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Session: Poster Session 1 (Even numbers)
Session starts: Thursday 26 January, 16:00
Presentation starts: 16:00

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Joosje de Bakker (Radboudumc)
Chris de Korte (Radboudumc)
Anne Saris (Radboudumc)

Abstract:
Stroke is a leading cause of death and major disability and is often caused by atherosclerosis. Complex blood flows (CBF) in the carotid arteries seem to play a crucial role in the atherosclerotic disease process. However, conventional ultrasound systems cannot measure these CBF. Ultrafast ultrasound, where thousands of images are acquired per second, enabled new opportunities for blood velocity imaging. Identification of CBF could aid in better patient-specific risk stratification and treatment planning. A downside of ultrafast ultrasound, where unfocused beams are transmitted, is the decreased signal-to-noise ratio (SNR) compared to conventional focused imaging. Cascaded Dual-polarity Waves (CDW)a overcomes this by transmitting a pulse-train instead of a single pulse. A postprocessing decoding scheme is applied to obtain recovered signals with increased SNR. This potentially enables blood velocity imaging under challenging conditions, such as deeper located vessels. However, its application in blood velocity estimation has not been shown yet. The performance of 4-CDW was compared to single pulse plane waves (PW) using Field IIb,c simulations of parabolic flow (vmax = 0.25, 2 m/s). Different attenuation situations were mimicked by adding two different noise levels (SNR = 6, 14 dB). Data were simulated for a 7.8 MHz linear array, subsequently transmitting -20° and +20° beams at a repetition frequency of 8 kHz. Blood velocities were estimated using normalized cross-correlation based compound speckle trackingd. For the peak velocity of 0.25 m/s and 14 dB SNR, CDW and PW performed very similar. For a reduced SNR of 6 dB, CDW demonstrates a thirteen fold lower lateral bias than PW. Increasing vmax to 2 m/s raised the bias for both imaging methods. PW outperformed CDW in the 14 dB SNR case, this reversed in the 6 dB case. Summarized, in low SNR conditions, CDW consistently outperformed PW due to the increased effective SNR for the recovered signals. However, since high velocities result in imperfect summation/cancellation of shifted pulse responses, CDW fails to outperform PW in case of sufficient SNR. To conclude, CDW could potentially aid in measuring CBF in high attenuating situations, such as in obese patients, enabling blood velocity imaging in all patients.