A Robust and Fast Method for 2D Shear Wave Speed Calculation.

We developed a new method, called the tangent plane method (TPM), for estimating 2D shear wave speed (SWS) from any direction of wave propagation more efficiently and accurately. In this technique, we estimate SWS by solving the Eikonal equation because this approach is more robust to noise. To further enhance performance, we computed the tangent plane of the arrival time surface. To evaluate the approach, we performed simulations and also conducted phantom studies. Simulation studies showed that TPM was more robust to noise than the conventional methods such as 2D CC (cross-correlation) and the distance method. Contrast/CNR for an inclusion (69kPa : manufacturer provided stiffness) of an inclusion phantom is 0.54/4.17, 0.54/1.82, and 0.46/1.22, respectively. SWS results (mean and standard deviation) were 4.41±0.49 m/sec, 4.62±0.85 m/sec, and 3.66±0.99 m/sec, respectively while the manufacturer's reported value (mean and range) is 4.81±0.49 m/sec. This shows that TPM has the higher CNR and lower standard deviation than other methods. To increase computation speed, an iterative version of TPM (ITPM) was also developed, which calculated the time-of-flight iteratively. ITPM reduced the computation time to 3.6%, from 748 sec to 27 sec. In vivo case analysis demonstrated the feasibility of using the conventional ultrasound scanner for the proposed 2D SWS algorithms.