Radiation detector and detection method

Abstract

The radiation detector uses a direct conversion layer 30 with first and second readout sensors 20, 24 disposed on opposite sides of the direct conversion layer 30. A biasing device provides a voltage bias across the direct conversion layer 30 using pixel electrodes 22, 26 of the first and second readout sensors. The use of the direct conversion layer 30 gives an inherent high spatial resolution and enables X-ray photon counting. This allows two independent readout sensors (e.g., with different technologies and associated back-end electronics) to be combined into one detector without compromising their functionality. The detector can be made at low cost by using a single direct conversion layer 30 coupled to multiple readout sensors on both sides.

Description

[Technical field]

[0001] The present invention relates to radiation detectors, for example for use in medical imaging. [Background technology]

[0002] X-ray detectors are commonly used for medical diagnostic imaging.

[0003] Modern medical X-ray detectors use either indirect or direct detection techniques. Indirect detection techniques use a scintillator X-ray absorber (usually cesium iodide, CsI) coupled to a matrix of photodiodes, such as amorphous silicon photodiodes. These photodiodes also act as storage capacitors. Direct detection techniques use a photoconductor (usually amorphous selenium, a-Se) coupled to an array of storage capacitors. Direct detection techniques generate a photocurrent directly from the incident radiation (without converting X-ray photons to light photons). New photoconductors with enhanced X-ray absorption have been developed for use in direct detection X-ray detectors. Summary of the Invention [Problem to be solved by the invention]

[0004] Today, most medical X-ray detectors are based on a single layer of a particular X-ray conversion material (e.g., CsI or a-Se as explained above) coupled to a single readout sensor fabricated in a particular technology (e.g., a-Si TFT or CMOS). The product properties and characteristics are specified within certain performance ranges to adequately fulfill the imaging tasks of a limited set of clinical applications.

[0005] In recent years, the increasing complexity, variety and requirements of diagnostic and interventional procedures have led to the demand for improved detector performance, such as improved dynamic range and spatial resolution. Unfortunately, existing common detector designs can only achieve relatively small performance improvements by optimizing the specifications of readout sensors and / or X-ray conversion materials. Furthermore, advanced image acquisition methods, signal data electronics and image processing techniques have their limitations in improving image processing performance.

[0006] Attempts have been made in the past to improve the performance and / or functionality of detectors by modifying the structural design of the detector.

[0007] As described in U.S. Pat. No. 9,588,235, a design has been proposed that uses a detector having an X-ray scintillator layer, a first readout sensor bonded to its upper surface, and a second readout sensor bonded to its lower surface.

[0008] Also, as described in U.S. Pat. No. 10,371,830, a detector has been proposed in which two X-ray scintillator layers are stacked and a first readout sensor is coupled to the upper surface and a second readout sensor is coupled to the lower surface.

[0009] Another design, as described in WO2004095069A1, has a single radiation conversion material for converting X-ray and gamma radiation doses into electrical signals that are amplified and analyzed to generate, for example, X-ray and PET images.

[0010] Also proposed is a design that combines a single direct x-ray conversion layer with a single readout sensor capable of simultaneous charge integration and photon counting.

[0011] US Patent Application Publication No. 2011 / 0155918A1 provides a system and method for sharing charge in a pixelated image detector. One method includes providing a plurality of pixels for a pixelated solid-state photon detector in a configuration such that a charge distribution is detected by at least two pixels, and acquiring charge information from the at least two pixels. The method further includes determining a position of interaction of the charge distribution with the plurality of pixels based on the acquired charge information.

[0012] US Patent Application Publication No. 2013 / 0284938A1 describes a gamma ray detector having a solid-state detector including a plurality of anode pixels and at least one cathode. The solid-state detector is configured to receive gamma rays during interaction and induce signals in the anode pixels and the cathode. An anode pixel readout circuit is coupled to the plurality of anode pixels and configured to read and process the induced signals in the anode pixels and provide triggering and addressing information. A waveform sampling circuit is coupled to the at least one cathode and configured to read and process the induced signals in the cathode and determine the energy of the interaction, the timing of the interaction, and the depth of the interaction.

[0013] China Patent Publication No. 108445525A describes an area array pixel detector, which at least includes a pixel array anode, a detection medium, and a cathode. The pixel array anode is disposed on a first surface of the detection medium, and the pixel array anode has a plurality of pixel anodes, each pixel anode detects a photon signal at a different position. The cathode is disposed on a second surface of the detection medium, and the cathode has a plurality of cathode electrode blocks each independent of each other, and the first surface and the second surface are disposed opposite to each other.

[0014] The paper "Status of Direct Conversion Detectors for Medical Imaging With X-Rays" (IEEE TRANSACTIONS ON NUCLEAR SCIENCE, DOI: 10.1109 / TNS.2009.2025041) reviews the detector requirements for advanced medical X-ray and CT imaging, as well as examples of the status and progress in this field. Emphasis is placed on direct conversion sensors for pixelated detectors. A discussion of readout concepts and related challenges such as interconnections is also presented.

[0015] There is still a need for improved detector performance and multi-functionality. It is technically difficult to achieve the desired multi-functionality (e.g., spectroscopic X-ray imaging and gamma-ray imaging) with existing X-ray detector designs. For example, starting from a standard design of a charge-integration (CI) X-ray detector, it is very difficult to add a new functionality, X-ray photon counting (PC), to this detector, because it would degrade the performance of most CI detection modes. Similarly, starting from an existing PC detector design and modifying the design to add CI functionality without sacrificing the properties of the PC detection mode, is currently technically impossible.

[0016] It is also difficult to improve the detector performance by combining a single X-ray conversion layer with a single readout sensor. For example, increasing the spatial resolution by making the pixels of the readout sensor smaller inevitably leads to increased electronic noise. This can be prevented by adding more sophisticated electronic circuits to the readout sensor, but at the cost of degrading other detector characteristics such as the dynamic range.

[0017] The use of a single detector, and the resulting limited available detection modes, also impacts the physician's workflow. For example, the ability to zoom in on a small field of view (FOV) region to examine anatomical details at high resolution is often limited by the spatial resolution of the detector. Also, high-speed image acquisition (e.g., 200 fps or more for 3D imaging) is often constrained by the maximum available frame rate of the detector (<100 fps). These issues can be solved by detectors that use two or more different readout sensors on one side of the X-ray conversion layer, but this has the disadvantage that it is not possible to image the entire region with one readout sensor type and that the detector (or the patient) must be moved from one imaging position to another.

[0018] It would be desirable to address these issues without the need for expensive manufacturing, for example avoiding the need for expensive multi-layer stacked detectors. [Means for solving the problem]

[0019] The invention is defined by the independent claims. The dependent claims define advantageous embodiments.

[0020] According to an embodiment of one aspect of the present invention, there is provided a radiation detector comprising a direct conversion layer (DCL) having first and second opposing sides, a first read sensor located on the first side of the direct conversion layer and having a first read sensor pixel electrode electrically connected to the direct conversion layer, a second read sensor located on the second side of the direct conversion layer and having a second read sensor pixel electrode electrically connected to the direct conversion layer, and a bias apparatus for providing a voltage bias across the direct conversion layer using the first and second pixel electrodes, the bias apparatus configured to control the voltage bias at the first and second pixel electrodes during readout of the first and / or second read sensor.

[0021] The use of a direct conversion layer provides an inherently high spatial resolution (based on the channeling of current in an electric field), which allows the use of small pixel sizes for the first and / or second readout sensors. The direct conversion layer allows single X-ray photon counting to be performed using existing large area detectors. Conversely, with commonly used X-ray scintillators, the signal pulse generated by a single X-ray photon is too low in intensity and too slow to be detected by the pixel electronics for photon counting.

[0022] The use of direct conversion layers has gained interest due to the emergence of improved photoconductive materials such as organic-inorganic hybrid perovskites, which are much cheaper than standard direct conversion materials such as cadmium telluride (CdTe) and cadmium zinc telluride (CZT) and perform much better than a-Se.

[0023] The detector of the present invention offers the possibility to combine two independent readout sensor technologies (and associated back-end electronics) in one detector without compromising their functionality. For example, a dedicated charge integration (CI) readout sensor can be coupled to one side of a direct conversion layer and a dedicated photon counting PC readout sensor can be coupled to the other side of the same direct conversion layer. In this way, there are multiple readout sensors in one detector, each of which can be optimally designed to achieve a specific performance level required within the intended application range of the detector.

[0024] The use of multiple readout sensor technologies allows, for example, zoom-in capabilities directly on the detector, expanding the range of clinical applications.

[0025] A single direct conversion layer is connected to multiple readout sensors on both sides, allowing the detector to be manufactured at low cost. It is also possible to cover only a portion of one side of the direct conversion layer with an associated active readout sensor, thereby further reducing the cost of the multifunction detector.

[0026] The bias device can be realized for example by the read sensor and its associated read-out electronics and / or by an additional bias electrode device. By means of the bias device a controllable bias voltage is provided across the direct conversion layer. This can allow dynamic control of the bias voltage depending on the detector imaging task of the first and second read-out sensor. The bias device allows decoupling the voltage level of the associated read-out sensor electronics of the respective read-out sensor from the (large) bias voltage on the direct conversion layer. The read-out on the first and second read-out sensor can be performed separately or simultaneously depending on the imaging task or tasks at hand while maintaining a controllable bias of each pixel. The risk of damage of the read-out electronics by the bias voltage on the direct conversion layer can be avoided. The detector can thus allow multifunctional detection with various options for generating for example a single image or two different images separately or simultaneously in a manner controlled for the imaging task at hand.

[0027] The biasing device allows control of both the polarity and magnitude of the voltage applied to the direct conversion layer, thereby optimizing the performance of one and / or both sensors for a particular imaging task. As a non-limiting example, the ability to control polarity may be required in a hybrid detector where one sensor is designed for charge integration (CI) and the opposite sensor is designed for photon counting (PC). When electrons are the fast charge carriers to be detected, the polarity of the pixel electrodes in the CI sensor is positive when the detector is used in CI mode. However, when the same detector is used in PC mode, the polarity is reversed to capture electrons in the opposite PC sensor.

[0028] The detector may for example comprise a hybrid detector, where the first and second readout sensors have different sensor manufacturing and / or radiation detection and / or sensor pixel technologies, in this way each readout sensor can be designed for a specific purpose.

[0029] The first and second readout sensors have different configurations, e.g., different pixel sizes and / or different readout sensor areas, and thus, in addition to different technologies (e.g., semiconductor fabrication technologies such as CMOS vs. TFT, or imaging modalities such as charge integration vs. photon counting), different readout sensor pixel layouts and different overall readout sensor areas may be employed.

[0030] The first read sensor may, for example, comprise a charge integrating read sensor and the second read sensor may comprise a photon counting read sensor.

[0031] In another example, the first and second readout sensors are of the same type (i.e., have the same sensor manufacturing technology, radiation detection technology, and sensor pixel technology) but have different configurations, such as different pixel sizes and / or different readout sensor areas. In this way, the same type of sensing may be used but with different configurations, for example to enable different fields of view or different resolutions.

[0032] The first readout sensor has, for example, a first readout electronic circuit and the second readout sensor has a second readout electronic circuit, and the first and second readout electronic circuits are controllable to read out the first and second readout sensors separately, simultaneously, or separately or simultaneously depending on the detector settings.

[0033] In this way, the two readout sensors can be used individually and therefore in sequence or simultaneously. The detector may allow the user to select between these two options as two different modes of operation, or the detector may only allow one mode.

[0034] The first and second readout electronics may be controllable to generate said voltage bias between the first and second readout sensors. The readout electronics may, for example, be for charge sensing and may hold the pixel electrodes at a reference voltage during charge sensing. By allowing control of this reference voltage, a desired voltage bias across the direct conversion layer may be generated.

[0035] However, instead of or in addition to using readout electronics to implement the desired voltage bias, the first and / or second readout sensor may have an interconnect grid that allows the first and / or second readout sensor pixel electrodes to be connected to a reference voltage. In this way, a voltage bias can be applied across the direct conversion layer between the reference voltage of one grid and the operating voltage of the readout electronics of the other readout sensor. In one example, the first and second readout sensors each have an interconnect grid that allows all readout sensor pixel electrodes to be connected to a reference voltage. In another example, one of the sensors is biased with an interconnect grid and the other sensor is biased by the readout electronics (e.g. no grid).

[0036] Each interconnect grid has, for example, a respective electrical switch between each pixel electrode and a common reference voltage terminal. This common reference voltage can then be set to a level different from the normal reference voltage of the readout electronics (the virtual ground of the charge-sensitive amplifier) ​​that is applied when the readout electronics is being used to capture image data. Thus, the common reference voltage applied to the interconnect grids allows a voltage different from that normally applied by the readout electronics to be applied to the pixel electrodes.

[0037] According to another aspect of the invention there is provided a radioimaging system comprising a radiation detector, which may advantageously be a system for diagnostic or therapeutic imaging, such as a tomography system, a radiology system or a fluoroscopy system or a combination of these systems.

[0038] The present invention provides a method of radiation detection comprising the steps of controlling a bias arrangement for providing a voltage bias across a direct conversion layer using pixel electrodes of first and second readout sensors, the first readout sensor being located on a first side of the direct conversion layer and the second readout sensor being located on an opposite second side of the direct conversion layer, receiving imaging data from the first readout sensor, and receiving imaging data from the second readout sensor, the voltage biases at the pixel electrodes of the first and second readout sensors being controlled by the bias arrangement during readout of the first and second readout sensors.

[0039] The method is preferably computer-implemented. The method provides a diagnostic image or pair of diagnostic images for review by a clinician. The invention does not relate to the interpretation of images, for example for the purposes of making a diagnosis.

[0040] The method may include receiving imaging data from the first and second readout sensors separately, simultaneously, or selectively separately or simultaneously.

[0041] The method may include applying a reference voltage to pixel electrodes of one of the first and second readout sensors using an interconnect grid connecting the pixel electrodes of the one of the first and second readout sensors to a reference voltage terminal, and reading out imaging data from the other of the first and second readout sensors.

[0042] This approach uses an additional interconnect grid to apply a reference voltage to the pixel electrodes on one side of the direct conversion layer so that there is a desired voltage bias relative to the pixel electrode voltages applied by the readout electronics in the other readout sensor.

[0043] The method may alternatively comprise controlling the first and second readout electronics of the first and second readout sensors to generate said voltage bias between the first and second readout sensors. This is possible if a voltage bias can be generated between the readout electronics of the two readout sensors. This approach uses the readout electronics to generate the voltage bias.

[0044] The invention further provides a computer program having a computer program code configured to perform the method defined above, when the computer program is run on a computer.

[0045] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0046] For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which: [Brief description of the drawings]

[0047] [Figure 1] Schematic cross-section of a typical direct X-ray conversion detector. [Diagram 2] FIG. 2 illustrates the approach disclosed in US Pat. No. 9,588,235, in which the detector has a single x-ray scintillator layer and first and second readout sensors on opposing surfaces. [Diagram 3] FIG. 1 illustrates a design according to an embodiment of the present invention. [Figure 4] FIG. 4 more clearly illustrates the grid layout used in the design of FIG. 3. [Diagram 5] FIG. 2 shows an example where both sides of a direct conversion layer are completely covered with one or more read sensors S1 and S2. [Figure 6] FIG. 13 illustrates an example where read sensors have different areas. [Figure 7] FIG. [Figure 8] FIG. 2 shows an electronic circuit that provides a voltage bias across the direct conversion layer. [Figure 9] FIG. 1 shows an electronic circuit that provides a voltage bias across the direct conversion layer by a bias grid. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] The present invention will now be described with reference to the drawings.

[0049] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the devices, systems and methods, are for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects and advantages of the devices, systems and methods of the present invention will become better understood from the following description, the appended claims and the accompanying drawings. It should be understood that the drawings are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings to denote the same or similar parts.

[0050] The present invention provides a radiation detector using a direct conversion layer with first and second readout sensors disposed on either side of the direct conversion layer. A biasing device provides a voltage bias across the direct conversion layer using pixel electrodes of the first and second readout sensors. The use of a direct conversion layer inherently provides high spatial resolution and enables x-ray photon counting. This allows two independent readout sensors (e.g., having different technologies and associated back-end electronics) to be combined into one detector without compromising their functionality. The detector can be manufactured at low cost by using a single direct conversion layer coupled to multiple readout sensors on either side of the layer.

[0051] 1 shows a schematic cross-sectional view of a standard direct x-ray conversion detector 10. A pixelated readout sensor 20 (e.g., a-Si TFT or CMOS) is bonded to one side of a direct conversion layer 30 material (e.g., CdTe, CZT, perovskite) and a common bias electrode 40 is connected to the opposite side of the direct conversion layer 30.

[0052] During radiation exposure of the object, electron-hole pairs are generated in the direct conversion layer 30. A bias electrode voltage ΔV applied to the readout sensor substrate creates a potential difference across the direct conversion layer 30. This potential difference attracts electrons to the individual readout sensor pixel electrodes 22 and holes to the common bias electrode 40, or vice versa. By precisely collecting and analyzing all the signals from the pixel electrodes in the readout sensor 20, a radiation image of the object is generated by additional electronics integrated into the readout sensor and / or detector.

[0053] It is known to apply different readout sensors on either side of a scintillator layer for indirect conversion detectors. Figure 2 shows an approach disclosed in US Patent No. 9,588,235, in which the detector has a single X-ray scintillator layer 50 (e.g., CsI), a first thin film transistor and readout sensor 60 coupled to its top surface, and a second CMOS readout sensor 70 coupled to its bottom surface. The two readout sensors share the same scintillator.

[0054] FIG. 3 shows a design according to an embodiment of the present invention.

[0055] The present invention is based on direct conversion, and therefore the design of FIG. 3 uses a single direct conversion layer 30 as its basic element.

[0056] Compared to the standard direct conversion detector of Fig. 1, the common bias electrode is replaced by a second read sensor 24. In the example shown, the second read sensor 24 has a second pixel electrode 26 of a larger area than the first pixel electrode 22 of the first read sensor 20 and therefore a lower spatial resolution. However, this is only one option. The pixel electrode is electrically connected to the direct conversion layer 30.

[0057] A voltage bias must be generated across the direct conversion layer 30 .

[0058] In the design according to the present invention, this voltage bias is generated by a bias device that provides a voltage bias across the direct conversion layer 30 by using the first and second pixel electrodes 22, 26 (at least a portion of the area of ​​the direct conversion layer 30 where the first and second read sensors overlap).

[0059] The voltage bias depends on the material of the direct conversion layer 30 and may be about 10V or 100V or more.

[0060] There are various ways to achieve the voltage bias.

[0061] Each read sensor 20, 24 comprises read-out electronics that are based on current detection, in particular detecting the current generated in response to incident radiation, for example incident X-ray photons or gamma radiation. The read-out electronics therefore typically comprise a charge-sensitive amplifier that holds the pixel electrode at a reference voltage and measures the charge that flows.

[0062] To generate a bias voltage across the direct conversion layer 30 using the pixel electrodes as voltage bias devices, the pixel electrodes of one readout sensor need to be held at a different voltage than the pixel electrodes of the other readout sensor. This can be accomplished in a variety of ways.

[0063] 3 shows an example where each read sensor comprises a common conductive bias grid to which all pixel electrodes can be connected via additional electrical switches. The first read sensor 20 has a first grid 23 and the second read sensor 24 has a second grid 27. The grid comprises an array of conductors extending between areas of the pixel electrodes.

[0064] The switches are not shown, nor are the additional conductors required to address the switches.

[0065] The grid layout is shown more clearly in Figure 4. Thus, the two readout sensors share the same direct conversion layer 30. During radiation exposure, the required voltage bias ΔV across the direct conversion layer 30 is applied by the bias grids 23, 27 and, in particular, when collecting image data, can be applied by a voltage between one bias grid and the pixel electrode of the other readout sensor.

[0066] For example, when the detector is used to read out a first read sensor 20, all pixel electrodes 26 of the opposite second read sensor 24 are connected via an electrical switch (not shown) to a bias grid line 27 and thus to a common reference potential V. The voltage at the pixel electrodes of the first read sensor 20 is set by the readout electronics of the first read sensor, i.e. to a virtual ground reference.

[0067] Similarly, when the detector is used for readout of the second read sensor 24, all pixel electrodes 22 of the first read sensor 20 are biased to a reference potential V by an integrated bias grid in the first read sensor. The voltages at the pixel electrodes of the second read sensor 24 are set by the readout electronics of the second read sensor, i.e. to a virtual ground reference.

[0068] The inputs of the charge integrator circuits (in unused readout sensors) are held at (or close to) the same potential as the associated bias grid to avoid any lateral current flow, thereby protecting the amplifier from overload.

[0069] An alternative to the use of a bias grid is to always use the charge integrating pixel amplifier itself, in which case the bias potentials of the two readout sensors (i.e. the ground reference mentioned above) are maintained at different values.

[0070] In use, every pixel is used to measure the displacement current in the direct conversion layer 30. This current can be measured anywhere in a closed circuit from one side of the detector to the other, and is measured by integrating the current flow into the pixel electrodes. Thus, the sum of the currents into all pixels measured on either detector side is the same.

[0071] Charge integration can be measured for a large pixel on one detector side and for a small pixel on the other detector side. This makes it possible to reduce the number of charge integration amplifiers or to create a zoom-in function. A large pixel can be used for charge integration on one detector side, for example, in combination with a small pixel for photon counting on the opposite detector side. This requires different sensor electronics for the two readout sensors.

[0072] The two read sensors may have the same or different overall sizes and, optionally, pixel electrodes of different sizes (and therefore different resolutions). Figure 5 shows various possible examples. In each case, the first read sensor is designated S1 and the second read sensor is designated S2. In the examples of Figure 5, both sides of the direct conversion layer 30 are completely covered with one or more read sensors S1 and S2.

[0073] FIG. 5a shows an example where both readout sensors are constructed from a single large area substrate (e.g., glasses), while FIGS. 5b-5d show examples where one or both readout sensors are formed from multiple tiled small area substrates (e.g., Si CMOS).

[0074] The direct conversion layer 30 may also consist of a single piece (FIGS. 5a-5c) or may be formed from multiple pieces (FIG. 5d).

[0075] A complete detector may be assembled from multiple tiled sub-detector modules, as shown diagrammatically in FIG. 5d.

[0076] When the readout sensors are formed as a tiled array, there can be different readout sensor designs, such as the different readout sensors S2a and S2b in FIG. 5c.

[0077] The required specifications of detector performance and / or functionality can be realized, or at least approached, by appropriate selection of a combination of two (or more) different readout sensor designs. A non-exhaustive list of possible readout sensor characteristics is shown in Table 1. Many combinations of different readout sensor functions, specifications, technologies and / or embedded readout sensor electronics are possible to realize a 2:1 detector that closely matches the increased requirements of the intended imaging application. [Table 1]

[0078] As can be seen from Table 1, the readout sensors can differ by one or more of the following: detection modality (e.g., charge integration vs. photon counting); Spectral capabilities; Radiation type; Intended type of medical imaging; speed, spatial resolution, dynamic range; Readout electronic circuit characteristics; Readout electronics; Output data characteristics.

[0079] One implementation of particular interest is a hybrid X-ray detector capable of both current integration (CI) and photon counting (PC) imaging. For example, a first conventional CI readout sensor can be used for all the usual standard (non-spectral) detector modes and applications, while a second dedicated PC readout sensor is used for (new) spectral imaging applications. In this case, a dedicated CI readout sensor is coupled to the bottom of the direct conversion layer 30 and a dedicated PC readout sensor is coupled to the top of the direct conversion layer 30 (or vice versa).

[0080] The pixel size in the PC readout sensor can be selected to be larger (e.g., 300 μm, CMOS) than the pixel size in the CI readout sensor (e.g., 100 μm, IGZO TFT), thereby improving spectral imaging performance and reducing manufacturing costs.

[0081] If both readout sensors are PC sensors, different pixel sizes can be chosen to provide two options of different compromises between spectral and spatial resolution.

[0082] If both readout sensors are CI sensors, a standard pixel size (e.g., 100 μm) can be used in one readout sensor in combination with a smaller pixel size (e.g., 50 μm) in the other readout sensor to provide a zoom-in function. Alternatively, a central portion of the readout sensor on one side of the direct conversion layer 30 (e.g., readout sensor S2a in FIG. 5c) can provide special features (e.g., high resolution, high SNR) while the surrounding readout sensors (e.g., readout sensor S2b in FIG. 5c) can provide standard detector functions.

[0083] The detector can be operated in different modes: (i) The first mode can use only one of the two readout sensors for imaging, depending on the specific needs of the application (spectrum, zoom mode, resolution, etc.). (ii) A second mode allows using both readout sensors simultaneously if the application benefits from it (e.g. large area overview images, zoomed details or spectral details). In this mode, the direct conversion layer 30 must be operated with a preselected bias voltage polarity, which leads to the collection of different charge carriers in the two readout sensors. For a given polarity of bias voltage, one sensor collects electrons and the other sensor collects holes. Since different types of charge carriers generally have different lifetimes and mobilities, the sensor electronics are adapted to the respective carrier type (depending on the selected direct conversion layer material).

[0084] The detector may only have the capability to operate according to the first mode, or, if the detector has the option of both modes of operation, the user may be able to select between both modes.

[0085] The example of Figure 5 shows the direct conversion layer 30 covered by the first and second read sensors. However, the read sensors can have different areas. Some examples are shown in Figure 6.

[0086] In Figure 6a, the top side of the direct conversion layer 30 is only partially covered by the second read sensor S2, and in Figure 6b, the bottom side of the direct conversion layer 30 is only partially covered by the first read sensor S1.

[0087] Since the pixel electrodes of the small readout sensors cannot provide the desired voltage bias across the entire area of ​​the direct conversion layer 30, bias electrodes can be provided outside the area of ​​the small readout sensors (S2 in FIG. 6a or S1 in FIG. 6b).

[0088] Figure 6c shows that the smaller read sensor S2 can be surrounded by dummy read sensors D2, and Figure 6d shows that the smaller read sensor S1 can be surrounded by dummy read sensors D1.

[0089] The options in Figures 6a-d are interesting if a particular required detector function (e.g., spectral photon counting) can be provided in a relatively cheap and simple way by adding a small-area readout sensor to an already existing full-area detector.

[0090] The pixels of the dummy readout sensor can in principle be used to provide a voltage bias function without the need for a separate bias electrode as described above and without the need for associated readout electronics.

[0091] The detector design should be optimized to ensure that the quality of the image acquired by a particular readout sensor is not adversely affected by the presence (or absence) of other readout sensors on the same or opposite side of the direct conversion layer 30. For example, due to X-ray absorption in the CMOS Si substrate of the small area PC readout sensor S2 (FIG. 6a) on the direct conversion layer 30, the image acquired by the large area readout sensor S1 at the bottom of the direct conversion layer 30 may be slightly disturbed.

[0092] The above-mentioned dummy readout sensor improves the "invisibility" of the readout sensor S2 in the image of the readout sensor S1, for example to avoid edge artifacts in the field of view of the readout sensor S1. A non-functional (dummy) readout sensor has the same thickness as the readout sensor it surrounds (in this example the PC readout sensor S2). The dummy readout sensor or sensors D2 can also be used to provide additional metal wiring from the detector periphery to the central PC readout sensor S2, for example for power and signal data transfer.

[0093] In general, when read sensors with different thicknesses (absorption thicknesses of X-ray, a-Si:H and CMOS detectors) are used, the thinner read sensor should be on the side of the detector facing the X-ray tube.

[0094] The electrical and physical coupling of both readout sensors to the direct conversion layer 30 must be sufficient to ensure proper signal transfer from the direct conversion layer 30 to all readout sensor pixel electrodes and to minimize interference between the two readout sensors.

[0095] Well-established interconnection techniques (ACF bonding, bump bonding, soldering, etc.) exist for coupling pixelated readout sensors to various direct conversion layer materials. When high voltages are applied via a bias grid on the pixel electrodes of the readout sensors on one side of the direct conversion layer 30, it may be necessary to protect the electronic circuitry of these temporarily inactive readout sensor pixels. This can be done by temporarily disconnecting all pixel circuitry from the bias grid and pixel electrodes by using an additional electrical switch per pixel.

[0096] If a grid is used, preferably the conductive bias grid lines and the electrical switches are realized at the end of the photolithography-based process commonly used to fabricate the read sensor itself (e.g. a-Si TFT or Si CMOS). The grid lines may be composed of metals or metal alloys (Cu, Al, Mo, W, Cr, Ti, etc.). Alternatively, non-photolithographic methods (3D metal printing, laser-induced metal deposition, screen-printed conductive inks, etc.) can be used to realize the bias grid. The electrical switches may be simple MOSFETs (CMOS) or TFTs (e.g. a-Si or IGZO).

[0097] The present invention can be applied to a wide variety of known direct conversion layer materials (e.g., amorphous Se, single crystal Si, single crystal GaAs, polycrystalline or single crystal CdTe and CZT). In particular, the use of polycrystalline or single crystal metal halide perovskite materials (MAPbI3, MAPbBr3) is attractive because they require smaller operating voltages (approximately 10 V) than more known direct conversion layer materials (>100 V).

[0098] FIG. 7 shows a radiation detection method including: in step 80, controlling a bias device to provide a voltage bias across the direct conversion layer 30 using pixel electrodes of the first and second readout sensors; in step 82, receiving imaging data from the first readout sensor, and in step 84, receiving imaging data from the second readout sensor.

[0099] A biasing device configured to provide a controllable voltage bias across the direct conversion layer 30 using the first and second pixel electrodes can be realized in different ways. By way of example, FIG. 8 shows an electrical circuit suitable for controlling the bias voltage when the voltage bias is realized by a readout sensor and its associated readout electronics. In this example, the first pixel electrode 22 in the detector is connected to a first integrator 92 at the input of a first readout amplifier 93. Similarly, the second pixel electrode 26 in the detector is connected to a second integrator 94 at the input of a second readout amplifier 95. The first integrator 92 maintains the (-) input at the same voltage as the (+) input. Any attempt to raise or lower the voltage on the (-) input by adding or removing charge results in a change in the output voltage V1, which compensates for that change in the (-) input via a feedback network of capacitors and resistors. As a result, the measured output voltage V1 corresponds to the amount of charge added or removed from the first pixel electrode 22, i.e. the measured data signal from the corresponding detector pixel. The feedback network maintains the required condition that the (-) input of the first integrator connected to the first pixel electrode remains at the same voltage as the (+) input. Similarly, a second integrator 94 in a second readout amplifier 95 measures the data signal from the second pixel electrode 26.

[0100] In FIG. 8, a controllable bias voltage source 96 is connected between the first readout amplifier 93 and the second readout amplifier 95 to generate a well-defined voltage difference ΔVbias between the two (+) inputs. A capacitor is added in parallel with ΔVbias to keep ΔVbias at a fixed level even with very fast signals from the detector. Thus, the direct conversion layer 30 in the detector is biased by two readout amplifiers separated by ΔVbias at their (+) inputs. At the same time, their (-) inputs are also separated by the same ΔVbias, as explained above. The first and second readout amplifiers may require separate internal power supplies, for example from a first DC / DC converter 97 and a second DC / DC converter 98, respectively. This provides sufficient isolation from a common power supply 99. The output voltages V1 and V2 are referred to as Vbias,1 and Vbias,2, respectively. These voltage measurements can be transferred to a common reference level, for example by using an optical isolator or another form of signal isolator.

[0101] Figure 9 shows an example of an electrical circuit suitable for controlling the voltage bias across the direct conversion layer 30 in the detector, where the voltage bias is achieved by interconnect grids 23, 27. The circuit of Figure 9 is very similar to the circuit shown in Figure 8, except that in Figure 9 the interconnect grids 23, 27 are directly connected to two outputs Vbias,1 and Vbias,2 of a controllable bias voltage source (96).

[0102] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0103] Measures recited in mutually different dependent claims can be combined to advantage.

[0104] The computer program may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

[0105] The term "adapted to" when used in the claims or the description is meant to be equivalent to the term "configured to." When the term "apparatus" is used in the claims or the description, the term "apparatus" is intended to be equivalent to the term "system," and vice versa.

[0106] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. a direct conversion layer having opposing first and second sides; a first read sensor disposed on the first side of the direct conversion layer and having a first pixel electrode electrically connected to the direct conversion layer; a second read sensor disposed on a second side of the direct conversion layer and having a second pixel electrode electrically connected to the direct conversion layer; a bias device that supplies a voltage bias across the direct conversion layer using the first and second pixel electrodes, the bias device controlling the voltage bias at the first and second pixel electrodes during readout of the first and second readout sensors; A radiation detector having:

2. a hybrid detector, the first and second read sensors comprising: Sensor manufacturing technology, Radiation detection technology, and Sensor Pixel Technology The radiation detector of claim 1 , wherein the radiation detector differs in one or more of:

3. The radiation detector of claim 2 , wherein the first and second readout sensors have different configurations, different pixel sizes and / or different readout sensor areas.

4. 4. A radiation detector according to claim 2 or 3, wherein the first read sensor comprises a charge integrating read sensor and the second read sensor comprises a photon counting read sensor.

5. 2. The radiation detector of claim 1, wherein the first and second readout sensors have the same sensor manufacturing technology, radiation detection technology, and sensor pixel technology, but have different geometric configurations, different pixel sizes, and / or different readout sensor areas.

6. 4. The radiation detector of claim 1, wherein the first readout sensor has a first readout electronic circuit and the second readout sensor has a second readout electronic circuit, the first and second readout electronic circuits being controllable to read out the first and second readout sensors separately, simultaneously, or separately or simultaneously depending on a setting of the radiation detector.

7. 7. The radiation detector of claim 6, wherein the first and second readout electronics are controllable to generate the voltage bias between the first and second readout sensors.

8. 4. A radiation detector according to claim 1, wherein the first and / or second readout sensor comprises an interconnect grid enabling the first and / or second pixel electrodes to be connected to a reference voltage.

9. 9. A radiation detector according to claim 8, wherein each interconnect grid has a respective electrical switch between each pixel electrode and a common reference voltage terminal.

10. A radiation imaging system comprising a radiation detector according to any one of claims 1 to 3, wherein the radiation imaging system is a tomography system, a radiology system, or a fluoroscopy system.

11. 1. A radiation detection method comprising: controlling a bias device that supplies a voltage bias across a direct conversion layer using pixel electrodes of first and second read sensors, the first read sensor being disposed on a first side of the direct conversion layer and the second read sensor being disposed on an opposite second side of the direct conversion layer; receiving imaging data from the first readout sensor; receiving imaging data from the second readout sensor; wherein voltage biases at pixel electrodes of the first and second readout sensors are controlled by the biasing device during readout of the first and second readout sensors.

12. 12. The method of claim 11, comprising receiving imaging data from the first and second readout sensors separately, simultaneously, or selectively separately or simultaneously.

13. applying a reference voltage to pixel electrodes of one of the first and second read sensors using an interconnect grid connecting all of the pixel electrodes of the one of the first and second read sensors to a reference voltage terminal; reading out imaging data from the other of the first and second readout sensors; 13. The method of claim 11 or 12, comprising:

14. 13. The method of claim 11 or 12, comprising controlling first and / or second readout electronics of the first and second readout sensors to generate the voltage bias between the first and second readout sensors.

15. A computer program having computer program code for causing a computer to carry out the method according to claim 11 or 12.

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