Harmonic imaging has been a breakthrough for the quality of clinical ultrasound imaging, greatly reducing the acoustic clutter that typically reduces in vivo image quality. The generation of the second harmonic signal by non-linear propagation is optimized for a focused transmission in which focal gain raises the fundamental pressure. However, the signal-to-noise ratio (SNR) of the harmonic backscattered signal is lower than for the fundamental frequency. We demonstrate the application of Retrospective Encoding For Conventional Ultrasound Sequences (REFoCUS), a framework for performing spatial decoding of existing pulse sequences irrespective of transducer or scan geometry, to improve transmit depth of field and SNR in harmonic imaging. Unlike other spatial coding methods, REFoCUS allows for maintaining a transmit focus and the corresponding harmonic generation. We demonstrate the ability to recover the effective transmit element sources that would linearly produce the observed harmonic fields, enabling individual transmit element processing. The technique is applied to in vivo liver and fetal targets to produce improved image quality away from the original transmit focal depth using the same data.
Nick Bottenus, Nick Bottenus,
"Synthetic recovery of the complete harmonic data set", Proc. SPIE 10580, Medical Imaging 2018: Ultrasonic Imaging and Tomography, 105800D (6 March 2018); doi: 10.1117/12.2293760; https://doi.org/10.1117/12.2293760