Cascaded Plane Wave Ultrasound Velocity Vector Imaging: In Vivo Feasibility in Carotid Arteries

Cascaded dual-polarity wave (CDW) imaging enhances signal-to-noise ratio (SNR) by transmitting polarity-alternating pulse sequences, followed by decoding to reinforce coherent signals. This study assesses the in vivo feasibility of CDWs for velocity vector imaging (VVI) in the carotid artery, compared to conventional plane waves (cPWs). Two decoding strategies were evaluated: frequency domain decoding of CDW (F-CDW), offering moderate SNR improvement with reduced motion sensitivity, and time-domain decoding of CDW (T-CDW), providing higher SNR gains but larger motion sensitivity. cPW imaging was performed using constant gain (cPWCG), set patient-specific to avoid clipping, and maximum gain (cPW-HG). VVI using CDW and cPW imaging was obtained in 20 carotid arteries, including ten hemodynamic significant stenoses. A comparison was made based on SNR, percentage of reliable velocity estimates, and agreement with conventional pulsed wave Doppler. Results showed improved SNR and reliability using CDW compared to cPW-CG. The median SNR at peak systole increased from 0.9 dB (cPW-CG) to 2.8 dB (F-CDW) and 4.7 dB (T-CDW). T-CDW showed the greatest improvement, even outperforming cPW-HG (SNR = 1.2 dB) based on SNR and reliability. All methods showed similar agreement with pulsed wave Doppler. Although CDW demonstrated clear benefits, its full potential was limited by restricted gain settings to prevent clipping. CDW is particularly promising for imaging deeper-located carotid arteries, where higher gains can be applied to further enhance SNR beyond conventional plane wave techniques.