Technical Note: Impact on detective quantum efficiency of edge angle determination method by International Electrotechnical Commission methodology for cardiac x-ray image detectors
Gislason-Lee, Amber J. Tunstall, C.M. Kengyelics, S.K. Cowen, A.R. Davies, A.G.
Gislason-Lee, Amber J.
Tunstall, C.M.
Kengyelics, S.K.
Cowen, A.R.
Davies, A.G.
Publication Date
2015-08
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2015-06-16
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Abstract
Cardiac x-ray detectors are used to acquire moving images in real-time for angiography
and interventional procedures. Detective quantum efficiency (DQE) is not generally measured on
these dynamic detectors; the required “for processing” image data and control of x-ray settings have
not been accessible. By 2016, USA hospital physicists will have the ability to measure DQE and
will likely utilize the International Electrotechnical Commission (IEC) standard for measuring DQE
of dynamic x-ray imaging devices. The current IEC standard requires an image of a tilted tungsten
edge test object to obtain modulation transfer function (MTF) for DQE calculation. It specifies the
range of edge angles to use; however, it does not specify a preferred method to determine this angle
for image analysis. The study aimed to answer the question “will my choice in method impact my
results?” Four different established edge angle determination methods were compared to investigate
the impact on DQE.
Methods: Following the IEC standard, edge and flat field images were acquired on a cardiac flat-panel
detector to calculate MTF and noise power spectrum, respectively, to determine DQE. Accuracy of
the methods in determining the correct angle was ascertained using a simulated edge image with
known angulations. Precision of the methods was ascertained using variability of MTF and DQE,
calculated via bootstrapping.
Results: Three methods provided near equal angles and the same MTF while the fourth, with an
angular difference of 6%, had a MTF lower by 3% at 1.5 mm−1 spatial frequency and 8% at 2.5 mm−1;
corresponding DQE differences were 6% at 1.5 mm−1 and 17% at 2.5 mm−1; differences were greater
than standard deviations in the measurements.
Conclusions: DQE measurements may vary by a significant amount, depending on the method used
to determine the edge angle when following the IEC standard methodology for a cardiac x-ray
detector. The most accurate and precise methods are recommended for absolute assessments and
reproducible measurements, respectively.
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Gislason-Lee AJ, Tunstall CM, Kengyelics SK et al (2015) Technical Note: Impact on detective quantum efficiency of edge angle determination method by International Electrotechnical Commission methodology for cardiac x-ray image detectors. Medical Physics. 42(8): 4423-4427.
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