title: Digitized hand-wrist radiographs: comparison of subjective and software-derived image quality at various compression ratios.
abstract: BACKGROUND
  The objectives of this study were to compare the effect of JPEG 2000 compression of hand-wrist radiographs on observer image quality qualitative assessment and to compare with a software-derived quantitative image quality index.
  
  
  METHODS
  Fifteen hand-wrist radiographs were digitized and saved as TIFF and JPEG 2000 images at 4 levels of compression (20:1, 40:1, 60:1, and 80:1). The images, including rereads, were viewed by 13 orthodontic residents who determined the image quality rating on a scale of 1 to 5. A quantitative analysis was also performed by using a readily available software based on the human visual system (Image Quality Measure Computer Program, version 6.2, Mitre, Bedford, Mass). ANOVA was used to determine the optimal compression level (P < or =.05).
  
  
  RESULTS
  When we compared subjective indexes, JPEG compression greater than 60:1 significantly reduced image quality. When we used quantitative indexes, the JPEG 2000 images had lower quality at all compression ratios compared with the original TIFF images. There was excellent correlation (R2 >0.92) between qualitative and quantitative indexes.
  
  
  CONCLUSIONS
  Image Quality Measure indexes are more sensitive than subjective image quality assessments in quantifying image degradation with compression. There is potential for this software-based quantitative method in determining the optimal compression ratio for any image without the use of subjective raters.
authors.affiliation: Graduate School, School of Dentistry, University of Louisville, Louisville, Ky 40202, USA.
authors.forename: Layne K
authors.initials: LK
authors.lastname: McCord
authors.forename: William C
authors.initials: WC
authors.lastname: Scarfe
authors.forename: Rachel H
authors.initials: RH
authors.lastname: Naylor
authors.forename: James P
authors.initials: JP
authors.lastname: Scheetz
authors.forename: Anibal
authors.initials: A
authors.lastname: Silveira
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Gillespie
mesh_terms: D000365:Age Determination by Skeleton / Q000379:methods; D000704:Analysis of Variance; D006225:Hand / Q000000981:diagnostic imaging*; D006801:Humans; D015588:Observer Variation; D011856:Radiographic Image Enhancement / Q000379:methods*; D012189:Retrospective Studies; D012984:Software; D014953:Wrist / Q000000981:diagnostic imaging