Showing papers by "John Law published in 1991"

A new phantom for mammography

Abstract: A new mammography phantom from Du Pont is described. It has a wider range of types of detail than in previous phantoms, including some which closely simulate breast tissues. Experience of its use, and comparisons with an earlier ("Barts") phantom, are reported. The Du Pont phantom appears to have greater sensitivity to changes in tube kV and focal spot size, and better discrimination between different film-screen combinations and between films from different breast screening centres.

Theory and Narrative in the History of Technology: Response

Abstract: For the last four years I have been collecting material about a major British aircraft project, the TSR.2 tactical strike and reconnaissance aircraft. This project, which was first conceived in about 1956 and was canceled amid much acrimony in 1965, employed at least 20,000 people at its height. As a part of my study I have read all the secondary material I can find, I have seen a great deal of primary source material of one kind or another, and I have interviewed more than thirty of the major participants. During the last eighteen months I have been writing this material up. This has, I confess, been a particularly difficult exercise. One of the reasons for this has been that it is possible to write it up in different ways. Let me simplify and say that I could write it up as critical narrative history. Alternatively, I could use parts of that narrative to explore more theoretically oriented questions that have to do with technology and the way in which it interacts with social relations.

Patient dose and risk in mammography

Abstract: Patient dose in mammography is estimated by two different methods which are compared and which give good agreement. A mean tissue dose of about 1 mGy per film is found for a breast of 4.5 cm compressed thickness. Variables which affect dose are then considered quantitatively, including compressed breast thickness, tube potential, grids, magnification and beam collimation. The variables having the greatest effect are breast thickness and magnification. For example, an 8 cm breast receives about four times the mean tissue dose of a 3.5 cm breast. Similarly, using a magnification factor of about 2, dose is increased about four times in the primary beam, but the adverse consequences may be largely removed with conventional collimation to part of the breast only. Finally, the dose estimates are combined with existing data on breast cancer induction to predict the risk of carcinogenesis in a breast screening programme. For example, in a screening centre performing 15000 examinations per year, only one ...