Abstract
PURPOSE: This study examined the variation in the thyroid volume determined by the ellipsoid approximation method due to differences in the measured length or area of the cross-sectional plane of CT images. METHODS: Forty-five patients with Graves' disease were included in this retrospective study. We designated the three-dimensional thyroid volumes extracted manually (V(CT) ) as the reference data and calculated five approximate volumes for comparison: (a) the mean volume of 8100 different thyroid volumes depending on the diameter of the cross-sectional plane at the midpoint of the major axis, (V(ellipsoid,mean) ); (b) the volume using the maximum diameter and its orthogonal diameter, (V(ellipsoid,maxlength) ); (c) the maximum (V(ellipsoid,maxvolume) ); (d) minimum (V(ellipsoid,minvolume) ) of the 8100 thyroid volumes; and (e) the volume determined with an equivalent circle diameter, (V(ellipsoid,Heywood) ). RESULTS: Thyroid volumes obtained via the ellipsoid approximation method varied depending on the diameter of the cross-sectional plane and included a mean error of approximately 20%, while the concordance correlation coefficient (CCC) differed for each approximate volume. Among these volumes, V(ellipsoid,mean) and V(ellipsoid,Heywood) were in good agreement with V(CT) , according to single regression analyses and the resultant CCC values, with mean errors of 0.1% and 10.4%, respectively. CONCLUSION: While V(ellipsoid,Heywood) approximated thyroid volumes with vastly reduced errors, we recommend utilizing three-dimensional thyroid volumetry if measurement accuracy is required.