A comparison of ultrasound image simulations with FOCUS and field II

To achieve significant improvements in both nearfield accuracy and memory efficiency in diagnostic ultrasound simulations, B-mode imaging simulations are performed with FOCUS. Improved nearfield accuracy and memory usage is achieved in FOCUS by combining the fast nearfield method with time-space decomposition to avoid the aliasing problems caused by the impulse response. The RF signals for pulse-echo imaging with FOCUS are calculated with the square root of the input signal. The transient pressure contributions are evaluated at a point scatterer by applying the square root signal to both the transmit and receive apertures, respectively, and the pulse-echo signal is then given by the convolution. An analytically equivalent result is calculated in Field II by the convolving the second derivative of the input signal with the impulse responses for the transmit and receive apertures. B-mode simulation results are compared for a 128 element linear array with 64 active elements over the aperture and focusing at 60 mm. The results show that Field II requires a sampling frequency of f_s = 500MHz to achieve a normalized error of 0.91%, whereas FOCUS achieves a smaller error of 0.78% with a sampling frequency of 35MHz.