Assessing Robustness of the Nonlinearity Parameter Estimation in the Depletion Method to Uncertainty Measurements of Acoustic Variables

The nonlinearity parameter (B/A) provides information about the composition and structure of a medium, which is particularly promising for hepatic steatosis. The depletion method, a recent pulse-echo B/A estimation technique, uses assumptions of several acoustic parameters for the unknown sample itself, the reference phantom used, and the ultrasonic settings. For this reason, the main objective of the study is to identify the robustness of the depletion method to inconsistencies or uncertainty measurements of the acoustic parameters involved in the B/A estimation. This study explores the impact of measurement errors on two acoustic parameters in the calculation of B/A: (a) the B/A of the reference for a range from 4 to 9 with a given true value of 6, and (b) the ACS of the sample for a range from 0.4 to 0.8 dB/cm/MHz with a given true value of 0.6 dB/cm/MHz. The methodology relies on computer simulations implemented with the k-Wave toolbox. The methodology builds on appropriate nonlinear conditions (a scaling factor of 5-10 and initial pressures of 40-400 kPa for an input signal of 50% -6 dB Gaussian pulse). The absolute percentage error of the bias is presented as a function of the error measurements. Results showed that the mean percentage error can increase up to an additional 29% with an uncertainty of +/-2 concerning the original value of B/A of the reference, and up to an additional 25% with an uncertainty of +/-0.2 compared to the original value of the sample ACS.