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Effects of collimator size of a dental X-ray unit on image contrast
1Department of Oral Radiology, Centre for Oral Health Sciences, Malmö University, Malmö, Sweden.
Objectives:
To examine the effect of collimator size on image contrast in dental radiography.
Methods:
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.
Results:
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.
Conclusions:
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.