The Influence of Scattered Radiation on the Quality of Intraoral Radiographs

The contrast in a radiograph increases when the relative proportion of scattered radiation reaching the film is decreased by reducing the field size. The effect of field size reduction in intraoral radiography has been investigated with respect to reduction in scattered radiation, increase in exposure time, and the detectability of any changes in contrast. The effect of alterations in kVp on these parameters was also examined. Series of images were made with an x-ray source, phantom and films mounted on an optical bench. Measurements were made with field diameters of 1, 2, 4 and 8 cm at 60 and 90 kVp. All images used for evaluation had the same density (D = 0.76) in the apical area. It was found that with an 8 cm field diameter 42% of the radiation reaching the film was scattered radiation: in contrast, with a field diameter of 1 cm scattered radiation was reduced to 4% of the total, whereas the exposure time was increased. Differences in contrast with field diameters of 8, 4 and 2 cm could be distinguished by observers and registered by microdensitometry, but not between 1 and 2 cm. The variation in kVp had no effect on either relative exposure time or scattered radiation: it did however influence contrast.