title: Free-response receiver operating characteristic evaluation of lossy JPEG2000 and object-based set partitioning in hierarchical trees compression of digitized mammograms.
abstract: OBJECTIVE
  To assess the effects of two irreversible wavelet-based compression algorithms--Joint Photographic Experts Group (JPEG) 2000 and object-based set partitioning in hierarchical trees (SPIHT)--on the detection of clusters of microcalcifications and masses on digitized mammograms.
  
  
  METHODS
  The use of the images in this retrospective image-collection study was approved by the institutional review board, and patient informed consent was not required. One hundred twelve mammographic images (28 with one or two clusters of microcalcifications, 19 with one mass, 17 with both abnormal findings, and 48 with normal findings) obtained in 60 women who ranged in age from 25 to 79 years were digitized and compressed at 40:1 and 80:1 by using the JPEG2000 and object-based SPIHT methods. Five experienced radiologists were asked to locate and rate clusters of microcalcifications and masses on the original and compressed images in a free-response receiver operating characteristic (FROC) data acquisition paradigm. Observer performance was evaluated with the jackknife FROC method.
  
  
  RESULTS
  The mean FROC figures of merit for detecting clusters of microcalcifications, masses, and both radiographic findings on uncompressed images were 0.80, 0.81, and 0.72, respectively. With object-based SPIHT 80:1 compression, the corresponding values were larger than the values for uncompressed images by 0.005, 0.009, and -0.005, respectively. The 95% confidence interval for the differences in figures of merit between compressed and uncompressed images was -0.039, 0.033 for the microcalcification finding; -0.055, 0.034 for the mass finding; and -0.039, 0.030 for both findings. Because each of these confidence intervals includes zero, no significant difference in detection accuracy between uncompressed and object-based SPIHT 80:1 compression was observed at a P value of 5%. The F test of the null hypothesis that all of the modes (uncompressed and four compressed modes) were equivalent yielded the following results: F = 0.255, P = .903 for the microcalcification finding; F = 0.340, P = .848 for the mass finding; and F = 0.122, P = .975 for both findings.
  
  
  CONCLUSIONS
  To within the accuracy of these measurements, lossy compression of digital mammographic data at 80:1 with JPEG2000 or the object-based SPIHT algorithm can be performed without decreasing the rate of detection of clusters of microcalcifications and masses.
authors.affiliation: Laboratorio de Imagen Médica, Hospital General Universitario Gregorio Marañón, C/Ibiza 43, 28009 Madrid, Spain. monica@mce.hggm.es
authors.forename: Mónica
authors.initials: M
authors.lastname: Penedo
authors.forename: Miguel
authors.initials: M
authors.lastname: Souto
authors.forename: Pablo G
authors.initials: PG
authors.lastname: Tahoces
authors.forename: José M
authors.initials: JM
authors.lastname: Carreira
authors.forename: Justo
authors.initials: J
authors.lastname: Villalón
authors.forename: Gerardo
authors.initials: G
authors.lastname: Porto
authors.forename: Carmen
authors.initials: C
authors.lastname: Seoane
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Vidal
authors.forename: Kevin S
authors.initials: KS
authors.lastname: Berbaum
authors.forename: Dev P
authors.initials: DP
authors.lastname: Chakraborty
authors.forename: Laurie L
authors.initials: LL
authors.lastname: Fajardo
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D005260:Female; D006801:Humans; D008327:Mammography; D008875:Middle Aged; D012372:ROC Curve; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies; D014584:User-Computer Interface