DETECTOR AND IMAGING SYSTEM FOR X-RAY PHASE CONTRAST TOMO-SYNTHESIS IMAGING

Abstract

The invention relates to an X-ray detector arrangement (10) for X-ray phase contrast tomo-synthesis imaging, a line detector (1) for X-ray phase contrast tomo-synthesis imaging, an imaging system (24) for X-ray phase contrast tomo-synthesis imaging, a method for X-ray phase contrast tomo-synthesis imaging, and a computer program element for controlling such arrangement and a computer readable medium having stored such computer program element. The X-ray detector arrangement (10) comprises several line detectors (1). Each line detector (1) is configured to detect a Moiré pattern in at least a portion of an X-ray beam (2) impacting such line detector (1). Each line detector (1) comprises several detector lines (11), wherein a width W of each line detector (1) equals one period or an integer multiple of the period of the Moiré pattern.

Claims

1. An X-ray detector arrangement for X-ray phase contrast tomo-synthesis imaging, wherein the X-ray detector arrangement comprises several line detectors, wherein each line detector is configured to detect a Moiré pattern in at least a portion of an X-ray beam impacting such line detector, wherein each line detector comprises several independent detector lines, and wherein a width W of each line detector equals one period or an integer multiple of the period of the Moiré pattern.

2. X-ray detector arrangement according to claim 1, wherein each line detector comprises eight detector lines.

3. X-ray detector arrangement according to claim 1, wherein each detector line is arranged along a direction perpendicular to the axis A of symmetry of the X-ray beam.

4. X-ray detector arrangement according to claim 1, wherein each detector line is inclined with an acute angle α relative to the axis A of symmetry of the X-ray beam.

5. (canceled)

6. (canceled)

7. (canceled)

8. An imaging system for X-ray phase contrast tomo-synthesis imaging of an object, comprising: an X-ray detector arrangement according to claim 1, an X-ray source arrangement, a grating arrangement configured to create a Moiré pattern in the X-ray beam, and a gantry, wherein the X-ray source arrangement, the grating arrangement and the X-ray detector arrangement are mounted to the gantry.

9. Imaging system according to claim 8, further comprising an object support configured to support the object, wherein the imaging system is configured for relatively moving the object support and the gantry.

10. Imaging system according to claim 8, wherein the imaging system is configured for rotating the gantry and/or the object support around an axis of rotation situated below the X-ray detector arrangement when seen in the direction of the X-ray beam.

11. Imaging system according to claim 9, wherein the imaging system is configured for translating the gantry and/or the object support in a direction perpendicular to the axis A of symmetry of the X-ray beam.

12. A method for X-ray phase contrast tomo-synthesis imaging, comprising the following steps: a) providing an X-beam passing through an X-ray detector arrangement, and b) detecting a Moiré pattern in at least a portion of the X-ray beam, wherein the X-ray detector arrangement is configured as defined in claim 1.

13. A computer program element for controlling an arrangement or system, which, when being executed by a processing unit, is adapted to perform the method steps of claim 12.

14. A computer readable medium having stored the computer program element of claim 13.

15. X-ray detector arrangement according to claim 8, wherein the grating arrangement comprises several grating components configured to create a Moiré pattern in the X-ray beam such that one grating component is arranged in front of each line detector when seen in the direction of the X-ray beam.

16. X-ray detector arrangement according to claim 8, wherein the grating arrangement comprises one grating unit configured to create a Moiré pattern in the X-ray beam such that the grating unit is arranged in front of and covers all line detectors at the same time when seen in the direction of the X-ray beam.

17. X-ray detector arrangement according to claim 15, wherein the grating component or the grating unit comprises a phase grating and an analyzer grating

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Exemplary embodiments of the invention will be described in the following with reference to the accompanying drawings:

[0029] FIG. 1 shows a schematic drawing of a line detector for X-ray phase contrast tomo-synthesis imaging according to the invention.

[0030] FIG. 2 shows a schematic drawing of an X-ray detector arrangement for X-ray phase contrast tomo-synthesis imaging according to the invention.

[0031] FIG. 3 shows a schematic drawing of an imaging system for X-ray phase contrast tomo-synthesis imaging of an object according to the present invention.

[0032] FIG. 4 shows a schematic overview of steps of an exemplary method for X-ray phase contrast tomo-synthesis imaging.

DETAILED DESCRIPTION OF EMBODIMENTS

[0033] Exemplarily, grating-based, differential phase contrast mammography is described in the following. Implementations of such differential phase contrast mammography make use of the inherent redundancy of data acquisition in slit-scanning mammography. To simultaneously acquire attenuation-, phase- and dark-field information for a two-dimensional image of a (female) breast, it is necessary to measure the X-ray intensity down-stream a Talbot-Lau interferometer (comprising a source grating, a phase grating and an analyzer grating and relying on coherent self-imaging of periodic gratings) for e.g. eight different relative lateral displacements between the local phase-, and analyzer gratings pitch for one and the same geometrical ray. This can be achieved by a process named phase-stepping but not necessarily in this way. In case of attenuation imaging by mammographic slit scanning, each geometric ray is sampled e.g. 18 times by 18 different detector pixels. This redundancy is only used for reducing noise but does not lead to new signals in the attenuation case. In differential-phase contrast slit-scanning mammography, the acquisition from 18 different detector lines does provide information equivalent to phase-stepping, with the advantage of the absence of the need for the actuation of highly aligned, micron-sized structures.

[0034] In implementations of tomo-synthesis systems based on slit-scanning, the geometrical redundancy on the geometrical ray basis is lost because the rotational scan is no longer performed around the X-ray focal spot but around a point below the slit scanning detector unit. The rotational scan comprises a relative rotation between (i) an aggregate of X-ray detector, gratings and X-ray source and (ii) the object to be examined. The data so acquired can be used to reconstruct 3D voxel data sets of the mammographic density of the female breast with all know complications of limited-angle tomography.

[0035] It is therefore clear that a straightforward generalization of phase-contrast mammography to phase-contrast tomo-syntheses is all but obvious for slit-scanning geometries. According to this invention, the combination of phase-contrast imaging and tomo-synthesis is achieved by an elegant, simple and minimal extension of the line detector geometry.

[0036] The extension of the geometry of a slit scanning tomo-synthesis system to a phase-contrast slit scanning tomo-synthesis imaging system according to the invention is called elegant, simple and minimal, because the X-ray detector and its collimator structure can remain in place. The necessary hardware change amounts to replacing the e.g. 18 conventional line detectors with the same number of line detectors according to the invention, wherein each of the line detectors now features of the order of e.g. eight adjacent detector lines. A pitch of the adjacent detector lines can either be identical to the conventional width of the line detector or smaller.

[0037] FIG. 1 shows schematically and exemplarily a detail of an X-ray detector arrangement 10 for X-ray phase contrast tomo-synthesis imaging according to the invention. The X-ray detector arrangement 10 comprises several line detectors 1. In FIG. 1, only one line detector 1 for X-ray phase contrast tomo-synthesis imaging according to the invention is shown. A multiplicity of such line detectors 1 arranged adjacent to each other gives X-ray detector arrangement 10 for X-ray phase contrast tomo-synthesis imaging according to the invention (see FIG. 2). Each of these line detectors 1 is configured to detect a Moiré pattern in at least a portion of an X-ray beam 2 impacting such line detector 1. Each line detector 1 comprises several detector lines 11, wherein a width W of each line detector 1 equals one period or an integer multiple of the period of the Moiré pattern. FIG. 1 thereto shows one line detector 1 with eight detector lines 11.

[0038] In FIG. 1, X-ray beams 2 are incident from the top of the figure indicated by the shaded band passing a Talbot-Lau interferometer comprising a phase-grating 31 and an analyzer grating 32. After the passage of the analyzer grating 32, a Moiré pattern is formed in the downstream intensity between two post-collimator blades 33 indicative of the changes induced by the presence of an object (upstream, not shown in the Figure) in terms of attenuation, phase-shift and scattering. In a conventional system, a single detector line 11 in form of a Si-sensor with a single Si-strip anode is used. In contrast thereto, the line detector 1 according to the invention and as shown in FIG. 1 comprises eight independent detector lines 11 in form of eight independent anode strips, or in other words, eight pixels of a pixelated silicon anode structure to sense the Moiré pattern.

[0039] The Moiré pattern frequency is adjusted to the total coverage of the (in the shown implementation) eight anode strips or sensor channels to sample at least one complete period of intensity modulation due to phase-contrast effects.

[0040] The Moiré pattern formed after the interferometer will be sensed by here eight independent readout channels allowing phase-retrieval with the Fourier method for each frame of readout. The channel density is thereby increased by a factor of eight.

[0041] In FIG. 1, the detector lines 11 are inclined in a non-perpendicular direction with an acute angle α relative to the axis A of symmetry of the X-ray beam 2. The detector lines 11 are inclined to improve an X-ray stopping power of the detector lines 11. In other words, a grazing-angle illumination of Si-wafers as detector lines 11 is used to improve stopping power in contrast to conventional systems. For example, the X-ray beam 2 after two post-collimator blades 33 has a width of about 100 micrometer. Due to the strongly inclined incidence on the detector lines 11, the X-ray beam 2 widens to a millimeter-sized footprint on the sensor surface. This effect renders the channel density on the detector lines 11 in the plane of the drawing comparable to the channel density perpendicular to the drawing (e.g. a chest-wall-mammilla direction). The shown inclination of the detector lines 11 is optional. Also a non-inclined 2D detector is possible e.g. in case a sensor with higher atomic number is used.

[0042] FIG. 2 shows schematically and exemplarily an X-ray detector arrangement 10 for X-ray phase contrast tomo-synthesis imaging according to the invention. Here, the relative arrangement of four line detectors 1 is shown. Any other number of line detectors 1 is also possible, e.g. 21 line detectors 1. The drawing is not for scale but indicates the small dimensions of each post-collimator 33 slit compared to the distance between two detector lines 11.

[0043] Several grating components (comprising a common source grating and each a phase grating 31 and an analyzer grating 32) configured to create a Moiré pattern in the X-ray beam 2 are shown in FIG. 2 as independently arranged in front of each line detector 1 when seen in the direction of the X-ray beam 2 (source grating is not shown). Not shown, but also possible is that one grating unit (source grating, phase grating 31 and analyzer grating 32) is arranged in front of and covers the entirety of all line detectors 1 at the same time when seen in the direction of the X-ray beam 2.

[0044] FIG. 3 shows a perspective view of a mammography system as an example for an imaging system 24 for X-ray phase contrast tomo-synthesis imaging of an object according to the present invention. The imaging system 24 comprises an X-ray source arrangement 12, a grating arrangement (not shown) and an X-ray detector arrangement 10 mounted to a gantry 30 or movement structure. The imaging system 24 further comprises an object support 36 or lower breast support paddle and an upper breast support paddle 38, which can be displaced in relation to each other in order to receive a breast to be examined as the object. For the acquisition, the breast stays in place and the gantry 30 during operation moves in relation to the breast. More specifically during operation the gantry 30 rotates, in directions 26 or 28, around an axis of rotation situated below the X-ray detector arrangement 10 when seen in the direction of an X-ray beam 2. It is also possible to implement a movement of the object, while the gantry 30 stays in place. The movement can be a rotational or a translational movement or a combination of both.

[0045] FIG. 4 shows a schematic overview of steps of an exemplary method for X-ray phase contrast tomo-synthesis imaging. The exemplary method comprises the following steps:

[0046] In a first step S1, providing an X-beam passing through an X-ray detector arrangement 10.

[0047] In a second step S2, detecting a Moiré pattern in at least a portion of the X-ray beam 2.

[0048] The X-ray detector arrangement 10 comprises several line detectors 1, wherein each line detector 1 is configured to detect the Moiré pattern in at least a portion of the X-ray beam 2. Each line detector 1 comprises several detector lines 11 and a width W of each line detector 1 equals one period or an integer multiple of the period of the Moiré pattern.

[0049] In an optional third step S3 (not shown), the exemplary method further comprises a using of the data detected by the detector lines 11 of each line detector 1 for generating images based on attenuation, phase-gradient and scatter information. The latter can be determined either by the Fourier method of phase-retrieval under the assumption that the spatial resolution in the scan direction is of the order of the width of a single line-detector followed by FBP reconstruction of the retrieved attenuation, phase-gradient and scatter information, or, if the above assumption is not valid, by a combined iterative reconstruction of the three images via phase detection or iterative reconstruction techniques.

[0050] In another exemplary embodiment of the present invention, a computer program or a computer program element is provided that is characterized by being adapted to execute the method steps of the method according to one of the preceding embodiments, on an appropriate system.

[0051] The computer program element might therefore be stored on a computer unit, which might also be part of an embodiment of the present invention. This computing unit may be adapted to perform or induce a performing of the steps of the method described above. Moreover, it may be adapted to operate the components of the above described apparatus. The computing unit can be adapted to operate automatically and/or to execute the orders of a user. A computer program may be loaded into a working memory of a data processor. The data processor may thus be equipped to carry out the method of the invention.

[0052] This exemplary embodiment of the invention covers both, a computer program that right from the beginning uses the invention and a computer program that by means of an up-date turns an existing program into a program that uses the invention.

[0053] Further on, the computer program element might be able to provide all necessary steps to fulfil the procedure of an exemplary embodiment of the method as described above.

[0054] According to a further exemplary embodiment of the present invention, a computer readable medium, such as a CD-ROM, is presented wherein the computer readable medium has a computer program element stored on it, which computer program element is described by the preceding section.

[0055] A computer program may be stored and/or distributed on a suitable medium, such as an optical storage medium or a solid state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the internet or other wired or wireless telecommunication systems.

[0056] However, the computer program may also be presented over a network like the World Wide Web and can be downloaded into the working memory of a data processor from such a network. According to a further exemplary embodiment of the present invention, a medium for making a computer program element available for downloading is provided, which computer program element is arranged to perform a method according to one of the previously described embodiments of the invention.

[0057] It has to be noted that embodiments of the invention are described with reference to different subject matters. In particular, some embodiments are described with reference to method type claims whereas other embodiments are described with reference to the device type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters is considered to be disclosed with this application. However, all features can be combined providing synergetic effects that are more than the simple summation of the features.

[0058] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing a claimed invention, from a study of the drawings, the disclosure, and the dependent claims.

[0059] In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfil the functions of several items re-cited in the claims. The mere fact that certain measures are re-cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.