The liver responds to many diseases that damage its cells by developing scar tissue or fibrosis. MRE uses a modified form of magnetic resonance imaging (MRI) to accurately measure the hardness or elasticity of the liver. By applying vibrations to the liver, MRE obtains pictures of the mechanical waves passing through the organ. The wave pictures are then processed to generate a quantitative image of tissue stiffness.
"Healthy liver tissue is very soft, while a liver with fibrosis is firmer, and a liver with cirrhosis is almost rock-hard", stated Richard Ehman, M.D., lead researcher on the MRE project. "If detected early, fibrosis of the liver can be treated, but once the disease has progressed to cirrhosis, the condition is irreversible."
Dr. Ehman and his imaging research team collaborated with Mayo Clinic gastro-enterologists to study whether MRE could provide reliable and accurate diagnoses in patients with varying degrees of liver disease.
One study involved MRE examinations of 57 individuals with chronic liver disease and 20 healthy volunteers. The researchers confirmed that MRE accurately detects fibrosis with high sensitivity and specificity. Researchers also found that steatosis, which causes deposits of fatty acids and triglycerides to reside in liver cells and which is a common condition in patients with liver disease, did not interfere with detection of fibrosis with MRE.
"Based on this research, we are now using MRE examinations in select patients to determine liver stiffness and assess the need for liver biopsies", stated Jayant Talwalkar, M.D., a Mayo Clinic gastro-enterologist and an investigator on the MRE studies. "More than 170 million people in the world are known to have hepatitis C, and nearly one-fourth of those will develop severe liver fibrosis. MRE can help us non-invasively identify fibrosis in this large patient population."
A second study looked at whether MRE can accurately measure portal hypertension, or high blood pressure in the portal vein that carries blood from the digestive track to the liver, usually as a result of cirrhosis of the liver. This study involved 35 individuals with varying degrees of chronic liver disease and 12 healthy volunteers. Researchers studied MRE examinations of liver and spleen stiffness and found that a highly significant correlation exists between liver and spleen stiffness in patients with portal hypertension. However, the validity of spleen stiffness as a non-invasive measure of portal venous pressure requires further study.
According to Dr. Ehman, many diseases cause the properties of tissue to change and will be likely candidates for diagnosis using MRE in the future. His research team is exploring the use of MRE in detecting breast cancer and Alzheimer's disease.
This research was funded in part by the National Institutes of Health. Co-authors of these studies include Meng Yin; Roger Grimm; Phillip Rossman; Armando Manduca, Ph.D.; Patrick Kamath, M.D. and Dr. Ehman; all from Mayo Clinic's campus in Rochester; and Anthony Romano, Ph.D., of the Naval Research Laboratory in Washington, D.C.
More news on Mayo Clinic research can be found in the VMW May 2007 article Mayo Clinic and IBM score significant advance in real-time medical imaging.