METHOD FOR IMAGING OF ACOUSTIC PROPERTIES BY NONLINEAR LOW FREQUENCY MANIPULATION OF HIGH FREQUENCY SCATTERING AND PROPAGATION PROPERTIES (VARIANTS) AND ACOUSTIC INSTRUMENT FOR IMPLEMENTING SAID METHOD

摘要

New methods of acoustic imaging are presented that provide images with reduced reverberation noise and images of nonlinear scattering and propagation parameters of the object, and estimation methods of corrections for wave front aberrations produced by spatial variations in the acoustic propagation velocity. The methods find use in a variety of applications such as acoustic imaging of geological structures, SONAR imaging of sub-sea objects, and medical ultrasound imaging. The methods are based on processing of the received signal from transmitted dual frequency band acoustic pulse complexes with overlapping high and low frequency pulses. The high frequency pulse is used for the image reconstruction and the low frequency pulse is used to manipulate the nonlinear scattering and/or propagation properties of the high frequency pulse. A 1-st method uses the scattered signal from a single dual band pulse complex for filtering in the fast time (depth time) domain to provide a signal with suppression of reverberation noise and with 1-st harmonic sensitivity and increased spatial resolution. In other methods two or more dual band pulse complexes are transmitted where the frequency and/or the pulse and/or amplitude of the low frequency pulse vary for each transmitted pulse complex. Through filtering in the pulse number coordinate and corrections for nonlinear propagation delays and optionally also amplitudes, a linear back scattering signal with suppressed pulse reverberation noise, a nonlinear back scattering signal, and quantitative nonlinear forward propagation and scattering parameters are extracted. The reverberation suppressed signals are further useful for estimation of corrections for wave front aberrations, where approximate estimates of aberration of corrections are given. The signals are further useful with broad transmit beams for multiple parallel receive beams to increase image frame rate with 2D and 3D IMAGING. The nonlinear signal is useful for imaging of differences in object properties, micro-calcifications, in growth of fibrous tissue or foam cells, or micro gas bubbles as found with decompression or injected as ultrasound contact agent. The methods are also useful with transmission imaging for generating the measured data for tomography and diffraction tomography image reconstructions.