title: The effect of anatomical noise on perception of low contrast in intra-oral radiographs: an in vitro study.
abstract: OBJECTIVE
  Radiographic images suffer from varying amounts of noise. The most studied and discussed of these is random noise. However, recent research has shown that the projected anatomy contributes substantially to noise, especially when detecting low-contrast objects in the images. Our aim, therefore, was to evaluate the extent to which overprojected anatomical noise affects the detection of low-contrast objects in intra-oral images.
  
  
  METHODS
  Our study used four common sensor models. With each sensor, we took four series of images, three series with and one series without an anatomical phantom present. In each series, we exposed a low-contrast phantom at 18 different exposure times using a standardized method. 4 observers evaluated all 288 images.
  
  
  RESULTS
  The low-contrast characteristics differed substantially when imaging low contrast on a homogeneous background compared with imaging low contrast when an anatomical phantom was present. For three of the sensors, optimal exposure times for low-contrast imaging were found, while the fourth sensor displayed a completely different behaviour.
  
  
  CONCLUSIONS
  Calibrating the low-contrast properties of an imaging system using low-contrast objects on a homogeneous background is not recommended. On an anatomical background, low-contrast properties are completely different, and these will mimic the clinical situation much more closely, directing the operator how to best use the system. There is a clear demand for further research on this subject.
authors.affiliation: 1 Department of Oral and Maxillofacial Radiology, Faculty of Odontology, Malmö University, Malmö, Sweden.|2 Department of Oral Radiology, Postgraduate Dental Education Center, Örebro, Sweden.
authors.forename: Lars
authors.initials: L
authors.lastname: Olsson
authors.affiliation: 1 Department of Oral and Maxillofacial Radiology, Faculty of Odontology, Malmö University, Malmö, Sweden.|3 Department of Radiation Physics, Skåne University Hospital, Malmö, Sweden.
authors.forename: Mats
authors.initials: M
authors.lastname: Nilsson
authors.affiliation: 4 Postgraduate Dental Education Center, Faculty of Medicine and Health, School of Health and Medical Sciences, Örebro University, Örebro, Sweden.
authors.forename: Björn
authors.initials: B
authors.lastname: Svenson
authors.affiliation: 1 Department of Oral and Maxillofacial Radiology, Faculty of Odontology, Malmö University, Malmö, Sweden.
authors.forename: Kristina
authors.initials: K
authors.lastname: Hellén-Halme
mesh_terms: D016477:Artifacts; D001641:Bicuspid / Q000000981:diagnostic imaging; D006801:Humans; D008334:Mandible / Q000000981:diagnostic imaging; D008963:Molar / Q000000981:diagnostic imaging; D015588:Observer Variation; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement / Q000592:standards*; D016300:Radiography, Bitewing / Q000295:instrumentation / Q000592:standards*; D019252:Radiography, Dental, Digital / Q000295:instrumentation / Q000592:standards*; D013997:Time Factors
keywords: contrast sensitivity; dental; digital; radiography