title: Correction for attenuation and visual response in digital radiography.
abstract: OBJECTIVE
  To derive a method to correct for the exponential attenuation adding visual linearization for digital radiography and to perform an experimental test to study effects on observer performance.
  
  
  METHODS
  A theoretical analysis was performed and expressions were derived to correct radiographic data for the attenuation. An experiment was performed exposing an aluminum step wedge with holes of increasing depths behind each step plus soft tissue simulation. Seven original images were created with a digital intraoral X-ray sensor and a further 14 transformed images produced. Ten observers examined the images in a randomized order reporting the number of holes seen per wedge step. The results were analysed by One Way ANOVA.
  
  
  RESULTS
  It was possible to correct for attenuation and the response of the human visual system to light intensities from a computer monitor. Perception was significantly improved in all recalculated radiographs that took both attenuation and the response of the eye into account (P-values ranged from <0.0001 to <0.0286).
  
  
  CONCLUSIONS
  The transforms may be useful for improved perception when viewing digital radiographs.
authors.affiliation: Department of Oral Radiology, Karolinska Institutet, Stockholm, Sweden. Ulf.Welander@ofa.ki.se
authors.forename: U
authors.initials: U
authors.lastname: Welande
authors.forename: K
authors.initials: K
authors.lastname: Yoshiura
authors.forename: G
authors.initials: G
authors.lastname: Li
authors.forename: P
authors.initials: P
authors.lastname: Sällström
authors.forename: W D
authors.initials: WD
authors.lastname: McDavid
mesh_terms: D015502:Absorptiometry, Photon; D000465:Algorithms; D000704:Analysis of Variance; D016288:Computer Terminals; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008027:Light; D008962:Models, Theoretical; D015588:Observer Variation; D011856:Radiographic Image Enhancement / Q000379:methods*; D019252:Radiography, Dental, Digital / Q000379:methods*; D013223:Statistics as Topic; D014796:Visual Perception