X-RAY DETECTION SYSTEM

Abstract

Aspects of the present disclosure relate to an X-ray detecting system. Further aspects of the present disclosure relate to an X-ray system comprising the X-ray detecting system, and to an X-ray detection method.

In an embodiment of the present disclosure, the X-ray detecting system comprises a processing unit for processing the pixel signals, wherein the processing unit comprises a frame summing unit configured to, for a pixel of the pixel array, compare the pixel values of the acquired frames that correspond to that pixel for detecting a pixel value in those frames that was adversely affected by a direct hit of that pixel by an X-ray photon during said single exposure, and generate a pixel value for that pixel in dependence of the pixel values of the acquired frames and detected pixel value for that pixel.

Claims

1. An X-ray detecting system, comprising: an X-ray detector comprising a pixel array and readout circuitry for reading out pixel signals of the pixel array, wherein the readout circuitry is configured for acquiring a plurality of frames related to a single X-ray exposure, each frame comprising pixel values for the pixels in the pixel array; and a processing unit for processing the pixel signals, wherein the processing unit comprises a frame summing unit and an X-ray image generating unit; wherein the frame summing unit is configured to, for each pixel of the pixel array: compare the pixel values of the acquired frames that correspond to that pixel for detecting a pixel value in those frames that was adversely affected by a direct hit of that pixel by an X-ray photon during said single exposure; and generate a pixel value for that pixel in dependence of the pixel values of the acquired frames, discarding the detected adversely affected pixel value for that pixel; wherein the X-ray image generating unit is configured to generate an X-ray image based on the generated pixel values for the pixels of the pixel array.

2. The X-ray detecting system according to claim 1, wherein the X-ray detecting system does not comprise a fiber optic plate.

3. The X-ray detecting system according to claim 1, wherein the frame summing unit is configured to detect the pixel value by determining, for that pixel, a median value of the pixel values of the acquired frames, and to determine that a pixel value among the pixel values of the acquired frames is adversely affected if that pixel value deviates more than a first threshold from the determined median value.

4. The X-ray detecting system according to claim 1, wherein the frame summing unit is configured to detect the pixel value by determining, for that pixel, an average value of the pixel values of the acquired frames, and to determine that a pixel value among the pixel values of the acquired frames is adversely affected if that pixel value deviates more than a second threshold from the average value.

5. The X-ray detecting system according to claim 1, wherein the pixel array comprises active pixels.

6. The X-ray detecting system according to claim 5, wherein the active pixels have a 3T or 4T layout.

7. The X-ray detecting system according to claim 5, wherein the pixel array comprises a CMOS pixel array on a Silicon substrate.

8. The X-ray detecting system according to claim 1, further comprising: a carrier; a scintillator arranged on the carrier; a semiconductor substrate attached to the carrier on which substrate the pixel array and the readout circuitry are integrated.

10-17. (canceled)

18. The X-ray detecting system according to claim 8, wherein the carrier is made of one or more materials out of the group consisting of aluminium, amorphous carbon, and other light flexible organic substrate such as Kapton or PET, wherein an absorption coefficient for X-ray radiation having an energy within a range between 20 and 150 keV lies in a range between 0.01 and 4 cm.sup.2/mg.

19. The X-ray detecting system according to claim 1, wherein the frame summing unit is integrated on the semiconductor substrate.

20. An X-ray system, comprising: an X-ray source; and the X-ray detecting system according to claim 1.

21. The X-ray system according to claim 20, wherein the pixels of the pixel array are active pixels that each have a storage capacity, wherein the X-ray system is operable in a first operational mode in which mode the X-ray source is configured to emit X-rays using a dose rate in a range between 0.01 and 10 mGy in a single exposure, wherein an integration time of the pixel array is such that a maximum filling level of the storage capacity stays between 1 and 50 percent during said single exposure and such that the number of acquired frames exceeds 4.

22. An X-ray detection method, comprising: emitting X-rays to an object; converting X-rays having passed through the object into visible light; detecting the visible light using a pixel array while X-rays generate direct hits in the pixel array, by acquiring multiple frames during a single X-ray exposure; for each pixel of the pixel array, comparing pixel values of the acquired frames that correspond to that pixel for detecting a pixel value in those frames that was adversely affected by a direct hit of that pixel by an X-ray photon during said single exposure, and generating a pixel value for that pixel in dependence of the pixel values of the acquired frames, while discarding the detected adversely affected pixel value for that pixel; generating an X-ray image based on the generated pixel values for the pixels of the pixel array.

23. The method according to claim 22, wherein said detecting said pixel value comprises determining, for that pixel, a median value of the pixel values of the acquired frames, and to determine that a pixel value among the pixel values of the acquired frames is adversely affected if that pixel value deviates more than a first threshold from the determined median value.

24. The method according to claim 22, wherein said detecting said pixel value comprises determining, for that pixel, an average value of the pixel values of the acquired frames, and to determine that a pixel value among the pixel values of the acquired frames is adversely affected if that pixel value deviates more than a second threshold from the determined average value.

25. The method according to claim 22, wherein said detecting the visible light comprises detecting the visible light using a pixel array while X-rays, which have not passed through a fiber optic plate, generate direct hits in the pixel array.

Description

DESCRIPTION OF THE DRAWINGS

[0032] So that the manner in which the features of the present disclosure can be understood in detail, a more particular description is made with reference to embodiments, some of which are illustrated in the appended figures. It is to be noted, however, that the appended figures illustrate only typical embodiments and are therefore not to be considered limiting of its scope. The figures are for facilitating an understanding of the disclosure and thus are not necessarily drawn to scale. Advantages of the subject matter claimed will become apparent to those skilled in the art upon reading this description in conjunction with the accompanying figures, in which like reference numerals have been used to designate like elements, and in which:

[0033] FIG. 1 illustrates a comparison between X-ray images obtained using an X-ray detecting system with and without a fiber optic plate;

[0034] FIG. 2 illustrates histograms corresponding to the X-ray images of FIG. 1;

[0035] FIG. 3 illustrates an embodiment of an X-ray system in accordance with an aspect of the present disclosure;

[0036] FIG. 4 illustrates a further embodiment of an X-ray system in accordance with an aspect of the present disclosure;

[0037] FIGS. 5-6 illustrate different methods for generating an X-ray image from a plurality of frames; and

[0038] FIG. 7 illustrates an exploded view of an X-ray detector in accordance with an aspect of the present disclosure.

[0039] FIG. 3 illustrates an embodiment of an X-ray system 100 in accordance with an aspect of the present disclosure. It comprises an X-ray source 110 and an X-ray detecting system 120. In the embodiment shown in FIG. 3, X-ray detecting system 120 comprises an X-ray detector 121 and a processing unit 122 that are embodied as separate units. X-ray detector 121 comprises a CMOS pixel array 1211 that is integrated on a Silicon substrate. On that same substrate, selecting circuitry 1212 is arranged for selecting a row of pixels of pixel array 1211 to be read out. In addition, the semiconductor substrate comprises readout circuitry 1213 for reading out the pixel signals from selected pixels of pixel array 1211, and a frame generating unit 1214 that generates a frame based on the pixel signals from pixel array 1211. Typically, readout circuitry 1213 converts the pixel signals of a row of pixels into corresponding digital numbers. The frame generated by frame generating unit 1214 then comprises a digital number for each of the pixels in pixel array 1211. The semiconductor substrate further comprises a controller 1215 for controller selecting circuitry 1212, readout circuitry 1213, and frame generating unit 1214.

[0040] Processing unit 122 comprises a frame summing unit 1221 and an X-ray image generating unit 1222. Frame summing unit 1221 receives the frames generated by frame generating unit 1214 and outputs a single frame comprising a pixel value for each pixel of the pixel array 1211 based on the frames received from frame generating unit 1214. X-ray image generating unit 1222 generates an X-ray image 130 based on the frame outputted by frame summing unit 1221.

[0041] In the embodiment in FIG. 3, an object 140 is arranged in between X-ray source 110 and X-ray detecting system 120. This object is visible in X-ray image 130.

[0042] FIG. 4 illustrates a further embodiment of an X-ray system 200 in accordance with an aspect of the present disclosure. This embodiment differs from the embodiment shown in FIG. 3 in that frame summing unit 1221 is now integrated on the same semiconductor substrate as pixel array 1211. As such, processing unit 122 is distributed over several subsystems.

[0043] It is noted that most X-ray detecting systems use multiple semiconductor substrates on which respective pixel arrays are integrated. These substrates are referred to as tiles and in such cases X-ray image generating unit 1222 generates an X-ray image based on the pixel values for all pixels of all tiles. Hence, when using multiple tiles, X-ray image generating unit is typically arranged separate from the semiconductor substrates on which the pixel arrays are integrated. However, the various frame summing units may still be integrated on the same substrates as the pixel arrays. In such case, X-ray image generating unit receives partial frames and constructs the X-ray image based on the partial frames. In other embodiments, a single frame summing unit is used that receives the partial frames from the various tiles and generates a single frame that is provided to the X-ray image generating unit. Additionally or alternatively, the frame summing unit may be part of the X-ray detector. In other embodiments, the frame summing unit and the image generating unit are arranged separate from the X-ray detector.

[0044] FIGS. 5-6 illustrate different methods for generating an X-ray image from a plurality of frames. In FIG. 5, the frame summing unit has received five frames 300A-300E that correspond to a single exposure. Each frame comprises pixel values corresponding to each pixel of the pixel array. These pixel values are indicated as digital numbers, DN. For example, frame 300A comprises a digital number equal to 201 corresponding to a pixel 301 of the pixel array. It is noted that FIG. 5 illustrates the position of pixel 301 in the corresponding pixel array.

[0045] The median value for pixel 301 among frames 300A-300E equals 205. Assuming that a threshold of 30 is used, it can be determined that the pixel value for pixel 301 in frame 300D deviates more than the threshold from the median value, i.e. 253−30>205. As such, this pixel value is detected as a pixel value that was adversely affected by a direct hit of pixel 301 by an X-ray photon during the exposure.

[0046] Next, the frame summing unit generates a single frame of which the pixel value for pixel 301 is computed by averaging the other pixel values for pixel 301, i.e. (201+205+198+208)/4=203. This process is performed for each pixel of the pixel array. If multiple tiles are used, the frame summing process described above can be performed independently for each tile, after which the various generated subframes are combined either by a dedicated subframe combining unit or by the X-ray image generating unit. The former subframe combining unit could be part of the X-ray detector. Alternatively, a single frame summing unit first combines the various subframes from the various tiles before performing the frame summing process.

[0047] FIG. 6 illustrates a different frame summing process. Compared to the process illustrated in FIG. 5, pixel values are now not compared to a median value but to an average value. For the values shown in FIG. 6, the average value can be computed to be (202+204+196+253+210)/5=213. Assuming that a threshold of 35 is used, it can be determined that the pixel value for pixel 301 in frame 300D deviates more than the threshold from the average value, i.e. 253−35>213. As such, this pixel value is detected as a pixel value that was adversely affected by a direct hit of pixel 301 by an X-ray photon during the exposure.

[0048] Next, the frame summing unit generates a single frame of which the pixel value for pixel 301 is computed by averaging the other pixel values for pixel 301, i.e. (202+204+196+210)/4=203.

[0049] In the embodiments in FIGS. 5 and 6, the detected pixel value was discarded when computing the pixel value of the pixel. In other embodiments, the detected pixel value is replaced by the median value or the average value, respectively.

[0050] FIG. 7 illustrates an exploded view of an X-ray detector 400 in accordance with an aspect of the present disclosure. It comprises a front cover 401, typically a carbon cover, and a back cover 408. A carrier 402 having a first surface and an opposing second surface is provided adjacent front cover 401. A scintillator is arranged on the first surface of carrier 402, which in FIG. 7 corresponds to the surface that is directed towards front cover 401. Carrier 402 may be a foil or another suitable carrier onto which the scintillator can be formed.

[0051] Adjacent carrier 402, four semiconductor tiles 403 are arranged that each comprise a CMOS pixel array. Tiles 403 are mounted on a supporting plate 404. On the other side, supporting plate 404 is connected to a metal frame 405 in which a printed circuit board 407 is arranged. Lead slabs 406 are provided to protect the electronics on printed circuit board 407 against X-ray radiation.

[0052] The frame summing unit described above can be realized on each of the tiles 403, where it will output subframes for the X-ray image to be constructed, or it can be realized on printed circuit board 407, will output an entire frame for the X-ray image to be constructed. In the former case, a dedicated subframe combining unit may be arranged on printed circuit board 407 that combines the various subframes received from the frame summing unit. The image generating unit may be provided separate from X-ray detector 400 and may for example be realized using a general purpose computer running image processing software. In other embodiments, the frame summing unit is also implemented using a general-purpose computer.

[0053] In the above, the present invention has been described using detailed embodiments thereof. However, the present invention is not limited to these embodiments. Instead, various modifications are possible without departing from the scope of the present invention which is defined by the appended claims and their equivalents.

[0054] Particular and preferred aspects of the invention are set out in the accompanying independent claims. Combinations of features from the dependent and/or independent claims may be combined as appropriate and not merely as set out in the claims.

[0055] The scope of the present disclosure includes any novel feature or combination of features disclosed therein either explicitly or implicitly or any generalization thereof irrespective of whether or not it relates to the claimed invention or mitigate against any or all of the problems addressed by the present invention. The applicant hereby gives notice that new claims may be formulated to such features during prosecution of this application or of any such further application derived therefrom. In particular, with reference to the appended claims, features from dependent claims may be combined with those of the independent claims and features from respective independent claims may be combined in any appropriate manner and not merely in specific combinations enumerated in the claims.

[0056] Features which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub combination.

[0057] The term “comprising” does not exclude other elements or steps, the term “a” or “an” does not exclude a plurality. Reference signs in the claims shall not be construed as limiting the scope of the claims.