title: Effects of niobium filtration and constant potential on image quality in dental radiography. 1: Subjective assessment and contrast.
abstract: Two half-wave, self-rectified dental X-ray units and two constant potential units were compared with respect to the image quality of dental radiographs, and the effect of additional niobium filtration on the half-wave beams was explored. Eight beam qualities were investigated and subjective assessments of the films were made by 20 observers. An aluminium phantom was constructed which produced densities similar to those found on dental radiographs in periapical regions and in enamel. The effect of beam quality on the radiographic contrast between these densities was studied. Subjectively, there was a preference for the softer beams and for films in the middle range of exposures. The addition of niobium reduced preference by 50% at both 70 and 90 kVp. With one exception, the constant potential units fell within the range of preferences recorded for the self-rectified units. However, the relationship of preference to half-value layer was not significant. Radiographic contrast decreased linearly as the half-value layer increased (r2 = 0.956, P less than 0.0005), and no specific effects of constant potential or niobium filtration were revealed.
authors.affiliation: Faculty of Dentistry, University of British Columbia, Vancouver.
authors.forename: D
authors.initials: D
authors.lastname: McDonnell
authors.forename: C
authors.initials: C
authors.lastname: Price
mesh_terms: D005069:Evaluation Studies as Topic; D005374:Filtration / Q000295:instrumentation; D006801:Humans; D009556:Niobium; D011856:Radiographic Image Enhancement; D011861:Radiography, Dental / Q000295:instrumentation*
chemical_list: D009556:Niobium