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Dentomaxillofacial Radiology, Vol 28, Issue 5 261-266, Copyright © 1999 by British Institute of Radiology

ARTICLES

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

A. Falk, J. E. Lindhe, M. Rohlin and M. Nilsson
Department of Oral Radiology, Centre for Oral Health Sciences, Malmo University, Malmo, 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.


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