Department of Electrical Engineering, University of Rochester.
*LJB Development, Inc.
Abstract of paper 712 presented at the 2000 American Institute of Ultrasound in Medicine Conference
Objective: To determine experimentally the coherence of pulse-echo wavefronts in the presence of aberration.
Methods: A 3.0 MHz two-dimensional array system with a pitch of 0.6x0.6 mm2 was used to acquire pulse-echo data at f/1.2 from a point reflector and from a region of random scattering each through a water path and through a path that included a tissue-mimicking aberration phantom. For the aberration path, data were acquired with and without using aberration correction on transmit. Aberration correction included time-shift compensation alone and with backpropagation. The temporal-spatial correlation function in the receive aperture was computed with Hamming apodization and the full width of the 0.8 maximum (FW@0.8M) Cartesian dimensions used to describe the coherence.
Results: The FW@0.8M spatial dimension for the point reflector data was reduced to 4.2 mm by aberration from 23.4 mm for the water path through which the spatial coherence was determined by the apodization. The corresponding widths for random scattering were 3.0 mm and 11.4 mm, respectively. The coherence width was restored, for example, to 17.4 mm for the point reflector by time-shift compensation. The coherence width for the random scattering was restored, for example, to 6.6 mm by backpropagation with time-shift compensation. The coherence obtained through an aberrating path using geometric focusing on transmit was not improved by aberration correction on receive.
Conclusions: The coherence of scattering is significantly decreased by aberration and restoration of coherence requires compensation of aberration on transmit as well as on receive.