title: Introduction of heat map to fidelity assessment of compressed CT images.
abstract: OBJECTIVE
  This study aimed to introduce heat map, a graphical data presentation method widely used in gene expression experiments, to the presentation and interpretation of image fidelity assessment data of compressed computed tomography (CT) images.
  
  
  METHODS
  The authors used actual assessment data that consisted of five radiologists' responses to 720 computed tomography images compressed using both Joint Photographic Experts Group 2000 (JPEG2000) 2D and JPEG2000 3D compressions. They additionally created data of two artificial radiologists, which were generated by partly modifying the data from two human radiologists.
  
  
  RESULTS
  For each compression, the entire data set, including the variations among radiologists and among images, could be compacted into a small color-coded grid matrix of the heat map. A difference heat map depicted the advantage of 3D compression over 2D compression. Dendrograms showing hierarchical agglomerative clustering results were added to the heat maps to illustrate the similarities in the data patterns among radiologists and among images. The dendrograms were used to identify two artificial radiologists as outliers, whose data were created by partly modifying the responses of two human radiologists.
  
  
  CONCLUSIONS
  The heat map can illustrate a quick visual extract of the overall data as well as the entirety of large complex data in a compact space while visualizing the variations among observers and among images. The heat map with the dendrograms can be used to identify outliers or to classify observers and images based on the degree of similarity in the response patterns.
authors.affiliation: School of Computer Science and Engineering, Seoul National University, 599 Kwanak-ro, Kwanak-gu, Seoul 151-742, Korea.
authors.forename: Hyunna
authors.initials: H
authors.lastname: Lee
authors.forename: Bohyoung
authors.initials: B
authors.lastname: Kim
authors.forename: Kil Joong
authors.initials: KJ
authors.lastname: Kim
authors.forename: Jinwook
authors.initials: J
authors.lastname: Seo
authors.forename: Seongjin
authors.initials: S
authors.lastname: Park
authors.forename: Yeong-Gil
authors.initials: YG
authors.lastname: Shin
authors.forename: Kyoung Ho
authors.initials: KH
authors.lastname: Lee
mesh_terms: D003196:Computer Graphics; D044962:Data Compression / Q000706:statistics & numerical data*; D016208:Databases, Factual; D006801:Humans; D015588:Observer Variation; D014057:Tomography, X-Ray Computed / Q000706:statistics & numerical data*