Geometry corrections in a rotating 3-dimensional sonographic system.

Objective: To devise a system for geometry corrections in a rotating 3-dimensional sonographic system.
Methods: A 3-dimensional sonographic imaging system based on a standard sonography machine was developed. The transducer mounted in a specially designed holder was rotated about its axis to acquire the spatial information. The most important postulate in rotating 3-dimensional systems is the assumption of parallelity between the rotation axis and the transducer axis. It allows the use of simple geometric relationships between 2-dimensional slices in a 3-dimensional reconstruction. The errors appearing in the 3-dimensional reconstruction when the axes are not parallel were investigated.
Results: A simple correction method based on phantom measurements is proposed. The phantom contains a plane, which is inclined to the rotation axis. The analysis of 2-dimensional plane images allows the geometric corrections. The construction of the phantom is described, and the formulas used in the calculations are presented. The method was tested in computer simulations and in patient investigations.
Conclusions: A complete method of the geometric investigations and corrections useful in 3-dimensional sonographic systems based on rotational geometry is proposed. Both the computer simulations and the phantom measurements confirmed the usefulness, precision, and simplicity of the proposed method.