Focus-detector arrangement of an X-ray apparatus for generating projective or tomographic phase contrast recordings
A focus-detector arrangement of an X-ray apparatus is disclosed for generating projective or tomographic phase contrast recordings of an observed region of a subject. In at least one embodiment, the arrangement includes a radiation source which emits a coherent or quasi-coherent X-radiation and irradiates the subject, a phase grating which is arranged behind the subject in the beam path of the radiation source and generates an interference pattern of the X-radiation in a predetermined energy range, and an analysis-detector system which detects at least the interference pattern generated by the phase grating in respect of its phase shift with position resolution. Further, the beam path of the X-radiation used diverges in at least one plane between the focus and the detector.
1. A focus-detector arrangement of an X-ray apparatus for generating at least one of projective and tomographic phase contrast recordings of an observed region of a subject, comprising:
a radiation source to emit at least one of a coherent and quasi-coherent X-radiation and to irradiate the subject;
a phase grating, arranged behind the subject in a direction of a beam path from the radiation source, to generate an interference pattern of the X-radiation in an energy range; and
an analysis-detector system including an analyzer grating, to detect at least the interference pattern generated by the phase grating in respect of its phase shift with position resolution, wherein the beam path of the X-radiation used diverges in at least one plane between the focus and the detector, wherein the following geometrical relationship is satisfied:
g
2
=
1
2
r
1
+
d
r
1
g
1
,
where d corresponds to the distance between the phase grating G 1 and the analyzer grating G 2 , r 1 corresponds to the distance between the radiation source and the phase grating, g 2 corresponds to the period of the analyzer grating (G 2 ), and g 1 corresponds to the period of the phase grating (G 1 ).
2. The focus-detector arrangement as claimed in claim 1 , wherein the beam path of the X-radiation used diverges in two planes between the focus and the detector.
3. The focus-detector arrangement as claimed in claim 1 , wherein the region of the subject, as seen in projection in the direction of the optical axis of the beam path, is relatively smaller than the utilized region of the phase grating downstream in the beam path, which in turn is relatively smaller than the utilized region of the analysis-detector system downstream in the beam path.
4. The focus-detector arrangement as claimed in claim 1 , wherein the distance from the radiation source to the analysis-detector system is at least two times as great as the distance from the radiation source to the subject.
5. The focus-detector arrangement as claimed in claim 1 , wherein the distance from the radiation source to the detector of the analysis-detector system is at least 10× as great as the distance from the radiation source to the subject.
6. The focus-detector arrangement as claimed in claim 1 , wherein the phase grating is arranged relatively closer to the analysis-detector system than to the subject in the beam direction.
7. The focus-detector arrangement as claimed in claim 1 , wherein the phase grating is arranged relatively closer to the subject than to the analysis-detector system in the beam direction.
8. The focus-detector arrangement as claimed in claim 1 , wherein the analysis-detector system comprises an analyzer grating with a detector downstream in the beam direction having a multiplicity of detector elements.
9. The focus-detector arrangement as claimed in claim 8 , wherein the distance (d m ) from the phase grating (G 1 ) to the analyzer grating (G 2 ) fulfills the following geometrical relationship:
d
m
=
(
m
-
1
2
)
·
g
1
2
4
·
λ
,
where:
d m =distance from the phase grating (G 1 ) to the analyzer grating (G 2 );
m=1,2,3,. . . ;
g 1 =grating period of the phase grating (G 1 );
λ=wavelength of the X-radiation used.
10. The focus-detector arrangement as claimed in claim 1 , wherein the radiation source comprises a focus which is designed as a microfocus in relation to the geometrical proportions of the focus-detector arrangement, such that:
s
≤
λ
r
1
g
1
with the size s of the focus, the wavelength λ of the radiation used, the radial distance r 1 from the focus to the phase grating and the grating period g 1 of the phase grating.
11. The focus-detector arrangement as claimed in claim 1 , wherein the radiation source comprises a focus and an X-ray optical grating arranged in the beam direction.
12. An X-ray system for generating projective phase contrast recordings with a magnified representation of a subject, comprising the focus-detector arrangement as claimed in claim 1 .
13. An X-ray computer tomography system for generating tomographic phase contrast recordings with a magnifying representation of a subject, comprising the focus-detector arrangement as claimed in claim 1 .
14. The focus-detector arrangement as claimed in claim 2 , wherein the region of the subject, as seen in projection in the direction of the optical axis of the beam path, is relatively smaller than the utilized region of the phase grating downstream in the beam path, which in turn is relatively smaller than the utilized region of the analysis-detector system downstream in the beam path.
15. The focus-detector arrangement as claimed in claim 1 , wherein the phase grating is arranged between the subject and the analysis-detector system.
16. The focus-detector arrangement as claimed in claim 1 , wherein the analysis-detector system measures a quantitative phase displacement of each ray of the emitted radiation using at least three measuring operations.