Grating for phase-contrast imaging

Abstract

The invention relates to gratings for X-ray differential phase-contrast imaging, a focus detector arrangement and X-ray system for generating phase-contrast images of an object and a method of phase-contrast imaging for examining an object of interest. In order to provide gratings with a high aspect ratio but low costs, a grating for X-ray differential phase-contrast imaging is proposed, comprising a first sub-grating (112), and at least a second sub-grating (114; 116; 118), wherein the sub-gratings each comprise a body structure (120) with bars (122) and gaps (124) being arranged periodically with a pitch (a), wherein the sub-gratings (112; 114; 116; 118) are arranged consecutively in the direction of the X-ray beam, and wherein the sub-gratings (112; 114; 116; 118) are positioned displaced to each other perpendicularly to the X-ray beam.

Claims

1. A grating for X-ray differential phase-contrast imaging, comprising: a first sub-grating; and at least a second sub-grating, the sub-gratings each comprising a body structure with bars, and gaps, arranged periodically with a pitch, said sub-gratings being arranged consecutively for receiving an X-ray beam and being positioned laterally displaced from each other, said grating being configured as one of a phase grating, an analyzer grating, and an absorption grating.

2. The grating of claim 1, projections of said sub-gratings resulting in an effective grating with a smaller effective pitch than the pitches of said sub-gratings.

3. The grating of claim 1, said sub-gratings having the same pitch.

4. The grating of claim 3, wherein the displacement of one of said sub-gratings from another one of said sub-gratings is an offset amounting to a fraction of half the pitch.

5. The grating of claim 1, wherein the sub-gratings have an equal bars/gap ratio.

6. A grating for X-ray differential phase-contrast imaging, comprising: a first sub-grating; and at least a second sub-grating, the sub-gratings each comprising a body structure with bars, and gaps, arranged periodically with a pitch, said sub-gratings being arranged consecutively for receiving an X-ray beam and being positioned laterally displaced from each other, wherein the pitch of one of said sub-gratings is a multiple of the pitch of another one of said sub-gratings.

7. A grating for X-ray differential phase-contrast imaging, comprising: a first sub-grating; and at least a second sub-grating, the sub-gratings each comprising a body structure with bars, and gaps, arranged periodically with a pitch, said sub-gratings being arranged consecutively for receiving an X-ray beam and being positioned laterally displaced from each other, wherein said sub-gratings each has a height that creates a π-phase shift at a design wavelength.

8. A grating for X-ray differential phase-contrast imaging, comprising: a first sub-grating; and at least a second sub-grating, the sub-gratings each comprising a body structure with bars, and gaps, arranged periodically with a pitch, said sub-gratings being arranged consecutively for receiving an X-ray beam and being positioned laterally displaced from each other, said sub-gratings being arranged on a single wafer.

9. A detector arrangement of an X-ray system for generating phase-contrast images of an object, said arrangement comprising: an X-ray source; a source grating; a phase grating; an analyzer grating; and a detector, wherein the X-ray source is adapted to generate polychromatic spectrum of X-rays; and wherein at least one of the phase and analyzer gratings is a grating according to claim 1.

10. An X-ray system for generating phase-contrast data of an object, said system comprising the detector arrangement of claim 9.

11. A method of phase-contrast imaging for examining an object of interest, comprising: applying X-ray radiation beams of an X-ray source to a source-grating splitting the beams; applying the splitted beams to a phase grating recombining the splitted beams in an analyzer plane; applying the recombined beams to an analyzer grating; and recording raw image data with a sensor while stepping the analyzer grating transversely over one period of the analyzer grating, wherein at least one of the phase and analyzer gratings is a grating according to claim 1.

12. A non-transitory computer-readable medium embodying a computer program for examination of an object of interest via phase-contrast imaging, said program having instructions executable by a processor of an X-ray system for causing the system to carry out a plurality of acts, among said plurality there being the acts of: applying (52) X-ray radiation beams of an X-ray source to a source-grating splitting the beams; applying the splitted beams to a phase grating recombining the splitted beams in an analyzer plane; applying the recombined beams to an analyzer grating; and recording raw image data with a sensor while stepping the analyzer grating transversely over one period of the analyzer grating; wherein at least one of the phase and analyzer gratings is a grating according to claim 1.

13. The grating of claim 1, said sub-gratings having respective front surfaces and being arranged so that said surfaces are disposed normal to said beam and face in a direction of arrival of said beam.

14. The grating of claim 1, a given sub-grating from among said sub-gratings comprising silicon, and an additional gold layer covering said bars, and said gaps, of the body structure of said given sub-grating.

15. The grating of claim 2, said effective grating being defined by sidewalls in a propagation direction of an X-ray beam, in which direction said sub-gratings face.

16. The grating of claim 15, a given sub-grating from among said sub-gratings comprising silicon, and an additional gold layer covering said bars, and said gaps, of the body structure of said given sub-grating.

17. The computer readable medium of claim 12, among said plurality of acts there being a further act of computing the recorded raw image data into display data.

18. The grating of claim 1, said sub-gratings facing in a same direction.

19. The grating of claim 18, the displacement being normal to said direction.

20. The grating of claim 18, the respective displacements of each of said sub-gratings from the other one or more of said sub-gratings being normal to said direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects of the invention will be apparent from the exemplary embodiments described hereinafter with reference to the drawings.

(2) FIG. 1 schematically shows an example of an X-ray system;

(3) FIG. 2 schematically shows a detection arrangement of an X-ray system with different gratings;

(4) FIG. 3 schematically shows a first embodiment of a grating comprising two sub-gratings;

(5) FIG. 4 schematically shows another embodiment with three sub-gratings;

(6) FIG. 5 schematically shows a further embodiment with two sub-gratings;

(7) FIG. 6 schematically shows a further exemplary embodiment with three sub-gratings;

(8) FIG. 7 schematically shows a further exemplary embodiment with four sub-gratings;

(9) FIG. 8 schematically shows a further exemplary embodiment with three sub-gratings; and

(10) FIG. 9 schematically shows a further exemplary embodiment with three sub-gratings;

(11) FIG. 10 schematically shows a further exemplary embodiment with two sub-gratings arranged on a single wafer;

(12) FIG. 11 schematically shows a further exemplary embodiment with two sub-gratings; p FIG. 12 schematically shows the arrangement of FIG. 2 as a phase grating for a detector arrangement of an X-ray system;

(13) FIG. 13 schematically shows the arrangement of FIG. 5 as a phase grating for a detector arrangement of an X-ray system;

(14) FIG. 14 shows an equivalent single grating for the two sub-gratings of FIG. 12 and FIG. 13;

(15) FIG. 15 schematically shows the arrangement of FIG. 2 as an absorption grating for a detector arrangement;

(16) FIG. 16 schematically shows the arrangement of FIG. 5 as an absorption grating for a detector arrangement;

(17) FIG. 17 shows an equivalent single grating for the two sub-gratings of FIG. 15 and FIG. 16; and

(18) FIG. 18 shows a method for generating phase-contrast X-ray images of according to the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(19) FIG. 1 schematically shows an X-ray imaging system 10 with an examination apparatus for generating phase-contrast images of an object. The examination apparatus comprises an X-ray image acquisition device with a source of X-ray radiation 12 provided to generate X-ray radiation beams with a conventional X-ray source. A table 14 is provided to receive a subject to be examined. Further, an X-ray image detection module 16 is located opposite the source of X-ray radiation 12, i.e. during the radiation procedure the subject is located between the source of X-ray radiation 12 and the detection module 16. The latter is sending data to a data processing unit or calculation unit 18, which is connected to both the detection module 16 and the radiation source 12. The calculation unit 18 is located underneath the table 14 to save space within the examination room. Of course, it could also be located at a different place, such as a different laboratory.

(20) Furthermore, a display device 20 is arranged in the vicinity of a table 14 to display information to the person operating the X-ray imaging system, which can be a clinician for example. Preferably, the display device is movably mounted to allow for an individual adjustment depending on the examination situation. Also, an interface unit 22 is arranged to input information by the user. Basically, the image detection module 16 generates image data by exposing the subject to X-ray radiation, wherein said image data is further processed in the data processing unit 18. It is noted that the example shown is of a so-called C-type X-ray image acquisition device. The X-ray image acquisition device comprises an arm in form of a C where the image detection module 16 is arranged at one end of the C-arm and the source of X-ray radiation 12 is located at the opposite end of the C-arm. The C-arm is movably mounted and can be rotated around the object of interest located on the table 14. In other words, it is possible to acquire images with different directions of view.

(21) FIG. 2 schematically shows a focus detector arrangement 24 of an X-ray system for generating phase-contrast images of an object 26. A conventional X-ray source 28 is provided applying X-ray radiation beams 30 to a source grating 32 splitting the beams 30. The splitted beams are then further applied to a phase grating 34 recombining the split beams in an analyzer plane. The object 26, for example a patient or a sample shown in FIG. 2, is arranged between the source grating 32 and the phase grating 34. After recombining the split beams behind the phase grating 34 the recombined beam 30 is applied to an analyzer grating 36. Finally a detector 38 is provided recording raw image data with a sensor while the analyzer grating 36 is stepped transversally over one period of the analyzer grating 36. The arrangement of at least one of the gratings 34, 36 comprising inventive sub-gratings is described in the following. It is noted that the sub-gratings according to the invention can also be applied to the source grating 32.

(22) In FIGS. 3 to 9 different exemplary embodiments of a grating according to the invention are shown comprising at least two sub-gratings.

(23) In FIG. 3 a first sub-grating 112a and a second sub-grating 114a are shown. The sub-gratings 112a, 114a each comprise a body structure 120a with bars 122a and gaps 124a being arranged periodically with a pitch a.sub.a. The sub-grating 112a, 114a are arranged consecutively in the direction of the X-ray beam (not shown in FIGS. 3 to 9). For an easier understanding the sub-gratings are shown horizontally, whereas the sub-gratings in FIG. 2 are arranged vertically. Simply said, in FIGS. 3 to 17 the direction of the X-ray beam is from top of the page to the bottom of the page.

(24) The sub-gratings 112a, 114a are positioned with a displacement d.sub.a in relation to each other in a perpendicularly direction to the X-ray beam. In other words, the sub-grating 114a is arranged in relation to the sub-grating 112a with the offset d.sub.a such that the sub-grating 114a is shifted towards the right in relation to sub-grating 112a.

(25) The sub-gratings 112a, 114a of FIG. 3 have the same pitch a.sub.a.

(26) Further, the sub-gratings 112a, 114a have an equal bars/gap ratio (s.sub.a/t.sub.a). Hence, the width s.sub.a of a bar 122a is equal to the width t.sub.a of a gap 124a.

(27) The displacement d.sub.a is a fraction of half the pitch a.sub.a.

(28) The projections of the sub-gratings 112a, 114a result in an effective grating 130a (depicted by lines 131a) with a smaller effective pitch z.sub.a than the pitch a.sub.a of the sub-gratings 112a, 114a. In FIG. 3 the displacement d.sub.a is equal to the effective pitch z.sub.a.

(29) In a further exemplary embodiment the grating comprises three sub-gratings 112b, 114b, 116b.

(30) It is noted that similar features of the different exemplary embodiments have the same reference numeral added by a letter to indicate the different embodiments. For easier reading of the claims, the reference numbers in the claims are shown without the letter indizes.

(31) The sub-gratings of FIG. 4 have the same pitch a.sub.b. Here too, the bars/gap ratio (s.sub.b/t.sub.b) is 1/1.

(32) The sub-gratings 112b, 114b, 116b also comprise a body structure 120b with bars 122b and gaps 124b. Although the gaps and the bars 124b, 122b have a larger width compared to the respective width of FIG. 3, an effective grating 130b is achieved with an effective pitch z.sub.b which is the same as the effective pitch z.sub.a of FIG. 3.

(33) In FIG. 5 the grating comprises two sub-gratings 112c and 114c. The sub-gratings also comprise a body structure 120c with bars 122c and gaps 124c. The width of the gaps 124c is larger than the width of the bar 122c, hence the bars/gap ratio (s.sub.c/t.sub.c) is smaller than 1. The two sub-gratings 112c and 114c are arranged such that the effective grating 130c and the effective pitch z.sub.c is the same as in the figures discussed above. In FIG. 5 the width of the bars s.sub.c is equal to the effective pitch z.sub.c. The width of the gap t.sub.c is 3 times the width of the bars s.sub.c. The pitch z.sub.c of the sub-gratings which is the same for both sub-gratings can be calculated by the equation: a=2*n*z where n is the number of sub-gratings and z is the effective pitch.

(34) In a further exemplary embodiment, shown in. FIG. 6, three sub-gratings 112d, 114d, 116d are provided in a similar way as discussed above. The width of the gap 124d can be larger compared to the sub-gratings of FIG. 5, although the same effective grating 130d is provided due to the larger number of sub-gratings.

(35) This is also shown in FIG. 7 where four sub-gratings 112e, 114e, 116e and 118e are shown. Here the sub-gratings have the same pitch z.sub.e and are arranged with an offset of: d.sub.e=2*z.sub.e; z.sub.e being the effective pitch illustrated for a better understanding beneath each schematic description of the sub-gratings in relation with the effective grating 130e.

(36) In a further exemplary embodiment in FIG. 8, three sub-gratings 112f, 114f, 116f are provided where one of the sub-gratings, in FIG. 8 the middle sub-grating 114f, is having a different pitch a.sub.f2 compared to the pitch a.sub.f1 of the other sub-gratings 112f and 116f. In fact, the pitch a.sub.f1 of the first and third sub-gratings 112f, 116f is a multiple of the pitch a.sub.f2 of the middle sub-grating 114f. In fact the ratio of the pitches of the sub-gratings is 1/2. Hence, the pitch a.sub.f1 of the upper sub-grating 112f is twice the pitch a.sub.f1 of the second sub-grating 114f. Here too, an effective 130f grating with an effective pitch similar to the embodiment discussed above is achieved.

(37) Whereas in FIG. 8 the width of the bars of all three sub-gratings is having the same size, in a further exemplary embodiment shown in FIG. 9 the width of the bars of the sub-gratings is different. In FIG. 9 three sub-gratings 112g, 114g and 116g are arranged such that the middle sub-grating 114g is having a pitch a.sub.g2 which is half the amount of a pitch a.sub.g1 of the upper and lower sub-gratings 112g, 116g. The three sub-gratings are offset to each other such that the effective grating 130g with an effective pitch, shown underneath by lines, is the same as the effective pitches of the embodiments discussed above.

(38) Providing sub-gratings which are arranged with an offset to each other allows an easier manufacturing of the sub-gratings because the gaps that are, for example, etched into the body structure's substance are wider and thus easier to apply during manufacture. However, the projections of the sub-gratings result in an effective grating with an effective pitch which is smaller than the pitches of the sub-gratings.

(39) In a further exemplary embodiment the sub-gratings 112h, 114h are arranged on a single wafer 111h, shown in FIG. 10. Here two sub-gratings are provided with offset pitches a.sub.h by offset d.sub.h and effective pitch z.sub.h, shown in FIG.10 on the effective grating 130h.

(40) In a further exemplary embodiment, two sub-gratings 112j, 114j having a pitch a.sub.j are configured such that they are arrangeable with their closed sides or flat sides 116j, 118j adjacent to each other (FIG. 11). This provides the advantage that two individual sub-gratings 112j, 114j can be manufactured which are then attached to each other so that no further positioning or alignment steps of the two sub-gratings in relation to each other are necessary. An effective grating 130j of smaller pitch z.sub.j results.

(41) In FIG. 12 a grating for a phase grating is shown comprising two sub-gratings 112k and 114k. The sub-gratings 112k, 114k each have the same pitch and the bars/gap ratio, i.e. s/t=1/1. FIG. 14 shows the equivalent grating 132 when providing only a single grating in order to achieve the same pitch as the effective pitch of the two sub-gratings 112k, 114k. It can be seen that the pitch a.sub.k of the sub-gratings is larger than the pitch z.sub.e of the equivalent grating 132.

(42) The same effective grating with the same effective pitch can also be achieved by providing two sub-gratings 1121, 1141 for a phase grating having the same pitch a.sub.1 but in contrary to the sub-gratings of FIG. 12, the bars/gap ratio (s/t) is smaller 1, in the exemplary embodiment in FIG. 13 the bars/gap ratio is 1/3. The equivalent is the same as for FIG. 12 (see FIG. 14).

(43) In FIGS. 15 and 16 a similar arrangement is provided for an absorption grating with high aspect ratio. In FIG. 15 two sub-gratings 112m, 114m having the same pitch are shown with a bars/gap ratio of 1/1; whereas, in FIG. 16 two sub-gratings 112n, 114n have a bars/gap ratio that is smaller than 1. The sub-gratings 112m, 114m, 112n, 114n respectively comprise silicon body structures 134m and 134n with an additional corresponding gold layer 136m, 136n. The results in an effective gold granting 138 shown underneath each pair of the sub-grantings 112m, 114m, 112n, 114n for illustrative purposes.

(44) FIG. 17 shows the equivalent grating 140 when providing only a single grating and the resulting pitch 142 due to the gold layer. It can be seen that in order to provide a grating with a high aspect ratio, a grating has to be provided with smaller gaps to provide the same effective grating as the combination of two sub-gratings shown in FIGS. 12, 13, 15 and 16. Hence, compared to the equivalent single gratings shown in FIGS. 14 and 17, the sub-gratings according to the invention can be manufactured in an easier and thus cheaper and more economic way.

(45) The sub-gratings can be used instead of single gratings, for example in phase-contrast X-ray imaging.

(46) The steps of an exemplary embodiment of a method are shown in FIG. 18. In a first step X-ray radiation beams of a conventional X-ray source 28 are applied 52 to a source-grating 32 where the beams are splitted 54. The source grating 32 comprises two sub-gratings (not shown in FIG. 18) arranged consecutively in the direction of the X-ray beam and positioned displaced to each other perpendicularly to the X-ray beam.

(47) The splitted beams are then transmitted 56 towards an object of interest 26, wherein the beams are passing through the object 26 where adsorption and refraction 58 occurs. The beams are further applied to a phase grating 34 where the splitted beams are recombined 60 in an analyser plane 62. Also, the phase grating 34 comprises two sub-gratings (not shown in FIG. 18). Then, the recombined beams are applied 64 to an analyzer grating 36 also comprising two sub-gratings (not shown in FIG. 18). Further, a sensor 38 is recording 66 raw image data 68 while the analyzer grating 36 is stepped transversely 70 over one period of the analyzer grating. Finally, the raw data 68 is transmitted 72 to a control unit 18 where the data is computed 74 into display data 76 to show 78 images on a display 20.

(48) 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.

(49) It should be noted that the term “comprising” does not exclude elements or steps and the “a” or “an” does not exclude a plurality. Also, elements described in association with different embodiments may be combined.