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Nodule detection in digital chest radiography: effect of system noise.

Journal article
Authors Markus Håkansson
Magnus Båth
Sara Börjesson
Susanne Kheddache
Åse (Allansdotter) Johnsson
Lars Gunnar Månsson
Published in Radiation protection dosimetry
Volume 114
Issue 1-3
Pages 97-101
ISSN 0144-8420
Publication year 2005
Published at Institute of Selected Clinical Sciences, Department of Radiation Physics
Institute of Selected Clinical Sciences, Department of Radiology
Pages 97-101
Language en
Links dx.doi.org/10.1093/rpd/nch525
Keywords Artifacts, Humans, Image Processing, Computer-Assisted, Lung, pathology, radiography, Lung Neoplasms, diagnosis, radiography, Models, Anatomic, Observer Variation, ROC Curve, Radiographic Image Enhancement, methods, Radiographic Image Interpretation, Computer-Assisted, methods, Radiography, methods, Radiography, Thoracic, methods, Scattering, Radiation, Software, X-Rays
Subject categories Radiological physics, Radiology

Abstract

Apart from the image content that is the reproduction of anatomy and possible lesions, an X-ray image also contains system noise due to the limited number of photons and other internal noise sources in the system (image plate artefacts, electronic noise, etc.). The aim of this study was to determine the extent to which the system noise influences the detection of subtle lung nodules in five different regions of the chest. This was done by conducting a receiver operating characteristic (ROC) study with five observers on two different sets of images; clinical chest X-ray images and images of a LucAl phantom at similar dose levels found in the different regions of the chest. In both image types, mathematically simulated nodules (with a full-width-at-fifth-maximum of 10 mm) were added to the images at varying contrast levels. As a measure of the influence of system noise on the detection of subtle lung nodules, the ratio between the contrast needed to obtain an area under the ROC curve of 0.80 in the system noise images to that needed in the clinical images was used. The contrast ratio between system noise images and clinical images ranged from approximately 0.02 (in the hilar region) to 0.18 (in the lower mediastinal region). The maximum difference in contrast needed for the corresponding system noise images, collected at the lowest and the highest dose represented in the anatomical image, was a factor of 2. These results indicate that probably no region in a chest X-ray image is limited by the number of quanta to the detector for the detection of 10 mm lung nodules when a radiation dose corresponding to a system with speed class 200 (leading to a detector dose of approximately 9 muGy behind the parenchyma) is used.

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