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Lucretiu M. Popescu. Nonparametric signal detectability evaluation using an exponential transformation of the FROC curve. Medical Physics, 38 (10) , pp. 5690-5702, 2011.

Abstract: Purpose: To develop an efficient nonparametric method for evaluation the detectability of signals
at unknown locations in images, as a mean for image quality assessment.
Methods: We use the free-response methodology that allows the image observer to mark and score
all locations found as suspicious in an image, summarizing these results in a free-response operating
characteristic (FROC) curve. However, unlike the relative (or receiver) operating characteristic
(ROC), or the localization ROC (LROC), the FROC curve has an undefined, theoretically infinite,
right side limit. Therefore area under the FROC curves cannot be directly used as an overall performance
index, as the area under the curve is for ROC or LROC. We circumvent this drawback by
using a transformation of the abscissa that leads to a finite integration range. By applying an exponential
transformation we derive a nonparametric estimator for such a metric, and we study its
properties by deriving analytical expressions for the mean and standard deviation in conditions of
scores independence.
Results: A comparative study with other related nonparametric estimators for ROC, LROC, and
alternative FROC (AFROC) method is presented.
Conclusions: The new nonparametric estimator has sensitivity and scalability properties that make
it particularly advantageous for signal detectability evaluation in phantom experiments using model
observers. VC 2011 American Association of Physicists in Medicine. [DOI: 10.1118/1.3633938]

Keywords: Signal detection, ROC, FROC


Posted by Lucretiu M. Popescu


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