New technologies continue to reduce the number of invasive, painful and sometimes unnecessary diagnostic procedures. Along those lines, doctors at the Mayo Clinic (Rochester, Minnesota) are putting into practice their invention of magnetic resonance elastography (MRE) to identify liver fibrosis with high accuracy, helping to eliminate the need for biopsies.
The theory behind MRE seems very straightforward: Using a standard MR machine, the add-on technology produces color-coded images known as elastograms that indicate how internal organs, muscles and tissues would feel to the touch. Red is the stiffest; purple, the softest. A liver's elasticity or stiffness is invaluable in diagnosing liver disease. Liver fibrosis — the development of excessive scar tissue resulting in stiffness — is a common condition that can lead to incurable cirrhosis if not treated in time.
Doctors can't base their diagnosis on simply palpating the abdomen. A biopsy is needed to confirm. Even with biopsies, the results are not fully reliable.
With MRE, a special pad is placed on the patient's abdomen above the liver during a standard MRI procedure. A remote machine, connected by a tube to the pad, generates pulses or vibrations. Like ripples in water, the vibration causes waves to appear on MRI. Those waves are then interpreted by software into colors.
"The pulse sequence can show waves traveling through the liver," Jayant Talwalkar, MD, MPH, a Mayo Clinic hepatologist told Medical Device Daily. "One is blue and the other is red. That data is converted using a sophisticated math algorithm in a computerized fashion into a map of stiffness. Different colors represent different values of stiffness. Reds and yellows are really stiff. Blues are soft."
He explained that the elastogram provides a topographic map of liver. "In a normal liver, you would see a lot of purple and blue. Somebody with cirrhosis, you would see a lot of red and yellow," he said.
Talwalkar is co-investigator of a 113-patient study of MRE. Results were just presented last weekend at The Liver Meeting, an annual gathering of the American Association for the Study of Liver Disease (Alexandria, Virginia), held in San Francisco.
Study participants all had liver biopsies in the year preceding the study and had a wide variety of liver diseases, including nonalcoholic and alcoholic fatty liver disease, hepatitis C, hepatitis B, autoimmune hepatitis, primary biliary cirrhosis and primary sclerosing cholangitis. Patients ranged in age from 19 to 78, and their body weight ranged from normal to severely obese.
"Results showed that elastography was highly accurate in detecting moderate-to-severe hepatic fibrosis even with the variety in age, types of liver disease and body size," Talwalkar said.
The underlying principle of MRE is that waves travel at a certain velocity; they move through stiffer tissue at faster speed and softer tissue at a slower speed.
Talwalkar said MRE could ultimately be used for other disease diagnoses. "I think there may be ways to develop this for cancer, muscle diseases, thyroid tests and Alzheimer's. There are a number of potential application in development now."
Meanwhile, physicians at all of the Mayo Clinic locations are using MRE as a standard part of practice for liver disease diagnoses.
"Based on data from our study, we've now started to use this technique in addition to MRI, in an attempt to determine advanced or no fibrosis," he said.
Specific findings from the study data just presented include:
• The detection of cirrhosis by MRE when compared to liver biopsy results was 88% accurate.
• Patients with nonalcoholic fatty liver disease and no significant inflammation or fibrosis were identified with 97% accuracy.
Liver biopsies, which involve extracting tissue samples with a needle, can underestimate the degree of hepatic fibrosis up to 30% of the time because of the patchy distribution of fibrosis that occurs in the liver. Another drawback is that since liver biopsy is invasive, patients may be reluctant to have a biopsy performed and sometimes delay the procedure when liver disease is first suspected.
Nonalcoholic fatty liver disease has become the most common liver disease in the U.S. and is linked to the growing numbers of patients with obesity and diabetes. The number of patients seeking medical care for hepatitis C also is increasing.