Correction of Nakagami shape parameter estimated from 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 the RF data amplitude typically covers several orders of magnitude between the sample surface and the deepest imaged regions. In addition, the saturated signal may decrease the accuracy of QUS methods because quantitative ultrasound (QUS) methods are sensitive to saturated data. In this study, the effects of saturation on QUS estimates of Nakagami shape parameter (Nakagami parameter) were quantified by analyzing data acquired from 20 dissected human lymph nodes with a single-element transducer operating at a center frequency of 26 MHz. Artificially saturated signals (x_sat) were produced by applying artificial saturation methods to the original unsaturated signals (x_ori). Saturation degree was quantified using an index termed Saturate-SNR (SSNR). Nakagami parameters were estimated from x_sat over a wide range of SSNR values. Nakagami parameters of saturated signals were increased (0.18 when the signal decremented 2 bit) significantly with decreasing SSNR. Nakagami parameters were corrected by pretreatment that applied a smoothing spline to the saturated signal. The smoothing spline restoration method is tuned P parameter. The best correction occurred when P was 1 (i.e., cubic spline interpolation). The maximum Nakagami parameter error in the corrected with 6-bit signal was 0.10, which is less than the average difference of 0.12 that existed between non-metastatic and metastatic lymph nodes.