| Popis: |
X-ray backscatter was used to detect near-surface fragments of chicken clavicle, 2 cm long and 20–60 mg in weight, in polystyrene phantoms and in samples of breast meat. The densities of clavicle fragments and pieces of breast meat were measured by Archimedes’ method, and were respectively 1·32±0·05 and 1·07±0·007 g cm −3 . Samples were prepared consisting of blocks of polystyrene, or of chicken breast, into which fragments of clavicle were inserted, approximately 0·1 cm below the surface. The samples were scanned in front of a 140 kVp X-ray source, and the backscattered X-rays were counted by a detector collimated at 135° to the beam. The spatial resolution was 0·1 by 0·1 cm in the source–sample–detector plane, and 2 cm in the perpendicular direction. The scattered spectra were collected, and for each spectrum, three quantities were plotted against sample position: the counts in a 10–40 keV energy window; the counts in a 40–95 keV energy window; and the mean spectral energy over the range 10–95 keV. The contrasts from these measurements were compared with those obtained in transmission images. The detected counts in the 10–40 keV energy window showed little positive contrast, but strong negative contrasts due to attenuation. The contrasts ranged from −13 to −25·8%, and the signal-to-noise ratios (normalised for a 30 mA source at 1 s sampling time) were 5·8–11·7. The detected counts in the 40–95 keV energy window showed peaks in the backscatter when the scan passed across a bone fragment. The contrasts ranged from 4·2 to 14·7%, and the signal-to-noise ratios from 1·6 to 5·6. The mean spectral energy gave results intermediate between the two, with contrasts in the range 1·7–6·7% and signal-to-noise ratios from 3·0 to 11·0. The 10–40 keV energy window gave contrasts which were larger than those in the transmission images, and the 40–95 keV energy window gave contrasts similar to the transmission images. |
Full Text from ScienceDirect