Accuracy of backscatter coefficient estimation in aberrating media using different phase aberration correction strategies - A simulation study

Phase aberration is the distortion of the diffraction pattern when a wave propagates in a medium with an inhomogeneous sound speed. In this study, the accuracy of the estimation of backscatter coefficients (BSCs) in the presence of near-field phase aberrations was studied through simulations. Further, the accuracy was also evaluated when using two different phase aberration correction strategies prior to BSC estimation. Simulations were performed using the FIELD II software for pulsed ultrasound field calculation. The simulation utilized a 45 element, 3.5 MHz linear array with 70% bandwidth. The imaging medium consisted of randomly positioned circular scatterers having a diameter of 176 microns. Near field phase aberrators were applied to the transmit and receive signals of the simulation having 50, 75, and 100 ns RMS strength and a 3 mm correlation length. Phase aberrations were estimated using a multi-lag least squares estimation technique. BSCs were estimated using the reference phantom method and radiofrequency data segments with a length of 14 wavelengths and centered around the transducer transmit focus. BSC estimation accuracy was quantified using the average difference in dB between the theoretical and estimated curves within the -10 dB bandwidth of the transducer. The mean BSC estimation errors were -9.31, -12.82 and -15.58 dB in the presence of the 50, 75 and 100 ns aberrators, respectively. The use of aberration correction on receive was inadequate for the BSC accuracy for all three cases. The estimation errors for the 50 ns, 75 ns and 100 ns aberrators were -7.24, -12.66 dB and -14.68 dB, respectively. In contrast, the use of aberration correction on transmit-receive allowed an accurate BSC estimation, with estimation errors lower than 0.7 dB for the first two cases. These results suggest that phase aberration effects may adversely influence the performance of BSC estimation, and that a robust BSC-based tissue characterization may require compensating for the effects of aberration on both transmit and receive beams.