Test of a vertical scan mode in 3-D imaging of residual limbs using ultrasound

We have developed a new ultrasound system for imaging residual limbs that employs two scan modes: a vertical scan mode (VSM) primarily used for capturing the skin surface, and a horizontal compound scan mode (HCSM) primarily used for imaging the internal tissue structures. Since the HCSM was described previously (J Rehabil Res Dev 1997;34(3):269-78), the main purpose of this article is to elucidate the principle of reconstructing the skin surface using the new VSM and to report the accuracy of volumetric measurement based on this reconstruction method. For a residual limb with a length of up to 26 cm, the vertical scan takes about 80 s. The acquired skin surface has a resolution of 144 points per circumference in the transverse direction and a resolution of 28 points per cm in the longitudinal direction. The measurement accuracy of the system is tested using a cylindrical phantom and a custom-made limb model. The diameter of the phantom measured by the ultrasound method is 113.8 +/- 0.23 mm, compared with a value of 113 mm measured by a caliper. For the limb model, cumulative segment volumes measured by the ultrasound method are compared with those measured by the hydrostatic weighing method. The relative errors are <1%. This study demonstrates the feasibility of using ultrasound to perform limb measurement for prosthetic CAD/CAM applications.