Electrostatic fields in ionography

Abstract

There is renewed interest in diagnostic radiology in electrostatic methods of imaging, such as xeroradiography and ionography. This is due to the fact that edge contrast can be achieved, aiding in the visualization of soft tissue tumors. In analyzing the image forming properties of these system, we chose to solve the electrostatic problems by the method of images. We present methods and recursion formulas for calculating electrostatic fields due to (a) any charge distribution on a slab of dielectric (the solution involves a single infinite series) or (b) the same as the above with the introduction of an additional ground plane parallel to the dielectric surface (the solution now involves double infinite series). Analysis of these fields suggests new methods of controlling edge contrast and development configurations where the field which penetrates through the foil is used to produce the final image rather than the field above the charged surface.

Edge contrast in ionography

“…The method of varying the edge contrast can also be applied to a closed transfer ionography system where the latent charge pattern may be copied several times onto separate thin Mylar foils (Plewes, Fenster and Johns 1975). From this point each of the thin Mylar foils may be mounted on additional Mylar foils of different thicknesses and each developed in turn to give images with varying degrees of edge enhancement.…”

“…2 where the depletion region starts is that point where the normal component of the field strength at the Mylar surface approaches zero. Using the method of images (Plewes and Johns 1975), the vertical electric field, E,, a distance one toner radius above a halfplane of charge with the charge edge at the origin is…”

“…Consequently, with ionography it is possible to alter the dielectric foil parameters and electrode configurations to adjust development sensitivity and image quality. Earlier calculations indicated that the electrostatic fields of ionography images (Plewes and Johns 1975) were highly dependent on the thickness of the Mylar foil used in the ion chamber and that it would be possible to use the foil thickness as a means of altering the edge contrast in the developedimage. This work also suggested a means of transferring the image on the inside of the ionography chamber by an induction technique to a second sheet of Mylar outside the chamber that could be removed and developed independently (Plewes, Fenster and Johns 1975).…”

“…Earlier calculations indicated that the electrostatic fields of ionography images (Plewes and Johns 1975) were highly dependent on the thickness of the Mylar foil used in the ion chamber and that it would be possible to use the foil thickness as a means of altering the edge contrast in the developedimage. This work also suggested a means of transferring the image on the inside of the ionography chamber by an induction technique to a second sheet of Mylar outside the chamber that could be removed and developed independently (Plewes, Fenster and Johns 1975). 0031-9l~~/78/0006-1060 $02.00 @ 1978 The Institute of Physics This copying procedure could be repeated to give several identical copies of the original charge pattern.…”

An atmospheric pressure inography system suitable for mammography

“…The gas is situated between two electrodes and the charges formed are collected on an insulating foil stretched over one of the electrodes. A great deal of work has already been undertaken on the physical processes involved in the production of the latent image (Fenster and 0031-9155/80/050893+ 10$1.50 @ 1980 The Institute of Physics , Fenster et af 1974, Jeffrey et af 1974, Johns et a1 1974 and also its development (Boag et af 1974, Plewes and Johns 1975, Muntz et al 1975. Most of this work has been concerned with the use of gas at high pressures as the x-ray absorbing medium.…”