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Plate-specific gain map correction for the improvement of detective quantum efficiency in computed radiography.
Date
2010
Author
Advisors
Dobbins, James
Samei, Ehsan
Das, Shiva
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Abstract
The purpose of this work is to improve the NPS, and thus DQE, of CR images by correcting
for pixel-to-pixel gain variations specific to each plate. Ten high-exposure open
field images were taken with an RQA5 spectrum, with a sixth generation CR plate suspended
in air without a cassette. Image values were converted to exposure, the plates registered
using fiducial dots on the plate, the ten images averaged, and then high-pass filtered
to remove low frequency contributions from field inhomogeneity. A gain-map was then
produced by converting all pixel values in the average into fractions with mean of
one. The resultant gain-map of the plate was used to normalize subsequent single images
to correct for pixel-to-pixel gain fluctuation. The normalized NPS (NNPS) for all
images was calculated both with and without the gain-map correction. The NNPS with
correction showed improvement over the non-corrected case over the range of frequencies
from 0.15 –2.5 mm-1. At high exposure (40 mR), NNPS was 50-90% better with gain-map
correction than without. A small further improvement in NNPS was seen from careful
registering of the gain-map with subsequent images using small fiducial dots, because
of slight misregistration during scanning. CR devices have not traditionally employed
gain-map corrections common with DR detectors because of the multiplicity of plates
used with each reader. This study demonstrates that a simple gain-map can be used
to correct for the fixed-pattern noise and thus improve the DQE of CR imaging. Such
a method could easily be implemented by manufacturers because each plate has a unique
bar code and the gain-map could be stored for retrieval after plate reading. These
experiments indicated that an improvement in NPS (and hence, DQE) is possible, depending
on exposure level,over all frequencies with this technique.
Type
Master's thesisDepartment
Medical PhysicsPermalink
https://hdl.handle.net/10161/2503Citation
Schnell, Erich A. (2010). Plate-specific gain map correction for the improvement of detective quantum efficiency
in computed radiography. Master's thesis, Duke University. Retrieved from https://hdl.handle.net/10161/2503.Collections
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