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Br J Radiol. 2016 Aug;89(1064):20160249. doi: 10.1259/bjr.20160249. Epub 2016 Jun 8.

The impact of greyscale inversion for nodule detection in an anthropomorphic chest phantom: a free-response observer study.

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Directorate of Radiology, University of Salford, Manchester, UK.
Radiology, University Hospitals of Morecambe Bay NHS Foundation Trust, Barrow-in-Furness, UK.
Lancaster Medical School, Lancaster University, Lancaster, UK.
Karolinska Institute, Stockholm, Sweden.



The aim of this work was to assess the impact of greyscale inversion on nodule detection on posteroanterior chest X-ray images. Previous work has attempted this, with no consensus opinion formed. We assessed the value of "fast-flicking" between standard and inverted display modes for nodule detection.


Six consultant radiologists (with 5-32 years' reporting experience) completed an observer task under the free-response paradigm. An anthropomorphic chest phantom was loaded with 50 different configurations of simulated nodules (1-4 nodules per case) measuring 5, 8, 10 and 12 mm in spherical diameter; each configuration represented a single case. In addition, 25 cases contained no nodules. Images were displayed in three modes: (i) standard, (ii) inverted and (iii) fast-flicking between standard and inverted display modes. Each observer completed the study in a different order of display (i, ii, iii) using a calibrated 5-megapixel monitor. Nodules were localized with mouse clicks and ratings assigned using a 1-10 discrete slider-bar confidence scale. Rjafroc (Pittsburgh, PA) was used for data analysis; differences in nodule detection performance were considered significant at 0.05.


The observer-averaged weighted jackknife alternative free-response receiver-operating characteristic figures of merit were 0.715 (standard), 0.684 (inverted) and 0.717 (fast-flicking). Random-reader fixed-case analysis revealed no statistically significant difference between any treatment pair [F(2,8) = 1.22; p = 0.345].


No statistically significant difference in nodule detection was found for the three display conditions.


We have investigated the impact of fast-flicking between standard and inverted display modes for the detection of nodules. We found no benefit.

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