Background 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' diseasewere included in this retrospective study. We designated the three-dimensional thyroid volumes extracted manually (VCT) as the reference data and calculated five approximate volumes for comparison: (1) the mean volume of 8100 different thyroid volumes depending on the diameter of the cross-sectional plane at the midpoint of the major axis, (Vellipsoid,mean); (2) the volume using the maximum diameter and its orthogonal diameter, (Vellipsoid,maxlength); (3) the maximum (Vellipsoid,maxvolume) and (4) minimum (Vellipsoid,minvolume) of the 8100 thyroid volumes; and (5) the volume determined with an equivalent circle diameter, (Vellipsoid,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, Vellipsoid,meanand Vellipsoid,Heywoodwere in good agreement with VCT, according to single regression analyses and the resultant CCC values, with mean errors of 7.0% and 2.5%, respectively.
Conclusion WhileVellipsoid,Heywoodapproximated thyroid volumes with vastly reduced errors, we recommend utilizing three-dimensional thyroid volumetry if measurement accuracy is required.