Generation of x-ray image datasets by means of photon counting x-ray detectors

Abstract

The invention relates to the generation of an X-ray image data set by means of a photon-counting X-ray detector, in which each pixel element of a plurality of pixel elements comprises a number of comparators, each of which has at least one threshold value, the number of comparators includes a first partial number of comparators and a second partial number of comparators for at least a partial number of pixel elements among the pixel elements, where the second partial number of comparators are each set to a threshold value different from a threshold value of the first partial number of comparators, where the second partial number of comparators is set to a threshold value different from a threshold value of the first partial number of comparators, and where the second partial number of comparators is set to a threshold value different from a threshold value of the second partial number of comparators. Each of the plurality of pixel elements is designed to form at least one count signal on the basis of an output signal of at least one of the first number of comparators, at least a portion of the plurality of pixel elements being designed to form one or more coincident count signals, the at least one coincidence count signal is formed based on an output signal of at least one of the second partial number of comparators of the one pixel element and / or the at least one further pixel element.

Description

Technical Field

[0001] The invention relates to a method for generating an X-ray image data set by means of a photon counting X-ray detector, a photon counting X-ray detector, an X-ray detector system and a medical imaging device. Background Art

[0002] The terms "masculine" and "feminine" are used together to include persons of both masculine and feminine identities, regardless of the grammatical gender of the particular term.

[0003] In a photon-counting X-ray detector of an X-ray imaging device, X-rays are converted into electrical signal pulses with the aid of a conversion material. A photon-counting X-ray detector typically has a plurality of detector elements, also referred to as pixels, which receive the charge carriers generated in the conversion material and further process them in circuit technology as electrical signal pulses. The size and distribution of the pixels determine the spatial resolution and image size of the X-ray detector. The height or length of the generated electrical signal pulse is generally proportional to the energy of the absorbed X-ray photons. Spectral information can thus be extracted by comparing the height or length of the electrical signal pulse with an energy threshold. A photon-counting X-ray detector generally has a plurality of settable energy thresholds for comparing the generated electrical signal pulses, so that energy-resolved measurements can be performed based on a plurality of energy ranges defined by the energy thresholds.

[0004] The use of photon-counting X-ray detectors in X-ray imaging offers a number of advantages over energy-integrating X-ray detectors. For example, photon-counting X-ray detectors enable high positional resolution and inherently energy-resolved measurements. However, the image quality of photon-counting X-ray detectors is often limited by the finite size of the generated charge cloud and by the generation of characteristic X-ray radiation in the detector material. This results in the X-ray photon's full energy not always being deposited in the relevant pixel, but rather a portion of the energy being recorded in adjacent pixels. As a result, photons are recorded at the wrong energy, while photons can also be counted multiple times in adjacent pixels. This phenomenon is known as charge sharing. Charge sharing not only degrades the X-ray detector's spectral properties but also generally reduces its efficiency (also known as DQS (Detective Quantum Efficiency)) due to increased noise and reduced positional resolution. Consequently, this effect can reduce image quality in all applications.

[0005] One approach to solving this problem is to implement a so-called "charge summing" circuit on the ASIC (Application Specific Integrated Circuit) of the X-ray detector. During the detection process, the analog part of the ASIC pixel detects that charge has already accumulated in multiple adjacent pixels, and the total charge of all pixels is assigned to one pixel (typically the pixel with the most charge or the fastest rising current). This not only prevents double counting but also virtually restores the original charge. A disadvantage of this circuit is that it significantly increases the pixel dead time. This exacerbates the problem of "pulse pile-up," in which the signals of multiple photons overlap and also lead to distorted measurements. Consequently, the good high-throughput capabilities required, for example, in computed tomography are generally no longer available.

[0006] Alternatively, the degradation of energy resolution and efficiency can be offset by increasing the pixel size (e.g., to >0.3 mm edge length), but also at the expense of high throughput capability (by superimposing individual photon signals, “pulse stacking”) and additionally at the expense of spatial resolution capability.

[0007] Another approach aims to solve this problem using digital circuit solutions, particularly digital addition. Here, instead of adding the analog measured charges in adjacent pixels together again, only the digital signals are added. Therefore, if a lower energy threshold is exceeded in two adjacent pixels, the two counting events are summarized as a counting event at a higher threshold, with one of the two pixels of the counting event being arbitrarily obtained. For example, this approach is described in “Digital count summing vs. analog charge summing for photon counting detectors: A performance simulation study,” by Scott Hsieh et al., Medical Physics, Vol. 45, No. 9, September 2018. In this approach, the logic must also correct for the overlap in real time, which in turn contributes to the occurrence of negative pile-up effects.

[0008] EP 3 839 577 A1 proposes another solution. Here, in addition to counting a count signal based on incident X-rays in each pixel element, at least one corresponding additional pixel element is also used to count the coincidence count signal of the pixel element. This allows the coincidence information obtained in this way to be taken into account to reduce the degradation of image quality due to coincidence occurring in the pixel elements of the X-ray detector. This improves the quality of the generated X-ray images and CT images. It also avoids or reduces negative effects on high-throughput capabilities. For example, EP 3 839 578 A1 and EP 3 839 576 A1 disclose special technical implementations for counting coincidence count signals. Summary of the Invention

[0009] The object of the present invention is to find a possibility for further improving the generation of x-ray image data sets, in particular taking into account any overlaps that occur.

[0010] This object is achieved by the method according to the invention, the photon counting X-ray detector according to the invention, the X-ray detector system according to the invention, and the medical imaging device according to the invention. Further features and advantages can be found in the description and the drawings.

[0011] According to a first aspect of the present invention, a method for generating an X-ray image data set by means of a photon counting X-ray detector is provided. The X-ray detector comprises at least one conversion element and a plurality of pixel elements connected to the conversion element, wherein the conversion element is configured to convert input X-ray radiation into an electrical signal, and the pixel elements of the plurality of pixel elements are configured to receive the electrical signal at corresponding positions of the pixel elements, wherein each of the plurality of pixel elements has a certain number of comparators, each of the comparators having at least one threshold value, wherein the comparators are respectively configured to output an output signal when the electrical signal exceeds the threshold value, wherein the certain number of comparators comprises a first portion of comparators and comprises a second portion of comparators for at least a portion of the plurality of pixel elements, wherein the second portion of comparators is respectively set to a threshold value different from the threshold value of the first portion of comparators, wherein the pixel elements of the plurality of pixel elements are respectively The method comprises forming at least one count signal based on an output signal of at least one comparator of a first portion of the number of comparators, wherein a second portion of the number of comparators is not used for forming the count signal, wherein at least the portion of the number of pixel elements of the plurality of pixel elements is configured to form one or more coincidence count signals, wherein the coincidence count signals are each based on an output signal generated by one of the comparators of the portion of the number of comparators in one of the pixel elements and based on an output signal generated coincidentally by one of the comparators of the portion of the number of comparators in at least one other pixel element of the plurality of pixel elements, wherein at least one coincidence count signal is formed based on an output signal of at least one comparator of the second portion of the number of comparators of one pixel element and / or at least one other pixel element, wherein the method comprises the following steps:

[0012] - performing a first counting of at least a certain number of count signals according to incident X-ray radiation in each of the plurality of pixel elements;

[0013] - performing a second counting of at least a certain number of coincidence count signals in each pixel element of a portion of the plurality of pixel elements using at least one other pixel element of the plurality of pixel elements; and

[0014] - generating an X-ray image data set based on at least a certain number of count signals counted in each of the plurality of pixel elements and at least a certain number of coincident count signals counted in each of a portion of the plurality of pixel elements.

[0015] The present invention is based on the understanding of the prior art. Counting the coincidence count signal (second count) provides the following advantages, namely, additional information can be detected without negatively affecting the actual count (first count), especially without negatively affecting the high-throughput situation. By being able to circumvent time-consuming real-time correction during the measurement itself, the extended dead time of the pixel element can be avoided. According to the present invention, additional coincidence measurements can be achieved by using a second portion of the number of comparators, and the additional coincidence measurements can be measured in particular between energy levels or next to energy levels that are not used as thresholds for the first count at the same time. In this regard, the comparators in the second portion of the number of comparators can be regarded as dedicated comparators, which are only provided for performing a second count on the coincidence count signal. The new concept of the present invention, that is, the appropriate or even optimal energy threshold for performing a second count on the coincidence count signal can be different from the appropriate or optimal one or more energy thresholds for the first count, expands the possibility of detecting the coincidence count signal in an advantageous manner. For example, the energy threshold of the coincidence count signal can be optimized individually and without considering the energy threshold or threshold for the first count.

[0016] The X-ray image dataset may, in particular, be an X-ray image dataset of an object and / or subject. The object may, for example, be an anatomical region, such as an organ or a portion of an organ, or an object. The subject may, for example, be a human, in particular a patient, or an animal. The photon-counting X-ray detector may be part of an imaging device, in particular a medical imaging device. The imaging device may, for example, be a computed tomography device.

[0017] The conversion element may in particular comprise a conversion material for converting input X-ray radiation into an electrical signal. The conversion material may be, for example, CdTe, CZT, HgI2, GaAs or other suitable materials. The use of CdTe may be particularly advantageous. The pixel element is in particular designed to receive the electrical signal generated by the conversion element. The pixel element may also be referred to as a detector element, an image element, a pixel or an image unit. A plurality of pixel elements may be arranged in a matrix-like pixel grid. The pixel elements may each comprise a circuit, which in particular comprises a certain number of comparators. In particular, the circuit may comprise a counter for performing a first count of a certain number of count signals and, in the case of a partial number of pixel elements, a coincidence counter for performing a second count of a certain number of coincidence count signals.

[0018] Each of the plurality of pixel elements includes a certain number of comparators, each of which has at least one threshold value. The threshold value can be designed to detect a parameter of an electrical signal, such as an amplitude. The threshold value can correspond to an energy threshold. The term "comparator" should be understood broadly within the scope of the present invention. Therefore, it usually refers to a comparison unit that triggers an output signal when the input electrical signal exceeds a set threshold value. The threshold value of the comparator can be fixedly set. For example, the threshold value can be fixedly preset by manufacturing the comparator. Alternatively, the threshold value of the comparator can be changeable or settable. For example, the threshold value can be set to multiple fixed threshold values. Alternatively or additionally, the threshold value can be settable within a threshold value range.

[0019] The coincidence logic can be configured to form a coincidence count signal. The coincidence logic can be configured to provide an output signal when at least two coincident signals occur, which can be counted as a coincidence count signal by means of a counter coupled to the coincidence logic in terms of signal technology.

[0020] Optionally, a plurality of count signals can be counted in corresponding pixel elements of the plurality of pixel elements. Optionally, each pixel element can include a plurality of comparators from a first portion of the number of comparators. Accordingly, a first count can be set for output signals of the plurality of comparators, wherein a certain number of count signals are counted for each of the plurality of comparators. For example, in each of the plurality of pixel elements, a plurality of count signals can be counted according to a plurality of threshold values ​​provided for energy-resolved measurements. An energy-resolved X-ray image dataset can advantageously be generated based on the plurality of count signals.

[0021] Alternatively, the second partial number of comparators may include exactly one comparator. Alternatively, each pixel element of the partial number of pixel elements of the plurality of pixel elements may include a plurality of comparators from the second partial number of comparators. Thus, it is possible to adapt particularly flexibly to the respective measurement situation.

[0022] Alternatively, a plurality of coincidence count signals may be counted in corresponding pixel elements of a portion of the plurality of pixel elements. In particular, the counting of the plurality of coincidence count signals may be set based on the output signals of a plurality of comparators in a certain number of comparators of corresponding pixel elements of a portion of the plurality of pixel elements and at least based on the output signal of one comparator in a certain number of comparators of at least one other pixel element of the plurality of comparators. In particular, counting the plurality of coincidence count signals based on a plurality of energy thresholds may enable more detailed coincidence information to be obtained. Thus, the possibility of correcting inaccuracies caused by coincidences may be improved.

[0023] Alternatively, a portion of the plurality of pixel elements may include all of the plurality of pixel elements. However, in addition to a portion of the pixel elements, the plurality may also include pixel elements constructed in other ways. These pixel elements may, for example, be configured only to form a count signal and count the count signal. By configuring only a portion of the pixel elements in the plurality of pixel elements to form a coincidence count signal and count the coincidence count signal, for example, a simplified connection of the pixel elements may be achieved.

[0024] At least one additional pixel element of the plurality of pixel elements on which the coincidence count signal to be counted is based may be comprised by a fraction of the plurality of pixel elements, i.e., may itself be part of a fraction of the plurality of pixel elements. However, embodiments are also possible in which the at least one additional pixel element is not part of a fraction of the plurality of pixel elements.

[0025] At least one coincidence count signal is formed based on the output signal of at least one comparator in the second portion of the comparators. Alternatively, a plurality of coincidence count signals may also be formed based on the output signal of at least one comparator in the second portion of the comparators.

[0026] In order to generate an X-ray image data set, at least a certain number of coincidence count signals can be taken into account, for example, in data preprocessing before image reconstruction, in image reconstruction, and / or in a post-processing step after image reconstruction. For example, at least in each pixel element of a portion of a plurality of pixel elements, at least a certain number of coincidence count signals can be subtracted from or added to at least a certain number of count signals. Here, the subtraction or addition can include weighted subtraction or addition. That is, only a portion or multiple of at least a certain number of coincidence count signals can be subtracted or added. However, other implementation schemes can also exist, with the help of which at least a certain number of count signals can be adapted. If, for example, a plurality of count signals are counted in a pixel element according to a plurality of energy thresholds, each number or only a portion of these numbers can be adapted with the help of the at least a certain number of coincidence count signals obtained. Similarly, if, for example, a plurality of coincidence count signals are obtained according to a plurality of energy thresholds, different numbers of coincidence count signals can be applied to different numbers of count signals for adaptation.

[0027] According to an embodiment, the outputs of the comparators in the first portion of the comparators are directly or indirectly connected to at least one counter for performing a first count of the count signal, while the outputs of the comparators in the second portion of the comparators are not connected to the counter for performing the first count of the count signal. Since the second portion of the comparators are not used to form the count signal, the circuit components required for this purpose can also be advantageously omitted. In particular, the connection of a counter for performing the first count of a certain number of count signals to the comparators in the second portion of the comparators can be omitted. Since such components, especially counters, can be relatively space-consuming due to their size, this can advantageously achieve space savings. Despite this space saving, the second portion of the comparators can also use threshold values ​​for the second count that do not exist as threshold values ​​for the first count.

[0028] According to embodiments, the threshold value of at least one of the second partial number of comparators is set to enable targeted detection of specific information relevant to the measurement and / or examination, in particular, to enable better detection than would be possible using only the threshold values ​​of the first partial number of comparators. For example, a lower threshold value than the threshold value of the first partial number of comparators can be used. This allows, for example, advantageous detection if a portion of the X-ray photons is distributed across multiple pixel elements, such that some portions fall below the lowest threshold value of the first partial number of comparators. This lower threshold value may not be relevant for the actual counting of events, but may be relevant for detecting coincidences. Accordingly, other threshold values ​​may also be used specifically for determining coincidences. Comparators with adjustable threshold values ​​may include an additional setting step. It may be provided that the threshold value of at least one of the second partial number of comparators is set to enable targeted detection of specific information relevant to the measurement and / or examination. It may be provided that the determination of multiple events leading to coincidence is combined, in particular by counting multiple coincidence events in the corresponding pixel elements. For example, not only symmetrical overlaps but also asymmetrical overlaps can be detected and taken into account. Thus, the corresponding effects of overlaps can be decomposed, if necessary.

[0029] According to an embodiment, the threshold value of at least one of the second portion of comparators is adapted to properties of the object to be examined, in particular material properties, and / or properties of the converter element, in particular material properties. Advantageously, the coincidence count can thus be specifically adapted to the respective current scan. Properties of the object to be examined may, for example, be an absorption coefficient, in particular energy-dependent.

[0030] According to one embodiment, the threshold value of at least one comparator of the second portion of the number of comparators is adapted to an X-ray spectrum of an X-ray source used to acquire the X-ray image data set.

[0031] According to embodiments, the threshold value of at least one of the second partial number of comparators is set relative to at least one fluorescence energy of the material of the conversion element. In particular, the threshold value of at least one of the second partial number of comparators can be set so that the threshold value of at least one of the second partial number of comparators and the lowest threshold value of the first partial number of comparators, in particular provided for the first count, lie on different sides of the fluorescence energy. In other words, the lowest threshold value of the first partial number of comparators can be below the fluorescence energy, while the threshold value of at least one of the second partial number of comparators can be above the fluorescence energy, or the lowest threshold value of the first partial number of comparators can be above the fluorescence energy, while the threshold value of at least one of the second partial number of comparators can be below the fluorescence energy. For example, for a fluorescence energy of 23 keV, one of the threshold values ​​can be 20 keV and the other can be 25 keV. It can be provided that the threshold value of at least one of the second partial number of comparators lies between the fluorescence energy and the nearest threshold value of the first partial number of comparators, i.e., lies on either side of the threshold value, and / or that the threshold value is closer to the fluorescence energy than each of the threshold values ​​of the first partial number of comparators. Fluorescence is an effect in which X-ray photons initially excite the material of the conversion element and are then spontaneously emitted therefrom shortly thereafter. If individual photons have sufficient energy, for example, above the K-edge of the conversion material, fluorescence can occur. Due to the mean free path length of the reemitted photons (typically on the order of approximately 100 μm), they can often reach adjacent pixel elements adjacent to the pixel element where the X-ray photons originally arrived. There, the photons are subsequently reabsorbed by the adjacent pixel element and, if necessary, recorded by a first count. Reabsorption in adjacent pixel elements can result in two counting events, with the energy of the primary X-ray photon being distributed across two pixel elements. This can lead to errors in both the count rate and the corresponding detected energy. This situation occurs more frequently the smaller the pixel elements are designed. Typically, the reabsorbed photons have less energy than the originally incident X-ray photons. Within the scope of the present invention, it has been recognized that the threshold used for the first count of at least a certain number of count signals is not necessarily well-suited for optimally determining fluorescence effects. Advantageously, this embodiment allows for targeted consideration of the effects of fluorescence, for example, in the evaluation of measurement data. Comparators with adjustable thresholds can include additional setting steps. It may be provided that a threshold value of at least one comparator of the second partial number of comparators is set in a targeted manner with respect to at least one fluorescence energy of the material of the conversion element.

[0032] Depending on the embodiment, the threshold value is higher or lower than all the main fluorescence energies of the material of the conversion element. For example, it can be provided that the threshold value of at least one of the second part of the number of comparators is lower than the fluorescence energy. In addition, the threshold value can, if necessary, be higher than the second lowest threshold value of the first part of the number of comparators. Therefore, coincidences based on fluorescence photons can be detected in a targeted manner. It can be provided that the threshold value of at least one of the second part of the number of comparators is higher than the fluorescence energy. Therefore, for example, coincidences that are not based on corresponding fluorescence effects can be searched for in a targeted manner. For example, coincidences can also occur if the finite size of the charge cloud causes the energy of the X-ray photons to be deposited in multiple adjacent pixel elements (also known as "charge sharing"). In particular, as described here, more precise spatial information about the incident X-ray photons can be obtained through asymmetric detection. However, in order to avoid mixing the effects of fluorescence and charge sharing, it may be sensible to specifically avoid detecting fluorescence and, for example, set the threshold value to be slightly higher than the fluorescence energy.

[0033] According to one embodiment, the threshold value lies between two fluorescence energies of the material of the conversion element. For example, individual fluorescence thresholds can thus be observed in a targeted manner.

[0034] According to an embodiment, for a second count of at least a certain number of coincidence count signals, a threshold value of at least one of a certain number of comparators corresponding to a portion of the plurality of pixel elements and a settable energy threshold value of at least one of a certain number of comparators of at least one other pixel element in the plurality of pixel elements on which the coincidence count signal is based have the same energy threshold value. Advantageously, therefore, coincidence count signals based on coincidence occurrences can be counted, where the signals exceed the same threshold value not only in the corresponding observed pixel element but also in at least one other pixel element. This can also be referred to as symmetrical detection of coincidences.

[0035] According to an embodiment, for a second count of at least a certain number of coincidence count signals, the threshold value of at least one comparator in a certain number of comparators corresponding to a portion of the plurality of pixel elements and the threshold value of at least one comparator in a certain number of comparators of at least one other pixel element on which the coincidence count signal is based are set to different threshold values. This can also be referred to as asymmetric detection of coincidences. Optionally, by correspondingly counting at least two coincidence count signals, asymmetric and symmetric detection can be provided. Asymmetric detection can be advantageous in order to assign X-ray photons to one of the two pixel elements and / or to enable proportional counting using a mixing factor. Using different energy thresholds for the threshold value allows, for example, targeted measurement of coincidence events in which the minimum value of energy deposited in the observed pixel is higher than the adjacent minimum value. In this way, coincidence events are preferably statistically counted in pixels where the highest energy deposition occurs. This improves the assignment of impacts to pixels and thus improves spatial resolution. By using a second portion of the number of comparators, the threshold value for asymmetric detection can be selected particularly flexibly.

[0036] According to embodiments, when a higher coincident exceeding of a comparator threshold is detected in a pixel element than in at least one other pixel element, a coincidence count signal is counted at the pixel element, and / or the coincidence count signal is calculated using a mixing factor as a function of the highest threshold exceeded at the pixel element and the highest threshold exceeded detected at at least one other pixel element. Multiple asymmetric events of the same type can be detected, in particular to determine in which pixel element the largest portion of X-ray photons is deposited. The mixing factor can be set to adapt the counted value according to the portion of X-ray photons deposited in the respective pixel element. For example, if one-third of the energy of the X-ray photons is deposited in the detector element, the mixing factor can be, for example, one-third. The grading of the mixing factor can be set based on the threshold used and the resulting accuracy. It can be provided that the mixing factor has a value less than 1. It can be provided that the mixing factor is adapted to the relative magnitude of the threshold for asymmetric detection and / or the relative energy content of adjacent coincidence events. For example, it can be provided that the mixing factor is set for all pixel elements with a common coincidence event. The sum of the mixing factors can be determined to be 1, for example. For example, the mixing factor can be 0.4 for the first pixel element and 0.6 for the second pixel element. For example, the threshold value of the corresponding pixel element of a portion of the plurality of pixel elements can be higher than the threshold value of at least one other pixel element of the plurality of pixel elements. It can thus be provided that the coincidence events are preferably statistically counted in the pixels in which the highest energy deposition occurs. This can improve the assignment of impacts to pixel elements and thus improve the spatial resolution. For example, the coincidence signal of a 30 keV threshold can be measured using the coincidence signal of a 20 keV threshold of an adjacent pixel. It can be provided that, in addition to the asymmetric detection for determining the location, a detection of fluorescence and / or other events that cause coincidence is also provided. Advantageously, the corresponding effects of the coincidence can therefore be decomposed if necessary.

[0037] According to an embodiment, in each of a portion of the pixel elements, not only at least a certain number of coincidence count signals based on the same threshold value but also at least a certain number of coincidence count signals based on different threshold values ​​are counted. This embodiment enables particularly detailed coincidence information.

[0038] According to an embodiment, at least one of the certain number of comparators is a switchable comparator whose threshold value can be set to different threshold values. The at least one switchable comparator can be a comparator in the first portion of the number of comparators. Additionally or alternatively, the at least one switchable comparator can be a comparator in the second portion of the number of comparators. Multiple switchable comparators can be provided. Optionally, all of the comparators in the certain number of comparators can be set to switchable. The switchable comparators make it possible to flexibly adapt the count of the coincidence count signal to the corresponding situation of the scan. A further method step can be provided: setting at least one of the certain number of comparators, in particular at least one of the second number of comparators, to a threshold value. For example, this setting can be performed automatically using a scan protocol. Alternatively, a user input can be detected, and the threshold value to be set can be preset using this user input. For example, the asymmetry of the two comparators used for the second count of the certain number of coincidence count signals can be adapted by setting at least one switchable comparator. For example, in some cases it may be advantageous to use a threshold value higher than the lowest threshold value for the first counting of the count signal to carry out a second count of the coincidence count signal. In view of focusing on higher spectral resolution and / or utilizing focusing on higher positional resolution, the threshold value can be adapted. In this case, a high threshold value and / or a high screening of the count signal may be advantageous, for example. If the goal is the highest possible signal intensity, it may be advantageous to use a lower threshold value to count the count signal. Optionally, the threshold value of at least one comparator in the second partial number of comparators can be set so that specific information related to measurement and / or inspection can be detected in a targeted manner. Alternatively, a switchable comparator of the corresponding pixel element of a partial number of pixel elements of a plurality of pixel elements can be provided. Alternatively, the comparator of at least one other pixel element of a plurality of pixel elements can additionally have a fixed threshold value, in particular a lowest threshold value. For example, using such a circuit with low cost can realize coincidence measurement of types a / a and b / a (e.g., 20 / 20keV and 30 / 20keV).

[0039] According to an embodiment, at least one additional pixel element comprises an adjacent pixel element. In particular, in the second count, at least one additional pixel element of the plurality of pixel elements may be adjacent to a corresponding pixel element of a portion of the plurality of pixel elements. Adjacent is particularly understood to mean that no additional pixel elements are arranged between the two pixel elements. For example, in a rectangular matrix of pixel elements, the pixel elements may be completely or diagonally adjacent to each other.

[0040] According to an embodiment, for each pixel element of the plurality of pixel elements, at least a certain number of coincidence count signals are determined, in particular either at the pixel element itself or at another pixel element. For example, a certain number of coincidence count signals can be determined at a pixel element and then also applied to at least one other nearby pixel element. "Nearby" can, for example, mean adjacent. "Nearby" can, for example, mean within the same subgroup of pixel elements. A subgroup can preferably consist of a coherent matrix of at most 40, preferably at most 30, pixel elements.

[0041] Another aspect of the present invention is a photon counting X-ray detector, which includes at least one conversion element and a plurality of pixel elements connected to the conversion element, as well as a counter for counting counting signals and a coincidence counter for counting coincidence counting signals, wherein the conversion element is constructed to convert input X-ray radiation into an electrical signal, and the pixel elements of the plurality of pixel elements are constructed to receive the electrical signal at the corresponding position of the pixel elements, wherein each of the plurality of pixel elements includes a certain number of comparators, each of which has at least one threshold value, wherein the comparators are respectively constructed to output an output signal when the electrical signal exceeds the threshold value, wherein the certain number of comparators includes a first part number of comparators and includes a second part number of comparators for at least a part number of the plurality of pixel elements, wherein the pixel elements of the plurality of pixel elements are respectively constructed to output an output signal based on at least one comparator of the first part number of comparators. At least one count signal is formed, wherein at least a portion of the plurality of pixel elements is configured to form one or more coincidence count signals, each of which is based on an output signal generated by one of a plurality of comparators in one of the portion of pixel elements and, coincidentally, on an output signal generated by one of a plurality of comparators in at least one other pixel element of the plurality of pixel elements. The outputs of the comparators in a first portion of the comparators are each directly or indirectly connected to at least one counter for counting count signals for individual electrical signals and, optionally, to at least one coincidence counter for counting coincidence signals for overlapping electrical signals. The outputs of the comparators in a second portion of the comparators are each connected to at least one coincidence counter for counting coincidence signals for overlapping electrical signals and not to a counter for counting count signals for individual electrical signals. All advantages and features of this method can be similarly transferred to the X-ray detector, and vice versa. Optionally, the first portion of the comparators can include a plurality of comparators. For example, the first portion of the comparators can include 1 to 10 comparators, preferably 2 to 8 comparators. For example, the second partial number of comparators may include 1 to 5 comparators, preferably 1 to 3 comparators. Alternatively, the partial number of pixel elements may include the entire plurality of pixel elements. The X-ray detector may be configured in particular to perform the first counting and second counting method steps according to the method described herein.

[0042] According to an embodiment, at least one of the plurality of comparators of the X-ray detector is a switchable comparator, whose threshold value can be set to different threshold values. In particular, at least one of the second portion of the comparators can be a switchable comparator. Alternatively, multiple or all of the plurality of comparators can be switchable comparators. In particular, the features and advantages of the settable comparators described elsewhere herein can be applied to this embodiment.

[0043] For example, it may be advantageous to adapt at least one threshold value of the comparator to the respective operating mode used or to the scanning protocol used by the X-ray detector or the imaging device in which the X-ray detector is used. For example, depending on the operating mode or scanning protocol, pile-up effects may occur earlier or more likely. Accordingly, a minimum threshold value may be adapted for the second count of the coincidence count signal.

[0044] Another aspect of the present invention is an X-ray detector system configured to implement the method described herein. The X-ray detector system includes a photon counting X-ray detector, in particular a photon counting X-ray detector as described herein, the X-ray detector including at least one conversion element and a plurality of pixel elements connected to the conversion element, wherein the conversion element is configured to convert input X-ray radiation into an electrical signal, and the pixel elements in the plurality of pixel elements are configured to receive the electrical signal at corresponding positions of the pixel elements, wherein each of the plurality of pixel elements includes a certain number of comparators, each of the comparators having at least one threshold value, wherein the comparators are each configured to output an output signal when the electrical signal exceeds the threshold value, wherein the certain number of comparators includes a first portion of the number of comparators. A second portion of the plurality of pixel elements is included for a portion of the plurality of pixel elements, wherein each pixel element in the plurality of pixel elements is configured to generate at least one count signal based on an output signal of at least one comparator in the first portion of the comparators, wherein at least a portion of the plurality of pixel elements is configured to generate one or more coincidence count signals, each of which is based on an output signal generated by one of the plurality of comparators in one of the plurality of pixel elements and based on an output signal generated coincidentally by one of the plurality of comparators in at least one other pixel element in the plurality of pixel elements. The X-ray detector system further includes a generation unit configured to generate an X-ray image dataset based on at least a certain number of count signals counted in each of the plurality of pixel elements and based on at least a certain number of coincidence count signals counted in each of the plurality of pixel elements. All advantages and features of the method and X-ray detector are similarly transferable to the X-ray detector system, and vice versa. Optionally, the portion of the pixel elements may include the entire plurality of pixel elements.

[0045] Another aspect of the present invention is a medical imaging device comprising an X-ray detector system as described herein. The medical imaging device may, for example, comprise a computed tomography device, a C-arm X-ray device, and / or an angiographic X-ray device. However, other medical imaging devices are also possible that are configured to generate a two-dimensional or three-dimensional image dataset of an object or subject, in particular a patient, based on X-ray radiation. All advantages and features of the method, X-ray detector, and X-ray detector system are similarly transferable to the imaging device, and vice versa.

[0046] Unless explicitly stated otherwise, all embodiments described herein can be combined with each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Hereinafter, embodiments will be described with reference to the accompanying drawings.

[0048] Figure 1 FIG. 1 shows a circuit of the pixel element 1 according to an embodiment of the present invention.

[0049] Figure 2 A flow chart showing a method for generating an X-ray image dataset by means of a photon counting X-ray detector according to an embodiment of the present invention is shown, and

[0050] Figure 3 A medical imaging apparatus having an X-ray detector system according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0051] Figure 1 The circuit of a pixel element 1 according to an embodiment of the present invention is shown. The pixel element 1 is connected to a conversion element 3 via an electrode 2. A corresponding counter electrode (not shown here) is typically provided on the opposite side of the conversion element 3. The incident X-ray radiation is converted into carriers in the conversion material of the conversion element 3 according to the energy locally deposited by the incident X-ray radiation, so that an electrical signal can be intercepted with the help of the electrode 2. Therefore, the pixel element 1 connected to the corresponding part can receive and further process the electrical signal, which is usually in the form of an electrical pulse. In order to further process the electrical pulse, the pixel element 1 has a conversion device 10. The conversion device can optionally include a signal amplifier 11. In addition, the pixel element 1 has a certain number of comparators 12, 13. In this example, the certain number of comparators 12, 13 includes three comparators 12, 13. However, other numbers can also be set. In addition, other numbers T of counting signals and / or coincidence counting signals C can be counted, as exemplarily described here.

[0052] The conversion device 10 is coupled to the portion of the conversion element 3 assigned to the pixel element 1 via the electrode 2 (optionally with the aid of a signal amplifier 11) for signal processing. The signal amplifier 11 can optionally amplify the electrical signal directly input into the pixel element 1 via the electrode 2 and generated by the incident X-ray radiation with the aid of the conversion element 3 for subsequent further processing. The comparators 12 and 13 of the illustrated pixel element 1 each have an adjustable threshold value S for setting an energy threshold. The adjustable threshold values ​​S of different comparators 12 and 13 can be set to different threshold values. The different threshold values ​​S are indicated by the symbols S1, S2, and S3. Two of the comparators 12 belong to the first portion of the number of comparators 12, and the third comparator 13 belongs to the second portion of the number of comparators 13. The threshold value S3 set for the comparator 13 in the second portion of the number of comparators 13 is different from the threshold values ​​S1 and S2 set for the first portion of the number of comparators 12.

[0053] Typically, the respective threshold values ​​S of different pixel elements 1 in the plurality of pixel elements 1 can be set to the same threshold value S. However, other embodiments of the threshold value S may also exist. The electrical signal directly input via the electrode 2 in the observed pixel element 1 is compared with the respective threshold values ​​S→S1, S→S2 and S→S3 of the comparators 12 and 13 by means of the comparators 12 and 13. When the respective threshold value S is exceeded, an output signal is formed at the signal output terminal 14 of the comparator 12 or 13 whose threshold value S is exceeded, which output signal serves as a counting signal or a coincidence counting signal. If multiple threshold values ​​S are exceeded, a counting signal is formed at all the signal output terminals of the comparators 12 or 13 whose threshold values ​​S are exceeded.

[0054] Based on the output signals at the signal outputs 14 of the comparators 12 in the first portion of the number of comparators 12, two numbers T of count signals are counted. In addition, the output signals of one of the comparators 12 in the first portion of the number of comparators 12 and the comparator 13 in the second portion of the number of comparators 13 are used to count the two numbers of coincidence count signals C. For this purpose, the output signals of the comparators 12, 13 in each of the number of comparators 12, 13 of at least one further pixel element 1 are also required.

[0055] In the illustrated embodiment, the signal outputs 14 of the comparators 12 in the first portion of the comparators 12 are each signal-linked to a counter 21. The signal outputs 14 of one of the comparators 12 in the first portion of the comparators 12 and the signal outputs 14 of the comparators 13 in the second portion of the comparators 13 are each signal-linked to a coincidence counter 22. Each counter 21 is configured to count a number of count signals T based on the output signal of the corresponding comparator 12. In this embodiment, one of the counters 21 counts the number of count signals T→T1 according to a threshold value S→S1, and another counter 21 counts the number of count signals T→T2 according to a threshold value S→S2. Therefore, when an electrical pulse generated in the pixel element 1 is above a predetermined threshold value S, that is, above an energy threshold, the electrical pulse input into the conversion element 3 is recorded as a count event in the pixel element 1 and counted as a count signal. In this case, the counter reading of the associated counter 21 is increased by one count unit.

[0056] Furthermore, the comparators 12, 13 with the threshold values ​​S→S2 and S→S3 are each signal-linked to a coincidence logic 23. In other embodiments, only one coincidence logic 23 or additional coincidence logics 23 may also be provided. However, in any case, it is provided that at least one of the comparators 13 in the second partial number of comparators 13 (in this example, the only comparator in the partial number of comparators 13) is linked to at least one of the coincidence logics 23.

[0057] The coincidence logic 23 is each configured to form a coincidence count signal based on a signal directly input into a pixel element 1 of a portion of the pixel elements 1 and a signal occurring in coincidence with at least one other pixel element 1 of the plurality of pixel elements 1. To this end, the respective coincidence logic 23 is associated with at least one other pixel element 1 of the plurality of pixel elements 1 via at least one other signal input 24 of the respective coincidence logic 23. In particular, according to a preferred embodiment, the respective coincidence logic 23 is configured to form a coincidence count signal based on the output signal of the respective comparator 12, 13 of the pixel element 1 under consideration, which is coupled to the coincidence logic 23, and at least based on the output signal of the comparator 12, 13 of at least one other pixel element 1 (not shown here), and to output the coincidence count signal at a signal output of the coincidence logic 23. In the exemplary embodiment shown here, the respective coincidence logic 23 is, by way of example, associated with four other pixel elements 1 of the plurality of pixel elements 1 in terms of signal technology and has four signal inputs 24 for this purpose.

[0058] For example, the four further pixel elements 1 may include four directly adjacent pixel elements 1 of the pixel element 1 under consideration in the matrix-like arrangement of the plurality of pixel elements 1. Based on the output signal of the corresponding coincidence logic 23, the number C of coincidence count signals may then be counted using the corresponding coincidence counter 22.

[0059] In this embodiment, the lower coincidence logic in the coincidence logic 23 is associated with a comparator 12 of a first part of the number of comparators 12 in the corresponding other pixel elements 1, said comparator having an energy threshold S→S1. Accordingly, the number C of coincidence count signals counted by means of the coincidence counter 22 associated with this coincidence logic 23 corresponds to the number of coincidence-occurring signals, said signal exceeding the threshold S→S2 in the observed pixel element 1 and exceeding the threshold S→S1 in at least one of the other pixel elements 1 associated with the coincidence logic 23. Thus, the number C→C of coincidence count signals is counted based on the different thresholds of the corresponding participating pixel elements 1. 21Counting is performed. This can also be referred to as asymmetric coincidence. For example, asymmetric coincidence can be used to improve the position resolution. For example, it can be provided that the coincidence count signal at a pixel element 1 is only counted if a higher coincidence exceeding the threshold value of the comparator 12, 13 is detected in this pixel element 1 than in at least one other pixel element 1. Alternatively or additionally, the use of a mixing factor can also be provided, which is determined based on at least one asymmetric coincidence.

[0060] In this embodiment, the upper coincidence logic in the coincidence logic 23 is associated with a comparator 13 having an energy threshold S→S3 among the second part of the number of comparators 13 of the corresponding other pixel elements 1. Accordingly, the number C of coincidence count signals counted by the coincidence counter 22 associated with this coincidence logic 23 corresponds to the number of coincidence-occurring signals, which respectively exceed the threshold S→S3 in the observed pixel element 1 and in at least one of the other pixel elements 1 associated with the coincidence logic 23. Therefore, the number C→C of coincidence count signals is calculated based on the same threshold value of the corresponding participating pixel elements 1. 33 This is also called symmetric coincidence.

[0061] In addition, Figure 1 In the example shown in , an output terminal 15 is respectively provided coupled to the comparators 12 and 13, by means of which a corresponding output signal can be output to one or more other pixel elements 1 among the said partial number of pixel elements 1, so as to also serve as an input signal of the coincidence logic 23 of one pixel element among the said partial number of pixel elements 1, which is not shown here.

[0062] The number of count signals T and the number of coincidence count signals C can be read from the counter 21 and the coincidence counter 22 by means of a readout element 30 and output to a generation unit 40 for generating an X-ray image data set. For this purpose, the readout element 30 can be connected to the generation unit 40, for example, via a connection and / or via peripheral electronics.

[0063] Generally, within the scope of the present invention, it is possible to determine the C→C connections of at least a certain number of the pixel elements 1 under consideration, depending on the connections of the pixel elements 1 under consideration among a portion of the pixel elements 1. nm The coincidence count signal is counted, where n∈{1,…,N}, where the threshold value S→S in the observed pixel element 1 is provided nThe number of is N, and wherein m∈(1, ..., M), wherein the number of provided threshold values ​​S→Sm of at least one further pixel element 1 on which the coincidence count signal of the plurality of pixel elements 1 is based is M. In this case, at least one threshold value S is used, which also does not have a first count for the count signal. Preferably, for each pixel element 1 in the partial number of pixel elements 1, a plurality of numbers C→C nm Advantageously, a plurality of counted coincidence count signals allow for an improved further correction of the X-ray image data set. In order to detect the coincidence count signals of all pixel elements 1 in the partial number of pixel elements 1, for example, a tensor may be provided. The tensor includes a number C for each pixel element in the partial number of pixel elements 1. nm , which is in the form of The number of said parts of pixel elements 1 is p.

[0064] Figure 2 A flow chart showing a method for generating an X-ray image data set by means of a photon counting X-ray detector 201 according to an embodiment of the present invention is shown. Figure 1The X-ray detector 201 is implemented using a plurality of pixel elements 1 designed for use with a plurality of pixel elements 1. The X-ray detector 201 includes at least one conversion element 3 and a plurality of pixel elements 1 connected to the conversion element. The conversion element 3 is configured to convert input X-ray radiation into an electrical signal, and the plurality of pixel elements 1 are configured to receive the electrical signal at their respective locations. Each of the plurality of pixel elements 1 includes a number of comparators 12, 13, each having at least one threshold value. The comparators 12, 13 are each configured to output an output signal when the electrical signal exceeds the threshold value. The number of comparators 12, 13 includes a first portion of comparators 12 and, for at least a portion of the plurality of pixel elements 1, a second portion of comparators 13. The second portion of comparators 13 is each set to a threshold value different from the threshold value of the first portion of comparators 12. The plurality of pixel elements 1 are each configured to generate at least one count signal based on the output signal from at least one of the first portion of comparators 12, wherein the second portion of comparators 13 is not used to generate the count signal. At least a portion of the plurality of pixel elements 1 is configured to generate one or more coincidence count signals, each based on an output signal generated by one of the plurality of comparators 12, 13 in one of the plurality of pixel elements 1 and, coincidentally, an output signal generated by one of the plurality of comparators 12, 13 in at least one other pixel element 1 in the plurality of pixel elements 1. The at least one coincidence count signal is generated based on the output signal of at least one of the second portion of comparators 13 in one pixel element 1 and / or at least one other pixel element 1. For example, the threshold value of at least one of the second portion of comparators 13 can be set to enable targeted detection of specific information relevant to the measurement and / or inspection. This allows for better information detection than would be possible using only the threshold values ​​of the first portion of comparators 12. For example, the threshold value of at least one of the second portion of comparators 13 can be set relative to at least one fluorescence energy of the material of the conversion element 3 to account for the effects of the fluorescence.

[0065] In a first step 101 of the method, at least a certain number of count signals are first counted in each of the plurality of pixel elements 1 as a function of incident X-ray radiation.

[0066] In a further step 102, a second count of at least a certain number of coincidence count signals is performed in each pixel element 1 of a portion of the plurality of pixel elements 1 and at least one further pixel element 1 of the plurality of pixel elements 1. The two steps 101, 102 are preferably performed substantially simultaneously.

[0067] In a further step 103, which in particular follows the other two steps, generation of an X-ray image data set is set based on at least a certain number of count signals counted in each pixel element 1 of a plurality of pixel elements 1 and at least a certain number of coincident count signals counted in each pixel element 1 of a part number of pixel elements of the plurality of pixel elements 1.

[0068] Optionally, at the beginning of the method, a step 100 of setting the threshold value S of at least one settable comparator can be provided. This setting can be performed, for example, according to a set scanning protocol. Optionally, all threshold values ​​S can be set at the beginning of the method.

[0069] Figure 3 The figure shows a medical imaging device, namely a computed tomography device, having an X-ray detector system according to an embodiment of the present invention. The X-ray detector system comprises a gantry having an X-ray radiation source 205 and an X-ray detector 201, which is part of the X-ray detector system. The generation unit 40 can, for example, be arranged outside the gantry. It is also conceivable that the generation unit 40 is located on the gantry 200 or integrated into the gantry. The generation unit 40 can optionally also be located at another location, spatially separated from the gantry 200. A computing unit 202 is provided for controlling the imaging device. For example, the generation unit 40 of the X-ray detector system according to the present invention can also be included in the computing unit 202.

Claims

1. A method for generating an X-ray image data set by means of a photon counting X-ray detector (201), in, The X-ray detector (201) comprises at least one conversion element (3) and a plurality of pixel elements (1) connected to the conversion element. wherein the conversion element (3) is configured to convert input X-ray radiation into an electrical signal, and the pixel elements (1) of the plurality of pixel elements (1) are configured to receive the electrical signal at corresponding positions of the pixel elements, Each pixel element (1) in the plurality of pixel elements (1) comprises a certain number of comparators (12, 13), each of the comparators having at least one threshold value. The comparators (12, 13) are respectively configured to output an output signal when the electrical signal exceeds the threshold value. The certain number of comparators (12, 13) includes a first number of comparators (12) and includes a second number of comparators (13) for at least a part of the pixel elements of the plurality of pixel elements (1), wherein the second portion of the comparators (13) are respectively set to thresholds different from the thresholds of the first portion of the comparators (12), wherein each pixel element (1) of the plurality of pixel elements (1) is configured to form at least one counting signal based on an output signal of at least one comparator of the first portion of the number of comparators (12); wherein the second portion of the comparators (13) are not used to form the count signal, wherein at least a portion of the plurality of pixel elements (1) are configured to form one or more coincidence count signals, each of which is based on the output signal generated by one of the plurality of comparators (12, 13) in one of the plurality of pixel elements (1) and based on an output signal generated in a coincident manner by one of the plurality of comparators (12, 13) in at least one other pixel element (1) of the plurality of pixel elements (1), wherein at least one coincidence count signal is formed based on an output signal of at least one of the second part number of comparators (13) of the one pixel element (1) and / or the at least one further pixel element (1), The method comprises the following steps: - in each of the plurality of pixel elements (1), performing a first counting of at least a certain number of count signals according to the incident X-ray radiation; - in each pixel element (1) of the portion of the pixel elements in the plurality of pixel elements (1), performing a second counting of at least a certain number of coincidence count signals using at least one other pixel element (1) of the plurality of pixel elements (1); and - generating an X-ray image data set based on the at least a certain number of count signals counted in each pixel element (1) in the plurality of pixel elements (1) and the at least a certain number of coincidence count signals counted in each pixel element (1) in the partial number of pixel elements in the plurality of pixel elements (1).

2. The method according to claim 1, in, The output terminals of the comparators (12) in the first portion of the comparators (12) are directly or indirectly connected to at least one counter (21) for performing a first counting of the counting signal. The output ends of the comparators (13) in the second portion of the number of comparators (13) are not connected to the counter (21) for performing a first counting of the counting signal.

3. The method according to any one of the preceding claims, in, The threshold value of at least one of the second portion of comparators (13) is set so that specific information related to the measurement and / or inspection can be detected in a targeted manner, in particular so that the information can be detected better than can be achieved using only the threshold values ​​of the first portion of comparators (12).

4. The method according to any one of the preceding claims, in, The threshold value of at least one comparator in the second portion of the number of comparators (13) is set relative to at least one fluorescence energy of the material of the conversion element (3), in particular so that the threshold value of at least one comparator in the second portion of the number of comparators (13) and the lowest threshold value of the first portion of the number of comparators (12) are located on different sides of the fluorescence energy.

5. The method according to any one of the preceding claims, in, For a second count of the at least a certain number of coincidence count signals, a threshold value of at least one of the certain number of comparators (12, 13) of the corresponding pixel elements (1) of the partial number of pixel elements of the plurality of pixel elements (1) and a threshold value of at least one of the certain number of comparators (12, 13) of the at least one other pixel element (1) on which the coincidence count signal is based are set to different threshold values.

6. The method according to claim 5, in, If a higher coincident exceeding of the comparator (12, 13) threshold value in a pixel element (1) than in the at least one other pixel element (1) is detected, a coincidence count signal is counted at the pixel element (1), and / or Therein, a coincidence count signal is calculated using a mixing factor as a function of the highest threshold value exceeded at the pixel element (1) and the highest threshold value exceeded detected at the at least one further pixel element (1).

7. The method according to any one of the preceding claims, in, At least one comparator among the certain number of comparators (12, 13) is a switchable comparator (12, 13), and the threshold value of the comparator can be set to different threshold values.

8. A photon counting X-ray detector (201), comprising: at least one conversion element (3) and a plurality of pixel elements (1) connected to the conversion element, as well as a counter (21) for counting count signals and a coincidence counter (22) for counting coincidence count signals, wherein the conversion element (3) is configured to convert input X-ray radiation into an electrical signal, and the pixel elements (1) of the plurality of pixel elements (1) are configured to receive the electrical signal at corresponding positions of the pixel elements, Each pixel element (1) in the plurality of pixel elements (1) comprises a certain number of comparators (12, 13), each of the comparators having at least one threshold value. The comparators (12, 13) are respectively configured to output an output signal when the electrical signal exceeds the threshold value. The certain number of comparators (12, 13) includes a first number of comparators (12) and includes a second number of comparators (13) for at least a part of the pixel elements of the plurality of pixel elements (1), wherein each pixel element (1) of the plurality of pixel elements (1) is configured to form at least one counting signal based on an output signal of at least one comparator of the first portion of the number of comparators (12); wherein at least a portion of the plurality of pixel elements (1) are configured to form one or more coincidence count signals, each of which is based on the output signal generated by one of the plurality of comparators (12, 13) in one of the plurality of pixel elements (1) and based on an output signal generated in a coincident manner by one of the plurality of comparators (12, 13) in at least one other pixel element (1) of the plurality of pixel elements (1), wherein the output ends of the comparators (12) in the first number of comparators (12) are respectively directly or indirectly connected to at least one counter (21) for counting count signals of respective electrical signals and optionally connected to at least one coincidence counter (22) for counting coincidence signals of coincident electrical signals, The output ends of the comparators (13) in the second part of the number of comparators are respectively connected to at least one coincidence counter (22) for counting coincidence signals of coincident electrical signals and are not connected to a counter (21) for counting count signals of individual electrical signals.

9. An X-ray detector system, configured to implement the method according to any one of claims 1 to 7, and comprising: a photon counting X-ray detector (201), in particular a photon counting X-ray detector according to claim 8, comprising at least one conversion element (3) and a plurality of pixel elements (1) connected to the conversion element, wherein the conversion element (3) is configured to convert input X-ray radiation into an electrical signal, and the pixel elements of the plurality of pixel elements (1) are configured to receive the electrical signal at corresponding positions of the pixel elements, Each pixel element (1) of the plurality of pixel elements (1) includes a certain number of comparators (12, 13), each of the comparators having at least one threshold value, wherein the comparators (12, 13) are respectively configured to output an output signal when the electrical signal exceeds the threshold value. The certain number of comparators (12, 13) includes a first number of comparators (12) and includes a second number of comparators (13) for at least a part of the pixel elements of the plurality of pixel elements (1), wherein each pixel element (1) of the plurality of pixel elements (1) is configured to form at least one counting signal based on an output signal of at least one comparator of the first portion of the number of comparators (12); wherein at least a portion of the plurality of pixel elements (1) are configured to form one or more coincidence count signals, each of which is based on the output signal generated by one of the plurality of comparators (12, 13) in one of the plurality of pixel elements (1) and based on an output signal generated in a coincident manner by one of the plurality of comparators (12, 13) in at least one other pixel element (1) of the plurality of pixel elements (1), - a generating unit (40) configured to generate an X-ray image data set based on at least a certain number of count signals counted in each pixel element (1) of the plurality of pixel elements (1) and based on at least a certain number of coincidence count signals counted in each pixel element (1) of the partial number of pixel elements in the plurality of pixel elements (1).

10. A medical imaging device, in particular a computed tomography device, comprising the X-ray detector system according to claim 9.

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