Amplitude-Modulated Singular Value Decomposition for Ultrafast Ultrasound Imaging of Gas Vesicles

Ultrasound imaging holds significant promise for the observation of molecular and cellular phenomena through the utilization of acoustic contrast agents and acoustic reporter genes. Optimizing imaging methodologies for enhanced detection represents an imperative advancement in this field. Most advanced techniques relying on amplitude modulation schemes such as cross amplitude modulation (xAM) and ultrafast amplitude modulation (uAM) combined with Hadamard encoded multiplane wave transmissions have shown efficacy in capturing the acoustic signals of gas vesicles (GVs). Nonetheless, uAM sequence requires odd- or even-element transmissions leading to imprecise amplitude modulation emitting scheme, and the complex multiplane wave transmission scheme inherently yields overlong pulse durations. xAM sequence is limited in terms of field of view and imaging depth. To overcome these limitations, we introduce an innovative ultrafast imaging sequence called amplitude-modulated singular value decomposition (SVD) processing. Our method demonstrates a contrast imaging sensitivity comparable to the current gold-standard xAM and uAM, while requiring 4.8 times fewer pulse transmissions. With a similar number of transmit pulses, amplitude-modulated SVD outperforms xAM and uAM in terms of an improvement in signal-to-background ratio of $+ 4.78~\pm ~0.35$ dB and $+ 8.29~\pm ~3.52$ dB, respectively. Furthermore, the method exhibits superior robustness across a wide range of acoustic pressures and enables high-contrast imaging in ex vivo and in vivo settings. Furthermore, amplitude-modulated SVD is envisioned to be applicable for the detection of slow moving microbubbles in ultrasound localization microscopy (ULM).