Provided by medicalphysicsweb
Mar 13, 2014
Millions of people throughout the world have diagnosed and undiagnosed chronic liver disease (CLD), including an estimated 40 million in the United States alone, according to the Chronic Liver Foundation. The most common types include chronic hepatitis B and C, alcoholic liver disease, hemochromatosis, nonalcoholic steatophepatits and nonalcoholic fatty liver disease. An aging global population, unhealthy diets and an obesity epidemic have contributed to its increase.
Ultrasound (US) elastography – and to a much lesser extent – magnetic resonance elastography (MRE) are increasingly being used to stage liver fibrosis and follow the impact of treatment by evaluating tissue elasticity in a non-invasive manner. The use of MR and US elastography was the topic of a scientific session at the European Congress of Radiology (ECR) in Vienna, Austria.
Untreated, CLD kills. The prognosis and management of the disease depends on the extent and progression of liver fibrosis. The gold standard for evaluating hepatic fibrosis is percutaneous biopsy followed by a histopathological examination of a liver sample. But this test is invasive, expensive, and because it is highly localized, targets only one small section of the liver.
A bigger picture is provided with US elastography, which was recommended in lieu of biopsy for liver fibrosis diagnosis in January 2013 by the Technology Assessment Centre (NTAC) of the UK's National Health Service. A concurrent economic modelling analysis based upon actual costs published by the York Health Economic Consortium estimated a gross saving of €616 per diagnosis.
The main techniques employed in US elastography are strain, shear wave, transient and acoustic radiation force imaging. Strain US elastography, also described as compression elastography, sonoelastography or real-time elastography, is the most commonly used method, explained Magdalena Wozniak of the Medical University of Lublin, Poland. To perform this exam, radiologists require dedicated software on a conventional higher-class ultrasound scanner, plus a transducer that's compatible with this software.
"The value of US elastography is the relatively low cost of the exam, that it is a proven diagnostic tool and the clinical availability and accessibility of ultrasound scanners," co-author Sabine Bensamoun, from the Université de Technologie de Compiègne in France, told medicalphysicsweb. "Like MRE, the probe sends vibrations inside the liver enabling a radiologist to analyse the displacement of the wave. It provides accurate information on tissue stiffness."
If the exam results merit further investigation, an MRE exam is appropriate. And if a patient is prescribed a hepatic MRI scan, it is easy to add the elastography portion, explained Bensamoun. This entails use of an active driver located outside the magnet room, which generates continuous low-frequency vibrations. The mechanical response to the pressure captures the type of manipulation that a doctor would perform when palpating an abdomen.
MRE is also performed on obese patients in lieu of an initial US elastography exam. The reason, explained Andrzej Pawel Wieczorek, director of the department of paediatric radiology at the Medical University of Lublin and chair of the ECR session, is that US elastography offers only a shallow wave depth. It has difficulty propagating itself with obese patients.
The benefits of MRE are that a comprehensive picture is produced and that all areas of fibrosis can be identified in the liver. "Seeing the total area of the liver through a series of slices enables a radiologist to more easily identify all the locations where the fibrosis is likely to exist. It is so much more comprehensive than biopsy. You can't biopsy 50 locations of suspected fibrosis, but the diagnostic images will show these clearly and also enable a radiologist to assess the surrounding tissue," said Bensamoun. Elastography can display the entire anatomical picture and also the functional properties of the tissue. MRE also is a very accurate way to follow up the patient and the effectiveness of treatment, she explained.
In addition to staging liver fibrosis, elastography is being used to help diagnose and follow treatment of many different types of diseases. Other presentations in the ECR session "Elastography as a new tool" session included the use of US elastography to help diagnose prostate cancer, and MR elastography of the brain to assess cerebral tissue structure. The technology is evolving rapidly, but its value is not as well understood as it should be, according to the presenters.
"Besides liver imaging, quite extensive applications in diagnosis of brain, testicles, breast and lymph nodes have been reported as well, some more extensively than others," Wiczorek told attendees. There are many other directions that are not well established, such as arterial wall/atheromatous plaque characterization, musculoskeletal applications, and diagnostics and evaluation of thrombosis or graft rejection of various transplanted organs.
Elastography is a new tool, and potentially a revolutionary technique that can make a great contribution to diagnostic imaging, the session presenters pointed out. It's time for radiologists to talk about it with their colleagues in medicine.
About the author
Cynthia E Keen is a freelance journalist specializing in medicine and healthcare-related innovations.