Methods, systems, and computer-readable storage media for enhanced phase-contrast x-ray imaging
Systems and methods that directly image attenuation-based object grid, use a source grid to improve imaging of the object grid using a high-energy polychromatic source, and use a detector grid having gratings oriented substantially orthogonally to that of the object grid, can address artifacts and beam hardening effects that limit the quality and discriminatory power of high-energy x-ray imaging that includes phase contrast.
1. A method comprising:
emitting x-rays from an x-ray source;
forming a patterned beam using an object grating placed proximal to an object to be imaged and between the x-ray source and a detector grating;
acquiring through the detector grating a first image with the object and a second image without the object;
measuring visibilities of the object grating from the first and second images to determine an object grating visibility reduction due to scatter and beam hardening;
measuring visibilities of the detector grating from the first and second images to determine a detector grating visibility reduction due to beam hardening; and
applying a beam hardening correction based on a comparison of the object grating visibility reduction and the detector grating visibility reduction to generate a corrected scatter image.
2. The method of claim 1 , comprising creating a series of periodically repeating apparent sources from the x-rays using a source grating situated proximal to the x-ray source, wherein the patterned beam is formed by patterning the series of periodically repeating apparent sources.
3. The method of claim 2 , wherein the source, object, and detector gratings have respective grating elements, wherein the object grating is placed at distances L 1 from the source grating and L 2 from the detector grating, wherein the periodicities, P, of the source and object grating elements are related by P source =P object *[(L 1 +L 2 )/L 2 ] and wherein the source and object grating elements are substantially parallel.
4. The method of claim 3 , wherein the detector grating elements are oriented substantially orthogonally relative to the object grating elements and a beam axis and wherein the object grating and the detector grating have a substantially equivalent x-ray attenuating factor.
5. The method of claim 2 , further comprising tilting the source grating by rotating the grating about an axis parallel to grating element lines.
6. The method of claim 2 , wherein the acquiring includes detecting the images with a detector, wherein the object grating is approximately equidistant between the source and the detector.
7. The method of claim 6 , wherein the detector grating has a periodicity, P detector , equivalent to that of the source grating, P source .
8. The method of claim 2 , wherein the source grating, object grating, detector grating, or combinations thereof have grating elements comprising a parallel line pattern.
9. The method of claim 1 , wherein the emitting the x-rays comprises emitting the x-rays from a polychromatic source operating at an endpoint energy greater than or equal to 100 keV and generating a spot size greater than or equal to 0.5 mm.
10. The method of claim 9 , further comprising operating the polychromatic source at an endpoint energy greater than or equal to 150 keV, 160 keV, 175 keV, 200 keV, or 450 keV.
11. The method of claim 1 , further comprising tilting the object grating and detector grating by rotating the gratings about an axis parallel to grating element lines.
12. The method of claim 1 , wherein the object and detector gratings comprise an equivalent material and have an equivalent thickness.
13. The method of claim 1 , wherein the object to be imaged is a scatter test object calibration standard and further comprising performing a calibration of x-ray scatter, the scatter test object calibration standard comprising metal or metal oxide particles distributed in a polymer matrix and having a stepped-wedge geometry of at least three different thicknesses.
14. The method of claim 1 , wherein the object to be imaged is a beam hardening test object calibration standard and further comprising performing a calibration of beam hardening, the beam hardening test object calibration standard comprising three or more homogeneous materials in a range of atomic numbers, with no large density variations on length scales between 10 nm and 200 microns, and have a thickness such that 10-90% of the x-ray intensity is transmitted through the test object.
15. A system comprising:
an x-ray source configured to provide source x-rays;
a detector;
an object grating and a detector grating, wherein the object grating is proximal to a position of an object to be imaged and situated between the x-ray source and the detector grating; and
processing circuitry operably connected to the detector and configured to execute computer-readable instructions to:
acquire through the detector grating a first image with the object and a second image without the object;
measure visibilities of the object grating from the first and second images to determine an object grating visibility reduction due to scatter and beam hardening;
measure visibilities of the detector grating from the first and second images to determine a detector grating visibility reduction due to beam hardening; and
apply a beam hardening correction based on a comparison of the object grating visibility reduction and the detector grating visibility reduction to generate a corrected scatter image.
16. The system of claim 15 , further comprising a source grating configured to create a series of periodically repeating apparent sources from the source x-rays, wherein the object grating is configured to pattern the series of periodically repeating apparent sources into a patterned beam.
17. The system of claim 16 , wherein the source, object, and detector gratings have respective grating elements, wherein the object grating is placed at distance L 1 from the source grating and distance L 2 from the detector grating, wherein the periodicities of the source and object grating elements are related by P source =P object *[(L 1 +L 2 )/L 2 ].
18. The system of claim 17 , wherein the detector grating elements are oriented orthogonally relative to the object grating elements and a beam axis and wherein the detector and object gratings having an equivalent x-ray attenuation factor.
19. The system of claim 17 , wherein the object grating and detector grating are positioned such that the object grating elements and the detector grating elements are tilted by a rotation of the gratings about an axis parallel to grating element lines.
20. The system of claim 16 , wherein the source grating is positioned such that source grating elements are tilted by a rotation of the grating about an axis parallel to grating element lines.
21. The system of claim 16 , wherein the object grating is positioned approximately equidistant between the source and the detector.
22. The system of claim 21 , wherein the detector grating has a periodicity, P detector , equivalent to that of the source grating, P source .
23. The system of claim 16 , wherein the source grating, object grating, detector grating, or combinations thereof have grating elements comprising a parallel line pattern.
24. The system of claim 15 , wherein the x-ray source comprises a polychromatic source configured to operate at an endpoint energy greater than or equal to 100 keV and a spot size greater than 0.5 mm.
25. The system of claim 24 , wherein the polychromatic source is configured to provide source x-rays at an endpoint energy greater than or equal to 150 keV, 160 keV, 175 keV, 200 keV, or 450 keV.
26. The system of claim 15 , wherein the detector grating abuts the detector.
27. The system of claim 15 , wherein the object and detector gratings comprise an equivalent material and have an equivalent thickness.
28. A non-transitory computer readable storage medium storing one or more programs, the one or more programs comprising instructions, which when executed by one or more processors operably connected to an x-ray imaging system that comprises:
an x-ray source;
an object grating proximal to a position of an object to be imaged; and
a detector grating having detector grating elements that are oriented orthogonally relative to object grating elements and a beam axis;
cause the x-ray imaging system to:
acquire through the detector grating a first image with the object and a second image without the object;
measure visibilities of the object grating from the first and second images to determine an object grating visibility reduction due to scatter and beam hardening;
measure visibilities of the detector grating from the first and second images to determine a detector grating visibility reduction due to beam hardening; and
apply a beam hardening correction based on a comparison of the object grating visibility reduction and the detector grating visibility reduction to generate a corrected scatter image.
29. The non-transitory computer readable storage medium of claim 28 storing one or more programs, the one or more programs comprising instructions, which when executed by one or more processors operably connected to the x-ray imaging system cause the x-ray imaging system to perform a calibration, wherein the object to be imaged is a scatter test object, a beam hardening test object, or both.