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

CE marking

The Somatom Definition Edge (Siemens) was originally launched in the UK in 2012. It has a CE marking as a class IIb device under the Medical Devices Directive 1993/42/EEC. This was renewed on 24 February 2015 after the addition of an optional hardware modification.


The Somatom Definition Edge (Siemens) is a helical (rotating with a constant radius) CT scanner with the following main features and specifications:

  • Single-source: a single X‑ray source within the scanner gantry.

  • Multi-slice: capable of imaging multiple parallel, cross-sectional slices in a single rotation.

  • Dual-energy: images are acquired at 2 different energies to allow differentiation between tissues.

  • 78 cm bore (aperture diameter) with a couch that can be driven low to the ground with a weight limit of 307 kg.

Table 1 Technical specifications

Technical specification

Somatom Definition Edge

1. X‑ray output

a. X-ray generator power

80 kW, with option of 100 kW

b. Tube potential of 100 kV

i. Maximum tube current

650 mA

ii. CTDIw/100 mA

5.5 mGy

c. Tube potential of 120 kV

i. Maximum tube current

800 mA

ii. CTDIw/100 mA

11.6 mGy

2. Volume coverage

a. Detector rows

64 individual detector elements
(proprietary Stellar array)

b. Detector row size

0.6 mm

c. z‑axis length

38.4 mm

d. Number of slices per rotation

128, via z-sampling of the 64 detector rows (384 slices can be generated with a reconstruction algorithm)

3. Temporal resolution

a. Minimum gantry rotation time

280 ms

b. Intrinsic temporal resolution

142 ms

c. Effective temporal resolution

71–142 ms

4. Spatial resolution

(proprietary Z-sharp technology to optimise spatial resolution)

a. Detectors per row


b. x–y plane spatial resolution (standard mode)

0.68 mm

c. x–y plane spatial resolution (high resolution mode)

0.53 mm

d. z‑width of detector row

0.6 mm

e. z‑spatial resolution

0.29 mm

Abbreviations: CDTIW, CT dose index weighted (the average absorbed dose across the field of view in a standard phantom); kV, kilovolt; kW; kilowatt; mA, milliamp; mGy, milligray; mm, millimetre; ms, millisecond.

According to the manufacturer, the Somatom Definition Edge includes the following software and capabilities, which are claimed to improve cardiac CT scanning in people in whom imaging is difficult:

  • Dose reduction and image quality

    • CARE Dose4D: automated X‑ray output modulation based on patient size and shape, which may be beneficial for people with obesity.

    • CARE kV: an extension of CARE Dose4D, which automates kV selection based on patient size and optimises the contrast‑to‑noise ratio. This may also be beneficial for people with obesity.

    • Sinogram Affirmed Iterative Reconstruction (SAFIRE) and Advanced Modeled Iterative Reconstruction (ADMIRE): both technologies have been shown to improve image quality and reduce image noise (Jensen et al. 2014). It is recommended to reduce blooming artefacts in people with high calcium scores.

  • Gating functionality (selective imaging at specific points in the cardiac cycle)

    • Cardiac prospective axial scanning: software which rapidly pulses the X‑rays on and off, so the person is only exposed to radiation during the cardiac phase or the phases needed for the diagnostic procedure. This means diagnostic image quality can be maintained while minimising radiation dose. This is beneficial for patients with high heart rates or arrhythmias.

    • Cardiac retrospective helical scanning: helical scanning of the heart over a number of cardiac cycles to allow retrospective reconstruction of the different phases, using a larger dose of radiation when compared to prospective gating. This is beneficial for patients with high heart rates or arrhythmias.

  • Workflow

    • FAST Cardio Wizard: a guidance system that facilitates training and provides guidance and support through step‑by‑step instructions for various cardiac examinations. The system includes tips for avoiding common problems. The steps, texts and images are delivered in a default format, but can be customised by users.

Setting and intended use

The Somatom Definition Edge is intended for use in secondary care settings, specifically by staff with expertise in conducting and interpreting cardiac CT imaging. Additionally, the hospital must comply with radiological protection standards, including basic standards for protection against the dangers inherent in exposure to ionising radiation. The test would be requested by a clinician involved in managing coronary artery disease, normally a cardiologist. A radiographer would carry out the scan and a radiologist or cardiologist would interpret the results.

Current NHS options

NICE diagnostics guidance on new generation cardiac CT scanners recommends 4 specific scanners (Somatom Definition Flash, Brilliance iCT, Discovery CT750 HD and Aquilion ONE), all of which have technical enhancements that can improve CTCA image acquisition, to be used to perform CTCA in the following groups:

  • people with chest pain who have an estimated likelihood of CAD of 10–29% and are difficult to image

  • people with known CAD in whom imaging is difficult with earlier generation CT scanners and for whom revascularisation is being considered.

NICE is aware of the following CE‑marked single source CT scanners that appear to fulfil a similar function to the Somatom Definition Edge.

  • Somatom Definition AS+ (Siemens)

  • Somatom Definition Flash (Siemens)

  • Somatom Force (Siemens)

  • Optima 660 (GE Healthcare)

  • Revolution GSI/HD (Discovery CT750 HD; GE Healthcare)

  • Revolution CT (GE Healthcare)

  • Brilliance iCT (first launch; Philips Healthcare)

  • iCT Elite (new generation; Philips Healthcare)

  • Ingenuity (Philips Healthcare)

  • IQon Spectral CT (Philips Healthcare)

  • Aquilion PRIME (Toshiba)

  • Aquilion ONE (Toshiba)

  • Aquilion ONE Vision (Toshiba).

NICE has produced a medtech innovation briefing on the Aquilion PRIME CT scanner. NICE has produced a technical supplement to the diagnostics guidance on new generation cardiac CT scanners to describe the newer versions of the scanners included in the guidance.

Costs and use of the technology

According to the manufacturer, the Somatom Definition Edge typically costs around £600,000 excluding VAT, depending on the configuration. The lifespan of a CT scanner is 7–10 years (Clinical Imaging Board 2015). Irrespective of the capital cost, the nationally representative unit cost for a cardiac CT scan including labour time, overheads and consumables is £259 (Department of Health 2014, code RA68Z).

Training to use the Somatom Definition Edge system is provided free of charge by the manufacturer.

Other diagnostic procedures used in the chest pain pathway include invasive coronary angiography (ICA), magnetic resonance imaging (MRI), single photon computed emission tomography (SPECT) and stress echocardiography (ECHO). The ICA procedure has a unit cost of £1,241 (NHS 2014/15 National tariff payment system, code EA36A). An outpatient cardiac MRI scan inclusive of contrast medium costs £527 (Department of Health 2014, code RA66Z). The unit cost for SPECT is £220 (NHS 2014/15 National tariff payment system, code RA37Z). The unit cost for stress ECHO is £74 (NHS 2014/15 National tariff payment system, code RA60Z).

CT scanner technologies need specific infrastructure and equipment, as well as suitably trained radiographic and radiological staff. There are no particular practical difficulties in using or adopting the Somatom Definition Edge.

Likely place in therapy

The Somatom Definition Edge would be used to perform cardiac CT imaging in adults (aged 18 years and over) with suspected CAD in whom imaging with earlier generation CT is difficult and who have an estimated likelihood of CAD of 10–29%, or known CAD in whom imaging with earlier generation CT is difficult and for whom revascularisation is being considered. The scanner may also be used to perform CTCA in people with stable angina whose symptoms are not satisfactorily controlled with medical treatment.

The Somatom Definition Edge can also be used for other clinical imaging applications in adults and children.

Specialist commentator comments

One commentator stated that although CTCA is predominantly used to rule out CAD in people with an estimated likelihood of 10–29% of having the disease, it can also be used as a rule-in test to confirm CAD in people at moderate risk (30–60%). The commentator said that, in practice, people at low, moderate and intermediate risk (10–90%) of CAD have CTCA. People at moderate risk with no sign of disease on CTCA do not have further investigations, whereas people with signs of disease are assessed further using functional imaging, the choice of which will depend on their individual circumstances. The NICE clinical guideline on the assessment and diagnosis of chest pain of recent onset recommended other forms of imaging such as SPECT, ECHO or MRI, or ICA for higher‑risk groups.

One specialist commentator noted that larger people need higher volumes of contrast medium or higher injection rates. The commentator added that this must be balanced with the advantage of better contrast that can be obtained at lower kV levels, because lowering the kV for people with obesity can result in added image noise and affect the quality of the images. Another specialist noted that the SAFIRE and ADMIRE software (both of which are available with the Somatom Definition Edge) are used to maintain image quality and similar noise characteristics (compared to standard filtered back projection) at reduced radiation doses. This may be particularly useful for people with obesity where it is desirable to reduce radiation dose without compromising image quality. The commentator also stated that SAFIRE and ADMIRE software can reduce blooming artefact in patients with high calcium scores.

Two specialist commentators noted that scanning people with elevated heart rates relies on the use of beta‑blockers to lower heart rates in order to obtain good‑quality images at an acceptable radiation dose. One commentator added that this requires a degree of supervision from a radiologist, which has workflow implications. It also has implications for people who are unable to take or tolerate beta‑blockers.

Because of the range of available CT scanners that are capable of assessing people with bypass grafts, 1 commentator did not believe people with previous bypass grafts were difficult to image. A second commentator noted that non‑invasive imaging of the grafts is often desirable before ICA, because ICA can be challenging in this group.

According to 1 specialist commentator, a scanner lifespan of 7 years is a long time given the rapid rate of technology evolution. The commentator also said that the nationally representative unit cost (which does not account for capital cost) underestimates the cost of advanced cardiac CT scanning in complex cases, which need more advanced (and expensive) hardware.

One specialist commentator noted that the NICE clinical guideline on the assessment and diagnosis of chest pain of recent onset was under review at the time they provided their comments, and that the NICE diagnostics guidance on new generation cardiac CT scanners is out of date because several of the models from the guidance have been superseded and are no longer available.

One specialist commentator noted that dual-source scanners have different technological solutions but are not necessarily superior to single‑source scanners for all applications. Two commentators noted that there are currently more advanced scanners on the market that can address all clinical challenges for all subgroups of people who are difficult to image. These include the Siemens Somatom Force, Toshiba Aquilion ONE Vision, Philips IQon and the GE Revolution.

One specialist commentator stated that the Somatom Definition Edge would be very useful in a general hospital setting for imaging people who have a low to intermediate risk of CAD, and it is also a very good general scanner for other body parts. However, for a high-volume cardiac centre, or in a setting where people with complex conditions are to be imaged, they noted there are other, more sophisticated, scanners that would out-perform the Somatom Definition Edge. Two specialist commentators agreed with this point. One stated that it would be advisable to buy a more advanced CT scanner with broad detector arrays if it is expected to be used for scanning patients in whom imaging is difficult. The second commentator stated that, in practice, the latest CT technology would offer more image improvement and dose‑saving capability, and thus be suitable for use in everyone, including those in whom imaging is difficult.

Equality considerations

NICE is committed to promoting equality, eliminating unlawful discrimination and fostering good relations between people with particular protected characteristics and others. In producing guidance, NICE aims to comply fully with all legal obligations to:

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

  • eliminate unlawful discrimination on grounds of race, disability, age, sex, gender reassignment, marriage and civil partnership, pregnancy and maternity (including women post-delivery), sexual orientation, and religion or belief (these are protected characteristics under the Equality Act 2010).

People with diabetes or obesity may be considered to be disabled under the Equality Act if these conditions have a substantial and long‑term adverse effect on their ability to carry out normal day‑to‑day activities. Disability is a protected characteristic defined in the Equality Act 2010.