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Flexible retrospective phase stepping in x-ray scatter correction and phase contrast imaging using structured illumination.

Wen H, Miao H, Bennett EE, Adamo NM, Chen L - PLoS ONE (2013)

Bottom Line: The development of phase contrast methods for diagnostic x-ray imaging is inspired by the potential of seeing the internal structures of the human body without the need to deposit any harmful radiation.However, in practical conditions the actual phase intervals can vary from step to step and also spatially.With this ability, grating-based x-ray imaging becomes more adaptable and robust for broader applications.

View Article: PubMed Central - PubMed

Affiliation: Imaging Physics Laboratory, Biochemistry and Biophysics Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, United States of America.

ABSTRACT
The development of phase contrast methods for diagnostic x-ray imaging is inspired by the potential of seeing the internal structures of the human body without the need to deposit any harmful radiation. An efficient class of x-ray phase contrast imaging and scatter correction methods share the idea of using structured illumination in the form of a periodic fringe pattern created with gratings or grids. They measure the scatter and distortion of the x-ray wavefront through the attenuation and deformation of the fringe pattern via a phase stepping process. Phase stepping describes image acquisition at regular phase intervals by shifting a grating in uniform steps. However, in practical conditions the actual phase intervals can vary from step to step and also spatially. Particularly with the advent of electromagnetic phase stepping without physical movement of a grating, the phase intervals are dependent upon the focal plane of interest. We describe a demodulation algorithm for phase stepping at arbitrary and position-dependent (APD) phase intervals without assuming a priori knowledge of the phase steps. The algorithm retrospectively determines the spatial distribution of the phase intervals by a Fourier transform method. With this ability, grating-based x-ray imaging becomes more adaptable and robust for broader applications.

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Related in: MedlinePlus

The arbitrary and position dependent (APD) phase stepping algorithm improves phase retrieval.(A) In an example of phase contrast imaging with electromagnetic phase stepping, the measured phase increment in the first of 6 steps is shown. Considerable variation can be seen over the oval area covered by the gratings. A profile across the center of the area (B) revealed a 20% gradual decrease of the phase increment. (C) For comparison, the differential phase contrast image of two horizontal polyacetal rods was retrieved with both the APD and the previous globally uniform algorithms. In the area outlined by the small square, the previous algorithm resulted in vertical fringe artifacts (D) which indicate incomplete demodulation of the moiré fringes, while the APD algorithm removed the artifacts (E). The scalebar in (C) is 3 mm long.
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pone-0078276-g002: The arbitrary and position dependent (APD) phase stepping algorithm improves phase retrieval.(A) In an example of phase contrast imaging with electromagnetic phase stepping, the measured phase increment in the first of 6 steps is shown. Considerable variation can be seen over the oval area covered by the gratings. A profile across the center of the area (B) revealed a 20% gradual decrease of the phase increment. (C) For comparison, the differential phase contrast image of two horizontal polyacetal rods was retrieved with both the APD and the previous globally uniform algorithms. In the area outlined by the small square, the previous algorithm resulted in vertical fringe artifacts (D) which indicate incomplete demodulation of the moiré fringes, while the APD algorithm removed the artifacts (E). The scalebar in (C) is 3 mm long.

Mentions: We compared the APD algorithm with the previous algorithm assuming globally uniform phase steps by Goldberg and Bokor [15]. A sample consisting of two horizontal polyacetal plastic rods was imaged for the comparison. The phase increments measured by the APD algorithm showed variations with position, in a peak-to-peak range of 20% of the global mean over the area covered by the gratings (Fig. 2A, B). The global mean phase increments among the 6 phase steps varied from −0.979 to 1.020. When spatially uniform phase increments were assumed, the retrieved differential phase maps contained residual fringe artifacts in the areas where the phase increment deviated from the global mean value (Fig. 2D). The artifacts represent incomplete demodulation of the carrier frequency fringes. When the APD algorithm was used, the artifacts were eliminated and the fringe demodulation was complete in the entire grating area (Fig. 2E).


Flexible retrospective phase stepping in x-ray scatter correction and phase contrast imaging using structured illumination.

Wen H, Miao H, Bennett EE, Adamo NM, Chen L - PLoS ONE (2013)

The arbitrary and position dependent (APD) phase stepping algorithm improves phase retrieval.(A) In an example of phase contrast imaging with electromagnetic phase stepping, the measured phase increment in the first of 6 steps is shown. Considerable variation can be seen over the oval area covered by the gratings. A profile across the center of the area (B) revealed a 20% gradual decrease of the phase increment. (C) For comparison, the differential phase contrast image of two horizontal polyacetal rods was retrieved with both the APD and the previous globally uniform algorithms. In the area outlined by the small square, the previous algorithm resulted in vertical fringe artifacts (D) which indicate incomplete demodulation of the moiré fringes, while the APD algorithm removed the artifacts (E). The scalebar in (C) is 3 mm long.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3814970&req=5

pone-0078276-g002: The arbitrary and position dependent (APD) phase stepping algorithm improves phase retrieval.(A) In an example of phase contrast imaging with electromagnetic phase stepping, the measured phase increment in the first of 6 steps is shown. Considerable variation can be seen over the oval area covered by the gratings. A profile across the center of the area (B) revealed a 20% gradual decrease of the phase increment. (C) For comparison, the differential phase contrast image of two horizontal polyacetal rods was retrieved with both the APD and the previous globally uniform algorithms. In the area outlined by the small square, the previous algorithm resulted in vertical fringe artifacts (D) which indicate incomplete demodulation of the moiré fringes, while the APD algorithm removed the artifacts (E). The scalebar in (C) is 3 mm long.
Mentions: We compared the APD algorithm with the previous algorithm assuming globally uniform phase steps by Goldberg and Bokor [15]. A sample consisting of two horizontal polyacetal plastic rods was imaged for the comparison. The phase increments measured by the APD algorithm showed variations with position, in a peak-to-peak range of 20% of the global mean over the area covered by the gratings (Fig. 2A, B). The global mean phase increments among the 6 phase steps varied from −0.979 to 1.020. When spatially uniform phase increments were assumed, the retrieved differential phase maps contained residual fringe artifacts in the areas where the phase increment deviated from the global mean value (Fig. 2D). The artifacts represent incomplete demodulation of the carrier frequency fringes. When the APD algorithm was used, the artifacts were eliminated and the fringe demodulation was complete in the entire grating area (Fig. 2E).

Bottom Line: The development of phase contrast methods for diagnostic x-ray imaging is inspired by the potential of seeing the internal structures of the human body without the need to deposit any harmful radiation.However, in practical conditions the actual phase intervals can vary from step to step and also spatially.With this ability, grating-based x-ray imaging becomes more adaptable and robust for broader applications.

View Article: PubMed Central - PubMed

Affiliation: Imaging Physics Laboratory, Biochemistry and Biophysics Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, United States of America.

ABSTRACT
The development of phase contrast methods for diagnostic x-ray imaging is inspired by the potential of seeing the internal structures of the human body without the need to deposit any harmful radiation. An efficient class of x-ray phase contrast imaging and scatter correction methods share the idea of using structured illumination in the form of a periodic fringe pattern created with gratings or grids. They measure the scatter and distortion of the x-ray wavefront through the attenuation and deformation of the fringe pattern via a phase stepping process. Phase stepping describes image acquisition at regular phase intervals by shifting a grating in uniform steps. However, in practical conditions the actual phase intervals can vary from step to step and also spatially. Particularly with the advent of electromagnetic phase stepping without physical movement of a grating, the phase intervals are dependent upon the focal plane of interest. We describe a demodulation algorithm for phase stepping at arbitrary and position-dependent (APD) phase intervals without assuming a priori knowledge of the phase steps. The algorithm retrospectively determines the spatial distribution of the phase intervals by a Fourier transform method. With this ability, grating-based x-ray imaging becomes more adaptable and robust for broader applications.

Show MeSH
Related in: MedlinePlus