Ultrasound nonlinearity parameter assessment using plane wave imaging

In this paper we investigate how to assess the ultrasound nonlinearity coefficient using plane wave imaging. We employ the technique based on excitation of the medium with ultrasonic pulses of increasing amplitude level. As the pulse pressure is increased, due to medium nonlinearity, higher fraction of energy is transferred from the fundamental to higher harmonics during the propagation. In this case the amplitude of the backscattered echo is not linear in respect to the initial pulse amplitude at source. This phenomenon can be used for the nonlinearity coefficient assessment and show its implementation for the plane wave imaging. The method was validated experimentally using a wire phantom immersed in water and scanned using the Verasonics scanner. We discuss the usefulness of the proposed technique and its shortcomings. In comparison to other nonlinearity coefficient assessment methods, the presented technique works in the pulse-echo mode and it doesn't require information on second harmonic or using a special wide-band transducer. The method can be implemented directly into a medical scanner.