MRE best for assessing fibrotic livers
Most chronic liver diseases lead to hepatic fibrosis — a wound-healing response to liver cell injury that increases stiffness of hepatic tissue. Without treatment, it can progress to cirrhosis and hepatocellular carcinoma, making accurate detection crucial in the early stages when therapy is considered more effective.
Although needle biopsy has traditionally been the primary method for detecting and staging liver fibrosis, it is invasive and has significant limitations, including sampling error and complications such as pain and bleeding. These drawbacks have prompted the development of many new, noninvasive techniques for measuring hepatic stiffness.
"Noninvasive diagnostics are more advantageous to the patient, as there are no serious side effects, and they may be more cost-effective, though this remains to be determined," says Jayant A. Talwalkar, M.D., of Mayo Clinic in Minnesota.
Of the new methods, which include serum markers and ultrasound-based transient elastography (UTE), magnetic resonance elastography (MRE) is the most accurate for detecting liver fibrosis, particularly early-stage disease. Unlike serum markers, MRE can detect all grades of fibrosis, and unlike UTE, it is not affected by obesity or ascites.
"MRE uses MR phase-contrast techniques to acquire images of acoustic waves generated by an external driver device," Dr. Talwalkar explains. "The images are interpreted with an inversion algorithm, developed at Mayo Clinic, to obtain an elastogram — a tissue stiffness map. Normal livers are soft and have shorter wavelengths, whereas cirrhotic and fibrotic livers have longer wavelengths and higher liver stiffness values." He adds that liver MRE takes about 15 seconds and can be added to any standard MRI examination of the abdomen.
In a 2007 study published in Clinical Gastroenterology and Hepatology, Dr. Talwalkar and colleagues assessed the specificity and sensitivity of MRE in diagnosing liver fibrosis. Thirty-five volunteers with normal livers and 50 patients with chronic liver disease underwent the procedure.
Findings showed that MRE had a sensitivity of 98 percent and a specificity of more than 99 percent for differentiating any stage of liver fibrosis from normal tissue. For identifying patients with moderate to severe compared with mild fibrosis, the sensitivity and specificity were 86 and 85 percent, respectively.
Finally, hepatic steatosis did not affect the ability of MRE to measure liver stiffness. A 2013 study by Dr. Talwalkar and colleagues, published in Radiology, confirmed that MRE is useful for detecting advanced fibrosis in patients with nonalcoholic fatty liver disease — a finding reported by other research groups.
Dr. Talwalkar says based on the growing evidence of its usefulness in diagnosing chronic liver disease, MRE is being adopted at major centers worldwide. "Over the past four years, more than 2,500 patients have undergone hepatic MRE exams at Mayo with excellent results," he notes. "The technique has definitely moved from the laboratory to the clinic."
Additional applications, including use of MRE in detecting liver fibrosis in patients with chronic hepatitis C or taking methotrexate, are discussed in a 2013 article in Applied Radiology.
For more information
Yin M, et al. Assessment of hepatic fibrosis with magnetic resonance elastography. Clinical Gastroenterology and Hepatology. 2007;5:1207.
Chen J, et al. MR elastography of liver disease: State of the art. Applied Radiology. 2013;42:e5.
Kim D, et al. Advanced fibrosis in nonalcoholic fatty liver disease: Noninvasive assessment with MR elastography. Radiology. 2013;268:411.