How Accurate Is Semi-quantitative Elastography for Calculating Strain Ratios? A Validity and Reliability Study

Background: Elastography is a promising imaging technique for evaluating various musculoskeletal tissues which uses acoustic radiation force pulse sequences to generate shear waves, which propagate perpendicular to the ultrasound beam causing transient displacements to calculate the tissues stiffness. Objective: The aims were to assess the validity, inter-examiner reliability and stability of semi-quantitative elastography for calculating strain ratios (SR) in a homogeneous gel phantom in different locations within the image. Methods: A diagnostic accuracy study was performed in a homogeneous stiffness phantom. Two examiners (one novice and one experienced) performed 50 imaging captures in 5 series of 10 captures with 1-minute difference between captures and 30 minutes difference be-tween series. Each examiner assessed the SR in two locations. Difference between-examiners, stability of measurements, SR error and absolute error, mean error of the measurements and coefficient of variation were calculated. Results: The agreement between examiners, validity and stability of measurements were higher in the central area than the lateral limits of the images. Thus, the experience of the examiner showed to be relevant for the concordance of the measurements in the lateral limits of the images (SR difference of 0.13 ± 0.02; p0.05). Conclusion: Semi-quantitative elastography seems to be an accurate tool for assessing stiffness differences within the same image. Further validity and reliability studies in different materials and in-vivo tissues are needed to ensure the utility of this method.