Photon-counting x-ray detector and method for operating a photon-counting x-ray detector

Description

[0001] The invention relates to a photon-counting X-ray detector for recording an X-ray image data set, a medical imaging device comprising a photon-counting X-ray detector and a method for operating the photon-counting X-ray detector.

[0002] Photon-counting X-ray detectors are used in many imaging applications. For example, these X-ray detectors are used in computed tomography scanners in medical imaging to generate a tomographic X-ray image of a patient's examination area.

[0003] A photon-counting, direct-conversion X-ray detector can be used as a photon-counting X-ray detector. In such X-ray detectors, incoming X-rays or photons can be converted into electrical pulses using a suitable converter material. The electrical pulses are evaluated by evaluation electronics, for example, an integrated circuit (Application Specific Integrated Circuit, ASIC). In counting X-ray detectors, incoming X-rays are then measured by counting the electrical pulses triggered by the absorption of X-ray photons in the converter material. The height or length of a generated electrical pulse is usually also proportional to the energy of the absorbed X-ray photon. This allows spectral information to be extracted by comparing the height or length of the electrical pulse with an energy threshold.Photon-counting X-ray detectors often provide several adjustable energy thresholds for comparison, allowing energy-resolved measurements depending on several energy ranges defined by the energy thresholds.

[0004] The use of photon-counting detectors in X-ray imaging offers several advantages over energy-integrating detectors. They enable high spatial resolution and intrinsically energy-resolved measurements.

[0005] The processing of the electrical signals generated in the converter element usually begins with electrical signal amplification and shaping. Depending on the design, the signals from several neighboring pixels are also combined (called "charge summing"). The level of the resulting signals is then typically compared with one or more thresholds using one or more comparators. The digitized signal can then be processed in different ways: For example, the number of times the comparator threshold is exceeded can be counted, e.g., by counting a rising clock edge using a so-called "rising edge counter." The comparator signals from several neighboring pixels can be combined, e.g., using gating or coincidence logic. Count values from neighboring counters can be combined, e.g.,by means of fusing, summing, the time of arrival and / or duration of the comparator signal can be determined and much more.

[0006] Typically, however, only one or two of these processes are actually implemented in the ASIC, and the sequence is determined by the design. Furthermore, the pixel-by-pixel switching is usually implemented identically for each pixel, and cross-pixel communication logic may be incorporated, allowing the acquired information to be read from the ASIC.

[0007] In document US 8 772 730 B2, a photon counting detector is disclosed having NxN readout circuits, wherein at least one readout circuit may comprise a comparison unit having a logic circuit configured to perform a logical operation using a plurality of comparison results with an n-th threshold value, wherein the plurality of comparison results are based on a comparison of an electrical signal converted by the sensor with the n-th threshold value in each of the NxN readout circuits, and the result of the logical operation is output to a common counter.

[0008] DE 10 2012 224209 A1 discloses a counting digital X-ray detector with a matrix of counting pixel elements, wherein at least some of the counting pixel elements have a first circuit which is designed to individually convert the signal directly received in the respective pixel element into a counting signal and to count it, and a second circuit which is designed to convert the signal directly received in the respective pixel element together with coincidentally occurring signals of at least one adjacent pixel element into a counting signal and to count it, and wherein when recording an X-ray image with the counting digital X-ray detector, the variant most favorable for the image quality (first or second circuit or both circuits) can be activated for each pixel element depending on one or more parameters of the X-ray system to which the X-ray detector is assigned.

[0009] Document WO 2017 / 144474 A1 discloses a device for imaging an object, wherein an X-ray detector of the device can be divided into pixel groups and different areas of the detection surface of the X-ray detector can be assigned to the pixel groups.

[0010] In the document DE 10 2015 215 086 A1, an X-ray detector is disclosed having an arrangement of detector elements and an evaluation logic of the arrangement of detector elements, wherein the evaluation logic has a multi-stage multiplexer.

[0011] The object of the invention is to provide an improved X-ray detector for flexible use.

[0012] The problem is solved by the features of the independent patent claims. Further advantageous and partly inventive embodiments and developments of the invention are set forth in the subclaims and the following description.

[0013] The invention relates to a photon-counting X-ray detector according to claim 1.

[0014] The photon-counting X-ray detector used in the invention can also be referred to as a direct-converting X-ray detector. Direct-converting X-ray detectors are usually implemented in a stacked structure, in which an associated evaluation unit is connected to the underside of a layer of the converter material, i.e., to the converter element. The underside of the converter element usually has a matrix-like plurality of electrodes, also referred to below as sensor pixel electrodes, in the form of metallized contact elements. The evaluation unit is contacted to these for signal transmission purposes, e.g., soldered. Typically, each contact element on the converter side is opposed by a pixel-shaped counter-contact element, also referred to below as a pixel electrode, on the evaluation unit side.The evaluation unit then typically provides pixel-by-pixel pixel electronics for the pixel-by-pixel processing of a signal received via the pixel electrodes. Incoming X-ray radiation is converted into charge carriers in the converter material of the converter element depending on the locally deposited energy of an X-ray photon. Based on these charge carriers, a signal, usually an electrical pulse, is generated in the pixel-by-pixel pixel electronics and then further processed. A corresponding detection volume in the converter element can be assigned to a pixel-by-pixel pixel electronics. This detection volume is essentially formed by the electric field between a respective sensor pixel electrode and a top electrode applied to the opposite side of the converter element, and forms the sensitive detection volume of a pixel element.

[0015] According to the invention, each pixel element of the plurality of pixel elements of the photon-counting X-ray detector according to the invention has a first, pixel-by-pixel signal processing stage, which essentially provides analog processing of the signal received via a pixel electrode of a pixel element. In particular, the received signal is amplified by the inventive signal amplifier of the first signal processing stage, and the amplified signal is compared by the at least one comparator with at least one threshold value representing an energy threshold. If the signal exceeds the threshold value, an output signal is output from the comparator.The transition to a digital signal (or several digital signals) thus essentially takes place in this step, so that a digital pixel signal is provided at a respective signal output of the first signal processing stage for further processing in the second signal processing stage.

[0016] The first signal processing stage of a pixel element of the plurality of pixel elements can also have more than one comparator, each with a threshold value, so that a plurality of digital pixel signals are provided as a function of the threshold values at a plurality of signal outputs of the first signal processing stage of a pixel element of the plurality of pixel elements.

[0017] According to the invention, at least one group of pixel elements of the plurality of pixel elements of the photon-counting X-ray detector has a common second signal processing stage. A selected subset of the plurality of pixel elements is combined in each group. The second common signal processing stage is thus provided jointly for at least the pixel elements of the group. All pixel elements of the plurality can be connected to a common processing stage. This means that the at least one group can comprise the entire plurality. However, the plurality of pixel elements can also be divided into several groups, each group being connected to a common second processing stage.

[0018] The plurality of digital logic elements provided in the second signal processing stage can then be understood as provided shared resources for the digital signal processing of the digital pixel signals, which can be used jointly for the signal processing of the digital pixel signals of the pixel elements of the group of the plurality of pixel elements. A digital logic element can be understood in particular as an electronic circuit that determines one or more output variables from one or more digitally represented input signals and from a set of configuration or control signals. The circuit can also have internal memory elements that influence the processing of the input signals (or the values of the memory elements). The operation of the circuit can be clocked, combinational, or event-driven.

[0019] The second signal processing stage comprises a configurable switching matrix, which can be configured for interconnecting the signal outputs assigned to a second signal processing stage, such that, for each assigned signal output, a processing chain of the digital pixel signal outputted via the signal output can be provided based on a selection of the provided digital logic elements. A processing chain represents, in particular, the interconnection and series connection of the digital logic elements and a respective signal output, such that the interconnection assigns the processing of a signal outputted at the signal output. At the end of the processing chain, one or more processed digital signals can then be provided, depending on the interconnection. The configurable switching matrix thus enables configurable interconnection of the signal outputs with at least a selection of the provided logic elements.The switching matrix can also enable a configurable interconnection of the logic elements.

[0020] The selection of digital logic elements comprises at least a subset of the provided digital logic elements.

[0021] The logic elements can each be connected to one or more signal outputs of the first signal processing stage and / or each again to one or more digital logic elements.

[0022] The processed digital pixel signal(s) may, but do not necessarily have to, be assigned to a specific pixel element. The processed pixel signal(s) may also be based on a plurality of digital pixel signals from different signal outputs and thus also from different pixel elements in the group. For example, the digital pixel signals from different signal outputs can be combined with one another, for example, using coincidence logic or summation logic.

[0023] The switching matrix can be designed similarly to an FPGA ("field-programmable gate array"). This means that the switching matrix can be designed as an integrated circuit into which a logic circuit can be loaded, whereby the desired circuit structure can be defined, i.e., adapted, by programming or configuring the switching matrix. This allows various circuits and functions to be implemented and, in particular, repeatedly reconfigured, by configuring the internal digital logic elements. The switching matrix can be reconfigured, particularly after delivery of the X-ray detector, during operation, and for different measurements and applications. This allows the signal processing chain of the digital pixel signals, and thus the functions of the X-ray detector, to be provided in an adaptable and configurable manner.

[0024] In this case, at least one processing chain can be provided for each signal output connected to the common second signal processing stage. However, there can also be configurations of the switching matrix in which processing of selected signal outputs is not provided, i.e. in which no processing chain is provided after a configuration of the switching matrix. This is particularly the case if certain pixel signals are to be dispensed with in favor of, for example, lower data rates, lower power consumption or the like. This means that after a configuration of the switching matrix, a digital processing chain can be provided for at least some or all of the signal outputs of the first signal processing stage of the at least one group of pixel elements.

[0025] Preferably, a processing chain of digital logic elements can be individually configured for each signal output linked to a common second signal processing stage. However, there may also be embodiments of the photon-counting X-ray detector in which the signal processing chains for the signal outputs of the pixel elements of a group can only be configured jointly, so that identical processing chains are provided for each pixel element for the provided digital pixel signals of a pixel element. However, this may nevertheless include providing different signal processing chains of logic elements for different pixel signals of a pixel element.

[0026] The first signal processing stage is to be understood as being formed by pixel-by-pixel pixel electronics. Each pixel element according to the invention of the plurality of pixel elements is then assigned a first signal processing stage, a corresponding pixel or sensor pixel electrode, and a detection volume in the converter element. In contrast, the second signal processing stage can provide the digital processing chain of the pixel-by-pixel pixel signals, but as a whole, it can be assigned not to a single, specific pixel element, but rather only to a group of pixel elements.

[0027] The inventive implementation of the X-ray detector advantageously enables a greater degree of decoupling of analog and digital signal processing. Advantageously, the analog signal processing (amplification and comparator) can be performed as close to the sensor as possible, while the digital processing can be significantly abstracted and applied jointly for a pixel group.

[0028] The abstraction of digital signal processing enables a high degree of flexibility and reusability of the evaluation unit. Combining pixel groups using a configurable matrix readout, i.e., a second signal processing stage with a configurable switching matrix, advantageously enables measurement-adapted processing of the pixel signals. Advantageously, the interconnection of the provided logic elements can be configured and adapted by the user.

[0029] By connecting each sensitive detection volume of a pixel element directly to the analog part of the signal preprocessing, analog signal preprocessing with minimal impedance, low noise, and low power consumption can be enabled. The amplified analog output signal of the signal amplifier is preferably connected directly to the at least one or more comparators. This enables high switching frequencies and precise timing and produces a digital pixel signal that is robust with respect to forwarding to the digital logic elements connected via the switching matrix.

[0030] The architecture according to the invention therefore enables a particularly advantageous analog performance of sensor-related signal processing and digitization to be combined with the flexibility of a highly configurable digital processing chain.

[0031] The inventive implementation of the X-ray detector also enables resource-efficient use of the evaluation unit, even with a large pixel pitch (e.g., providing an electrically conductive connection between the evaluation unit and the converter element only every second pixel electrode). Specifically, those pixel electrodes and the associated corresponding first signal processing stages that are not connected to a sensor pixel electrode via the electrically conductive connection can simply be deactivated or remain unused in the switching matrix. The used pixels, however, can still be connected to their actual neighbors, e.g., using coincidence logic.

[0032] For this purpose, it can advantageously be provided that the X-ray detector according to the invention or the at least one switching matrix can be configured via adjustable register parameters, so that different digital processing chains for the digital pixel signals can be provided depending on the set register parameters.

[0033] The register parameters can be adapted, i.e., essentially programmable, via a control interface of the X-ray detector, for example. In this way, the logic of the switching matrix can be re-parameterized and thus adapted for different measurements and / or applications by adjusting the register parameter values.

[0034] This also makes automatic parameterization possible in a simple and advantageous manner. For example, multiple sets of register parameter values can be stored externally in a memory unit or in several registers of the switching matrix.

[0035] A set of register parameter values can be specific to an X-ray application. The selection of a specific X-ray application, for example, with regard to an object to be examined, a specific acquisition area, an application sequence, or a specific acquisition modality, allows for a large degree of insight into the acquisition conditions during the acquisition of the X-ray image dataset, the desired image quality, and / or the image information to be achieved, thus advantageously allowing for needs-based adjustment of the X-ray detector.

[0036] The sets of register parameter values can also be linked, for example, to one or more application parameters. An application parameter can be a parameter of the X-ray application and / or the medical imaging device to which the X-ray detector according to the invention is assigned and / or to which it is structurally connected.

[0037] This means that an application parameter can be directly linked to an X-ray application or derived from it. For example, the application parameter can be based on an X-ray flux, a point in time or a duration, a control parameter of the medical X-ray device, such as an X-ray tube current or voltage, or an image parameter of the X-ray image dataset to be acquired, such as a spectral resolution or spatial resolution.

[0038] An application parameter can also be based, for example, on boundary conditions predetermined by the medical imaging device to which the X-ray detector according to the invention is assigned, for example an available cooling capacity or a power supply.

[0039] Advantageously, a simple and, if necessary, automatic configuration of the X-ray detector is possible, so that the most favorable configuration of the X-ray detector can always be provided for an X-ray application, the given boundary conditions of a medical X-ray device and / or a measurement.

[0040] In a further embodiment of the photon-counting X-ray detector, a first processing chain can be provided for a first number of signal outputs of the group of pixel elements and a second processing chain different from the first processing chain can be provided for a second number of signal outputs.

[0041] The advantage is that flexible configuration and adaptation of the signal processing to meet requirements are possible.

[0042] Different processing chains can be provided for different signal outputs of a pixel element. For example, depending on requirements, some of the signal outputs of a pixel element can be connected to coincidence logic or to a summing circuit. For example, this can enable independent configuration of spatial and spectral resolution by partially transmitting digital pixel signals from one pixel element at full spatial resolution, while another portion of the pixel element's digital pixel signals can be offset against pixel signals from other pixel elements.

[0043] Likewise, different signal processing chains can be configured for the digital pixel signals of pixel elements subject to different boundary conditions. For example, pixel elements located at the edges within the matrix-like arrangement of pixel elements, and thus having fewer directly adjacent pixel elements, can be configured differently than pixel elements located centrally.

[0044] Furthermore, the plurality of digital logic elements comprises at least one counting element and one readout element.

[0045] This allows a simple photon-counting X-ray detector to be provided in the simplest configuration of the X-ray detector.

[0046] The counting element comprises a plurality of counters.

[0047] A counter is designed to increase a counter reading of the counter by one counting unit based on an incoming signal.

[0048] The counting element can thus correspond to a resource block having a plurality of counters, so that based on a plurality of signal outputs, a number of generated digital pixel signals can be counted and at least temporarily stored.

[0049] Instead of, for example, 4 counters per pixel element, a configurable resource block, i.e. a counting element, with 48 counters can be provided, which can be used jointly in a configurable manner by a group of, for example, 16 pixel elements.

[0050] The reading element can then be used to read out the counter readings of the counting element so that an X-ray image data set can be generated based on this.

[0051] According to a further preferred embodiment of the photon-counting X-ray detector, the plurality of digital logic elements also comprises at least one element from the following list a coincidence logic element, a signal delay element, a buffer element, a switching element for preventing paralysis of a counting element, a combinational logic gate, a multiplexer, a register element, an element which generates a pulse of fixed or configurable length when triggered, or an element which measures the time or duration of a trigger.

[0052] Advantageously, preferred circuits of the X-ray detector can be implemented. In particular, the plurality of digital logic elements comprises a combination of elements from the list. Furthermore, other types of digital logic elements can also be provided.

[0053] Furthermore, it can be provided that a digital logic element of the plurality of digital logic elements is provided multiple times in the second signal processing stage.

[0054] The respective digital logic elements can be available in different selections and quantities depending on the application, available space, and available power. Suitable signal processing chains can be provided for the signal outputs.

[0055] In a further embodiment of the photon-counting X-ray detector according to the invention, after a configuration of the configurable switching matrix, unconnected digital logic elements of the plurality of digital logic elements are disconnected from a power supply.

[0056] Advantageously, unused logic elements can be switched off. For example, this can be specified and configured using adjustable register parameters. Advantageously, a power-efficient X-ray detector can be provided that is adapted to the application and the boundary conditions. Furthermore, by deliberately and economically using resources, the same evaluation unit can also be used for applications / products in which less power / cooling budget is available. Alternatively, the usable performance and functional scope of the evaluation unit can be easily and subsequently increased by optimizing the cooling budget. The invention thus advantageously enables the use of the same evaluation unit in different products and / or applications, thus enabling flexible use.

[0057] According to a further embodiment of the photon-counting X-ray detector, the plurality of pixel elements is divided into a plurality of groups of pixel elements, each group being assigned a configurable switching matrix.

[0058] For example, a group can be assigned to one ASIC. However, multiple pixel groups can be assigned to one ASIC. A group can also comprise a different selection of pixel elements. For example, a group can be defined by its arrangement relative to an anti-scatter grid (ASG). For example, a group comprises one ASG pixel group, each of which is assigned to a through-channel of the ASG. Other groupings can also exist. For example, each group can comprise a fixed number of pixel elements that have a similar relationship to one another. For example, the relationship is determined by their arrangement relative to one another. For example, a group of pixel elements comprises a composite of 8x8 or 16x16 pixel elements.Such a cluster can also be referred to as a macropixel, whereby signals from the pixel elements of a cluster are preferentially offset against each other if necessary.

[0059] By dividing the multitude of pixel elements into several groups of pixel elements, each of which is assigned to a switching matrix, the complexity of a particular switching matrix or the configuration of the switching matrix can be kept to a lower level. Furthermore, the configuration of a switching matrix can be easily transferred to a multitude of switching matrices.

[0060] According to an alternative embodiment of the photon-counting X-ray detector, the plurality of pixel elements is divided into a plurality of groups of pixel elements, wherein a common configurable switching matrix is assigned to the plurality of groups.

[0061] Advantageously, interconnection and signal exchange can be simplified across groups of pixel elements. For example, coincidence analysis can be simplified across pixel groups. The groups can be defined, for example, using shared external parameters. For example, the groups can each comprise an ASG pixel group or a macropixel.

[0062] In an advantageous variant, it can nevertheless be provided that the one configurable switching matrix can be configured on a group basis.

[0063] For example, the switching matrix provides the same number and selection of digital logic elements per pixel group. For example, the configuration of a submatrix of the switching matrix can be transferred to the rest of the switching matrix on a group-by-group basis, i.e., the configuration can be replicated and applied on a group-by-group basis.

[0064] In a further embodiment of the photon-counting X-ray detector according to the invention, the evaluation unit provides at least a first region for the first processing stage and a second region for the second processing stage, wherein the at least one first region is provided in an island-like manner within the second region or at the edge along the second region.

[0065] By decoupling the first, essentially analog signal processing stage and the second, digital signal processing stage, a more flexible arrangement and floor planning (i.e., the layout of the subcircuits in the evaluation unit) of the digital and analog signal processing components is possible. This advantageously allows for smaller pixel-specific circuitry, i.e., the respective first signal processing stage, to be implemented in a smaller area, and also enables smaller pixel element spacing.

[0066] Specifically, the decoupling of the first signal processing stage and the second signal processing stage can advantageously enable, for example, the region of the evaluation unit provided for the first signal processing stage of a respective pixel element to be embedded in an island-like manner within a region that provides the digital signal processing stage for at least one group of pixel elements. Likewise, the surface areas of the first signal processing stages of a group of pixel elements can also be combined into strips, centers, or rings. For example, the first signal processing stages can be combined and arranged along the edges of the second region provided for the second signal processing stage.For example, the first signal processing stages can be arranged centrally within the second area which is provided for the second signal processing stage.

[0067] According to a further embodiment of the photon-counting X-ray detector, the evaluation unit is constructed in layers, wherein the first processing stage is provided in a first layer and the second processing stage is provided in a second layer located behind the first layer in the direction of radiation incidence.

[0068] Advantageously, for example, the pixel-specific first signal processing stage, which can be designed with a smaller area, can enable smaller pixel element spacing.

[0069] In a further development of this, a division of the analog and digital circuits, i.e. the respective first processing stages and the second processing stage, into separate wafer dies (separate sub-regions of one or more semiconductor wafers) can be provided. With such a division into separate dies, these can be combined to form an evaluation unit in a die stacking process. If the first and second signal processing stages are provided in separate dies, the analog and digital circuits are no longer tied to the same technology, so that, for example, different structure sizes can be used in the provision and can therefore also be optimized independently of one another. In this way, for example, different pixel sizes can also be achieved with the same implementation of the second signal processing stage.

[0070] According to one embodiment variant, the photon-counting X-ray detector according to the invention can have a rewiring layer along the X-ray incidence direction between the converter element and the evaluation unit.

[0071] A rewiring layer comprises, in particular, electrically conductive connections that transfer a first spatial distribution of input contact elements to a second spatial distribution of output contact elements. Advantageously, by providing a rewiring layer, the position of the sensor pixel electrodes and the evaluation-side pixel electrodes can be decoupled, thus enabling a flexible arrangement of the regions assigned to the circuit components, i.e., the first signal processing stages and the second signal processing stage of a respective group of pixel elements.

[0072] The invention also relates to a medical imaging device comprising a photon-counting X-ray detector according to the invention.

[0073] The features and advantages of the photon-counting X-ray detector can be directly transferred to the medical imaging device.

[0074] The medical imaging device can be designed, in particular, as a medical X-ray device. The medical imaging device can, in particular, comprise an X-ray source associated with the photon-counting X-ray detector for illuminating the X-ray detector. Typically, the medical imaging device comprises at least one photon-counting X-ray detector according to the invention and, in opposition thereto, at least one X-ray source, for example, an X-ray tube. To record the X-ray image dataset, an object to be imaged can then be placed, in particular, between the X-ray source and the photon-counting X-ray detector and irradiated by the X-ray source. In particular, the medical imaging device can be designed as a computed tomography system. However, it can also be designed, for example, as a C-arm X-ray device and / or Dyna-CT or otherwise.

[0075] The invention also relates to a method for operating a photon-counting X-ray detector, according to claim 12.

[0076] The X-ray detector is assigned to an X-ray source for emitting X-ray radiation.

[0077] Due to the possibility of adapting the register parameter values of the register parameters, the logic of the switching matrix can be advantageously easily and repeatedly parameterized and thus adapted for different measurements and / or applications.

[0078] In one embodiment of the method according to the invention, in a second adaptation step, the adjustable register parameters are adapted based on a second set of register parameter values, wherein in a second configuration step of the at least one configurable switching matrix, a second digital processing chain, different from the first, is provided for at least some of the signal outputs of the first signal processing stage of the at least one group of pixel elements by means of the second set of register parameter values.

[0079] According to an advantageous method variant, the first and / or second set of register parameter values is determined depending on an X-ray application.

[0080] The choice of an X-ray application, for example with regard to an object to be examined, a specific acquisition area, an application sequence or a specific acquisition modality, largely determines the acquisition conditions during the acquisition of the X-ray image dataset, as well as the desired image quality and / or image information to be achieved.

[0081] The determination of the register parameter values depending on the X-ray application thus advantageously allows an adaptation of the X-ray detector according to requirements.

[0082] In addition to the embodiments of the invention expressly described in this application, numerous further embodiments of the invention are conceivable, which the person skilled in the art can arrive at without departing from the scope of the invention which is defined by the claims.

[0083] The use of the indefinite articles "ein" or "eine" does not exclude the possibility that the characteristic in question may be present more than once.

[0084] The invention is explained below using exemplary embodiments with reference to the accompanying figures. The representation in the figures is schematic, highly simplified, and not necessarily to scale. They show: Fig. 1 schematically an exemplary embodiment of an X-ray detector 1, Fig. 2 a diagram illustrating a signal-technical interconnection of a group of pixel elements 5 with a first and a second signal processing stage, Fig. 3 a diagram illustrating a signal-technical interconnection of several groups of pixel elements 5 with a first and a second signal processing stage, Fig. 4 a diagram illustrating a signal-technical interconnection of a group of pixel elements 5 with an exemplary processing chain according to a first configuration variant, Fig. 5 a diagram illustrating a signal-technical interconnection of a group of pixel elements 5 with an exemplary processing chain according to a second configuration variant, Fig. 6 a diagram illustrating a signal-technical interconnection of a group of pixel elements 5 with an exemplary processing chain according to a third configuration variant, Fig. 7 bis Fig. 10 each an illustration of an exemplary relative arrangement of the areas of an evaluation unit provided for a first and a second processing stage, Fig. 11 an exemplary medical imaging device, and Fig. 12 a schematic process flow of a method for operating a photon-counting X-ray detector to generate an X-ray image data set.

[0085] The Fig. 1 schematically shows an exemplary embodiment of an X-ray detector 1.

[0086] In this example, the X-ray detector 1 according to the invention is part of a detector module with a plurality of X-ray detectors 1 according to the invention. In a preferred embodiment, the detector module has a two-dimensional matrix or arrangement of a plurality of X-ray detectors 1. Each X-ray detector 1, in turn, has a plurality of pixel elements 5 in a matrix-like arrangement.

[0087] A respective X-ray detector 1 in the example shown has a converter element 3. The converter element 3 can be designed as a planar direct converter, for example, comprising CdTe, CZT, CdZnTeSe, CdTeSe, CdMnTe, InP, TlBr2, HgI2, GaAs, Si, or other materials as converter material. The top side of the converter element 3 has a first electrode 18 (top electrode). The bottom side of the converter element 3 has sensor pixel electrodes 16. The sensor pixel electrodes 16 are connected to the evaluation unit 59 via the electrically conductive connections 69 and the pixel electrodes 57. The evaluation unit 59 can, for example, comprise an ASICS ("Application Specific Integrated Circuit"). The electrically conductive connections 69 can be formed, for example, as solder balls ("bump bonds") or solder material in combination with copper pillars ("copper pillars") or in other ways.The combined number of sensor pixel electrodes 16, the number of conductive connections 69, the number of pixel electrodes 57, and the number of pixel elements 5 are generally the same. An electric field between the first electrode 18 and a respective sensor pixel electrode 16 determines a sensitive detection volume in the converter element 3, each associated with a pixel element 5 of the plurality of pixel elements 5.

[0088] In the example shown, according to an advantageous embodiment, a rewiring layer 65, also called an interposer, is also arranged between the converter element 3 and the evaluation unit 59 of a respective X-ray detector 1. A rewiring layer 65 comprises, in particular, electrically conductive connections which transfer a first spatial distribution of input contact elements to a second spatial distribution of output contact elements. The input contact elements of the rewiring layer 65 are then arranged, in particular, on a side of the rewiring layer 65 facing the sensor pixel electrodes 16 and are signal-coupled to them. The output contact elements are then arranged, in particular, on a side of the rewiring layer 65 facing the pixel electrodes 57 of the evaluation unit 59 and are signal-coupled to them.The spatial distribution of the input contact elements essentially corresponds to the spatial distribution of the sensor pixel electrodes 16. The spatial distribution of the output contact elements then essentially corresponds to the pixel electrodes 57 of the evaluation unit 59. The rewiring layer 65 can also be applied in direct contact and on the converter element 3 or in direct contact and on the evaluation unit 59.

[0089] In the example shown, the rewiring layer 65 extends over a plurality of evaluation units 59 and converter elements 3. This can be particularly advantageous for the stability of the X-ray detector. However, other designs are also possible. There may also be design variants in which multiple evaluation units 59 are assigned to a common, flat converter element 3.

[0090] In addition, the X-ray detector 1 or the X-ray detector module can also comprise further components not shown here, for example a substrate or peripheral electronics.

[0091] The evaluation unit 59 is designed to process electrical signals generated by X-rays incident on the converter element 3. According to the invention, each pixel element 5 of the plurality of pixel elements 5 of the X-ray detector 1 has a first, in particular pixel-by-pixel, signal processing stage for processing the electrical signals, wherein a digital pixel signal is provided at a respective signal output 7 of the first signal processing stage of a respective pixel element 5 of the plurality of pixel elements.

[0092] According to the invention, the signal outputs 7 of the first signal processing stage of at least one group 20 of pixel elements 5 of the plurality of pixel elements 5 are further signal-coupled to a common second signal processing stage. The second signal processing stage then serves, in particular, for the digital further processing of the provided digital pixel signals of the group 20 of pixel elements 5.

[0093] The Fig. 2 shows a diagram for illustrating a signal-technical interconnection of a group 20 of pixel elements 5 of the plurality of pixel elements 5 with a first and a second signal processing stage in a highly abstracted form.

[0094] The number of pixel elements 5 in a group of 20 is purely exemplary and chosen for illustrative purposes only. More or fewer pixel elements 5 can be assigned to a group of 20.

[0095] The sensor pixel electrode 16 assigned to a respective pixel element 5 of group 20 is signal-coupled to the first signal processing stage provided in the evaluation unit 59. In particular, each pixel element 7 has a first pixel-by-pixel signal processing stage.

[0096] The first signal processing stage of a pixel element 5 for processing the signals fed in by the converter element 3 comprises at least one signal amplifier 17 and at least one comparator 19. The comparator has at least one adjustable threshold value THR.

[0097] A signal received via the pixel electrode is amplified in the first signal processing stage of a pixel element 5 by means of the signal amplifier 17, and the amplified signal is compared by means of the at least one comparator 19 with at least the threshold value THR, representing an energy threshold. If the signal exceeds the threshold value THR, an output signal is output at signal output 7. In particular, a digital pixel signal is provided at signal output 7 of the first signal processing stage.

[0098] The first signal processing stage of a pixel element 5 of the plurality of pixel elements 5 can also have more than one comparator 19, each with a threshold value THR, so that a plurality of digital pixel signals can be provided at a plurality of signal outputs 7 of a pixel element 5 of the plurality of pixel elements as a function of the plurality of threshold values THR.

[0099] The signal outputs 7 of the first signal processing stage of at least the group 20 of pixel elements 5 of the plurality of pixel elements 5 are further signal-coupled to a common second signal processing stage.

[0100] The common second signal processing stage comprises a plurality of digital logic elements 9 for digitally processing the digital pixel signals provided at the signal outputs 7. The plurality of digital logic elements 9 provided in the second signal processing stage can be understood as provided common resource elements for the digital signal processing of the digital pixel signals, which can be used jointly for the signal processing of the digital pixel signals of the pixel elements 5 of the group of the plurality of pixel elements.

[0101] In addition, the common second signal processing stage comprises a configurable switching matrix 11 for the signal-technical interconnection of at least a portion of the plurality of digital logic elements 9 with the respective signal outputs 7 of the first signal processing stage of the group 16 of pixel elements 5 of the plurality of pixel elements.

[0102] After configuring the switching matrix 11, a processing chain for the digital processing of the provided digital pixel signals can then be provided for each signal output 7 of the first signal processing stage of the group 16 of pixel elements 5 of the plurality of pixel elements. The processing chain can thus, in particular, represent the interconnection and cascade connection of a selection of digital logic elements 9 and a respective signal output 7, so that the interconnection provides for the digital processing of a digital pixel signal output at the signal output 7.

[0103] The switching matrix 11 can be designed similarly to an FPGA ("field-programmable gate array"). This means that the switching matrix 11 can be designed as an integrated circuit into which a logic circuit can be loaded. The desired circuit structure can be defined, i.e., adapted, by programming or configuring the switching matrix 11 (not only specifying timing sequences, but also).

[0104] The selection of digital logic elements 9 comprises at least a subset of the provided digital logic elements 9. The logic elements can each be connected to one or more signal outputs 7 of the first signal processing stage and / or each again to one or more digital logic elements 9.

[0105] In this case, according to a configuration, a first processing chain can be provided for a first number of the signal outputs 7 of the group 16 of pixel elements 5 and a second processing chain different from the first processing chain can be provided for a second number of signal outputs 7.

[0106] According to a further advantageous embodiment, the configurable switching matrix 11 is also configurable in particular by means of adjustable register parameters, so that different digital processing chains can be provided for the signal outputs 7 depending on the set register parameters.

[0107] The plurality of digital logic elements 9 comprises at least one counting element 13 and one readout element 14.

[0108] As a result, in a simplest configuration of the X-ray detector 1, a simple photon-counting X-ray detector can be provided, which counts the number of signals received directly in a pixel element 5 as a function of the provided threshold values THR of a respective pixel element 5, based on which an X-ray image data set can be created.

[0109] A counting element 13 comprises a plurality of counters.

[0110] A counter can, in particular, be designed to increment a counter reading by one counting unit upon receipt of a signal. The counter can, for example, comprise a so-called "rising edge counter" or "falling edge counter" (counter based on a rising edge or based on a falling edge of a signal). The counting element 13 can thus correspond to a resource block having a plurality of counters, so that, for example, based on a plurality of signal outputs 7 coupled to the counting element 13, a number of generated digital pixel signals can be counted and at least temporarily stored.

[0111] The counter readings of the counter element 14 can then be read out using a readout element 14. A readout element 14 can, for example, comprise a shift register or a so-called readout tree.

[0112] Furthermore, according to an advantageously expedient embodiment, the plurality of digital logic elements 9 may also comprise at least one element from the following list: a coincidence logic, a signal delay element, a buffer element, a switching element for preventing paralysis of a counting element, a combinational logic gate, a multiplexer, a register element, an element which generates a pulse of fixed or configurable length upon triggering, an element which measures the time or duration of a trigger.

[0113] By providing at least one or more of the above-mentioned elements, suitable interconnections for the use of the photon-counting X-ray detector can be realized in an advantageous manner.

[0114] For example, coincidence logic allows for registering coincidences between two or more pixel elements 5 of the plurality of pixel elements. Collecting coincidence information and incorporating it into the X-ray image dataset can enable improved spatial resolution and / or spectral resolution.

[0115] A signal delay element can be used particularly advantageously to compensate for signal differences between two digital pixel signals, for example due to different line lengths.

[0116] A switching element for preventing paralysis can be advantageously used to improve the high-flux behavior of the X-ray detector. Such a switching element can induce additional signals if a comparator threshold is continuously exceeded. Such a switching element can be designed, for example, as a pile-up trigger (see, for example, Kraft et al. "Experimental evaluation of the pile-up trigger method in a revised quantum-counting CT detector", Proc. SPIE 8313, Medical Imaging 2012: Physics of Medical Imaging, 83134A (2012); https: / / doi.org / 10.1117 / 12.911231) or as a so-called "instant retrigger" (Loeliger et al. "The new PILATUS3 ASIC with instant retrigger capability", 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS / MIC) (2012); https: / / doi.org / 610-615.10.1109 / NSSMIC.2012.6551180).

[0117] A combinational logic gate can comprise AND, NAND, OR, NOR, XOR, or NOT gates. Advantageously, various arithmetic or logical functions can be implemented based on these gates, such as adding or subtracting signals. Furthermore, elements for data transmission, such as a multiplexer, demultiplexer, encoder, and decoder, can be implemented.

[0118] For example, a multiplexer can advantageously switch one selected from a number of input signals to the output of the multiplexer.

[0119] Using an element that generates a pulse of fixed or configurable length upon triggering, a so-called "time-over-threshold" measurement (the duration of a threshold being exceeded) can be performed, for example, in the field of photon-counting detectors. An element that measures the time or duration of a trigger can, for example, enable a so-called "time-of-arrival" measurement (the arrival time of a signal), which is widely known in the field of photon-counting detectors. This can be advantageously used, for example, for collecting coincidence information.

[0120] A register element can advantageously enable configuration using register parameters stored in the register element, synchronization, and / or readout.

[0121] A buffer element can advantageously be provided for driving nodes with higher loads.

[0122] In addition, other types of logic elements can also be provided. For example, a logic element can be provided that triggers upon the occurrence of a (specific or configurable) pattern at its inputs. Connection elements to one or more clock signals, or monitoring elements (e.g., digital buffers for external signal observation), can also be provided.

[0123] Preferably, in particular, a respective logic element 9 of the plurality of logic elements 9 in the second signal processing stage can also be provided multiple times. Depending on the intended use and the available space and power, the respective digital logic elements 9 can then be provided in a suitable selection and number for a practical provision of signal processing chains for a plurality of signal outputs 7.

[0124] When planning and synthesizing the digital logic, suitable placement or suitable synthesis constraints can also advantageously ensure that the typical connection paths and node impedances are optimized, especially in the fast-switching region. For example, it may be useful to distribute the coincidence logic between adjacent pixel elements 5.

[0125] It can advantageously be provided for a resource-saving and consumption-efficient X-ray detector 1 that, after a configuration of the configurable switching matrix 11, non-connected logic elements 9 of the plurality of logic elements 9 are disconnected from a power supply.

[0126] According to a further embodiment of the photon-counting X-ray detector 1, the plurality of pixel elements 5 is divided into a plurality of groups 20 of pixel elements 5, each group 20 being assigned a configurable switching matrix 11. For example, each group can be assigned to an ASIC. A group can also comprise a different selection of pixel elements 5, for example, an ASG pixel or a macropixel.

[0127] Signal connections can still be provided between the groups 20, ie also between the switching matrices, so that a signal exchange across groups is also possible, for example for a coincidence analysis.

[0128] As in Fig. 3 As indicated schematically, several groups 20 of pixel elements 5 can also be assigned to a switching matrix 11. This means that the plurality of pixel elements 5 is divided into a plurality of groups 20 of pixel elements 5, wherein a configurable switching matrix 11 is assigned to the plurality of groups 20 together.

[0129] However, it can preferably be provided that the one configurable switching matrix 11 is configurable on a group basis, so that the configuration of a submatrix of the switching matrix can be replicated to the rest of the switching matrix on a group basis.

[0130] It can be provided that the same number and selection of digital logic elements (indicated by the frame 201 in Fig. 3 ) is repeatedly provided for each group, so that for each group of 20 pixel elements the same signal processing chains for the digital pixel signals can be configured by means of the switching matrix 11.

[0131] The configurability of the switching matrix 11 and thus of the signal processing chains results in a multitude of possibilities for signal processing. The selection and interconnection of the logic elements can be adapted depending on the X-ray application: For very low X-ray fluxes, e.g., in screening applications, a configuration with weighted pixel fusing (combining the digital pixel signals of several pixel elements) or with maximum spatial and / or spectral resolution can be advantageous. For high-flux applications, however, the use of coincidence logic can be activated to reduce or measure the negative influence of charge sharing / pulse pile-up. For examinations that require high spatial resolution (e.g.,For examinations of hearing or osteoporosis, a configuration that uses the counter resources to maximize spatial resolution and measures the signals based on a smaller number of spectral thresholds can be advantageous. For examinations that require high soft tissue contrast or precise material identification, an opposite configuration (noise reduction through lower spatial resolution, weighted pixel fusing, a high number of spectral thresholds or spectral weighting) can be advantageous. For time-critical examinations (e.g., in cardiology or in the emergency room), however, a measurement with maximum frame rate may be desirable in order to minimize scan time and motion artifacts. This can be achieved by a configuration with minimal data volume.By reducing the spectral and spatial resolution (by combining neighboring pixels), the raw data volume can be reduced. This can be achieved, for example, by summing the comparator signals of neighboring pixels (ORing) or by adding neighboring counter readings directly on the chip. In addition to enabling shorter readout intervals, this has the particular advantage of simultaneously reducing power consumption during readout. For examinations with unclear or polymorbid questions (patients with multiple diseases), however, a configuration that offers less speed but delivers the maximum amount of information in a single scan pass may be useful.

[0132] Furthermore, the spatial and spectral resolution can also be configured independently of each other. A concrete example might include measuring a first and second threshold at full spatial resolution, but measuring a third threshold at only half the spatial resolution, while allocating the available counter resources for a coincidence counter in conjunction with the first threshold.

[0133] Advantageously, the flexibility and performance of the coincidence circuits can also be improved. Depending on the application, the flexible circuitry also allows for the detection of higher-order coincidences, for example, a coincidence of a second, higher-energy threshold value THR in a pixel element with a signal having a first, lower-energy threshold value of a neighboring pixel.

[0134] The Fig. 4 shows a diagram illustrating a signal-technical interconnection of a group 20 of pixel elements 5, wherein an exemplary processing chain according to a first configuration variant is illustrated.

[0135] In particular, only those digital logic elements 9 that are interconnected in this simplified variant are indicated by boxes in the illustration. Furthermore, additional logic elements 9 not shown here can be provided in the second signal processing stage.

[0136] In this variant, the first pixel-by-pixel signal processing stage of a respective pixel element 5 has three comparators 19 and three signal outputs 7 each. Each signal output 7 of the pixel elements of the group 20 is coupled to the common second signal processing stage comprising the configurable switching matrix 11 and the plurality of logic elements 9.

[0137] The signal outputs 7 of the respective first and second comparators 19 of each pixel element 5 are connected to the counting element 13 having a plurality of counters, so that based on the output signals of the respective first and second comparators 19, a number of digital pixel signals can be counted in each case as a function of the threshold values THR.

[0138] In addition, the signal output 7 of the respective third comparator 19 of a pixel element 5 is connected together with the corresponding signal output 7 of an adjacent pixel element 5 via a summation element 18 to the counting element 13, so that a summed number of pixel signals of two adjacent pixel elements 5 is counted as a function of the threshold value THR of the respective third comparator 19.

[0139] As a result, in this configuration variant, digital pixel signals are counted with full spatial resolution based on the first and second comparator thresholds THR, whereas the third comparator threshold THR is measured with only half the spatial resolution. It is assumed that the threshold values of the pixel signals are set identically. This means that the first comparator 19 has the same energy threshold across all pixel elements 5, as do the second comparator 19 and the third comparator 19.

[0140] In addition, each signal output 7 in this example is connected to an element to prevent paralysis of the respective coupled counter for improved high flow behavior.

[0141] The Fig. 4 shows a diagram illustrating a signal-technical interconnection of a group 20 of pixel elements 5, wherein an exemplary processing chain according to a second configuration variant is shown.

[0142] In this variant, the first pixel-by-pixel signal processing stage of a respective pixel element 5 again has three comparators 19 and three signal outputs 7 each. However, only the digital pixel signals provided based on the signal outputs 7 of the first two comparators 19 are further processed. For this purpose, the signal outputs 7 of each two adjacent pixel elements 5 are additionally coupled to a coincidence logic 12 based on the respective first comparator 19.

[0143] In this variant, signals based on the first two threshold values of each pixel element 5 are again counted by means of the counting element 13, and in addition, coincident signals between two adjacent pixel elements 5 are counted. In this example, the spectral resolution is omitted in order to collect the coincidence information between two adjacent pixel elements 5.

[0144] Fig. 6 shows a diagram illustrating a signal-technical interconnection of a group 20 of pixel elements 5, wherein an exemplary processing chain according to a third configuration variant is shown.

[0145] In this case, the digital pixel signals of corresponding comparators 19 of two adjacent pixel elements 5 are combined via a summation logic 18 and counted by means of the counting element 13, whereby a lower spatial resolution but a reduction in the data volume and thus a fast recording frequency can be achieved.

[0146] The configuration variants described above represent simple interconnections for exemplary illustration. Furthermore, much more complex configuration variants can be implemented and easily derived from the described variants.

[0147] Fig. 7 bis 9 each show an illustration of an exemplary relative arrangement of the areas of an evaluation unit 59 provided for a first and a second processing stage, which provides the first processing stage and the second processing stage for at least the one group 20 of pixel elements 5 of the plurality of pixel elements.

[0148] The area can be understood as a surface area of the evaluation unit 59. A respective surface area 59 can, in particular, be formed in a planar manner perpendicular to a beam incidence direction or stacking direction of the stack arrangement comprising converter element 3 and evaluation unit 59.

[0149] According to one embodiment variant of the X-ray detector 1, the evaluation unit 59 can provide at least one first region 61 for the first processing stage and a second region 63 for the second processing stage, wherein the at least one first region 61 is arranged in an island-like manner within the second region 63, as shown by way of example in the Figuren 7 und 8 illustrated, is provided.

[0150] According to an embodiment variant of the X-ray detector 1, the evaluation unit 59 can, however, also provide at least one first region 61 for the first processing stage and a second region 63 for the second processing stage, wherein the at least one first region 61 is arranged at the edge along the second region 63, as shown by way of example in Fig. 9 illustrated, is provided.

[0151] The area 61 of the evaluation unit 59 provided for the first signal processing stage of a respective pixel element 5 can, as in Fig. 7 As shown, it can be embedded in an island-like manner within the region 63, which provides the digital signal processing stage for a group of 20 pixel elements. The region 63 of the digital signal processing stage can, for example, occupy the area of the entire pixel group.

[0152] It can also be provided that the areas of the first signal processing stages of a group of pixel elements are also arranged together to form stripes, centers, or rings. For example, the first signal processing stages can be arranged centrally and in island form as in Fig. 8 For example, the first signal processing stages can be arranged together at the edge along the second region 63, as shown in Fig. 9 illustrated, arranged.

[0153] The Fig. 10 shows an illustration of a further exemplary relative arrangement of the first and a second processing stage, wherein the evaluation unit 59 is constructed in layers, and wherein the first processing stage is provided in a first layer 62 and the second processing stage is provided in a second layer 64 located behind the first layer 62 in the beam incidence direction 65.

[0154] In a further development thereof, a division of the analog and digital circuits, ie the respective first processing stages and the second processing stage, into separate wafer dies (separate partial regions of one or more semiconductor wafers) can be provided, which can then be assembled to form an evaluation unit 59.

[0155] Fig. 11 shows an exemplary embodiment of a medical imaging device according to the invention in the form of a computed tomography system 32. The computed tomography system 32 has a gantry 33 with a rotor 35. The rotor 35 comprises a detector device 2 and a radiation source 37, for example an X-ray tube, for illuminating the detector device 2. The detector device 2 has at least one photon-counting X-ray detector 1 according to the invention. The detector device 2 can have a detector module with a number of X-ray detectors 1.

[0156] The object 39, here the patient, is supported on the patient bed 41 and is movable along the rotation axis z 43 by the gantry 33. In general, the object 39 can comprise, for example, an animal patient and / or a human patient.

[0157] In the case of a computed tomography system 32, a (raw) X-ray image dataset of the object is typically acquired from a plurality of angular directions using the X-ray detector. The (raw) X-ray image dataset is then essentially based on the output processed digital pixel signals. Subsequently, based on the (raw) X-ray image datasets, a final X-ray image dataset, a volume image dataset, or a tomographic image dataset can be reconstructed using a mathematical method, for example, comprising a filtered backprojection or an iterative reconstruction method.

[0158] A system controller in the form of a computing unit 45 is provided for controlling the medical imaging device and / or for creating an X-ray image data set based on the measurement data recorded by the photon-counting X-ray detector 1, ie the processed digital pixel signals.

[0159] The computing unit 45 can comprise a control unit 53, which can be configured to adapt register parameter values of register parameters for a configuration of a configurable switching matrix of the photon-counting X-ray detector 1. For this purpose, the control unit 53 can be coupled to the at least one X-ray detector via a control interface in order to transmit control commands and / or register parameter values. The control unit can also be configured to determine a set of register parameter values depending on an X-ray application or to query and / or determine application parameters to determine a suitable set of register parameter values.

[0160] The control unit 53 and / or the computing unit 45 can be implemented in the form of a computer, a microcontroller, or an integrated circuit. The control unit 53 and / or the computing unit 45 can comprise hardware or software elements, for example, a microprocessor or a so-called FPGA (English acronym for "Field Programmable Gate Array"). It can also be a real or virtual network of computers (the technical term for a real network is "cluster," the technical term for a virtual network is "cloud").

[0161] Furthermore, an input device 47 and an output device 49 are connected to the computer unit 45. The input device 47 and the output device 49 can, for example, enable interaction, such as a manual adjustment of register parameter values, the input of a parameter based on which register parameter values can be determined, a confirmation, or the triggering of a method step by a user. The medical imaging device can also include a storage unit 55.

[0162] The Fig. 12 shows a schematic process flow of a method for operating a photon-counting X-ray detector 1, which is designed according to one of the previously described variants, for recording an X-ray image data set, wherein the at least one switching matrix 11 is configurable via adjustable register parameters.

[0163] The method comprises the step of adjusting S1 the adjustable register parameters based on a first set of register parameter values.

[0164] The method further comprises step S2 of configuring the at least one configurable switching matrix 11 based on the adjusted register parameters and thus providing a digital processing chain for at least some of the signal outputs 7 of the first signal processing stage of the at least one group 20 of pixel elements 5, which are signal-coupled to the at least one switching matrix 11. This also includes the provision of a digital processing chain for all signal outputs 7 of the first signal processing stage of the at least one group 20 of pixel elements 5, which are signal-coupled to the at least one switching matrix 11.

[0165] The method further comprises the step of receiving X-ray radiation with the X-ray detector 1, based on which electrical signals are generated in the converter element 3, which are processed in the processing step S4 by means of the first and second processing stages of the X-ray detector 1, wherein digital pixel signals are provided at a respective signal output 7 of the first signal processing stage of a pixel element 5 of the at least one group 20 of pixel elements 5 of the plurality of pixel elements 5, which are further processed in the second signal processing stage by means of the digital processing chain provided for a respective signal output 7.

[0166] The method further comprises the step of outputting S5 the processed digital pixel signals, based on which an X-ray image data set is determined.

[0167] According to a further development of the method of an embodiment variant of the method according to the invention, in a step S6 of the second adaptation, the adjustable register parameters can be adapted based on a second set of register parameters, and wherein in a step S7 of the second configuration of the at least one configurable switching matrix 11, a second digital processing chain, different from the first, is provided for at least part of the signal output 7 of the first signal processing stage of the at least one group 20 of pixel elements 5 of the plurality of pixel elements 5 by means of the second set of register parameter values.

[0168] According to an advantageous method variant, the first and / or second set of register parameters can be determined depending on the X-ray application. Advantageously, the X-ray detector 1 can be optimally adapted to the current boundary conditions for acquiring the X-ray image dataset and the requirements of the X-ray application. This allows for extremely flexible adaptation of the X-ray detector.

[0169] For example, multiple sets of register parameter values can be stored externally in a memory unit 55 or in several register elements of the switching matrix 11 itself. Depending on the X-ray application, one set of register parameter values can then be determined and applied from the plurality of sets.

[0170] The sets of register parameter values can, for example, be linked to one or more application parameters related to the X-ray application. For example, an application parameter can be based on an X-ray flux, a time point, or a duration, a control parameter of the medical imaging device, such as an X-ray tube current or voltage, or an image parameter of the X-ray image dataset to be acquired, such as a spectral resolution or spatial resolution. Based on the application parameters, an advantageous set of register parameter values can then be determined.

[0171] The application parameters can be queried, for example, by an external storage unit 55, external sensor units, or a control unit 53 by means of the X-ray detector 1. The application parameters can, for example, be measured, i.e., determined, by means of the X-ray detector 1 itself, for example, an X-ray flux or an energy of the X-ray radiation. Based on the queried and / or determined application parameters, a set of register parameter values can then be determined and selected for the configuration of the switching matrix 11. The application parameters can also be queried and / or determined by a control unit 53 coupled to the X-ray detector 1, and then a control command and / or new register parameter values can be transmitted to the X-ray detector 1 via a control interface.

[0172] In addition to application parameters related to an X-ray application, there may also be other application parameters. For example, an application parameter may also be based on boundary conditions specified by the medical imaging device to which the X-ray detector 1 according to the invention is assigned, such as the available cooling capacity or a power supply.

[0173] Advantageously, a simple and, if necessary, automatic configuration of the X-ray detector 1 is possible, so that the most favorable configuration of the X-ray detector 1 for an X-ray application, the given boundary conditions of a medical imaging device and / or measurement can always be provided.

Claims

1. Photon-counting X-ray detector (1) having a converter element (3) for converting X-rays into electric signals and a plurality of pixel elements (5), wherein a. each pixel element (5) of the plurality of pixel elements (5) has a first signal processing stage for processing the electric signals in each case with at least one signal amplifier (17) and at least one comparator (19) for providing a digital pixel signal at a respective signal output (7) of the first signal processing stage of a pixel element (5) of the plurality of pixel elements (5), b. the signal outputs (7) of the first signal processing stage of at least one group (20) of pixel elements (5) of the plurality of pixel elements (5) are coupled by means of signal technology to a common second signal processing stage having a multiplicity of digital logic elements (9) for digitally processing the digital pixel signals provided, c. the common second signal processing stage has a configurable switching matrix (11) for interconnecting by means of signal technology at least one partial number of the multiplicity of digital logic elements (9) with the respective signal outputs (7) of the first signal processing stage of the group (20) of pixel elements (5) of the plurality of pixel elements (5), wherein the multiplicity of digital logic elements (9) comprises at least one counting element (13) and one readout element (14), wherein the at least one counting element (13) comprises a multiplicity of counters, d. so that, following a configuration of the switching matrix (11), a processing chain can be provided for the digital processing of the digital pixel signals provided for each signal output (7) of the first signal processing stage of the group (20) of pixel elements (5) of the plurality of pixel elements (5), and wherein the first signal processing stage is embodied by pixelwise pixel electronics so that a first signal processing stage, a corresponding pixel and sensor pixel electrode (16, 57) and a detection volume in the converter element (3) can be assigned to a pixel element (5) of the plurality of pixel elements (5) in each case, and the second signal processing stage can be assigned as a whole only to the group (20) of pixel elements (5).

2. Photon-counting X-ray detector (1) according to claim 1, wherein a first processing chain can be provided for a first number of the signal outputs (7) of the group (20) of pixel elements (5) and wherein a second processing chain different from the first processing chain can be provided for a second number of signal outputs (7).

3. Photon-counting X-ray detector (1) according to claim 1 or 2, wherein the multiplicity of digital logic elements (9) also comprises at least one element from the following list - a coincidence logic, - a signal-delay element, - a buffer element, - a switching element to prevent paralysis of a counting element, - a combinational logic gate, - a multiplexer, - a register element, - an element which, when triggered, creates a pulse of a fixed or configurable length, - an element which measures the point in time or the duration of a trigger.

4. Photon-counting X-ray detector (1) according to one of claims 1 to 3, wherein a digital logic element (9) of the multiplicity of digital logic elements (9) is provided multiple times in the second signal processing stage.

5. Photon-counting X-ray detector (1) according to one of claims 1 to 4, wherein, following a configuration of the configurable switching matrix (11), non-interconnected digital logic elements (9) of the multiplicity of digital logic elements (9) are separated from a power supply.

6. Photon-counting X-ray detector (1) according to one of claims 1 to 5, wherein the plurality of pixel elements (5) is divided into a multiplicity of groups (20) of pixel elements (5), wherein each group (20) is in each case assigned to a configurable switching matrix (11).

7. Photon-counting X-ray detector (1) according to one of claims 1 to 5, wherein the plurality of pixel elements (5) is divided into a multiplicity of groups (20) of pixel elements, wherein a common configurable switching matrix (11) is assigned to the multiplicity of groups (20).

8. Photon-counting X-ray detector (1) according to claim 7, wherein the one configurable switching matrix (11) is configurable in groups.

9. Photon-counting X-ray detector (1) according to one of claims 1 to 8 having an evaluation unit (59) which provides the first processing stage and the second processing stage for at least one group (20) of pixel elements (5) and wherein the evaluation unit (59) provides at least one first region (61) for the first processing stage and one second region (63) for the second processing stage, wherein the at least one first region (61) is arranged in the form of an island within the second region (63) or on the edge along the second region (63).

10. Photon-counting X-ray detector (1) according to one of claims 1 to 8, having an evaluation unit (59) which provides the first processing stage and the second processing stage for at least one group (20) of pixel elements (5) and wherein the evaluation unit (59) has a layered structure and wherein the first processing stage is provided in a first layer (62) and the second processing stage is provided in a second layer (64) located after the first layer (62) in the direction of radiation incidence.

11. Medical imaging device having at least one photon-counting X-ray detector (1) according to one of the preceding claims.

12. Method for operating a photon-counting X-ray detector (1) embodied according to one of claims 1 to 10 for creating an X-ray image data set, wherein the at least one switching matrix (11) of the X-ray detector (1) can be configured by means of adjustable register parameters comprising the steps a. adapting (S1) the adjustable register parameters based on a first set of register parameter values, b. configuring (S2) the at least one configurable switching matrix (11) based on the adapted register parameters and thereby in each case providing a digital processing chain for at least one part of the signal outputs (7) of the first signal processing stage of the at least one group (20) of pixel elements (5) which is coupled to the at least one switching matrix (11) by means of signal technology, c. receiving (S3) X-rays with the photon-counting X-ray detector (1) on the basis of which electric signals are created in the converter element (3), d. processing (S4) the electric signals created by means of the first processing stage and the second processing stage of the photon-counting X-ray detector (1), wherein digital pixel signals are provided at a respective signal output (7) of the first signal processing stage of a pixel element (5) of the at least one group (20) of pixel elements (5) of the plurality of pixel elements (5) which are further processed by means of the digital processing chain provided in the second signal processing stage for a respective signal output (7), e. outputting (S5) the processed digital pixel signals on the basis of which an X-ray image data set is created.

13. Method according to claim 12 , wherein in one step (S6) of the second adaptation, the adjustable register parameters are adapted based on a second set of register parameter values and wherein in one step (S7) of the second configuration of the at least one configurable switching matrix (11) by means of the second set of register parameter values, a second digital processing chain different from the first is provided for at least one part of the signal outputs (7) of the first signal processing stage of the at least one group (20) of pixel elements (5).

14. Method according to one of claims 12 or 13, wherein the first and / or second set of register parameter values is determined as a function of an X-ray application.