Magnetic Resonance Elastography (MRE) is an advanced, non-invasive medical imaging technique that provides a quantitative map of the mechanical properties of internal organs. MRE combines a standard Magnetic Resonance Imaging (MRI) scanner with specialized technology to assess the stiffness of soft tissues. The principle is that tissue stiffness, which often changes due to disease, can be accurately measured and visualized. This provides diagnostic information unavailable through conventional imaging.
How MR Elastography Measures Tissue Stiffness
MRE operates by introducing low-frequency mechanical vibrations into the body and then using the MRI scanner to visualize how those waves travel through the target organ. The process begins with an external acoustic driver or actuator, which generates continuous, gentle vibrations (typically 20 to 500 Hertz) on the patient’s body surface. These vibrations create tiny shear waves that propagate through the internal tissues.
The speed at which these shear waves move is directly related to the stiffness of the material they are passing through. In softer tissue, the waves travel more slowly, resulting in a shorter wavelength. Conversely, in stiffened or scarred tissue, the waves encounter greater resistance and travel faster, leading to a longer wavelength.
A specialized MRI pulse sequence captures the minute displacement of the tissue caused by these shear waves. This information is processed by a sophisticated mathematical tool called an inversion algorithm. The algorithm analyzes the wave speed and wavelength data to calculate the quantitative stiffness value for each point in the organ. The final output is an elastogram, a color-coded map showing tissue stiffness, usually expressed in kilopascals (kPa).
Key Diagnostic Uses
The ability to precisely measure tissue stiffness makes MRE valuable, particularly in diagnosing and staging chronic liver disease. The primary application is the non-invasive assessment of hepatic fibrosis, which is the scarring of the liver tissue that occurs with conditions like chronic hepatitis or Non-Alcoholic Fatty Liver Disease (NAFLD). MRE-measured liver stiffness correlates strongly with the stage of fibrosis, providing an accurate, quantifiable measure of disease progression.
MRE is considered superior to the traditional liver biopsy, which is invasive and carries risks of complications, pain, and sampling error because the needle only captures a tiny portion of the organ. Unlike a biopsy, MRE assesses the stiffness of the entire liver volume, offering a comprehensive and representative measurement. MRE-based liver stiffness measurements are also not significantly affected by steatosis (the accumulation of fat in the liver).
MRE is also effective in assessing Non-Alcoholic Steatohepatitis (NASH), a more aggressive form of fatty liver disease that includes inflammation and cell damage. Studies show that MRE can help identify individuals with NASH, even before significant fibrosis has developed, by detecting the increased stiffness associated with inflammation. This distinction helps guide treatment decisions and monitor therapy effectiveness.
Beyond the liver, MRE is gaining importance for measuring stiffness in other organs.
Other Applications
Stiffness measurements of the spleen are being investigated as a non-invasive way to detect portal hypertension, a complication of advanced liver disease where blood pressure in the portal vein is abnormally high. In the kidneys, MRE holds potential for the non-invasive evaluation of renal fibrosis, a common pathway in chronic kidney diseases. MRE is also being researched for applications in the brain to detect subtle changes in tissue mechanics associated with neurodegenerative disorders, such as Alzheimer’s disease.
What to Expect During the Procedure
The MRE examination is often integrated into a standard MRI session and generally lasts only a few minutes. Patients may be asked to fast for three to four hours before a liver MRE to ensure optimal imaging quality. Fasting minimizes blood flow changes and reduces motion caused by digestion.
During the scan, the patient lies on the MRI table, and the acoustic driver is placed near the organ of interest (e.g., the right side of the rib cage for a liver examination). This driver is connected to a device outside the scanner room that generates the mechanical waves. The patient typically feels a mild, rhythmic vibration or a gentle tapping.
The imaging sequence requires the patient to hold their breath briefly, usually for a few periods lasting 15 to 20 seconds each, while data is acquired. Since MRE utilizes an MRI scanner, it shares the same safety considerations. People with certain metal implants, such as pacemakers or some aneurysm clips, may not be able to undergo the procedure. The MRE procedure is considered safe and offers a comfortable, non-invasive alternative to surgical tissue sampling.