The use of three-dimensional ultrasound for thyroid volumetry

Conventional two-dimensional (2-D) ultrasound is the standard method for th e investigation of thyroid morphology. Volume calculations need model assum ptions and are observer dependent. The present study per formed with a comm ercially available three-dimensional (3-D) system Freescan added to a conve ntional ultrasound scanner compares the accuracy of conventional thyroid vo lumetry to several methods of 3-D volume determination. In vitro measuremen ts were performed on thyroid phantoms with known volumes. The standard devi ation of the normalized differences was 8.0% (3-D segmentation) and 10.5% ( conventional). For the accuracy of volume determination in human thyroids w e performed a postmortem study. The thyroid volume was calculated conventio nally by the ellipsoid model and by two 3-D methods (segmentation and the n ewly developed multiplanar volume approximation). The reference volume was determined after resection by submersion. The standard deviation of the nor malized differences was 26.9% for the conventional method, 9.7% for 3-D seg mentation and 11.5% for the multiplanar volume approximation, showing signi ficant better results for both 3-D methods and no significant difference be tween the 3-D methods. The 3-D system, therefore, achieves a better accurac y for thyroid volumetry than the conventional volumetry using planar images . In addition, the 3-D images are stored electronically and can be used for follow-up studies.