Improved image acquisition

Abstract

The invention relates to a detection device for X-rays, an imaging system and a method for detecting electromagnetic radiation using a detection device for X-rays, wherein an estimate of an unfinished measurement is obtained before a discontinuity in the electromagnetic radiation, wherein the discontinuity is a change or interruption in the beam or intensity of the electromagnetic radiation.

Description

Technical Field

[0001] The invention relates to a detection device for X-rays, a corresponding imaging system, a method for detecting electromagnetic radiation using a detection device for X-rays, a computer program element and a computer-readable medium. Background Art

[0002] The emergence of new computed tomography (CT) image acquisition methods, such as sparse sampling utilizing grid switching tubes, kVp switches (kVp is the common symbol for tube accelerating voltage), or grid filters, requires that the readout electronics not propagate signal information across significant discontinuities in X-ray intensity that may occur due to spectral variations or blanking periods of the X-ray tube.

[0003] A known readout topology is that of a CT readout ASIC comprising a current to frequency converter or a ratiometric converter or a folded integral converter, which allows a large dynamic range and resolution to be achieved. However, a certain amount of error is inherently introduced in the signal quantization, for example when the X-rays are switched off for a short period of time. In addition, other methods adapted to the readout architecture can be used to obtain additional spectral information by estimating the variance of the signal. Such methods are also known as Campbell readouts. However, these methods do not take into account significant discontinuities.

[0004] Ewals Roessl et al., in Nuclear Science Symposium Conference Record (NSS / MIC), 2010 IEEE, 2010, pp. 2112-2115, doi:10.1109 / NSSMIC.2010.5874151, discloses a dual-energy imaging technique based on simultaneous acquisition of the mean (DC) and variance (AC) components of the electrical detector signal, i.e., simultaneous integration mode readout and Campbell mode readout (fluctuation mode). The method is based on the "Campbell theorem", which states that the variance of the deviation from the mean detector signal is proportional to the second moment of the incident X-ray energy spectrum.

[0005] US 2011 / 216878 discloses processing a detector signal indicative of polychromatic radiation detected by an imaging system, the imaging system comprising a first processing channel, the first processing channel generating a first spectral signal derived from the detector signal, wherein the first spectral signal comprises first spectral information about the detector signal; and a second processing channel, the second processing channel generating a second spectral signal derived from the same detector signal, wherein the second spectral signal comprises second spectral information about the detector signal, wherein the first spectral signal and the second spectral signal are used to spectrally resolve the detector signal. Summary of the invention

[0006] Therefore, improvements in CT image acquisition methods may be needed.

[0007] The objects of the invention are solved by the subject-matter of the independent claims; further embodiments are incorporated in the dependent claims.It should be noted that the hereinafter described aspects of the invention also apply to the detection device, the imaging system and the method, and vice versa.

[0008] An imaging system according to the invention, such as a CT device, for example, comprises: a source for providing electromagnetic radiation, such as X-rays, and a detection device accordingly. The generated X-rays form a beam of electromagnetic radiation. The beam penetrates an object under examination, such as a patient. After having penetrated the object under examination, the beam impinges on a detection device according to the invention for X-rays.

[0009] According to the present invention, the detection device for X-rays comprises: at least one sensor adapted to provide a current in response to electromagnetic radiation exposure during at least one image acquisition frame; at least one electronic device board including at least one integrator providing a capacitor, the capacitor being configured to discharge in response to the current provided by the sensor, wherein the discharge of the capacitor defines at least one cycle; a capacitor discharge analyzer, a counter and a processor unit. The capacitor discharge analyzer is configured to analyze the discharge of the capacitor and provide a full discharge signal when the capacitor is fully discharged in response to the current provided by the sensor. The counter is configured to measure a cycle time based on the full discharge signal provided to the counter by the capacitor discharge analyzer, the cycle time being defined as the period between the start of a new cycle and the full discharge of the capacitor. The processor unit is configured to: obtain the cycle time of the at least one cycle from the counter; store the provided cycle time of the at least one cycle; and compare the cycle time of the at least one cycle by comparing with one or more previously stored cycle times. An estimate of the uncompleted cycle is obtained before a discontinuity of electromagnetic radiation, wherein the discontinuity is a change or interruption in the beam of electromagnetic radiation or the intensity of electromagnetic radiation.

[0010] The detection device for X-rays comprises at least one sensor for sensing incident electromagnetic radiation after having penetrated the object under examination during at least one image acquisition frame. The image acquisition frame is defined as a time interval during which the object under examination is exposed to the electromagnetic radiation. The image acquisition frame can be defined as a time interval comprising a predetermined number of cycles. The number of cycles can vary depending on the image acquisition method used and / or on the electronic device board used. In addition, a discontinuity during an image acquisition frame can indicate its termination, followed by a subsequent image acquisition frame. During the subsequent image acquisition frame, the object will be exposed to the electromagnetic radiation.

[0011] The one or more sensors provide the current in response to the electromagnetic radiation exposure.It should be noted that the present invention encompasses any direction of current provided by the sensor(s), including any suitable sensor type.

[0012] The current provided by the at least one sensor is provided to an electronics board. The electronic circuit of the electronics board may include analog / digital (A / D) conversion electronics. The basic circuit of the electronic circuit board includes a current to frequency converter, wherein the current provided by the sensor is applied to the input of an integrator that provides a capacitor (which is charged). The integrator output is a voltage ramp whose slope is proportional to the input current provided by the sensor. When the integrator output reaches a threshold (which can be defined), the current charge of the capacitor is discharged. The capacitor discharges in response to the current (and bias) provided by the sensor. The capacitor can be a feedback capacitor. The discharge of the capacitor causes a new cycle in response to the current provided by the sensor. The discharge of the capacitor is referred to as a cycle in this article. In some examples, the complete discharge of the capacitor can define the cycle.

[0013] A capacitor discharge analyzer is configured to analyze the discharge of the capacitor and provide a complete discharge signal when the capacitor is fully discharged in response to the current provided by the sensor. The capacitor discharge analyzer may be configured to receive an input signal from a charge measurement device coupled to the capacitor, the charge measurement device being configured to measure the charge of the capacitor over time from an initial capacitor charge to a complete discharge (zero capacitor charge). The capacitor discharge analyzer may be included in a processor unit.

[0014] The one or more sensors may for example comprise an array of photodiodes held on a substrate, typically made of ceramic. In some examples, the photodiodes can be equipped with a scintillator for X-ray to optical conversion.

[0015] The time taken to completely discharge the amount of charge present in the capacitor is referred to herein as the cycle time. The cycle time is indicative of the intensity of the electromagnetic radiation.

[0016] The at least one cycle time is stored, for example, in a storage element associated with the processor unit. The cycle time(s) for one or all cycles can be retrieved and stored in the storage element. It should be noted that discharging the capacitor typically also (implicitly) specifies a current direction, the invention encompassing any current direction.

[0017] The cycle time of the at least one cycle is compared with one or more previously stored cycle times. Before the first discharge of the capacitor, i.e. before the first cycle time can be provided, a default value may be stored as the cycle time. The default value is then replaced by the first cycle time.

[0018] In the case of a discontinuity of the electromagnetic radiation, wherein the discontinuity is a change or interruption in the intensity of the electromagnetic radiation beam or the electromagnetic radiation, an estimate of the corresponding unfinished cycle is obtained. The discontinuity can be caused by a grid switch, a change in the incident spectrum, a shutdown, etc. In other words, if a cycle is interrupted before its completion, i.e., the elapsed time of the unfinished cycle is less than the cycle time for the last completed cycle, the ratio of these two cycle times represents an estimate of the unfinished cycle before the discontinuity of the beam. The unfinished cycle can also be referred to as a residual signal. The cycle is taken into account by providing an estimate of the unfinished cycle, for example by correcting the output of the detection device for the corresponding image acquisition frame. The evaluation of the cycle time after the discontinuity allows the elimination of crosstalk across adjacent image acquisition frames or projections.

[0019] According to the present invention, the imaging system comprises: a source for providing electromagnetic radiation; and a detection device which provides an estimate of an uncompleted cycle acquired before a discontinuity in the electromagnetic radiation, wherein the discontinuity is a change or interruption in the beam of the electromagnetic radiation or the intensity of the electromagnetic radiation.

[0020] According to the present invention, a method for detecting electromagnetic radiation using a detection device for X-rays includes the following steps: sensing electromagnetic radiation exposure during at least one image acquisition frame; providing a cycle time for at least one cycle, wherein the cycle time is defined as a period of time for fully discharging a capacitor of at least one integrator of an electronic device board of the detection device; storing the provided cycle time of the at least one cycle; and comparing the cycle time of the at least one cycle with one or more previously stored cycle times, wherein an estimate of an uncompleted cycle is obtained before a discontinuity in the electromagnetic radiation, wherein the discontinuity is a change or interruption in the beam of the electromagnetic radiation or the intensity of the electromagnetic radiation.

[0021] According to the example, if the at least one cycle is completed, the cycle time of the at least one cycle replaces the stored cycle time of the last completed cycle. If the cycle time of the actual cycle has been completely completed, the previously stored cycle time is updated / replaced with the cycle time of the actual cycle. A default value is provided as the cycle time before the first cycle time can be provided. The default value is then replaced with the first cycle time. Thus, the cycle time of the last complete cycle is continuously acquired and updated. At the end of each cycle, the cycle time is stored for the completely completed cycle, and the cycle time for the next cycle of the image acquisition frame is provided. If the next cycle is completely completed, the previously stored cycle time is replaced with the actual cycle time, i.e., only one elapsed time measurement result is stored at any given time.

[0022] According to an example, the estimate for the uncompleted cycle is obtained for a cycle time that is less than the stored cycle time of the last completed cycle. The time elapsed before the discontinuity is compared with the stored cycle time for the last completed cycle. In this example, only the last completed cycle time is available for comparison with the provided cycle time of the actual cycle.

[0023] According to an example, the ratio of the provided cycle time to the cycle time for the last completed cycle represents an estimate of the uncompleted cycle. The ratio between these two cycle times represents an estimate of the uncompleted cycle before the discontinuity of the beam.

[0024] According to an example, the cycle times of all cycles during at least one image acquisition frame are provided, and the variance of the cycle times is calculated. The cycle times of all events during the at least one image acquisition frame are used. The variance is calculated, which is the expected value of the squared deviation of the cycle time from the mean of the cycle time. The cycle time is weighted according to the square of the amplitude (this is also called Campbell mode readout). The distribution of the cycle time of each cycle during the image acquisition frame is a measure of the variation in the intensity of the X-ray beam within the image acquisition frame. Therefore, a second readout channel (or Campbell channel) is provided, which has a spectral footprint different from the integration mode (integrating capacitor charge). Providing such a Campbell mode readout allows for energy separation of the electromagnetic radiation. The variance of the cycle time can be calculated for each cycle of each image acquisition frame (or multiple image acquisition frames).

[0025] According to an example, the discontinuity comprises a change in the wavelength of the electromagnetic radiation and / or a blanking period of the electromagnetic radiation. The blanking period of the electromagnetic radiation can be caused, for example, by a grid switch. Such a discontinuity will result in a partial cycle during the radiation exposure. This may result in an erroneous output of the detection device, for example, in the case of switching off the X-ray beam for a short period of time. With the proposed method, an estimate of the uncompleted cycle is obtained, and the measurement results during one or more image acquisition frames are compensated or corrected, and the image acquisition is improved.

[0026] Among the image acquisition methods, for some applications it may be desirable to focus on the use of a fine pitch grid in front of the X-ray tube (source) and to exploit the focal deflection functionality. The X-ray beam can then be filtered by the grid or substantially unchanged by the grid. Thus, the beam has a distinct spectral footprint at each position of the focal deflection (DFS = double focal spot). In such a grid-based image acquisition method, the filtered beam may have a significant change (reduction) in the intensity of the electromagnetic radiation, i.e. there are discontinuities in the electromagnetic radiation. In order to compensate for such intensity losses, image acquisition frame-by-frame X-ray dose modulation can be performed, however, the corresponding X-ray tube and speed requirements must be met.

[0027] According to an example, the discontinuity of the electromagnetic radiation is compensated by modifying the gain of at least one period during the at least one image acquisition frame. By modifying the gain during the at least one image acquisition frame, an optimal spectral result, such as an optimized quantum noise ratio, is obtained. For example, this reduces or eliminates the need to acquire image acquisition frames with different integration periods depending on the DFS position. In other words, such a frame-based automatic change of gain can be implemented in any suitable readout topology.

[0028] According to an example, the modification of the gain comprises adding a reference voltage which resets the capacitor when the signal reaches a certain threshold. For example, the threshold can be ground. Thus, an efficient current to frequency converter is provided (by calculating the amount of charging cycles within a frame).

[0029] According to an example, the reference voltage is different for subsequent image acquisition frames. Using a different reference voltage for each image acquisition frame allows effectively modifying the gain of the front-end readout electronics. In some examples, the image acquisition frames are numbered and the reference voltage used for odd frames is half of the reference voltage used for even frames. This results in the gain for odd frames being effectively twice the gain for even frames. In some examples, the ratio between two such reference voltages can be selected or tuned so that the detection device operates in an optimal configuration, which is given by the change in the tube focal spot (e.g., DFS explained above) combined with the expected signal intensity changes caused by the grid, thereby enhancing the spectral separation across the focal spot position. Alternatively, such changes in intensity can also account for the photon flux caused by the kVp switch.

[0030] The present invention can be used in various image acquisition methods and systems, such as CT, spectral CT, grid-based spectral CT, kVp switching, sparse sampling, etc.

[0031] According to the invention, a computer program element for controlling the device according to the invention is proposed, which, when run by a processing unit, is adapted to perform the above-mentioned method steps. Likewise, a corresponding computer-readable medium having stored the program element is proposed.

[0032] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Exemplary embodiments of the present invention will be described below with reference to the following drawings:

[0034] Figure 1 : Schematic illustration of the imaging system;

[0035] Figure 2 : Schematic illustration of a timing diagram;

[0036] Figure 3: Example integrator output;

[0037] Figure 4: Measured time periods across all periods of Figure 3;

[0038] Figure 5 : Flow chart of the method according to the present invention;

[0039] Figure 6 : Another schematic illustration of a timing diagram. DETAILED DESCRIPTION

[0040] Figure 1 An imaging system 10 for imaging an object according to the present invention is schematically and exemplarily shown, which in this example is a computed tomography (CT) device. The CT device 10 comprises a gantry 12 that can rotate about a rotation axis R extending parallel to the z-direction. A radiation source 14 (also referred to as a photon source), which may be a polychromatic X-ray tube, is mounted on the gantry 12. The radiation source 14 is provided with a collimator 16, which forms a (e.g., cone-shaped) radiation beam 18 from the radiation (photons) generated by the radiation source 14. The radiation passes through an object under examination (such as a patient), which is arranged in a (e.g., cylindrical) imaging zone 20 (also referred to as an examination zone).

[0041] After having passed through the imaging zone 20, the radiation beam 18 is incident on a detection device 22 for X-rays (a detector for detecting ionizing radiation), which includes a two-dimensional detection surface. The detection device 22 is also mounted on the frame 12. The detection device 22 includes (one or more) sensors 21. (One or more) sensors 21 provide current in response to electromagnetic radiation exposure. The electromagnetic radiation is provided by the radiation source 14. The detection device 22 includes at least one capacitor and at least one photodiode coupled to the at least one capacitor. The photodiode can be equipped with a scintillator, which is used for X-ray to optical conversion. The full cycle time is defined as the time it takes to completely discharge the capacitor in response to the photodiode current signal provided by the (one or more) sensors. The current also depends on whether the photodiode is a common cathode or a common anode. The present invention is not limited by the sign of the current (the only change required is the threshold at which the capacitor is recharged). This embodiment includes a common cathode, but is not limited to this.

[0042] The CT device 10 comprises two motors 24, 26. The gantry 12 is driven by the motor 24 at a preferably constant but adjustable angular velocity. The motor 26 is provided for displacing an object, such as a patient, arranged on a patient table in the imaging zone 20 parallel to the direction of the rotation axis R or the z-axis. These motors 24, 26 are controlled, for example, by a control unit 28, so that the radiation source 14, the (detector) detection device 22 and the imaging zone 20 are moved relative to each other along a spiral direction. However, it is also possible that the object does not move, but only the radiation source 14 and the detector 22 are rotated, that is, the radiation source 14 moves along a circular trajectory relative to the object or the imaging zone 20. In addition, in another embodiment, the collimator 16 can be adapted to form another beam shape, in particular a fan beam, and the detector 22 can include a detection surface, which is shaped to correspond to other beam shapes, in particular to a fan beam.

[0043] During the relative movement of the radiation source 14 and the imaging zone 20, the (one or more) sensors 21 provide a current in response to the electromagnetic radiation exposure (the provided current can also be referred to as a detection signal or detection value; preferably one signal value per pixel, i.e. per sensor or detection element). The signal is evaluated in a readout electronics device that can be included in the detector 22. The processor unit 30 is configured to: provide a cycle time of at least one cycle, store the provided cycle time of the at least one cycle; and compare the cycle time of the at least one cycle with one or more previously stored cycle times. An estimate of the uncompleted cycle is obtained before a change or interruption of the beam of the electromagnetic radiation or the intensity of the electromagnetic radiation. The image reconstructed by the processor unit 30 can be provided to a display unit 32 for displaying the reconstructed image. The control unit 28 is preferably also suitable for controlling the radiation source 14, the detection device 22 and the processor unit 30.

[0044] According to further embodiments, a direct conversion detector can also be used. It typically includes a direct conversion semiconductor layer, such as cadmium telluride or CZT (cadmium zinc telluride), or silicon (Si), GaAs, etc. In this layer, charge-carrying particles such as electrons and holes are generated in response to incident ionizing radiation. The carriers are detected via multiple electrodes by means of an electric field between an anode and a cathode. In other words, incident photons (e.g., X-ray photons) generate charge carriers or charge carrier clouds when they are incident in the layer. By evaluating the number of charge carriers detected at different electrodes, a reading of the spatial position of the incident radiation in the direct conversion semiconductor layer can be obtained. Thus, an image of an object in an imaging area can be derived.

[0045] Figure 2A schematic illustration of a timing diagram according to the present invention is shown. The timing diagram demonstrates the functionality proposed by the present invention. The integrator output (vertical axis) is shown as a function of time (horizontal axis). The integrator output is a voltage ramp 42, the slope of which is proportional to the input current provided by the (one or more) sensors 21 of the detection device 22. The integrator includes a capacitor. When the integrator output reaches a threshold value (which can be defined), the current charge of the capacitor is discharged. The discharge of the capacitor causes a new cycle 46 in response to the current provided by the sensor.

[0046] Within an image frame 40, which can also be referred to as a projection, the charge of the capacitor is discharged during several cycles 46. The cycle time 44, i.e. the time taken for each cycle 46, is measured. At the end of each cycle 46, the time is stored 48 and a new measurement is made. If the subsequent cycle 46 is completely completed, i.e. a full cycle time 44 is measured, the previously stored cycle time 44 is replaced by the actual cycle time 44. In this case, the last full cycle time 44 is stored.

[0047] Likewise, however, all cycle times 44 are stored and provided for determining changes in cycle times 44 within an image acquisition frame 40 or within a plurality of image acquisition frames. Such changes are identified as changes in cycle times 44 for all events.

[0048] If a cycle 46 is interrupted 50 before it is completed, the time 52 that has elapsed until that moment is compared (ratio) with the stored cycle time 44 for the last completed cycle. The ratio between these two cycle times represents an estimate of the uncompleted cycle integrated on the capacitor before the discontinuity 54 of the electromagnetic radiation.

[0049] In this embodiment, the discontinuity 54 is a blanking period following a grid switch event. The capacitor is reset and remains reset, thereby preventing the integrator output of bias current, leakage current, etc. when the X-ray source is turned off. At the end of the discontinuity 54, the capacitor reset is released and the next cycle 46 begins from a known initial condition, i.e., without any discontinuity. This is shown as the integrator output 58.

[0050] Image acquisition methods such as, for example, a kVp switch or a grid filter (both used for dual energy spectral CT) for known changes in the intensity of electromagnetic radiation (e.g., a kVp switch or a dual focal spot (DFS) change), as explained above, obtain an estimate of the uncompleted cycles before the intensity change. Therefore, the proposed methods can be combined in a single implementation covering sparse sampling, kVp switching, grid switching, and grid-based spectral CT.

[0051] The measurement of the cycle time can be accomplished by a counter. The cycle time is defined as the period between the start of a new cycle and the complete discharge of the capacitor based on a complete discharge signal provided to the counter by the capacitor discharge analyzer. The counter preferably operates at a high frequency. Counter frequencies in the range of 50 MHz or higher can be used.

[0052] FIG3 shows an exemplary measured integrator output IO versus time t measured in seconds. In the embodiment shown, the period for the actual measurement is obtained by using a fast scintillator (exemplary LaBr) and a fast photodiode (see Figure 2 The measurements include the Poisson arrival times of incident photons corresponding to a polychromatic 120 kVp spectrum.

[0053] FIG. 4 shows the cycle time t measured in seconds on the vertical axis for a plurality of N cycles 44 within the image acquisition frame shown in FIG. 3 (see FIG. 4 ). Figure 2 In this example, this corresponds to a change in signal current of approximately 8e-17.

[0054] Figure 5 A flow chart of a method according to the invention is shown. Step S1 provides sensing of electromagnetic radiation exposure during at least one image acquisition frame. A cycle time of at least one cycle is provided S2. The cycle time of at least one event is stored S3. The cycle time of at least one event is evaluated S4, wherein an estimate of an uncompleted cycle is obtained before a discontinuity in the electromagnetic radiation, wherein the discontinuity is a change or interruption in the beam of the electromagnetic radiation or in the intensity of the electromagnetic radiation. A default value DV is provided before storing the first cycle time.

[0055] Figure 6 Another schematic illustration of an example of a timing diagram for a current to frequency type circuit is shown. The integrator output (vertical axis) is shown as a function of time (horizontal axis).

[0056] Discontinuities in the intensity of the electromagnetic radiation may occur, for example, when using a fine pitch grid in front of the X-ray tube (source) and utilizing focal spot deflection (DFS). In the example shown, such discontinuities are compensated by gain modification.

[0057] In the current image acquisition frame N, a first position DFS1 of the focal spot is provided. The previous acquisition frame N-1 and the subsequent acquisition frame N+1 provide an alternative position DFS2 of the focal spot.

[0058] For each image acquisition frame N-1, N, N+1, the gain is modified by adding a reference voltage. In this example, the reference voltage is automatically switched on and off for each image acquisition frame in synchronization with a trigger for the image acquisition frame. In this example, the effective change of the gain G occurs only in the first cycle of the image acquisition frame of the subsequent frame N+1.

[0059] As in Figure 6 As can be seen in , a change in gain means that the offset frequency is also affected by the same gain. Although not strictly necessary, the bias current can also be changed at the same ratio as the reference voltage. This allows to adjust the current (reduce the bias) for higher gain regions and thereby reduce the noise caused by unnecessary large currents. This may be particularly desirable if the frame time does not remain the same, i.e. in the case where the image acquisition frame with the alternative position DFS2 of the focal spot is longer than the image acquisition frame with the first position DFS1 of the focal spot. In other examples, the DFS positions may be associated with different kVp settings in the eg-kVp switch.

[0060] The gain changes described above are consistent with known changes in beam quality expected from kVp switching or DFS applications. The gain changes have been illustrated in the form of a current-to-frequency type readout circuit. Other circuits (e.g., gain amplifiers) can be similarly adapted to respond to known changes in tube beam quality by changing operating settings accordingly.

[0061] In a further exemplary embodiment of the present invention, a computer program or a computer program element is provided, characterized in that it is adapted to: execute the method steps of the method according to one of the preceding embodiments on a suitable system.

[0062] Therefore, the computer program element may be stored on a computer unit, which may also be part of an embodiment of the present invention. The computing unit may be suitable for executing or inducing the steps of the method described above. In addition, it may be suitable for operating the components of the device described above. The computing unit can be suitable for automatically operating and / or executing the user's commands. The computer program can be loaded into a working memory of a data processor. The data processor can therefore be equipped to perform the method of the present invention.

[0063] This exemplary embodiment of the invention covers both a computer program that right from the beginning uses the invention and also a computer program that by means of an update turns an existing program into a program that uses the invention.

[0064] Furthermore, the computer program element may be able to provide all necessary steps to implement the procedure of the exemplary embodiment of the method as described above.

[0065] According to a further exemplary embodiment of the present invention, a computer readable medium, such as a CD-ROM, is provided, wherein the computer readable medium has a computer program element stored thereon, the computer program element being described in part by the foregoing text. The computer program may be stored and / or distributed on a suitable medium, such as an optical storage medium or solid-state medium provided with or as part of other hardware, but may also be distributed in other forms, for example via the Internet or other wired or wireless telecommunication systems.

[0066] However, the computer program may also be provided via a network like the World Wide Web and can be downloaded from such a network into a working memory of a data processor. According to a further exemplary embodiment of the present invention, a medium for making a computer program element available for downloading is provided, the computer program element being arranged to perform a method according to one of the aforementioned embodiments of the present invention.

[0067] It must be noted that embodiments of the present invention are described with reference to different subject matters. Specifically, some embodiments are described with reference to method type claims, while other embodiments are described with reference to device type claims. However, a person skilled in the art will deduce from the above and following description that, unless otherwise indicated, any combination of features relating to different subject matters, in addition to any combination of features belonging to one type of subject matter, is also considered to be disclosed with the present application. However, all functions can be combined to provide a synergistic effect, not just a simple sum of these functions.

[0068] Although the present invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description should be considered illustrative or exemplary rather than restrictive. The present invention is not limited to the disclosed embodiments. Other variations of the disclosed embodiments may be understood and implemented by those skilled in the art in practicing the claimed invention by studying the drawings, the disclosure, and the appended claims.

[0069] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A detection device for X-rays, comprising: at least one sensor adapted to provide a current in response to electromagnetic radiation exposure during at least one image acquisition frame; at least one electronics board including at least one integrator, the at least one integrator providing a capacitor configured to discharge in response to the current provided by the sensor, wherein the discharge of the capacitor defines at least one cycle; a capacitor discharge analyzer configured to analyze the discharge of the capacitor and provide a complete discharge signal when the capacitor is fully discharged in response to the current provided by the sensor; a counter configured to measure a cycle time based on the full discharge signal provided to the counter by the capacitor discharge analyzer, the cycle time being defined as a period between the start of a new cycle and full discharge of the capacitor; and A processor unit configured to: obtaining the cycle time measured by the counter; storing the obtained cycle time; and In the event that a cycle (46) is interrupted (50) before its completion, the error in signal quantization caused by the interrupted cycle is estimated by calculating the ratio of the time of the uncompleted cycle to the stored cycle time of the last completed cycle, wherein the discontinuity is a change or interruption in the beam of electromagnetic radiation or the intensity of the electromagnetic radiation.

2. An imaging system, comprising: a source for providing electromagnetic radiation; as well as A detection device according to claim 1.

3. A method for detecting electromagnetic radiation using a detection device for X-rays, the method comprising the following steps: a) sensing electromagnetic radiation exposure during at least one image acquisition frame; b) measuring a cycle time, wherein the cycle time is defined as the period of time in which a capacitor of at least one integrator of an electronics board of the detection device is fully discharged; c) storing the measured cycle time; and d) in the event that a cycle (46) is interrupted (50) before its completion, estimating the error in the quantization of the signal caused by the interrupted cycle by calculating the ratio of the time of the uncompleted cycle to the stored cycle time of the last completed cycle, wherein the discontinuity is a change or interruption in the beam of said electromagnetic radiation or in the intensity of said electromagnetic radiation.

4. The method according to claim 3, wherein: The cycle times of all cycles during at least one image acquisition frame are used to calculate the variance of the cycle times.

5. The method according to one of claims 3 to 4, wherein: The discontinuity is caused by a change in the wavelength of the electromagnetic radiation and / or a blanking period or change in the electromagnetic radiation.

6. The method according to claim 3, wherein: The change in the intensity of the electromagnetic radiation is compensated by modifying a reference voltage used to reset the capacitor charge during the at least one image acquisition frame.

7. A computer program product comprising a computer program element for controlling a detection device according to claim 1 or an imaging system according to claim 2, said computer program element being adapted to perform the steps of the method according to one of claims 3 to 6 when run by a processing unit.

8. A computer-readable medium having stored thereon a program element according to claim 7.

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