direction coinciding with the direction of the detector modules. The collimator assembly further includes side support structures arranged on sides extending in a direction substantially perpendicular to the direction of incident X-rays for physical stabilization.

[0013] In this way, the collimator is less susceptible to deformation caused by various forces that occur during operation of the x-ray imaging system (e.g., when performing a patient scan). Furthermore, the improved stiffness allows the use of collimator plates with a relatively large height in the direction of incident x-rays that still provide sufficient scatter rejection.

[0014] By way of example, the X-ray imaging system may be a rotational computed tomography (CT) system.

[0015] The proposed technology, as will be understood by reference to the description of the various exemplary embodiments, provides one or more of the following advantages for an X-ray imaging system including a collimator assembly: -Improved rigidity Reduced manufacturing complexity -Sufficient scatter removal - Reduced deformation during operation -Improved detection efficiency [Brief explanation of the drawings]

[0016] The embodiments, together with further objects and advantages of the embodiments, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which: [Figure 1A] 1 is a schematic diagram illustrating an embodiment of an overall X-ray imaging system. [Figure 1B] 1 is a schematic diagram illustrating an embodiment of an overall X-ray imaging system. [Figure 2] FIG. 1 is a schematic diagram illustrating another embodiment of an X-ray imaging system, such as a CT imaging system. [Figure 3] 1 is a schematic block diagram of a CT imaging system, with an X-ray imaging system as an exemplary embodiment; [Figure 4] FIG. 1 is a schematic diagram illustrating another embodiment of relevant components of an X-ray imaging system, such as a CT imaging system. [Figure 5] 1 is a schematic diagram of a photon counting circuit and / or device according to the prior art; [Figure 6] FIG. 1 is a schematic diagram illustrating an example of a solid-state detector module according to an exemplary embodiment. [Figure 7] FIG. 10 is a schematic diagram illustrating an example of a solid-state detector module according to another exemplary embodiment. [Figure 8A] FIG. 10 is a schematic diagram illustrating an example of a solid-state detector module according to yet another exemplary embodiment. [Figure 8B] FIG. 1 is a schematic diagram showing an example of a set of arrayed detector modules, each of which is a depth-separated detector module, with an application specific integrated circuit (ASIC) or corresponding circuitry located below the detector element as viewed from the direction of incident X-rays. [Figure 9] 1 is a schematic diagram showing an example of an overview of a CT imaging system. [Figure 10] FIG. 1 is a schematic diagram illustrating an example of the overall design of an X-ray source-detector system. [Figure 11A]1 is a schematic diagram illustrating an example of a detector-collimator assembly having a one-dimensional collimator assembly consisting of multiple collimator plates arranged in a line along the axis of rotation of the CT imaging system (also referred to as the z-direction), thereby defining a z-direction collimator. [Figure 11B] 1 is a schematic diagram illustrating an example of a detector-collimator assembly having a one-dimensional collimator assembly consisting of multiple collimator plates aligned in an angular direction (also designated x-direction) of the CT imaging system to define an x-direction collimator. [Figure 12] 1 is a schematic cross-sectional view illustrating an example of a detector-collimator assembly according to one embodiment. [Figure 13] FIG. 10 is a schematic cross-sectional view illustrating another example of a detector-collimator assembly according to an embodiment. [Figure 14] FIG. 10 is a schematic cross-sectional view illustrating yet another example of a detector-collimator assembly according to an embodiment. [Figure 15] FIG. 1 is a schematic perspective view showing an embodiment of a one-dimensional collimator assembly having side support structures for physical stabilization to improve the rigidity of the one-dimensional collimator assembly. [Figure 16] FIG. 1 is a schematic perspective view showing an example of a practical implementation of a one-dimensional collimator assembly. [Figure 17] 1 is a schematic perspective view showing a particular example of a practical implementation of a one-dimensional collimator assembly having a retaining plate on which the collimator plates are attached; FIG. [Figure 18A] FIG. 10 is a schematic perspective view showing another embodiment of a one-dimensional collimator assembly having side support structures for physical stabilization to improve the rigidity of the one-dimensional collimator assembly. [Figure 18B] FIG. 18B is a schematic diagram showing a cross section of a portion of the collimator assembly of FIG. 18A. [Figure 19A]FIG. 10 is a schematic perspective view showing yet another embodiment of a one-dimensional collimator assembly having side support structures for physical stabilization to improve the rigidity of the one-dimensional collimator assembly. [Figure 19B] 19B is a schematic diagram showing a cross section of a portion of the collimator assembly of FIG. 19A. FIG. [Figure 20] FIG. 10 is a schematic perspective view showing yet another embodiment of a one-dimensional collimator assembly having side support structures for physical stabilization to improve the rigidity of the one-dimensional collimator assembly. [Figure 21] FIG. 10 is a schematic perspective view showing another embodiment of a one-dimensional collimator assembly having side support structures for physical stabilization to improve the rigidity of the one-dimensional collimator assembly. [Figure 22] FIG. 10 is a schematic perspective view showing another alternative embodiment of a one-dimensional collimator assembly having side support structures for physical stabilization to improve the rigidity of the one-dimensional collimator assembly. DETAILED DESCRIPTION OF THE INVENTION

[0017] Embodiments of the present disclosure will now be described, by way of example only, with reference to the drawings in which:

[0018] For a better understanding, it is useful to follow with an introductory description of a non-limiting example of an overall X-ray imaging system in which data processing and data transmission according to the concepts of the present invention can be implemented.

[0019] 2 is a schematic diagram of an example of an X-ray imaging system 100 (e.g., a CT imaging system). The X-ray imaging system 100 includes an X-ray source 10 that emits X-rays, an X-ray detector 20 that has an X-ray detector that detects the X-rays after passing through an object, an analog processing circuit 25 that processes and digitizes raw electrical signals from the X-ray detector, a digital processing circuit 40 that performs further processing operations on the measurement data (e.g., correcting, temporarily storing, or filtering the measurement data), and a computer 50 that can store the processed data and perform further post-processing and / or image reconstruction. According to an exemplary embodiment, all or part of the analog processing circuit 25 may be implemented in the X-ray detector 20. The X-ray source and the X-ray detector may be coupled to a rotating member of a gantry 11 of the CT imaging system 100.

[0020] The entire x-ray detector may be considered the x-ray detector 20, or the x-ray detector 20 combined with the associated analog processing circuitry 25.

[0021] In communication with and electrically coupled to the analog processing circuitry 25 is an image processing system 30, which may include digital processing circuitry 40 and / or a computer 50, which may be configured to perform image reconstruction based on image data from the x-ray detector. Thus, the image processing system 30 may be considered the computer 50, or alternatively, a system combining the digital processing circuitry 40 and the computer 50, or may be considered the digital processing circuitry 40 itself, where the digital processing circuitry is dedicated to image processing and / or reconstruction.

[0022] One example of a commonly used X-ray imaging system is a CT imaging system, which may include an X-ray source or tube that produces a fan or cone beam of X-rays and an opposing array of X-ray detectors that measure the X-rays transmitted through the patient or object. The X-ray source or tube and X-ray detectors are mounted on a gantry 11 that rotates around the object being imaged.

[0023] FIG. 3 shows a schematic diagram of a CT imaging system 100 as an exemplary embodiment of an X-ray imaging system. The CT imaging system includes a computer 50 that receives commands and scanning parameters from an operator via an operator console 60, which may have a display 62 and some form of operator interface (e.g., a keyboard, mouse, joystick, touchscreen, or other input device). The computer 50 then uses the operator-supplied commands and parameters to provide control signals to an X-ray controller 41, a gantry controller 42, and a table controller 43. Specifically, the X-ray controller 41 provides power and timing signals to the X-ray source 10, which controls the emission of X-rays to an object or patient residing on a table 12. The gantry controller 42 controls the rotational speed and position of the gantry 11, which includes the X-ray source 10 and the X-ray detector 20. By way of example, the X-ray detector 20 may be a photon-counting X-ray detector. The table controller 43 controls and determines the position of the patient table 12 and the scan area on the patient. A detector controller 44 is also provided and is configured to control and / or receive data from the x-ray detector 20 .

[0024] In one embodiment, computer 50 also performs post-processing and image reconstruction of image data output from x-ray detector 20. As such, computer 50 corresponds to image processing system 30 as shown in Figures 1A and 2. An associated display 62 allows an operator to observe reconstructed images and other data from computer 50.

[0025] An X-ray source 10 disposed on a gantry 11 emits X-rays. An X-ray detector 20, which may be in the form of a photon-counting X-ray detector, detects the X-rays after they pass through an object or patient. The X-ray detector 20 may be formed, for example, by a plurality of pixels, also called sensors or detector elements, and associated processing circuitry (such as an application-specific integrated circuit (ASIC)) disposed on a detector module. Part of the analog processing may be implemented in the pixels, while the remaining processing is implemented, for example, in the ASIC. In one embodiment, the processing circuit (ASIC) digitizes the analog signals from the pixels. The processing circuit (ASIC) may include a digital processing unit, which may perform other processing operations on the measurement data (such as applying corrections, temporarily storing the measurement data, and / or filtering). During a scan to acquire X-ray projection data, the gantry and its mounted components rotate about an isocenter 13.

[0026] Modern X-ray detectors typically require the conversion of incident X-rays into electrons. This conversion is usually achieved by the photoelectric effect or Compton interaction, where the resulting electrons produce secondary visible light until they lose energy, which is then detected by a photosensitive material. Semiconductor-based detectors also exist, where the electrons generated by the X-rays create charge in the form of electron-hole pairs, which are collected by applying an electric field.

[0027] Some detectors operate in an energy-integrated mode, providing a signal integrated from many x-rays, with the output signal being proportional to the total energy deposited by the detected x-rays.

[0028] In the field of medical x-rays, x-ray detectors with photon counting capability and energy resolution have become common. Photon counting detectors have the advantage that, in principle, the energy of each x-ray can be measured, thereby providing additional information about the composition of the object. This information can be used to improve image quality and / or reduce radiation dose.

[0029] Typically, photon-counting X-ray detectors determine the energy of a photon by comparing the height of the electrical pulse generated by the photon's interaction with the detector material to a set of comparator voltages. These comparator voltages are also called energy thresholds. The analog voltage of the comparator is typically set by a digital-to-analog converter (DAC). The DAC converts the digital setting sent by the controller into an analog voltage that can be compared to the height of the photon pulse.

[0030] Photon-counting detectors count the number of photons that interact within the detector during a measurement period. A new photon is typically identified by an electrical pulse whose height exceeds the comparator voltage of at least one comparator. Once a photon is identified, the event is stored by incrementing a digital counter associated with that channel.

[0031] When multiple different thresholds are used, an energy-discriminating photon counting detector is obtained that can separate detected photons into energy bins corresponding to the various thresholds. This type of photon counting detector is sometimes called a multi-bin detector. In general, the energy information allows the creation of new types of images that can utilize new information and eliminate image artifacts that appear in prior art techniques. That is, in an energy-discriminating photon counting detector, the comparator has multiple programmable thresholds (T1 to T2) with programmable pulse heights. 1N) and classified according to pulse height, which is proportional to energy. That is, a photon counting detector that includes two or more comparators is referred to herein as a multi-bin photon counting detector. In a multi-bin photon counting detector, photon counts are stored in a set of counters (typically one counter for each energy threshold). For example, a counter can be assigned to correspond to the highest energy threshold exceeded by a photon pulse. In another embodiment, a counter records the number of times a photon pulse exceeds each energy threshold.

[0032] As one example, edge-on is a non-limiting specific design technique for photon-counting detectors in which the x-ray sensors (e.g., x-ray detector elements or pixels) are positioned with their edges facing the incident x-rays.

[0033] For example, such a photon counting detector can have pixels in at least two directions, one of the at least two directions of the edge-on photon counting detector having a component in the direction of the x-rays. Such an edge-on photon counting detector is sometimes referred to as a depth-segmented photon counting detector, having two or more depth segments of pixels in the direction of the incident x-rays.

[0034] Alternatively, the pixels may be arranged in an array in a direction substantially perpendicular to the direction of the incident X-rays (not segmented in depth), and each pixel may be positioned with its edge facing the incident X-rays, in other words, the photon-counting detector may be positioned with its edge facing the incident X-rays, but may not be segmented in depth.

[0035] The absorption efficiency can be increased by placing the edge-on photon counting detector edge-on, in which case the absorption depth can be chosen to be any length, and the edge-on photon counting detector can be fully depleted without applying very high voltages.

[0036] The traditional mechanism for detecting X-ray photons with direct semiconductor detectors basically works as follows: the energy of the X-ray interaction with the detector material is converted into electron-hole pairs within the semiconductor detector. The number of electron-hole pairs is roughly proportional to the photon energy. These electrons and holes drift towards (or away from) the electrodes and backside of the detector. During this drift, the electrons and holes induce a current in the electrodes, which can be measured.

[0037] As shown in FIG. 4, signals 26 are sent from detector elements 22 of the X-ray detector to the input of an analog processing circuit (e.g., an ASIC) 25. It should be understood that the term application specific integrated circuit (ASIC) should be broadly interpreted as any general circuit configured for a specific application. The ASIC processes and converts the electrical charge generated from each X-ray into digital data that can be used to derive measurement data (such as photon counts and / or estimated energy). The ASIC is configured to interface with the digital processing circuit so that the digital data is sent to digital processing circuit 40 and / or one or more memory circuits or components 45, and ultimately the data is input to image processing circuit 30 or computer 50 of FIG. 2 to generate a reconstructed image.

[0038] Because the number of electrons and holes generated by an X-ray event is proportional to the energy of the X-ray photon, the total charge of an induced current pulse is proportional to that energy. After filtering in the ASIC, the pulse amplitude is proportional to the total charge of the current pulse and therefore to the X-ray energy. The pulse amplitude can be measured by comparing the pulse amplitude value with one or more thresholds (THR) in one or more comparators (COMP), and a counter is used to record the number of times the pulse is greater than the threshold. In this way, it is possible to count and / or record the number of X-ray photons detected within a certain time frame that have energies greater than the respective thresholds (THR).

[0039] The ASIC typically samples the analog photon pulse once per clock cycle and stores the outputs of the comparators. The comparators (thresholds) output a 1 or 0 depending on whether the analog signal is above or below the comparator voltage. The information available at each sample is, for example, a 1 or 0 for each comparator indicating whether the comparator was triggered (photon pulse greater than threshold) or not.

[0040] Photon counting detectors typically have a photon counting logic section that determines whether a new photon has been stored and stores the photon in a counter. Multi-bin photon counting detectors typically have multiple counters, e.g., one for each comparator, and the photon count is stored in the counter according to an estimate of the photon energy. This logic section can be implemented in several different ways. The two most common types of photon counting logic section are non-paralyzed counting mode and paralyzed counting mode. Other photon counting logic sections, such as a maximum detector, count the detected maximums in the voltage pulse and, if possible, store the pulse height.

[0041] Photon-counting detectors have many advantages, including but not limited to high spatial resolution, low sensitivity to electronic noise, excellent energy resolution, and material discrimination (spectral imaging). However, energy-integrating detectors have the advantage of high count-rate tolerance. Count-rate tolerance comes from the fact / realization that because the total energy of the photons is measured, each additional photon will always increase the output signal (within reasonable limits), regardless of the amount of photons currently stored in the detector. This advantage is one of the main reasons why energy-integrating detectors are the standard in medical CT today.

[0042] FIG. 5 is a schematic diagram of a photon counting circuit and / or device according to the prior art.

[0043] When photons interact with the semiconductor material, a cloud of electron-hole pairs is generated. By applying an electric field to the detector material, charge carriers are collected by electrodes in the detector material. Signals are sent from the detector elements to the inputs of a parallel processing circuit (e.g., an ASIC). It should be understood that the term application specific integrated circuit (ASIC) should be broadly interpreted as a general circuit used and configured for a specific application. The ASIC processes the charge generated from each X-ray and converts it into digital data, which can be used to derive measurement data (e.g., photon count and / or estimated energy). In one example, the ASIC can process the charge to generate a voltage pulse having a maximum height proportional to the amount of energy deposited in the detector material by the photon.

[0044] The ASIC can include a set of comparators 302. Each comparator 302 compares the magnitude of the voltage pulse with a reference voltage. The comparator output is typically 0 or 1 (0 / 1), depending on which of the two compared voltages is greater. Here, the comparator output is "1" if the voltage pulse is higher than the reference voltage, and "0" if the reference voltage is higher than the voltage pulse. A digital-to-analog converter (DAC) 301 can be used to convert a digital setting, which can be provided by a user or a control program, into a reference voltage that can be used by the comparators 302. If the height of the voltage pulse exceeds the reference voltage for a particular comparator, that comparator is said to be triggered. Each comparator is typically coupled to a digital counter 303, which increments based on the comparator output in accordance with photon-counting logic.

[0045] As mentioned before, for each projection line, the resulting estimated basis coefficient line integrals

number

[0046] It will be understood that the techniques and arrangements described herein can be implemented, combined, and rearranged in various ways.

[0047] For example, embodiments may be implemented in hardware, or at least partially implemented in software executed by suitable processing circuitry, or a combination thereof.

[0048] The steps, functions, procedures, and / or blocks described herein can be implemented in hardware using conventional techniques (such as discrete or integrated circuit techniques) including both general-purpose electronic circuitry and application-specific circuitry.

[0049] Alternatively, or supplementarily, at least some of the steps, functions, procedures, and / or blocks described herein may be implemented in software (e.g., a computer program) executed by suitable processing circuitry (e.g., one or more processors or processing units).

[0050] Non-limiting examples of specific detector module implementations are described below. More specifically, these examples refer to edge-on oriented detector modules and depth-segmented detector modules. Other types of detectors and detector modules are also possible.

[0051] 6 is a schematic diagram illustrating an example of a solid-state detector module according to an exemplary embodiment. This is an example of a detector module 21 in which the solid-state sensor has multiple detector elements or pixels 22, each of which typically consists primarily of a diode with a charge collection electrode. X-rays enter the detector module from the edge.

[0052] 7 is a schematic diagram showing an example of a semiconductor detector module according to another exemplary embodiment. In this example, a detector module 21 having a semiconductor sensor is also divided into a plurality of depth segments or detector elements 22 in the depth direction, assuming that X-rays are incident from the edge of the detector module.

[0053] Typically, a detector element is an individual sub-element of the detector that is sensitive to X-rays. Generally, photon interactions occur at the detector element, and the charge thus generated is collected at the corresponding electrode of the detector element.

[0054] Each detector element typically measures the incident x-ray flux as a series of frames, where a frame is a set of measured data over a specified time interval (called the frame time).

[0055] Depending on the detector's architecture, one detector element may correspond to one pixel, particularly if the detector is a flat panel detector. A depth-segmented detector may be considered to have multiple detector strips, with each strip having multiple depth segments. In such a depth-segmented detector, each depth segment may be considered to be a separate detector element, particularly if each depth segment is coupled to its own separate charge collection electrode.

[0056] The detector strips in a depth-segmented detector are sometimes called pixel strips, as they correspond to the pixels in a regular flat panel detector. However, a depth-segmented detector can also be thought of as a three-dimensional pixel array, where each pixel (sometimes called a voxel) corresponds to an individual depth segment / detector element.

[0057] The semiconductor sensor can be implemented as a so-called multi-chip module (MCM), in the sense that it serves as a base substrate for electrical wiring, preferably attached by so-called flip-chip technology, and used as a base substrate for several ASICs. The wiring includes connections for signals from each pixel or detector element to the ASIC inputs, as well as connections from the ASIC to external memory and / or digital data processing. Power to the ASIC can be supplied by similar wiring, taking into account the increased cross-sectional area required to carry high currents through these connections, but the power can be supplied by a separate connection. The ASIC can be located next to the active sensor, which means that an absorbing cover can be placed on top to protect the ASIC from incident X-rays, and an absorber can be placed in the direction of the scattered X-rays to protect the ASIC from side scattered X-rays.

[0058] FIG. 8A is a schematic diagram showing a detector module implemented as an MCM similar to the embodiment in U.S. Pat. No. 8,183,535. This example illustrates how a detector module 21 can function as the substrate of an MCM. Signals are transmitted by routing paths 23 from detector elements 22 to inputs of parallel processing circuits 24 (e.g., ASICs) located next to the active sensor area. It is understood that the term application-specific integrated circuit (ASIC) should be broadly interpreted as a general integrated circuit used and configured for a specific application. The ASIC processes the charge generated by each X-ray and converts it into digital data that can be used for photon detection and / or photon energy estimation. The ASIC can include digital processing circuits and memory for smaller tasks. The ASIC can then be configured to interface with digital processing and / or memory circuits or components located outside the MCM, and the data is ultimately used as input for image reconstruction.

[0059] However, depth segmentation also poses two major challenges for silicon-based photon-counting detectors. First, a large number of ASIC channels must be used to process the data provided by the combined detector segments. In addition to the increased channel count due to the small pixel size and depth segmentation, the multiple energy bins further increase the data size. Second, because the input counts for a given X-ray are divided into small pixels, segments, and energy bins, each bin has a low signal, and detector calibration / correction requires orders of magnitude more calibration data to minimize statistical uncertainty.

[0060] Naturally, orders of magnitude larger data sizes require larger computer resources, hard drives, memory, and central processing units (CPUs) / graphics processing units (GPUs), as well as slower data processing and pre-processing. For example, if the data size is 10 gigabytes instead of 10 megabytes, data processing, read and write times will be 1000 times longer.

[0061] A problem that plagues any X-ray photon-counting detector is pile-up. At high X-ray photon flux rates, problems can arise in distinguishing between two subsequent charge pulses. As mentioned above, the pulse length after filtering depends on the shaping time. If this pulse length is longer than the time between the two charge pulses induced by the X-ray photons, the two pulses may grow together, resulting in two photons that cannot be distinguished and are counted as a single pulse. This is called pile-up. One way to avoid pile-up at high photon flux is to shorten the shaping time or use depth segmentation.

[0062] FIG. 8B is a schematic diagram showing an example of a set of arrayed detector modules, each of which is a depth-wise divided detector module, with an ASIC or corresponding circuit 24 positioned below the detector element 22 as viewed from the direction of incident X-rays, and routing paths 23 extending from the detector element 22 to the parallel processing circuit 24 (e.g., ASIC) in the spaces between the detector elements.

[0063] 9 is a schematic diagram illustrating an example overview of a CT imaging system. In this schematic example, CT imaging system 100 includes a gantry 111 and a patient table 112 that can be fed into an opening 114 in gantry 111 for patient and / or calibration scans. The direction of the axis of rotation of the gantry around the object or patient being imaged is referred to as the z-direction. The angular direction of the CT imaging system is referred to as the x-direction, and the direction of incident x-rays is referred to as the y-direction.

[0064] FIG. 10 is a schematic diagram illustrating an example of the overall arrangement of an X-ray source-detector system. In this example, a schematic diagram of an X-ray detector including multiple detector modules and an X-ray source is shown. Each detector module can have a set of detector elements that define corresponding pixels. For example, the detector modules can be edge-on detector modules arranged side-by-side and oriented edge-on toward the X-ray source, and these detector modules can be arranged in a slightly curved overall configuration. As mentioned above, the direction of incident X-rays is referred to as the y-direction. By arranging multiple detector pixels in the direction of the gantry's rotation axis (called the z-direction), multi-slice images can be acquired. Furthermore, by arranging multiple detector pixels in the angular direction (called the x-direction), multiple projections on the same plane can be measured simultaneously, as is used in fan-beam and cone-beam CT. The x-direction is sometimes referred to as the channel direction. Many detectors have detector pixels arranged in both the slice (z) and angular (x) directions.

[0065] Anti-scatter collimators or object collimators, or more generally collimator assemblies (also called anti-scatter grids or anti-scatter grids), are commonly used in modern CT imaging systems to reduce the amount of scatter from the object, for example, to improve image quality. Such collimator assemblies are typically positioned in the x-ray path between the x-ray source and the x-ray detector. When the collimator assembly is positioned "downstream" of the object or patient being imaged, i.e., positioned between the object being scanned and the x-ray detector, the collimator assembly is often referred to as a post-collimator.

[0066] The present invention relates to an X-ray imaging system including an X-ray source, an X-ray detector, and a collimator assembly coupled to the X-ray detector. The X-ray detector includes a plurality of detector modules arranged side by side, the detector modules facing the X-ray source, the detector modules arranged side by side along a direction substantially perpendicular to the direction of incident X-rays. The collimator assembly includes a plurality of collimator plates arranged at intervals, the collimator plates arranged side by side in a direction coinciding with the direction of the detector modules. The collimator assembly further includes side support structures arranged on sides extending in a direction substantially perpendicular to the direction of incident X-rays for physical stabilization.

[0067] As an example, an X-ray imaging system can include an X-ray source, an edge-on X-ray detector, and an intermediate collimator assembly located on the X-ray path between the X-ray source and the X-ray detector.

[0068] In a particular example, the X-ray detector includes a plurality of edge-on detector modules arranged side by side and adapted with their edges facing the X-ray source, the detector modules arranged side by side along a main direction of extension substantially perpendicular to the direction of the incident X-rays.

[0069] For example, the collimator assembly may use a plurality of collimator plates spaced apart and arranged to align in only a single direction that coincides with the main extension direction of the detector module, thereby defining a one-dimensional collimator assembly consisting of a single collection of collimator plates.

[0070] As an example, the collimator assembly further includes a side support structure for physical stabilization arranged on a side extending in the main extension direction and the direction of the incident X-rays, and the side support structure for physical stabilization is attached to at least a portion of the short sides of at least some of the collimator plates among the plurality of collimator plates to improve the rigidity of the one-dimensional collimator assembly.

[0071] The collimator is less susceptible to deformation caused by various forces that occur during operation of the x-ray imaging system (e.g., when performing a patient scan). Furthermore, the increased rigidity allows for the use of collimator plates with a relatively large height in the direction of incident x-rays, resulting in sufficient scatter rejection. The ability to use one-dimensional collimator assemblies is relatively easier to manufacture than complex two-dimensional collimator assemblies.

[0072] As an example, the X-ray imaging system may be a computed tomography (CT) imaging system (such as the CT imaging system shown in FIG. 9 and / or FIG. 10).

[0073] In a particular example, the collimator plates are arranged to be aligned with the axis of rotation of the CT imaging system (also referred to as the z-direction), thereby defining a z-direction collimator.

[0074] Alternatively, the collimator plates can be arranged to align with the angular direction (also referred to as the x-direction) of the CT imaging system, thereby defining an x-direction collimator.

[0075] In a specific example, the side support structure for physical stabilization includes a plurality of strips and / or wires extending along the sides and attached to at least a portion of the short sides of at least some of the collimator plates.

[0076] In another example, the side support structures for physical stabilization are formed as fences and / or grids attached to at least a portion of the short sides of at least some of the collimator plates of the plurality of collimator plates.

[0077] In yet another example, the side support structure for physical stabilization includes at least one side plate having a plurality of openings attached to at least a portion of a short side of at least some of the collimator plates of the plurality of collimator plates.

[0078] By way of example, the side plate having the plurality of openings may be a honeycomb shaped plate.

[0079] In yet another example, the side support structure for physical stabilization includes at least one side cover sheet attached to at least a portion of the short sides of at least some of the collimator plates of the plurality of collimator plates.

[0080] Optionally, side support structures for physical stabilization may be placed on either side of the plurality of collimator plates.

[0081] For example, the stabilizing side support structures may include or be fabricated from carbon fiber reinforced polymer (CFRP). Indeed, experimental studies have shown that using CFRP as the base material for the stabilizing side support structures significantly reduces the maximum deformation of the collimator during operation of the rotational CT imaging system.

[0082] In certain embodiments, the collimator assembly further includes an upper retaining plate and a lower retaining plate to which the collimator plates are attached.

[0083] By way of example, the upper and lower retaining plates may be carbon caps.

[0084] Optionally, the collimator assembly further includes a hardened foam layer provided between at least some of the collimator plates, For example, ROHACELL® can be used as a core material of the foam layer.

[0085] In a specific example, at least some of the collimator plates may be positioned to align with spaces or gaps defined between adjacent detector modules.

[0086] Optionally, an X-ray attenuation assembly can be disposed between at least some of the detector modules of the plurality of detector modules. In a practical example, at least one collimator plate of the plurality of collimator plates can be provided as an extension of the X-ray attenuation assembly.

[0087] By way of example, the X-ray attenuation assembly may include at least one X-ray attenuating plate or sheet or at least one anti-scatter foil.

[0088] In a particular example, each detector module has an array of detector elements extending in the direction of the incident X-rays and in a direction orthogonal to both the direction of the incident X-rays and the main extension direction, and each collimator plate extends in the same direction.

[0089] Optionally, the side support structures for physical stabilization are attached to at least a portion of the short sides of at least some of the collimator plates of the plurality of collimator plates by adhesive (epoxy, glue, potting, etc.).

[0090] For a better understanding, the proposed technique will be explained in more detail with reference to the non-limiting examples of FIGS.

[0091] 11A is a schematic diagram illustrating an example of a detector-collimator assembly having a one-dimensional collimator assembly made up of multiple collimator plates arranged in the direction of the rotation axis of the CT imaging system (also referred to as the z-direction), thereby defining a z-direction collimator.

[0092] As can be seen, there is shown a plurality of edge-on detector modules 21 arranged side by side, adapted to be edge-pointed towards the X-ray source, the detector modules 21 arranged side by side along a main extension direction (z) that is substantially perpendicular to the direction of incident X-rays (y).

[0093] The collimator assembly is based on a plurality of collimator plates 71 arranged spaced apart in only a single direction that coincides with the main extension direction (z) of the detector module, thereby defining a one-dimensional collimator assembly consisting of a single collection of collimator plates.

[0094] In this particular example, the collimator plates are aligned with the axis of rotation (z) of the CT imaging system, forming a z-collimator.

[0095] By way of example, the collimator plate 71 may comprise a high-Z material (such as tungsten).

[0096] In certain examples, an X-ray attenuation assembly 81 may be disposed between at least some of the edge-on detector modules 21. As an example, the X-ray attenuation assembly 81 may include at least one X-ray attenuation plate or sheet or at least one anti-scatter foil. In other words, for at least some of the detector modules 21, adjacent edge-on detector modules 21 may have an anti-scatter foil, sheet, or plate 81 located in the gap between the detector modules 21. This may provide additional anti-scatter protection and / or reduce detector crosstalk. In certain embodiments, the anti-scatter foil, sheet, or plate may include a high-Z material (such as tungsten), similar to the collimator plates.

[0097] 11B is a schematic diagram illustrating an example of a detector-collimator assembly having a one-dimensional collimator assembly made up of multiple collimator plates arranged in an angular direction (also referred to as the x-direction) of the CT imaging system, thereby defining an x-direction collimator.

[0098] When comparing z-collimators with x-collimators, the inventors have found that z-collimators are less susceptible to deformation due to rotational forces in CT imaging systems.

[0099] 12 is a schematic cross-sectional view of an example of a detector-collimator assembly according to one embodiment. In this example, detector modules 21 are arranged side by side with spaces / gaps defined between them, and the spaces / gaps are provided with anti-scatter foils, sheets, or plates 81 that can be fixed or otherwise attached to the detector modules 21. Here, multiple collimator plates 71 collectively define a one-dimensional collimator assembly 70 and are aligned with the anti-scatter foils, sheets, or plates 81. By aligning the collimator plates with and / or over inactive (non-functioning / gap) areas of the overall detector, detection efficiency is improved.

[0100] 13 is a schematic cross-sectional view of another example of a detector-collimator assembly according to an embodiment, in which not all spaces / gaps between adjacent detector modules are provided with anti-scatter foils, sheets or plates 81.

[0101] For example, not all spaces / gaps may be provided with anti-scatter foil, sheet, or plate 81 when detector modules are arranged in pairs (e.g., with the fronts of two detector modules facing each other). Assuming that the front-end electronics of the detector modules are located at the front of the detector modules, it may be preferable to place anti-scatter foil, sheet, or plate 81 in the space between the front and front of two adjacent detector modules 21. However, the space between the rear and rear of two adjacent detector modules 21 may not need to be provided with an anti-scatter assembly. It may be sufficient to provide spacers 82 in the space between the rear and rear of two adjacent detector modules 21. These spacers 82 may be three-dimensionally (3D) printed.

[0102] As can be seen from Figure 13, it is not necessary to have a collimator plate above each gap / space between adjacent detector modules, for example, placing a collimator plate above the spacer 82 is merely an option.

[0103] FIG. 14 is a schematic cross-sectional view illustrating yet another example of a detector-collimator assembly according to an embodiment.

[0104] In this particular embodiment, at least one collimator plate of the plurality of collimator plates is provided as an extension of the X-ray attenuation assembly. More specifically, a practical solution is to integrate each collimator plate 71 with a corresponding anti-scatter foil, sheet or plate 81.

[0105] In other words, the post-collimator 70 may be separately attached to the X-ray detector or may be integrated with the X-ray detector. The purpose of the collimator 70 is to eliminate object scatter, which is detrimental to image quality. However, the collimator plate 71 blocks a portion of the primary X-rays, thereby reducing detection efficiency. Some embodiments of the present invention alleviate this problem by directly integrating the post-collimator as an integral part of the detector. For example, the present invention is particularly well suited for certain types of detectors, such as those in which individual detector modules / slices (channels) are separate physical units and / or edge-on detector modules, such as silicon-based depth-wise edge-illuminated detector modules.

[0106] Edge-illuminated detectors typically have internal plates between detector modules / slices, primarily to suppress internal scattering. As mentioned above, according to certain embodiments, such as that shown in FIG. 14, these internal plates extend further outward to form post-collimators. This approach has the following advantages: 1) the outer portions of the plates are placed directly over the existing space / gap between the detector modules / slices, so they do not further reduce geometric efficiency, and 2) the outer portions of the plates are self-aligned to the detector cells.

[0107] FIG. 15 is a schematic perspective view showing an example of a one-dimensional collimator assembly 70 having side support structures 72 for physical stabilization to improve the rigidity of the one-dimensional collimator assembly.

[0108] In this particular embodiment, the side support structures 72 for physical stabilization include a plurality of strips and / or wires that i) extend within a side defined by the main extension direction and the direction of the incident X-rays, and ii) are attached to at least a portion of the short sides of at least some of the collimator plates of the plurality of collimator plates 71. As an example, the strips and / or wires may be made of carbon fiber, and the strips and / or wires are attached at selected contact points to each collimator plate of the plurality of collimator plates 71 or to some of the plurality of collimator plates by, for example, an adhesive (epoxy, glue, potting, etc.).

[0109] It should be appreciated that various side support structures for stabilization may be employed, as exemplified below.

[0110] FIG. 16 is a schematic perspective view showing an example of a practical implementation of a one-dimensional collimator assembly.

[0111] FIG. 17 is a schematic perspective view showing a particular example of a practical implementation of a one-dimensional collimator assembly 70 having holding plates 73; 74 on which a collimator plate 71 is mounted.

[0112] By way of example, these retaining plates 73; 74 may be secured to respective end blocks 76 of the overall collimator with fasteners 75. Additionally, the end blocks 76 may have locating pins that can be aligned with locating holes in the retaining plates 73; 74.

[0113] For example, in this particular design, two carbon caps can be used as the entire upper and lower connecting surfaces (retaining plates 73; 74) of the collimator 70.

[0114] The inventors have recognized that a viable implementation of this collimator may still be susceptible to deformation due to rotational and other forces that occur, for example, during operation of an X-ray imaging system (such as a CT imaging system). For example, because the centers of the retaining plates 73; 74 are not fixed, vibrations caused by high speed rotation may cause the centers of the plates to move.

[0115] The proposed stabilizing side support structure, which is arranged on the side extending in the main extension direction and the direction of the incident X-rays and attached to at least a part of the short sides of at least some of the collimator plates among the plurality of collimator plates, can significantly improve the rigidity of the one-dimensional collimator assembly.

[0116] FIG. 18A is a schematic perspective view of another embodiment of a one-dimensional collimator assembly 70 having side support structures 72 for physical stabilization to improve the rigidity of the one-dimensional collimator assembly.

[0117] FIG. 18B is a schematic diagram showing a cross section of a portion of the collimator assembly of FIG. 18A.

[0118] As described above, the side support structure 72 for physical stabilization may include a plurality of strips that extend within the defined side surfaces and are attached to at least a portion of the short sides of all or at least some of the collimator plates 71. In this particular example, the side support structure 72 is formed as a set of elongated strips or sheets that extend in the primary extension direction (z / x) from one end block to the other end block of the entire collimator assembly 70. As an example, the strips may be carbon-based strips, for example, made of CFRP. As an example, the thickness of the strips may be 0.1 mm or more, preferably 0.3 mm or more.

[0119] As an example, fixed carbon fiber strips are preferably provided on both short sides to improve overall stiffness.

[0120] Because strips of side support structure are added, a small amount of X-ray dose is lost.

[0121] 19A is a schematic perspective view showing yet another embodiment of the one-dimensional collimator assembly 70. The one-dimensional collimator assembly 70 has a side support structure 72 for physical stabilization to improve the rigidity of the one-dimensional collimator assembly.

[0122] FIG. 19B is a schematic cross-sectional view of a portion of the collimator assembly 70 of FIG. 19A.

[0123] In this example, the side support structure 72 for physical stabilization includes at least one side plate or side cap having a plurality of openings and attached to at least a portion of the short sides of some of the collimator plates 71.

[0124] Preferably, the size and distribution of the openings defined in the side plate are set to achieve a balance or trade-off between stiffness and X-ray dose loss. If the area of ​​the fixed side plate attached to the short side of the collimator plate is large, the overall stiffness increases. On the other hand, if the amount of material used in the side plate increases, the X-ray dose loss increases. By providing multiple openings in the side plate, both improved stiffness and reduced X-ray dose loss are achieved. Preferably, the side plate may include or be made of, for example, CFRP. For example, the thickness of the side plate or side cap may be 0.1 mm or more, preferably 0.3 mm or more.

[0125] By way of example, the side plate having the openings may be a honeycomb shaped plate, such as that illustrated in FIG.

[0126] FIG. 21 is a schematic perspective view showing another example of a one-dimensional collimator assembly having a side support structure for physical stabilization in order to improve the rigidity of the one-dimensional collimator assembly.

[0127] In this particular embodiment, the side support structures 72 for physical stabilization are formed as fences and / or grids attached to at least a portion of the short sides of at least some of the collimator plates 71.

[0128] FIG. 22 is a schematic perspective view showing another further embodiment of a one-dimensional collimator assembly having side support structures for physical stabilization to improve the rigidity of the one-dimensional collimator assembly.

[0129] In this example, the side support structure 72 for physical stabilization includes at least one side cover sheet attached to at least a portion of the short sides of at least some of the collimator plates. When two intact side caps (e.g., made of CFRP with an exemplary thickness of more than 0.1 mm) are used, the overall rigidity or stiffness is very good. However, the intact side caps result in a greater loss of X-ray dose compared to other embodiments.

[0130] The embodiments of the present disclosure illustrated in the drawings and described above are merely exemplary embodiments and are not intended to limit the scope of the claims (including any equivalents thereof). Those skilled in the art will understand that various modifications, combinations, and alterations can be made to the embodiments without departing from the scope defined by the claims. Any combination of non-mutually exclusive features described herein is intended to be within the scope of the present invention. That is, features of the described embodiments may be combined with any appropriate aspect described above, and any feature of any one aspect may be combined with any other appropriate aspect. Similarly, features recited in a dependent claim may be combined with non-mutually exclusive features of other dependent claims, particularly if the dependent claims are dependent on the same independent claim. As required by the practice of some jurisdictions, features may be recited as dependent in a single claim, but this should not be construed to mean that the features of the dependent claims are mutually exclusive.

[0131] Furthermore, it should be noted that the inventive concept relates to all possible combinations of features unless expressly stated otherwise, in particular different part solutions in the different embodiments can be combined in other configurations, where technically possible. [Explanation of symbols]

[0132] 10 X-ray source 11 Gantry 12 tables 13 Isocenter 20 X-ray detector 21 Detector Module 22 detector elements 23 Routing Route 24 Parallel Processing Circuit 25 Analog Processing Circuit 26 signals 30 Image Processing System 40 Digital Processing Circuit 41 X-ray controller 42 Gantry Controller 43 Table Controller 44 Detector Controller 45 Components 50 Computers 60 Operator Console 62 Display 70 One-dimensional collimator assembly 71 Collimator Plate 72 Side support structure 73 Retaining Plate 74 Retaining Plate 75 Fasteners 76 End Block 81 X-ray attenuation assembly 82 spacer 100 X-ray Imaging System 111 Gantry 112 Patient Table 114 Opening 301 DAC 302 Comparator 303 Digital Counter

Claims

1. 1. An x-ray imaging system comprising: X-ray source, X-ray detector, and a collimator assembly coupled to the x-ray detector; Including, the X-ray detector includes a plurality of detector modules arranged in a line and directed toward the X-ray source, the detector modules being arranged in a line along a direction substantially perpendicular to an incidence direction of the X-rays; the collimator assembly includes a plurality of spaced apart collimator plates arranged in a direction coincident with a direction of the detector modules; the collimator assembly further includes a side support structure disposed on a side extending in a direction substantially perpendicular to a direction of the incident x-rays for physical stabilization; The side support structure for physical stabilization includes at least one side plate having a plurality of openings, the at least one side plate being attached to at least a portion of a short side of at least some of the collimator plates of the plurality of collimator plates.

2. The x-ray imaging system of claim 1 , wherein the x-ray imaging system is a computed tomography (CT) imaging system.

3. The X-ray imaging system of claim 2 , wherein the collimator plates are arranged to be aligned in a direction of a rotation axis (also referred to as the z-direction) of the CT imaging system.

4. The x-ray imaging system of claim 2 , wherein the collimator plates are arranged to align in an angular direction (also referred to as the x-direction) of the CT imaging system.

5. 2. The X-ray imaging system of claim 1, wherein the side support structure for physical stabilization includes a plurality of strips and / or wires extending along the sides and attached to at least a portion of a short side of at least some of the collimator plates of the plurality of collimator plates.

6. 2. The X-ray imaging system of claim 1, wherein the side support structures for physical stabilization are formed as fences and / or grids attached to at least a portion of a short side of at least some of the collimator plates of the plurality of collimator plates.

7. The x-ray imaging system of claim 6 , wherein the at least one side plate having the plurality of openings is a honeycomb shaped plate.

8. 2. The x-ray imaging system of claim 1, wherein the side support structure for physical stabilization includes at least one side cover sheet attached to at least a portion of a short side of at least some of the collimator plates of the plurality of collimator plates.

9. The x-ray imaging system of claim 1 , wherein the side support structures for physical stabilization are disposed on either side of the plurality of collimator plates.

10. The x-ray imaging system of claim 1 , wherein the side support structures for physical stabilization include or are fabricated from carbon fiber reinforced polymer (CFRP).

11. The x-ray imaging system of claim 1 , wherein the collimator assembly further includes an upper retaining plate and a lower retaining plate to which the collimator plates are attached.

12. The x-ray imaging system of claim 11 , wherein the upper and lower retaining plates are carbon caps.

13. The X-ray imaging system of claim 1 , wherein the collimator assembly further comprises a hardened foam layer disposed between at least some of the collimator plates of the plurality of collimator plates.

14. The x-ray imaging system of claim 1 , wherein at least some of the collimator plates are positioned to align with spaces or gaps defined between adjacent detector modules.

15. The X-ray imaging system of claim 1 , further comprising an X-ray attenuation assembly disposed between at least some of the plurality of detector modules.

16. The x-ray imaging system of claim 15 , wherein at least one collimator plate of the plurality of collimator plates is provided as an extension of the x-ray attenuator assembly.

17. 16. The X-ray imaging system of claim 15, wherein the X-ray attenuating assembly includes at least one X-ray attenuating plate or sheet or at least one anti-scatter foil.

18. 2. The X-ray imaging system of claim 1, wherein each detector module has an array of detector elements extending in a direction of incident X-rays and in a direction orthogonal to both the direction of incident X-rays and the main direction of extension, and each collimator plate extends in the same direction.

19. 10. The x-ray imaging system of claim 1, wherein the side support structures for physical stabilization are attached to at least a portion of a short side of at least some of the collimator plates of the plurality of collimator plates by an adhesive.

Images