Synthetic Transmit Aperture Imaging Using Orthogonal Coded Sequences With Separate Transmitters-Receivers

Recently, ultrafast ultrasound unlocked unprecedented frame rate, which turns out on new diagnostic tools. However, in all ultrafast methods, there is a tradeoff between acquisition time and image quality. It has been shown that coded excitations have the potential to overcome this tradeoff by emitting multiple orthogonal sequences simultaneously. However, orthogonal sequence design and experimental validation of these are still open problems in the ultrasound community. This paper proposes to improve orthogonality between the transmitted codes by increasing the sequence length. To overcome the blind zone issue linked to long sequences, emitters and receivers are separated. This study shows that it is possible to achieve similar spatial resolution using just 1 transmission with 8 active emitters excited simultaneously rather than 8 successive transmissions with short pulses. The frame rate is increased by a factor of 2.7 with the proposed method, at the cost of a decrease in SNR of about 20 dB.