Using image-based regression to acquire freehand 3D ultrasound

In freehand 3D ultrasound, a position sensor is attached to the probe of a 2D ultrasound machine. The resulting 3D data permits flexible visualisation and more accurate volume measurement than can be achieved using 2D B-scans alone; however the use of the position sensor can be inconvenient for the clinician. The objective is thus to replace the sensor with a technique for estimating the probe trajectory based on the B-scan images themselves. One such technique exists, based on decorrelation algorithms. This report presents an alternative approach based on linear regression of the echo envelope intensity signal. A probabilistic analysis of the speckle characteristics of the ultrasound signal leads to a linear model on which the regression algorithm is based. The gradient parameter of this model is shown to be directly related to probe motion. The viability of the new approach is demonstrated through simulations, and in vitro and in vivo experiments.