Advice

Technology overview

Technology overview

This briefing describes the regulated use of the technology for the indication specified, in the setting described, and with any other specific equipment referred to. It is the responsibility of healthcare professionals to check the regulatory status of any intended use of the technology in other indications and settings.

About the technology

Ultrasound elastography uses a compression source to apply force to the tissue and an imaging system to measure the resultant tissue displacement. Compression sources can be either static or dynamic. Static forces are manually applied by the operator or generated by the patient through physical movement. In the dynamic approach, forces are applied using a sequence of intense focused ultrasound pulses produced by the imaging transducer, which generate shear waves in the tissue that propagate outwards, perpendicular to the direction of each pulse. Both static and dynamic forms of compression provide qualitative imaging. Dynamic elastography provides additional quantitative data, and is claimed to be less operator‑dependent and more reproducible than static elastography.

The Aixplorer system's ShearWaveElastography mode uses dynamic force to induce a shear wave, the velocity of which is used to calculate a quantitative measure of elasticity (called the Young's modulus) in units of kilopascals. Results are presented as a colour‑coded, real‑time ShearWave Elastography map of local tissue elasticity, overlaid on the greyscale image. Benign breast lesions, for example fibroadenomas, tend to be relatively elastic with low elasticity values of less than 30 kilopascals, shown on the elastography map as blue. Malignant breast lesions, such as invasive ductal carcinomas, tend to be stiffer with high elasticity values greater than 120 kilopascals, shown as red. Dynamic ShearWave Elastography produces quantitative elasticity values for different tissue types.

CE marking

The Aixplorer ShearWaveElastography ultrasound diagnostic imaging system ('the Aixplorer system') and its related probes were CE‑marked to SuperSonic Imagine in March 2009 as a class IIa medical device. Current certification is effective from November 2013 to 2016.

Description

The Aixplorer system is a complete mains‑powered ultrasound system based on a 4‑wheeled cart. It comprises 4 main components:

  • A central processing unit enclosed in the main body of the system, with image acquisition and analysis software and memory storage.

  • An adjustable control panel with touch‑screen display, trackball and gel holders.

  • An adjustable LCD monitor for image viewing and analysis.

  • Six ultrasound transducers, each designed for multiple clinical applications (for example abdominal, breast, genitourinary, thyroid and vascular imaging).

The use of the Aixplorer system for general purpose B‑mode greyscale ultrasound imaging, doppler fluid flow analysis and non‑breast clinical application areas are beyond the scope of this briefing.

The system's ultrasound transducers connect and lock into 1 of 4 ports on the main body below the control panel. Although 4 different transducers can be connected at once, only 1 can be selected and active at a time. Probe holders allow transducers to be stored when not in use.

The 3 transducers designed for breast imaging applications are:

  • SuperLinear SL10‑2 transducer with 192 elements and 2–10 megahertz bandwidth, used for 2D breast and deep breast imaging.

  • The SuperLinear SL15‑4 transducer with 256 elements and 4–15 megahertz bandwidth, used for 2D breast, deep breast and superficial breast imaging.

  • The SuperLinear Volumetric SLV16‑5 transducer with 192 elements and
    5–16 megahertz bandwidth, used for 3D breast imaging and volumetric acquisition.

When using the Aixplorer system, the operator selects a transducer and operates the system in B‑mode. This produces a 2D, greyscale, ultrasound image tissue anatomy where areas of different tissue density are shown in various shades of grey. The operator adjusts the B‑mode imaging parameter controls to obtain the best possible 2D greyscale image, and then the ShearWaveElastography mode may be selected.

The ShearWaveElastography mode creates a real‑time colour elasticity map which is superimposed on the greyscale image. The operator can optimise elastography resolution and penetration of the scanned area. A customisable and adjustable elasticity colour bar, displayed alongside the elastography image, provides a visual indication of tissue stiffness. In the default elasticity scale blue indicates soft tissue whereas yellow, orange and red indicate progressively stiffer tissue.

In addition to basic ultrasound imaging measurements such as distance, area and perimeter of the tissue being examined, the Aixplorer system's ShearWaveElastography mode has 4 additional measurement tools. These provide quantitative elasticity information on the stiffness of an area, expressed in kilopascals, or shear wave velocity, expressed in metres per second. The 4 tools are as follows:

  • The Quantification Box (Q‑Box) shows a moveable and resizable circle on the colour elasticity map. The circle is duplicated on the same region of interest on the B‑mode image for reference purposes. This tool measures maximum, minimum, mean and standard deviation elasticity values in the region of interest.

  • The Q‑Box ratio tool displays 2 separate circles, allowing the tissue elasticity values of 2 different areas to be compared.

  • The Q‑Box trace tool allows the operator to manually trace around an area to measure the elasticity values within.

  • The Multi Q‑Box tool calculates the average of several Q‑Box measurements.

After analysing the breast images and obtaining quantitative elasticity measurements, the results can be automatically classified according to the BI‑RADS scale, which is included in the Aixplorer system software. Images stored on the system's internal hard drive can be sent to the integrated CD/DVD drive, USB‑linked printers and memory devices, or DICOM‑compatible network devices.

Optional accessories for the Aixplorer system include:

  • an integrated black and white thermal printer

  • an external colour printer

  • a 2‑pedal, USB‑linked, configurable footswitch (whose function can be configured by the user).

Intended use

Aixplorer ShearWave Elastography, as described in this briefing, is intended for use in non‑invasive diagnostic imaging of the breast.

Setting and intended user

Aixplorer ShearWave Elastography is intended for use in secondary care breast assessment clinics. It would be used to assess women referred from the breast screening programme with a positive or inconclusive result, and for people with symptoms or clinical signs of breast cancer referred from primary care. The device is intended for use by qualified sonographers and radiologists who are specifically trained in its use and familiar with ultrasound elastography.

Current NHS options

Ultrasound elastography may come installed as standard, or as an optional add‑on for existing ultrasound imaging systems that are widely used in the NHS in breast assessment clinics (NHSBSP Publication No 49 2010). If optional, it will usually require the installation or activation of an elastography software package on the system, and may require the purchase of an additional transducer.

NICE is aware of the following CE‑marked device that appears to provide a similar dynamic elastography function to the Aixplorer ShearWave Elastography system:

  • Virtual Touch IQ (Siemens).

Costs and use of the technology

The Aixplorer system consists of several essential components for breast imaging and a number of optional accessories. List prices (excluding VAT) for the essential components are as follows:

  • The Aixplorer system, including ShearWave Elastography (with no transducers): £74,095

  • SuperLinear SL10‑2 transducer: £6000

  • SuperLinear SL15‑4 transducer: £6000

  • SuperLinear Volumetric SLV16‑5 transducer: £12,000.

List prices for optional accessories (excluding VAT) are:

  • Integrated black and white thermal printer: £600

  • External colour printer: £1660

  • 2‑pedal footswitch: £260.

Standard ultrasound consumables, including water‑based gels and transducer covers, can be purchased from NHS Supply Chain. Costs for alternatives to the Aixplorer system (that is, cart‑based general ultrasound imaging systems with ultrasound elastography options) are also available to NHS organisations, with price on application, from the Supply Chain capital equipment framework.

The manufacturer provides at least 1 day's clinical application training with each Aixplorer system. Further training days may be customised to the needs of each installation at a cost of £500 per day.

The Aixplorer system has an anticipated lifespan of 7 to 10 years. The manufacturer offers 4 annual maintenance contract options that can be tailored to customer requirements, costing from £3000 to £8000. Each of these options can include preventative and corrective maintenance, safety and performance checks, replacement transducers and spare parts, telephone technical support and remote diagnosis, and software updates. Immediate transducer replacement in the event of accidental damage is also a contract option.

Likely place in therapy

The standard breast cancer screening test for women aged 50 to 70 years is 3‑yearly X‑ray mammography in the NHS Breast Screening Programme, with a rolling programme to extend the invited age range to 47 to 73 years by 2016. Women over 70 years are not routinely invited to screening, but may continue to be screened if they wish.

Any person presenting to general practice with a palpable breast mass or other clinical signs that could indicate a diagnosis of breast cancer may be referred directly for diagnostic ultrasound imaging, with or without biopsy.

Aixplorer ShearWave Elastography would be used for breast ultrasound assessment, either in those referred from a screening programme or after symptomatic referral. Using Aixplorer ShearWave Elastography mode may improve diagnostic confidence and better indicate whether a biopsy is necessary. Aixplorer ShearWave Elastography mode is not intended to replace biopsy as a diagnostic tool. It claims to improve identification of benign breast lesions with a low level of suspicion (BIRADS 4a) using elasticity information, thereby avoiding unnecessary biopsies of non‑malignant tissue.

Specialist commentator comments

One specialist commentator highlighted, with reference to the BMUS 2010 ultrasound safety guidelines, that, in terms of ShearWave elastography exposure time, users should practise the 'As Low As Reasonably Achievable' (ALARA) principle during their clinical scanning. Users should be aware that the maximum thermal index values produced by the Aixplorer system's ShearWave Elastography mode are greater than those produced in B‑mode, colour doppler mode and pulsed‑wave doppler mode. The maximum thermal index values are given in chapter 11 of the Aixplorer user's guide.

A second specialist commentator noted that the BI‑RADS classification system is not routinely used in the UK, but that the U1‑U5 classification system, which is roughly analogous, is used and endorsed by both the British Society of Breast Radiology and the NHS Breast Screening Programme. Radiologists using the Aixplorer system's ShearWave Elastography mode must use the correct elasticity parameters and Q‑Box size in order to accurately discriminate between benign and malignant lesions. There is no clear consensus in the evidence on which quantitative measurement (for example mean or maximum elasticity) gives the best diagnostic information, what size Q‑Box should be used, or how many shear wave images of each lesion need to be assessed.

A third specialist commentator concluded that the evidence summarised in this briefing demonstrates that Aixplorer ShearWave Elastography improves the sensitivity and specificity of the breast ultrasound examination, and enables more reliable lesion classification before a biopsy is done. However, it has not yet been shown whether this actually results in fewer biopsies in clinical practice and, if so, in which patient groups. Clinical practice is unlikely to change until prospective clinical studies showing the technology's clinical impact are conducted.

Equality considerations

NICE is committed to promoting equality and eliminating unlawful discrimination. We aim to comply fully with all legal obligations to:

  • promote race and disability equality and equality of opportunity between men and women, and

  • eliminate unlawful discrimination on grounds of race, disability, age, sex, gender reassignment, pregnancy and maternity (including women post‑delivery), sexual orientation, and religion or belief, in the way we produce our guidance (these are protected characteristics under the Equality Act [2010]).

Breast cancer is a condition which predominantly affects women, with less than 1% of cases affecting men. NHS Breast Screening Programme referrals to breast assessment clinics involve women only. Sex is a protected characteristic under the Equality Act (2010).

In both women and men, the incidence of breast cancer increases with age. Age is also a protected characteristic under the Equality Act (2010).

Patient and carer perspective

In terms of advantages for patients, Aixplorer ShearWave Elastography may more accurately differentiate between benign breast lumps and breast tumours. This would mean that fewer patients would face the pain and discomfort of unnecessary biopsies. These patients and their carers would also be spared the anxiety of waiting for biopsy results.