George W. Seeley

Effect of noise correlation on detectability of disk signals in medical imaging

Pixel signal-to-noise ratio is one accepted measure of image quality for predicting observer performance in medical imaging. We have found, however, that images with equal pixel signal-to-noise ratio (SNRp) but different correlation properties give quite different observer-performance measures for a simple detection experiment. The SNR at the output of an ideal detector with the ability to prewhiten the noise is also a poor predictor of human performance for disk signals in high-pass noise. We have found constant observer efficiencies for humans relative to the performance of a nonprewhitening detector for this task.

Design and testing of artifact-suppressed adaptive histogram equalization : a contrast-enhancement technique for display of digital chest radiographs

One of the goals of our research in the field of digital radiography has been to develop contrast-enhancement algorithms for eventual use in the display of chest images on video devices with the aim of preserving the diagnostic information presently available with film, some of which would normally be lost because of the smaller dynamic range of video monitors. The ASAHE algorithm discussed in this article has been tested by investigating observer performance in a difficult detection task involving phantoms and simulated lung nodules, using film as the output medium. The results of the experiment showed that the algorithm is successful in providing contrast-enhanced, natural-looking chest images while maintaining diagnostic information. The algorithm did not effect an increase in nodule detectability, but this was not unexpected because film is a medium capable of displaying a wide range of gray levels. It is sufficient at this stage to show that there is no degradation in observer performance. Future tests will evaluate the performance of the ASAHE algorithm in preparing chest images for video display.

Fractal Physiology And Nuclear Medicine Scans

Measurement of the power spectra of liver scans reveals that the radiocolloid distribution in the human liver behaves as a fractal object. Analysis of the power spectra suggests that the fractal dimension of the functional units of the liver changes with disease state, and that power spectral slope may be a useful classifier for the presence of disease. Models are proposed that relate the power spectral slope to the fractal dimension of the liver parenchyma.

Detection of Breast Abnormalities on Teleradiology Transmitted Mammograms

The authors conducted an observer performance study to compare breast lesion detection of conventional mammography (CM) with teleradiology (TE) transmitted mammograms. One hundred four abnormal, single-projection mammographic images were transmitted by teleradiology. Abnormalities included 11 cases with skin thickening or retraction, 48 cases with microcalcifications, and 52 with parenchymal masses. The CM and TE images were reviewed by four mammographers who indicated the type and location of abnormalities and a level of confidence for their diagnostic decisions. For each of three detection tasks--skin and nipple abnormalities, microcalcifications, and masses--receiver operating characteristic curve analysis was performed for individual readers and all readers as a group. For detecting skin and nipple abnormalities, readers performed significantly better with CM than with TE (z = 2.05, P = less than 0.04). However, no significant differences were found among readers for detection of either microcalcifications or masses. Further improvements in hardware and imaging parameters may improve detection of soft tissue abnormalities. Further evaluation is necessary to determine whether teleradiology might be applicable to breast cancer screening.

Computed radiographic evaluation of simulated pulmonary nodules. Preliminary results.

We evaluated the capabilities of a computed radiography system (CRS) and a standard radiography system (SRS) in the detection of simulated solitary pulmonary lung nodules of various sizes and contrast. A phantom simulated the pulmonary anatomy, and specially shaped plexiglass disks were externally mounted to simulate solitary pulmonary nodules of different diameters and thicknesses. ROC curves were generated based on the performance of each of the radiologists observing each film set. In this preliminary study, the overall performance for both the CRS and the SRS were comparable in detecting simulated pulmonary nodules.

Development Of A Digital Video Subtraction System For Intravenous Angiography

This paper represents the third presentation to the SPIE that has dealt with our research activities in photoelectronic radiology and intravenous angiography. The earlier papers have been published in Volumes 1271 and 1642 of the Proceedings, and cover the evolution of the technical facilities and associated radiographic images obtained with dogs. We have now reached a level of competence suitable for the examination of patients, and we present examples of the images obtained to date. Although the research activity reported here began with the task of non-invasive imaging of arteries for the early detection of atherosclerosis, it is becoming increasingly clear that the method is applicable to all areas of the body to which angiography is being currently applied. Furthermore, with the advantages of this technique, new applications are being developed. Thus, we are now beginning examination of animals and patients to determine the utility of intravenous (non-invasive) angiography for examination of the head, coronary arteries, heart, lungs, kidneys, and extremities, and look forward with considerable optimism to the results.

Computer-simulated lung nodules in digital chest radiographs for detection studies.

Computer simulations of lung nodules overcome many shortcomings of creating radiographs using anthropomorphic nodule phantoms for lung nodule detection studies, but these algorithms can be cumbersome and involved. A simple, fast, and flexible computer program to simulate lung nodules in digital chest radiographs for detection studies is reported. To verify the realism of the simulated nodules, a psychophysical study and a statistical study were conducted. In the psychophysical study, six radiologists and four nonradiologists were asked to distinguish between 17 real lung nodules and 17 computer-simulated lung nodules shown in eight radiographs. The results show that the computer-simulated lung nodules are indistinguishable visually from real lung nodules. Using parameters from the Rose model of vision, results show that the simulated and real nodules are the same statistically. Thus, besides visual validity, statistical analysis in confirming the validity of the simulated lung nodules is included.

Comparison Of Digital Workstations And Conventional Reading For Evaluation Of User Interfaces In Digital Radiology

The User Interface Study Group at the University of Arizona is investigating the interaction of Radiologists with digital workstations. Using the Arizona Viewing Console we have conducted an experiment to compare a digital workstation with a particular conventional reading process used for cases from a local Health Maintenance Organization. A model consisting of three distinct phases of activity was developed to describe conventional reading process. From this model software was developed for the Arizona Viewing Console to approximate the process. Radiologists were then video taped reading similar sets of cases at each workstation and the tapes were analyzed for frequency of hand movements and time required for each phase of the process. This study provides a comparison between conventional reading and a digital workstation. This paper describes the reading process, the model and its approximation on the digital workstation, as well as the analysis of the video tapes.

Psychophysics From A Radiologist's Point Of View

With only a handful of physicians in this large audience, I find myself in a rather pre-carious position trying to relate a complex topic to a group of scientist primarily from the physical sciences. Perhaps I can make an analogy. We spent a significant amount of time this morning elaborating on signal to noise ratio. If one looks at the spectrum of signal to noise ratio, in trying to quantitate factual information regarding the physical sciences on one hand and the biological sciences, particularly medicine, on the other, the results are rather interesting. There is no question in my mind, having spent a few years in physics, that the signal to noise ratio in the physical sciences is quite high. As one approaches the biological sciences, it diminishes significantly and as one approaches medicine it becomes quite small, particularly in fields such as psychiatry where information is extremely difficult to quantitate. The reason for this is relatively simple; in physical sciences an equation needs to be solved, an integral needs to be worked out or mathematical postulate is either proven or not proven. However, as one approaches biological systems, the number of variables, one depending on another, sometimes almost appears infinite. Therefore, to try to take some of these physical measurements, used in the day-to-day analysis of mathematical equations, etc., and use these tools and each of the variables in our biological systems sets up an extremely complex situation to solve. Therefore, for me to talk about the psychophysics from a physician-radiologist point of view is somewhat presumptuous on my part. However, our challenge in medicine today is to use the tools of the physical sciences to better quantitate these variables and it is for this reason that I appear before you today.

Detection of small radiation sources: The effect of mode of count‐rate presentation

We used an observer-performance study to compare four different modes of presenting count-rate data from a radiation detector. Observers searched for small, concealed radioactive sources using a hand-held radiation-detector probe. The modes of count-rate presentation were a ratemeter, howler, multichannel scaler, and HRM III. The HRM III calculates the statistical significance of the difference between current and previous count rates and presents the result as an audio signal. We tested six observers with each mode of count-rate presentation, calculated receiver operating characteristic (ROC) curves, and used the areas under the ROC curves to compare the different modes. Observer performance was better with the multichannel scaler and HRM III than with either the ratemeter or the howler. The results suggest that observer performance with devices that use ratemeters or howlers can be enhanced by improving the mode of count-rate presentation.