Coded Excitation and Annular Arrays for High-Frequency Ultrasound Imaging

High-frequency ultrasound (HFU) shows promises for with fine-resolution imaging. However, the limited depth of field (DOF) and penetration depth of HFU waves mitigates in significance for clinical evaluation. The aim of this study is to use modern annular transducer technology and coded excitation to simultaneously improve DOF and penetration depth. A 20-MHz, five-element annular array with a focal length of 18 mm and a total aperture of 6 mm was custom made using a 25-mum thick polyvinylidene fluoride membrane. The annular array was excited by a 8-mus coded signal to image a phantom made of seven regularly spaced 25-mum wire. The coded signal was a chirp linearly spanning the frequency range to 40 MHz. Results of this study demonstrate that the DOF can be improved by factor of 3 and signal-to-noise ratio (SNR) can improved by more than 24 dB with coded-excitation methodologies. The increased SNR offers the potential to increase the penetration depth when imaging in vivo