title: Focal hepatic lesions: effect of three-dimensional wavelet compression on detection at CT.
abstract: OBJECTIVE
  To evaluate the effect of three-dimensional, wavelet-based compression on the detection of focal hepatic lesions at computed tomography (CT).
  
  
  METHODS
  CT images obtained in 69 patients with focal hepatic lesions were studied (35 consecutive cases and 34 cases selected to be difficult on the basis of lesion size or contrast). Image data were compressed by means of a three-dimensional, wavelet-based algorIthm at ratios of 10:1, 15:1, and 20:1. Normal and abnormal sections (on original and compressed images) were reviewed by using an interactive workstation. Four readers rated the presence or absence of a lesion with a five-point scale.
  
  
  RESULTS
  At receiver operating characteristic analysis, no statistically significant difference was detected for all cases considered together. Differences approached but did not reach statistical significance for the diagnostic performance of one reader with compressed images (15:1, P = .054; 20:1, P = .051). For the subset of difficult cases, a significant difference was observed with 20:1 compressed images for one reader (P = .026). Diagnostic performance of readers was less certain in normal than in abnormal cases with both original and compressed images (difference was significant for 15:1 [P = .035] and 20:1 [P < .0001] compressed images).
  
  
  CONCLUSIONS
  Three-dimensional wavelet compression is satisfactory at ratios of at least 10:1. Additional studies with a larger sample would help confirm findings with higher ratios.
authors.affiliation: Department of Radiology, Harvard Medical School, Boston, MA, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Goldberg
authors.forename: G S
authors.initials: GS
authors.lastname: Gazelle
authors.forename: G W
authors.initials: GW
authors.lastname: Boland
authors.forename: P F
authors.initials: PF
authors.lastname: Hahn
authors.forename: W W
authors.initials: WW
authors.lastname: Mayo-Smith
authors.forename: M
authors.initials: M
authors.lastname: Pivovarov
authors.forename: E F
authors.initials: EF
authors.lastname: Halpern
authors.forename: J
authors.initials: J
authors.lastname: Wittenberg
mesh_terms: D003560:Cysts / Q000000981:diagnostic imaging; D006391:Hemangioma / Q000000981:diagnostic imaging; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008107:Liver Diseases / Q000000981:diagnostic imaging*; D008113:Liver Neoplasms / Q000000981:diagnostic imaging* / Q000556:secondary; D012372:ROC Curve; D014057:Tomography, X-Ray Computed / Q000379:methods*