High frame rate tissue Doppler imaging

In tissue Doppler and strain rate imaging of the heart, a high frame rate is necessary to capture the rapid relaxations and contractions of the myocardium. Previously, the Doppler and tissue B-mode images have been calculated from different pulse transmissions. To improve the temporal resolution, we present a new acquisition technique where the Doppler based images are calculated from the same pulse transmissions as the tissue B-mode images. By constructing the image from 10-15 transmit beams, frame rates above 300 frames/second are possible when imaging the heart. To get adequate spatial resolution, the small number of transmit beams limits the width of the image, but the image is wide enough to cover a heart wall, i.e. the interventricular septum. The Doppler pulse repetition frequency equals the frame rate and is relatively low. Tissue velocity estimates calculated from these data therefore suffer from aliasing. However, we present a robust technique that corrects the aliased velocities. A significant advantage of the new technique is the continuous stream of data with constant sampling intervals. Doppler spectra and sound signals can thus be calculated at arbitrary points in the 2D image.