A 3-D Region-Growing Motion-Tracking Method for Ultrasound Elasticity Imaging

A three-dimensional (3D) region-growing motion tracking (RGMT) method for ultrasound elasticity imaging is described. This 3D RGMT method first estimates the displacements at a sparse subset of points, called seeds, uses an objective measure to determine, among those seeds, which displacement estimates to trust, and then performs RGMT in 3D to estimate displacements for the remaining points in the field. During the growing process in 3D, the displacement estimate at one grid point is employed to guide the displacement estimation of its neighboring points using a 3D small search region. To test this algorithm, volumetric ultrasound radiofrequency echo data was acquired from a phantom and five in vivo human breasts. Displacement estimates obtained with the 3D RGMT method were compared with a published two-dimensional (2D) RGMT method via the motion-compensated cross correlation (MCCC) of pre- and post-deformation radiofrequency echo signals. For data from experiments with the phantom, the average MCCC values in the entire tracking region of interest (ROI) were approximately 0.95 and the contrast to noise ratios were 4.6 for both tracking methods. For all 5 human subjects, the average MCCC values within the ROI obtained with the 3D RGMT were consistently higher than those obtained with the 2D RGMT method. These results demonstrated that the 3D RGMT algorithm has the ability to track displacements with increased accuracy and generate higher-quality 3D elasticity images than the 2D RGMT method.