Somatom Definition Edge CT scanner for imaging coronary artery disease in adults in whom imaging is difficult

About the technology

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:

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.