Analysis of linear, area and volume distortion in 3D ultrasound imaging

We have developed a three-dimensional (3D) ultrasound imaging system that uses a side-firing probe, axially rotated under computer control, to acquire a series of 2D images, from which the 3D image is reconstructed, For an undistorted reconstruction, the inner radius R-0 of the 2D images and the total scanning angle theta must be known accurately, Here, we describe (a) a theoretical analysis of the relative distortion in image shape, length, area, and volume due to an error Delta R in R-0 or Delta theta in theta; (b) measurements of these in simulated and real 3D images; and (c) a method to calibrate R-0, theta, and image scale accurately, Theoretically, all four relative distortions vary as P Delta R/R + Q Delta theta/theta, where \P\ less than or equal to 1, \Q\ less than or equal to 1, and R is the average distance of the object from the axis, In every case, the simple theoretical formulas for P and Q agree with image measurements to within the measurement uncertainty. (C) 1998 World Federation for Ultrasound in Medicine & Biology.