Modeling 2D speckle images accounting for 3D strain effects

Strain imaging can derive clinically important information regarding tissue elasticity. In relatively incompressible materials (such as tissue), a strain in one direction is accompanied by strain of opposite polarity in one or more orthogonal directions. When a regular ultrasound array - long in the azimuth and narrow in elevation - is pressed into soft tissue one expects the primary Poisson ratio related strain to be in the elevation direction. One objective is to determine whether the resultant 'y' strained image is distinguishable from the unstrained case. A second objective is to compare the degree of decorrelation due to elevation strain with that due to small, practically unavoidable, elevational translational offsets. Hence, it is necessary to model full 3D strain effects on speckle. Our conclusion from initial analysis of the impact of elevational strain on 2D speckle patterns is that the associated decorrelation is very small. Consequently, any small elevational translation that occurs during the strain application process will have a dominant effect on the net 2D image decorrelation.