NIOBIUM FILTRATION OF CONVENTIONAL AND HIGH-FREQUENCY X-RAY GENERATORBEAMS FOR INTRAORAL RADIOGRAPHY - EFFECTS ON ABSORBED DOSES, IMAGE DENSITY AND CONTRAST, AND PHOTON SPECTRA

We have studied the effects of niobium beam filtration on absorbed dos es, on image density and contrast, and on photon spectra with conventi onal and high-frequency dental x-ray generators. Added niobium reduced entry and superficial absorbed doses in periapical radiography by 9% to 40% with film and digital image receptors, decreased the radiation necessary to produce a given image density on E-speed film and reduced image contrast on D- and E-speed films. As shown by increased half-va lue layers for aluminum, titanium, and copper and by pulse-height anal yses of beam spectra, niobium increased average beam energy by 6% to 1 9%. Despite the benefits of adding niobium on patient dose reduction a nd on narrowing the beams' energy spectra, the beam can be overhardene d. Adding niobium, therefore, strikes the best balance between radiati on dose reduction and beam attenuation, with its risks of increased ex posure times, motion blur, and diminished image contrast, when it is u sed at modest thicknesses (30 pm) and at lower kVp (70) settings.