Detection of electromagnetic interference fields during the operation of an X-ray detector

Abstract

A method for detecting electromagnetic interference fields (EMI) during the operation of an X-ray detector (30) is described. First, a value (W) is determined which represents a variation of temporally successive detector signal values ​​(DSW) of a pixel (P) not exposed to X-rays. i ) or a group of pixels (P i The value of the X-ray detector (30) is displayed. The value is compared with a predetermined threshold (SW), and it is determined that a disturbance (ST) due to electromagnetic interference fields (STF) occurs if the determined value exceeds the predetermined threshold (SW). A disturbance detection device (20) is also described. Furthermore, an X-ray detector (30) is described.

Description

[0001] The invention relates to a method for detecting electromagnetic interference fields during the operation of an X-ray detector. The invention further relates to an interference detection device. The invention also relates to an X-ray detector.

[0002] X-ray imaging systems are susceptible to electromagnetic interference, which can cause distortions and, in particular, image artifacts in image data acquired by flat-panel detectors of an X-ray imaging system. This phenomenon particularly affects X-ray detectors with a switched readout matrix, e.g., those based on ASi (amorphous silicon) technology or a technology with a similar readout method.

[0003] Currently, measures are taken to electromagnetically shield X-ray detectors. In the simplest case, certain distances to electrical devices or installations are maintained. However, no detection of electromagnetic interference fields is currently provided for.

[0004] Currently, when evaluating the detector signal of an X-ray detector exposed to X-rays, a so-called offset signal is subtracted from the detector signal for each pixel of the X-ray detector. For this purpose, an average value is calculated for each pixel from a series of detector signals from an X-ray detector not exposed to X-rays. This value is then subtracted from the detector signal of the respective pixel of the X-ray-exposed X-ray detector. However, this method does not remove dynamic interference effects from the detector signals.

[0005] DE 10 2011 077 087 A1 describes a method for generating images, particularly in the field of medical technology, using a radiation source and a radiation detector, wherein the radiation generated by the radiation source hits an object to be examined and subsequently the radiation detector.

[0006] From DE 10 2020 208 000 A1 a method for generating an X-ray image data set using a photon-counting X-ray detector is known.

[0007] DE 10 2012 205 051 A1 discloses a method for reducing artifacts caused by X-ray radiation directly impacting a measurement pixel of a detector after passing through a scintillator.

[0008] The task is therefore to specify a method and a device for reducing dynamic external interference effects, in particular electromagnetic interference fields, of an X-ray imaging system or an X-ray detector.

[0009] This problem is solved by a method for detecting electromagnetic interference fields during the operation of an X-ray detector according to claim 1, an interference detection device according to claim 11 and an X-ray detector according to claim 13.

[0010] In the inventive method for detecting electromagnetic interference fields during the operation of an X-ray detector, a value is determined which represents a variation of temporally successive detector signal values ​​of at least one pixel of the X-ray detector that is not exposed to X-ray radiation.

[0011] This can refer to either a pixel or a group of pixels whose measurement was determined without exposure to X-rays, or a group of pixels that was covered with a shielding material (lead, tungsten, ...) during the exposure of the detector to X-rays.

[0012] Variation is defined as a measure of a time-limited change, in particular an oscillatory behavior of a function value, especially a detector signal value. Such a detector signal value exhibits, in particular, a signal amplitude that can fluctuate due to disturbances. An electromagnetic interference field is defined as an electromagnetic field whose effect on the operation of the X-ray detector, through emission, radiation, or induction, or a combination thereof, causes an undesirable effect on the X-ray detector's measurement. In particular, it causes a variation in the offset of a detector signal, which can contribute to undesirable measurement fluctuations.The electromagnetic interference field is usually an external interference field that does not originate from the X-ray source that bombards the X-ray detector with X-rays to generate X-ray projection data or image data.

[0013] A pixel in an X-ray detector is defined as a sensor area within a group of adjacent sensor areas arranged on a sensor array. Each pixel can be assigned a separate sensor signal.

[0014] The measured value is compared to a predetermined threshold. This threshold specifies a maximum value that must not be exceeded. The threshold depends on the X-ray detector technology and its sensitivity to interference. Detector-type-specific tests must be conducted to determine the threshold up to which interference from a stray field is still tolerable.

[0015] The system determines whether interference from electromagnetic fields is present if the measured value exceeds the predetermined threshold. Otherwise, it assumes no electromagnetic interference is present, and image data is generated and output, if necessary, in a subsequent imaging process based on detector signals. The detection of an interference field is advantageous, preventing the measurement of an incorrect offset value for a detector signal or the acquisition and processing of measurement data distorted by the interference field. This allows the user to be informed and / or warned in a timely manner, preventing the acquisition of image data containing artifacts that would otherwise have to be discarded.If necessary, unnecessary repetition of X-ray images can be prevented, thus avoiding increased radiation exposure resulting from repeating an X-ray image.

[0016] The interference detection device according to the invention has an input interface for receiving detector signals from one or more pixels of an X-ray detector. The interference detection device according to the invention also includes a variation detection unit for determining a value that represents a variation of temporally successive detector signal values ​​of at least one pixel of the X-ray detector that is not exposed to X-rays.

[0017] Part of the fault detection device according to the invention is also a comparison unit for comparing the value with a predetermined threshold value.

[0018] Furthermore, the interference detection device according to the invention comprises an interference detection unit for determining that interference is caused by electromagnetic interference fields if the determined value exceeds the predetermined threshold. The interference detection device according to the invention shares the advantages of the inventive method for detecting electromagnetic interference fields during the operation of an X-ray detector.

[0019] The X-ray detector according to the invention comprises a detector unit with a plurality of detector pixels, an interference detection device according to the invention, and an evaluation unit configured to evaluate detector signals from the detector unit if the interference detection device has determined that no interference from electromagnetic fields is present. The X-ray detector according to the invention offers the advantages of the interference detection device according to the invention.

[0020] A large proportion of the aforementioned components of the interference detection device according to the invention can be implemented wholly or partially as software modules in a processor of a corresponding computer system, e.g., a control unit of an X-ray imaging system or X-ray detector, or a computer used to control such a system. A largely software-based implementation has the advantage that even previously used computer systems can be easily retrofitted by means of a software update to operate in the manner of the invention.

[0021] Therefore, the problem is also solved by a corresponding computer program product with a computer program that can be directly loaded into a computer system, containing program sections to execute the steps of the inventive method for detecting electromagnetic interference fields during the operation of an X-ray detector when the program is executed in the computer system. Such a computer program product may, in addition to the computer program, optionally include additional components such as documentation and / or additional components, including hardware components such as hardware keys (dongles, etc.) for using the software.

[0022] For transport to and / or storage on or in the computer system, a computer-readable medium, such as a memory stick, a hard drive, or other portable or permanently installed data carrier, can be used, on which the program sections of the computer program that can be read and executed by a computer system are stored. The computer system may, for example, have one or more cooperating microprocessors or similar components for this purpose.

[0023] The dependent claims and the subsequent description each contain particularly advantageous embodiments and further developments of the invention. In particular, the claims of one claim category may also be further developed analogously to the dependent claims of another claim category. Furthermore, within the scope of the invention, the various features of different embodiments and claims may also be combined to form new embodiments.

[0024] In a preferred embodiment of the inventive method for detecting electromagnetic interference fields during the operation of an X-ray detector, a value of a variation per pixel is determined in the step of determining a value. Then, in the step of comparing the value, the value is compared with a predetermined threshold. Finally, in the step of determining a possible interference, it is determined whether interference due to electromagnetic interference fields occurs if one of the determined values ​​exceeds the predetermined threshold. In this embodiment, a variation per pixel of an X-ray detector is determined, so that it is possible to determine very precisely which part of an X-ray detector is affected by an electromagnetic interference field.

[0025] In one variant of the inventive method for detecting electromagnetic interference fields during the operation of an X-ray detector, the comparison step begins with the calculation of an average variation value across a plurality of pixels, based on the variation values ​​determined for each pixel. This average value is then compared with a predetermined threshold. In the step of determining a possible interference, it is then established that interference caused by electromagnetic interference fields occurs if the average value exceeds the predetermined threshold. Advantageously, interferences that may only affect individual pixels and are likely intrinsic are compensated for by the averaging process.

[0026] In a preferred embodiment of the inventive method for detecting electromagnetic interference fields, the variation of temporally successive detector signal values ​​comprises a variance of temporally successive detector signal values ​​of an X-ray detector not exposed to X-rays. The variance of temporally successive detector signal values ​​is understood as a distribution of these detector signal values ​​around a mean value. The variance is calculated by dividing the sum of the squared deviations of the detector signal values ​​from the arithmetic mean of the detector signal values ​​by the number of detector signal values. The variance is a measure of the dispersion of values ​​around a mean value.

[0027] In a preferred embodiment of the inventive method for detecting electromagnetic interference fields, the variation of successive detector signal values ​​comprises a standard deviation of successive detector signal values ​​of an X-ray detector not exposed to X-rays. The standard deviation is understood to be the square root of the variance of the successive detector signal values. If the distribution of the detector signal values ​​follows a normal distribution, then 68 percent of the detector signal values ​​lie within the standard deviation.

[0028] In an alternative embodiment of the method according to the invention, the value represents a variation of temporally successive detector signal values ​​of a group of pixels of the X-ray detector. Advantageously, measured values ​​of an entire group of pixels are included in the determination of the variation, so that measurement errors caused by defects in individual pixels are compensated.

[0029] In this variant, during the step of determining a value for a variation of temporally successive detector signal values, spatially averaged values ​​of simultaneously acquired detector signal values ​​for the group of pixels are calculated, and the value of the variation is determined based on these averages. In the comparison step, the value is compared with a predetermined threshold, and in the step of determining potential interference, it is determined whether interference from electromagnetic fields is present if the determined value exceeds the predetermined threshold. In this variant, the variation is determined based on average detector signal values. This variant can also average out design-related deviations of individual pixels in their response behavior. However, the variation only needs to be calculated once, i.e., only based on the average values.

[0030] In this variant, the variation preferably includes a variance of location-related mean values ​​of simultaneously recorded detector signal values ​​for the group of pixels, if a variance is to be calculated as a comparison quantity.

[0031] Alternatively, the variation exhibits a standard deviation of spatially related means of simultaneously recorded detector signal values ​​for the group of pixels, if a standard deviation is to be calculated as a comparison quantity.

[0032] In one variant of the inventive method, the comparison step begins with the calculation of an average variation value across multiple groups of pixels, based on the variation values ​​determined for each group of pixels. This average value is then compared to a predetermined threshold. Advantageously, a broad range of pixels is included in the calculation of the comparison value. Subsequently, in the step of determining a potential disturbance, it is established that a disturbance caused by electromagnetic interference fields occurs if the average value exceeds the predetermined threshold.

[0033] Advantageously, a user is informed of the interference, and in particular warned, when an interference has been detected by the method according to the invention. The user can advantageously be informed or warned by means of a user interface, in particular an optical and / or acoustic display. Such information or warning to the user has the advantage that the user can react appropriately before acquiring medical image data with the X-ray detector, for example by repositioning devices that generate interfering fields.

[0034] An advantageous embodiment of the fault detection device has a user interface, in particular an optical and / or acoustic display, which is designed to inform a user about a fault that can be detected or has been detected by a method according to the invention.

[0035] The invention is explained in more detail below with reference to the accompanying figures and exemplary embodiments. The figures show: Fig. 1 a flowchart illustrating a method for detecting electromagnetic interference fields during the operation of an X-ray detector according to an embodiment of the invention, Fig. 2 a schematic representation of a fault detection device according to an embodiment of the invention, Fig. 3 A schematic representation of an X-ray detector system according to an embodiment of the invention.

[0036] In Fig. Figure 1 shows a flowchart 100, which describes a method for detecting electromagnetic interference fields STF during the operation of an X-ray detector 30 (see Figure 1). Fig. 3) illustrated according to an embodiment of the invention.

[0037] In step 1.I, a value W is calculated, which represents a standard deviation (STBW) of temporally successive detector signal values ​​(DSW) of a group of pixels P not exposed to X-rays. i determined by the X-ray detector 30.

[0038] In step 1.II, the value W is compared with a predetermined threshold SW.

[0039] In the event that step 1.II determined that the predetermined threshold SW was exceeded, which in Fig. If step 1 is marked with "y", the process proceeds to step 1.III, in which it is determined whether a disturbance ST is caused by electromagnetic interference fields STF. If step 1.II determined that the predetermined threshold SW was not exceeded, which is the case in Fig. If 1 is labelled with "n", then the process returns to step 1.I and signals from neighboring groups of pixels P are used. ior again the same group of pixels P i examined at a later date.

[0040] In Fig. Figure 2 shows a schematic representation of a fault detection device 20 according to an embodiment of the invention.

[0041] The interference detection device 20 has an input interface 21 for receiving detector signals DS from one or more pixels P i of an X-ray detector 30 (see Fig. 3) on.

[0042] Part of the interference detection device 20 is also a variation determination unit 22 for determining a value W, which is a standard deviation STABW of temporally successive detector signal values ​​of a pixel P not exposed to X-rays. i reproduces the X-ray detector 30.

[0043] The fault detection device 20 also includes a comparison unit 23 for comparing the value W with a predetermined threshold SW. If the threshold SW is exceeded by the value W or the value of the standard deviation STABW, a fault message ST is generated.

[0044] Furthermore, the fault detection device 20 includes a fault investigation unit 24 for determining that a fault is caused by electromagnetic interference fields STF, in the event that a fault ST has been detected.

[0045] In Fig. Figure 3 is a schematic representation of an X-ray detector 30 according to an embodiment of the invention. The X-ray detector 30 itself is designed to detect X-ray radiation RS incident upon it.

[0046] The X-ray detector 30 according to the invention comprises a detector unit 31 with a plurality of detector pixels. Part of the X-ray detector 30 according to the invention is also an interference detection device 20 as described in Fig. Figure 2 shows which one is set up for this purpose.

[0047] The X-ray detector 30 according to the invention also includes an evaluation unit 32, which is configured to evaluate detector signals DS of the detector unit 31 in the event that the interference detection device 20 has determined that no interference is caused by electromagnetic interference fields and to generate image data BD based on detector signals or, in the event of an interference, to output an interference message regarding an interference field STF.

[0048] Finally, it should be noted once again that the methods and devices described above are merely preferred embodiments of the invention and that the invention can be varied by a person skilled in the art without departing from the scope of the invention, insofar as it is defined by the claims. For the sake of completeness, it should also be noted that the use of the indefinite articles "a" or "an" does not preclude the possibility that the features in question may be present multiple times. Likewise, the term "unit" does not preclude the possibility that it consists of several components, which may also be spatially distributed. Regardless of the grammatical gender of a particular term, persons of male, female, or other gender identities are included.

Claims

[1] Method for detecting electromagnetic interference fields (STF) during the operation of an X-ray detector (30), comprising the steps: - Determining a value (W) which represents a variation in temporally successive detector signal values ​​(DSW) of at least one pixel not exposed to X-rays (P). i ) of the X-ray detector (30) reproduces, - Comparing the value (W) with a predetermined threshold (SW), - Determine that a disturbance (ST) occurs due to electromagnetic interference fields (STF) if the determined value (W) exceeds the predetermined threshold (SW). [2] Method according to claim 1, wherein - in the step of determining a value (W) a value (W) of a variation per pixel (P) i ) is determined, - in the comparison step, the values ​​(W) are compared with a predetermined threshold (SW) and - in the step of determining a possible disturbance (ST), it is determined that a disturbance (ST) occurs due to electromagnetic interference fields (STF) if one of the determined values ​​(W) exceeds the predetermined threshold (SW). [3] Method according to claim 2, wherein - in the comparison step, initially based on each pixel (P i ) determined values ​​(W) of the variation each a mean value over a plurality of pixels (P) i ) is determined and the mean is compared with a predetermined threshold (SW) and - in the step of determining a possible disturbance (ST), it is determined that a disturbance due to electromagnetic interference fields (STF) occurs if the mean value exceeds the predetermined threshold (SW). [4] Method according to one of the preceding claims, wherein the variation of temporally successive detector signal values ​​(DSW) comprises a variance of temporally successive detector signal values ​​(DSW) of an X-ray detector (30) not exposed to X-ray radiation. [5] Method according to any of the preceding claims, wherein the variation of temporally successive detector signal values ​​(DSW) comprises a standard deviation (STABW) of temporally successive detector signal values ​​(DSW) of an X-ray detector (30) not exposed to X-ray radiation. [6] Method according to claim 1, wherein the value (W) is a variation of temporally successive detector signal values ​​(DSW) of a group of pixels (P) i ) of the X-ray detector (30). [7] Method according to claim 6, wherein - in the step of determining a value (W) of a variation of temporally successive detector signal values ​​(DSW), spatially averaged values ​​of simultaneously acquired detector signal values ​​(DSW) for the group of pixels (P) i ) are determined and the value of the variation is determined based on the means, - in the comparison step the value (W) is compared with a predetermined threshold value (SW) and - in the step of determining a possible disturbance (ST), it is determined that a disturbance (ST) occurs due to electromagnetic interference fields (STF) if the determined value (W) exceeds the predetermined threshold (SW). [8] Method according to claim 7, wherein the variation is a variance of spatially related mean values ​​of simultaneously acquired detector signal values ​​(DSW) for the group of pixels (P i ) includes. [9] Method according to one of claims 7 or 8, wherein the variation is a standard deviation (STD) of spatially related mean values ​​of simultaneously acquired detector signal values ​​(DSW) for the group of pixels (P i ) includes. [10] Method according to claim 7, wherein - in the comparison step, initially based on each group of pixels (P i ) determined values ​​(W) of the variation each represent a mean value over a plurality of groups of pixels (P) i ) is determined and the mean is compared with a predetermined threshold (SW) and - in the step of determining a possible disturbance (ST), it is determined that a disturbance due to electromagnetic interference fields (STF) occurs if the mean value exceeds the predetermined threshold (SW). [11] Fault detection device (20), comprising: - an input interface (21) for receiving detector signals (DS) of at least one pixel (P) i ) of an X-ray detector (30), - a variation detection unit (22) for determining a value (W) which represents a variation of temporally successive detector signal values ​​(DSW) of at least one pixel (P) not exposed to X-rays i ) of the X-ray detector (30) reproduces, - a comparison unit (23) for comparing the value (W) with a predetermined threshold value (SW), - a fault detection unit (24) for determining that a fault (ST) is caused by electromagnetic interference fields (STF) if the determined value (W) exceeds the predetermined threshold (SW). [12] Fault detection device (20) according to claim 11, which has a user interface, in particular an optical and / or acoustic display, which is configured to inform a user of a fault which can be detected by a method according to any one of claims 1 to 10. [13] X-ray detector (30), comprising: - a detector unit (31) with a plurality of detector pixels, - a fault detection device (20) according to claim 11 or 12, - an evaluation unit (32) which is set up to evaluate detector signals (DS) of the detector unit (31) in the event that the interference detection device (20) has determined that no interference (ST) is caused by electromagnetic interference fields (STF). [14] Computer program product comprising instructions which, when the program is executed by a computer, cause it to perform the steps of the method according to any one of claims 1 to 10. [15] Computer-readable storage medium comprising instructions which, when executed by a computer, cause it to perform the steps of the method according to claims 1 to 10.

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