Radiology, Vol 157, 243-246, Copyright © 1985 by Radiological Society of North America
CT measurement of the diameter of spinal and other bony canals: effects of section angle and thickness
BA Eubanks, CE Cann and M Brant-Zawadzki
The effects of section angle and thickness on the measurement of spinal
canal diameter by computed tomography (CT) were tested. A phantom of three
spinal canals was constructed of three Lucite rods of different diameters,
each covered with 1.8-mm-thick Teflon. A second phantom was constructed of
two Lucite rods of the same diameter covered with 1.8- and 8.8-mm-thick
Teflon, respectively. CT sections 10, 5, and 1.5 mm thick were obtained at
various angles relative to the transverse plane of each canal.
Anteroposterior diameters were measured at bone window settings using a
standard software package and a method that uses a CT- number profile.
Results show that sections obtained at an angle to the transverse plane of
the canal do not always overestimate its diameter, as previously suggested,
but can make it appear artifactually stenotic. The effect is from volume
averaging and is most marked when thick, severely angled sections are used.
