title: Three-dimensional craniocervical helical CT: is isotropic imaging possible?
abstract: OBJECTIVE
  To assess whether isotropic resolution is attainable in three-dimensional craniocervical helical computed tomography (CT).
  
  
  METHODS
  Two cadaveric cervical spine and two orbital phantoms were scanned in air and water by using 180 degrees-interpolated helical CT with three-dimensional reconstruction. Scan parameters yielded nominally isotropic voxels with reconstruction of 1-mm collimated and incremental sections at 0.2-mm intervals. CT scan angle was varied with the assumption that volume-averaging artifacts should be scan angle-independent with isotropic voxels. Twelve blinded observers analyzed three-dimensional images generated from multiple CT orientations to assess changes in volume-averaging artifacts that would indicate voxel anisotropy.
  
  
  RESULTS
  Significant observable differences in three-dimensional image representation were present in test anatomic regions in one cervical spine phantom (two-tailed P < .006) and in both orbital phantoms (P < .008 and P < .006). No statistically significant differences were present for control anatomic regions.
  
  
  CONCLUSIONS
  Isotropic scanning is not possible in three-dimensional craniocervical helical CT.
mesh_terms: D000328:Adult; D000388:Air; D016477:Artifacts; D002102:Cadaver; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging*; D003626:Data Display; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008961:Models, Structural; D015588:Observer Variation; D009915:Orbit / Q000000981:diagnostic imaging*; D011856:Radiographic Image Enhancement / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014867:Water
chemical_list: D014867:Water