Private practice in developing countries.
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Developing Countries↗
Biomedical subjects
I Brodie
Publications and source records attributed to I Brodie.
Radiographic information theory and application to mammography.
A theoretical estimate is made for the lowest exposure necessary to record the smallest feature of interest, using various radiographic detecting surfaces and allowing for the probability of making errors to be within certain specified bounds. These calculated exposures are compared with the errors to be within certain specified bounds. These calculated exposures are compared with the actual exposures given in clinical situations in order that the smallest feature of interest can be observed by the practitioner with the same probability of error. A measure of the viewing efficiency of a radiographic process is given by the ratio of these exposures. The application of these concepts to mammography for three different recording media--film, film/screen, and xeroradiography--shows that the minimum entrance exposure necessary for recording information by each receptor varies with the energy of the x-ray beam, and that the optimal photon energy lies in the 21- to 25-keV region. All three methods with their present modes of processing use at most only a few percent of the information they actually intercept. This argues, for example, that if some more efficient method of reading xerographic plates were found, entrance exposures as low as 9 mR per exposure would suffice for a mammogram.
Calcinosis↗
Radiographic information theory: correction for x-ray spectral distribution.
A more complete computational method is developed to account for the effect of the spectral distribution of the incident x-ray fluence on the minimum exposure required to record a specified information set in a diagnostic radiograph. It is shown that an earlier, less rigorous, but simpler computational technique does not introduce serious errors provided that both a good estimate of the mean energy per photon can be made and the detector does not contain an absorption edge in the spectral range. Also shown is that to a first approximation, it is immaterial whether the detecting surface counts the number of photons incident from each pixel or measures the energy incident on each pixel. A previous result is confirmed that, for mammography, the present methods of processing data from the detector utilize only a few percent of the incident information, suggesting that techniques can be developed for obtaining mammograms at substantially lower doses than those presently used. When used with film-screen combinations, x-ray tubes with tungsten anodes should require substantially lower exposures than devices using molybdenum anodes, when both are operated at their optimal voltage.
Humans↗
Minimum entrance exposure estimates for information recording in diagnostic radiology.
Based upon previously derived expressions, a procedure is given for estimating the minimum entrance exposure necessary to record a desired information set for use in any diagnostic radiological situation. By separating the different variables contributing to the final image and making suitable approximations, a simple relationship of four separable components is obtained. Some typical examples are given to illustrate the relative importance of each component, and to obtain numerical estimates of exposure values. These examples show that the theoretical entrance exposure range for most diagnostic situations, where a realistic information set is desired, lies between 2.5 X 10(-3) and 1.2 X 10(-2) mC/kg (10-50 mR). It is also concluded that a 75-kVp x-ray source, filtered to remove the low-energy photons and with a mean photon energy of 40 keV, should be sufficiently close to optimum in most diagnostic situations to record the desired information in the above entrance exposure range.
Bone and Bones↗