Delay-encoded transmission in synthetic transmit aperture (DE-STA) imaging

Synthetic transmit aperture (STA) ultrasound imaging offers dynamic focusing in both transmission and receiving, leading to high image resolution. The major problem of this technique is the low signal to noise ratio (SNR) compared to the conventional B-mode ultrasound method. Hadamard encoded transmission is an approach to overcome this difficulty, but it requires transducer array to transmit a pulse in some array elements and the inverted pulse in the other elements simultaneously, which is not compatible with many commercial scanners. In this paper, we propose delay-encoded synthetic transmit aperture (DE-STA) imaging to encode the transmission elements to increase the SNR of the radiofrequency (RF) echo signals. In this technique, selected transmitting elements are encoded with half period delay and then a decoding process is applied to the acquired RF signals to obtain the equivalent traditional STA signals with a better SNR. The proposed protocol (DE-STA) was tested with both simulated data using Field II and experimental data acquired with a commercial linear array imaging system (Ultrasonix RP). The results from both the simulations and the experiments demonstrated improved image quality compared with the traditional STA images with the same amount of measurement noise in the RF data. This SNR improvement in the RF data is comparable with the Hadamard encoded method.