1A-5 Coded-Signal Imaging Using High-Frequency Annular Arrays

High-frequency (i.e., > 15 MHz) ultrasound (HFU) permits fine-resolution imaging. However, the limited depth of field (DOF) and acoustic penetration depth of HFU waves limits its clinical use to the assessment of shallow diseases such as ocular or dermatological conditions. The aim of this study is to use modern annular array transducer technology and coded signals to improve DOF and penetration depth simultaneously. Two 17-MHz, five-element annular arrays with focal lengths of 18 mm and 31 mm and total apertures of 6 mm and 10 mm were custom made using a 25-mum thick copolymer membrane. For imaging, the annular arrays were excited by coded chirp signals that linearly spanned frequency ranges between 0 and 40 MHz. Images of a phantom consisting of seven regularly spaced 25-mum wires demonstrated that DOF can be improved by a factor of 3 and that signal-to-noise ratio (SNR) can increase by more than 24 dB with coded-excitation methodologies