Shear wave elastography (SWE) of the liver is a non-invasive imaging technique that uses ultrasound to assess liver tissue stiffness. SWE measures this stiffness to evaluate liver health without a biopsy.
Why Liver Stiffness Matters
Liver stiffness is a significant indicator because various liver diseases can lead to inflammation and subsequent scarring, known as fibrosis. Conditions like chronic hepatitis, fatty liver disease, or excessive alcohol consumption can initiate this process. As fibrosis advances, the liver tissue becomes progressively stiffer.
This increasing stiffness reflects the accumulation of scar tissue, which can eventually disrupt the liver’s normal function. Untreated fibrosis can lead to cirrhosis, a severe and irreversible condition characterized by widespread scarring and impaired liver function. Measuring liver stiffness helps in the early identification and ongoing monitoring of liver disease progression, allowing for timely medical interventions.
How Shear Wave Elastography Works
Shear wave elastography works by measuring how sound waves travel through tissue. The procedure uses ultrasound to generate shear waves within the liver. These waves travel perpendicular to the primary ultrasound beam.
The speed at which these shear waves move through the liver is then measured. Stiffer tissues cause the shear waves to travel faster, while softer tissues result in slower wave propagation. This measured speed is converted into a numerical value, expressed in kilopascals (kPa), which quantifies the liver’s stiffness.
The Procedure and What to Expect
Undergoing a liver SWE exam is a straightforward and comfortable experience. Patients are asked to fast for at least three hours before the test to ensure accurate results. During the procedure, the patient lies flat on an examination table, and a trained technologist applies a gel to the skin over the liver area, usually on the right side of the upper abdomen.
The technologist then presses an ultrasound probe against the skin, delivering low-frequency pulses that generate the shear waves. Patients may feel a gentle “flick” or mild pressure as these pulses are applied. Brief breath-holds may be requested to ensure clear measurements. The entire test is quick, taking about 10 to 15 minutes, and is painless with no radiation exposure.
What the Results Reveal
The kilopascal (kPa) values obtained from SWE measurements reveal liver stiffness, which correlates with stages of liver fibrosis. Higher kPa values indicate greater stiffness and more advanced fibrosis. For instance, a measurement below 5 kPa might suggest no significant fibrosis (F0-F1), while values above 12 kPa could indicate advanced fibrosis, potentially cirrhosis (F4).
These results are categorized into different stages of fibrosis: F0 (no fibrosis), F1 (mild fibrosis), F2 (significant fibrosis), F3 (severe fibrosis), and F4 (cirrhosis). Healthcare providers use these stiffness measurements to assess the extent of liver damage, guide treatment decisions, and monitor how well therapies are working. While SWE offers high accuracy, it is used in conjunction with other clinical data for a comprehensive understanding of liver health.