New simple method for thyroid volume determination by ultrasonography.

A new, simple, and accurate ultrasonic method is elaborated for thyroid volume determination with commercially available high-resolution real-time equipment. The method takes into account the special and variable shape of the thyroid. The measurements were taken in three perpendicular sections. Volume calculations were done by applying the corrected ellipsoid model and computer-aided numerical integration, as well as by the conventional simple ellipsoid model. The accuracy of the method was tested by comparing direct measurements of a silicone rubber phantom with ultrasonography of a tissue-equivalent thyroid phantom. Both phantoms were modeled as casts of the same thyroid, which was obtained at autopsy. From the phantom measurements the deviation between the volume calculated by numerical integration or the corrected ellipsoid method and the real volume determined directly with the silicone rubber phantom was less than 5% on average, while volume calculations using the conventional ellipsoid model involved about +20% systematic error. In vivo studies in 40 subjects gave similar results: the ratios of the volumes calculated by simple and corrected ellipsoid method and by numerical integration [V(E), V(CE), and V(NI), respectively] were [V(E)/V(CE)] = 1.19 +/- 0.11 and [V(NI)/V(CE)] = 1.02 +/- 0.11. In conclusion corrected ellipsoid method is suggested for the clinical practice.