Shear Wave Speed Dispersion Characteristics of Seafloor Sediments in the Northern South China Sea

To accurately characterize the shear wave speed dispersion of seafloor sediments in the northern South China Sea,five types of sediments including silty clay,clayey silt,sandy silt,silty sand,and clayey sand were selected,on which the measurements of the shear wave speed at 0.5-2.0 kHz and related physical properties were performed.Results reveal that the shear wave speed of sediments increases as the frequency increases,and the dispersion enhanced in the sediments in the order of silty clay,clayey silt,sandy silt,silty sand,and clayey sand,at a linear change rate of 0.727,0.787,3.32,4.893,and 6.967 m s−1 kHz−1,respectively.Through regression analysis,linear and logarithmic regression equations for the correlation between shear wave speed and frequency were established for each sediment type and the determination coefficients of regression equations indicate that the correlation is closer to a logarithmic relationship.The Grain-Shearing(GS)and Biot-Stoll models were used to calculate the shear wave speed dispersion of the five sediment types,and the comparison between theoretical prediction and measured results of shear wave speeds shows that the GS model can more accurately describe the shear wave speed dispersion characteristics of these sediments in the frequency band of 0.5-2.0 kHz.In the same band,the predictions obtained by using the Biot-Stoll model are significantly different from the measured data.

Novel multi-parametric diagnosis of non-alcoholic fatty liver disease using ultrasonography,body mass index,and Fib-4 index

BACKGROUND Shear wave speed(SWS),shear wave dispersion(SWD),and attenuation imaging(ATI)are new diagnostic parameters for non-alcoholic fatty liver disease.To differentiate between non-alcoholic steatohepatitis(NASH)and non-alcoholic fatty liver(NAFL),we developed a clinical index we refer to as the“NASH pentagon”consisting of the 3 abovementioned parameters,body mass index(BMI),and Fib-4 index.AIM To investigate whether the area of the NASH pentagon we propose is useful in discriminating between NASH and NAFL.METHODS This non-invasive,prospective,observational study included patients diagnosed with fatty liver by abdominal ultrasound between September 2021 and August 2022 in whom shear wave elastography,SWD,and ATI were measured.Histological diagnosis based on liver biopsy was performed in 31 patients.The large pentagon group(LP group)and the small pentagon group(SP group),using an area of 100 as the cutoff,were compared;the NASH diagnosis rate was also investigated.In patients with a histologically confirmed diagnosis,receiveroperating characteristic(ROC)curve analyses were performed.RESULTS One hundred-seven patients(61 men,46 women;mean age 55.1 years;mean BMI 26.8 kg/m2)were assessed.The LP group was significantly older(mean age:60.8±15.2 years vs 46.4±13.2 years;P<0.0001).Twenty-five patients who underwent liver biopsies were diagnosed with NASH,and 6 were diagnosed with NAFL.On ROC curve analyses,the areas under the ROC curves for SWS,dispersion slope,ATI value,BMI,Fib-4 index,and the area of the NASH pentagon were 0.88000,0.82000,0.58730,0.63000,0.59333,and 0.93651,respectively;the largest was that for the area of the NASH pentagon.CONCLUSION The NASH pentagon area appears useful for discriminating between patients with NASH and those with NAFL.