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Reduction of a grid moiré pattern by integrating a carbon-interspaced high precision x-ray grid with a digital radiographic detector
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10.1118/1.2775743
/content/aapm/journal/medphys/34/11/10.1118/1.2775743
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/34/11/10.1118/1.2775743

Figures

Image of FIG. 1.
FIG. 1.

Schematic for the aliasing and frequency matching method. (a) Fourier transform of an ideal grid shadow [ in Eq. (2)]. : spatial frequency variable, : pitch of the grid line, : grid line frequency. (b) Sampling function denoted by a comb function in the frequency domain. [: pitch of the detector pixel, : detector sampling frequency] (c) The Fourier transform of a discretely sampled grid line shadow distribution is represented by a convolution of Fig. 1(a) with Fig. 1(b), which is denoted by in Eq. (4). The aliasing frequency can be observed when the grid line frequency is higher than the Nyquist frequency of the detector. The observable frequency range below the Nyquist frequency is marked as the shaded box. (d) Sampling at the grid line frequency makes the aliasing frequency appears around zero frequency.

Image of FIG. 2.
FIG. 2.

Alignment tools used to align the grid and detector. Four micropositioners at each corner of the grid allowing the magnification adjustment of the grid shadow and microstepper driven stages on two axes for the horizontal translation and rotation of the grid.

Image of FIG. 3.
FIG. 3.

Moiré pattern frequency as a function of the grid line shadow frequency. The detector sampling frequency is . The solid line indicates the theoretical prediction.

Image of FIG. 4.
FIG. 4.

Line profiles of the simulated moiré patterns at different translation distances (sampling period: ; grid line pitch: ; septa width: ): (a) 0, (b) 20, (c) 70, (d) .

Image of FIG. 5.
FIG. 5.

Moiré pattern acquired at different rotation angles: (a) , (b) , (c) , (d) .

Image of FIG. 6.
FIG. 6.

The rotation angle of the moiré pattern as a function of the grid rotation angle. The solid line indicates the theoretical prediction.

Image of FIG. 7.
FIG. 7.

Images obtained using a grid with a grid line frequency of at different gaps between the grid and detector: (a) , (b) , (c) , (d) . The corresponding projected grid line frequencies are specified within the parentheses (detector sampling frequency: ).

Image of FIG. 8.
FIG. 8.

Nonuniformity of the images at different frequency differences between the grid line and the detector sampling (detector sampling frequency: ).

Image of FIG. 9.
FIG. 9.

Comparison of the signal-to-noise ratios using an aluminium step wedge phantom with and without moiré pattern.

Tables

Generic image for table
TABLE I.

Specification of the carbon-interspaced grids used in the experiments.

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/content/aapm/journal/medphys/34/11/10.1118/1.2775743
2007-10-05
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Reduction of a grid moiré pattern by integrating a carbon-interspaced high precision x-ray grid with a digital radiographic detector
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/34/11/10.1118/1.2775743
10.1118/1.2775743
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