Gas ionization methods of electrostatic image formation in radiography

Johns, H. E.; Fenster, Aaron; Plewes, Donald B.; Boag, J. W.; Jeffery, P N

doi:10.1259/0007-1285-47-561-519

Cited by 33 publications

(12 citation statements)

References 5 publications

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“…Fig. 17 shows a typical avalanche multiplication curve in a quenching gas mixture (Johns, Boag and Jeffery 1972). This method has also been used by Colvett, Rossi, Mills and Goodman (1970) to enhance the ion current in an ionization chamber used for measuring Potential across gap V 1 examination of many of the parameters involved in the gas-avalanche ionization chamber (Reiss 1972 private communication).…”

Section: Ioonogruphymentioning

confidence: 98%

Xeroradiography

Boag

1973

pmb

105

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Section: Ioonogruphymentioning

confidence: 98%

Xeroradiography

Boag

1973

pmb

105

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“…Further, a high enough voltage should be used so that sensibly all the ions are collected. These conditions can all be satisfied Johns et al, 1974).…”

Section: Ionographymentioning

confidence: 93%

New methods of imaging in diagnostic radiology (Sylvanus Thompson Memorial Lecture)

Johns¹

1976

BJR

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A brief history of the recent developments in computer-assisted tomography (CAT) is presented. The development of whole-body scanners from the basic brain scanner, the trend towards higher-speed scanners using multiple detectors in a fan-type geometry, and some of the unsolved problems related to CAT scanners are discussed, as well as the potential use of whole-body scanning in radiotherapy treatment planning and in radiobiology. A review of recent developments in electrostatic imaging is presented and a new method of imaging called ionography is described in detail. It is shown how a single exposure can be used to produce a number of copies, each with a different amount of edge contrast, under the control of the radiologist. Further, it is shown how this can be done using a closed system so that the ionography chamber never needs to be opened. Some of the recent commercial developments in this field are described. It is suggested that in the future radiology departments may be replaced by departments of imaging, which will include all ways of obtaining diagnostic information and where such a department would be problem oriented rather than technique oriented. The need for basic scientific support by a medical physics and engineering group in such a department is emphasized.

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“…Initial recombination of ions takes a heavy toll even at very high field strength, and there seems to be no way of avoiding this. Tetramethyl tin has been used experimentally by Fenster & Johns (1974) and a few other possible liquids have been examined for suitability by Dance & Boag (1977)-The principal advantage of liquid over gas is that it can be used without excess pressure. This permits the use of a thin foil window, with virtually no X-ray absorption, and allows the image to be copied by induction through the window (Fenster & Johns 1976).…”

Section: Sensitivity O F Ionographymentioning

confidence: 99%

“…The relative sensitivities of gas and liquid ionography have been calculated by Fenster & Johns (1974) and by Dance & Boag (1977). A synopsis is given in table 1.…”

Section: Sensitivity O F Ionographymentioning

confidence: 99%

“…Thus, experiment confirms that 10 line pairs per millimetre can be resolved when 60 kVp X-rays are absorbed in a 1 cm layer of xenon at 10 atm although the extreme range of the most energetic photoelectrons released under these conditions exceeds 1.5 mm and th at of the Auger electrons is 0.4 mm. U nder these conditions, also, only 37 % of the ions created by the X-ray pencil are collected within a circle of 0.12 mm radius on the foil (Johns et al 1974), so the range of the secondary electrons does reduce the efficiency of high resolution imaging, even though the extreme peakiness of the distribution still preserves fine detail. The K-fluorescent photons, on the other hand, can travel several cms from their point of origin and their reabsorption in the gas merely increases the general background level of ionization, which does not appear as fog if edge contrast development is adopted.…”

Section: R Esolutionmentioning

confidence: 99%

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Electrostatic imaging in radiology: limitations and prospects

Boag

1979

Phil. Trans. R. Soc. Lond. A

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In this radiographic technique, the latent image takes the form of a surface distribution of electric charge which may be rendered visible in various ways. The charge distribution is formed either on a selenium surface (xeroradiography) or by collecting ions on an insulating foil (ionography). Conventional powder development techniques yield visible images in which high spatial frequencies are enhanced (‘edge contrast’) and low frequencies largely suppressed. This contrast pattern is useful for the radiological study of soft tissues, vascular structure, bones and joints. Xeroradiography is less sensitive than film-screen radiography and this restricts its medical application to sites where gonad exposure is minimal. Ionography with compressed xenon has high sensitivity but is not yet fully developed commercially. It requires a rigid link between the X-ray tube and the recording chamber. The latent image is produced on plastic foil which can then be developed in many different ways to yield either edge contrast or density images. Liquid ionography avoids the need for high pressure and allows multiple copies of the latent image to be made. There are some special applications of ionography in the research laboratory but in industrial work xeroradiography, despite lower sensitivity, is likely to be more convenient for any applications which demand edge contrast pictures.

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Gas ionization methods of electrostatic image formation in radiography

Cited by 33 publications

References 5 publications

Xeroradiography

Xeroradiography

New methods of imaging in diagnostic radiology (Sylvanus Thompson Memorial Lecture)

Electrostatic imaging in radiology: limitations and prospects

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