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State-of-the-Art Pediatrics

January 2019

Ultrasound Elastography: An Emerging Technique in Ultrasound and Clinical Applications in Pediatrics

Authors:

Erin Opfer, DO | Section Chief, Cardiac Imaging |Assistant Professor of Pediatric Radiology, UMKC School of Medicine

Sherwin Chan, MD | Vice Chair, Radiology | Assistant Professor of Pediatric Radiology, UMKC School of Medicine

Column editor: Amita R. Amonker, MD | Pediatric Hospitalist | Assistant Professor of Pediatrics, UMKC School of Medicine

Ultrasound is one of the main modalities used for advanced imaging in the pediatric population. It is noninvasive, easily accessible, portable, lacks ionizing radiation and requires no sedation, which makes it appealing for use in pediatric patients. Common ultrasound examinations include evaluation of the head/neck, soft tissues, vessels, joints and various abdominal structures. The use of advanced ultrasound techniques has continued to expand and offers noninvasive methods to evaluate and diagnose various disease processes in pediatric patients. One such emerging technique, ultrasound elastography, has been shown to accurately assess the elasticity or stiffness of tissues.1 It has shown promising applications for the assessment of liver disease, such as fibrosis and hepatic vascular congestion.2 Applications in musculoskeletal and small organ imaging are also being evaluated for clinical significance.3

Ultrasound elastography uses sound waves to assess the stiffness or elasticity of the tissues by applying a force and measuring the resultant pressure or displacement. The two main elastography techniques are strain imaging and shear wave imaging.1 Strain imaging uses an external force applied to the tissue of interest. The amount of displacement compared to surrounding tissues is displayed in color in a strain image. It does not directly quantify the tissue stiffness, but rather compares the displacement relative to other tissues. In shear wave imaging, a force is applied to the tissue by using an acoustic radiation force impulse that is generated by the ultrasound transducer.1,4 This force is applied to a focal area of tissue and the shear waves are measured.4 The speed of the shear waves is related to the stiffness of the tissue. The stiffer the tissue interrogated, the faster the shear waves.

The most common application for ultrasound elastography is in the evaluation of a number of different liver pathologies. The most widely studied is the efficacy of ultrasound elastography to predict liver fibrosis. Several literature reviews have shown elastography to be an excellent non-invasive way to diagnose and grade hepatic fibrosis that is highly correlated to histologic grading on biopsies.2 A meta-analysis by Kim et al., determined that elastography has a sensitivity of 81% and a specificity of 91% to detect stage 2 liver fibrosis, and even greater accuracy for higher stages of fibrosis.5 This has led to the use of elastography in several conditions that may result in liver fibrosis. It has been used in grading of hepatic fibrosis in cirrhosis,6 evaluation of liver stiffness in patients’ post Fontan procedure for congenital heart disease,7 assessment of nonalcoholic fatty liver disease,8 and for the assessment of biliary atresia.9 In a study done at Children’s Mercy by Reddivalla et al., increasing shear wave values were detected in patients with hepatic sinusoidal obstruction syndrome post hematopoietic stem cell transplantation before other clinical or ultrasound changes. In the clinical setting, this advanced detection would be beneficial for use in monitoring such patients and detecting complications of transplant earlier than currently used clinical signs. In the future, elastography may serve as a noninvasive alternative to biopsy in the assessment and diagnosis of fibrosis in these patient populations.

There have been several studies which have examined the application of elastography in various small organs for the evaluation of the elasticity of the different tissues and to find noninvasive ways of monitoring and diagnosis. Studies in the kidney, for example, have looked at use of SWE in determining changes in the renal parenchyma in chronic renal disease, although results have been inconsistent.11 Future studies may focus on complications of renal transplant or evaluation of benign versus malignant lesions.12 Studies involving the pancreatic tissues and musculoskeletal lesions have also examined the application of elastography to distinguish between benign and malignant lesions in such tissues.4,13 Several others applications include the evaluation of muscle stiffness in cerebral palsy and congenital torticollis, and differentiating between benign and malignant thyroid nodules.14-16

Ultrasound elastography is an emerging technique that offers promising applications to several disease processes within the pediatric population. The most studied clinical application is the use in pediatric liver diseases resulting in fibrosis and congestion. It has demonstrated a high specificity and sensitivity for the accurate noninvasive detection of fibrosis. Additional studies are looking into the application in other small organs of the body, although further research is needed in these areas.

References:

  1. Ultrasound Elastography: Review of Techniques and Clinical Applications. Sigrist RMS, Liau J, Kaffas AE, et al.  Theranostics. 2017;7:1303–1329.
  2. Ultrasound Elastography is Useful for Evaluation of Liver Fibrosis in Children—A Systematic Review. Andersen SB, Ewertsen C, Carlsen JF, et al.  J Pediatr Gastroenterol Nutr. 2016;63:389–399.
  3. Review-Ultrasound Elastrography Applications in Pediatrics. Thumar V, Squires JH, Spicer PJ, Robinson AL, Chan SS. Ultrasound Quarterly. 2018.
  4. Shear-wave Elastography: Basic Physics and Musculoskeletal Applications. Taljanovic MS, Gimber LH, Becker GW, et al.  Radiographics. 2017;37:855–870.
  5. The Diagnostic Performance of Shear-wave Elastography for Liver Fibrosis in Children and Adolescents: A Systematic Review and Diagnostic Meta-analysis. Kim JR, Suh CH, Yoon HM, et al.   Eur Radiol. 2018;28:1175–1186.
  6. Elastography Assessment of Liver Fibrosis: Society of Radiologists in Ultrasound Consensus Conference Statement. Barr RG, Ferraioli G, Palmeri M, et al.  Radiology. 2015:276(3):845-861.
  7. Assessment of Liver Stiffness in Pediatric Fontan Patients Using Transient Elastography. Chen B, Schreiber RA, Human DG, et al.  Can L Gastroenterol Hepatol. 2016;2016:7125193.
  8. Liver Ultrasound Elastography: An Update to the World Federation for Ultrasound in Medicine and Biology Guidelines and Recommendations. Ferraioli G, Wong VW, Castera L, et al. Ultrasound Med Biol. 2018;44(12):2419-2440.
  9. Contribution of Acoustic Radiation Force Impulse (ARFI) Elastography to the Ultrasound Diagnosis of Biliary Atresia. Hanquinet S, Courvoisier DS, Rougemont A-L, et al.  Pediatr Radiol. 2015;45:1489–1495.
  10. Using Liver Elastography to Diagnose Sinusoidal Obstruction Syndrome in Pediatric Patients Undergoing Hematopoietic Stem Cell Transplant. Reddivalla N, Robinson AL, Reid KJ, et al.  Bone Marrow Transplant. 2018.
  11. Renal Shear Wave Velocity and Estimated Glomerular Filtration Rate in Children with Chronic Kidney Disease. Bruno C, Brugnara M, Micciolo R, et al. Saudi J Kidney Dis Transpl. 2016;27:1139–1147.
  12. Value of Shear Wave Elastography for Differentiating Benign and Malignant Renal Lesions. Aydin S, Yildiz S, Turkmen I, et al.  2018;2018(20):6.
  13. Usefulness of Acoustic Radiation Force Impulse Elastography in the Differential Diagnosis of Benign and Malignant Solid Pancreatic Lesions. Park MK, Jo J,Kwon H, et al. Ultrasonography. 2014;33:26–33.
  14. Feasibility and Reliability of Quantifying Passive Muscle Stiffness in Young Children by Using Shear Wave Ultrasound Elastography. Brandenburg JE, Eby SF, Song P, et al.  J Ultrasound Med. 2015;34:663–670.
  15. Diagnostic Value of Real-time Sonoelastography in Congenital Muscular Torticollis. Kwon DR, Park GY.  J Ultrasound Med. 2012;31:721–727.
  16. Diagnostic Performance of Shear Wave Elastography in the Identification of Malignant Thyroid Nodules: A Meta-analysis. Lin P, Chen M, Liu B, et al.  Eur Radiol. 2014;24:2729–2738.