The Use of Ultrasound Elastography for the Detection and Assessment of Liver Fibrosis. A Technology Implementation Study Within Secondary Care.

2012 NHS Technology Adoption Center

WHAT IS ULTRASOUND ELASTOGRAPHY?
As discussed above, ultrasound elastography provides a non-invasive and cost effective alternative to liver biopsy. This section will describe in more detail the 'Gold Standard measure of liver biopsy and then take a closer look at two qualitative ultrasound elastography technologies; Transient Elastography and Acoustic Radiation Force Impulse (ARFI) technology. Example patient pathways for both liver biopsy and UE are also presented.
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ULTRASOUND ELASTOGRAPHY TECHNOLOGIES
The project implementation sites used two different technologies to measure liver stiffness. The two technologies used were the FibroScan made by Echosens and Acoustic Radiation Force Impulse (ARFI) technology made by Siemens.
These two systems have differences; the FibroScan system is designed specifically to perform a liver stiffness assessment and is a standalone technology whilst the ARFI is an add-on to an ultrasound system and has imaging capabilities that can be used alongside the liver stiffness assessment. The benefits of each of these will be discussed in the 'why to section of this pack. Having decided to implement one of these technologies, individual trusts should select the most appropriate equipment for their organisation based upon the evidence available, clinical opinion, cost and system considerations.
Consideration should also be given with regard to the limitations in the application of each technology across the clinical spectrum and geographical locations - these issues should be considered when selecting equipment to use on a patient-by-patient basis. Information to guide clinicians is available from the manufacturers and in many peer-reviewed publications.
FibroScan
FibroScan, produced by Echosens, is a diagnostic device that uses transient elastography to measure liver stiffness. FibroScan generates a low-frequency shear wave from a probe applied to the patients skin between the ribs. The speed of the wave spread is then measured between two points within the liver to allow the livers stiffness to be quantified. The wave will travel more rapidly through stiff tissue. An examination using the Echosens FibroScan consists of ten signal acquisitions at a single point; the whole process lasts around 15 minutes. The results are instantly displayed on a screen and the value for stiffness, after the clinician allows for possible confounding factors, can be matched to a fibrosis stage. The examination is non-invasive and painless.
Echosens offer a range of FibroScan products, the FibroScan 502 Touch, FibroScan 502 and FibroScan 402; these are designed to be used alongside a FibroScan probe. The probes come in small, medium or extra-large sizes. The small probe can be used with paediatric patients, the medium with adults and the extra-large with obese patients (due to power supply limitations in the smaller form of the FS 402, this device is compatible with the medium probe only).
The FS 502 Touch also offers the option of a new parameter, CAP (Controlled Attenuation Parameter). CAP provides an assessment of the amount of attenuation to the FibroScans ultrasound signal as it passes through the liver. This can in turn be correlated to the amount of steatosis present in the patients liver.
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THE BENEFITS OF USING ULTRASOUND ELASTOGRAPHY TECHNOLOGIES
When replacing liver biopsy with ultrasound elastography for the detection and monitoring of liver fibrosis within the secondary care setting, the following benefits have been noted:
Benefits to patients
- Low risk of complications - no complication recorded when using Ultrasound Elastography
- Non-invasive procedure
- No pain
- Reduced length of hospital stay - from (up to) three day stay to 15 minute OPD appointment
- More frequent monitoring of disease progress
- High degree of patient satisfaction
Opportunities for the service / Trust Managers
- Reduced hospital costs made possible by:
- Reduced procedure costs - Average Biopsy costs £474 compared to £47 for UE procedure
- Released bed days - from those liver biopsy patients requiring an inpatient stay
- Reduced costs per patient episode
- Freeing up of consultant time - UE can be nurse led service
- Potential for increased capacity and activity
- Improved clinical risk management
Benefits to clinical staff
- Minimal training required
- Easy to use
- Enhancing nursing roles
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EVIDENCE FOR ULTRASOUND ELASTOGRAPHY TECHNOLOGIES
There is a large body of evidence in support of ultrasound elastography. As discussed in the introduction, a comprehensive literature search and critical appraisal of the evidence base is outside the scope of this pack. NTAC has not critically appraised this evidence and would strongly recommend that a suitably qualified clinician undertakes a review of the available literature before drawing any conclusion with regard to which is the most appropriate technology to either purchase or use in practice within their local setting.