Doppler tissue imaging in the new era of digital echocardiography

Doppler tissue imaging is one of the most recent technical achievements of clinical echocardiography. Different Doppler modes are encompassed by Doppler tissue imaging: tissues velocity, pulsed wave-doppler, acceleration, phase, synchronicity and energy modes. With the exception of the energy mode, all modes are based on the Doppler shift, according to the strength of the Doppler signals from the tissues. The most widely used mode is tissue velocity, in which the velocity of moving tissue is calculated in relation to the transducer from the Doppler shift and is displayed as colour-encoded velocity maps in M-mode and two-dimensional imaging formats. Both curved M-mode, applied on two-dimensional images, and three-dimensional reconstruction appear among the most promising applications of velocity mode for the quantitative assessment of regional left ventricular function. A second Doppler mode, pulsed wave-doppler tissue imaging, displays the velocity profile of a region of interest versus time. The velocity data are displayed with a high temporal resolution, but with the disadvantage of a low spatial resolution. A third Doppler mode, tissue acceleration, displays the differences in velocity between subsequent frames in colour-encoded maps. A clinical application has been found in the electrophysiologic field. Other Doppler modes, phase and synchronicity, still require clinical assessment. Lastly, the tissue energy or power mode displays the strength of the Doppler signal from the tissues as gradations of the colour intensity in colour-encoded maps. One of its fields of application appears to be the study of myocardial perfusion with contrast agents. The development of new dedicated algorithms for colour quantification, along with the beginning of the new era of digital echocardiography, should help bring Doppler tissue imaging into the clinical arena.