A new technique has been developed for imaging small concentrations of elements having K absorption edges in the diagnostic x-ray energy range. Highly sensitive video image subtraction apparatus is used to take the difference between images formed by x-ray spectra peaked above and below the absorption edge. All portions of the image field are detected simultaneously using a conventional image intensifier, eliminating the need for scanning the x-ray defector. Quasi-monoenergetic x-rays are obtained by filtering conventional fluoroscopic x-ray beams. Compared with other methods the technique could lead to a low cost system offering a large reduction in imaging time, with resolution comparable to conventional image intensified fluoroscopy. The results of tests involving periodic images generated electrically or by periodic insertion of x-ray absorbers are presented to illustrate the properties of the imaging electronics. The feasibility of the technique is demonstrated by images of phantoms containing small concentrations of iodine and xenon.
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