ARRS 2022 Abstracts

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E1883. Guide to Shear Wave Elastography of the Liver: Societies’ Positions with Recent Updates
Authors
  1. Madhangi Parameswaran; Center for Ultrasound Research and Translation, Massachusetts General Hospital
  2. Arinc Ozturk; Center for Ultrasound Research and Translation, Massachusetts General Hospital
  3. Firouzeh Heidari; Center for Ultrasound Research and Translation, Massachusetts General Hospital
  4. Theodore Pierce; Center for Ultrasound Research and Translation, Massachusetts General Hospital; Department of Radiology, Massachusetts General Hospital
  5. Anthony Samir; Center for Ultrasound Research and Translation, Massachusetts General Hospital; Department of Radiology, Massachusetts General Hospital
Background
Chronic liver disease (CLD) is increasingly common and leads to substantial healthcare burden. Liver biopsy remains the gold standard to stage liver fibrosis, the main prognostic factor in CLD. Shear wave elastography (SWE) is an ultrasound technique that measures tissue elasticity, a surrogate marker of liver fibrosis. It uses a focused pulse to generate laterally propagating shear waves in tissue, which are tracked using high resolution B-mode imaging to measure the shear wave propagation speed. This speed reflects tissue elasticity and stiffness which are correlated to fibrosis levels. The use of SWE as an alternative to biopsy has grown in recent years due to its accessibility, low cost, and noninvasiveness. Studies have shown good accuracy in identifying clinically significant fibrosis in many causes of CLD. Adherence to recommended standards is critical to mitigate variability in measurements due to imaging techniques, vendors, and patient and operator-related factors.

Educational Goals / Teaching Points
In this exhibit, we highlight the need for noninvasive liver fibrosis diagnosis; describe patient preparation and appropriate technique for SWE examinations; outline image acquisition requirements; and discuss exam interpretation and identify common pitfalls.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Fasting for 4 hours before imaging is recommended, as eating can increase liver stiffness. Supine positioning of the patient with their arm raised above the head increases acoustic windows via the intercostal space. Known clinical confounders of fibrosis estimation include acute hepatitis and obstructive cholestasis. Measurements are obtained from the right lobe of the liver via the intercostal space during neutral breath hold. Artifacts such as shadowing must be avoided in B-mode images as the shear waves may be poorly tracked, leading to variable measurements. Five to 10 measurements are recommended depending on the availability of quality assessments. Measurements are considered optimal if they are taken 1.5–2 cm below the liver capsule and = 6–7 cm from the transducer to prevent reverberation artifacts and attenuation of the push pulse, respectively. The liver capsule should also be parallel to the transducer face to prevent attenuation. Images from the left lobe, perivascular tissue, subcapsular tissue, or surrounding focal lesions must be avoided, as it may artifactually increase SWE measurements. The radiologist should assess if each image meets the criteria described above to ensure reliability of acquired measurements. An important reliability criterion is the interquartile range to median ratio, which should be = 30% in kilopascals (kPa) or = 15% in meters per second (m/s). To interpret SWE measurements, the Society of Radiologists in Ultrasound have proposed thresholds of = 5 kPa (1.3 m/s) to indicate normal tissue and > 13 kPa (2.1 m/s) to rule in advanced CLD.

Conclusion
In conclusion, SWE is safe and reliable for liver fibrosis assessment; however, assessment of image quality and adherence to acquisition parameters is required to maintain diagnostic accuracy.