Photon counting data acquisition module and method for photon counting

Abstract

The present invention relates to photon counting. Specifically, a photon counting data acquisition module is provided. The photon counting data acquisition module includes a signal input unit and one or more data acquisition channels, each channel being suitable for converting at least one queue of pulses received from the signal input unit into a counter signal. Each data acquisition channel includes a pulse maximum value identifier and a discriminator / counter pair including a discriminator and a counter. The pulse maximum value identifier is configured to identify the maximum value of the pulses in the at least one queue of received pulses. The discriminator is configured to be triggered by detecting the maximum value of the pulses in the at least one queue of received pulses, comparing the pulses with at least one signal threshold to generate a counter signal. Alternatively, the counter is configured to be enabled to generate a counter signal in response to detecting the maximum value of the pulse.

Description

Technical Field

[0001] The present invention relates to photon counting. In particular, the present invention relates to a photon counting data acquisition module, a pixelated photon counting detector, a method for photon counting, and a computer program element and a computer readable medium. Background Art

[0002] Photon counting detectors that can distinguish photon energies (e.g., X-ray photon energies) have been developed over the past few decades for a variety of applications, such as medical imaging and materials science. Photon counting detectors operate in a pulsed mode based on single events, meaning that in theory every interaction occurring within the probe material can be individually processed and recorded.

[0003] Photon counting data acquisition modules have been developed to convert the energy of photons into a counting signal indicating the number of photons with energy above a threshold. For example, US 2018 / 0329086 A1 describes a photon counting data acquisition module in the form of a readout application specific integrated circuit (ASIC) for an X-ray detector, in which pixels are clustered using an anti-charge sharing grid.

[0004] In photon counting, two or more photons incident nearly simultaneously can be treated as a single event with higher energy, resulting not only in dead-time penalties but also in distortion of the recorded pulse height spectrum. Due to pile-up effects and dead-time penalties, there is a progressive lack of linearity between the detected photon rate and the incident photon rate as the photon flux increases. If the dead-time is extended by subsequent events arriving within their dead-time, there can be an ambiguity between the observed count rate and the event count rate. This count rate performance is also known as paralysis.

[0005] WO 2008 / 146230A2 describes a photon rate counter comprising a radiation detector and a signal conditioning circuit. The photon rate counter generates a count value indicating the total number of photons received by the detector. One or more photon counters generate count values ​​indicating photons with different energy characteristics. The counter ignores accumulated pulses.

[0006] WO 2016 / 096622 A1 relates to a detector for detecting ionizing radiation, comprising a direct conversion semiconductor layer for generating charge carriers in response to incident ionizing radiation and a plurality of electrodes corresponding to pixels, for recording the ionizing radiation and generating signals corresponding to the recorded charge carriers, wherein one electrode of the plurality of electrodes is configured to be two-dimensionally interlaced with at least two adjacent electrodes to record the charge carriers through the electrode and at least one adjacent electrode. Summary of the invention

[0007] It may be necessary to provide non-paralyzable photon counting data acquisition equipment.

[0008] The objects of the invention are solved by the subject-matter of the independent claims, wherein further embodiments are incorporated in the dependent claims. It should be noted that the following described aspects of the invention also apply to the photon counting data acquisition module, the pixelated photon counting detector, the photon counting method as well as the computer program element and the computer readable medium.

[0009] A first aspect of the present invention relates to a photon counting data acquisition module. The photon counting data acquisition module comprises a signal input unit and one or more data acquisition channels, each channel being adapted to convert at least one queue of pulses received from the signal input unit into a counter signal. Each data acquisition channel comprises a pulse maximum identifier and a discriminator / counter pair comprising a discriminator and a counter. The pulse maximum identifier is configured to identify the maximum value of pulses in the at least one queue of received pulses. The discriminator is configured to be triggered by detecting the maximum value of pulses in the at least one queue of received pulses, comparing the pulses with at least one signal threshold to generate a counter signal. Alternatively, the counter is configured to be enabled to generate the counter signal in response to detecting the maximum value of pulses in the at least one queue of received pulses.

[0010] Since the discriminator / counter pair is only allowed to evaluate the signal in discrete time intervals, the system is inherently non-paralyzable in the sense that the observed count rate increases monotonically with the input count rate. In one example, the discriminator can be a time-discrete discriminator that can be triggered by detecting the maximum value of a pulse to compare the pulse with at least one signal threshold. Alternatively, the discriminator can be time-continuous, but the associated counter is allowed to be incremented only when enabled. In other words, the discriminator works normally, and the time-discrete component is completed by digitally enabling / disabling the counting function. In particular, if a local maximum is detected (for example, during accumulation), the next local maximum will be detected again and the discriminator will be evaluated. Therefore, increasing the counter in the case of a large amount of accumulation is controlled by the detection of the local maximum. There may be some randomization of the output count rate, and the problem of multi-energy situations can be circumvented. The non-paralyzable count rate behavior can be considered to be advantageous, without the ambiguity between the count rate and the event count rate as observed in the paralyzable case.

[0011] The photon counting data acquisition module can be connected to various photodetectors, including but not limited to photomultiplier tubes, Geiger counters, single photon avalanche diodes, superconducting nanowire single photon detectors, transition edge sensors, charge coupled devices or scintillation counters. Various spectral ranges can be covered for different applications (such as chemical analysis, medical imaging and laser measurement), from near infrared and ultraviolet wavelengths to high energy regions such as X-rays and gamma rays. The photon counting data acquisition module can be or include an ASIC, an electronic circuit, a processor and / or memory, a combinational logic circuit and / or other suitable components that execute one or more software or firmware programs to provide the described functions. For example, the photon counting data acquisition module can be a readout ASIC for a photon counting computed tomography (CT) detector.

[0012] The pulse maximum identifier may include a zero crossing threshold before the differentiator. Figure 4 One possible implementation of a pulse maximum identifier is shown.

[0013] The discriminator may include one or more comparators. Each comparator compares the amplitude of the pulse with one or more predetermined energy thresholds corresponding to one or more different energy ranges. This can be triggered by detecting a maximum value of the pulses in the at least one queue of received pulses. Alternatively, the counter can be enabled in response to detecting the maximum value of the pulses. Therefore, the input of each comparator is evaluated only when the input signal in the form of a queue of pulses reaches a local maximum. The benefit may be the resulting non-paralyzable counting rate behavior. The comparator can generate an output signal indicating whether the energy of the detected photon event is above or below the threshold, respectively. For each energy range, the counter counts the number of pulses falling within the energy range based on the comparator output signal.

[0014] According to an embodiment of the present invention, each data acquisition channel is suitable for being connected to a pixel of a pixelated photon counting detector to receive a queue of pulses indicating the energy of photons incident on the pixel, or being connected to a cluster of sub-pixels of a pixelated photon counting detector to receive multiple queues of pulses, each queue indicating the energy of photons incident on a corresponding sub-pixel of the cluster.

[0015] The pixelated photon counting detector can be a detector used for, for example, X-ray, gamma ray or fluorescence imaging. In one example, the photon counting data acquisition module can be connected to a pixelated detector without sub-pixelation, such as Philips' proprietary ChromAIX2, which has a pixel pitch of approximately 500 μm. In another example, the photon counting data acquisition module can be connected to a pixelated detector with sub-pixelation. In this case, each data acquisition channel can be linked to an analog front end for processing sub-pixels and implementing charge sharing correction, as will be explained below and in particular with respect to Figure 3 The exemplary embodiments are explained in FIG.

[0016] According to a first aspect of the present invention, at least one queue of pulses received from a signal input unit comprises a first queue of pulses and a second queue of pulses. The data acquisition channel further comprises selection logic. The pulse maximum identifier is configured to identify the maximum of a first pulse in the first queue of pulses and a second pulse in the second queue of pulses. The selection logic is configured to determine whether the maximum of the first pulse and the second pulse is within a coincidence window and enable the discriminator to directly evaluate the first pulse in the first queue of pulses or the second pulse in the second queue of pulses if the first pulse and the second pulse are not within the coincidence window, or to evaluate the sum of the first pulse and the second pulse if the first pulse and the second pulse are within the coincidence window.

[0017] The at least one queue of pulses may also include a third queue of pulses, a fourth queue of pulses, etc. In other words, the following discussion may also be extended to a large number of queues of pulses. The selection logic may determine whether a given event, i.e. a pulse indicating energy incident on one or more sub-pixels, is confined to a single sub-pixel or a charge shared across one or more adjacent pixels. The input of the threshold, i.e. the energy discriminator, depends on the decision. That is, for each individual photon, a decision is made whether to feed the shaper directly to the discriminator or to take the signal from the continuously available shaper summing mode.

[0018] This can allow charge sharing compensation while avoiding degradation of count rate performance and spectral performance. This can be beneficial for smaller pixels, which on the one hand relax the stringent requirements on the photon counting channel, but on the other hand can be severely compromised by the need to correct for charge sharing. The use of in-flight coincidence detection and a time-discrete discriminator circuit or a time-discrete counter can facilitate the path towards using smaller pixels while preserving count rate and spectral performance.

[0019] According to an embodiment of the present invention, the selection logic includes i) a coincidence detector, ii) a switch control, and iii) a threshold sampling control. The coincidence detector is configured to evaluate the state of the output of the pulse maximum identifier and determine whether the first pulse in the first queue of pulses, the second pulse in the second queue of pulses, or both the first pulse and the second pulse are within the coincidence window; the switch control is configured to determine whether to feed through the first pulse, the second pulse, or the sum of the first and the second pulses to the input of the discriminator based on the evaluation and determination of the coincidence detector. The threshold sampling control is configured to evaluate the output state of the pulse maximum identifier and trigger the discriminator to perform a comparison based on the evaluated state.

[0020] The coincidence detector may represent a logical response to a plurality of inputs. Examples of coincidence detectors include, but are not limited to, truth tables, combinational logic, and state machines. This will be discussed in detail below with regard to Figure 3 Provide explanation.

[0021] According to an embodiment of the present invention, the data acquisition channel further comprises an adder configured to add the first and second queues of pulses.

[0022] The adder may be an analog adder. This may be done with an amplifier, for example in the voltage domain or in the current domain. In one example, the signal is continuously accumulated into a single node. In another example, for example for a large number of pixels or sub-pixels, it may be advantageous to only add the pixels or sub-pixels that are actually processing the shaped pulse.

[0023] According to one embodiment of the present invention, the data acquisition channel further comprises a multiplexer adapted to forward the first queue of pulses, the second queue of pulses and the sum of the first queue and the second queue of pulses to the discriminator in a multiplexed manner over a period of time.

[0024] In other words, the threshold system, ie the energy discriminator, can be time multiplexed across all, for example, sub-pixels. Thus, the sub-pixels within a cluster share a set of energy thresholds, ie the energy discriminator.

[0025] According to an embodiment of the invention, the discriminator / counter pair further comprises a charge sharing counter adapted to be triggered to increase in value by detecting a maximum value of the first pulse and the second pulse within the coincidence window.

[0026] The charge sharing counter may also be helpful in determining pile-up correction.

[0027] A second aspect of the present invention relates to a pixelated photon counting detector. The pixelated photon counting detector comprises an array of pixels and a photon counting data acquisition device, as described above and below. Each data acquisition channel of the photon counting data acquisition device is configured to receive a queue of pulses indicating the energy of photons incident on a corresponding pixel of the pixelated photon counting detector.

[0028] As described above, pixelated photon counting detectors can exhibit non-paralyzable count rate behavior, which can be advantageous because there is no ambiguity between the count rate and the incident count rate observed in the paralyzable case.

[0029] According to an embodiment of the present invention, the pixel is a cluster of sub-pixels. Each data acquisition channel is configured to receive a plurality of pulse trains, each pulse train indicating the energy of a photon incident on a corresponding sub-pixel of the cluster.

[0030] As mentioned above, this may facilitate the use of smaller pixels to relax the stringent requirements of the photon counting channel while preserving count rate and spectral performance.

[0031] According to one embodiment of the present invention, the pixelated photon counting detector is at least one of an X-ray detector, a gamma-ray detector and a fluorescence detector.

[0032] A third aspect of the invention relates to a method for photon counting. The method comprises identifying the maximum value of pulses in the at least one queue of received pulses using a pulse maximum identifier and triggering a discriminator by detecting the maximum value of pulses in the at least one queue of received pulses to compare the pulses with at least one signal threshold. Alternatively, the counter is enabled to generate the counter signal in response to detecting the maximum value of pulses in the at least one queue of received pulses.

[0033] According to a third aspect of the present invention, the at least one queue of received pulses includes a first queue of pulses and a second queue of pulses. The method further includes: identifying a maximum value of a first pulse in the first queue of pulses and a second pulse in the second queue of pulses, determining whether the maximum values ​​of the first pulse and the second pulse are within a coincidence window, and evaluating the first pulse in the first queue of pulses, the second pulse in the second queue of pulses, or the sum of the first pulse and the second pulse based on the determination result.

[0034] According to an embodiment of the invention, said at least one train of received pulses is indicative of the energy of photons incident on a corresponding pixel or a cluster of corresponding sub-pixels of a pixelated photon counting detector.

[0035] A fourth aspect of the invention relates to a computer program element or a computer program product for controlling a photon counting data acquisition module as described above and below, which, when executed by a processing unit, is adapted to perform the steps of the method as described above and below.

[0036] A fifth aspect of the invention relates to a computer readable medium storing a computer program product or means.

[0037] 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

[0038] Exemplary embodiments of the present invention will be described below with reference to the accompanying drawings:

[0039] Figure 1 A photon counting data acquisition module as part of a pixelated photon counting detector according to some embodiments of the present disclosure is schematically illustrated.

[0040] Figure 2 Schematically illustrated is a 3×3 clustering of sub-pixels according to some embodiments of the present disclosure.

[0041] Figure 3 The data acquisition channel according to some embodiments of the present disclosure is schematically shown.

[0042] Figure 4 A pulse maximum identifier according to some embodiments of the present disclosure is schematically illustrated.

[0043] Figure 5 A distinguisher according to some embodiments of the present disclosure is schematically illustrated.

[0044] Figures 6A-6D Two pulses and corresponding outputs representing two single events of a discriminator according to some embodiments of the present disclosure are schematically shown.

[0045] Figures 7A-7D Two pulses and corresponding outputs are schematically shown representing an event of charge sharing of a discriminator according to some embodiments of the present disclosure.

[0046] Figures 8A-8D Schematically shown are two queues of pulses representing a mix of single and charge sharing events and the corresponding output of a discriminator according to some embodiments of the present disclosure.

[0047] Fig. 9 The effect of charge sharing on tube spectra and correction according to some embodiments of the present disclosure is schematically illustrated.

[0048] Fig.10Schematically illustrates a stacking curve according to some embodiments of the present disclosure.

[0049] Fig.11 An imaging system for generating an image of an object according to some embodiments of the present disclosure is schematically illustrated.

[0050] Fig.12 A flow chart illustrating a method according to some embodiments of the present disclosure is schematically shown. DETAILED DESCRIPTION

[0051] Figure 1 A photon counting data acquisition module 10 is shown according to some embodiments of the present disclosure, in this embodiment as part of a pixelated photon counting detector. The photon counting data acquisition module may be or include an ASIC, electronic circuit, processor and / or memory executing one or more software or firmware programs, combinational logic circuits, and / or other suitable components that provide the described functionality.

[0052] The photon counting data acquisition module 10 includes a signal input unit 12, one or, in this embodiment, a plurality of data acquisition channels 14a, 14b, 14c, also collectively referred to herein as data acquisition channels 14, and a signal output unit 16. The signal input unit 12 may include one or more signal inputs (not shown), each adapted to receive a train of pulses. For simplicity, Figure 1 Only three data acquisition channels 14a, 14b, 14c are shown. The following discussion can also be extended to a large number of data acquisition channels. Each data acquisition channel 14 is suitable for converting at least one series of pulses 18 (e.g. Fig. 8A , 8B The two queues of pulses shown in the figure are received from the signal input unit 12) and converted into counter signals. The signal output unit 16 is suitable for outputting the counter signals. Each data acquisition channel 14 includes a pulse maximum identifier 20a, 20b, 20c, also collectively referred to as a pulse maximum identifier 20, and a discriminator / counter pair 22a, 22b, 22c, including a discriminator 23 (see Figure 5 ) and counter 25 (see Figure 5 ), also collectively referred to herein as a distinguisher / counter pair 22.

[0053] Optionally, each data acquisition channel 14 may also include an analog pre-processing chain 19a, 19b, 19c, also collectively referred to herein as an analog pre-processing chain 19. The analog pre-processing chain 19 is configured to amplify and filter at least one queue 18 of pulses. The analog pre-processing chain 19 may include one or more charge sense amplifiers (CSA) and one or more pulse shapers.

[0054] The pulse maximum identifier 20 is configured to identify a maximum value of a pulse 24 in at least one queue 18 of received pulses, e.g. Fig. 6A and Fig. 7A The pulse maximum identifier 20 may include a zero crossing threshold before the differentiator. Figure 4 A possible implementation is shown in the figure.

[0055] The discriminator 23 is configured to be triggered by detecting a maximum value of a pulse 24 in the at least one queue 18 of received pulses to compare the pulse 24 with at least one signal threshold to generate a counter signal. Figure 5 As shown, the discriminator 23 may include one or more comparators 27, each of which compares the amplitude of the pulse 24 to one or more predetermined energy thresholds corresponding to one or more different energy ranges.

[0056] The counter 25 counts the number of pulses falling within the energy range for each energy range based on the comparator output signal. The counter 25 can be enabled to generate a counter signal in response to detecting the maximum value of the pulse 24; that is, the discriminator itself can be time-continuous, but only allows the associated counter to be increased when enabled.

[0057] The pixelated photon counting detector 100 includes an array of pixels 110a, 110b, 110c, also collectively referred to as pixels 110. For simplicity, Figure 1 Each data acquisition channel 14a, 14b, 14c may be adapted to be connected to a corresponding pixel 110a, 110b, 110c of the pixelated photon counting detector 100 to receive a queue 18 of pulses indicative of photon energies incident on the corresponding pixel 110a, 110b, 110c of the pixelated photon counting detector 100.

[0058] For example, the pixelated photon counting detector 100 can be a semiconductor-based photon counting detector comprising two core components: a semiconductor material, such as Si, CdTe or CZT, having two electrodes, and a readout photon counting module 10 in the form of an ASIC. When incident X-ray photons interact within the semiconductor material, electric charges, i.e. electron-hole pairs, are generated, the number of which is proportional to the deposited energy of the incident photons, and drift towards the monolithic and pixelated electrodes respectively under the influence of an externally applied electric field. During the drift of the electron-hole pairs, transient currents are generated, which are then processed by each connected data acquisition channel 14 through an optional analog pre-processing chain 19, including, for example, Figure 2 One or more charge sensitive preamplifiers (not shown) and one or more pulse shapers as shown, and Figure 5The pulse maximum value identifier 20 and the discriminator 23 are shown as having multiple pairs of voltage pulse height comparators and digital counters.

[0059] In some applications, sub-pixelation techniques may be implemented. For example, US 2008 / 0329086 A1 describes the use of an anti-scattering grid to cluster pixels. Figure 2 A sub-pixel 120 representing a pixel 110 is shown. N,M A conceptual 3×3 clustering of where N and M are positive integers. Figure 2 As shown in FIG. 1 , each sub-pixel 120 N，M The output of the photon-counting detector 100 is subjected to pulse shaping in a shaper (eg, filter) of an optional analog preprocessing chain 19. Each data acquisition channel 14 is adapted to be connected to a sub-pixel 120 of the pixelated photon counting detector 100. N，M , to receive a plurality of queues 18 of pulses, each indicating a pulse incident on a respective sub-pixel 120 of the cluster N,M The energy of the photon on.

[0060] In some cases, it is important to note that the spectral performance of photon counting data acquisition modules may be limited by the so-called charge sharing effect, in which the charge caused by a single photon is shared between neighboring sub-pixels. Charge sharing effects are almost unavoidable in photon counting detectors because the radiative semiconductors are pixelated electrically, not physically. Charge sharing effects are more pronounced for small pixels, especially those smaller than 0.5 mm.

[0061] Figure 3 FIG. 1 shows a data acquisition channel 14 suitable for providing charge sharing compensation according to some embodiments of the present disclosure. For simplicity, only two sub-pixels are shown, namely, sub-pixel 120 1,1 and sub-pixel 120 1,2 represents a 1×2 cluster of sub-pixels. Note that the discussion and model described below are scalable to a large number of sub-pixels. There are no other restrictions except for noise and numerical complexity.

[0062] Thus, the at least one queue 18 of pulses received from the signal input unit comprises a first queue 18a of pulses and a second queue 18b of pulses, such as Fig. 8A and 8B As shown in FIG. 1 , each pixel from its respective sub-pixel 120 1,1 , 120 1,2 The data acquisition channel 14 also includes a selection logic 26 .

[0063] In this embodiment, the pulse maximum identifier 20 is configured to identify the maximum of a first pulse 24a in the first queue 18a of pulses and a second pulse 24b in the second queue 18b of pulses, as will be explained below and in particular with respect to exemplary embodiments 6 to 8. The first queue and the second queue of pulses may be sub-pixels 120. 1,1 , 120 1,2的 The pulse maximum identifier 20 may include a zero-crossing threshold before the differentiator (or delay line summation). When the pulse reaches its maximum value, its output goes high and remains high for a predefined time. It can be used as coincidence logic. It is based on the fact that the charge sharing between sub-pixels for a single event is instantaneous in nature. That is, the sub-pixel 120 1,1 and 120 1,2 The signal output units must present the maximum value simultaneously. The above delays can establish a compliance window. Due to noise and circuit tolerances, the minimum window is set by the uncertainty in finding the maximum value. A possible implementation of the pulse maximum identifier 20 (but other solutions may be applicable) is in Figure 4 Shown in.

[0064] Back to Figure 3 , the selection logic 26 is configured to determine whether the maximum of the first pulse 24a and the second pulse 24b is within the coincidence window and enables the discriminator to directly evaluate the first pulse 24a in the first queue 18a of pulses or the second pulse 24b in the second queue 18b of pulses if the first pulse and the second pulse are not within the coincidence window, or to evaluate the sum of the first pulse 24a and the second pulse 24b if the first pulse and the second pulse are within the coincidence window. This will be explained below and in particular with respect to the exemplary embodiments in Figures 6 to 8. In other words, the selection logic is configured to detect charge sharing events based on on-the-fly coincidence detection and to sum the signals from the sub-pixels of one cluster in the case of charge sharing. If no charge sharing event is detected, the signal from the sub-pixel is directly transmitted to the discriminator. This can allow charge sharing compensation based on on-the-fly coincidence detection and a time-discrete discriminator, thereby allowing an accurate decision when to evaluate the shaper signal for the energy threshold.

[0065] Figure 3 An example of the selection logic 26 is shown in FIG. 1 , but other solutions may be applied. In this example, the selection logic 26 includes a coincidence detector 28 , a switch control 30 and a threshold sampling control 32 .

[0066] The coincidence detector 28 is configured to evaluate the output state of the pulse maximum identifier 20 and determine whether the first pulse 24a in the first queue 18a of pulses, the second pulse 18b in the second queue 18b of pulses, or both the first pulse and the second pulse are within the coincidence window. For example, it can indicate how many sub-pixels are simultaneously active within the coincidence window. For example, a truth table can be used to decode which sub-pixel is active, for example, [0 0]→none, [0 1]→120 1,2 ,[1 0]→120 1,1 ,[1 1]→both.

[0067] Switch control 30 is configured to determine whether to feed the first pulse, the second pulse or the sum of the first and second pulses to the input of discriminator / counter pair 22 based on coincidence detector 28. In other words, it decides which signal is connected to the discriminator, i.e. which sub-pixel or the sum of both.

[0068] The threshold sampling controller 32 is used to evaluate the output state of the pulse maximum identifier 20 and trigger the discriminator 23 to perform the comparison based on the evaluated state. In other words, the threshold sampling control 32 monitors the state of the shaped pulse and it enables the discriminator to evaluate the result accordingly. The output may remain high for a short time, such as 0.5ns, 2ns or 10ns, depending on the count rate performance and the noise requirements of the channel. This can work in the digital domain, that is, the threshold counter can be allowed or not allowed to increment.

[0069] To sum the signals, the data acquisition channel 14 may also include an adder 34 configured to add the first and second queues of pulses. The adder 34 may operate in an analog summing mode. The adder 14 may include a high bandwidth amplifier with an input differential pair, with N inverting input branches, where N is the number of clustered sub-pixels. Other implementations may include adding a current branch of a shaper circuit.

[0070] In addition, the data acquisition channel 14 may also include a multiplexer 36, such as an analog multiplexer, adapted to forward the first queue of pulses, the second queue of pulses, and the sum of the first queue and the second queue of pulses to the discriminator in a time multiplexed manner. In other words, the sub-pixels are clustered in such a way that they share a set of energy thresholds. This is not energy staggering, the threshold system is time multiplexed across all sub-pixels within a cluster. The input to the threshold system (each discriminator) depends on the decision whether a given event is limited to the signal sub-pixel but also the charge shared across one or more neighbors. That is, for each single photon, a decision is made whether to feed the shaper directly to the discriminator or to take the signal from the continuously available shaper summing mode. The multiplexer 36 can take the result from the switch control 30 and connect the required signal to the discriminator 23 accordingly. For the overall pile-up requirements, it may be beneficial to have a high-speed multiplexer. If necessary, propagation delays can be added to all signals.

[0071] The discriminator / counter pair 22 may include at least one threshold 38 and a charge sharing counter 40. The at least one threshold 38 may be a conventional discriminator and counter. However, the counters are only allowed to increase their values ​​within a given time interval, i.e. when a decision to evaluate which signal is available is required. A simple enable bit in the digital counter may be sufficient to implement this functionality. FIG. 7 shows an exemplary implementation. The charge sharing counter 40 is adapted to be triggered to increase the value by detecting the maximum of the first pulse and the second pulse within a compliance window. In other words, the control signal that governs the decision may also be used to output a count value indicating how many events have been considered to be charge sharing. This may also prove valuable in determining pile-up corrections.

[0072] To illustrate the working principle of the photon counting data acquisition module 10, Figures 6A-6D The simulation results for a single event that is not shared across two sub-pixels are shown. For simulation purposes, Figure 3 The sub-pixel 120 shown in 1，1 and 120 1，2 Both provide trains of identical pulses, however, with a time delay relative to each other. In this case, the time delay was set to only 1ns. The simulations show the ability to distinguish pulses considered as single events within a very short time interval, allowing very high count rates to be accommodated.

[0073] like Fig. 6A As shown, two sub-pixels 120 1,1 and 120 1,2 Both processes are two unrelated single events. Indicating that the incident light is incident on sub-pixel 120 1,1 The first pulse 24a of photon energy and the incident light incident on the sub-pixel 1201,2 The second pulse 24b of photon energy at 100 keV is only 1 ns apart, both having 60 keV energy (0.6 in the simulation). The switch control 30 indicates that the first sub-pixel 120 1,1 is active, having an output of "1", and shortly afterwards the second sub-pixel 120 1,2 is also active, with an output of "2". Since the maximum value is not within the predefined compliance window of 0.5 ns, the switch control does not indicate the presence of charge sharing, with an output of "3".

[0074] exist Figure 6B In the first case, the multiplexer 34 switches the sub-pixel 120 1,1 The output of is directed to the input of the discriminator 23. Soon after, the sub-pixel 120 1,2 The output of is directed to a discriminator 23. Since the two signals have very similar values, Figure 6B No changes in selection can be observed.

[0075] exist Figure 6C In the embodiment, at least one threshold 36 of the discriminator 23 is correspondingly enabled twice, once for each pulse, so that the sub-pixel 120 1,1 is evaluated and immediately thereafter sub-pixel 120 is evaluated 1,2 .

[0076] exist Fig.6D In the example, the lowest threshold set to 50 keV records two counts, sufficient to indicate two independent signal events reaching two sub-pixels 120 1,1 and 120 1,2 .

[0077] Figures 7A-7D The simulation results for a single event shared across two sub-pixels are shown. In this case, sub-pixel 120 1,1 and 120 1,2 Again there is the same queue of pulses, but without the delay. This is used to simulate the correct properties of the charge sharing compensation mechanism. The output sub-pixel 120 1,2 Also scaled by 50%, this requires splitting the single 90keV event into two smaller events, and the subpixel 120 1,2 The remaining 30keV is received.

[0078] exist Fig. 7A As described above, sub-pixel 120 1,1 exhibits a 60keV event, while the sub-pixel 120 1,2 30 keV is indicated. Since both maxima are found to occur within the coincidence window of 0.5 ns, the switch control 30 indicates with a "3" that the two signals must be considered as a single charge sharing event.

[0079] Therefore, if Figure 7B As shown, the multiplexer 36 directs the addition of the two signals to the discriminator input, showing a total energy of 90 keV (0.9 in the simulation).

[0080] exist Figure 7C In this case, at least one threshold value 36 of the discriminator 23 is activated once, so that the sum of the two signals is evaluated.

[0081] exist Fig.7D In the figure, since the total energy is 90keV, the 50keV and 80keV thresholds are increased only once, indicating that in the two sub-pixels 120 1,1 and 120 1,2 The arrival of a single event recorded on.

[0082] Figures 8A to 8D The simulation results for multiple events with a mixture of single events and charge sharing events are shown. Fig. 8A and Figure 8B As shown in FIG. 1 , in this simulation, each sub-pixel 120 1,1 and 120 1,2 The trains 18a, 18b with unique pulses are 60keV monochromatic. A third independent train of pulses is generated and split between the two sub-pixels, simulating a charge sharing event in the two trains 18a, 18b of pulses. In this simulation, the sub-pixel 120 1,1 Receives 60% of the charge, i.e. 36keV, and sub-pixel 120 1,2 40% of the charge is received, which is 24keV. All events have 60keV. Therefore, if the model behaves as expected, the 50keV threshold should count as many events as in the combined third independent pulse train if there is no pile-up. Specifically, the first queue 18a of pulses has a total of 19 events in 30μs. The second queue 18b of pulses has a total of 14 events. The third queue of pulses simulating charge sharing events has a total of 7 events in two sub-pixels 120. 1,1 and 120 1,2 , i.e. each event has 7 smaller events.

[0083] from Figure 8C As can be seen in Figure 3, a 50keV threshold of 36 is sufficient to identify 40 events.

[0084] from Fig.8D As can be seen in FIG, the charge sharing counter 38 also correctly identifies seven events that are shared across sub-pixels. The position of the second cursor shows that although a total of seven shaper pulses occurred, only six were counted, including five single events and one charge sharing event that was split across the pixel.

[0085] Fig. 9 A count rate simulation of a multicolor tube spectrum using the illustrated two sub-pixel energy spectra 50, the output of the model 52 and the base case 54 is shown. For ease of explanation, a low rate of 0.5 Mcp was used to ensure that no pile-up occurred. The benefit of using the model may become more apparent where the resulting recorded spectrum falls above the true case 54. In this simulation, the intention is to show the resulting observed count rate as a function of the subsequently increasing event count rate. Due to execution time, this simulation is limited to 20 Monte Carlo realizations for each event count rate point. The tube spectrum has been used for this simulation.

[0086] Fig.10 The results of this simulation at a 30keV threshold are shown. Four traces are shown:

[0087] i) Model output 56: The result of feeding the model with the train of pulses described. It shows the non-paralyzable property.

[0088] ii) Equivalent 1x2 sub-pixel 58: It shows the rate curve for a larger equivalent sub-pixel, ie it is used as a comparison. The model and this figure serve the same equivalent area.

[0089] iii) Sub-pixels with charge sharing 60: The queue of pulses of one sub-pixel with additional charge sharing forms the adjacent sub-pixel.

[0090] iv) Sub-pixel without charge sharing 62: Queue of pulses of one of the sub-pixels before any charge sharing is added.

[0091] The pixelated photon counting detector 100 may be at least one of an X-ray detector, a gamma ray detector, and a fluorescence detector. Possible implementations of the pixelated photon counting detector 100 may be in an imaging system 200, for example Fig.11Schematically illustrated is a computed tomography (CT) scanner in FIG. 2 . The imaging system 200 comprises a gantry 202 which is rotatable about a rotation axis R extending parallel to the z direction. A radiation source 204, in this embodiment an X-ray tube, is mounted on the gantry 202 and is provided with a collimator 206 which forms a conical radiation beam 208 from the radiation generated by the radiation source 204. In this embodiment, the radiation passes through a human patient within a cylindrical examination region 210 and thus through the patient. The radiation beam 208 is incident on a photon counting detector 100 mounted on the gantry 202. The pixelated photon counting detector 100 may have a one-dimensional or two-dimensional array of pixels 110 which are connected to a photon counting data acquisition module 10 to count individual photons incident on the pixels 110. Since the discriminator is only allowed to evaluate the signal in discrete time intervals, the system is inherently non-paralyzable in the sense that the observed count rate increases monotonically with the input count rate. In some embodiments, each pixel 110 may be a cluster of sub-pixels 120 , and the photon counting data acquisition module 10 may be configured to count single photons incident on the clustered sub-pixels 120 and provide charge sharing compensation.

[0092] The imaging system 200 comprises two motors 214, 216. The gantry 202 is driven by the motor 214 at an angular velocity which is preferably constant but adjustable. The motor 216 is provided for moving a patient, who is arranged on a patient table in the examination region 210, in a direction parallel to the rotation axis R axis or z axis. The motors 214, 216 are controlled, for example, by a control unit 218, so that the radiation source 204 and the patient in the examination region 210 are moved relative to each other along a spiral trajectory. However, the radiation source 204 and the patient may also be moved relative to each other along another trajectory. For example, in one embodiment, the radiation source 204 may be moved around the patient along a circular trajectory.

[0093] The imaging system 200 may further include an input unit 220 such as a keyboard, a computer mouse, a touchpad, etc. and a display 222. The input unit 220 may be adapted to allow a user to enter an input defining a desired clustering of pixels. The photon counting data acquisition module 10 of the pixelated photon counting detector 100 may be adapted to take into account the desired clustering defined by the clustering input when determining the charge sharing photon counts of the macropixels. The input unit 220 may be adapted to allow a change in software and / or hardware configuration in order to modify the sub-clustering, in particular the size of the sub-clustering.

[0094] Fig.12A flow chart of a method 300 for photon counting is shown. In step 310, a pulse maximum identifier is used to identify a pulse maximum in the at least one queue of received pulses. In step 320, a discriminator is triggered by detecting a maximum of pulses in the at least one queue of received pulses to compare the pulse with at least one signal threshold; alternatively, in step 320, a counter is enabled to generate a counter signal in response to detecting a maximum of pulses in the at least one queue of received pulses.

[0095] Optionally, said at least one train of received pulses is indicative of the energy of photons incident on a corresponding pixel or a cluster of corresponding sub-pixels of a pixelated photon counting detector.

[0096] The method 300 may include additional steps. In one option, the at least one queue of received pulses includes a first queue of pulses and a second queue of pulses; the method further includes: identifying a maximum value of a first pulse in the first queue of pulses and a second pulse in the second queue of pulses, determining whether the maximum values ​​of the first pulse and the second pulse are within a coincidence window, and evaluating the first pulse in the first queue of pulses, the second pulse in the second queue of pulses, or the sum of the first pulse and the second pulse based on the determination result.

[0097] 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 perform the method steps of the method according to one of the preceding embodiments on a suitable system.

[0098] The computer program element can therefore be stored on a computing unit, which can also be part of an embodiment of the present invention. The computing unit can be suitable for executing the steps of the above method or causing the execution of the steps of the above method. In addition, it can be suitable for operating the components of the above device. The computing unit can be suitable for automatically operating and / or executing the user's command. The computer program can be loaded into the working memory of a data processor. The data processor can therefore be equipped to implement the method of the present invention.

[0099] This exemplary embodiment of the invention covers both a computer program that right from the beginning uses the invention and a computer program that by means of an update turns an existing program into a program that uses the invention.

[0100] Furthermore, the computer program element may be able to provide all necessary steps to implement the procedures of an exemplary embodiment of the method as described above.

[0101] According to another exemplary embodiment of the present invention, a computer readable medium, such as a CD-ROM, is proposed, wherein the computer readable medium has a computer program element stored thereon, the computer program element being as described in the previous section.

[0102] The computer program can be stored and / or distributed on suitable media, such as optical storage media or solid-state media provided together with other hardware or as part of other hardware, but the computer program can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

[0103] However, the computer program may also be provided over a network like the World Wide Web and may be downloaded from such a network into a working memory of a data processor. According to a further exemplary embodiment of the invention, a medium for making a computer program element available for downloading is provided, the computer program element being arranged to perform one of the previously described embodiments of the invention.

[0104] It must be noted that embodiments of the present invention are described with reference to different subject matters. In particular, some embodiments are described with reference to method claims, while other embodiments are described with reference to device claims. However, it can be concluded by a person skilled in the art from the above and following descriptions that, unless otherwise indicated, any combination of features relating to different subject matters, in addition to any combination of features belonging to the same type of subject matter, is also considered to be disclosed by the present application. However, all features can be combined to provide synergistic effects that exceed the simple sum of the features.

[0105] 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 can be understood and implemented by those skilled in the art in practicing the claimed invention by studying the drawings, the disclosure, and the dependent claims.

[0106] In the claims, the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. A single processor or other unit may perform the functions of several items recited in the claims. Although specific measures are recited in mutually different dependent claims, this does not indicate that a collection 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 photon counting data acquisition module (10), comprising: A signal input unit (12); One or more data acquisition channels (14, 14a, 14b, 14c), each channel is adapted to receive at least the signal from the first sub-pixel (120 1,1 ) and the first queue (18a) of pulses from the second sub-pixel (120 1,2 ) into a second queue (18b) of pulses of the counter signal; and a signal output unit (16), adapted to output the counter signal; Each data acquisition channel includes a pulse maximum value identifier (20, 20a, 20b, 20c) and a discriminator / counter pair (22, 22a, 22b, 22c) including a discriminator (23) and a counter (25); wherein the pulse maximum identifier is configured to identify a maximum value of a first pulse (24a) in the first queue of received pulses and a second pulse (24b) in the second queue of received pulses; wherein the discriminator is configured to be triggered by detecting a maximum value of pulses in at least the first queue and the second queue of received pulses to compare the pulses with at least one signal threshold to generate the counter signal; or wherein the counter is configured to be enabled to generate the counter signal in response to detecting a maximum value of pulses in at least the first queue and the second queue of received pulses; Characterized in that the data acquisition channel also includes: Selection logic (26) is configured to determine whether the maximum values ​​of the first pulse and the second pulse are within a compliance window and enable the discriminator to directly evaluate the first pulse in the first queue of pulses or the second pulse in the second queue of pulses if the first pulse and the second pulse are not within the compliance window, or to evaluate the sum of the first pulse and the second pulse if the maximum values ​​of the first pulse and the second pulse are within the compliance window.

2. The photon counting data acquisition module according to claim 1, in, The selection logic includes: i) a coincidence detector (28); ii) a switch control (30); and iii) threshold sampling control (32); wherein the coincidence detector is configured to evaluate a state of an output of the pulse maximum identifier and determine whether the first pulse in a first queue of pulses, the second pulse in a second queue of pulses, or both the first pulse and the second pulse are within the coincidence window; wherein the switch control is configured to determine whether to feed through the first pulse, the second pulse, or the sum of the first pulse and the second pulse to the input of the discriminator based on the evaluation and determination of the coincidence detector; and The threshold sampling control is configured to evaluate an output state of the pulse maximum identifier and trigger the discriminator to perform a comparison based on the evaluated state.

3. The photon counting data acquisition module according to claim 1, in, The data acquisition channels also include: An adder (34) is configured to add the first queue and the second queue of pulses.

4. The photon counting data acquisition module according to any one of claims 1 to 3, in, The data acquisition channel also includes: A multiplexer (36) adapted to forward the first queue of pulses, the second queue of pulses, and the sum of the first queue and the second queue of pulses to the discriminator in a time multiplexed manner.

5. The photon counting data acquisition module according to any one of claims 1 to 3, in, The discriminator / counter pair further includes: A charge sharing counter (40) is adapted to be triggered to increase in value by detecting a maximum value of the first pulse and the second pulse within a coincidence window.

6. A sub-pixelated photon counting detector (100), comprising: an array of pixels, each pixel being a cluster of sub-pixels (110, 110a, 110b, 110c); as well as The photon counting data acquisition module according to any one of claims 1 to 5; Wherein each data acquisition channel of the photon counting data acquisition device is configured to receive at least two queues of pulses, each queue indicating the energy of a photon incident on a corresponding sub-pixel of the pixelated photon counting detector.

7. The detector according to claim 6, in, The pixelated photon counting detector is at least one of an X-ray detector, a gamma ray detector, and a fluorescence detector.

8. A method (300) for photon counting, comprising: The first pulse maximum identifier is used to detect the pulse from the first sub-pixel (120 1,1 ) in a first queue of received pulses of the second sub-pixel (120) and identifying (310) a maximum value of a first pulse and using a second pulse maximum identifier to identify a maximum value of a first pulse from a second sub-pixel (120) 1,2 ) of the received pulses; identifying a maximum value of a second pulse in a second queue of received pulses; triggering (320) a discriminator by detecting a pulse maximum in at least one of at least said first and second queues of received pulses to compare said pulses with at least one signal threshold; or enabling a counter to generate said counter signal in response to detecting a maximum value of pulses in at least said first queue and said second queue of received pulses; Characterized in that the method further comprises: determining whether the maximum values ​​of the first pulse and the second pulse are within a coincidence window; directly evaluating the first pulse in the first queue of pulses or the second pulse in the second queue of pulses if the first pulse and the second pulse are not within the coincidence window; or In case the maximum values ​​of the first pulse and the second pulse are within the coincidence window, the sum of the first pulse and the second pulse is evaluated.

9. A computer program product comprising readable instructions, which, when executed by at least one processor, cause the at least one processor to control the photon counting data acquisition module according to one of claims 1 to 5 or the detector according to one of claims 6 to 7, and the readable instructions, when executed by a processing unit, are suitable for performing the steps of the method according to claim 8.

10. A computer readable medium having stored thereon the computer program product according to claim 9.

Images