THE ACCURACY OF A NEW SYSTEM FOR ESTIMATING ORGAN VOLUME USING ULTRASOUND

A new system is described for estimating volume from a series of multi planar 2D ultrasound images. Ultrasound images are captured using a pe rsonal computer video digitizing card and an electromagnetic localizat ion system is used to record the pose of the ultrasound images. The ac curacy of the system was assessed by scanning four groups of ten cadav eric kidneys on four different ultrasound machines. Scan image planes were oriented either radially, in parallel or slanted at 30 degrees to the vertical. The cross-sectional images of the kidneys were traced u sing a mouse and the outline points transformed to 3D space using the Fastrak position and orientation data. Points on adjacent region of in terest outlines were connected to form a triangle mesh and the volume of the kidneys estimated using the ellipsoid, planimetry, tetrahedral and ray tracing methods. There was little difference between the resul ts for the different scan techniques or volume estimation alogorithms, although, perhaps as expected, the ellipsoid results were the least p recise. For radial scanning and ray tracing, the mean and standard dev iation of the percentage errors for the four different machines were a s follows: Hitachi EUB-240, -3.0 +/- 2.7%; Tosbee RM3, -0.1 +/- 2.3%; Hitachi EUB-415, 0.2 +/- 2.3%; Acuson, 2.7 +/- 2.3%.