Reference voltage system for a radiation detector

Abstract

Reference voltage system (30) for a CT detector (21), comprising a reference voltage source (31), a plurality of sensor units (32), each comprising at least one sensor element and an evaluation unit in the form of an ASIC, and a supply voltage source (33), wherein an operating voltage (UB) for the reference voltage source (31) and a supply voltage (US) for the sensor units (32) can be applied with the aid of the supply voltage source (33), and wherein the reference voltage source (31) provides a reference voltage (UR) for the plurality of sensor units (32).

Description

[0001] The invention relates to a reference voltage system for a CT detector, a CT detector, a medical imaging modality and a method for its operation.

[0002] In the development of radiation detectors – for example, X-ray detectors for CT systems (computed tomography systems) – the goal is to continuously reduce manufacturing costs. The main cost (~80%) of a CT detector lies in the so-called sensor board. This typically includes the direct-converting or indirect-converting sensor material, possibly photodiodes, and the evaluation electronics (ASIC, "application-specific integrated circuit").

[0003] The evaluation electronics often include ASICs in the form of integrated analog-to-digital converters (ADCs), which require a clean, i.e., noise-free, supply voltage. This is necessary to ensure very good analog-to-digital conversion performance. The ADC's task is to convert the current supplied, for example, by the photodiode, into a digital data stream. In the photodiode, the current is generated by the UFC ceramic through the incident X-ray radiation and thus represents a measurement signal from the CT scan.

[0004] In CT sensors with integrated ASICs, the so-called reference voltage components are of particular importance. These components are highly precise, exhibit very low temperature drift, and provide a particularly low-noise and interference-free reference voltage for the CT sensors. Modern analog-to-digital converters have a resolution of 20 bits and more. Consequently, with a voltage range of 2.5 V, a single bit corresponds to a voltage of only 2.4 µV. This high-precision conversion performance underscores the importance of a reference voltage supply that is as noise-free and interference-free as possible.

[0005] From the publication DE 10 2014 213 047 A1, an X-ray detector with a planar detector array with several detector sensor modules arranged side by side is known, wherein each detector sensor module has several detector sensor elements that subdivide the detector sensor module into pixels, and a system for supplying the detector sensor modules with high voltage, wherein a high-voltage supply module is provided for each individual detector sensor module, supplying only this detector sensor module.

[0006] A detector device for a medical imaging system is known from German patent application DE 10 2016 207 904 A1. The detector device comprises a plurality of individual detectors and at least one detector control unit. The detector device is designed to be switchable to at least one power-saving mode in which at least some of the components of the individual detectors are deactivated and at the same time at least some of the components of the detector control unit are not deactivated.

[0007] Document WO 2016 / 194 286 A1 discloses a radiation imaging device with a plurality of sensor units as pixels, each comprising at least one comparator unit which compares a voltage signal with a reference voltage, wherein a reference voltage can be supplied to several pixels together.

[0008] The publication “Analog Devices: Data Sheet: ADR440 / ADR441 / ADR443 / ADR444 / ADR445. 2005-2018. 1-19” reveals a datasheet for reference voltage devices.

[0009] German patent application DE 10 2016 217 993 A1 discloses a device for spatially resolved measurement of photons comprising a plurality of photoelectric converters, a plurality of current measuring devices, and a third plurality of voltage conditioners, wherein a voltage conditioner is configured to convert a supply voltage down to an operating voltage of a current measuring device. The current measuring devices can be supplied with the operating voltage in groups by a single voltage conditioner.

[0010] German patent application DE 10 2016 221 209 A1 discloses an X-ray detector with a number of detector modules comprising an X-ray-sensitive layer, a readout electronics associated with the X-ray-sensitive layer comprising preferably an ASIC, and a first interface, wherein the first interface is configured for power transmission to the readout electronics, and wherein a plurality of detector modules can be connected via the first interfaces to a data processing module for providing a supply voltage for the operation of a respective detector module.

[0011] To ensure optimal conditions for a low-noise and interference-free reference voltage supply, each CT sensor in previously known CT detectors is assigned its own dedicated reference voltage module. This is intended to minimize interference, which increases with the size of the circuits being supplied. However, these standard reference voltage modules represent a significant portion of the manufacturing costs for a CT detector.

[0012] The object of the present invention is to provide a more cost-effective reference voltage supply for a CT detector.

[0013] This problem is solved according to the invention by a reference voltage system according to claim 1, a CT detector according to claim 8, a medical imaging modality according to claim 10, and a method for operating a medical imaging modality according to claim 11.

[0014] The reference voltage system for a CT detector mentioned at the beginning comprises only one reference voltage source, a plurality of sensor units, and a supply voltage source. The supply voltage source provides an operating voltage for the reference voltage source and a supply voltage for the sensor units. The reference voltage source provides a reference voltage for the plurality of sensor units.

[0015] In contrast to the prior art, a single reference voltage source supplies several sensor units, whereby an operating voltage for the reference voltage source and a supply voltage for the sensor units can be applied using the supply voltage source. As already described at the outset, for the purposes of the invention, a reference voltage source is understood to be a voltage source that outputs a precisely defined voltage to other electronic components connected to it with particularly low noise and essentially without interference. "Precisely defined" means that any deviations from the absolute value provided are very small.

[0016] A sensor unit comprises a sensor element, such as a direct-converting, optionally photon-counting or energy-resolving semiconductor sensor (e.g., Si, GaAs, CdTe, CdZnTe, HgI2, a-Se, etc.) or a combination of photodiode and scintillator, and an evaluation unit in the form of an ASIC. Furthermore, the sensor unit preferably includes an evaluation unit, which in particular comprises an integrating analog-to-digital converter, e.g., in the form of an ASIC.

[0017] In addition to the reference voltage source, the supply voltage source and the majority of sensor units, the reference voltage system can include further components, as will be explained in more detail later.

[0018] The invention thus departs from the previously common concept of assigning a reference voltage source to each sensor unit. According to the invention, a plurality of sensor units share a single reference voltage source. "Million" here refers to a number greater than 1, for example, 2, 4, 6, 8, 16, etc.

[0019] Accordingly, according to the invention, exactly one single reference voltage source is used to provide a reference voltage for a plurality of sensor units. That is, only one reference voltage source is assigned to several sensor units for the reference voltage supply.

[0020] Care must be taken to ensure that the influence of any coupled interference does not become too great and that the circuits are dimensioned accordingly. However, the reference voltage system according to the invention advantageously allows for considerable cost savings compared to the prior art.

[0021] The CT detector according to the invention mentioned at the outset has a number of reference voltage systems according to the invention.

[0022] When designing a CT detector according to the invention, depending on the application requirements, it is advantageous to weigh the sensitivity to interference against cost savings by considering the number of sensor units supplied per reference voltage source.

[0023] The medical imaging modality according to the invention mentioned at the outset comprises a CT detector according to the invention. In particular, it is a CT scanner (computed tomography scanner).

[0024] In the aforementioned method according to the invention for operating a medical imaging modality, the latter comprises a CT detector, which in turn includes a reference voltage system. The reference voltage system comprises a reference voltage source, a plurality of sensor units, and a supply voltage source. The method for operating the medical imaging modality comprises at least the steps described below. A supply voltage is applied to the reference voltage source using the supply voltage source. A further supply voltage is applied to the sensor unit using the supply voltage source. Additionally, a reference voltage is applied to the sensor unit using the reference voltage source.

[0025] The supply voltage source provides the reference voltage system with one or more operating voltages. It can, for example, be implemented as a connection to an external power supply and, if necessary, transform the external voltage to one or more suitable operating or supply voltages and rectify it.

[0026] Depending on the system design, the supply voltages for the reference voltage source and the sensor unit can be different or the same. Different supply voltages can be achieved, for example, by using different transformers.

[0027] Further particularly advantageous embodiments and developments of the invention result from the dependent claims and the following description, wherein the independent claims of a claim category may also be further developed analogously to the dependent claims of another claim category and their associated descriptive parts, and in particular individual features of different embodiments or variants may be combined to form new embodiments or variants.

[0028] As the number of sensor units per reference voltage source increases, so does the risk of picking up interference at the local level, for example, on a PCB (printed circuit board). This interference can then potentially couple onto the sensitive reference voltage line. This is because the larger the assembly, the greater the number of components used, such as DC-DC converters, which exhibit certain switching operations in relevant frequency ranges. This can lead to interference being coupled into the reference voltage system.

[0029] To avoid such interference, the reference voltage source preferably provides the reference voltage for a maximum of 8, and more preferably a maximum of 6, sensor units. Most preferably, the reference voltage source provides the reference voltage for exactly 4 sensor units. This dimensioning reduces or largely eliminates the aforementioned interference.

[0030] As described earlier, the reference voltage for the sensor units should be as low-noise as possible. Therefore, the reference voltage source preferably has a noise level lower than 10 µV. pp , particularly preferably less than 5 µV pp , especially preferably less than 2 µV pp Despite these high demands on the noise performance of the reference voltage source and the associated higher costs for the component, the described reference voltage system makes it possible to provide both a high-quality reference voltage supply and to achieve overall cost savings compared to the state of the art. This is because the cost of the reference voltage source is distributed across several sensor units.

[0031] Furthermore, the generated reference voltage should be as independent of temperature fluctuations as possible. Therefore, the reference voltage source preferably exhibits a temperature drift of less than 9 ppm / °C, particularly preferably less than 6 ppm / °C, and most preferably less than 3 ppm / °C. This allows the reference voltage system to advantageously operate over a relatively wide temperature range without significant fluctuations in the provided reference voltage.

[0032] The reference voltage source can, in principle, be any suitable electronic component, such as an ADR5420, MAX6143, LTC6655, or the like. Preferably, however, the reference voltage source is implemented as an ADR440. This component meets high requirements for both noise performance and temperature drift.

[0033] The reference voltage source and the sensor units are powered by a supply voltage source. As explained above, the voltages for the reference voltage source and the sensor units can have different values. They can also have different characteristics due to additional components. For example, the operating voltage for the sensor units can be provided as a regulated, noise-free supply voltage using an LDO (Linear Drop-Out) regulator.

[0034] Preferably, the connection between the reference voltage source and a sensor unit is currentless. Particularly preferably, the connections between a reference voltage source and all associated sensor units are each currentless.

[0035] This means the reference voltage source preferably has its own reference ground, through which only the supply current of the reference voltage source flows, and not the potentially pulsating supply current of the sensor units. The sensor units have their own sensor ground for this purpose. The reference voltage source is preferably decoupled from the sensor units by means of resistors. For this purpose, the reference voltage source is connected to the supply voltage via a first resistor and optionally to the supply ground via a second resistor. The reference voltage source is connected to the respective sensor unit via a third resistor. The resistors preferably have a high impedance compared to the connecting line. This allows unavoidable alternating voltages between the sensor ground and the supply ground to be kept away from the reference voltage.

[0036] Preferably, the reference voltage source and the sensor units are spatially separated. That is, the reference voltage source is located, for example, on a different printed circuit board (PCB) than the sensor units, with both PCBs preferably connected at a distance via plug connectors. This spatial separation makes it possible to shield the reference voltage source from the X-ray radiation incident on the sensor elements of the sensor units. This can be achieved, for example, by inserting a suitable material, such as lead, into the space between the two. This advantageously allows a particularly accurate reference voltage to be provided largely independently of the X-ray radiation.

[0037] In the radiation detector according to the invention, the reference voltage systems preferably extend over a number of sensor assemblies, which in turn comprise a number of sensor units. That is, several sensor units are combined as a module in a sensor assembly and can thus be advantageously easily replaced as a unit.

[0038] The invention is explained in more detail below with reference to the accompanying figures and exemplary embodiments. The same components are designated with identical reference numerals in the various figures. The figures are generally not to scale. They show: Fig. 1. A schematic block diagram of a state-of-the-art power supply, Fig. 2 a schematic block diagram of an embodiment of a reference voltage system according to the invention, Fig. 3 a rough schematic representation of an embodiment of a CT detector according to the invention and Fig. 4 a perspective view of an embodiment of a medical imaging modality according to the invention.

[0039] Fig. Figure 1 shows an example of a schematic block diagram of a power supply system for a radiation detector, as is commonly used in practice. An external voltage UE, for example 12 V, is stepped down to an operating voltage UB, for example 3.1 V, by means of a DC-DC converter. The operating voltage UB is applied in parallel to three reference voltage sources 31 and to an LDO regulator 34 (linear dropout). The LDO regulator 34 provides a regulated, noise-free supply voltage US, for example 2.5 V. Three sensor units 32 are connected in parallel to the noise-free supply voltage US. Each sensor unit 32 is connected to its own dedicated reference voltage source 31 and is thus supplied with a reference voltage UR. Therefore, a total of three reference voltage sources 31 are required to supply the three sensor units 32 with a reference voltage UR. The sensor units 32 comprise at least one sensor or...Detector element and an evaluation unit, for example an ASIC for reading the sensor elements (not shown here).

[0040] Reference voltage source 31 and are thus assigned to a reference voltage system 30.

[0041] In Fig. Figure 4 shows an exemplary and roughly schematic medical imaging system 20 according to the invention, here a computed tomography device 20 as a specific example. The computed tomography device 20 comprises a patient table 25 for positioning a patient 24 as the examination subject.

[0042] The patient table 25 is adjustable along a system axis 26 into the measurement field, allowing the patient 24 to be positioned within the measurement field. The computed tomography system 20 further comprises a gantry 22 with a source-radiation detector assembly 23, 21 rotatably mounted about the system axis 26. The source-radiation detector assembly 23, 21 includes an X-ray source 23 and an embodiment of a radiation detector 21 according to the invention, which are aligned opposite each other such that, during operation, X-rays emitted from the focus of the X-ray source 23 strike the radiation detector 21. The radiation detector 21 is structured into individual sensor modules 27, which are arranged modularly into several radiation detector rows. For each projection, the radiation detector 21 generates a set of projection data. This projection data is then further processed and combined to create a resulting image.

[0043] A computed tomography (CT) scanner 20 is known to be used for 3D image reconstruction. To acquire an image of an area of ​​interest (region of interest), projection data from a multitude of different projection directions are acquired as the source-radiation detector assembly 23, 21 rotates. In the case of spiral scanning, for example, the patient table 25 is simultaneously and continuously adjusted in the direction of the system axis 26 during rotation of the source-radiation detector assembly 23, 21. In this type of scanning, the X-ray source 23 and the radiation detector 21 thus move along a helical path around the patient 24. The exact structure and specific operation of such a CT scanner are known to those skilled in the art and are therefore not explained in detail here.

[0044] Finally, it should be noted once again that the devices and methods described in detail above are merely exemplary embodiments, which can be modified in various ways by a person skilled in the art without departing from the scope of the invention. Furthermore, the use of the indefinite articles "a" or "an" does not preclude the possibility that the features in question may be present multiple times. Likewise, the terms "system," "unit," and "device" do not preclude the possibility that the component in question consists of several interacting sub-components, which may also be spatially distributed.

Claims

[1] Reference voltage system (30) for a CT detector (21), comprising a reference voltage source (31), a plurality of sensor units (32), each comprising at least one sensor element and an evaluation unit in the form of an ASIC, and a supply voltage source (33), wherein an operating voltage (UB) for the reference voltage source (31) and a supply voltage (US) for the sensor units (32) can be applied by means of the supply voltage source (33), and wherein the reference voltage source (31) provides a reference voltage (UR) for the plurality of sensor units (32). [2] Reference voltage system (30) according to claim 1, wherein the reference voltage source (31) provides the reference voltage (UR) for a maximum of 8, preferably 4, sensor units (32). [3] Reference voltage system (30) according to one of the preceding claims, wherein the reference voltage source (31) has a noise level lower than 10 µV pp , preferably less than 5 µV pp, particularly preferably less than 2 µV pp , exhibits. [4] Reference voltage system (30) according to one of the preceding claims, wherein the reference voltage source (31) has a temperature drift of less than 9 ppm / °C, preferably less than 6 ppm / °C, particularly preferably less than 3 ppm / °C. [5] Reference voltage system (30) according to one of the preceding claims, wherein the reference voltage source (31) is designed as an ADR440. [6] Reference voltage system (30) according to one of the preceding claims, wherein a connection of the reference voltage source (31) to a sensor unit (32) is designed to be currentless. [7] Reference voltage system (30) according to one of the preceding claims, wherein the reference voltage source (31) and the sensor units (32) are spatially separated. [8] CT detector (21) with a number of reference voltage systems (30) according to one of the preceding claims. [9] CT detector (21) according to claim 8, wherein the reference voltage systems (30) each extend over a number of sensor assemblies (27). [10] Medical imaging modality (20), in particular CT device, with a CT detector (21) according to claim 8 or 9. [11] Method for operating a medical imaging modality (20) with a CT detector (21) comprising a reference voltage system (30) with a reference voltage source (31), a plurality of sensor units (32), each comprising at least one sensor element and an evaluation unit in the form of an ASIC, and a supply voltage source (33), comprising the following steps: - Applying an operating voltage (UB) to the reference voltage source (31) using the supply voltage source (33), - Applying a supply voltage (US) to the sensor unit (32) using the supply voltage source (33), - Applying a reference voltage (UR) to the sensor unit (32) using the reference voltage source (31).

Images