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Validity of the line-pair bar-pattern method in the measurement of the modulation transfer function (MTF) in megavoltage imaging
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10.1118/1.2816108
/content/aapm/journal/medphys/35/1/10.1118/1.2816108
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/35/1/10.1118/1.2816108

Figures

Image of FIG. 1.
FIG. 1.

Geometric artifacts in line-pair modulations due to beam divergence. Note that these effects have been greatly exaggerated here for the sake of display. In reality, they are visually undetectable with typical imaging geometries.

Image of FIG. 2.
FIG. 2.

Variation of the normalization value relative to the normalization condition for the phosphor screen only, and for and video EPIDs.

Image of FIG. 3.
FIG. 3.

The typical arrangement of the three bars for MTF measurement. The center of the right edge of the uncut bar is aligned with the center of the field, while the two bars containing line pairs are symmetrically placed about the line passing through this edge (alignment requirements are only approximate). The above image was cropped for display purposes.

Image of FIG. 4.
FIG. 4.

The LSF for the Elekta iViewGT system obtained from slit response measurements.

Image of FIG. 5.
FIG. 5.

The LSF for the Elekta iViewGT system obtained from edge response measurements.

Image of FIG. 6.
FIG. 6.

Bar-pattern images along with their modulation profiles are shown for the Elekta iViewGT system.

Image of FIG. 7.
FIG. 7.

Correction of the bar-pattern normalization profile for baseline artifacts. The baseline profile was determined by imaging the bar patterns without the normalization bar. The above profiles were measured for the Elekta iViewGT system.

Image of FIG. 8.
FIG. 8.

The MTF measured for the Siemens BEAMVTEW video EPID, Elekta iViewGT EPID, and the brass plate-Kodak X-OmatV film combination using the slit, edge, and bar-pattern methods. Also shown is the MTF for a Lanex Fast-B screen from LSF and bar response profiles generated using Monte Carlo simulations. Error bars indicate one standard error.

Tables

Generic image for table
TABLE I.

Comparison of MTFs obtained for the BEAMVIEW, iViewGT, and film systems with those reported for similar prototype systems. The italicized entries indicate our measurements. (A) Comparison with prototype EPIDs. (B) Comparison with prototype lens-coupled EPIDs. (C) Comparison with film.

Generic image for table
TABLE II.

Summary of statistical comparisons of MTF measurements. Boldface -values indicate significant difference. (A) Siemens BEAMVIEW. (B) Elekta iViewGT. (C) Brass build-up plate-Kodak X-Omat V film.

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/content/aapm/journal/medphys/35/1/10.1118/1.2816108
2007-12-21
2014-04-17
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Validity of the line-pair bar-pattern method in the measurement of the modulation transfer function (MTF) in megavoltage imaging
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/35/1/10.1118/1.2816108
10.1118/1.2816108
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