A mechanical arm for spatial registration of two-dimensional echocardiographic sections.

The accurate calculation of left ventricular (LV) wall motion from two-dimensional echocardiographs will require the accurate registration of the position from which each two-dimensional (2-D) view was obtained. This paper describes a mechanical arm with five degrees of freedom that was developed so that the position and orientation of 2-D echo sections could be calculated in three-dimensional space. High precision potentiometers, direct or gear driven, permit calibration and measurement of each of the five movements. Using the length of the arm and the angles measured by these potentiometers, the position of a 2-D section can be calculated with respect to a fixed reference point outside the body. The measurement arm was extensively retested after six months of clinical use. In patient studies, 95% confidence interval for positioning a cross-section of the long axis is +/- 6 mm. This error is similar to the cross-plane resolution to most contemporary two-dimensional transducers. On the basis of an extensive analysis of variance, recommendations are made to improve the accuracy of the arm.