X-ray interferometric imaging system
An x-ray interferometric imaging system in which the x-ray source comprises a target having a plurality of structured coherent sub-sources of x-rays embedded in a thermally conducting substrate. The system additionally comprises a beam-splitting grating G 1 that establishes a Talbot interference pattern, which may be a π phase-shifting grating, and an x-ray detector to convert two-dimensional x-ray intensities into electronic signals. The system may also comprise a second analyzer grating G 2 that may be placed in front of the detector to form additional interference fringes, a means to translate the second grating G 2 relative to the detector. The system may additionally comprise an antiscattering grid to reduce signals from scattered x-rays. Various configurations of dark-field and bright-field detectors are also disclosed.
1. An x-ray transmission imaging system comprising:
a source of x-rays comprising:
a vacuum chamber;
an emitter for an electron beam; and
an electron target comprising:
a substrate comprising a first material and, embedded in the substrate,
at least a plurality of discrete structures comprising a second material selected for its x-ray generating properties,
and in which said plurality of discrete structures; are arranged within a periodic pattern of sub-sources;
a stage to position and orient an object to be examined;
an x-ray detector comprising a two-dimensional array of x-ray detecting elements, positioned to detect x-rays transmitted through the object to be examined;
said x-ray transmission system additionally comprising:
a scattering rejection apparatus placed between the position of the object to be examined and the detector, comprising:
a beam-splitting x-ray grating comprising periodic structures that form an x-ray phase-shifting grating positioned to diffract x-rays generated by the sub-sources of x-rays so that a Talbot interference pattern is formed by the interaction of the x-rays generated by the source of x-rays with the beam splitting grating; and
an antiscattering grid having a periodic array of septa comprising an x-ray absorbing material positioned between the beam splitting x-ray grating and the detector; and
a controller for adjusting the position of the anti-scattering grid relative to the Talbot interference pattern;
in which the dimensions and periodicity of the septa of the antiscattering grid are selected to correspond to the dimensions of the Talbot interference pattern, and the septa of the antiscattering grid are positioned such that the septa are aligned with the nodes of the Talbot interference pattern.
2. The x-ray transmission imaging system of claim 1 , in which
the x-ray phase shifting grating comprises structures to introduce a phase-shift of approximately π radians for a predetermined x-ray wavelength.
3. The x-ray transmission imaging system of claim 1 , in which
the x-ray phase shifting grating comprises structures to introduce a phase-shift of approximately π/2 radians for a predetermined x-ray wavelength.
4. The x-ray transmission imaging system of claim 1 , in which
the periodic structures of the x-ray phase-shifting grating have a period p 1 related to a dimension a for at least one of the discrete structures of the x-ray target by:
p
1
<
λ
L
a
where λ is a predetermined x-ray wavelength,
and L is the distance between the target and the beam-splitting x-ray grating.
5. The x-ray transmission imaging system of claim 1 , in which the septa of the antiscattering grid comprise
a high Z material selected from the group consisting of:
tin, platinum, gold, tungsten, tantalum, molybdenum, nickel, lead, copper and gadolinium.
6. The x-ray transmission imaging system of claim 1 , in which
the antiscattering grid additionally comprises a substrate comprising an x-ray transparent material.
7. The x-ray transmission imaging system of claim 1 , in which
one or more of the septa have a height that is greater than 5 times the width of the gap between said one or more of the septa and its neighboring septa.
8. The x-ray transmission imaging system of claim 1 , in which
the period of the septa of the antiscattering grid is an integer multiple of the lateral period of the Talbot interference pattern.
9. The x-ray transmission imaging system of claim 1 , additionally comprising:
a second antiscattering grid comprising an x-ray absorbing material positioned between the first antiscattering grid and the detector.
10. The x-ray transmission imaging system of claim 1 , in which the contrast of the Talbot interference pattern is greater than 20%.
11. The x-ray transmission imaging system of claim 1 , in which
the plurality of discrete structures are arranged in a two-dimensional periodic pattern of sub-sources.
12. The x-ray transmission imaging system of claim 11 , in which
the two-dimensional periodic pattern of sub-sources comprises a mesh pattern.
13. The x-ray transmission imaging system of claim 11 , in which
the two-dimensional periodic pattern of sub-sources comprises a checkerboard.
14. The x-ray transmission imaging system of claim 11 , in which
the x-ray phase shifting grating comprises a two-dimensional periodic pattern of phase-shifting structures.
15. The x-ray transmission imaging system of claim 1 , additionally comprising:
an analyzer grating having periodic structures of x-ray absorbing material positioned between the antiscattering grid and the detector.
16. The x-ray transmission imaging system of claim 1 , in which
the Talbot interference pattern comprises diverging interference fringes.