title: Pixel intensity and fractal dimension of periapical lesions visually indiscernible in radiographs.
abstract: BACKGROUND
  The purpose of the study was to analyze pixel intensity (PI) and fractal dimension (FD) values in radiographs of chemically created but visually undetectable periapical lesions.
  
  
  METHODS
  Artificial lesions were created by applying 70% perchloric acid to the sockets of left and right first premolars in 12 cadaver mandibles. For preparation of relatively small lesions, the acid was applied for 30 and 60 minutes. Before and after each acid application, radiographs were taken (60 kVp, 7 mA, and 1.5 mm Al equivalent filtration for 0.12 second) with storage phosphor plates. An optical bench was used to standardize projection geometry. Image plates were scanned immediately after exposure, and the acquired images were saved uncompressed in TIF format. Six observers evaluated the images by using a 5-grade scale, and the images scored as "definitely absent" by all observers were used for the calculations of PI and FD. Box-counting FDs and differences in mean PI were computed for regions of interest at the apical areas of each premolar. Repeated-measures analysis of variance, Tukey test, and Pearson correlation coefficient test were used for statistical analysis.
  
  
  RESULTS
  A significant difference was found in FD values after both acid application periods (P < .05), whereas a difference in PI was detected only in images obtained after 60-minute acid application (P < .05). There was a negative correlation between FD and PI values (-0.754, P < .05).
  
  
  CONCLUSIONS
  Calculation of FD can be a tool for the early detection of periapical lesions given the presence of baseline radiographs.
authors.affiliation: Department of Oral Diagnosis and Radiology, School of Dentistry, Ege University, Izmir, Turkey. esogur@yahoo.com
authors.forename: Elif
authors.initials: E
authors.lastname: Soğur
authors.forename: B Güniz
authors.initials: BG
authors.lastname: Baksı
authors.forename: Hans-Göran
authors.initials: HG
authors.lastname: Gröndahl
authors.forename: B Hakan
authors.initials: BH
authors.lastname: Sen
mesh_terms: D001641:Bicuspid / Q000000981:diagnostic imaging; D002102:Cadaver; D017709:Fractals; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods* / Q000706:statistics & numerical data; D008334:Mandible / Q000000981:diagnostic imaging / Q000187:drug effects; D010472:Perchlorates / Q000494:pharmacology; D010483:Periapical Diseases / Q000139:chemically induced / Q000000981:diagnostic imaging*; D011856:Radiographic Image Enhancement; D019252:Radiography, Dental, Digital / Q000295:instrumentation / Q000379:methods; D013997:Time Factors; D020390:Tooth Socket / Q000000981:diagnostic imaging / Q000187:drug effects; D014963:X-Ray Intensifying Screens
chemical_list: D010472:Perchlorates; C576518:Perchloric Acid