Correction of refraction and other angle errors in beam tracking speed of sound estimations using multiple tracking transducers.

The beam tracking approach to the estimation of the speed of sound has shown potential for making unbiased estimates in tissues. The speed of sound in a medium can be found from the arrival times of echoes as a function of the position of a tracking transducer. There is a problem in this approach if the angle between the direction of tracked beam and the direction of tracking translation is not zero due to refraction or other effects. An angle error as small as 1 degree would result in an error that is too large for diagnostic applications. A modified technique using three or more tracking transducers is described. This yields a corrected speed of sound estimate, and calculates the angle error. A simulation program has shown that this modified technique could indeed correct for the angle errors.