RADIATION DETECTOR AND IMAGING SYSTEM

The present invention relates to a radiation detector which can be used to detect electromagnetic radiation, in particular X-ray or gamma radiation. The invention furthermore relates to an imaging system, comprising such a radiation detector.

Imaging systems appertaining to medical technology are becoming increasingly important nowadays. Systems of this type are used to generate two- or three-dimensional image data of organs and structures of the human body, which can be used for example for diagnosing causes of illness, for carrying out operations and for preparing therapeutic measures. The image data can be generated on the basis of measurement signals obtained with the aid of a radiation detector.

This is the case for example in X-ray and computed tomography systems (CT). In systems of this type, the body or a body section of a patient to be examined is radiographed by means of X-ray radiation generated by a radiation source. The non-absorbed, transmitted portion of radiation is detected by a detector.

A further example is image generation with the aid of radionuclides, such as is used in positron emission tomography systems (PET) and single photon emission computer tomography systems (SPECT). In this case, the patient to be examined is injected with a radiopharmaceutical which generates gamma quanta either directly (SPECT) or indirectly (PET) through emission of positrons. The gamma radiation is detected by a corresponding radiation detector.

Detectors which can be used for the energy-resolved detection or “counting” of radiation quanta can operate according to different measurement principles. Radiation can be detected either directly, i.e. by direct conversion of the radiation energy into electrical energy, or indirectly. In the case of the last-mentioned variant, use is generally made of a so-called scintillator, which is excited in response to the action of radiation to be detected and reemits the excitation energy by emitting lower-energy electromagnetic radiation. Only the radiation emitted by the scintillator is converted into electrical measurement signals in this case. Detectors of planar construction (so-called “flat detectors”) which are used in the medical field and operate in accordance with these measurement principles are described for example in M. Spahn, “Flat detectors and their clinical applications”, Eur Radiol (2005), 15: 1934-1947.

The conversion of the radiation emerging from a scintillator into an electrical signal can be effected in various ways. Besides use of a photomultiplier provided with a photocathode in the form of an evacuated electron tube, one concept that is common at the present time consists in using a so-called silicon photomultiplier (“SiPM”). This involves a matrix arrangement of avalanche photodiodes (APD) embodied on a shared substrate, electrons being generated in said photodiodes as a result of incident photons, and said electrons being multiplied in an avalanche-like manner.

One disadvantage of silicon photomultipliers, however, is that only part of the total area available for irradiation can be utilized as sensitive or “active” area. The reason for this is that between the active or radiation-sensitive regions there are also insensitive regions, in which resistors and signal lines or wiring structures are arranged. A silicon photomultiplier therefore has a relatively small ratio of active area to (irradiated) total area, said ratio also being designated as “filling factor”. Further disadvantages include noise that occurs during operation, and a relatively high dark rate or dark count, that is to say that signal generation takes place even without irradiation.

A detector comprising a scintillator and a silicon photomultiplier is usually embodied in such a way that the silicon photomultiplier is opposite an end face or rear side of the scintillator. An opposite end face or front side of the scintillator faces the radiation to be detected. As a result, the silicon photomultiplier can detect only that portion of the radiation converted in the scintillator which emerges at the rear side thereof. Proceeding from the respective excitation or interaction location in the scintillator, however, the scintillation radiation is emitted not only in the direction of the rear side, but also in other directions. Furthermore, the radiation is subject to loss processes such as reflection, absorption and scattering. Particularly in the case of scintillators having a high aspect ratio, i.e. a high ratio of height to width, as may be the case for example in a PET system, the losses are therefore relatively high. In the case of an aspect ratio of greater than 7:1, the radiation emerging from a scintillator may make up a proportion of merely 40-60% of the total radiation generated. Although a higher intensity of the incident radiation can be provided in order to compensate for the losses, as a result a patient is also exposed to an increased radiation dose.

It is furthermore disadvantageous that an interaction location of incident radiation in a scintillator cannot be detected or can be detected only with very great difficulty on the basis of the radiation emerging at the rear side of the scintillator. Moreover, it is not possible to obtain information about the height or depth of an interaction in the scintillator. Such disadvantages therefore restrict the resolution of an imaging system provided with such a detector construction.

For image intensification and for electron multiplication, it is furthermore known to use so-called microchannel plates (MCP) having a multiplicity of channels. During operation, an electrical voltage present along the channels is generated, whereby entering electrons can be accelerated within the channels and multiplied by impacts with the channel walls. Use of a microchannel plate in connection with an image intensifier is described in US 2009/0256063 A1, for example.

The object of the present invention is to specify a solution for improved radiation detection in the medical field.

This object is achieved by means of a radiation detector as claimed in claim 1 and by means of an imaging system as claimed in claim 15. Further advantageous embodiments of the invention are specified in the dependent claims.

The invention proposes a radiation detector comprising a scintillator for generating electromagnetic radiation in response to the action of incident radiation. The scintillator has two mutually opposite end faces and a lateral wall between the end faces. The radiation detection furthermore comprises a conversion device arranged on the lateral wall of the scintillator and having a plurality of channels. In this case, each channel has a photocathode section for generating electrons in response to the action of the electromagnetic radiation generated by the scintillator, said electrons being multipliable as a result of impact processes in the channels. A detection device for detecting electrons multiplied in the channels of the conversion device is furthermore provided.

During the operation of the radiation detector, with one of the end faces the scintillator can face the radiation to be detected (in particular X-ray or gamma radiation). The electromagnetic radiation (for example visible or ultraviolet light) generated by the incident radiation in the scintillator and passing to the lateral wall thereof can be converted into electrons directly by the conversion device arranged at this location, which conversion device can be regarded as a combination of a microchannel plate and a photocathode. In this case, the radiation emitted by the scintillator is firstly taken up or absorbed by the photocathode sections of the channels, as a result of which electrons are liberated, which can be multiplied further in the channels (“electron path”). The conversion device can thus convert the scintillation radiation rapidly and directly into a multiplicity of electrons which can be detected by the detection device. The arrangement of the conversion device on the lateral wall of the scintillator affords the possibility of utilizing a large part of the radiation converted in the scintillator for generating electrons. This holds true particularly in the case of one possible configuration of the scintillator having a high aspect ratio, as a result of which the lateral wall can also have a relatively large surface area in comparison with the end faces. On account of these properties, the radiation detector can be distinguished by a high temporal resolution and high efficiency.

It is furthermore advantageous that the radiation detector can have (significantly) less noise and a lower dark rate compared with the conventional detector comprising a silicon photomultiplier. This can be attributed to the fact that without radiation of the scintillator no electrons are generated by the photocathode sections and, consequently, (substantially) no electron multiplication takes place in the channels of the conversion device. Moreover, the channels of the conversion device can be arranged at a small distance from one another or alongside one another on the lateral wall of the scintillator, as a result of which a high filling factor (ratio of active area to irradiated total area) can be present, which can be (significantly) higher than in the case of a conventional silicon photomultiplier. This likewise fosters a high efficiency of the radiation detector.

In one preferred embodiment, the detection device has an electrode for trapping electrons, said electrode being arranged at one end of the channels. Furthermore, a counterelectrode is arranged at an opposite end of the channels in order to bring about a movement of electrons to the electrode of the detection device. As a result, the electrons generated by the photocathode sections can be reliably moved or accelerated in the direction of the electrode. Moreover, the electrons can collide with the channel walls during the movement, as a result of which a multiplicity of (further) electrons can be liberated.

In a further preferred embodiment, the lateral wall of the scintillator is embodied in a planar fashion. Furthermore, the conversion device is embodied in the form of a plate-shaped structure on the lateral wall of the scintillator. This affords the possibility of a space-saving configuration of the conversion device, which can furthermore be realized in a relatively simple manner. In particular, the conversion device (or part thereof) can arise from a structured substrate which can be arranged on or connected to the planar lateral wall of the scintillator.

In one preferred embodiment constituting an alternative to this, the lateral wall of the scintillator has depressions through which the channels of the conversion device are formed. Such a configuration can likewise be distinguished by a space-saving and simple construction. The channels embodied in the form of depressions can be closed in a suitable manner on the lateral wall of the scintillator, for example with the aid of a substrate or carrier element arranged on the lateral wall.

In a further preferred embodiment, which can be realized in a simple and cost-effective manner, the photocathode sections of the channels of the conversion device are embodied in the form of a continuous photocathode. In this case, the photocathode is preferably arranged on a carrier element.

In a further preferred embodiment, the lateral wall of the scintillator is provided with a layer transmissive to the electromagnetic radiation generated by the scintillator. Such a layer, which can serve as an entrance window for the channels of the conversion device, can minimize or suppress reflection of the radiation converted by the scintillator at the lateral wall. In this way, a high efficiency of the radiation detector can be fostered further.

This likewise applies to one further preferred embodiment, according to which the channels of the conversion device have a wall coating designed to liberate a plurality of electrons per impact process of an electron. In particular, a material having high secondary electron emission is used for the wall coating.

The channels of the conversion device preferably run parallel to a longitudinal axis of the scintillator, said longitudinal axis extending between the end faces. In this configuration, the detection device can be arranged in the region of an end face of the scintillator, as a result of which a relatively compact detector construction is possible.

In a further preferred embodiment, the scintillator is embodied in a parallelepipedal fashion and has four lateral walls between the end faces. A conversion device having a plurality of channels is arranged on each of the four lateral walls.

As a result, a significant part of the electromagnetic radiation generated in the scintillator can be converted into electrons, which is furthermore advantageous for a high efficiency of the radiation detector.

In a further preferred embodiment, the detection device is designed for separately detecting electrons generated and multiplied in channels of different conversion devices or in channels of different subsections of a conversion device. This affords the possibility of accurately detecting the lateral location of an interaction of a radiation quantum interacting with the scintillator. In this case, the detection device can have different electrode regions or segments for separately trapping electrons.

In a further preferred embodiment, the radiation detector is designed to bring about a movement of electrons in channels of different conversion devices or in channels of different subsections of a conversion device in different directions. This can be realized with corresponding electrode arrangements. On the basis of this or as a result of (separate) detection of the electrons accelerated in different directions, the possibility is afforded of accurately detecting the height or depth of an interaction in the scintillator.

In a further preferred embodiment, the radiation detector is additionally designed to convert part of the electromagnetic radiation generated in the scintillator and emerging at an end face into electrons and to detect the electrons. For this purpose, the radiation detector can comprise, for example, a further photocathode section for generating electrons in response to the action of the electromagnetic radiation generated by the scintillator in the region of the end face of the scintillator. The electrons emitted here can be multiplied with the aid of a (conventional) microchannel plate, and subsequently be detected by the detection device. Such a configuration can likewise be advantageous for a high efficiency of the radiation detector.

In a further preferred embodiment, the radiation detector comprises two scintillators arranged alongside one another. In this case, provision is made of conversion devices arranged in an interspace between the scintillators and on opposite lateral walls of the scintillators and assigned to the scintillators and having a plurality of channels. The radiation detector further comprises a detection device for detecting electrons, said detection device being assigned to the conversion devices. In the case of such a modular construction of the radiation detector, which can also be realized with more than two scintillators arranged alongside one another, it is possible to make use of the fact that the conversion devices can be configured in a space-saving manner, as a result of which the interspace between the scintillators can also be kept as small as possible. A high filling factor and hence efficiency can be obtained as a result.

The invention furthermore proposes an imaging system which comprises a radiation detector in accordance with one of the embodiments described above, and in which, therefore, the advantages described above can likewise be manifested. Such an imaging system can be, for example, an X-ray or computed tomography system or else a positron emission tomography or single photon emission computed tomography system. With regard to such imaging systems, provision can be made for the above-described detector construction or one of the above-described embodiments to constitute in each case an individual detector element or a “pixel” of an associated detector, and for a multiplicity of such detector elements or “pixels” to be arranged alongside one another in particular in a planar fashion and/or in a circular or partly circular fashion.

The above-described properties, features and advantages of this invention and the way in which they are achieved will become clearer and more clearly understood in association with the following description of exemplary embodiments which are explained in greater detail in association with the drawings, in which:

FIG. 1 shows a schematic illustration of an X-ray system;

FIG. 2 shows a schematic perspective illustration of component parts of a detector element, comprising a scintillator and a conversion device for converting scintillation radiation into electrons, said conversion device being arranged on a lateral wall of the scintillator;

FIG. 3 shows a schematic plan view illustration of an excerpt from a plate-shaped conversion device arranged on a scintillator;

FIG. 4 shows a schematic perspective illustration of the conversion device from FIG. 3;

FIG. 5 shows a schematic plan view illustration of an excerpt from a further plate-shaped conversion device arranged on a scintillator;

FIG. 6 shows a schematic perspective illustration of a detector element comprising a plurality of conversion devices, which is designed to detect segment by segment electrons generated in the different conversion devices;

FIG. 7 shows a schematic perspective illustration of a further detector element comprising a plurality of conversion devices, which is designed to move electrons generated in the different conversion devices in different directions;

FIG. 8 shows a schematic plan view illustration of an excerpt from two scintillators arranged alongside one another and conversion devices which are assigned to the scintillators and which are arranged in an interspace between the scintillators;

FIG. 9 shows a schematic perspective illustration of a further detector element constructed in a manner corresponding to FIG. 8;

FIGS. 10 to 13 show a schematic illustration of a production of the construction comprising two scintillators and conversion devices assigned to the scintillators, as shown in FIG. 8;

FIG. 14 shows a schematic plan view illustration of an excerpt from two scintillators arranged alongside one another and conversion devices which are assigned to the scintillators and the channels of which are embodied in the form of depressions in the scintillators;

FIG. 15 shows a schematic perspective illustration of the two scintillators from FIG. 14;

FIG. 16 shows a schematic perspective illustration of a further detector element constructed in a manner corresponding to FIG. 15; and

FIG. 17 shows a schematic lateral illustration of a further detector element, which is designed additionally to convert a portion of scintillation radiation that emerges at an end face of a scintillator into electrons.

Embodiments of a detector or detector element which can be used to detect electromagnetic radiation, in particular high-energy radiation such as X-ray or gamma radiation, are described with reference to the following figures. In order to produce the embodiments described, method processes known from the field of semiconductor and detector technology can be carried out and customary materials can be used, and so they will be discussed only in part.

The detector concept described here is provided for use in association with imaging systems appertaining to medical technology. In systems of this type, two- or three-dimensional image data of organs and structures of the human body are generated on the basis of measurement signals obtained with the aid of a corresponding radiation detector.

For exemplary elucidation, FIG. 1 illustrates an X-ray system 110 which can be used for diagnostic and interventional imaging. The X-ray system 110 comprises a radiation source 111 for emitting X-ray radiation (“X-ray emitter”) and an associated detector 100 of planar construction (“flat detector”) for detecting the radiation. Radiation source 111 and detector 100 are arranged opposite one another at the ends of a C-shaped holding device 112. On account of this configuration, this arrangement is also designated as “C-arc” or “C-arm”.

A patient to be examined is situated on a patient supporting couch 117 and in this case is arranged between radiation source 111 and detector 100. During the operation of the X-ray system 110, the body or a body section of the patient is radiographed with the X-ray radiation generated by the radiation source 111, and the non-absorbed, transmitted portion of radiation is detected by means of the detector 100.

The holding device 112 is furthermore fixed to a robot 113 provided with a plurality of axes and/or articulations, with the aid of which robot the radiation source 111 and the detector 100 can be brought to a desired position in relation to the patient. For controlling the X-ray system 110 and for processing and/or evaluating measurement signals of the detector 100, in particular for generating the desired image data, the X-ray system 110 furthermore comprises a control and/or evaluation device 114. The latter is connected to a corresponding display device or a display, as is indicated in FIG. 1.

Alongside the X-ray system 110 from FIG. 1, the detector concept described below can also be used in association with other imaging systems (not illustrated). By way of example, systems comprising a gantry, such as a computed tomography system (CT), for example, are appropriate. Such a system can comprise an annular or circular-cylindrical detector and a rotatable X-ray source. Further exemplary applications with a gantry include positron emission tomography systems (PET) and single photon emission computed tomography systems (SPECT). In this case, the patient to be examined is injected with a radiopharmaceutical which generates gamma quanta either directly (SPECT) or indirectly (PET) through emission of positrons. Said quanta can be detected likewise by an annular or circular-cylindrical detector.

FIG. 2 shows a schematic perspective illustration of a basic construction of a detector element 101 which can be used for detecting incident high-energy radiation. The embodiments of detector elements described further below with reference to the other figures are constructed on the basis of the detector principle shown here, and so the aspects described below can also apply to these embodiments. Furthermore, it is pointed out that a radiation detector of an imaging system, for example the detector 100 of the system 110 from FIG. 1, can comprise a multiplicity of detector elements constructed in this way, wherein said detector elements can be arranged alongside one another in the form of “pixels” in a matrix-like manner. In this case, in particular, planar, but also annular or partly annular arrangements can be present. The image data respectively desired can be generated on the basis of the measurement signals generated by the individual pixels or detector elements of a detector.

As is illustrated in FIG. 2, the detector element 101 has a scintillator 120, which serves to convert the high-energy radiation to be detected into a low(er)-energy radiation. The scintillator 120 is embodied in a parallelepipedal fashion and has two mutually opposite end faces 121, 122 and four lateral walls 123 between the two end faces 121, 122, said lateral walls adjoining one another at a right angle. The end face 122 directed toward the top in FIG. 2 is also designated hereinafter as “front side” and the end face 121 directed toward the bottom as “rear side” of the scintillator 120. Front and rear sides 122, 121 are connected to one another via the lateral walls 123 at the periphery or edge.

As is furthermore indicated in FIG. 2, the scintillator 120 has a high aspect ratio, i.e. a high ratio of height (distance between the end faces 121, 122) to width (lateral dimension or distance between two mutually opposite lateral walls 123), which is greater or significantly greater than one. In this way, it is possible to obtain a high absorption of the high-energy radiation to be detected, which is indicated on the basis of a radiation quantum 200 in FIG. 2, in the scintillator 120. In this connection it is pointed out that the components illustrated in FIG. 2, but also in the other figures, and their dimensions may be illustrated in a manner not true to scale. By way of example, it is possible for the scintillator 120 to have a larger height or a larger aspect ratio.

During the operation of the detector element 101, the front side 122 of the scintillator 120 faces the radiation to be detected, such that the radiation can be incident or coupled into the scintillator 120 via the front side 122. A radiation quantum 200 (in particular X-ray quantum or gamma quantum) of the incident radiation can bring about an excitation locally upon passing through the scintillator 120. The excitation energy deposited or absorbed during this process is reemitted by the scintillator 120 in the form of lower-energy radiation quanta or photons 202. In this case, the number of emitted photons 202 may be proportional to the original energy of the radiation quantum 200 that interacts with the scintillator material. The scintillation mechanism which takes place in this case will not be discussed in more specific detail. The scintillation radiation generated by the scintillator 120 may be visible or ultraviolet light, in particular.

Alongside radiation emission in the direction of the end faces 121, 122 of the scintillator 120, a large part of the scintillation radiation or photons 202 generated in the scintillator 120 is emitted in the direction of the lateral walls 123. This is the case, in particular, if the scintillator 120, as in the present case, has a high aspect ratio, and, consequently, the lateral walls 123 have a relatively large surface area in comparison with the end faces 121, 122 of the scintillator 120. The detector element 101, as illustrated in FIG. 2, is designed to utilize that portion of the scintillation radiation which passes to a lateral wall 123 for the purpose of detecting radiation. The construction shown here and described below can be provided, in particular, on all of the four lateral walls 123, as a result of which a high detection efficiency or a high efficiency can be achieved.

For detecting the scintillation radiation, the detector element 101 comprises a conversion device 160 arranged on the relevant lateral wall 123. With the aid of the conversion device 160, photons 202 emitted in the direction of the lateral wall 123 and emerging from the scintillator 120 at the lateral wall 123 can be converted into electrons 204, and the electrons 204 can be multiplied further. Preferably, the conversion device 160 has substantially the same external dimensions as the lateral wall 123, such that the lateral wall 123 can be substantially completely “covered” by the conversion device 160.

The conversion device 160 comprises a channel structure 161, 162, 163 having a plurality of microscopically fine channels 165, which can also be designated as “microchannel”, “cell” or “microcell”. Various configurations are possible for the conversion device 160 or the channel structure 161, 162, 163 thereof. By way of example, a conversion device 160 embodied in the form of a plate-shaped structure can be involved, in which the associated channel structure 161, 162 can comprise a structured substrate arranged on the lateral wall 123, as is described in even greater detail further below in association with FIGS. 3 and 5. In an alternative configuration, the conversion device 160 can comprise a channel structure 163 in which the channels 165 are formed by indentations or depressions embodied in the lateral wall 123 of the scintillator 120, which will be described in even greater detail in particular with reference to FIG. 14.

The channels 165, which, in a departure from the spaced-apart illustration in FIG. 2, are arranged in a plane alongside one another in the region of the lateral wall 123 of the scintillator 120 and extend along the lateral wall 123 or along a plane predefined by the lateral wall 123, preferably run—as indicated in FIG. 2—parallel to a longitudinal axis of the scintillator 120, said longitudinal axis extending between the end faces 121, 122. Each channel 165 of a channel arrangement 161, 162, 163 is furthermore provided with an internal photocathode section, illustrated on the basis of a continuous photocathode 130 in FIG. 2, such that photons 202 emerging at the lateral wall 123 can be converted into electrons 204 (photoelectrons) using the photoelectric effect in the channels 165. An electron 204 can be liberated for each photon 202 which impinges on the photocathode 130 or on a photocathode section and is absorbed here. In this case, in a departure from the spaced-apart illustration in FIG. 2, the photocathode 130 is situated in the region of or within the channels 165. Furthermore, it is pointed out that instead of the provision of the continuous photocathode 130 illustrated in FIG. 2, a configuration comprising separate internal photocathode sections is also possible, which sections can be arranged separately from one another on or in each channel 165.

The electrons 204 emitted by the photocathode 130 or the photocathode sections can furthermore be multiplied by impact processes in the channels 165 of the respective channel structure 161, 162, 163, and can subsequently be detected. For this purpose, the detector element 101 comprises an electrode arrangement comprising an electrode 150 and a counterelectrode 140 corresponding thereto, which, in a departure from the spaced-apart illustration in FIG. 2, are arranged at opposite ends of the conversion device 160 or the channel structure 161, 162, 163 thereof. An electrical voltage (acceleration voltage) is applied to the two electrodes 140, 150, as a result of which an electric field present along the channels 165 is generated, which can be used to bring about a movement of the electrons 204 reliably in the direction of the electrode 150. In this case, the electrode 140 constitutes a cathode, and the other electrode 150 constitutes an anode. For applying the voltage, which can be in the high-voltage range, in particular, the detector element 101 comprises a suitable connection structure (not illustrated).

The electrons 204 (primary electrons) emitted by the photocathode 130 or the photocathode sections in the channels 165 can impact the (inner) walls of the associated channels 165 multiply during the movement or acceleration in the direction of the electrode 150 brought about by the electric field, and upon each impact can eject or liberate further electrons 204 (secondary electrons), which for their part can likewise be accelerated within the channels 165 and liberate further electrons 204 as a result of impacts with the channel walls. This process continues over the length of the channels 165 and is therefore associated with an avalanche- or cascade-like increase in electrons 204. For such functioning, the channels 165 have small lateral dimensions, for example in the micrometers range.

The electrons 204 multiplied in accordance with this process in the channels 165 can pass to the electrode 150, which is simultaneously used as a trapping or readout electrode (“readout pad”) for trapping or collecting the (multiplied) electrons 204. The electrode 150, as indicated in FIG. 2, is part of a detection device 170 provided for detecting electrons 204, which detection device can additionally comprise a carrier element or a substrate 171, on which the electrode 150 is arranged. The detection device 170 can be designed to generate, on the basis of the electrons 204 trapped by the electrode 150, a corresponding electrical output signal (for example voltage drop across a resistor). Such an output signal is dependent on the number or total charge of the collected electrons 204, and thus on the excitation energy originally deposited in the scintillator 120.

The detection device 170, as indicated in FIG. 2 is preferably arranged in the region of the rear side 121 of the scintillator 120, as a result of which a compact detector construction is possible. In this case, in a departure from the illustration in FIG. 2, the carrier substrate 171 can also extend below the scintillator 120, such that the carrier substrate 171 can furthermore be utilized for bearing or supporting the scintillator 120 (cf. the exemplary embodiment in FIG. 9).

The arrangement of the conversion device 160 on the lateral wall 123 of the scintillator 120 affords the possibility of obtaining fast access to a large number of scintillation photons 202 by an extremely short route. In this case, the first “contact” of a photon 202 with the lateral wall 123 or a photocathode section 130 arranged in the region of the lateral wall 123 can lead to the generation of an electron 204 which can be multiplied further directly in the conversion device 160 or in a channel 165 thereof. In one preferred configuration comprising conversion devices 160 on all four lateral walls 123 (cf. the exemplary embodiment in FIG. 6), what can furthermore be achieved is that the radiation is (largely) prevented from being “reflected back and forth” in the scintillator 120, this being associated with corresponding loss processes, and a significant part of the radiation is therefore converted into electrons 204. In this way, the detector element 101 (and a comparably constructed detector element) can have a high efficiency and a high temporal resolution. These advantages correspondingly also hold true for a detector constructed from a plurality of such detector elements, and thus for an associated imaging system. This affords the possibility, in particular, of exposing a patient to be examined only to a low radiation dose.

The use of the channel structure 161, 162, 163 used for electron multiplication furthermore makes it possible for the detector element 101 (and a comparably constructed detector element) to have a low noise proportion and a low dark rate. This is owing to the fact that the production of electron avalanches in the channels 165 and thus the generation of a corresponding signal in the detection device 170 take place (substantially) only if the scintillator 120 emits radiation and the photocathode 130 generates photoelectrons 204 in response to the action of the scintillation radiation. Furthermore, the channels 165 can be at relatively small distances from one another, as a result of which a high filling factor (ratio of active area to irradiated total area) can be present, which is likewise advantageous for the detection efficiency.

The above-described functioning of the detector element 101 requires the presence of an evacuated atmosphere or a vacuum (at least) in that region in which free electrons 204 are present, i.e. starting from generation with the aid of the photocathode sections 130 through to detection with the aid of the detection device 170. For this purpose, provision can be made, for example, for each channel 165 of the conversion device 160 to be individually closed or sealed, and therefore to be under vacuum. At the opposite ends of the channels 165, sealing can be realized in particular with the aid of the two electrodes 140, 150. Alternatively, “global” sealing of all channels 165 of the conversion device 160 together can also be provided. For this purpose, the detector element 101 can have, for example, a corresponding housing (cf. the exemplary embodiment in FIG. 9 with the housing 190).

The conversion device 160 arranged on the lateral wall 123 of the scintillator 120, which conversion device can be regarded as a combination of a planar or two-dimensional microchannel plate having channels 165 arranged “on a line” or in a plane and a photocathode 130, can, as has already been indicated above, be constructed in various ways.

One possible embodiment, illustrated in the schematic plan view illustration in FIG. 3, is a plate-shaped conversion device 160 having a channel structure 161 formed from a structured substrate. In the case of such a configuration, the lateral wall 123 of the scintillator 120 on which the conversion device 160 or the channel structure 161 thereof is arranged is furthermore embodied in a planar fashion. Only an individual channel 165 of the channel structure 161 is illustrated in FIG. 3. However, the construction shown here applies to all channels 165 of the channel structure 161, and is thus provided multiply alongside one another on the lateral wall 123 of the scintillator 120 (see FIG. 4).

As is illustrated in FIG. 3, the channel 165 has a rectangular geometry in plan view. The channel 165, the longitudinal axis of which runs perpendicularly to the plane of the drawing in FIG. 3, comprises, on two mutually opposite sides, in each case a cell or channel wall 166 present in the form of a web. The channel walls 166, which can arise as a result of structuring or production of trenches in a substrate 168 (see FIG. 10), are connected at one end to the lateral wall 123 of the scintillator 120 or to a layer 180 optionally provided on the lateral wall 123.

The layer 180 constitutes an optical input or entrance window for the channel 165, via which window scintillation photons 202 emitted in the direction of the lateral wall 123 of the scintillator 120 can be coupled into the channel 165, i.e. into an (evacuated) interior enclosed by the channel 165. For this purpose, the layer 180 comprises a corresponding material which is transmissive to the scintillation radiation generated by the scintillator 120. The layer 180 can furthermore serve as an antireflection layer in order to minimize or suppress reflection of the scintillation radiation at the lateral wall 123 and, consequently, foster the detection efficiency further. The lateral wall 123 of the scintillator 120 can be substantially completely covered by the layer 180, which can thus serve as entrance window and antireflection layer for all channels 165 of the associated channel structure 161. Furthermore, the layer 180 can provide, if appropriate, for vacuum-tight closure of the channels 165 in the region of the lateral wall 123 of the scintillator 120.

At an opposite end with respect thereto, the channel walls 166 of the channel 165 shown in FIG. 3 are connected to a section 186 which can extend along all channels 165 of the channel structure 161. The section 186 can be embodied, in particular, in the form of a separate substrate or carrier element, which can be connected to the channels walls 166 or the associated structured initial substrate 168 from which the channel walls 166 can arise. Vacuum-tight closure of the channels 165 can likewise be effected by means of the section 186.

As is furthermore illustrated in FIG. 3, a section 131 of a photocathode 130 is arranged on that side of the carrier section 186 which faces the enclosed interior of the channel 165. This involves a reflectively operating, so-called reflection photocathode, which emits photoelectrons 204 from that side on which the radiation coming from the scintillator 120 also impinges. With regard to such reflective functioning, the photocathode section 131 can be embodied in a solid fashion and with a relatively large thickness or layer thickness. This leads to a high reliability and efficiency in the conversion of the radiation emitted by the scintillator 120 into photoelectrons 204.

A configuration in the form of separate photocathode sections 131 assigned only to individual channels 165 on the section 186 is indicated in FIG. 3. Preferably, however, all photocathode sections 131 of the channels 165 are present in the form of a continuous (reflection) photocathode 130 arranged on the section 186 (cf. the exemplary embodiment in FIG. 8), as a result of which simple and cost-effective production is made possible. In this case, the channel walls 166 of the channels 165 can be connected to the carrier section 186 via the photocathode 130.

FIG. 3 furthermore illustrates that the channel 165, at the interior enclosed by the channel 165, is preferably provided with an additional wall coating 181. The wall coating 181, which can be arranged both on the web-shaped channel walls 166 and on the layer 180, serves to enable a multiplicity of electrons 204 to be liberated per impact process of an electron 204, as a result of which the detection efficiency can be fostered further. For this purpose, the wall coating 181 comprises, in particular, a material having high secondary electron emission.

FIG. 3 furthermore illustrates the process of the generation and multiplication of electrons 204 taking place in the illustrated channel 165 of the channel structure 161. The scintillation photons 202 emitted by the scintillator 120 to the lateral wall 123 can penetrate through the layer 180 and the region of the wall coating 181 arranged thereon, enter into the interior of the channel 165, pass further to the reflective photocathode section 131 and be absorbed by the latter. On the basis of this, the photocathode section 131 can emit electrons 204. In this case, as is shown in the schematic perspective illustration in FIG. 4, the electrons 204 can be accelerated in the direction of the electrode 150 with the aid of the two electrodes 140, 150. FIG. 4 illustrates a view proceeding from the scintillator 120, wherein the scintillator 120 and the layer 180 are omitted. The small lateral dimensions of the channel 165 have the effect that the electrons 204 can impact the wall or the wall coating 181 provided here multiply during this movement. Upon each impact, further electrons 204 can be released or ejected, which for their part can likewise be accelerated within the channel 165 and liberate further electrons 204 as a result of impacts with the wall coating 181. The electrons 204 multiplied in this way are trapped at the end of the channel 165 by the electrode 150 arranged at this location.

FIG. 5 shows a schematic plan view illustration of a further embodiment of a plate-shaped conversion device 160 having a channel structure 162, which can be embodied in a manner similar to the channel structure 161 described above, and likewise from a structured substrate. In this configuration, too, the lateral wall 123 of the scintillator 120 on which the conversion device 160 or the channel structure 162 thereof is arranged is embodied in a planar fashion. Only an individual channel 165 of the channel structure 162 is illustrated in FIG. 5. However, this construction applies to all channels 165 of the channel structure 162, and is therefore provided multiply alongside one another on the lateral wall 123 of the scintillator 120.

As is illustrated in FIG. 5, the channel 165 once again has a rectangular geometry in plan view. The channel 165, the longitudinal axis of which runs perpendicularly to the plane of the drawing in FIG. 5, comprises two mutually opposite channel walls 166. The channel walls 166 are connected to one another at one end by means of a further channel wall 167. With regard to the entire channel structure 162, the channel wall 167 can extend along all channels 165, and, therefore, all channel walls 166 of the individual channels 165 in accordance with the construction shown in FIG. 5 can be connected to the channel wall 167. In this case, there is the possibility of producing the arrangement comprising the channel walls 166, 167 by producing trenches in a substrate, with the removal of substrate regions between the channel walls 166, 167.

At an opposite end relative to the channel wall 167, the channel walls 166 are connected to the lateral wall 123 of the scintillator 122 or to a layer 180 once again optionally provided on the lateral wall 123. The layer 180 can again serve as an entrance window for the channel 165 or the channels 165 of the channel structure 162, and as an antireflection layer, and, if appropriate, provide for vacuum-tight closure of the channels 165 in the region of the lateral wall 123. For further details concerning the layer 180, reference is made to the above explanations concerning FIG. 3.

As is furthermore illustrated in FIG. 5, a section 132 of a photocathode 130 is arranged on that side of the layer 180 which faces the enclosed interior of the channel 165. This involves a semitransparent photocathode or transmission photocathode which operates transmissively. In this case, the photocathode section 132 is irradiated at the side facing the scintillator 120, and electrons 204 are emitted at the opposite side of the photocathode section 132 relative thereto into the interior enclosed by the channel 165.

A configuration in the form of separate photocathode sections 132 assigned only to individual channels 165 on the layer 180 is indicated in FIG. 5 as well. Alternatively, it is possible for all photocathode sections 132 of the channels 165 to be present in the form of a continuous (semitransparent) photocathode 130 arranged on the layer 180, as a result of which simple and cost-effective production is made possible. In this case, the channel walls 166 of the channels 165 can be connected to the layer 180 via the photocathode 130.

As is furthermore shown in FIG. 5, in the case of the channel structure 162, too, the provision of an additional wall coating 181 in the interior enclosed by the channel 165 can be considered, which additional wall coating can be arranged both on the channel walls 166 and on the channel wall 167. It once again serves to enable a multiplicity of electrons 204 to be liberated per impact process of an electron 204.

FIG. 5 furthermore illustrates the process of the generation and multiplication of electrons 204 taking place in the illustrated channel 165 of the channel structure 162. The scintillation photons 202 emitted by the scintillator 120 to the lateral wall 123 can penetrate through the layer 180, and can be absorbed by the photocathode section 132 arranged here. On the basis of this, the photocathode section 132 can emit electrons 204 into the interior of the channel 165, which are accelerated in the direction of the electrode 150 with the aid of the electrodes 140, 150 (see FIG. 1), which are once again arranged at the ends of the channel structure 162. On account of the small lateral dimensions of the channel 165, the electrons 204 can impact the wall, or the wall coating 181 provided here, multiply during this movement. Upon each impact, further electrons 204 can be liberated, which for their part are likewise accelerated within the channel 165 and contribute to the electron multiplication as a result of impacts. The electrons 204 multiplied in this way are trapped at the end of the channel 165 by the electrode 150 arranged at this location.

Materials known from semiconductor and detector technology can be used for the detector components of the detector elements described here (and possibly modifications thereof). The use of an inorganic material or of a crystal is considered for the scintillator 120. Preferably, this involves a “fast” scintillator 120, in which the scintillation mechanism, i.e. the conversion of the incident high-energy radiation into the lower-energy scintillation radiation, takes place in a short time duration. One material considered for this purpose is CsF or LSO, for example. With regard to a possible size of the scintillator 120, consideration is given, for example, to lateral dimensions or a width in the range of a few 100 μm to a few mm, and a height in the range of a few mm to a few 10 mm. In this case, the scintillator 120 has an aspect ratio of (significantly) greater than one, which can be greater than 7:1, for example, with regard to PET applications.

Materials such as, for example, CsI, CsTe, Cs3Sb, diamond and GaN are considered for the photocathode 130 or the photocathode sections 131, 132. In this case, the photocathode material used is coordinated with the material of the scintillator 120 in such a way that the scintillation radiation coming from the scintillator 120 can be converted into free electrons 204 in the photocathode 130 or the sections 130, 131. The photocathode 130, as has already been indicated above, can furthermore be embodied in the form of a continuous photocathode 130 or layer for all channels 165 of the conversion device 160, as a result of which simple and cost-effective production is possible. Particularly in the case of such a configuration, there is the possibility that the photocathode 130 is arranged on a (separate) carrier element 186 (cf. FIGS. 3, 8 and 14, for example) and can thus simultaneously serve as a channel wall for the channels 165. Alternatively, the possibility of a configuration in the form of separate photocathode sections 131, 132 is possible, which can be arranged separately from one another in the channels 165 on corresponding sections or wall sections. In this respect, a (possible) arrangement on the section 186 and on the layer 180 is indicated in the exemplary embodiments in FIGS. 3 and 5.

For the channel walls 166, 167—shown in the embodiments in FIGS. 3 and 5—of the respective channel structures 161, 162 or for the associated initial substrate from which the channel structures 161, 162 (or else differently constructed plate-shaped channel structures) and thus the channel walls 166, 167 thereof can be formed, consideration is given, for example, to a semiconductor material such as silicon, in particular, or else to a glass material. Such materials afford the advantage of simple structuring, and enable a high dimensional stability. Furthermore, the possibility is afforded of reliably providing such materials with a wall coating 181 having high secondary electron emission. The wall coating 181 can be formed for example in the context of a chemical vapor deposition (CVD), which can be carried out in particular after a structuring of the respective substrate for forming trenches for the channels 165. It is also possible, if appropriate, to omit such a wall coating 181 or to provide a wall coating 181 only in a partial region. For the channels 165, the length of which can be equal to the height of the scintillator 120, it is possible to provide lateral dimensions in the range of, for example, a few 10 μm to a few 100 μm.

The section 186 shown in FIG. 3 can be a separate carrier element composed of aluminum oxide, for example, which is coated with the photocathode 130 or photocathode sections 131 and is arranged on the channel structure 161 (or a differently configured channel structure). Alternatively, the possibility is afforded that the section 186 is not a separate element, but rather constitutes a (remaining) section of an initial substrate which was subjected to structuring for the production of the channels 165 and channel walls 166. In this regard, the section 186 can (likewise) comprise a semiconductor material such as silicon, in particular, or else a glass material.

The layer 180 serving as an entrance window can comprise, for example, silicon oxide (SiOx) or silicon nitride, or else be embodied in the form of a glass window. Such materials can be fully transparent to the scintillation radiation emitted by the scintillator 120. Since such materials can furthermore be suitable for the emission of (secondary) electrons 204, it is possible in this case, contrary to the configuration shown in FIG. 3, if appropriate also to provide (partial) omission of the wall coating 181 on the layer 180.

With regard to use as an antireflection layer on the lateral wall 123 of the scintillator 120, consideration can furthermore be given to embodying the layer 180 with a thickness which corresponds to one quarter of the wavelength of the scintillation radiation or to a multiple thereof (“quarter-wave layer”). Radiation reflection can be (largely) suppressed as a result. With the use of LSO as scintillator material, in the case of which the scintillation radiation has a wavelength of approximately 420 nm, the layer 180 can have a thickness of 55 nm, for example. Such a layer thickness can be realized reliably and accurately by the layer 180 being embodied, for example, as a (thin) silicon oxide layer. With the use of LSO as scintillator material having a refractive index of 1.82 and silicon oxide as material of the layer 180 having a refractive index of 1.48, reflection at the lateral wall 123 (interface) of less than 1% for example can be achieved in this way.

The layer 180 can furthermore be embodied in the form of a glass window bonded onto the lateral wall 123 or in the form of a coating of the lateral wall 123 composed of, in particular, silicon oxide or silicon nitride. Alternatively, the possibility is also afforded that the layer 180 is produced in the context of production of the channel structures 161, 162 (or else of differently constructured plate-shaped channel structures). By way of example, provision can be made for producing a layer 180 on an initial substrate, wherein channels 165 extending to the layer 180 are subsequently formed in the substrate by the substrate being structured, such that the layer 180 constitutes an entrance window for the channels 165. Such a structured substrate provided with the layer 180 can subsequently be arranged on the lateral wall 123 of a scintillator 120 in accordance with the construction shown in FIGS. 3 and 5.

Alternatively, the possibility is also afforded of omitting the (optional) layer 180. This affords the possibility of arranging a structured substrate of a channel structure, for example the channel structures 161, 162 in FIGS. 3 and 5, directly on the lateral wall 123 of the scintillator 120. In this regard, furthermore, consideration can be given to arranging a wall coating 181 or part thereof directly on the lateral wall 123, or else a semitransparent photocathode 130 or a photocathode section 132 directly on the lateral wall 123 of the scintillator 120.

The electrodes 140, 150 used for accelerating and detecting electrons 204 can be embodied in a planar fashion and from an electrically conductive or metallic material. The detection device 170 or the carrier substrate 171 thereof can be embodied in particular in the form of a semiconductor or silicon substrate, on which the electrode 150 provided for trapping electrons 204 is arranged. The detection device 170 can furthermore also be present in the form of an application specific integrated circuit (ASIC). In this way, the detection device 170 can be designed not only for detecting or reading out a total charge of an electron avalanche and for generating an output signal on the basis thereof, but also for (at least partly) conditioning or evaluating the same.

Further possible configurations of detector elements are described with reference to the following figures. In this case, it is pointed out that, with regard to already described details relating to aspects and components of identical type or corresponding aspects and components, functioning, usable materials, size dimensions, possible advantages, etc., reference is made to the above explanations. In the same way, aspects described below with regard to individual embodiments of detector elements can also apply to other embodiments of detector elements from among those described below.

FIG. 6 shows a schematic perspective illustration of component parts of a further detector element 102, which comprises a parallelepipedal scintillator 120 and a respective conversion device 160 on each of the four lateral walls 123 of the scintillator 120. In this case, a conversion device 160 can be constructed in accordance with the approaches described above. As is furthermore indicated in FIG. 6, the detector element 102 comprises two electrodes 140, 150 arranged in the region of the end faces 121, 122 of the scintillator 120 and serving for generating an electric field, whereby electrons 204 generated in the conversion devices 160 can be accelerated in the direction of the electrode 150 and can be trapped by the electrode 150. In this case, the electrode 150 is a component of a detection device 170 and can be arranged on a carrier substrate 171 thereof. The two electrodes 140, 150 are furthermore provided with a frame-shaped structure, in a manner corresponding to the conversion devices 160 peripherally surrounding the scintillator 120.

The detector element 102 can be designed, in particular, to separately detect the electrons 204 generated and multiplied in the different conversion devices 160. For this purpose, the electrode 150, that is indicated in FIG. 6, has four segments or electrode regions 155 which are assigned to the individual conversion devices 160 and by means of which electrons 204 “originating” from the individual conversion devices 160 can be detected separately from one another. On the basis of this, corresponding output signals can be generated with the aid of the quantities of charge detected by the individual electrode regions 155.

The separate and segment-by-segment detection of electrons 204 generated by means of different conversion devices 160 affords the possibility of determining, simply and accurately, the lateral location of the interaction (“x/y position”) of a radiation quantum 200 which excites the scintillator 120. In this case, it is possible to make use of the fact that the point in time or the temporal development and/or the magnitude of the charge signals obtained by the electrode regions 155 are/is dependent on the proximity of the interaction to the respective lateral walls 123 on which the conversion devices 160 are arranged. In order to determine the lateral interaction location, it is possible, for example, to form summation and/or difference signals from the individual signals. Particularly in the case of one possible configuration of the detection device 170 in the form of an ASIC circuit, this can be carried out by the detection device 170 itself.

Making it possible to determine a lateral interaction location in a scintillator 120 proves to be expedient for an imaging system in which the associated detector is constructed from a plurality of detector elements 102 constructed in this way. Alongside a high efficiency and a high temporal resolution, the relevant detector can have a high lateral spatial resolution as a result even in the case of relatively large lateral scintillator dimensions.

In the embodiments described above, the detection device 170 having the trapping electrode or anode 150 is arranged in the region of the rear side 121 of the scintillator 120, and the electrode 140 serving as cathode is provided in the region of the front side 122 of the scintillator 120 (see FIGS. 2 and 6). Alternatively, however, a configuration symmetrical thereto, with the detection device 170 in the region of the front side 122 and the electrode 140 in the region of the rear side 121, is also possible. In this case, the high-energy radiation to be detected can be transmitted (without interaction) through the detection device 170 and can be subsequently incident in the scintillator 120, wherein the processes described above can once again occur.

A further possible variant consists in providing a cathode-anode structure and detection devices 170 on both end faces 121, 122 of the scintillator 120, and bringing about movements of electrons 204 of different conversion devices 160 in different or mutually opposite directions. This affords the possibility of also detecting the height or depth of an interaction in the scintillator 120.

For exemplary elucidation, FIG. 7 shows a further detector element 103, which comprises a parallelepipedal scintillator 120 and a respective conversion device 160 constructed in accordance with the above-described approaches on each of the four lateral walls 123 of the scintillator 120. The detector element 103 furthermore comprises a mirror-symmetrical electrode arrangement for bringing about different electron movements.

The electrode arrangement comprises two L-shaped electrodes 141, 152 in the region of the front side 122, and two further L-shaped electrodes 142, 151 in the region of the rear side 121 of the scintillator 120. In a manner corresponding to the conversion devices 160 peripherally surrounding the scintillator 120, both the electrodes 141, 152 and the electrodes 142, 151 in each case form a frame-shaped structure. The electrodes 141, 142, 151 and 152 are furthermore arranged on carrier substrates 171 in the region of the two end faces 121, 122 of the scintillator 120 and can be components of detection devices 170 provided on the two end faces 121, 122.

The electrodes 141, 151 arranged one above the other, as shown in FIG. 7, form an electrode pair which can be used to accelerate electrons 204 from two of the four conversion devices 160 (on the left and at the front in the plane of the drawing) adjoining one another or running at right angles with respect to one another in a first direction or in the direction of the electrode 151. This is indicated in FIG. 7 on the basis of a downwardly directed arrow, which can simultaneously represent the direction of an electric field that can be generated by the electrodes 141, 151. In this case, the electrode 141 serves as cathode, and the other electrode 151 as anode and trapping electrode.

The other two electrodes 142, 152 arranged one above the other also form an electrode pair which can be used to accelerate electrons 204 from the other two conversion devices 160 (on the right and offset toward the rear in relation to the plane of the drawing) in a second direction, opposite thereto, in the direction of the electrode 152.

This is indicated in FIG. 7 on the basis of an upwardly directed arrow, which can simultaneously represent the direction of an electric field that can be generated by the electrodes 142, 152. In this case, the electrode 142 functions as cathode, and the other electrode 152 as anode and trapping electrode.

The acceleration and detection of electrons 204 or electron avalanches in different directions affords the possibility of determining the height or depth (“z-position”) of an interaction of a radiation quantum 200 that excites the scintillator 120. In this case, it is possible to make use of the fact that the point in time or the temporal development and/or the magnitude of the quantities of charge detected via the trapping electrodes 151, 152 are/is dependent on the proximity of the interaction to the front or rear side 122, 121 of the scintillator 120. In this case, too, it is possible to form corresponding summation and/or difference signals from individual measurement signals obtained by means of the two trapping electrodes 151, 152 or detection devices 170.

In the case of the detector element 103 from FIG. 7, provision can alternatively be made, contrary to the illustration in FIG. 7, for using the electrode pair 141, 151 to produce an electron movement directed upward in the direction of the electrode 141 or front side 122 of the scintillator 120, and using the electrode pair 142, 152 to produce an electron movement directed downward in the direction of the electrode 142 or rear side 121 of the scintillator 120, which can be defined depending on the voltage respectively applied to the electrode pairs 141, 151 and 142, 152. In the case of such “mirror-symmetrical” functioning, the above-indicated functions of the electrodes 141, 142, 151 and 152 as cathode and (trapping) anode are also interchanged. In this regard, provision can furthermore be made for designing the detector element 103 for a flexible mode of operation in which all electrodes 141, 142, 151, 152 can be operated optionally as cathode or anode. In this case, it is also possible to “drive” the electrodes 141, 142, 151, 152 in such a way that the electrode pairs 141, 151 and 142, 152 bring about electron movements in each case in the same direction.

Instead of designing a detector element with only a single scintillator 120, modular configurations of detector elements comprising a plurality of scintillators 120 arranged alongside one another are also possible, which can be constructed in accordance with the approaches demonstrated above. In this case, conversion devices 160 assigned to the individual scintillators 120 and serving for converting scintillation radiation into (multiplied) electrons 204 can be arranged in interspaces between the scintillators 120 and on opposite lateral walls 123 of the scintillators 120. One possible exemplary embodiment will be described in greater detail with reference to the following figures.

FIG. 8 shows a schematic plan view illustration of two (parallelepipedal) scintillators 120 arranged alongside one another and conversion devices 160 assigned to the scintillators 120, said conversion devices being arranged in an interspace between the scintillators 120 on opposite lateral walls 123 of the scintillators 120. The conversion devices 160 have the plate-shaped construction with the channel structure 161 as described with reference to FIG. 3. In this case, web-shaped channel walls 166 of the channels 165 are connected at one end to the lateral wall 123 of the associated scintillator 120 or to the layer 180 (entrance window) optionally provided on the lateral wall 123.

At an opposite end of the channel walls 166 with respect thereto, a carrier element 186 provided with a reflectively operating photocathode 130 on both sides is provided, said carrier element being assigned to the two conversion devices 160 or channel structures 161. By means of the coated carrier element 186, the channels 165 of the two channel structures 161 are closed at this location, and each channel 165 of the two channel structures 161 is provided with an associated photocathode section 131. On account of the joint utilization of the carrier element 186 coated with the photocathodes 130 on both sides for both conversion devices 160, a simple and cost-effective detector construction is made possible.

FIG. 9 shows a schematic perspective illustration of a detector element 104 which is constructed in a manner corresponding to FIG. 8 and comprises two scintillators 120 arranged alongside one another and associated conversion devices 160, including the carrier element 186 provided with photocathodes 130, in the interspace between the scintillators 120. The detector element 104 furthermore comprises the components described above, i.e. electrodes 140, 150 at the ends of the channels 165 for accelerating and trapping electrons 204, and a carrier substrate 171 or a detection device 170, which are assigned to the scintillators 120. In this case, the two scintillators 120 can be placed or supported on the carrier substrate 171. The electrode 150 can be designed for joint, or alternatively separate or segment-by-segment, trapping of electrons 204 of the individual conversion devices 160. For this purpose, the electrode 150 can comprise electrode regions assigned to the individual conversion devices 160 in a manner comparable with the exemplary embodiment shown in FIG. 6, or else can be subdivided into separate electrodes (not illustrated).

FIG. 9 furthermore indicates a presence of a housing 190 arranged on the carrier substrate 171, said housing surrounding the scintillators 120. The housing 190 can be utilized for providing a (global) vacuum or an evacuated environment for all channels 165 of the conversion devices 160. The housing 190 can furthermore be used for carrying the electrode 140.

In accordance with the approaches described above, in the case of the detector element 104 as well, conversion devices 160 can be arranged on all four lateral walls 123 of the scintillators 120. In this case, associated electrodes 140, 150 can be designed for accelerating and trapping electrons 204 of the two scintillators 120 and, in a manner comparable with FIG. 6, comprise a respective frame-shaped section per scintillator 120. Here, too, the electrode 150 can comprise, if appropriate, electrode regions assigned to the individual conversion devices 160, or else can be subdivided into separate electrodes in order to be able to detect, in particular, a lateral interaction location in the scintillators 120. A configuration comparable with FIG. 7 is also possible, that is to say that provision is made of one (per scintillator 120) frame-shaped cathode-anode structure and detection devices 170 on both end faces 121, 122 of the scintillators 120, as a result of which electrons 204 of different conversion devices 160 of a scintillator 120 can be accelerated in different directions, and by detecting the same it is possible to determine an “interaction depth” in the scintillators 120.

These approaches correspondingly also hold true for such configurations of the detector element 104 in which the detector element 104 comprises more than the two scintillators 120 arranged alongside one another as shown. In this case, the scintillators 120 can be arranged for example in a pixel- or matrix-type fashion in the form of rows and columns alongside one another, and on the carrier substrate 171, and can once again be surrounded by a corresponding housing 190. In such a configuration, too, conversion devices 160 can be arranged on all four lateral walls 123 of the scintillators 120, wherein conversion devices 160 can be present (in each case) in an interspace between two scintillators 120 in accordance with the construction illustrated with reference to FIGS. 8 and 9.

A plate-shaped conversion device 160, for example having the channel structure 161 shown in FIG. 3, can be realized in a space-saving, simple and cost-effective manner on a lateral wall 123 of a scintillator 120. This applies, in particular, to the configuration shown in FIG. 8, in which the carrier element 186 coated with photocathodes 130 on both sides is utilized for two conversion devices 160.

For exemplary elucidation, FIGS. 10 to 13 illustrate a schematic plan view illustration of steps for producing the construction shown in FIG. 8. In accordance with FIG. 10, a planar initial substrate 168, for example a thin silicon substrate, is provided for each of the conversion devices 160, channels 165 (or trenches as “precursors” of the later channels 165) being produced in said substrate. They are separated from one another by channel walls 166. By way of example, a dry etching process can be carried out for this purpose. The trenches or channels 165 extend perpendicular to the plane of the drawing in FIGS. 10 to 13 and furthermore, at a “top side and underside” running parallel to the plane of the drawing, adjoin corresponding plate-shaped sections of the substrate 168 by which the channel walls 166 are connected.

As is furthermore shown in FIG. 11, a carrier element 186 is provided, which can be, for example, a substrate or a plate composed of aluminum oxide. A photocathode material for a respective photocathode 130 is deposited on both sides of the carrier element 186. In this case, by way of example, GaN can be deposited by means of a CVD method.

Furthermore, the scintillators 120 are provided with a layer 180 serving as an entrance window on the lateral walls 123, as is indicated in FIG. 12 on the basis of a scintillator 120 and the coating of two lateral walls 123 of the scintillator 120. By way of example, LSO is considered as scintillator material. The layer 180 is, for example, a silicon oxide layer having a layer thickness of 55 nm, which can be realized by means of a suitable coating method.

Subsequently, as is indicated in FIG. 13, two scintillators 120 coated in this way, and therebetween two structured substrates 168 and the carrier 186 provided with the photocathodes 130 are positioned with respect to one another in the arrangement illustrated in FIG. 13, and are connected to one another or “clamped together”. In this way, the conversion devices 160 provided on the lateral walls 123 of the scintillators 120, or the channel structures 161 of said conversion devices, are substantially completed.

Afterward, the abovementioned “top side and underside” sections of the substrates 168 which run parallel to the plane of the drawing in FIGS. 10 to 13 and via which the channel walls 166 are connected can be removed, such that the opposite ends of the channels 165 are exposed. This can be done by means of chemical mechanical polishing (CMP), for example. Furthermore, electrodes 140, 150 (or corresponding electrode sections) can be provided in these regions and thus at the ends of the channels 165, and this construction can be arranged on a corresponding carrier substrate 171, such that a structure corresponding to FIG. 9 can be present.

With regard to a configuration comprising a plurality of scintillators 120 arranged, in particular, in a matrix-type fashion with respect to one another, the abovementioned steps can be carried out in an analogous manner. In this case, two scintillators 120 adjoining one another can in each case be connected in the manner illustrated with reference to FIG. 13. For scintillators 120 arranged at the edge of the matrix, consideration can furthermore be given to leaving the associated outer lateral walls 123 uncoated, or to arranging thereon structured substrates 168 and carrier elements 186 coated with a photocathode 130 only on one side.

A modular configuration of a detector element comprising a plurality of scintillators 120 arranged alongside one another can also be realized with conversion devices 160 in which a differently constructed channel structure deviating from the channel structure 161 from FIG. 3 is used. In particular, the channel structure 162 having the semitransparent photocathode 130 shown in FIG. 5 can also be used. In this case, the possibility is likewise afforded that two channel structures 162 of this type, in the manner similar to the construction shown in FIG. 8, are arranged in each case in an interspace between two scintillators 120 on the opposite lateral walls 123 thereof.

In the case of such a configuration, consideration can furthermore be given to “combining” two channel structures 162 provided in an interspace to form a common channel structure on both sides. By way of example, the channel wall 167 shown in FIG. 5 can function as a central web, on the opposite sides of which the construction having the channels 165 as shown in FIG. 5 is provided “mirror-symmetrically”, such that channel walls 166 extending “laterally” from the channel wall 167, contrary to the “one-sided” construction from FIG. 5, can be provided on both opposite sides of the channel wall 167. In this case, there is likewise the possibility that the arrangement comprising the channel wall 167 and the channel walls 166 extending on both sides thereof is produced by trenches being produced in a substrate, with the removal of substrate regions between the channel walls 166, 167.

Furthermore, with the use of the channel structure 162 or else differently constructed channel structures, the above-described configurations are likewise possible in which, for example, provision is made of conversion devices 160 on all lateral walls 123 of a scintillator 120, a matrix arrangement comprising a plurality of scintillators 120, and/or an electrode structure comprising electrodes 140, 150 having frame-shaped sections per scintillator 120. Furthermore, consideration is given to separate or segment-by-segment detection of electrons 204 of different conversion devices 160 in accordance with the approach shown in FIG. 6, and to bringing about different electron movements in accordance with the approach shown in FIG. 7.

Such embodiments can be realized with correspondingly configured electrode arrangements (separate electrode regions, electrode pairs for different conversion devices). For further details in this respect, reference is made to the above explanations.

As has already been indicated above, the detector concept described here, that of providing a conversion device 160 on a (at least one) lateral wall 123 of a scintillator 120, is not restricted to plate-shaped conversion devices 160 having a channel structure comprising a structured substrate (for example the channel structure 161 or 162).

In one alternative configuration, a conversion device 160 can comprise a channel structure 163 in which the channels 165 are formed by cutouts or depressions 125 formed in the lateral wall 123 of a scintillator 120, and, consequently, the scintillator 120 has a lateral wall 123 having a structured surface. This enables a particularly space-saving, simple and cost-effective construction, which is advantageous in particular for modular configurations comprising a plurality of scintillators 120. One possible embodiment will be described in greater detail with reference to the following figures.

FIG. 14 shows a schematic plan view illustration of two scintillators 120 arranged alongside one another and comprising conversion devices 160 or channel structures 163 constructed in accordance with this approach on the lateral walls 123. A perspective illustration, with the aid of which the (substantially) parallelepipedal construction of the scintillators 120 once again becomes clear, is furthermore shown in FIG. 15.

In this case, the mutually opposite lateral walls 123 of the scintillators 120 have depressions 125 through which channels 165 are formed. The depressions 125 and thus the channels 165, which run parallel to a longitudinal axis of the respective scintillator 120, said longitudinal axis extending between the end faces 121, 122, can have an elliptic or oval geometry in plan view. Alternatively, other shapes for the depressions 125 and thus the channels 165, such as a rectangular or triangular shape, for example, are also possible (not illustrated).

Furthermore, the carrier element 186 provided with reflectively operating photocathodes 130 on both sides, as described above with reference to FIGS. 3 and 8, is arranged in an interspace between the scintillators 120. The depressions 125 and thus channels 165 of the conversion devices 160 on the lateral walls 123 of the associated scintillators 120 are closed in this way. Furthermore, the channels 165 are thereby assigned corresponding sections of the photocathode 130 which can be used to convert scintillation photons 202 that are emitted in the direction of the respective lateral wall 123 of a scintillator 120 and enter into the channels 165 into photoelectrons 204 in the manner described above.

As is furthermore shown in FIG. 14, the depressions 125 of the scintillators 120 are furthermore preferably provided with a wall coating 181, for example composed of silicon oxide. As in the case of the exemplary embodiments described with reference to FIGS. 3 and 5, said coating serves to make it possible to liberate a multiplicity of electrons 204 per impact process of an electron 204 with the channel wall. For this purpose, the wall coating 181 comprises, in particular, a material having high secondary electron emission.

FIG. 14 furthermore illustrates the process of generation and multiplication of electrons 204 that takes place in a channel 165 of the channel structure 163. The scintillation photons 202 emitted by the scintillator 120 in the direction of the lateral wall 123 can penetrate through the (semitransparent) wall coating 181 and enter into the interior of the channel 165, pass further to the reflective photocathode 130 and be absorbed by the latter. On the basis of this, the photocathode 130 can emit electrons 204 into the interior of the channel 165, wherein electrons 204 are liberated as a result of impacts with the wall coating 181, which electrons for their part can likewise contribute to the electron multiplication within the channel 165 as a result of impacts with the wall coating 181. In this case, provision is made for accelerating the electrons 204 once again along the channels 165, wherein corresponding electrodes 140, 150 can be provided at the ends of the channels 165.

For elucidation, FIG. 16 illustrates a detector element 105 constructed in a manner corresponding to FIGS. 14 and 15. The detector element 105 once again comprises the components described above, i.e. electrodes 140, 150 for accelerating and trapping electrons 204, and a carrier substrate 171 or a detection device 170. In this case, the two scintillators 120 can be placed or supported on the carrier substrate 171. The electrode 150 can be designed for joint, or alternatively separate or segment-by-segment, trapping of electrons 204 of the individual conversion devices 160. For this purpose, the electrode 150 can comprise electrode regions assigned to the individual conversion devices 160 in a manner comparable with the exemplary embodiment shown in FIG. 6, or else can be subdivided into separate electrodes (not illustrated).

FIG. 16 furthermore indicates a presence of a housing 190 arranged on the carrier substrate 171, which housing 190 can be utilized for providing a (global) vacuum for all channels 165 of the conversion devices 160. The housing 190 can furthermore be used for carrying the electrode 140.

In accordance with the approaches described above, in the case of the detector element 105 as well, conversion devices 160 having channel structures 163 can be arranged on all four lateral walls 123 of the scintillators 120. In this case, associated electrodes 140, 150 can be designed for accelerating and trapping electrons 204 of the two scintillators 120 and, in a manner comparable with FIG. 6, comprise a respective frame-shaped section per scintillator 120. Here, too, the electrode 150 can comprise, if appropriate, electrode regions assigned to the individual conversion devices 160, or else can be subdivided into separate electrodes in order to be able to detect, in particular, a lateral interaction location in the scintillators 120. A configuration comparable with FIG. 7 is also possible, that is to say that provision is made of one (per scintillator 120 frame-shaped) cathode-anode structure and detection devices 170 on both end faces 121, 122 of the scintillators 120, as a result of which electrons 204 of different conversion devices 160 of a scintillator 120 can be accelerated in different directions, and by detecting the same it is possible to determine an “interaction depth” in the scintillators 120.

These approaches correspondingly also hold true for configurations comprising only one scintillator 120, or comprising more than two scintillators 120, which can be arranged, in particular, in a matrix-type fashion on the carrier substrate 171. In this case, too, conversion devices 160 having channel structures 163 can be arranged on all four lateral walls 123 of the scintillators 120, wherein conversion devices 160 can be present (in each case) in an interspace between two scintillators 120 in accordance with the construction elucidated with reference to FIG. 14. In a configuration comprising only one scintillator 120, which has a conversion device 160 or channel structure 163 on a (at least one) lateral wall 123, or for the case of an outer lateral wall 123 of a scintillator 120 of a scintillator arrangement or scintillator matrix, provision can be made for the depressions 125 or channels 165 formed at the respective lateral wall 123 to be closed with a carrier element 186 coated with the photocathode 130 only on one side.

Modifications are also conceivable for the conversion device 160 having the channel structure 163 as shown in FIG. 14. For example, provision can be made for providing the depressions 125 or a partial region thereof with semitransparent photocathodes or photocathode sections, such that functioning comparable to the channel structure 162 from FIG. 5 can be present. In the case of such a configuration as well, consideration can be given to closing the depressions 125 or channels 165 at the lateral wall 123 with a corresponding substrate or carrier element 186. In this case, a wall coating 181 used for electron multiplication can be arranged in a manner adjoining a photocathode section of a depression 125, and also on the carrier element 186 provided for closure. With regard to shared utilization of such a carrier element 186 for conversion devices 160 having channel structures 163 on mutually opposite lateral walls 123 of two scintillators 120, the carrier element 186 can be provided with a wall coating 181 on both sides.

A conversion device 160 having one of the above-described channel structures 161, 162, 163 (and possibly modifications thereof) can be embodied in a relatively space-saving manner and with a relatively small width or thickness on account of the channels 165 arranged alongside one another in a plane at a lateral wall 123 of a scintillator 120. This affords the possibility, in the case of modular configurations comprising a plurality of scintillators 120 arranged alongside one another, as illustrated in FIGS. 9 and 16, of also keeping the interspace between two scintillators 120 relatively small. By way of example, the interspace or distance between two scintillators 120 can be less than 100 μm. In this way, a detector element comprising a plurality of scintillators 120 (in particular arranged in a matrix-type fashion) can have a very high filling factor (ratio of active area, i.e. all “sensitive” front sides 122, of the scintillators 120 to irradiated total area), which can be greater than 98%.

The detector elements described above are designed to convert the scintillation radiation emitted to a (at least one) lateral wall 123 of a scintillator 120 into multiplied electrons 204 by means of a conversion device 160 and to detect the electrons 204. However, an “extension” of the detector elements is also possible to the effect that in addition part of the radiation emitted to one or both end faces 121, 122 of a scintillator 120 is also converted into electrons 204 that are detected. If appropriate, a relatively high efficiency can be obtained as a result.

For exemplary elucidation, FIG. 17 shows a schematic lateral illustration of a further detector element 106, which is designed for such functioning. The detector element 106 comprises a parallelepipedal scintillator 120, on the lateral wall 123 of which a conversion device 160 embodied in accordance with the approaches demonstrated above is arranged. An electric field can be generated by means of electrodes 140, 150, whereby electrons 204 converted and multiplied in the conversion device 160 can be accelerated to the electrode 150 and trapped by the latter. The electrode 150, as indicated in FIG. 17, is part of a detection device 170 provided for detecting electrons 204, which detection device can additionally comprise a substrate 171, on which the electrode 150 is arranged.

Furthermore, an additional semitransparent photocathode section 139 is arranged at the rear side 121 of the scintillator 120, with the aid of which photocathode section scintillation photons 202 emerging at this location can be converted into electrons 204. Furthermore, a microchannel plate 169 is arranged below the photocathode 139, in which microchannel plate the electrons 204 coming from the photocathode 139 can be multiplied further, and can subsequently be detected by the electrode 150 arranged below the microchannel plate 169. As is shown in FIG. 17, the electrode 150 can be designed for separately detecting the electrons 204 coming from the conversion device 160 and from the microchannel plate 169, and for this purpose can have electrode regions 158, 159 assigned to the microchannel plate 169 and to the conversion device 160.

The microchannel plate 169 is provided with a multiplicity of channels within which the electrons 204, as in the channels 165 of the conversion device 160, can be multiplied in an avalanche-like manner as a result of impact processes with the channel walls. During operation, an electrical voltage (acceleration voltage) is applied between the main surfaces or main sides, i.e. between front and rear sides of the microchannel plate 169, between which the channels thereof also extend, as a result of which an electric field is present along the channels. This can be effected with the aid of the electrode 150 at the rear side of the microchannel plate 169, and with the aid of an additional electrode or dynode (not illustrated) at the front side of the microchannel plate 169.

The concept illustrated in FIG. 17 of (also) converting the scintillation radiation emerging at an end face of a scintillator 120 into electrons 204 and multiplying the latter, can be provided in all of the above-described configurations of detector elements (for example comprising conversion devices 160 on all four lateral walls 123, modular configurations comprising a plurality of scintillators 120, etc.). Furthermore, it is possible also to detect the scintillation radiation emitted at both end faces 121, 122 of a scintillator 120, wherein the construction comprising a microchannel plate 169 and a detection device 170 as shown in FIG. 17 can be provided on both end faces 121, 122.

The embodiments explained with reference to the figures constitute preferred or exemplary embodiments of the invention. Alongside the embodiments described and depicted, further embodiments are conceivable which can comprise further modifications and/or combinations of features described. Moreover, the detectors or detector elements explained with reference to the figures can also comprise further structures (not illustrated) alongside the structures shown and described. Furthermore, it is possible to use different materials than those indicated above for a detector element or the components thereof, and to design a detector element or the components thereof with different dimensions than those indicated.

In the same way, a detector element or the components thereof can be embodied with other geometries which deviate from the exemplary embodiments shown in the figures. Other geometries can be considered for example for electrodes for accelerating and trapping electrons, and for electrode arrangements for bringing about electron movements in opposite directions. Moreover, a conversion device 160 embodied as a “two-dimensional channel system” and having channels 165 running along or arranged in a plane on a lateral wall of a scintillator 120 can have different shapes than those described above.

This is the case, in particular, if a scintillator 120 has, instead of a parallelepipedal shape, a different shape having two mutually opposite end faces and a (at least one) lateral wall between the end faces, wherein the end faces are connected to one another via the lateral wall. One possible example is a scintillator 120 having a cylindrical or circular-cylindrical shape. In this case, a conversion device 160 arranged on the lateral wall (lateral surface) of such a scintillator 120 can comprise channels 165 arranged in a curved plane or area in a manner corresponding to the shape of the lateral wall of the scintillator 120. In this case, by way of example, a configuration comprising a grooved channel structure 163 corresponding to FIG. 14 can be provided, wherein the lateral wall of the scintillator 123 comprises a structured surface, and the channels 165 are present in the form of indentations or depressions formed in the lateral wall of the scintillator 120. In this configuration, a curved or circular carrier element 186 can be used for closing the channels 165. Said carrier element can furthermore be provided with a photocathode 130 on the side facing the channels 165. Electrodes 140, 150 used for accelerating and trapping electrons can in this case be embodied in a curved or circular fashion. In this case, provision can furthermore be made for arranging the channels 165 along the entire periphery of the scintillator 120 in order to convert scintillation radiation emitted to the lateral wall into electrons in an efficient manner.

With regard to a scintillator 120 having two mutually opposite end faces and a plurality of lateral walls situated therebetween, provision can furthermore be made for arranging a conversion device 160 only on one individual lateral wall or conversion devices 160 only on a portion of the lateral walls, such that one or more lateral walls are utilized not just for converting scintillation radiation into multiplied electrons. It is also possible, in the case of a scintillator 120 having one or a plurality of lateral walls arranged between two end faces, for one or a plurality of lateral walls to be provided with a conversion device 160 only in a partial region, rather than completely.

With regard to an electrode 150, 151, 152 used for trapping multiplied electrons, it can furthermore be provided that, instead of a planar configuration having one or, if appropriate, a plurality of electrode regions, such an electrode is embodied in the form of separate individual electrodes which are assigned in each case to an individual or a plurality of channels 165 of a conversion device 160.

Furthermore, the possibility is afforded of separately detecting electrons of different subsections of an individual or one and the same conversion device 160. In this case, in particular, an electrode 150 subdivided into different electrode regions can be used. Such a configuration is possible for example for the above-described exemplary embodiment with a circular-cylindrical scintillator 120 and a (in plan view) curved or circular conversion device 160 arranged on the lateral wall. In this case, an annular trapping electrode 150 can be provided, which is subdivided into four electrode regions, for example, in order to separately detect electrons generated and multiplied by four sections (arranged alongside one another) of the conversion device 160. On the basis of this or by evaluating the different charge signals obtained via the electrode regions (“summation and/or difference formation”), it is possible to determine a lateral interaction location in the circular-cylindrical scintillator 120.

In the same way it is conceivable for electrons of different subsections of an individual conversion device 160 to be accelerated in different or opposite directions, and detected separately, which is possible with the aid of a corresponding electrode arrangement arranged on the conversion device 160. For the above-described exemplary embodiment with a circular-cylindrical scintillator 120 and a (in plan view) curved or circular conversion device 160 arranged on the lateral wall, by way of example, corresponding annular cathode-anode structures and detection devices 170 can be provided on both end faces of the scintillator 120 and can be used to deflect electrons of a (for example semi-annular) section of the conversion device 160 in one direction and electrons of another (semi-annular) section in a direction opposite thereto. On the basis of this or by evaluating charge signals (“summation and/or difference formation”) which can be obtained with the aid of the (trapping) anodes arranged on the different end faces, it is possible to determine an “interaction depth” in the circular-cylindrical scintillator 120.

With regard to the approach demonstrated above in particular with reference to FIGS. 8 and 14, that of jointly utilizing components arranged in an interspace between two scintillators 120 for two conversion devices 160, other configurations are also possible. By way of example, the carrier element 186 shown in FIG. 8, like the channel walls 166, can be formed from a shared initial substrate and thus serve as a central web of the channel walls 166 extending “laterally” therefrom. In this configuration, it can furthermore be provided that, instead of the continuous photocathodes 130, separate photocathode sections of the channels 165 are arranged on both sides at the “central web” 186, corresponding to the construction comprising the photocathode sections 131 as illustrated in FIG. 3.

Although the invention has been described and illustrated more specifically in detail by means of preferred exemplary embodiments, the invention is nevertheless not restricted by the examples disclosed and other variations can be derived therefrom by a person skilled in the art, without departing from the scope of protection of the invention.

RADIATION DETECTOR AND IMAGING SYSTEM

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