(a) A pressure field is generated by driving each of transducer elements with a unique frequency within the bandwidth of the transducer, creating a complicated broadband field pattern. (b) This field is assumed to encounter variation in density and sound speed within a region of interest (ROI) causing weak scattering, (first-order Born approximation). (c) Each point in the ROI is tested using the inverse of the kernel for the location. The rest of the signal will present itself as noise . (d) If this process is repeated with a new randomization, the “noise” averages toward zero, while the signal gets stronger.
Slice from a three-dimensional k-space simulation of a focused, pulsed wave traveling through a medium with scatterers smaller than the imaging wavelengths. Scattering from two objects is present in the image.
Simulated B-scan images resulting from scattering from two wires separated by (a) , (b) , (c) , and (d) .
(a) Comparison of the random frequency method (top) with a traditional B-scan (bottom) using the same frequency bandwidth. (b) A more magnified view compared with the actual position of the scatterers.
(a) An image of two scatterers separated in the direction parallel to the transducer face at the resolution limit of over the entire ROI and (b) a magnified view compared with the actual position of the scatterers.
(a) An image of two scatterers separated in the axial direction at the resolution limit of over the entire ROI and (b) a magnified view compared with the actual position of the scatterers indicates the distortion observed at small separations.
(a) Two reconstructed objects in the ROI with scattering strengths and . The speed of sound of is varied and the ratio of the measured scattering ratio of the two coefficients is plotted as a function of frequency (squares). The reconstructed values are compared with the actual (circles).
A series of simulations with multiple scatterers (right column) and their reconstruction (left column) demonstrating application at distances of (a) 3–, (b) 10–, and (c) 26– in front of the transducer.
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