There are few professions in which visual acuity is as important as it is to radiologists. The diagnostic decision making process is composed of a number of events (detection or observation, interpretation and reporting), where the detection phase is subject to a number of physical and psychological phenomena that are critical to the process. Visual acuity is one phenomenon that has often been overlooked, and there is very little research assessing the impact of reduced visual acuity on diagnostic performance. The aim of this study was to investigate the impact of reduced visual acuity on an observer’s ability to detect simulated nodules in an anthropomorphic chest phantom

Hogg, Peter

Lança, Carla Costa

Lança, Luís

Thompson, J. D.

Lança, Carla

Repositório Científico do Instituto Politécnico de Lisboa

Page 1 of 9A method to determine the impact of visual function onlesion detection performancePoster No.: C-0230Congress: ECR 2016Type: Scientific ExhibitAuthors: J. D. Thompson1, C. Lança2, L. J. O. Lança3, P. Hogg1;1Manchester/UK, 2Lisbon/PT, 3Lisboa/PTKeywords: Eyes, Experimental, Experimental investigations, QualityassuranceDOI: 10.1594/ecr2016/C-0230Any information contained in this pdf file is automatically generated from digital materialsubmitted to EPOS by third parties in the form of scientific presentations. Referencesto any names, marks, products, or services of third parties or hypertext links to third-party sites or information are provided solely as a convenience to you and do not inany way constitute or imply ECR's endorsement, sponsorship or recommendation of thethird party, information, product or service. ECR is not responsible for the content ofthese pages and does not make any representations regarding the content or accuracyof material in this file.As per copyright regulations, any unauthorised use of the material or parts thereof aswell as commercial reproduction or multiple distribution by any traditional or electronicallybased reproduction/publication method ist strictly prohibited.You agree to defend, indemnify, and hold ECR harmless from and against any and allclaims, damages, costs, and expenses, including attorneys' fees, arising from or relatedto your use of these pages.Please note: Links to movies, ppt slideshows and any other multimedia files are notavailable in the pdf version of presentations.www.myESR.orgPage 2 of 9Aims and objectivesThere are few professions in which visual acuity is as important as it is to radiologists [1].The diagnostic decision making process is composed of a number of events (detectionor observation, interpretation and reporting), where the detection phase is subject to anumber of physical and psychological phenomena that are critical to the process [2].Visual acuity is one phenomenon that has often been overlooked, and there is verylittle research assessing the impact of reduced visual acuity on diagnostic performance[3]. The aim of this study was to investigate the impact of reduced visual acuity on anobserver's ability to detect simulated nodules in an anthropomorphic chest phantom.Methods and materialsSummaryAn anthropomorphic chest phantom containing simulated nodules was used for thedetection task. The observers completed the task under three conditions: (i) normal visualacuity, (ii) reduced visual acuity (level 1), (iii) and reduced visual acuity (level 2). Observerdata was collected under the free-response receiver operating characteristic (FROC)paradigm. Local ethical approval was gained prior to the commencement of this study.Vision Testing and Reduction of Visual AcuityThe normal visual function of the observers was ensured using the tests described ina previous paper [4]. Lenses used in a traditional vision test were used to reduce thevisual acuity of the observers. The lenses were used to reduce retinal image contrastand alter spatial frequency [5]. We will refer to this 'optically induced defocus'. Defocuswas applied at two different levels. We based this on the dioptre (D) scale, which is a unitmeasurement of the optical power of a lens, equal to the reciprocal of the focal length ofthe lens [6]. This is reflective of a typical prescription lens. We applied defocus at -1.00 Dand -2.00 D, and also at 0.00 D - this would be a refractive correction for some observers.Trial lenses were applied in a different random order for the five observers.Anthropomorphic Chest PhantomThe anthropomorphic chest phantom (Lungman N1 multipurpose chest phantom, KyotoKagaku Company Ltd, Japan) was loaded with fifty different configurations of thefollowing simulated nodules: 5, 8, 10 and 12mm spherical diameter, all measuringapproximately 100 Hounsfield Units density. These would be used as 'abnormal' casesPage 3 of 9in the observer study. Images were also acquired with no nodules present to provide'normal' cases.Observer Performance StudyThree radiologists (aged 31, 35 & 50) and two radiographers (aged 32 and 47) completedthe observer study. Each observer completed the study in a different order. The observerswere trained to understand the appearance of the phantom without nodules and werealso introduced to sample images containing nodules that were not used in the observerstudy. Training requirements are minimal for phantom studies since there is no casevariation.All image evaluations were completed on the same specification of monitor (EizoRadiForce GS521 10-Bit digital imaging and communications in medicine (DICOM)compliant monitor, 2048x2560, 5 megapixel resolution, Eizo Corporation, Japan) usingROCView [7] to complete the image evaluations. Ambient lighting was consistent at 225lux.The nodule detection task was completed under the FROC paradigm; observers wereinstructed to mark the centre of each nodule using a mouse click. This would prompt a10-point rating scale to appear. Localisations were classified as lesion localisation (LL)or non-lesion localisation (NL) by an acceptance radius. The acceptance radius was setat 25, 50 and 100 pixels for this task. The average size of the largest nodule was 100pixels diameter.Statistical AnalysisObserver data were analysed using an R implementation of jackknife alternativeFROC (JAFROC) analysis, Rjafroc, available at https://cran.r-project.org/web/packages/RJafroc/index.html. The weighted JAFROC figure of merit (FOM) defines the probabilitythat a lesion localisation is rated higher than a non-lesion localisation on a normal case[8]. A difference in nodule detection performance was declared significant if the p-valueof the overall F-test was less than 0.05 and the 95% confidence interval of the treatmentdifference did not include zero.ResultsObserver Performance StudyPage 4 of 9No statistical difference in nodule detection was found for the three treatments(conditions) using random reader fixed case analysis. The choice of acceptance radiushad no impact on statistical significance (F(2,8) = 1.41, p = 0.299). The observer averagedFOM and 95% confidence intervals for all three treatments are displayed in Table 1 andFig. 1 on page 4 for the strict acceptance radius (AR-25). The observer averagedAFROC curves for all three treatments are displayed in Fig. 2 on page 5. Thetreatment differences are display in Fig. 3 on page 6.Table 1: Observer Averaged JAFROC FOMs (all treatments, AR-25)Treatment JAFROC FOM (95% CI)0.00 D 0.606 (0.513,0.700)-1.00 D 0.571 (0.487,0.656)-2.00 D 0.596 (0.482,0.710)Vision TestingFor near vision, visual acuity should be equal to or better than 20/50. Stereoacuity ismeasured in seconds of arc, and should be equal or less than 50. Contrast sensitivitywas assessed with gratings of 18 cycles per degree, to assess vision at high spatialfrequency; it should be equal to or better than 0.56.For all observers, visual acuity and contrast sensitivity was acceptable at 0.00 D. Forobserver 3 (radiologist aged 50), visual acuity was not acceptable when lenses simulating-2.00 D were applied. However, this change in acuity was not influential on the noduledetection task. Stereoacuity was normal for all except observer 3.Images for this section:Page 5 of 9Fig. 1: The observer averaged wJAFROC figure of merit and 95% confidence intervalsfor all treatments.© Directorate of Radiography, University of Salford - Manchester/UKPage 6 of 9Fig. 2: The observer averaged AFROC curves for all treatments.© Directorate of Radiography, University of Salford - Manchester/UKPage 7 of 9Fig. 3: The inter-treatment differences for all treatment pairs. For a difference to bedeclared significant, the 95% confidence interval of the treatment pair must not containzero and the p value of the overall F-test must be less than 0.05. No significant differencesobserved in this study.© Directorate of Radiography, University of Salford - Manchester/UKPage 8 of 9ConclusionWe found no statistically significant difference in nodule detection performance whenreducing visual acuity.Personal informationReferences[1] Halpenny, D., O'Driscoll, D., & Torreggiani, W. C. (2012). Ocular health amongradiologists in the age of PACS: is it time for our profession to open its eyes to thisissue in light of existing European legislation? The British journal of radiology, 85(1020),e1309-11. doi:10.1259/bjr/27200799[2] Straub, W., Gur, D., & Good, B. C. (1991). Visual acuity testing of radiologists - is ittime? American Journal of Roentgenology, 156(5), 1107-1108.[3] Tahmasebi, M., & Joorabian, M. (2011). Eye Problems in Radiologists. In EuropeanCongress of Radiology (pp. C-2038). Vienna. Retrieved from http://dx.doi.org/10.1594/ecr2011/C-2038[4] Lança, C., Thompson, J. D., & Lança, L. (2015). Visual Function Assessment inMedical Imaging Research. Radiologic Technology, 87(2), 129-138.[5] Ravikumar, S., Bradley, A., & Thibos, L. (2010). Phase changes induced byoptical aberrations degrade letter and face acuity. Journal of vision, 10(14), 1-12.doi:10.1167/10.14.18[6] Lang, G. (2000). Ophthalmology. New York: Thieme.[7] Thompson, J. D., Hogg, P., Thompson, S., Manning, D. J., & Szczepura, K. (2012).ROCView: prototype software for data collection in jackknife alternative free-responsePage 9 of 9receiver operating characteristic analysis. The British Journal of Radiology, 85(1017),1320-6. doi:10.1259/bjr/99497945[8] Chakraborty, D. P., & Berbaum, K. S. (2004). Observer studies involving detectionand localization: Modeling, analysis, and validation. Medical Physics, 31(8), 2313-2330.doi:10.1118/1.1769352

A method to determine the impact of visual function on lesion detection performance

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A method to determine the impact of visual function on lesion detection performance

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