12 research outputs found

    Principle of the reverse projection method.

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    <p>Starting from the phase stepping curve (a) that is recorded without sample (reference scan), the sample is measured with grating positions corresponding to the two linear regions of the stepping curve. The two recorded intensities can then be used to obtain the attenuation of the sample as well as its differential phase shift Δ<i>φ</i><sub><i>s</i></sub>. Panel (b) shows the histogram of the differential phase-contrast projections of a tomographic scan of a biomedical sample. The red lines mark the region where the error of the linear approximation is less than 5%. Only 0.1% of all pixels lie outside of this region.</p

    Mean values and the corresponding standard deviation of the refractive index decrement <i>δ</i> relative to water, exemplary for the materials formalin (fluid inside the tube), PMMA and the Falcon tube.

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    <p>Mean values and the corresponding standard deviation of the refractive index decrement <i>δ</i> relative to water, exemplary for the materials formalin (fluid inside the tube), PMMA and the Falcon tube.</p

    Root mean squared error and structure similarity of the tomographic reconstructions displayed in Figs 6 and 7 compared to the reference scan.

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    <p>Root mean squared error and structure similarity of the tomographic reconstructions displayed in Figs <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184217#pone.0184217.g006" target="_blank">6</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184217#pone.0184217.g007" target="_blank">7</a> compared to the reference scan.</p

    Dark-field/scattering signal strength.

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    <p>(a) Exemplary dark-field projection of the measured biological sample. The sample shows a smooth dark-field signal close to unity, a prerequisite for successful application of the reverse projection method. (b) Histogram of dark-field values in all projections of one tomographic scan. The peak of the sample’s dark-field is narrow and close to unity. Further, there are next to no pixels with extreme values, which could hinder the applicability of the RP method.</p

    Comparing the tomographic reconstructions of a high statistic scans obtained by widely-used phase stepping approach and the reverse projection method.

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    <p>(a) Tomographic reconstructions of the differential phase contrast projections, obtained with the PS approach (left) and the RP method (right). (b) Line plot at the position marked by the dashed lines in (a). Both images appear very similar, which is also apparent in the line plot. The contrast in the RP image is slightly weaker, since high values are underestimated by this method.</p

    Image quality and quantitative accuracy of the RP method in a low-dose scenario.

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    <p>Comparison of the reconstructions obtained with the PS method (a, 111 counts/pixel/projection) and the RP method (b, 44.4 mean counts) with a reference scan (c). Remarkably, the RP reconstruction shows superior image quality compared to the PS method, even though only 2 of the 5 steps of the PS approach are used to generate the RP reconstruction. Panel (d) shows a difference image of (b) and (c), which is dominated by noise. That implies a good quantitative accuracy of the RP method. This finding is confirmed by line plot in panel (e) which shows plots along the lines displayed in panels (b) and (c). Note that the values for the RP method were averaged over 4 slices and 4 pixels in direction perpendicular to the line for improved readability.</p

    Two-directional, grating-based mammograms of the invasive ductal carcinoma with correlated histopathology.

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    <p>(a) Sharpened, two-dimensional integrated phase image of the invasive ductal carcinoma. The frames in (a) and (c) indicate three locally separated tumor lesions (apparently trifocal). Arrows in (a) and (c) indicate fine tumor branches. (b) Sharpened, absorption image of the invasive ductal carcinoma. Circles indicate position of relevant tumor details. (c) Histological slice (Hematoxylin and Eosin stain) of the invasive ductal carcinoma. (d) Directional dark-field image of the invasive ductal carcinoma. Preferred scattering direction is color-coded ranging from -directed (red) over isotropic (purple) to -directed (blue). (e) 200x magnified histological image of the tumor branch, as indicated by white diamond in (c) and (d). The 2-dimensional FFT is shown as an inlay. (d) 200x magnified histological image of the tumor lesion, as indicated by black diamond in (c) and (d). The 2-dimensional FFT is shown as an inlay.</p

    Conventional and grating-based mammograms of a breast specimen with invasive ductal carcinoma.

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    <p>Conventional mammogram (a), grating-based absorption (b), differential phase (c) and dark-field image (d) of the breast specimen. The field of view has a size of 12.8×12.8 cm<sup>2</sup>. Images (b)–(d) were obtained by stitching together 4×4 low-statistic projections. Arrows indicate the direction of scanning. The high-statistic images of the invasive ductal carcinoma are shown as inlays.</p

    Two-directional, grating-based mammograms of the invasive ductal carcinoma.

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    <p>Two-directional differential phase (a), (b) and sharpened, two-dimensional integrated phase image (c). Dark-field (d), (e) and mean dark-field image (f). Arrows indicate the direction of scanning. Red and blue boxes indicate tumor branches exclusively perceivable in the images obtained with scanning performed in - or -direction, respectively.</p
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