An atmospheric pressure inography system suitable for mammography

Abstract

Ionography is a possible replacement for silver halide based imaging systems in diagnostic radiology. This type of imaging depends upon the ionisation produced in a gas by incident x-radiation. The ions formed are collected on a plastic foil and the image is made visible by a suitable development process. The physical design properties which can affect sensitivity and image quality of an ionography system are outlined in this paper. Based upon the requirements of adequate sensitivity and resolution an atmospheric pressure ionography system is described which has been designed primarily for use in mammography. Freon 13B1 gas was chosen as the x-ray absorbing medium because it contains a relatively high atomic number atom (bromine, Z = 35) and also has a high density. It is a relatively cheap gas, has a high breakdown potential and has satisfactory resolving capability, particularly when employed at atmospheric pressure with low energy x-ray beams. The performance of the system is discussed in terms of sensitivity and resolution. Problems associated with an atmospheric pressure system are outlined and possible solutions described. Preliminary clinical results obtained with the system are also presented.

Model sensitivity of theoretical results for ionization–excitation of helium

“…The latter results, obtained within a distorted-wave model for the projectile and a convergent R-matrix with pseudo-states (RMPS) close-coupling treatment of the initial bound state and the ejected-electron-residualion interaction, finally established a converged (with respect to the number of coupled states) first-order benchmark. As seen in figure 1, these predictions are in good agreement with the revised numbers of Kuplyauskene and Matnitskas [22], with the calculation by Moores [24] and also in reasonable agreement with the renormalized data of the Reno group [14]. Note, however, that the attempt to account for second-order effects apparently failed.…”

“…The same approach, or other sophisticated representations, was used for the initial He(1s 2 ) bound state. Results using these models were obtained by Rudge [23] (plane wave plus 3-state close-coupling), Moores [24] (distorted wave plus 3-state close-coupling, also including an exchange and an 'interference' term in the calculation), Raeker et al [25] (distorted wave plus 6-state close-coupling) and Bartschat and Grum-Grzhimailo [26]. The latter results, obtained within a distorted-wave model for the projectile and a convergent R-matrix with pseudo-states (RMPS) close-coupling treatment of the initial bound state and the ejected-electron-residualion interaction, finally established a converged (with respect to the number of coupled states) first-order benchmark.…”