The nonlinear field produced by 1-D and 2-D imaging arrays with plane and diverging wave modes for ultrafast imaging

Abstract

Combining plane and diverging wave imaging (PWI/DWI) with tissue harmonic imaging (THI) may offer improvements in image quality in applications requiring very high frame rates (ultrafast). The beam shape and magnitude of the 2nd harmonic in tissue are important design considerations. We developed a numerical model based on the KZK equation and modeled three 1-D diagnostic arrays, L11-4v linear array, P4-2v phased array, and C5-2 convex array operating in PWI/DWI. Our numerical code predicts the nonlinear field of nonaxisymmetric sources and source configurations with elevation and no azimuthal foci (plane/diverging fields), which have not been modeled before. We showed that the second harmonic produced by ultrafast THI is 2-16 dB lower than that of focused beams for the imaging arrays considered when operated at the same maximum MI. This moderate difference of the second harmonic between PWI/DWI and focused ultrasound suggests that it is feasible to combine PWI/DWI and THI. We have also investigated harmonic generation produced by diagnostic 2-D arrays for 4-D THI. From our predictions for the second harmonic field we propose beamforming approaches for 4-D cardiac THI with focused ultrasound, PWI, and DWI that would result in frame rates of 10, 81, and 1275 Hz, respectively.