Universal coded ultrasound imaging system with software processing

Coded transmission is a technique to solve the inherent compromise between penetration
and resolution required in ultrasound imaging. Our aim was to examine the performance of
the coded excitation in HF (20–35 MHz) ultrasound imaging. For this purpose a novel realtime
imaging system has been developed. The digital programmable coder-digitizer module
supports arbitrary coded waveform generation and RF echoes sampling up to 200 MSPS.
All digital RF and image processing was implemented in software. The system performance
was evaluated with a single thick-film transducer (focused 25 MHz, 75% bandwidth) scanning
head. The RF echoes were acquired from a perfect reflector located with 1 cm of tissue
mimicking material. Single sinus burst and 16-bits Golay codes excitations were evaluated.
SNR gain for the Golay codes (referenced to single burst) of 15 dB for 20 MHz and 16 dB
for 35 MHz were obtained. The axial resolution measured at half maximum was 35 ns for
20 MHz and 25 ns for 35 MHz for both single burst and the Golay codes. It clearly shows that
the Golay codes can perfectly restore the resolution while giving respectable SNR gain.