Abstract
There has been great interest in developing accurate ultrasonic velocity estimators to measure wall shear rate (WSR), in vivo. In this study, we implemented coded pulse excitation methods onto a commercial scanner and used flow-angle-corrected correlation methods to obtain WSR estimates with high spatial resolution near vessel walls. We tested the method on flow phantoms that generated a similar time-averaged shear range to human arteries (100-600 1/s), and on carotid arteries of a volunteer. Phase-modulated (PM = 13-bit Optimal) code and frequency-modulated (FM = 2.1mus pseudo-chirp) pulse with similar excitation energies were programmed into a Siemens Antares system. RF data recorded using ultrasound research interface (URI) was decoded offline. The accuracy and precision of WSR measurements were compared among broadband (BB)/narrowband (NB) and coded/uncoded data. eSNR was enhanced 15 dB using codes compared with BB pulses, and 5 dB compared with NB pulses. Experimental results show that coded pulses overall yield the minimal errors in WSR estimation (-10 % bias (B) and 4% standard deviation (SD)), compared with those of BB (30% B, 15% SD) and NB pulses (20% B, 10% SD). Errors increase with WSR for all pulses. ECG-gated acquisitions from the carotid artery of a volunteer yielded the comparable WSR values at peak systole of 853 1/s (PM), 820 (FM), 729 1/s (NB), and 590 1/s (BB), while the coded pulses provided the lowest variances. Our study shows that coded excitation techniques can increase both the precision and accuracy in WSR estimation over a broad range of shear rate. The study also demonstrates the feasibility of in vivo application of coded excitation in WSR flow imaging
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