Relations between physical properties of local and global image-based elements and the performance of human observers in lung nodule detection

Aim: The study aims to help our understanding of the relationship between physical characteristics of local and global image features and the location of visual attention by observers. Background: Neurological visual pathways are specified at least in part by particular spatial frequency ranges at different orientations. High spatial frequencies, which carry the information of local perturbations like edges, are assembled mainly by foveal vision, whereas peripheral vision provides more global information coded by low frequencies. Recent visual-search studies in mammography (C Mello-Thoms et al) have shown that observers allocate visual attention to regions of the image depending on; i) spatial frequency characteristics of regions that capture attention and ii) the level of experience of the observer. Both aspects are considered in this study. Methods: A spatial frequency analysis of postero-anterior (PA) chest images containing pulmonary nodules has been performed by wavelet packet transforms at different scales. This image analysis has provided regional physical information over the whole image field on locations both with nodules present and nodules absent. The relationship between such properties as spatial frequency, orientation, scales, contrast, and phase of localised perturbations has been compared with eye-tracked search strategies and decision performance of observers with different levels of expertise. Results: The work is in progress and the results of this initial stage of the project will be presented with a critical appraisal of the methods used