published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

This dissertation addresses two problems dealing with detection sensitivity in radiology. First, is a 100-mm format adequate for displaying enhanced radiographic images in a photoelectronic imaging system and can the same format be used for permanent storage of these images? Second, what are the effects of training on the radiologist's sensitivity? Controlled 14-in. x 17-in. x-ray images were reduced to 100 mm to investigate which factors caused the decrement noted in the radiology literature. The 14-in. x 17-in. images used were generated from a 3M phantom. Three levels of kilovolt potential (80 kVp, 110 kVp, and 140 kVp) and two types of film (RPR and Cronex) were used to make the images. Twenty-four images, six for each of four quadrants, contained a simulated lung nodule and six contained no nodule. The 100-mm images were precisely controlled, miniaturized images of the above films. The task of the 16 non-radiologists was to decide if a simulated nodule was present or not. A signal detection experimental paradigm with a 10-point certainty scale was used for analysis. Correction for location was also implemented. For the first problem, results showed that kilovolt potential and film type interacted with the reduction procedure to change the direction of sensitivity (both in the positive and the negative directions) in the reduced format stimulus set, thereby indicating that the 100-mm format was not the main reason for reduced sensitivity noted in the literature. Our conclusion was that the 100-mm format would be suitable for image enhancement displays and for permanent hard copy in a photoelectronic radiologic imaging system. The second problem explores the effects of training on detection and sensitivity. The responses of the untrained observers to the 14-in. x 17-in. images were compared to previously gathered data of the staff and residents of the Arizona Health Sciences Center Radiology Department. Results indicated that the residents, even before formal training, were much better than the untrained observers, but well below the staff, in detection sensitivity. Within 6 months to a year later, they were equivalent to the staff. The main conclusion was that sensitivity does increase with training fairly rapidly and that the findings would be useful in designing further studies to investigate means to speed up or enhance the procedures used to train new radiologists.

The objective of this study was to enable the removal of developer depletion and diffusion effects (i.e., adjacency effects from noisy photographic images, thus, providing a potential for improvement in the reliability of restored object and aerial image estimates. The investigation was based on the use of a previously formulated image resortation model which characterized the exposure, latent image and development interactions of the photographic process in terms of statistical estimation theory. This study addressed the application and appropriate modification of the formulated model in the removal of adjacency effects from noisy images of selected line targets. Literature pertaining to the initial observations of adjacency effects, their recognition as a nonlinear chemical development effect and the pertinent models (forward) used to predict their effects was reviewed. This was followed with a review of the statistical restoration (inverse) model and its comparison to previously derived forward models. X-ray quanta exposures were then used to obtain noisy photographic images, free of optical scattering effects, for the purpose of empirically determining a chemical spread function to characterize chemical adjacency effects. Photographic images were obtained that contained lines of 0.010, 0.100 and 1.000 mm widths to enable comparison between the magnitude of the chemical spread function and the Eberhard effect. A segmented polynomial (cubic spline function) approach was used to calculate the chemical spread function. Separate light quanta exposures were used to obtain gross grain density sensitometric curves and noisy line images. The covering power relationship between mass of developed silver and diffuse density was empirically derived for Panatomic-X film processed without agitation in D-76 developer (diluted 1:1). Emperical verification of the statistical restoration model was achieved. Chemical adjacency effects were successfully removed from noisy line images using an appropriately scaled version of the statistical restoration model. The spatial frequency content of the noisy line images was approximately 1, 10, 15, 20, 25 and 40 cycles/mm. The proportionality factor, used to scale the chemical spread function required in the restoration model, was found to be equivalent to the ratio of the empirically derived chemical spread function and a magnitude estimate of the Eberhard effect. The maximum diffuse density correction for edge effects was found to be 0.14, or approximately 11.1% of the gross grain density level, 1.20. Similar diffuse density corrections for fine line images were found to range between 0.14 and 0.36, or approximately 11.1% to 28.3% of the gross grain density level associated with a specific line element.

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Online news sites are some of the most useful and popular information retrieval systems in use today. Thousands of articles in different languages and on a variety of subjects are posted every day and updated every hour. Most articles are uninteresting and unimportant to a particular individual, and individuals may not want to review entire websites for stories of interest. Systems have been developed that provide summaries from online news websites but finding a means to rapidly scan stories of potential interest remains an open problem. In this thesis, we introduce a novel visualization system that uses geographical location combined with image collages and tag clouds to provide a tool for rapidly reviewing news stories. Tag clouds are arrangements of tags with the most important tags allocated a bigger font size or otherwise more prominent visual properties; and image collages provide a compact, effective and attractive representation for photos on one page. Bringing these media representations together over a geographic map offers a new style of interaction for online news browsing. The usability of our application was evaluated with two user studies. We aimed to determine how best to configure our visualization to communicate more information in less time to users than traditional feed-based news aggregators. We were particularly interested in knowing whether users interpret text/image size and placement as indications of a news item’s prominence. We also wanted to establish whether users understand the semantic relationship between zoom level on the map and the regional relevance (municipal, provincial, national) of news items displayed at that zoom level. The results of user feedback and data analysis (e.g., eye tracking logs) were examined to improve the usability of the system. Data analysis from the second user study suggests that, in general, the system is highly effective in helping users achieve an immediate and effortless bird’s-eye-view of news summaries within a large geographic region. However, users had varying opinions about the level of detail in the user interface (e.g., the number of images).

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