Pulse‐compression ultrasound imaging using a 40‐MHz annular array Available to Purchase

High‐frequency ultrasound allows fine‐resolution imaging at the expense of limited depth‐of‐field and acoustic penetration depth. Coded‐excitation imaging allows a significant increase in the signal‐to‐noise ratio (SNR) and acoustic penetration depth. A 40‐MHz, five‐element annular array with a focal length of 12 mm and a total aperture of 6 mm was made using a 9‐μm thick PVDF‐TrFe membrane. The transducer was excited with an optimized, custom design, 4‐μs, linear chirp spanning 15 to 65 MHz that was deduced from ex vivo experiments and computer simulations. Images of a 12‐μm wire were generated to quantify lateral and axial resolutions. All 25 transmit/receive signal combinations were digitized and post‐processed for compression and synthetic focusing. Compression consisted of linearly filtering the signals with the time‐reversed excitation chirp modulated by a Dolph‐Chebyshev window. Results showed that resolutions were not significantly degraded when compared to a conventional monocycle excitation and that SNR was improved by more than 14 dB. Images of mouse embryos showed marked improvements in image‐quality. [Work supported in part by NIH Grant R21 EB006509.]