FLUOROSCOPIC FILTERING

A radiation source emits a beam of penetrating radiation toward an examination object. A protective filter, fabricated of yttrium foil attached to a bakelite card, is positioned in the path of the radiation beam between the source and the examination object. The yttrium filter has a preselected critical absorption edge operable to obstruct from the beam photon energy below 20 keV and permit a filtered beam having a photon energy above 20 keV to pass through the examination object. The filtered radiation emerging from the examination object is detected by preselected means, such as illuminated film, an X-ray intensifier, a CT scanner, or the like. The detector generates an output signal corresponding to the intensity of the emerging filtered radiation. An image processor converts the output signals to a radiographic image displaying the examination object.