title: Effects of collimator size of a dental X-ray unit on image contrast.
abstract: OBJECTIVE
  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.
authors.affiliation: Department of Oral Radiology, Centre for Oral Health Sciences, Malmö University, Malmö, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Falk
authors.forename: J E
authors.initials: JE
authors.lastname: Lindhe
authors.forename: M
authors.initials: M
authors.lastname: Rohlin
authors.forename: M
authors.initials: M
authors.lastname: Nilsson
mesh_terms: D015502:Absorptiometry, Photon / Q000295:instrumentation; D002648:Child; D019140:Dental Care for Children / Q000295:instrumentation; D006801:Humans; D015588:Observer Variation; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011861:Radiography, Dental / Q000295:instrumentation*; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D013673:Technology Assessment, Biomedical; D013679:Technology, Radiologic / Q000295:instrumentation