System and method for quantitative reconstruction of Zernike phase-contrast images
The principle of reciprocity states that full-field and scanning microscopes can produce equivalent images by interchanging the roles of condenser and detector. Thus, the contrast transfer function inversion previously used for images from scanning systems can be applied to Zernike phase contrast images. In more detail, a full-field x-ray imaging system for quantitatively reconstructing the phase shift through a specimen comprises a source that generates x-ray radiation, a condenser x-ray lens for projecting the x-ray radiation onto the specimen, an objective x-ray lens for imaging the x-ray radiation transmitted through the specimen, a phase-shifting device to shift the phase of portions of x-ray radiation by a determined amount, and an x-ray detector that detects the x-ray radiation transmitted through the specimen to generate a detected image. An image processor then determines a Fourier filtering function and reconstructs the quantitative phase shift through the specimen by application of the Fourier filtering function to the detected image. As a result, artifacts due to absorption contrast can be removed from the detecting image. This corrected image can then be used in generating three dimensional (3D) images using computed tomography.
1. A full-field x-ray imaging system for quantitatively reconstructing the phase shift through a specimen, the system comprising:
a source that generates x-ray radiation;
a condenser x-ray lens for projecting the x-ray radiation onto the specimen;
an objective x-ray lens for imaging the x-ray radiation transmitted through the specimen;
a phase-shifting device to shift the phase of portions of x-ray radiation by a determined amount;
an x-ray detector that detects the x-ray radiation transmitted through the specimen to generate a detected image; and
an image processor that determines a Fourier filtering function and reconstructs the quantitative phase shift through the specimen by application of the Fourier filtering function to the detected image.
2. An x-ray imaging system as claimed in claim 1 , where the x-ray radiation is between 0.2 keV and 100 keV.
3. An x-ray imaging system as claimed in claim 1 , wherein the source is a sealed tube source.
4. An x-ray imaging system as claimed in claim 1 , wherein the source is a rotating anode x-ray source.
5. An x-ray imaging system as claimed in claim 1 , wherein the source is a micro-focus x-ray source.
6. An x-ray imaging system as claimed in claim 1 , wherein the source is a synchrotron radiation source.
7. An x-ray imaging system as claimed in claim 1 , wherein the condenser lens is a capillary lens with ellipsoidal shape.
8. An x-ray imaging system as claimed in claim 1 , wherein the condenser lens is a capillary lens with paraboloidal shape.
9. An x-ray imaging system as claimed in claim 1 , wherein the condenser lens is a Fresnel zone plate lens.
10. An x-ray imaging system as claimed in claim 1 , wherein the objective lens is a Fresnel zone plate lens.
11. An x-ray imaging system as claimed in claim 1 , wherein the phase shifting device is a ring-shaped transmissive device.
12. An x-ray imaging system as claimed in claim 1 , wherein the phase ring is placed between the objective lens and the detector.
13. An x-ray imaging system as claimed in claim 1 , wherein the phase ring is placed near the back focal point of the objective lens.
14. An x-ray imaging system as claimed in claim 1 , wherein the phase ring shifts the phase by π/2 or 3π/2.
15. A transmission electron microscope system for quantitatively reconstructing the phase shift through a specimen, the system comprising:
a source that generates an electron beam;
a condenser lens for projecting the electron beam onto the specimen;
an objective lens for imaging the electron beam transmitted through the specimen;
a phase-shifting device to shift the phase of portions of electron beam by a determined amount;
a detector that detects the x-ray radiation transmitted through the specimen to generate a detected image; and
an image processor that determines a Fourier filtering function and reconstructs the quantitative phase shift through the specimen by application of the Fourier filtering function to the detected image.
16. An electron microscope system as claimed in claim 15 , wherein the electron beam has an energy between 100 keV and 1 MeV.
17. An electron microscope system as claimed in claim 15 , wherein the phase shifting device shifts the phase by π/2 or 3π/2.
18. An electron microscope system as claimed in claim 15 , wherein the phase shifting device is placed between the objective lens and detector.
19. An electron microscope system as claimed in claim 15 , wherein the phase ring is placed near the back focal point of the objective lens.
20. A full-field x-ray imaging method for quantitatively reconstructing the phase shift through a specimen, the method comprising:
generating x-ray radiation;
projecting the x-ray radiation onto the specimen;
imaging the x-ray radiation transmitted through the specimen;
shifting the phase of portions of x-ray radiation by a determined amount;
detecting the x-ray radiation transmitted through the specimen to generate a detected image; and
determining a Fourier filtering function; and
reconstructing the quantitative phase shift through the specimen by application of the Fourier filtering function to the detected image.
21. An x-ray imaging method as claimed in claim 20 , where the x-ray radiation is between 0.2 keV and 100 keV.