Blurring of vessels in spiral CT angiography: effects of collimation width, pitch, viewing plane, and windowing in maximum intensity projection

J Comput Assist Tomogr. Nov-Dec 1996;20(6):965-74. doi: 10.1097/00004728-199611000-00018.

Abstract

Purpose: Our goal was to examine the effects of collimation width (CW), pitch, viewing plane, and windowing on the display of in-plane vessels in maximum intensity projection (MIP).

Method: A theoretical concept based on partial volume averaging of vessels was developed to describe the contents of voxels (densities) in MIP and to derive cross-sectional vessel diameters and blurring. To validate the concept and to describe the influence of pitch, a Plexiglas cone submerged in water was scanned with varying CW and pitch. Binary MIP with three representative window levels was chosen so that definitive vessel diameters could be quantitated.

Results: The theoretical concept correctly predicted voxel contents and blurring for CW > or = 3 mm and low pitch. For high pitch, actual blurring was larger; however, for a given table speed, blurring of the cone decreased with pitch while increasing with CW. Overall blurring was most effectively reduced by using a thin CW and the transverse viewing plane. In the transverse viewing plane, the least blurring was found using binary MIP with a low window level. On the contrary, in the longitudinal viewing plane, blurring was minimized using a window level halfway between the density of the cone and that of the surrounding water.

Conclusion: For CW > or = 3 mm, blurring of in-plane vessels can be explained with a simple geometrical concept based on partial volume. For accurate display, the transverse viewing plane should be used, a proper windowing must be chosen, and the CW should be kept below vessel size while raising the pitch to cover a reasonable volume.

MeSH terms

  • Artifacts*
  • Humans
  • Linear Models
  • Phantoms, Imaging
  • Radiographic Image Interpretation, Computer-Assisted / methods
  • Tomography Scanners, X-Ray Computed / statistics & numerical data
  • Tomography, X-Ray Computed / instrumentation
  • Tomography, X-Ray Computed / methods*
  • Tomography, X-Ray Computed / statistics & numerical data