Body habitus vs. hepatic steatosis: Understanding the drivers of non-diagnostic shear wave elastography

Shear Wave Elastography (SWE) is frequently non-diagnostic in obese patients, a key cohort at risk for liver disease. Subcutaneous fat and hepatic steatosis are suspected drivers, but their relative contribution is unknown. We compare ultrasound-guided attenuation parameter (UGAP), a marker of steatosis, body mass index (BMI), and skin-to-liver capsule distance (SCD) to predict non-diagnostic SWE. This IRB approved, single center retrospective study included adults with SWE and diagnostic UGAP exams between June and December 2023. Fasting patients were imaged in supine position with right arm abducted, via an intercostal window during neutral breath hold. The median of 10 measurements in the right lobe was analyzed for SWE and UGAP. SWE measurements were ≥ 2 cm from the capsule while UGAP depth was fixed at 4 cm from the probe. Exams were considered non-diagnostic for SWE (measured in m/s) if the Interquartile Range/Median Ratio (IQR/M) was > 15% or if diagnostic measurements could not be obtained. UGAP IQR/M > 30% or complete measurement failure was considered non-diagnostic. Univariate Receiver Operating Characteristic (ROC) curves compared UGAP (dB/cm/MHz), BMI (kg/m 2 ), and SCD (mm) prediction of non-diagnostic SWE by the DeLong test. 87 participants (48 male) with mean age of 54.7 ± 15.7 years were analyzed. UGAP [OR: 1.63 per 0.1 dB/cm/MHz, p=0.02, AUC=0.66], BMI [OR: 1.23, p<0.001, AUC=0.77], and SCD [OR: 1.27, p<0.001, AUC=0.81) were predictors of non-diagnostic SWE. UGAP prediction of non-diagnostic SWE was similar in subgroups with the measurement region at least 1 cm (OR: 1.64, n = 68), and 2 cm (OR: 1.54, n = 16) from the liver capsule. UGAP was a worse predictor than SCD (p = 0.04), while not significantly different than BMI (p = 0.15). BMI and SCD did not differ in predicting non-diagnostic SWE (p = 0.44). Our small preliminary study demonstrated that body habitus and hepatic attenuation, a marker of steatosis, both contribute to non-diagnostic SWE exams, however body wall thickness is the key driver. This informs patient selection for SWE exams and guides future research to mitigate these technical shortcomings. Patients with hepatic steatosis and large body habitus are at increased risk of non-diagnostic ultrasound shear wave elastography (SWE) exams. These patients, particularly those with increased body wall thickness, may benefit from liver fibrosis evaluation with alternative approaches following an initial non-diagnostic SWE exam. Researchers working to improve SWE technique should pay particular attention to mitigating attenuation and phase aberration from the body wall as this is the key driver of non-diagnostic exams.