A novel coding scheme and its application to ultrafast ultrasound imaging

Abstract

Ultrafast ultrasound imaging using plane or diverging waves, not focused beams, has enabled quantitative assessment of biological tissue elasticity, kinematics, and hemodynamics beyond anatomical information in the past decade. However, its sonographic signal-to-noise ratio (SNR) and penetration depth are limited by insufficient energy delivery under safety limits. We hereby propose a novel coding scheme and apply it to ultrafast ultrasound imaging to increase the SNR without compromising the spatial resolution and frame rate. In our coded ultrafast ultrasound imaging scheme, each transmit is a long pulse containing N (N = 2k, k = 0, 1, 2,…) waves with short time intervals and polarity coefficients of + 1 or −1, instead of the conventional short pulse with single wave. In reception, a linear decoding scheme comprised of addition, subtraction and delay operations is devised to recover N times higher intensity backscattered signals to gain SNR of 10·log10(N). Experimental results acquired by the Verasonics Vantage system from the calibration phantom and in vivo human back muscle show that the proposed method using two transmits of N = 32 waves achieves 13.0 ± 0.5 dB SNR improvement at 40 mm depth at 4000 frames/sec, leading to better image contrast and larger penetration depth.