to the bivot savot rule if r is the position vector from point x y z to the current element di and r is the scalar magnitude of position vector r the gain of the signal received by surface coil 20 is equ1 for a circular coil of radius a a discrete implementation of eq 1 becomes equ2 where u03c1 is radial distance away from the axis of the coil and z is the distance along the axis of the coil it can seen that as the as the relative angle between surface coil 20 and location x y z of the tissue element emitting a signal increases radial distance r away from the axis of surface coil 20 increases the intensity of the signal received decreases also the intensity of the signal received decreases as the distance along the axis of the coil increases by adjusting the data set for this change in sensitivity of surface coil 20 the data set is normalized by approximating the surface coil centered at x o y o z o by a polygon having a 2n segments the equation in cartesian coordinates would be equ3 where x y z are the cartesian coordinates of x y z with respect to the center of surface coil 20 respectively u03c1 u221a x x o 2 y y o 2 and.