2-D tissue motion compensation of synthetic transmit aperture images

Synthetic transmit aperture (STA) imaging is susceptible to tissue motion because it uses summation of low-resolution images to create the displayed high-resolution image. A method for 2-D tissue motion correction in STA imaging is presented. It utilizes the correlation between highresolution images recorded using the same emission sequence. The velocity and direction of the motion are found by cross correlating short high-resolution lines beamformed along selected angles. The motion acquisition is interleaved with the regular B-mode emissions in STA imaging, and the motion compensation is performed by tracking each pixel in the reconstructed image using the estimated velocity and direction. The method is evaluated using simulations, and phantom and in vivo experiments. In phantoms, a tissue velocity of 15 cm/s at a 45° angle was estimated with relative bias and standard deviation of -6.9% and 5.4%; the direction was estimated with relative bias and standard deviation of -8.4% and 6.6%. The contrast resolution in the corrected image was -0.65% lower than the reference image. Abdominal in vivo experiments with induced transducer motion demonstrate that severe tissue motion can be compensated for, and that doing so yields a significant increase in image quality.