Biomedical subjects
Publications and source records attributed to R F Wagner.
Tissue from an amelanotic melanoma which involved the lung and brain was studied by electron microscopy. Endothelial fenestrae were found in the intrinsic tumor capillaries at both locations, a finding which does not appear to have been previously reported for amelanotic melanoma. Pitfalls in the diagnosis of this rare tumor are discussed.
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An image often contains information that is not extracted by the human decision maker. This is due to two limitations of the eye-brain system: the existence of a contrast threshold, as with any device that works in the presence of noise (internal or external), and an evolutionary pattern that has not fitted us for viewing noisy scenes, leaving us suboptimal in that regard. Since it is often impossible to overcome these limitations simultaneously--even electronically--multiple displays of the image content must be available to the human viewer, and contrast scale and degree of sharpness/smoothing must be tunable. Our planning must anticipate these requirements, a greater dependence on digital computers for the image manipulation, and the computer's inevitable involvement in the decision process.
From measurements of screen-film sensitometry, Wiener spectra, and x-ray spectra, the speed, mottle, and quantum efficiency of several rare earth screen-film systems have been characterized. These systems offer exposure reductions of from two- to tenfold over conventional calcium tungstate systems. At the slower end, the noise (mottle) and resolution are comparable to what is available with conventional systems. Moreover, films designed to be used in such systems can be made with significantly lower silver content. As the speed advantage is increased from two- to genfold, however, the mottle also increases.
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The occurrence of anogenital warts has increased both in clinic and in private practice. Both sexes and all races are affected, with the highest prevalence in patients aged 15 to 40 years. The etiologic agent, the human papillomavirus (HPV), has been classified by DNA hybridization techniques into at least 42 types, of which types 16 and 18 are considered to carry a high risk for cancer. A patient who had been seen intermittently over a period of 26 years with perianal and anal warts that responded to treatment finally developed two granulomatous nodules morphologically different from the previous lesions. A biopsy confirmed that the nodules were typical of Bowen's disease, a precancerous lesion, and they were surgically excised. Thus, anogenital warts that fail to respond to conventional therapy or change in appearance warrant a biopsy and, where the technique is available, DNA typing to identify the viral pathogen.
The advent of fast Fourier techniques has greatly facilitated the digital analysis of noise power spectra (Wiener spectra) by circumventing the need for the autocorrelation function. We are now able to Fourier analyze film data at about the same rate the microdensitometer-computer system can collect it (1000 points/sec). The new technique has been applied to the analysis of the quantum mottle of several rare earth intensifying screen systems confirming earlier estimates from our pilot studies that such screens are capable of reducing exposure by a factor of about 2 with imaging parameters comparable to those of conventional calcium tungstate systems.
"The imaging process is fundamentally a sampling process." This philosophy of Otto Schade, utilizing the concepts of sample number and sampling aperture, is applied to a systems analysis of radiographic imaging including some aspects of vision. It leads to a simple modification of the Rose statistical model; this results in excellent fits to the Blackwell data on the detectability of disks as a function of contrast and size. It gives a straightforward prescription for calculating a signal-to-noise ratio, which is applicable to the detection of low-contrast detail in screen-film imaging, including the effects of magnification. The model lies between the optimistic extreme of the Rose model and the pessimistic extreme of the Morgan model. For high-contrast detail, the rules for the evaluation of noiseless images are recovered.
The imaging process has two fundamental stages: detection and display. The detection stage can be quantified rigourously using Shannon's information theory. This requires the contrast scale (CS), modulation transfer function (MTF), and noise power spectrum [N(f)] to be combined into a signal-to-noise ratio (SNR). This results in two fundamental summary figures of merit: the density of noise equivalent quanta (NEQ) in the image and the information bandwidth integral (IBWI). These algorithm-independent measures are used to quantify the recording stage. The display stage is less well understood since it couples to an external observer. Several types of decision makers are treated. Examples are drawn from first and second generation CT, demonstrating that thye are nearly quantum limited for large signals, indicating how their algorithms are matched or mismatched to the geometry, and calculating the contrast-detail diagrams for those decision makers.
If a normal screen-film exposure is made using a conventional grid, a reduced exposure may be used with a superior scatter removal device to record the same image information. This theoretical conclusion is not readily demonstrated because of the limited visibility on the underexposed film. In this study radiographs underexposed by a factor of three with a scanning multiple slit assembly (SMSA) were enhanced autoradiographically and found visually to contain more information than properly exposed radiographs obtained under similar conditions using a conventional Bucky grid. This observation was confirmed by contrast scale and noise measurements. Furthermore, the entrance skin exposure of the radiograph using the SMSA was 45% of that required with the grid technique at the same beam quality.
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