X-ray interferometer
Embodiments relate to an X-ray interferometer for imaging an object comprising: a phase grating for effecting in correspondence with the phase grating geometry a phase shift to at least a part of X-ray incident onto the phase grating; and an absorption grating for effecting in correspondence with the absorption grating geometry absorption to at least a part of X-ray incident onto the absorption grating. The grating period of the phase grating, and the grating period of the absorption grating may be dimensioned such that a detector for X-rays can be placed at a relatively large distance away from the absorption grating such the phase contrast sensitivity of the image of the object detected by the detector remains substantially unaffected.
1. A method for performing phase contrast imaging with an X-ray interferometer that is operative to irradiate an object with X-ray at a given radiation energy, the X-ray interferometer having a total setup length L tot , the method comprising:
a detector detecting radiation emitted by an X-ray source with a projection magnification M greater than 1 and having a sensor plane, wherein the total setup length L tot is a distance from a focal spot of the X-ray source to a plane of the detector;
a phase grating phase-shifting X-ray emanating from the object and which is incident onto the phase grating;
an absorption grating intensity modulating the phase-shifted X-ray from the phase grating;
positioning the phase grating between the X-ray source and the absorption grating at a distance I from the X-ray source;
positioning the absorption grating between the phase grating and the detector at a distance d from the phase grating;
positioning the detector at a distance d M from the absorption grating, the distance d M being at least 5 cm and up to 2 meters, and the distance d being less than half the total setup length L tot , where
M
=
d
M
+
d
+
1
1
-
d
s
;
positioning the object between the X-ray source and the phase grating at a distance d s from the phase grating, the distance d s being a distance between the phase grating and the plane which is perpendicular to an optical axis and intersects a geometric center of the object;
dimensioning the grating period of the phase grating and the grating period of the absorption grating such that,
d
=
n
.
η
.
p
1
.
p
2
8.
λ
and
l
=
d
.
p
1
η
.
p
2
-
p
1
where λ denotes a wavelength of the X-ray emitted by the X-ray source, n denotes a fractional Talbot order, η denotes a symmetry parameter, p 1 denotes the grating period of the phase grating and p 2 denotes the grating period of the absorption grating; and
dimensioning d s and d m so that a phase contrast sensitivity of an image of the object detected by the detector is not reduced with M greater than 1.
2. The method according to claim 1 , further comprising positioning the object at a distance from the phase grating which substantially equals zero.
3. The method according to claim 1 , further comprising dark-field illuminating the object to obtain a dark-field image thereof.
4. The method according to claim 1 , wherein the X-ray interferometer is implemented as a Talbot-Lau interferometer.
5. The method according to claim 1 , wherein the X-ray interferometer is implemented as a Talbot interferometer.
6. The method according to claim 1 , wherein the X-ray interferometer is operative at a fractional Talbot order of n=4.
7. The method according to claim 1 , further comprising laterally extensioning the phase grating, the absorption grating and the detector to cover a diverging field size of the X-ray emanating from the imaged object.
8. The method according to claim 1 , wherein during imaging, the distance between the object and the phase grating substantially equals zero.
9. The method according to claim 1 further comprising laterally dimensioning the phase grating and the absorption grating to allow for selecting the distance between the detector and the absorption grating to obtain, when imaging the object, a corresponding change in the projection magnification M between lateral dimensions of the image of the object and the object itself.
10. The method according to claim 8 , wherein the projection magnification M ranges from more than 1 to about at least 50.
11. The method according to claim 1 , wherein the grating period of the phase grating is equal or less than about 5 μm.
12. The method according to claim 1 , wherein the grating period of the absorption grating is equal or less than about 5 μm.
13. The method according to claim 1 , wherein the gratings periods of the absorption and phase grating are dimensioned such that the distance between the phase grating and absorption grating is small compared to the distance between the detector and the absorption grating and the distance between the source and the phase grating.
14. The method according to claim 1 , wherein lateral dimensions of the phase grating, the absorption grating and the detector are dimensioned such to cover a diverging field size of the X-ray emanating from the imaged object and wherein, during imaging, the distance between the object and the phase grating substantially equals zero.
15. The method according to claim 1 , wherein the gratings periods of the absorption and phase grating are dimensioned such that the distance between the phase grating and absorption grating is small compared to the distance between the source and the phase grating.
16. The method according to claim 1 , wherein the gratings periods of the absorption and phase grating are dimensioned such that the distance between the phase grating and absorption grating is small compared to the distance between the detector and the absorption grating and the distance between the source and the phase grating, and wherein, during imaging, the distance between the object and the phase grating substantially equals zero.