title: Detecting radiation-induced injury using rapid 3D variogram analysis of CT images of rat lungs.
abstract: OBJECTIVE
  To investigate the ability of variogram analysis of octree-decomposed computed tomography (CT) images and volume change maps to detect radiation-induced damage in rat lungs.
  
  
  METHODS
  The lungs of female Sprague-Dawley rats were exposed to one of five absorbed doses (0, 6, 9, 12, or 15 Gy) of gamma radiation from a Co-60 source. At 6 months postexposure, pulmonary function tests were performed and four-dimensional (4D) CT images were acquired using a respiratory-gated microCT scanner. Volume change maps were then calculated from the 4DCT images. Octree decomposition was performed on CT images and volume change maps, and variogram analysis was applied to the decomposed images. Correlations of measured parameters with dose were evaluated.
  
  
  RESULTS
  The effects of irradiation were not detectable from measured parameters, indicating only mild lung damage. Additionally, there were no significant correlations of pulmonary function results or CT densitometry with radiation dose. However, the variogram analysis did detect a significant correlation with dose in both the CT images (r = -0.57, P = .003) and the volume change maps (r = -0.53, P = .008).
  
  
  CONCLUSIONS
  This is the first study to use variogram analysis of lung images to assess pulmonary damage in a model of radiation injury. Results show that this approach is more sensitive to detecting radiation damage than conventional measures such as pulmonary function tests or CT densitometry.
authors.affiliation: Systems Toxicology, 902 Battelle Blvd., Pacific Northwest National Laboratory, Richland, WA 99352. Electronic address: richard.jacob@pnnl.gov.
authors.forename: Richard E
authors.initials: RE
authors.lastname: Jacob
authors.forename: Mark K
authors.initials: MK
authors.lastname: Murphy
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Creim
authors.forename: James P
authors.initials: JP
authors.lastname: Carson
mesh_terms: D000465:Algorithms; D000818:Animals; D005260:Female; D021621:Imaging, Three-Dimensional / Q000379:methods*; D011829:Radiation Dosage; D017564:Radiation Pneumonitis / Q000000981:diagnostic imaging* / Q000209:etiology*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D011874:Radiometry / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000009:adverse effects* / Q000379:methods*
keywords: CT imaging; Octree; irradiation; lung; variogram
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