Apparatus and method for detecting x-ray radiation with background suppression

Abstract

An X-ray detector apparatus 100 for detecting incident X-ray photons of X-ray radiation to be sensed, comprising: an X-ray detector device 10 having an X-ray detector portion 11 and an entrance portion 12, the X-ray detector portion 11 being arranged to detect X-ray photons incident through the entrance portion 12 by generating photoelectrons in response to interaction of the incident X-ray photons with the X-ray detector portion 11, and to provide an X-ray output signal determined by the detected X-ray photons; and a background suppression device 20 configured to suppress background contributions in the X-ray output signal caused by escape electrons emitted from the X-ray detector portion 11 in response to absorption of X-ray radiation and extraneous electrons generated outside the X-ray detector portion 11. Further, an X-ray detection method is described.

Description

[Technical Field]

[0001] The present invention relates to an X-ray detector device configured to detect incident X-ray photons of X-ray radiation to be sensed. Furthermore, the present invention relates to an X-ray detection method for detecting X-ray photons of X-ray radiation. The present invention also relates to the use of the X-ray detector device and / or the X-ray detection method for X-ray fluorescence imaging of an object under investigation. The applications of the present invention are particularly applicable in fields employing X-rays for measurement, imaging, in particular medical imaging, material processing and / or testing purposes. [Background technology]

[0002] The following prior art is referenced herein to provide the technical background of the present invention: [1] C. Koernig et al. “In-situ x-ray fluorescence imaging of the endogenous iodine distribution in murine thyroids” in “Scientific Reports” (2022)12:2903, https: / / doi.org / 10.1038 / s41598-022-06786-4, [2] H. Kahl et al. “Feasibility of Monitoring Tumor Response by Tracking Nanoparticle-Labeled T Cells Using X-ray Fluorescence Imaging-A Numerical Study” in “Int.J.Mol.Sci.”2021,22,8736,https: / / doi.org / 10.3390 / ijms22168736, [3] T. Staufer et al. “Assessing Cellular Uptake of Exogenous Coenzyme Q10 into Human Skin Cells by X-ray Fluorescence Imaging” in “Antioxidants” 2022,11,1532, https: / / doi.org / 10.3390 / antiox11081532, [4] E. Vergucht et al. “In vivo X-ray elemental imaging of single cell model organisms manipulated by laser-based optical tweezers” in “Scientific Reports” (2015)5:9049,10.1038 / srep09049, [5]F.Scholze et al. “Modelling the response function of energy dispersive X-ray spectrometers with silicon detectors” in “X-Ray Spectrom.”38,312-321,2009, [6]T.Papp “On the response function of solid-state detectors,based on energetic electron transport processes” in “X-Ray Spectrom.”32(6):458-469,DOI:10.1002 / xrs.672 2003, [7] U.S. Patent Application Publication No. 2019 / 0011577, and [8] U.S. Patent Application Publication No. 2015 / 0053863.

[0003] X-ray-based imaging is commonly known to involve detecting X-ray photons with semiconductor detectors. X-ray photons absorbed in the semiconductor detector material generate photoelectrons, which release their energy into electron-hole pairs in a cascade process. The generated electrons are collected at the anode of the semiconductor detector. The number of electron-hole pairs, and therefore the amplitude of the semiconductor detector's current output signal, is determined by the energy of the absorbed photons. Such semiconductor detectors are by far the most frequently used detectors for measuring X-rays, whether in hospitals, laboratories, materials science applications, nondestructive testing, or synchrotron facilities.

[0004] In X-ray absorption imaging (e.g., in any clinical CT system), the sensitivity of X-ray detection is limited by the ratio of the measured contrast to the background statistical noise. X-ray images are, in principle, noisy, firstly due to finite counting statistics (so-called quantum noise) and secondly due to scattered radiation. In X-ray fluorescence imaging (XRF imaging), the number of signal photons is directly proportional to the mass of so-called XRF markers in the sample volume covered by the scanning X-ray beam, which excites these markers (e.g., atoms, molecules, or nanoparticles) and emits X-ray fluorescence photons. It is generally known from practice that spectral background noise limits the detection sensitivity of XRF imaging within the signal energy range of the measured X-ray spectrum. To date, background noise has been assumed to arise due to multiple scattering and incomplete counting of X-ray photons in the sample, whereby not the full energy of the incident photons is detected, but only a portion of it, due to, for example, charge trapping or different drift velocities of photoelectron-hole pairs generated within the X-ray detector.

[0005] In contrast to conventional X-ray-based imaging, nuclear medicine PET and SPECT techniques have no inherent background, since the measured photons can only emerge from the radioactive markers used. This is why the sensitivity of PET / SPECT is orders of magnitude higher and cannot be matched by conventional X-ray-based imaging such as CT imaging. If the spectral background within the energy range of the fluorescence photons can be eliminated, XRF will provide background-free measurements, and therefore XRF can approach the high sensitivity of PET / SPECT.

[0006] A known approach to improving XRF sensitivity is to select an optimized spectral X-ray energy range to reduce scattering background. For preclinical XRF imaging, it has been proposed to employ X-rays in an X-ray energy range with a low energy, typically around 55 keV, to minimize scattering background in the signal region (for an energy of 53 keV, see, for example, [1] or [2]). Apart from preclinical imaging, XRF imaging can also be used (especially at synchrotron facilities) for so-called single-cell XRF imaging, e.g., to investigate the uptake of labeled coenzymes in individual living cells (see, for example, [3] or [4]). Single-cell XRF tends to use X-ray energies around 10 keV.

[0007] However, selecting an optimized spectral X-ray energy region only has a limited effect on improving sensitivity. Typical X-ray spectra from both XRF application fields usually show clear peaks (A) due to single and multiple Compton scattering, a drop from this to lower energies, and then a pronounced background plateau (B') with a nearly constant height until the spectrum can rise again toward the lowest energies (see the dashed line in the schematic diagram in Figure 3). A major drawback is that the fluorescence line (C) to be detected lies in the plateau region (B'), and the height of this plateau (B') therefore defines the XRF detection limit. If the number of fluorescence photons from the local mass of the XRF marker (and / or natural element in single-cell imaging) is too low compared to the statistical noise at this plateau height, the XRF marker or element cannot be detected by prior art XRF imaging.

[0008] In the energy range below 20 keV, the background contribution in the spectrum of detected X-ray photons has been found to be affected by additional processes inherent in the detection process ([5], [6]). So-called "imperfect counting" (imperfect charge collection) can occur, caused, for example, by photons reaching the edge of the semiconductor detector material, resulting in the electron-hole pairs they generate not all reaching the anode, resulting in an erroneously measured signal that is too low and, accordingly, too low in energy. To avoid imperfect counting, multilayer collimators have been proposed to capture photons that strike the edge region. Furthermore, electrons can escape from the semiconductor detector material after X-ray photon absorption, especially if the X-ray photon is absorbed sufficiently close to the surface of the semiconductor detector. These escape electrons have been explained as being associated with spectral peaks and steps in the spectrum of detected X-ray photons ([6]). Until now, escape electrons were thought to be uncontrollable and to produce only defined spectral peaks, so no techniques for suppressing escape electrons have been previously disclosed.

[0009] The sensitivity and background problems in prior art techniques for detecting X-ray photons arise not only in imaging applications, but also in other applications of X-ray detection, such as for measurement purposes, diagnostic or monitoring tasks, for example.

[0010] Further examples of conventional detection of photons of X-ray or gamma radiation by semiconductor detectors are disclosed in [7] and [8], where some, but limited, background suppression can be obtained from the use of detector housing materials that can shield photons from the surroundings of the semiconductor detector. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] US Patent Application Publication No. 2019 / 0011577 [Patent Document 2] US Patent Application Publication No. 2015 / 0053863 [Non-patent literature]

[0012] [Non-Patent Document 1] C. Koernig et al.,Scientific Reports 2022,12,2903 [Non-patent document 2] H.Kahl et al.,International Journal of Molecular Sciences 2021,22,8736 [Non-patent document 3] T.Staufer et al.,Antioxidants 2022,11,1532 [Non-patent document 4] E. Vergucht et al.,Scientific Reports 2015,5,9049 [Non-Patent Document 5] F.Scholze et al.,X-Ray Spectrometry 2009,38,312-321 [Non-patent document 6] T.Papp,X-Ray Spectrometry 2003,32(6),458-469 Summary of the Invention [Problem to be solved by the invention]

[0013] It is an object of the present invention to provide an improved X-ray detector device and method for detecting X-ray photons, which can avoid the limitations of the prior art. In particular, the X-ray device and method shall be capable of detecting X-rays with improved sensitivity and / or reduced spectral background, in particular comparable to the sensitivity of PET and SPECT methods, and / or detecting X-ray sources, such as XRF markers or elements, at lower concentrations, for example in XRF imaging. [Means for solving the problem]

[0014] The object of the present invention is solved by an X-ray detector arrangement and / or an X-ray detection method with the features of the independent claims. Preferred embodiments and applications of the invention result from the dependent claims.

[0015] According to a first general aspect of the present invention, the above object is solved by an X-ray detector apparatus configured to detect incident X-ray photons of X-ray radiation to be sensed, comprising an X-ray detector device having an X-ray detector portion and an entrance portion, the X-ray detector portion being arranged to detect X-ray photons incident through the entrance portion by generating photoelectrons in response to an interaction of the incident X-ray photons with the X-ray detector portion, and to provide an X-ray output signal determined by the detected X-ray photons.

[0016] According to the present invention, the X-ray detector apparatus further comprises a background suppression device configured to suppress background contributions in the X-ray output signal caused by escape electrons emitted from the X-ray detector portion in response to absorption of X-ray radiation and extraneous electrons generated outside the X-ray detector portion.

[0017] According to a second general aspect of the present invention, the above object is solved by an X-ray detection method for detecting X-ray photons of X-ray radiation, the method comprising the steps of receiving X-ray radiation at an X-ray detector device of an X-ray detector apparatus, the X-ray detector device having an X-ray detector portion and an entrance portion; generating photoelectrons in the X-ray detector portion in response to an interaction of the X-ray photons with the X-ray detector portion; and providing an X-ray output signal, the X-ray output signal being determined by the detected X-ray photons.

[0018] According to the present invention, an X-ray detection method includes suppressing background contributions to an X-ray output signal caused by escape electrons emitted from an X-ray detector portion in response to absorption of X-ray radiation and extraneous electrons originating outside the X-ray detector portion. Preferably, the X-ray detection method or an embodiment thereof is performed in an X-ray detector apparatus of the first general aspect of the present invention or an embodiment thereof.

[0019] Further general aspects include an X-ray fluorescence imaging apparatus and a method of using the X-ray detector apparatus of the first general aspect of the invention or an embodiment thereof, and / or an X-ray detection method of the second general aspect of the invention or an embodiment thereof for X-ray fluorescence imaging of an object of investigation, such as a biological organism or part thereof.

[0020] X-ray detector devices generally comprise solid-state detectors, particularly semiconductor detectors, in which an X-ray detector section (also called a detector chip) is made of a detector material suitable for absorbing X-ray photons, generating photoelectrons, and internal cascade multiplication of the photoelectrons, and is provided with readout electronics. The amplitude of the detector output (X-ray output signal) provided by the readout electronics is determined by, for example, proportional to, the energy of the X-ray photons. An X-ray detector device may include a single X-ray detector section or multiple X-ray detector sections. In the latter case, the X-ray output signal may be provided by superposition of the detector outputs of the X-ray detector sections. Furthermore, an X-ray detector device may comprise a detector housing (or detector casing, detector package) that houses the X-ray detector section(s). The entrance section is a portion of the X-ray detector device located on the irradiation side of the X-ray detector section(s). The entrance section is configured to receive X-ray radiation to be sensed along the irradiation direction, i.e., the entrance section is a portion of the X-ray detector device through which X-ray radiation passes to impinge on the X-ray detector section.

[0021] An X-ray detector apparatus may comprise a single X-ray detector device combined with a single background suppression device. Alternatively, an X-ray detector apparatus (pixelated X-ray detector apparatus) may comprise multiple X-ray detector devices (detector pixels), where a detector pixel may be combined with a single background suppression device, or each of the detector pixels may be combined with one of multiple background suppression devices.

[0022] A background suppression device generally comprises components of an X-ray detector apparatus that can provide an X-ray detector output signal with reduced, or even no, contributions caused by escape electrons and extraneous electrons. Suppressing the background contribution in the X-ray output signal includes suppressing the background contribution caused by escape electrons when the initially sensed X-ray output signal is dominated by it, and / or suppressing processes that generate extraneous electrons and cause the background contribution in the X-ray output signal. In particular, suppressing the background contribution includes reducing the background contribution to a level that allows detection of marker fluorescence, for example for XRF imaging, or eliminating the background contribution entirely.

[0023] Suppressing the background contribution in the x-ray output is advantageously energy independent, such that suppressing the background contribution may result in a broadband reduction of the background signal contribution, preferably covering an energy range of at least 10 keV, preferably at least 20 or 30 keV, or even more within the range below the simple and multiple Compton scatter peaks caused by the x-ray radiation to be sensed. Thus, suppressing the background contribution in the x-ray output signal is not limited to a single band or step in the x-ray spectrum.

[0024] The present invention is based on the following discovery by the inventors: Prior to the present invention, experts assumed that the background plateau portion of the detected X-ray spectrum could not be avoided as a result of the inherent occurrence of multiple Compton scattering events. The inventors performed extensive simulations of the detection process using an ideal detector that detects each incident X-ray photon at its exact energy. As a result of these simulations and deviating from the above assumptions, the inventors found that the background plateau portion of the detected X-ray spectrum is not primarily caused by multiple Compton scattering events, i.e., is not generated by photons, but is instead generated by sensing electrons that occur in and affect the detection process.

[0025] More specifically, the inventors have found two sources of contribution to the background plateau, including escape electrons emitted from the X-ray detector device, particularly from the X-ray detector portion, and external electrons generated outside the internal X-ray detector device, particularly inside, for example, outside the central detector portion (or solid-state detector chip). Thus, the background contribution sources include electrons that are generated inside the X-ray detector device, particularly the detector chip, and leave it again (called escape electrons), or electrons that impinge on the X-ray detector device, particularly the detector chip, from the outside (called external electrons). External electrons that are generated outside the X-ray detector portion and reach it cause erroneous signals therein.

[0026] Electrons that strike the X-ray detector from the outside are generated by components of the X-ray detector device other than the X-ray detector, such as the detector housing, and electrons that are knocked out from other components, such as the detector housing, can reach the X-ray detector device from the outside by X-ray photons via Compton scattering or optical absorption, thus generating a noisy background signal with non-specific energy. Due to this generation process, these electrons from the outside can also be understood as escape electrons. Although escape electrons have already been mentioned in [4], they always refer only to processes in the detector material itself and not to interactions in the surrounding structure of the detector.

[0027] Furthermore, the inventors have found that electrons from surrounding components (e.g., the detector housing as shown in Figure 5 of [7]) can outnumber electrons escaping from the X-ray detector section. In particular, at higher photon energies (>20 keV) preferred for preclinical X-ray fluorescence imaging, these electrons escaping from, for example, the housing dominate. Another source of external electrons can be provided by cosmic radiation and / or the surrounding atmosphere, particularly air.

[0028] By a further step of the present invention, the inventors have found that the effect of these sources, i.e., the background contribution to the X-ray output signal, can be suppressed. Therefore, a main advantage of the present invention is that an X-ray detector apparatus equipped with a background suppression device can substantially reduce the background plateau portion in the detected X-ray spectrum. It is possible to reduce the background to a limit that allows reliable detection of the X-ray output signal to be sensed, in particular to a negligible background or even to zero, so that for the first time the sensitivity of PET and SPECT methods can be reached in X-ray detection.

[0029] Advantageously, various configurations of the background suppression device are available, which will be described in detail below. According to a first variant, the background suppression device is an active signal processor configured to classify the currently measured X-ray detector output signal affected by escape electrons and extraneous electrons by employing a VETO detector element as described below. Alternatively or additionally, the background suppression device is a passive absorber configured to absorb X-ray photons that can generate extraneous electrons. Depending on the application of the invention, employing only passive absorbers may be sufficient for effective background suppression, especially in the energy range above 20 keV, or employing only active signal processors may be sufficient for effective background suppression, especially when escape electrons are dominant, or both passive absorbers and active signal processors may be combined. The latter embodiment has the advantage that the number or size of the VETO detector element(s) can be reduced, since the number of potentially generated extraneous electrons is substantially reduced.

[0030] Thus, according to a preferred embodiment of the present invention (hereinafter referred to as a first embodiment or an active signal processor embodiment), the background suppression device may comprise a VETO detector device having at least one VETO detector section configured to detect escaped electrons and external electrons and provide a VETO output signal determined by the detected escaped electrons and external electrons. In the first embodiment, the background suppression device further comprises a VETO trigger control device connected to the X-ray detector section and the at least one VETO detector section, the VETO trigger control device configured to control the output of the X-ray detector apparatus in response to the X-ray output signal and the VETO output signal. The VETO trigger control device may be configured to provide an X-ray output signal (e.g., trigger output of an X-ray output signal) when each VETO output signal is less than a predetermined background magnitude or zero, and not provide an X-ray output signal when at least one VETO output signal of the at least one VETO detector section is equal to or greater than the predetermined background magnitude.

[0031] Regarding this method, a first embodiment of the X-ray detection method may preferably include the steps of: providing a VETO detector device, the VETO detector device having at least one VETO detector section capable of detecting escape electrons and external electrons; providing a VETO output signal in each VETO detector section, each VETO output signal being determined by the escape electrons and external electrons detected by an associated VETO detector section; and providing an X-ray output signal in response to the X-ray output signal and the VETO output signal, wherein if each VETO output signal is less than a predetermined background magnitude or zero, an X-ray output signal is provided as an output of the X-ray detector device, and if at least one VETO output signal of the at least one VETO detector section is greater than or equal to a predetermined background magnitude, no X-ray output signal is provided.

[0032] The inventors have found that even if an initially incident X-ray photon is absorbed near one of the surfaces of the X-ray detector section and / or at least one other component of the X-ray detector device, such as a housing wall, where extraneous electrons may be generated, escape electrons and extraneous electrons will occur because the range of electrons emitted by the photon is sufficient to allow them to leave the X-ray detector section or other component. When this event occurs, the X-ray detector device records only a small portion of the incident X-ray photon's energy, rather than the full energy, resulting in a background plateau of a certain height and no X-ray output signal being provided. Thus, the X-ray detector device can record escape electrons and extraneous electrons and discard X-ray output signals that are temporally correlated with these events.

[0033] Therefore, as long as no VETO output signal is greater than or equal to the predetermined background magnitude and an X-ray output signal is currently sensed at the X-ray detector section, the current X-ray output signal is determined to contain no background contribution. In other words, if all VETO output signals are less than the predetermined background magnitude, it is determined that escape electrons and external electrons are not being generated, and the acquired X-ray output signal cannot be affected by them. Therefore, the output signal of the X-ray detector device is acquired based on the current X-ray output signal. Providing the X-ray output signal may include directly outputting the X-ray output signal or generating the detector device output signal based on the X-ray output signal; that is, the output signal of the X-ray detector device may be acquired by further processing the initially sensed X-ray output signal.

[0034] Otherwise, if at least one VETO detector section generates a VETO output signal that is equal to or greater than a predetermined background magnitude and an X-ray output signal is simultaneously sensed at the X-ray detector section, the current X-ray output signal is determined to include a background contribution and the current X-ray output signal is discarded. Advantageously, by discarding all X-ray output signals that include a background contribution, a background-free output of the X-ray detector device can be obtained.

[0035] The at least one VETO detector section is preferably arranged adjacent to the X-ray detector section and / or at least one other component of the X-ray detector device in a side-by-side arrangement. The distance between the at least one VETO detector section and the X-ray detector section and / or at least one other component is selected so that the at least one VETO detector section can collect escape electrons and external electrons. Due to this side-by-side arrangement, the X-ray detector device is called a VETO embedded detector (or trigger embedded detector, TED).

[0036] The VETO detector device may generally comprise a solid-state electron detector, particularly a semiconductor detector, where the VETO detector portion may be made of a detector material configured to collect and sense electrons and connected to readout electronics. The amplitude of the VETO detector output signal provided by the readout electronics is determined by, e.g., proportional to, the number of sensed electrons. The VETO detector device may include a single VETO detector portion or multiple VETO detector portions.

[0037] Preferably, at least one VETO detector element may be arranged on the irradiation side of the X-ray detector element, for example, at the entrance of the X-ray detector device. In particular, the VETO detector device may include only a single VETO detector element arranged on the irradiation side of the X-ray detector element. Thus, escape electrons and external electrons are preferably detected on the irradiation side of the X-ray detector element. Advantageously, most escape electrons are generated within the X-ray detector element near its irradiation surface, so that collecting escape electrons on the irradiation side allows detection of most background events. Detecting external electrons on the irradiation side of the X-ray detector element has a corresponding advantage in that most background events generated by external electrons are captured.

[0038] Alternatively, the VETO detector device may comprise multiple VETO detector sections arranged on multiple sides of the X-ray detector section. With regard to the method, the escape electrons and external electrons are detected on multiple sides of the X-ray detector section. Advantageously, this embodiment makes it possible to capture all or almost all background events generated by the escape electrons and external electrons.

[0039] According to a further preferred variant of the invention, the at least one VETO detector section may have a flat or curved shape. A flat shape may be advantageous in terms of arranging the VETO detector section adjacent to the plane of the X-ray detector section. A curved shape, e.g. a partially spherical shape, may improve the surrounding of the X-ray detector section by the at least one VETO detector section. The curved shape may have any shape that is selected in particular depending on the application conditions of the X-ray detector device.

[0040] Preferably, the material and / or thickness of the at least one VETO detector element may be selected, for example based on reference data, numerical simulations or experimental tests, so as to be mainly transparent to the X-ray radiation to be detected. Particularly preferably, at least 80%, for example at least 90%, of the X-ray radiation is transmitted. Advantageously, the at least one VETO detector element may be arranged on the irradiation side of the X-ray detector element, and still allow sufficient X-ray radiation to be detected by the X-ray detector device.

[0041] According to a further variant of the invention, at least one VETO detector section may have lateral dimensions that are greater than the lateral dimensions of the X-ray detector section. In particular, the surface area of ​​a VETO detector section completely covers the surface area of ​​the adjacent X-ray detector section. Advantageously, the reliability of detecting background events may be improved in this embodiment.

[0042] According to a further preferred embodiment of the present invention, at least one VETO detector section may comprise a detector layer, preferably a planar detector layer, whose thickness is less than that of the X-ray detector section. Thus, as a further advantage of the active signal processing embodiment, the inventors preferably employ the following properties of semiconductor detectors: Since all common semiconductor detectors have a nearly 100% detection probability for electrons, in contrast to photons, they can be constructed much thinner than the X-ray detector section and therefore do not interfere with incident photons. Preferably, the thickness of the detector layer of the VETO detector section is selected so that the photon detection efficiency of the detector layer is significantly lower than that of the embedded X-ray detector section, since VETO detectors mainly detect only electrons and need to provide almost complete transmission for photons.

[0043] A further advantage of the present invention is the availability of different detector materials, which can be selected depending on the application conditions of the present invention. The inventors have found that escape electrons can occur regardless of the detector material and / or the energy of the incident X-ray photons. Preferably, the X-ray detector section can include at least one of silicon (Si), germanium (Ge), cadmium telluride (CdTe), gallium arsenide (GaAs), and carbon (C). Alternatively or additionally, at least one VETO detector section preferably includes, but is not limited to, Si.

[0044] According to a particularly preferred embodiment of the invention, the VETO detector device may comprise two VETO detector sections (for example having a flat or curved shape and arranged parallel to one another, in particular at a certain mutual distance), with the X-ray detector section being arranged between the VETO detector sections, in particular along the irradiation direction. Advantageously, in this embodiment, almost all spatial directions around the X-ray detector section are covered by the two VETO detector sections, as a result of which a high efficiency of background event detection can be obtained with a relatively simple arrangement of the VETO detector sections.

[0045] Advantageously, the X-ray detector arrangement may comprise a collimator device and an X-ray entrance window defining an entrance aperture of the X-ray detector portion and arranged in front of the VETO detector device, so that the incident X-ray radiation can be efficiently guided at the irradiation side of the X-ray detector portion.

[0046] According to a further advantageous embodiment of the present invention, the VETO detector device and / or the VETO trigger control device may be configured in an operating mode in which an X-ray output signal is provided based on the X-ray output signal independently of the VETO output signal. Regarding the method, an operating mode in which the X-ray output signal is provided independently of the VETO output signal may be set. Thus, the X-ray detector apparatus may be switched between a background suppression mode in which the VETO trigger control device is operated and a background mode in which the VETO trigger control device is not operated (switched off). The adoption of the background mode may be advantageous, particularly when detecting high-intensity X-ray radiation with a relatively weak background that is negligible from the standpoint of signal detection, and / or for monitoring and diagnostic purposes.

[0047] According to a first embodiment of the present invention, the VETO trigger control device may be operated in response to the generation of a VETO output signal(s). If all VETO output signals are less than a predetermined background magnitude or zero, a background event is excluded. Thus, even if the VETO detector device detects some escape electrons and external electrons and there is a non-zero VETO output signal, if the non-zero VETO output signal is still less than a predetermined background magnitude, the detected event is not counted by the VETO trigger control device. The background magnitude may be selected based on, for example, reference data, numerical simulation, or experimental testing, depending on the application conditions of the X-ray detector apparatus. The background magnitude may be selected so that the X-ray output signal to be acquired can be measured with a sufficiently small level of noise. In particular, the background magnitude may be selected so that the X-ray output signal is greater than the statistical fluctuations (noise) of the background.

[0048] Optionally, the VETO trigger control device may be configured to adaptively control the magnitude of the background depending on the amplitude of the X-ray output signal and / or the VETO output signal. In particular, when the amplitude of the VETO output signal is relatively low, the magnitude of the background may be reduced as well. Advantageously, this allows for enhanced X-ray detection when the background level is low. A control loop may be provided in which the amplitude of the X-ray output signal and / or the VETO output signal is sensed and compared to a target value, and the magnitude of the background is set depending on the deviation of the sensed amplitude from the target value.

[0049] Since both the X-ray detector portion and the VETO detector portion(s) may be configured to detect X-rays or electrons, for example by both being made of Si, the functions of the X-ray detector portion and the VETO detector portion(s) may be reversed, i.e. the detector chip may be employed as a VETO detector portion and the VETO detector portion may be used for X-ray detection, as shown in particular in attached Figure 1.

[0050] According to a further preferred embodiment of the present invention (hereinafter referred to as the second embodiment or passive absorber embodiment), the background suppression device may comprise a shielding casing made of an X-ray photon absorbing casing material that suppresses the emission of electrons, surrounding the X-ray detector device, preferably the X-ray detector device and the VETO detector device, at least except for their entrance portions. Regarding the method, the background suppression step may comprise a step of absorbing X-ray photons with a shielding casing made of an X-ray photon absorbing casing material that suppresses the emission of electrons, surrounding the X-ray detector device, at least except for its entrance portion. While detector casings are already known from the prior art (see, for example, [7]), it has not been proposed to use an X-ray photon absorbing casing material that suppresses the emission of electrons. On the contrary, the casing known, for example, from [7], may itself generate extraneous electrons, so that in [7] background suppression can be obtained in a form that is limited only by suppressing escape electrons.

[0051] Advantageously, the inventors have found that external electrons can already be reduced very efficiently by the passive embedding provided by the shielding casing. The shielding casing is provided in addition to the detector housing of the X-ray detector device. The entire detector housing of the X-ray detector device (except the entrance part) can be surrounded by a material that absorbs X-ray photons but suppresses escaping external electrons. The choice and thickness of the material can be found by numerical simulation.

[0052] Particularly preferably, the shielding casing may surround the X-ray detector device, preferably the X-ray detector device and the VETO detector device, except for the entrance portion of the X-ray detector device and the back side opposite to the irradiation side. Thus, the shielding casing may have a sleeve shape that covers the X-ray detector device in a lateral direction perpendicular to the irradiation direction, preferably completely surrounds the X-ray detector device in the lateral direction, and is open towards the irradiation side and the back side of the X-ray detector device.

[0053] Preferably, the shielding casing may be made of at least one of Pb, W, and Mo, and an element whose atomic number matches that of Pb, W, or Mo, particularly a composition (e.g., alloy) of W, Ni, and Fe, such as the alloy of W, Ni, and Fe known as "DENSIMET" (trademark), or another wall material having a density similar to DENSIMET. Additionally or alternatively, the shielding casing may have a casing wall thickness greater than 1 mm. The thickness of the shielding casing wall may be selected, for example, in the range of 1 mm to 4 mm. As the energy increases, even greater thicknesses may be employed.

[0054] According to a further preferred variant of the embodiment of the passive absorber, the shielding casing may restrict the path of the incident photons only to the detector volume of the X-ray detector section where the photons are detected without incomplete counting caused by incomplete charge collection, e.g. due to different drift velocities of photoelectron-hole pairs generated in the X-ray detector section. Advantageously, the shielding casing may be used to mask the X-ray detector device on its irradiation side so that occurrence of incomplete counting is avoided.

[0055] As mentioned above, the X-ray detector device may optionally comprise a plurality of X-ray detector portions, preferably arranged in a stack. Particularly preferably, the X-ray detector portions are in layers, each having a thickness selected such that the detector volume of each X-ray detector portion layer, in particular the layer thickness of each X-ray detector portion layer, is so small that incomplete counts are not generated that may be caused by incomplete charge collection due to different drift velocities of photoelectron-hole pairs generated in the X-ray detector portion layer.

[0056] According to the invention, multiple X-ray detector devices may be combined in an array, for example as a line array or matrix array, to provide an X-ray fluorescence imaging device for the simultaneous spectrally and spatially resolved detection of X-ray radiation from a sample under investigation, which may be considered as an independent subject of the invention.

[0057] Further details and advantages of the present invention are described below with reference to the accompanying drawings. [Brief explanation of the drawings]

[0058] [Figure 1] 1 is a schematic cross-sectional view illustrating preferred features of an embodiment of an X-ray detector device according to the present invention; [Figure 2] FIG. 10 further illustrates the function of the VETO detector device. [Figure 3] FIG. 1 is an exemplary diagram of background suppression according to the present invention. [Figure 4] FIG. 10 shows an example of a curved VETO detector section. DETAILED DESCRIPTION OF THE INVENTION

[0059] A preferred embodiment of the present invention will be described below with exemplary reference to an X-ray detector device that combines both an active signal processor embodiment and a passive absorber embodiment. It should be noted that the present invention is not limited to this combination of features and can be implemented using only the features of the active signal processor embodiment or only the features of the passive absorber embodiment. In particular, the present invention will be described with reference to components that allow for the provision of an output signal with reduced or completely eliminated background. Details of the X-ray detector device, such as details of the X-ray detector section or its readout electronics, the casing of the X-ray detector device, the collimator device and / or the X-ray entrance window, will not be described insofar as they are known per se from the prior art, for example from X-ray detectors of the type FAST SDD detector (manufactured by AMPTEK, Massachusetts, USA).

[0060] 1 shows schematically an X-ray detector arrangement 100 for detecting X-ray photons of an X-ray radiation 1 to be sensed, in particular a so-called header of the X-ray detector arrangement 100. The X-ray detector arrangement 100 comprises an X-ray detector device 10 having an X-ray detector section 11 and a background suppression device 20 having VETO detector sections 21A, 21B and a shielding casing 23. The X-ray detector section 11 is arranged to receive X-ray photons of the X-ray radiation 1 to be sensed at an irradiation side of the X-ray detector arrangement 100. The X-ray radiation 1 has an irradiation direction (z-direction). The X-ray detector section 11 and the VETO detector sections 21A, 21B have lateral extensions that are preferably perpendicular to the irradiation direction.

[0061] FIG. 1 schematically illustrates a single X-ray detector element 11 based on a semiconductor chip, for example, having a thickness in the z-direction in the range of 1 mm to 3 mm. Alternatively, as shown schematically by dashed lines in the X-ray detector element 11, multi-layer X-ray detector elements can be provided between the VETO detector elements 21A, 21B. Preferably, each multi-layer X-ray detector element has a thickness of less than 1 mm, for example, in the range of 0.1 mm to 0.9 mm, particularly 0.1 mm to 0.5 mm. Within these thickness ranges, imperfect counts can only be generated in a substantially limited manner. The X-ray output signal of a multi-layer X-ray detector element can be provided by superposition of its detector outputs.

[0062] 1 are shown separated from one another primarily for clarity. In practice, it is possible, but not necessary, to arrange, for example, the X-ray detector section 11 and the VETO detector sections 21A, 21B with a distance between them. Alternatively, at least some, and preferably all, of the components of the X-ray detector device 100, for example the multi-layer X-ray detector sections, may be arranged directly adjacent to one another in a stack with no space between them.

[0063] The X-ray detector section 11 and the VETO detector sections 21A, 21B are supported by a substrate 41, which may be arranged in thermal contact and preferably in direct mechanical contact with a cooling device 42, such as a thermoelectric cooler. Except for the shielding casing 23, the components of the X-ray detector arrangement 100 are housed in a detector casing 43, e.g. made of Ni, e.g. having a thickness of 0.25 mm.

[0064] More specifically, the X-ray detector portion 11 of the X-ray detector device 10 has a thickness of, for example, 1 mm and a lateral area of, for example, 0.5 cm 2The X-ray detector section 11 comprises a planar detector chip of a detector material such as Si or Ge. The X-ray detector section 11 is provided with readout electronics 11A. At the output of the X-ray detector section 11, and in particular the readout electronics 11A, an X-ray output signal is generated in response to X-ray photon or electron absorption within the detector chip. As outlined below, in response to the output of the VETO detector sections 21A, 21B, an X-ray output signal is provided as an output of the X-ray detector arrangement 100.

[0065] On the irradiation side of the X-ray detector arrangement 100, an entrance section 12 is provided which comprises an X-ray entrance window 13 and a collimator device 14. The X-ray entrance window 13 is a 12.5 μm thick plate made of beryllium. The collimator device 14 forms an X-ray receiving window. For this purpose and to avoid incomplete charge collection by the detector chip, the collimator device 14 consists, for example, of an X-ray absorbing material, such as W, Cr, Ti, Al, with a thickness of 15 to 100 μm, and a window whose lateral extension (perpendicular to the irradiation direction) is smaller than the extension of the X-ray detector section 11. In particular, an overlap is provided between the collimator device 14 and the X-ray detector section 11.

[0066] The VETO detector device 21 of the background suppression device 20 comprises two VETO detector sections 21A, 21B, each of which is made of, for example, a flat plate made of Si, and which has a thickness, for example, 20 μm, smaller than that of the X-ray detector section 11. The VETO detector sections 21A, 21B are arranged parallel to each other and spaced apart on either side of the X-ray detector section 11. Both VETO detector sections 21A, 21B are provided with readout electronics (not shown) connected to a VETO trigger control device 22. At the outputs of the VETO detector sections 21A, 21B, and in particular their readout electronics, a VETO output signal is generated in response to electron absorption in the VETO detector sections 21A, 21B. Depending on the temporal correlation between the VETO output signal and the X-ray output signal, as outlined below, the X-ray output signal may or may not be provided as an output of the X-ray detector arrangement 100.

[0067] As an alternative to the planar shape of the VETO detector sections 21A, 21B of the VETO detector device 21, the VETO detector sections may have a curved shape as shown diagrammatically for VETO detector section 21C in FIG.

[0068] The VETO trigger control device 22 is a computer circuit that controls the output of the X-ray detector apparatus 100. The VETO trigger control device 22 may be integrated into the main control device 30 of the X-ray detector apparatus 100, as shown schematically in Figure 2. Alternatively, the VETO trigger control device 22 may be provided as a separate control unit.

[0069] Furthermore, the background suppression device 20 may comprise a shielding casing 23 enclosing at least the X-ray detector device 10 and the VETO detector sections 21A, 21B, and preferably all remaining parts of the X-ray detector apparatus 100 except for its entrance section 12. The shielding casing 23 may comprise a box with an open side towards the irradiation side, and may in particular be made of "DENSIMET" (trademark) with a thickness of 3 mm and containing more than 90% by volume of W.

[0070] The X-ray detector arrangement 100 is operated to detect X-ray photons of background-reduced or -eliminated X-ray radiation 1 as follows: X-ray radiation 1 is received by the X-ray detector device 10. In response to the interaction of the X-ray photons with the X-ray detector portion 11, photoelectrons are generated within the X-ray detector portion 11. The number of photoelectrons is increased by cascade multiplication in the detector material by a factor determined by the spectral energy of the X-ray photons. Thus, the amplitude of the X-ray output signal of the X-ray detector portion 11 is determined by the spectral energy of the detected X-ray photons.

[0071] Concurrent with the generation of photoelectrons, electrons may leave the detector chip as escape electrons, which alter the x-ray output signal as fewer electrons are sensed by the readout electronics 11A, thus indicating detected events that appear to have reduced energy. In particular, these events are eliminated in embodiments of the active signal processor.

[0072] According to an embodiment of the active signal processor, escape electrons are detected by at least one of the VETO detector sections 21A, 21B, which generates a VETO output signal in response to absorption of the escape electrons. The VETO trigger control device 22 temporally correlates the occurrence of the VETO output signal with the occurrence of the X-ray output signal. For this purpose, a predetermined correlation time window, e.g., the integration time of the detector sections, is monitored. If both at least one VETO output signal and an X-ray output signal are detected during a correlation time window, e.g., with a duration of approximately 4 μs, the X-ray output signal is classified as having been altered by the occurrence of escape electrons and is therefore blocked, as determined by the background to be eliminated. If no substantial VETO output signal is detected during the correlation time window including the X-ray output signal, the X-ray output signal is detected as an output S of the X-ray detector device 100. o,11 It is provided as.

[0073] The VETO output signal(s) are considered to have occurred or not occurred during the correlation time window if the amplitude(s) of the signal(s) is / are equal to, greater than, or less than a predetermined background magnitude. By defining the background magnitude, it is possible to pass the X-ray output signal to the output of the X-ray detector device 100 even with a small but acceptable background contribution. The background magnitude can be set depending on the application conditions, for example, the amplitude of the sensed X-ray output signal and / or the number of escaped electrons expected.

[0074] As a result, using two VETO detector sections 21A, 21B, the VETO trigger control device 22 is operated like a logical NOR gate, and outputs (X-ray output signal S) only if both VETO output signals are below the background magnitude, as shown in FIG. o,11 ) is provided.

[0075] The VETO detector sections 21A, 21B are not only responsive to escape electrons, but also to the generation of external electrons that occur outside the X-ray detector device 10, for example, due to absorption of X-ray radiation in other components of the X-ray detector apparatus 100 and / or as a result of cosmic radiation. The external electrons may also generate background contributions due to absorption in the X-ray detector sections 11. Detection of the external electrons by the VETO detector sections 21A, 21B determines an event that generates a burst of external electrons. The VETO output signal caused by the external electrons can also be used to cancel out the corresponding background contribution in the output of the X-ray output signal.

[0076] Additionally, in the passive absorber embodiment, the generation of external electrons, particularly external electrons impinging on the X-ray detector device 100 from the side, is suppressed by the shielding casing 23, resulting in fewer events blocking the sensed X-ray output signal and the X-ray output signal provided by the X-ray detector device 100 having a reduced background contribution.

[0077] The function of the VETO trigger control device 22 can be turned off by stopping the VETO trigger control device 22 or by setting the background magnitude level to a level such that no VETO output signal is used by the VETO trigger control device 22 to block the X-ray output signal.

[0078] The effect of background suppression is illustrated schematically in experimental results in FIG. 3, which shows the x-ray output signal (e.g., event counts) as a function of energy. Curve B' represents a conventional measurement showing a plateau section at energies below peak A due to single and multiple Compton scattering. In the plateau section, the x-ray output signal C to be sensed cannot be measured. In accordance with the present invention, the background events that cause the plateau section are eliminated or suppressed, so that the plateau section is substantially reduced and the x-ray output signal C is sensed with sufficient discrimination against the background. Note that FIG. 3 represents a schematic diagram only. In an actual measurement, peak A may be broadened compared to the extension of plateau section B'.

[0079] In summary, when an X-ray photon strikes, for example, the detector casing 43 and / or the X-ray detector unit 11, photoionizing electrons may leave the materials (i.e., the housing and the chip), and thus the X-ray detector unit 11 will erroneously record these electrons from the housing as photons (which will cause spectral background), or the electrons may leave the chip, and thus the X-ray detector unit 11 will measure an energy lower than that of the absorbed photon (which will also contribute to the spectral background). However, the VETO trigger control device 22 triggers on both types of electrons and therefore discards these events, so that these energy "false positives" are not recorded in the spectrum and only pure X-ray photon events are preferably measured, which is why the corrected spectrum no longer includes the spectral background in the X-ray fluorescence imaging signal region of FIG. 3. Thus, removing spurious (photon) energy input to the spectrum by rejecting escape and / or extraneous electrons significantly reduces the final background plateau (B) compared to the uncorrected one (B'), thus improving the detection sensitivity of the fluorescence line (C).

[0080] The features of the present invention disclosed in the above description, drawings, and claims may be relevant both individually and in combination or subcombination for realizing the invention in various embodiments. The present invention is not limited to the preferred embodiments described above. Rather, multiple variations and derivations are possible that use the inventive concept and thus fall within the scope of protection. Furthermore, the present invention also claims protection for the subject matter and features of the dependent claims, independently of the referenced features and claims.

Claims

1. An X-ray detector device (100) configured to detect incident X-ray photons of an X-ray radiation (1) to be sensed, comprising: an X-ray detector device (10) having an X-ray detector portion (11) and an entrance portion (12), the X-ray detector portion (11) being arranged to detect the X-ray photons incident through the entrance portion (12) by generating photoelectrons in response to an interaction of the incident X-ray photons with the X-ray detector portion (11), and to provide an X-ray output signal determined by the detected X-ray photons; a background suppression device (20) configured to suppress background contributions in the X-ray output signal caused by escape electrons emitted from the X-ray detector portion (11) in response to absorption of the X-ray radiation (1) and by external electrons generated outside the X-ray detector portion (11). An X-ray detector device (100).

2. The background suppression device (20) comprises: a VETO detector device (21) having at least one VETO detector portion (21A, 21B) arranged to detect the escape electrons and the external electrons and to provide a VETO output signal determined by the detected escape electrons and the external electrons; a VETO trigger control device (22) connected to the X-ray detector section (11) and the at least one VETO detector section (21A, 21B), and configured to control output of the X-ray output signal in response to the VETO output signal; 2. The X-ray detector apparatus of claim 1, wherein the VETO trigger control device (22) is configured to provide the X-ray output signal when each VETO output signal is less than a predetermined background magnitude or zero, and not to provide an X-ray output signal when at least one VETO output signal of the at least one VETO detector section (21A, 21B) is equal to or greater than the predetermined background magnitude.

3. The at least one VETO detector unit (21A, 21B) is arranged on the irradiation side of the X-ray detector unit (11). The X-ray detector device according to claim 2 .

4. The VETO detector device (21) includes a plurality of VETO detector sections (21A, 21B) arranged on a plurality of sides of the X-ray detector section (11). The X-ray detector device according to any one of claims 2 to 3.

5. the at least one VETO detector unit (21A, 21B) has a flat plate shape; the at least one VETO detector portion (21A, 21B) has a curved shape; the material and / or thickness of said at least one VETO detector portion (21A, 21B) is selected to be predominantly transparent to said X-ray radiation (1) to be sensed, and the at least one VETO detector section (21A, 21B) has a lateral dimension greater than a lateral dimension of the X-ray detector section (11); 5. The X-ray detector device according to claim 2, further comprising at least one of:

6. the at least one VETO detector portion (21A, 21B) comprises a detector layer having a thickness less than the thickness of the X-ray detector portion (11); The X-ray detector device according to any one of claims 2 to 5.

7. The X-ray detector unit (11) includes at least one of Si, Ge, CdTe, GaAs, and C; and the at least one VETO detector portion (21A, 21B) includes Si; 7. The X-ray detector device according to claim 2, further comprising at least one of:

8. The VETO detector device (21) comprises two VETO detector sections (21A, 21B), The X-ray detector unit (11) is disposed between the VETO detector units (21A, 21B). The X-ray detector device according to any one of claims 2 to 7.

9. The entrance section (12) comprises an X-ray entrance window (13) and a collimator device (14) arranged in front of the VETO detector device (21). The X-ray detector device according to any one of claims 2 to 8.

10. The VETO detector device (21) and / or the VETO trigger control device (22) 10. The X-ray detector apparatus of any of claims 2 to 9, configured in an operational mode in which the X-ray output signal is provided based on the X-ray output signal independent of the VETO output signal.

11. the VETO trigger control device (22) is adapted to adaptively control the magnitude of the background depending on the amplitude of the X-ray output signal and / or the VETO output signal. The X-ray detector device according to any one of claims 2 to 10.

12. The background suppression device (20) comprises: a shielding casing (23) made of an X-ray photon absorbing casing material that suppresses electron emission, surrounding the X-ray detector device (10) except for the entrance portion thereof; The X-ray detector device according to any one of claims 1 to 11.

13. The electron absorbing casing comprises: the shielding casing (23) comprises a composition of at least one of Pb, W, Mo, and elements whose atomic numbers correspond to those of Pb, W, or Mo, in particular W, Ni, and Fe; the shielding casing (23) has a casing wall with a thickness of more than 1 mm; The X-ray detector device according to claim 12, comprising at least one of:

14. the shielding casing (23) is configured to restrict the path of the incident photons to only a detector volume of the X-ray detector section (11) where the photons are detected without incomplete counting caused by incomplete charge collection due to different drift velocities of the photoelectron-hole pairs generated in the X-ray detector section (11).

14. The X-ray detector device according to claim 12 or 13.

15. The X-ray detector device (10) comprises a plurality of X-ray detector portions (11). The X-ray detector device according to any one of claims 1 to 14.

16. 1. An X-ray detection method for detecting X-ray photons of X-ray radiation (1), comprising: receiving the X-ray radiation (1) at an X-ray detector device (10) of an X-ray detector apparatus (100), the X-ray detector device (10) having an X-ray detector portion (11) and an entrance portion (12); generating photoelectrons in the X-ray detector portion (11) in response to an interaction of the X-ray photons with the X-ray detector portion (11); providing an X-ray output signal, the X-ray output signal being determined by the detected X-ray photons; suppressing background contributions in the X-ray output signal caused by escape electrons emitted from the X-ray detector portion (11) in response to absorption of the X-ray radiation (1) and by external electrons generated outside the X-ray detector portion (11). X-ray detection methods.

17. The background suppression step comprises: providing a VETO detector device (21), the VETO detector device (21) having at least one VETO detector portion (21A, 21B) capable of detecting the escape electrons and the external electrons; providing a VETO output signal at each VETO detector section (21A, 21B), each VETO output signal being determined by the escape electrons and the external electrons detected by the associated VETO detector section (21A, 21B); and providing the X-ray output signal in response to the VETO output signal, wherein the X-ray output signal is provided if each VETO output signal is less than a predetermined background magnitude or zero, and no X-ray output signal is provided if at least one VETO output signal of the at least one VETO detector portion (21A, 21B) is equal to or greater than the predetermined background magnitude.

18. setting an operating mode in which the X-ray output signal is provided based on the X-ray output signal independent of the VETO output signal.

18. The method of x-ray detection according to claim 17.

19. adaptively controlling the magnitude of the background in response to the amplitude of the X-ray output signal and / or the VETO output signal; The X-ray detection method according to any one of claims 17 to 18.

20. The escape electrons and the external electrons are detected on the irradiation side of the X-ray detector unit (11). The X-ray detection method according to any one of claims 17 to 19.

21. The escape electrons and the external electrons are detected on multiple sides of the X-ray detector unit (11). The X-ray detection method according to any one of claims 17 to 20.

22. The background suppression step comprises:

22. The method for X-ray detection according to claim 16, further comprising the step of absorbing X-ray photons with a shielding casing (23) made of an X-ray photon absorbing casing material that suppresses emission of electrons and that surrounds the X-ray detector device (10) except for the entrance portion thereof.

23. Use of an X-ray detector device (100) according to any of claims 1 to 15 or an X-ray detection method according to any of claims 16 to 22 for X-ray fluorescence imaging of an object of investigation.

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