A XENON IONIZATION DETECTOR FOR SCANNED PROJECTION RADIOGRAPHY - 95-CHANNEL PROTOTYPE EVALUATION

A 95-channel prototype Xe ionization detector was designed, constructed, and tested for use in scanned projection radiography (SPR). This detector has higher spatial resolution, is more dose efficient, and is easier to construct than computed tomography (CT) Xe ionization detectors. It consists of 2 parallel plates separated by a 2-mm gap filled with Xe gas at 2 mPa [megapascals] (20 atm). One plate is a high-voltage electrode while the other is a circuit board etched to form an array of metal collector strips focused on the X-ray source. The resulting detector channels are 0.5 mm wide and 6 cm long. Results were presented from measurements of system noise and detector channel calibration. The detector system was compared to a screen/film system. It allows the detection of structures with 0.17% radiographic contrast compared to 2% contrast required for detection with screen/film when tested by imaging a 10-cm-thick Lucite phantom with a 10 .times. 10-6 C/kg exposure. From images of resolution test patterns, the limiting resolution of the detector is 2.0 1p/mm at 1.6 magnification. Images of reduction mammoplasty tissue samples, obtained 1/17 the exposre of screen/film images, had the same low-contrast sensitivity but contained less high-contrast detail than the film images.