Modular X-ray detector

Abstract

The present invention provides a detector module (1) for a modular X-ray detector, wherein the detector module (1) includes a plurality of X-ray detector substrates (10) and associated anti-scatter collimators (20). Each X-ray detector substrate (10) has a plurality of detector diodes, and each X-ray detector substrate has an associated anti-scatter collimator (20). Each X-ray detector substrate (10) has an integrated circuit (30) for collecting X-ray signals from the diodes; the integrated circuit is attached to the X-ray detector substrate at the bottom of the X-ray detector substrate, assuming that the top of the X-ray detector substrate is the place where X-rays enter, and the associated anti-scatter collimator (20) is disposed above the integrated circuit (30).

Description

[0001] This application is a divisional application of the application with the filing date of March 23, 2018, application number 201680055420.7, and invention title "Modular X-ray Detector". Technical Field

[0002] The technology proposed by the present invention generally relates to X-ray detectors, and more specifically to a modular X-ray detector and a detector module for such a modular X-ray detector. Background Art

[0003] When constructing an X-ray detector, the main challenge is to achieve high detection efficiency, such that a modular arrangement of the detector and / or ensuring encapsulation and wiring is feasible, so as to enable efficient production of the detector. Additionally, it is beneficial to meet all requirements simultaneously, which is a challenge as some of these requirements are conflicting. For example, the wiring and encapsulation required for a modular arrangement typically mean sacrificing the active detector area, thus reducing the geometric efficiency.

[0004] Furthermore, in most cases, the X-ray detector must be integrated with an anti-scatter collimator or grid to eliminate scatter from the object and / or between detector modules. It is also necessary to protect sensitive integrated circuits from direct radiation, as high cumulative doses may negatively impair the functionality of the circuits.

[0005] Meanwhile, each detector module and anti-scatter grid are preferably precisely aligned with the incident X-rays from the radiation source.

[0006] Prior art detectors in, for example, computed tomography are based on scintillators that convert X-rays into visible light, which is detected by specific-purpose photodiodes that integrate the signals of multiple X-rays. The photodiodes are connected to an integrated circuit that digitizes the generated current, and this value is used to calculate the gray-scale values displayed in the X-ray image. One-dimensional or two-dimensional anti-scatter grids are placed on top of the scintillator and the diodes. To avoid crosstalk, trenches are used to separate each scintillator diode assembly. The anti-scatter collimator is positioned to match the trenches in order to minimize any dead zones. There are several ways to address the challenges of encapsulation and wiring: connecting the diodes to the integrated circuit to provide power and data transfer. There are good examples of how to address these challenges. An embodiment is disclosed in reference [1], where a fully modular arrangement that can be tiled two-dimensionally is presented. Another example of an interconnection and encapsulation method is given in reference [2], where elastomeric conductive contacts are configured to provide a high-voltage anode signal.

[0007] In recent years, a large amount of research focus in academia and industry has been concentrated on how to provide X-ray detectors with high spatial and contrast resolution. One of the most promising ways to achieve this goal is through photon counting spectral detectors. However, these imaging detectors can only be used in mammography for early breast cancer detection, see reference [3], but the next use can be in computed tomography. Two different solutions have emerged. One solution is based on heavy detector elements such as CdTe or CdZnTe, as described in reference [4] for example, while the other solution is based on silicon as the detector material, as outlined in reference [5].

[0008] In a silicon detector assembly as described in reference [5], the challenges of detection efficiency and modularity are very different compared to assemblies with heavy elements as the detector material, because in the direction of the incident X-rays, the silicon detector requires a longer path (about 30 - 40 times) to absorb the main part of the X-rays. This means that the geometric structure and mechanical constraints are very different. Summary of the Invention

[0009] An object of the present invention is to provide an improved detector module for a modular X-ray detector.

[0010] Another object of the present invention is to provide an improved modular X-ray detector based on such detector modules.

[0011] These and other objects are achieved by specific embodiments of the proposed technology.

[0012] In a first aspect of the proposed technology, a detector module for a modular X-ray detector is provided, wherein the detector module includes a plurality of X-ray detector substrates and associated anti-scatter collimators. Each X-ray detector substrate has a plurality of detector diodes, and each X-ray detector substrate has an associated anti-scatter collimator. Each X-ray detector substrate has an integrated circuit for collecting X-ray signals from the diodes; the integrated circuit is attached to the bottom of the X-ray detector substrate, assuming the top of the X-ray detector substrate is where the X-rays enter, and the associated anti-scatter collimator is disposed above the integrated circuit.

[0013] This type of detector module enables the construction of a modular X-ray detector in an efficient manner.

[0014] In a second aspect of the proposed technology, a modular X-ray detector is thus provided, which includes a plurality of detector modules as described in the first aspect.

[0015] Other advantages will be appreciated when reading the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic view showing one embodiment of an X-ray detector module and a corresponding modular detector assembly.

[0017] Figure 2 is a schematic view showing one embodiment of a detector module for a modular X-ray detector.

[0018] Figure 3 is a schematic view showing a Figure 2 partial close-up of an exemplary module shown in

[0019] Figure 4 is a schematic view showing an embodiment of how to obtain a conical geometry, in which an anti-scatter collimator and a detector substrate are pointed at a radiation source to provide an overall curved detector geometry.

[0020] Figure 5 is a schematic view showing an embodiment of how to flip-chip an ASIC onto a silicon detector substrate, in which an input signal is routed from a single diode to an input of the ASIC.

[0021] Figure 6 is a schematic view shown from a side view, which shows a space below the detector substrate for wire bonding, passive components, and cables.

[0022] Figure 7 is a schematic view showing an embodiment of an architecture for electronic readout of data and for distributing control instructions to detector modules. DETAILED DESCRIPTION

[0023] In Figure 1 an illustrative non-limiting embodiment of the present invention is shown, in which an X-ray detector module and a corresponding modular detector assembly 100 are shown, and these modules can be tiled to acquire any area of the entire detector assembly, as long as the boundary conditions of the maximum power supply and data transfer rate can be handled.

[0024] Figure 2FIG. 0 is a schematic view showing an embodiment of a detector module for a modular X-ray detector. In this embodiment, the detector module 1 includes a plurality of X-ray detector substrates 10 and associated anti-scatter collimators 20. Each X-ray detector substrate 10 has a plurality of detector diodes, and each X-ray detector substrate 10 has an associated anti-scatter collimator 20. Moreover, each X-ray detector substrate 10 has an integrated circuit 30 for collecting X-ray signals from the diodes, and the integrated circuit 30 is attached to the X-ray detector substrate at the bottom of the X-ray detector substrate, assuming that the top of the X-ray detector substrate is the place where X-rays enter, and the associated anti-scatter collimator 20 is disposed above the integrated circuit 30.

[0025] This type of detector module can effectively construct a modular X-ray detector. The specific implementation of the modular X-ray detector has several structural advantages, which will be understood from the embodiments described herein.

[0026] In a second aspect of the proposed technology, there is thus provided a modular X-ray detector 100 including a plurality of detector modules 1 of the first aspect.

[0027] The described detector module can be embodied in many different variants.

[0028] By way of example, the integrated circuit can be an application-specific integrated circuit, i.e., an ASIC.

[0029] For example, the ASIC can extend along the edge of the X-ray detector substrate such that a portion of the ASIC is located outside the silicon detector substrate so that power and data can be transmitted to the ASIC without having to route the ASIC on the silicon detector substrate.

[0030] For example, the signal can be routed from a single diode to the input of the ASIC.

[0031] Optionally, the power line and data transmission line are wire-bonded to power and data transmission pads on the ASIC outside the substrate, or a redistribution layer on the substrate is used to connect to power, data transfer pads, and input signal pads and redistribute the input signals from the X-ray detector substrate to the ASIC.

[0032] As a supplement, a heat conductor can be connected to the ASIC as a means for cooling.

[0033] As an example, the anti-scatter collimator can be an anti-scatter foil or plate.

[0034] For example, the anti-scatter foil can be located between the X-ray detector substrates.

[0035] The anti-scattering foil can be made of a heavy material such as tungsten.

[0036] In a particular embodiment, the integrated circuit is an application specific integrated circuit, i.e., an ASIC, and the anti-scattering collimator is a tungsten foil; the ASIC is placed on an X-ray detector substrate below the tungsten foil such that the so-called dead zone in the detector is minimized and the ASIC is protected from direct radiation.

[0037] Preferably, for each X-ray detector substrate, it has a conical geometry and the X-ray detector substrate and the associated anti-scattering collimator are directed towards the radiation source, which is provided by a spacer located at the silicon detector substrate or at the anti-scattering collimator.

[0038] Typically, a plurality of X-ray detector substrates are tiled relative to each other to form a detector module.

[0039] As an example, each X-ray detector substrate and the corresponding integrated circuit are formed as a sensor multi-chip module, i.e., an MCM assembly; a plurality of sensor MCM assemblies are connected into the detector module.

[0040] For example, the detector module is subdivided into a plurality of detector blocks, where each detector block includes a plurality of sensor MCM assemblies, as Figure 7 shown in

[0041] In a particular example, each detector block includes means for demultiplexing instructions from the corresponding detector module into the detector block to reduce the number of connections between the detector block and the detector module, as Figure 7 shown in

[0042] Typically, the instructions are control instructions directed to the sensor MCM assemblies.

[0043] The detector module includes a plurality of data storage circuits and data processing circuits, where each detector block is managed by the data processing circuits.

[0044] For example, the detector module includes control and communication circuits for allocating control instructions to the sensor MCM assemblies and for controlling the reading of stored scan data from the data storage circuits.

[0045] In a particular embodiment, the X-ray detector substrate is a silicon detector substrate.

[0046] For better understanding, the proposed technology will now be described with reference to non-limiting exemplary embodiments.

[0047] To avoid any dead zones, an integrated circuit (ASIC) collects X-ray signals from diodes. The integrated circuit is attached to the X-ray detector substrate at the bottom of the X-ray detector substrate, and the top of the X-ray detector substrate is where X-rays enter. The anti-scatter collimator is composed of, for example, tungsten foils between each silicon detector substrate. To minimize the so-called dead zones in the detector (the areas that do not function as detectors but are mechanical supports, tungsten foils, air gaps, etc.), the ASIC for collecting X-ray signals from the diodes is placed under the tungsten foil. This also means that the ASIC will be protected from the effects of direct radiation. To be not significantly thicker than the tungsten foil, the ASIC is thinned to 50 - 100 μm.

[0048] In a specific embodiment, the ASIC is flip-chip mounted on the silicon detector substrate, and each diode is connected to a dedicated ASIC input through a trace. Moreover, the ASIC is dropped off at the edge of the silicon detector substrate. This gives space for larger components, and the larger components are similar to capacitors that must be close to the ASIC to optimize reliability and noise performance.

[0049] This means that thick traces for power are not required, which would otherwise make the silicon substrate more expensive. The power connection to the ASIC can be provided by other means. For example, the power line can be wire-bonded to the power pads on the ASIC.

[0050] Another solution is to use a redistribution layer connected to the power supply, data transfer pads, and input signal pads, and redistribute the signals from the ASIC to the silicon detector substrate.

[0051] After the silicon detector substrate, there will be space for electronic components. The electronic components should be positioned, for example, close to the capacitance of the electronic device. An X-ray absorber can also be placed in heavy metals such as tungsten or molybdenum to prevent any X-rays transmitted through the silicon from further penetrating the assembly. Radiation protection materials can also be placed around the integrated circuit to minimize any radiation damage.

[0052] As a device for cooling the heat conductor, preferably, a device with a coefficient of thermal expansion matching that of silicon can be attached to the ASIC, and the heat generated by the ASIC can be transferred to a place that can be easily taken care of by standard air or liquid cooling devices.

[0053] Figure 1 is a schematic diagram showing an embodiment of an X-ray detector module and a corresponding modular detector assembly. Figure 1 Examples of the modules are shown and how these modules build a corresponding modular detector assembly with a full detector area of a desired size. Note that these modules are pointed towards the X-ray source.

[0054] Figure 2 is a schematic diagram showing an embodiment of a detector module for a modular X-ray detector. Thus, Figure 2 shows an example of the module design. Starting from the top, an anti-scatter foil made of a heavy material such as W is shown, which is typically significantly thinner than the silicon detector substrate, which is an active detector volume composed of diodes. The X-ray detector substrate is located between these foils. The X-ray detector substrate can be, for example, 0.5 mm thick. Both foils and the X-ray detector substrate are pointed towards the X-ray source to avoid parallax errors and shadows from the anti-scatter foil. At the bottom, the ASICs are shown, which are typically as thin as the W foils and are located behind these foils (when viewed from above).

[0055] Figure 3 is Figure 2 a close-up view of, showing the anti-scatter foil, the silicon detector substrate, and the ASIC.

[0056] Figure 4 is a schematic diagram showing an embodiment of how a conical geometry is obtained when the tungsten and the silicon detector substrate are pointed towards the radiation source, by placing spacers, such as bolts, at the silicon detector substrate or at the anti-scatter grid.

[0057] To make all the tungsten foils and the silicon detectors point precisely towards the radiation source, spacers can be used between each element. Due to this spacer, the whole detector will be curved. Figure 4 shows an example of how a conical geometry is achieved by placing spacers, such as bolts, at the silicon detector substrate or on the tungsten foil.

[0058] Figure 5 shows an embodiment of how the ASIC is flip-chip mounted to the silicon detector substrate, where the input signal is routed from a single diode to the ASIC input terminal. A part of the ASIC is located outside the silicon detector substrate to enable the connection for power and data transfer to the ASIC without routing the ASIC on the silicon detector substrate.

[0059] Figure 6 is a schematic diagram of the embodiment shown from a side view, which shows that there is space for wire bonding, passive components, and cables below the detector substrate. The thermal conductor is not shown in the image, but it can be attached to the ASIC.

[0060] Figure 7 is a schematic diagram showing an embodiment of the architecture for the electronic readout of data.

[0061] An important challenge is to read out data from multiple X-ray detector modules.

[0062] In Figure 7An embodiment of a possible architectural solution is shown. In this example, multiple sensor MCM (multi-chip module) components are connected to form a detector module. In this context, a sensor MCM component refers to a silicon substrate detector and an ASIC component.

[0063] For example, each detector module can be managed by a small FPGA (field programmable gate array) or similar circuitry that handles clock distribution, loads configuration data, and assigns instructions to the sensor MCMs.

[0064] As an example, the entire detector can contain several tenths of thousands of ASICs, so connecting and setting / programming all ASICs in the detector is a particular challenge.

[0065] Each detector module can be based on the sensor MCMs in these steps. For example, by placing the sensor MCMs on the detector blocks and then building the detector module based on multiple detector blocks. In other words, each detector module can include multiple detector blocks, where each detector block includes multiple sensor MCM components.

[0066] To physically accommodate all the connections and meet the bandwidth requirements, the scheme shown in Figure 7 can be used.

[0067] Each sensor block includes a small FPGA for demultiplexing low information content signals such as clock and / or instructions from the module to the sensor block. As Figure 7 shown, this can, for example, reduce the number of connections between the sensor block and the module from 42 + 21 to 3 + 21.

[0068] The local memory (3 * DDR in Figure 7 ) distributed among these modules stores / buffers data to relax the bandwidth requirements for the downstream connections. When the acquisition is complete, the data from all these memories is read out at a lower rate. This arrangement can reduce the number of connections from the module to the motherboard, which, in the embodiment shown in Figure 7 , is reduced from 72 (3 × 24) to 8 connections.

[0069] The local memory and the processor / FPGA are preferably used to handle the setup of the processing circuitry in order to parallelize the tasks. Configuring several tenths of thousands of ASICs from a single source is too slow. The preferred approach can be to broadcast the common information part and send the specific information separately. Calibration can be processed locally at the module level, including calculations, storage, loading, etc.

[0070] As an example, the detector motherboard has the control of the entire system, can be regarded as the overall control system, and is connected to an external system.

[0071] In a particular embodiment, three detector blocks are placed together to form a detector module. Each detector block is managed by processing circuitry with associated storage / data memory, such as a data storage FPGA or similar circuitry. This FPGA / circuit locally stores all the scan data from a sensor MCM component and sends control instructions for the sensor MCM component. Control and communication FPGA or similar circuitry can also be provided in the detector module. Upon power-up, the unit manages the configuration of other FPGA circuits in the detector module, using configuration data stored in local FLASH. When the system is powered up and running, it assigns control instructions to the sensor MCM component and controls the reading of the stored scan data from three processing circuits with associated memory / data memory (such as a data storage FPGA). This data is sent to the detector motherboard.

[0072] By way of example, instructions can be broadcast to all detector modules for synchronous execution, or addressed individually to other tasks. It controls the reading out of scan data from the detector modules, downloads calibration data to the sensor MCM, etc.

[0073] Data from the detector motherboard can be further transmitted to one or more external computers for post-processing and / or image reconstruction.

[0074] Those skilled in the art should be clear that various different modifications, combinations, and alterations can be made to these specific embodiments without departing from the scope of the invention defined by the appended claims. From the specific embodiments, it can be seen that the arrangements described herein can be implemented, combined, and rearranged in many different ways. In particular, in different specific embodiments, different partial solutions can be combined in other configurations, which are technically feasible.

[0075] References

[0076] [1] U.S. Patent No. 7,582,879.

[0077] [2] U.S. Patent No. 7,560,702

[0078] [3] M. Danielsson, H. Bornefalk, B. V. Chmill, B. Hasegawa, M. Lundqvist, D. Nygren and T. Tabár, “Dose-efficient system for digital mammography”, Proc. SPIE, Physics of Medical Imaging, vol. 3977, pp. 239 - 249, San Diego, 2000。

[0079] [4] C. Xu, M. Danielsson and H. Bornefalk, “Evaluation of Energy Loss and Charge Sharing in Cadmium Telluride Detectors for Photon-Counting Computed Tomography”, IEEE Transactions on Nuclear Science, vol. 58, no. 3, pp. 614–625, June 2011。

[0080] [5] U.S. Patent No. 8,183,535。

Claims

1. A detector module (1) for a modular X-ray detector, characterized in that: The detector module (1) includes a plurality of X-ray detector substrates (10) and associated anti-scatter collimators (20); Wherein each X-ray detector substrate (10) has a plurality of detector diodes, and each X-ray detector substrate has an associated anti-scatter collimator (20), The plurality of X-ray detector substrates are tiled relative to each other to form the detector module, The anti-scatter collimator is an anti-scatter foil or plate interposed between the plurality of X-ray detector substrates, The anti-scatter foil or plate is thinner than the X-ray detector substrate, The diodes of the X-ray detector substrate define an active detector volume, The X-ray detector substrate and the anti-scatter foil or plate have a length direction, and the anti-scatter foil or plate and the X-ray detector substrate point to the X-ray source along the length direction; Wherein each X-ray detector substrate (10) has an integrated circuit (30) for collecting X-ray signals from the diodes, wherein the integrated circuit is attached to the X-ray detector substrate at the bottom of the X-ray detector substrate along the length direction of the X-ray detector substrate, the top of the X-ray detector substrate is where X-rays enter, and the associated anti-scatter collimator (20) is disposed above the integrated circuit (30) to protect the integrated circuit from radiation.

2. The detector module according to claim 1, characterized in that: The integrated circuit is an application-specific integrated circuit, ASIC.

3. The detector module according to claim 2, characterized in that: The ASIC extends on the edge of the X-ray detector substrate, so that a part of the ASIC is located outside the X-ray detector substrate to enable electrical and data transmission connections to the ASIC without having to route the electrical and data transmission connections to the ASIC on the X-ray detector substrate.

4. The detector module according to claim 2, characterized in that: Signals are routed from a single diode to the input of the ASIC.

5. The detector module according to claim 2, characterized in that: Power lines and data transmission lines are wire-bonded to power and data transmission pads on the ASIC outside the substrate, or a redistribution layer on the substrate is used to connect to power, data transfer pads and input signal pads and redistribute the input signals from the X-ray detector substrate to the ASIC.

6. The detector module according to claim 2, characterized in that: A heat conductor is connected to the ASIC for providing cooling.

7. The detector module according to claim 1, characterized in that: The anti-scatter foil is made of a heavy material.

8. The detector module according to claim 7, characterized in that: The heavy material is tungsten.

9. The detector module according to claim 1, characterized in that: The integrated circuit is an application specific integrated circuit, ASIC; the anti-scatter collimator is a tungsten foil; the ASIC is placed on an X-ray detector substrate below the tungsten foil so as to minimize a so-called dead zone in the detector, thus protecting the ASIC from direct radiation.

10. The detector module according to claim 1, wherein: For each X-ray detector substrate, it has a conical geometry, the X-ray detector substrate and the associated anti-scatter collimator are directed towards a radiation source, and the radiation source is provided by a spacer located at the X-ray detector substrate or at the anti-scatter collimator.

11. The detector module according to claim 1, wherein: Each X-ray detector substrate and the corresponding integrated circuit are formed as a sensor multi-chip module, MCM assembly; a plurality of sensor MCM assemblies are connected into the detector module.

12. The detector module according to claim 11, wherein: The detector module is subdivided into a plurality of detector blocks, where each detector block includes a plurality of sensor MCM assemblies.

13. The detector module according to claim 12, wherein: Each detector block includes means for demultiplexing instructions from the corresponding detector module into the detector block to reduce the number of connections between the detector block and the detector module.

14. The detector module according to claim 13, wherein: The instructions are control instructions directed to the sensor MCM assemblies.

15. The detector module according to claim 12, wherein: The detector module includes a plurality of data storage circuits and data processing circuits, and each detector block is managed by the data processing circuits.

16. The detector module according to claim 15, wherein: The detector module includes control and communication circuits for allocating control instructions to the sensor MCM assemblies and for controlling the reading of stored scan data from the data storage circuits.

17. The detector module according to claim 1, wherein: The X-ray detector substrate is a silicon detector substrate.

18. A modular X-ray detector (100) comprising a plurality of detector modules (1) according to any one of claims 1 to 17.

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