A novel elastography phantom prototype for assessment of ultrasound elastography imaging performance

The aims of this study were firstly to manufacture and evaluate a novel elastography test phantom and secondly to assess the performance of an elastography system using this phantom. A novel ‘L-STEP’ test phantom consisting of 5 soft PVA-cryogel pipes of varying diameters (2-12mm), embedded at 450 within an agar-based tissue mimicking material was developed. A shear wave elastography (SWE) scanner was used by 2 blinded operators to image and assess longitudinal sections of the pipes. Young’s Modulus (YM) estimates were dependent on the diameter of pipes and at superficial depths were greater than deeper depths (mean 98 kPa vs 59 kPa), and had lower coefficient of variation (mean 21% vs 53%). The penetration depth (maximum depth at which a SWE signal was obtained) increased with increasing pipe diameter. Penetration depth measurements had excellent inter- and intra- operator reproducibility (intra-class correlation coefficients >0.8) and coefficient of variation range 2-12%. A new metric, called the Summative Performance Index (SPI) was defined as the sum of the ratios of the penetration depth/pipe diameter. The L-STEP phantom is suitable for assessing key aspects of elastography imaging performance: resolution, accuracy, reproducibility, depth dependence, sensitivity and our novel SPI.