1,721,162 research outputs found
Reverse hierarchy theory and medical image perception
No full textWe are unsure about what information is extracted from an image to allow a decision about pathology to be made. Our knowledge of the interplay between top down processing or bottom up, local or global perception, perceptual or cognitive processes is uncertain. However recent research has emphasised the importance of the global or holistic look in medical image perception in which recognition of abnormalities precedes search. Reverse Hierarchy Theory [1] is a useful general theory that helps to explain this. It also enables us to understand what information is extracted from an image and how this relates to expertise. Essentially the theory states that perceptual learning begins at high levels areas and progresses down to lower level areas when better signal to noise is needed. So perceptual learning, defined as an improvement in sensory abilities after training, stems from a gradual top down guided increase in usability of first high then lower level task relevant information. Evaluation of the scan paths of groups of observers with different levels of expertise when undertaking a lung nodule perception task seems to be consistent with the theory. Experts' perception is generally immediate and holistic suggesting high level representations whereas those with an intermediate level of expertise tend to be more variable in their scan paths. Interestingly naïve observers have eye tracking metrics that are more similar to experts suggesting they take a common sense approach using perceptual skills we all have as they lack experience in being able to access the low level information from the chest radiograph
Medical Imaging 2010: Image Perception, Observer Performance, and Technology Assessment (Proceedings Volume)
No full textn/
Spatial frequency characteristics at image decision-point locations for observers with different radiological backgrounds in lung nodule detection
No full textAim: The goal of the study is to determine the spatial frequency characteristics at locations in the image of overt and covert observers' decisions and find out if there are any similarities in different observers' groups: the same radiological experience group or the same accuracy scored level.
Background: The radiological task is described as a visual searching decision making procedure involving visual perception and cognitive processing. Humans perceive the world through a number of spatial frequency channels, each sensitive to visual information carried by different spatial frequency ranges and orientations. Recent studies have shown that particular physical properties of local and global image-based elements are correlated with the performance and the level of experience of human observers in breast cancer and lung nodule detections. Neurological findings in visual perception were an inspiration for wavelet applications in vision research because the methodology tries to mimic the brain processing algorithms.
Methods: The wavelet approach to the set of postero-anterior chest radiographs analysis has been used to characterize perceptual preferences observers with different levels of experience in the radiological task. Psychophysical methodology has been applied to track eye movements over the image, where particular ROIs related to the observers' fixation clusters has been analysed in the spaces frame by Daubechies functions.
Results: Significance differences have been found between the spatial frequency characteristics at the location of different decisions
Learning from others : effects of viewing another person’s eye movements while searching for chest nodules.
No full textWe report a study that investigated whether experienced and inexperienced radiographers benefit from knowing where another person looked during pulmonary nodule detection. Twenty-four undergraduate radiographers (1 year of experience) and 24 postgraduate radiographers (5+ years of experience) searched 42 chest x-rays for nodules and rated how confident they were in their decisions. Eye movements were also recorded. Performance was compared across three within-participant conditions: (1) free search—where radiographers could identify nodules as normal; (2) image preview—where radiographers were first shown each chest x-ray for 20 seconds before they could then proceed to mark the location of any nodules; and (3) eye movement preview—which was identical to image preview except that the 20 second viewing period displayed an overlay of the real-time eye movements of another radiographer’s scanpath for that image. For this preview condition half of each group were shown where a novice radiographer looked, and the other half were shown where an experienced radiologist looked. This was not made known to the participants until after the experiment. Performance was assessed using JAFROC analysis. Both groups of radiographers performed better in the eye movement preview condition compared with the image preview or free search conditions, with inexperienced radiographers improving the most. We discuss our findings in terms of the task-specific information interpreted from eye movement previews, task difficulty across images, and whether it matters if radiographers are previewing the eye movements of an expert or a novice
Implication of the first decision on visual information-sampling in the spatial frequency domain in pulmonary nodule recognition
No full textAim: To investigate the impact on visual sampling strategy and pulmonary nodule recognition of image-based properties of background locations in dwelled regions where the first overt decision was made.
Background: Recent studies in mammography show that the first overt decision (TP or FP) has an influence on further image reading including the correctness of the following decisions. Furthermore, the correlation between the spatial frequency properties of the local background following decision sites and the first decision correctness has been reported.
Methods: Subjects with different radiological experience were eye tracked during detection of pulmonary nodules from PA chest radiographs. Number of outcomes and the overall quality of performance are analysed in terms of the cases where correct or incorrect decisions were made. JAFROC methodology is applied. The spatial frequency properties of selected local backgrounds related to a certain decisions were studied. ANOVA was used to compare the logarithmic values of energy carried by non redundant stationary wavelet packet coefficients.
Results: A strong correlation has been found between the number of TP as a first decision and the JAFROC score (r = 0.74). The number of FP as a first decision was found negatively correlated with JAFROC (r = -0.75). Moreover, the differential spatial frequency profiles outcomes depend on the first choice correctness
Relations between physical properties of local and global image-based elements and the performance of human observers in lung nodule detection
No full textAim: 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
Performance changes in lung nodule detection following perceptual feedback of eye movements.
No full textIn a previously reported study we demonstrated that expert performance can decline following perceptual feedback of eye movements in the relatively simple radiological task of wrist fracture detection [1]. This study was carried out to determine if the same effect could be observed using a more complicated radiological task of identifying lung nodules on chest radiographs. Four groups (n=10 in each group) of observers with different levels of expertise were tested. The groups were naïve observers, level 1 radiography students, level 2 radiography students and experts. Feedback was presented to the observers in the form of their scan paths and fixations. Half the observers had feedback and half had no perceptual feedback. JAFROC analysis was used to measure observer performance. A repeated measures ANOVA was carried out. There was no significant effect between the pre and post “no feedback” condition. There was a significant difference between the pre and post “feedback” condition with a significant improvement following feedback (F(1,16)=6.6,p = 0.021). Overall the mean percentage improvement was small of 3.3%, with most of the improvement due to the level 1 group where the percentage increase in the figure of merit (FOM) was 8.4% and this was significant (p<0.05). Eye tracking metrics indicate that the expert and naïve observers were less affected by feedback or a second look whereas there were mixed results between the level 1 and level 2 students possibly reflecting the different search strategies used. Perceptual feedback may be beneficial for those early in their training
Searching in axial and 3D CT visualisations
Get PDFTraditional diagnostic modalities have been, for the most part, static two-dimensional images displayed on film or computer screen. More recent diagnostic modalities are solely computer-based and consist of large data-sets of multiple images. Image perception and visual search using these new modalities are complicated by the need to interact with the computer in order to navigate through the data. This paper reports the late-breaking results from two small studies into visual search within two types of CT Colonography (CTC) visualisations. The twelve novice observers in the study were taking part in a week-long course in CTC and were tested at the beginning and end of the course. A number of expert observers were also recorded. The two visualisations used in the study were 2D axial view and 3D colon fly-through. In both cases, searching was performed by inspecting the colon wall, but by two distinct mechanisms. The first study recorded observer eye-gaze and image navigation in a CTC axial view. The search strategy was to follow the lumen of the colon and detect abnormalities in the colon wall. The observer used the physical computer interface to navigate through the set of axial images to perform this task. The 3D fly-through study recorded observer eye-gaze whilst watching a recording of a computed flight through the colon lumen. Unlike the axial view there was no computer control, so inspection of the colon surface was dictated by the speed of flight through the colon
The effect of fluorine on the structure of hydrous aluminosilicate melts (extended abstract)
No full textLiquidus phase relations have been determined for a portion of the water saturated system SiO2-NaAlSi3O8-KAlSi3O8-F2 at 1 kb. The stability field of quartz expands and liquidus temperatures decrease when fluorine is added to the initially F2 free system. Fluorine is probably present in the melt as the free fluoride ion and as the aluminofluoride complex (AlFg63-).Les relations de phases de liquidus ont été déterminées pour une partie du système SiO2-NaAlSi3O8-KAlSi3O8-F2 saturé d'eau à 1 kbar. Le champ de stabilité du quartz s'étend et les températures de liquidus diminuent quand on ajoute du fluor. Le fluor est probablement présent dans le bain sous forme d'ion fluor libre et de complexe aluminofluoré (AlF63-).Manning David A.C. The effect of fluorine on the structure of hydrous aluminosilicate melts (extended abstract). In: Bulletin de Minéralogie, volume 106, 1-2, 1983. Silicates liquides
- …
