title: Effects of window and threshold levels on the accuracy of three-dimensional rendering techniques in coronary artery electron-beam CT angiography.
abstract: OBJECTIVE
  The authors performed this study to evaluate the effect of window level and gray-scale threshold on the demonstration of coronary artery lumina at three-dimensional electron-beam computed tomographic (CT) angiography.
  
  
  METHODS
  Forty-four coronary artery branches in postmortem pigs were evaluated with electron-beam CT angiography, and the findings were compared with those from conventional angiography. Images from electron-beam CT angiography were reconstructed with maximal intensity projection (MIP), multiplanar reformation (MPR), and shaded-surface display (SSD). Four categories of window level and gray-scale threshold were evaluated.
  
  
  RESULTS
  Three-dimensional electron-beam CT angiography accurately depicted the luminal diameters of the coronary arteries compared with conventional angiography (r = 0.83-0.90, P < .0001). The length of lumina visualized at electron-beam CT angiography was significantly shorter than that visualized with conventional angiography (P < .001). The use of MPR enabled visualization of longer segments of coronary arteries than did the use of MIP or SSD (P < .05). The higher the window level and gray-scale threshold used, the smaller the coronary luminal diameters measured (P < .05). The most accurate window level and gray-scale threshold (82.6 HU +/- 29.8 and 89.5 HU +/- 29.7, respectively) were found to correspond to the attenuation of the lumina (275.8 HU +/- 58.8). Results of simple linear regression showed a strong correlation between luminal attenuation and window level (r = 0.89, P < .0001) or gray-scale threshold (r = 0.95, P < .0001).
  
  
  CONCLUSIONS
  Electron-beam CT angiography shows promise in the visualization of coronary artery lumina. For accurate display of lumina, a proper window level and gray-scale threshold for three-dimensional rendering techniques should be determined and used on the basis of the attenuation of the target vessel.
authors.affiliation: Department of Radiology FuWai Cardiovascular Institute and Hospital, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing.
authors.forename: B
authors.initials: B
authors.lastname: Lu
authors.forename: R P
authors.initials: RP
authors.lastname: Dai
authors.forename: S L
authors.initials: SL
authors.lastname: Jiang
authors.forename: H
authors.initials: H
authors.lastname: Bai
authors.forename: S
authors.initials: S
authors.lastname: He
authors.forename: N
authors.initials: N
authors.lastname: Zhuang
authors.forename: X
authors.initials: X
authors.lastname: Sun
authors.forename: M J
authors.initials: MJ
authors.lastname: Budoff
mesh_terms: D000818:Animals; D017023:Coronary Angiography / Q000379:methods / Q000592:standards*; D003331:Coronary Vessels / Q000033:anatomy & histology; D006321:Heart / Q000033:anatomy & histology; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional / Q000379:methods*; D023421:Models, Animal; D013552:Swine; D014057:Tomography, X-Ray Computed / Q000379:methods*