Thyroid volume measurement in patients prior to radioiodine therapy: comparison between three-dimensional magnetic resonance imaging and ultrasonography.

Because of its cost effectiveness, wide availability, and technical ease of application, ultrasonography is the reference method for determining the thyroid volume prior to radioiodine therapy. The goal of the study is a prospective assessment of the deviation between volumetric ultrasonography measurements in comparison to those performed with three-dimensional magnetic resonance imaging (MRI). To that end, 60 consecutive patients with multinodular toxic goiter (n = 28, 46.7%) or Graves' disease (n = 32, 53.3%) were included in the study. Ultrasonographic volumetry according to the well-known ellipsoid formula was performed by three different technicians. In addition, three-dimensional MRI scans of the neck area were acquired and evaluated by the ellipsoid formula as well as by a dedicated region-of-interest technique (MRI-ROI), which was used as standard of reference. While there was no significant difference between the ultrasonographic examinations of the three technicians, a highly significant mean deviation of 22.7% (10.4 mL) was found between the sonographic measurements and the MRI-ROI results (p < 0.01) that were underestimated in 80% of the cases. Correlation coefficients between the various volumetric approaches were highly significant, with values of at least 0.886 (p < 0.01). An additional analysis of volume-dependent subgroups revealed that thyroid volume had no significant influence on the results of ultrasonographic volumetry (p > 0.15). In conclusion, the study showed ultrasonography to be a reliable method of satisfactory accuracy that is appropriate for volumetric thyroid measurements. The findings indicate that the use of a correction factor higher than 0.52 in the ellipsoid formula is recommended to improve accuracy. However, further studies are necessary to confirm these findings.