Shear Wave Sonoelastography in Pediatric Liver Fibrosis

Reliable methods of evaluating liver fibrosis using noninvasive techniques in the pediatric population are limited and inconclusive. Liver biopsy remains the gold standard; however, it requires sedation in pediatric patients, has a risk of hemorrhage, and provides unreliable results secondary to sampling error. Sonoelastography is a new method of evaluating liver disease that eliminates these pitfalls. There are 3 types of quantitative sonoelastography currently in use. Transient elastography is a non-imaging based technique used in adults to measure liver fibrosis in which a mechanical vibrator creates a low-frequency wave causing shear stress in the liver at a fixed depth. This technique does not work in small livers and, therefore, is not appropriate for pediatric patients. Acoustic Radiation Force Impulse Imaging (ARFI) and Shear Wave Imaging (SWE) use real-time ultrasonography and administer focused high-intensity, short-duration pulses to produce shear waves in the liver tissue. ARFI calculates the degree of tissue displacement and creates an elastogram or measurement of the stiffness of the sampled liver tissue without corresponding images. It is limited since only a small sample or region of interest (ROI) can be obtained, and it is unable to provide a corresponding elasticity map of the tissue. SWE is the newest elastography technique. It measures tiny displacements of tissue in a larger ROI with corresponding ultrasound images which provides a side by side image of the liver and color-coded elasticity map of the sampled tissue. Advantages include a larger ROI and simultaneous viewing of the selected region of interest which provides better anatomic detail with a corresponding color map of the tissue elasticity which may result in more accurate scoring of the stage of fibrosis. There are a few studies of ARFI in the pediatric population. Studies using SWE for evaluation of liver fibrosis are also few, and, all but one in adults. However, these studies have shown it to be an accurate method for liver fibrosis staging. Use of SWE in assessing liver fibrosis in pediatric patients may represent an accurate noninvasive alternative to liver biopsy in evaluating liver fibrosis as well as avoid the use of sedation.