Non-invasive, ultrasound-based elastography devices are changing and simplifying regular monitoring for scarring and fibrosis in patients with certain chronic liver diseases, in many cases replacing the need for biopsy.1 Karen L. Krok, M.D., Penn State Hershey Gastroenterology and Hepatology, says, “In patients with an established diagnosis of chronic liver disease, such as hepatitis C or B or nonalcoholic steatohepatitis (NASH), elastography can be used to monitor fibrosis and scarring, with a level of accuracy comparable to biopsy. The procedure is quick, painless and less expensive.”
Ultrasound-based methods of elastography use a vibrating device attached to an ultrasound transducer, which is placed in an intercostal position with the patient lying supine. The velocity of vibration waves (also called shear wave velocity), expressed in kilopascals (kPa), is determined by measuring the time the vibration wave takes to travel to and bounce back from the liver. Shear wave velocity is directly related to tissue stiffness, an indicator of hepatic fibrosis (Figure). Ten successful measurements are required for the test to be reliably interpreted; a median value is generated to indicate the degree of liver fibrosis. Krok says, “It’s like bouncing a tennis ball against a soft versus hard surface. The ball will bounce back more quickly from a firm surface like pavement than it would if it were bounced against something soft, like a pillow.”
Elastography can be paired with traditional ultrasound, which can measure the size of the portal vein and spleen, as well as detect and measure any masses. If the portal vein is larger than 1.2 cm or the spleen is larger than 12 cm, there is likely to be portal hypertension present. Krok says, “Since we began using elastography shortly after its approval, there has been a significant decrease in the frequency of scheduled biopsies in patients with established diagnoses of liver disease. Although it’s a relatively new type of test, we’ve found that most insurance plans pay for it.”
Interpreting the elastography results is dependent on the underlying diagnosed liver disease; there are different kPa threshold values indicative of fibrosis for different disease states. Elastography may be particularly useful in patients with NASH, since it’s often difficult to obtain a good tissue sample in patients who are obese. Krok notes, however, “It’s important for physicians to understand that this is a not a diagnostic tool; elastography cannot tell you why a person has elevated liver enzymes, or whether a transplant patient is showing signs of tissue rejection. Biopsy is still needed for a number of clinical scenarios.”
Ultrasound-based elastography is also not feasible in patients with perihepatic ascites. Approved for use in Europe since the mid 2000s, elastography is currently available only at a few tertiary care centers in the U.S. At Penn State Hershey Medical Center, the Acuson® S2000 device (Siemens, Mountain View, Calif.), which uses acoustic radiation force impulse (ARFI) technology, is employed for elastography. Expanded availability of elastography testing at other U.S. centers is expected in the coming years.
Karen L. Krok, M.D.
Associate Professor of Medicine
Penn State Hershey Gastroenterology and Hepatology
Fellowships: Transplant Hepatology, Gastroenterology, Johns Hopkins Hospital, Baltimore, Maryland
Residency: Internal Medicine, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania
Medical School: University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania