A xenon ionization detector for scanned projection radiography: Theoretical considerations

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Abstract
Xe ionization detectors have been used successfully in computed tomograpy (CT) scanners; however, the detector design used in CT scanners does not provide sufficient spatial resolution for scanned projection radiography. A new design of Xe detector with individual element widths of 0.5 mm was investigated. In this design, there are no metal septa separating individual elements. As a result, detection efficiency is better than the design with septa, and construction of an array with submillimeter element widths is simpler; however, crosstalk will now occur between elements. Theoretical calculations of efficiency and resolution for the septaless design of a Xe detector are presented. Results of these calculations indicate that for a spectrum of 100 kVp [kilovolt peak], element dimensions of 0.5 mm .times. 0.5 mm .times. 10 cm, a front window of 0.5-mm Al, and a Xe pressure of 20 atm, quantum efficiency will be > 95%, detective quantum efficiency (DQE) will be .apprx. 75% and both energy and conversion efficiencies will be limited to 50% by K-fluorescent escape. The calculations also predict that for the same design, the reduction in lesion contrast induced by crosstalk will be < 10% for all typical spectra. These theoretical results have encouraged the pursuit of the construction of a prototype septaless Xe detector for scanned projection radiography.