| The techniques of volume calculation. Both figures show the typical multiplanar display of a three-dimensional sonographic dataset of the uterus with the three mutually related orthogonal planes at 90-degrees to one another. The upper left image in both displays represents the longitudinal plane (the A plane), the upper right image the transverse plane (the B plane) and the lower left image the coronal plane (the C plane). Volume calculation can be conducted in either the B or C plane. (a) shows the conventional technique of volume calculation in which a series of 'slices' are taken through the volume of interest whilst the contour is outlined in another plane (the transverse plane in this case). The distance between consecutive slices can be varied according to the degree of change in the surface contour and increased for more complex structures. (b) shows the rotational technique of volume calculation in which the dataset is rotated through 180° about a central axis defined by the application of two callipers. The number of planes available for volume calculation are determined by the rotation step shown in the lower left of the image. Here the 30-degree rotation step has been used and the contour outlined in the coronal or C plane using the manual mode. The resultant three-dimensional model is shown in the lower right of the image. |