4 The diagnostic tests
4.1 New generation cardiac CT scanners identified and included in this evaluation have advanced technical features that address drawbacks associated with earlier generation CT scanners. These drawbacks include spatial resolution, low contrast detection, noise artefacts and higher levels of radiation. The scanners included in this evaluation are Aquilion ONE, Brilliance iCT, Discovery CT750 HD and Somatom Definition Flash.
4.2 The Aquilion ONE is a CT scanner with 320 × 0.5 mm detector rows giving z-axis coverage of 160 mm. This specification allows the imaging of whole organs in a single non-helical rotation, for example, an image of the heart can be captured within a single heartbeat. As well as reducing the examination time, the radiation and the contrast dose are also reduced.
4.3 The Brilliance iCT is a CT scanner with 128 × 0.625 mm detector rows providing total z-axis coverage of 80 mm. Each detector row is double sampled to increase spatial resolution. It is claimed that it can capture an image of the heart in two heart beats.
4.4 The Discovery CT750 HD is a 64 × 0.625 mm detector dual-energy CT scanner. It has a single X-ray source that switches between two energy levels, allowing two data sets – high energy and low energy – to be acquired simultaneously. It uses a Gemstone detector that contributes to high image quality, and a prospectively gated axial scanning technique called SnapShot Pulse, which allows a complete picture of the heart to be captured in three or four 'snapshots' taken at precise table positions and timed to correspond to a specific phase of the cardiac cycle.
4.5 The Somatom Definition Flash is a second-generation 64 × 0.6 mm detector dual-source CT scanner designed to provide high resolution images at a fast scanning speed with low-dose radiation. It has two X-ray tubes and two detector arrays mounted at 95° to each other. It has a maximum scan speed of 458 mm/s. Fast acquisition times may be of benefit for use with people who cannot remain still or who have difficulty holding their breath. The scanner also uses different strategies to reduce the radiation dose associated with imaging.
4.6 Because earlier generation CT scanners are not considered viable for imaging some people (see section 3.4), and it is this population that is of interest, the comparator is invasive coronary angiography. Invasive coronary angiography uses a contrast dye and X-rays to provide anatomical information about the degree of stenosis in the coronary arteries. A catheter is generally inserted into an artery in the groin or wrist and is moved up the aorta and into the coronary arteries. Once in place, the dye is injected through the catheter, and a rapid series of X-ray images is taken to show how the dye moves through the branches of the coronary arteries. Narrowing of the arteries will show up on the X-ray images.
4.7 Invasive coronary angiography is considered the reference standard for providing anatomical information and defining the site and severity of coronary artery lesions. Some rare but serious complications include death, myocardial infarction, cerebrovascular accident, arrhythmia, vascular complications, allergic reaction to contrast media, haemodynamic complications and perforation of the heart chamber.