Effects of collimator size of a dental X-ray unit on image contrast.

Abstract

To examine the effect of collimator size on image contrast in dental radiography. Two conventional collimators, one circular (53 mm in diameter) and one rectangular (35x45 mm2), were compared with a small rectangular collimator (26x39 mm2). Low-contrast and high-contrast resolution was assessed with the aid of contrast-detail and line-pair phantoms. Shallower holes were observed with the small rectangular collimator. Two-thirds of 17 observers assessing high-contrast resolution considered the small collimator to result in a clearer image than the conventional collimators. The same effect was demonstrated with the line-pair phantom and by microdensitometry. With the small collimator the energy imparted is estimated to be reduced by 54 and 36% compared with the conventional circular and rectangular collimators respectively. Decrease of the collimator size to fit the film size used for children will result in improved low-contrast and, under some conditions, improved high-contrast resolution. This improvement might have implications for caries diagnosis and monitoring.