Towards sub-Nyquist tissue Doppler imaging using non-uniformly spaced stream of pulses

Tissue Doppler ultrasound imaging enables quantification of the heart function by mapping the velocity of the tissue in different regions within the left ventricle. This estimation is performed by transmitting a series of evenly spaced pulses at a specific direction and analyzing phase shifts in the returning echoes. Traditionally the received signals are sampled at the Nyquist rate. However, high sampling rates produce high volumes of data. In addition, the number of consecutive pulses needed for reliable velocity estimation at each orientation in the presence of clutter limits the size of the sectors that can be imaged simultaneously. In this work, compressed sensing techniques that were suggested for solving similar problems in radar signal processing are adapted to tissue Doppler ultrasound imaging. The proposed method reduces the amount of data propagated through the scanner in two ways: A non-uniformly spaced stream of pulses is transmitted and each received echo is sampled at a sub-Nyquist rate. In addition, the time needed for each velocity estimation is reduced. The proposed method was evaluated using realistic synthetic echocardiographic sequences.