Correction of scatterer-diameter and acoustic-concentration estimates in Saturated high-frequency ultrasound signals acquired from cancerous human lymph nodes

Choosing an appropriate dynamic range for acquiring radio-frequency (RF) data from a high-frequency ultrasound (HFU) system is challenging because signals can vary greatly in amplitude because of focusing and attenuation effects. In addition, quantitative ultrasound (QUS) methods are sensitive to saturated data. In this study, the effects of saturation on QUS estimates of effective scatterer diameter (ESD) and effective acoustic concentration (EAC) were quantified using data acquired from 69 dissected human lymph nodes with a single-element transducer operating at a center frequency of 26 MHz. Artificially saturated signals (x_c) were produced by thresholding the original, unsaturated RF echo signals (x). Saturation degree was quantified using Saturate-SNR. ESD and EAC were estimated from x_c over a wide range of Saturate-SNR values. The value of the ESD estimate was minimally affected when Saturate-SNR ranged from infinity to 3.99 dB. However, the value of the EAC estimate decreased significantly with decreasing Saturate-SNR. EAC estimates were corrected using a linear relationship between EAC values over a range of Saturate-SNR values and l¹ - norm of x (i.e., the sum of absolute values of the true RF echo signal). To correct the estimates for ESD and EAC of saturated signals, the estimated original RF signal was derived from x_c by a cubic spline. A linear-regression line was computed for the EAC values of a set of Saturate-SNR values vs. l¹ - norm. The intersection of the regression line and l¹- norm of the estimated original signal gave a corrected value for EAC. The maximum error in the corrected EAC estimate was 0.48 dB/mm³. The average differences in corrected ESD and EAC estimates of non-metastatic and metastatic lymph nodes were 7.80 μm and 4.18 dB/mm³, respectively. The error in the corrected EAC value was much smaller than the difference in the corrected values of non-metastatic and metastatic lymph nodes.