Hadamard-encoded synthetic transmit aperture imaging for improvement of strain estimation

Lateral estimation has been a challenge in ultrasound elastography mainly due to the low resolution, low sampling frequency and lack of phase information in the lateral direction. Synthetic transmit aperture (STA) can achieve high resolution thanks to two-way focusing for improved lateral estimation, with the disadvantages of low signal-to-noise ratio (SNR) and limited penetration depth. In this study, we propose Hadamard-encoded STA (Hadamard-STA), which has been demonstrated to enhance the SNR of STA imaging, for improvement of strain estimation in elastography. Simulations and experiments were conducted on a heterogeneous model and an elasticity phantom with the same Young's modulus contrast. White Gaussian noise with different noise levels was added on the simulated channel dataset of Hadamard-STA to investigate its de-noising performance. The results show that Hadamard-STA outperforms STA with higher lateral and axial strain estimation qualities and may be a competitive method for quasi-static elastography.