Table 3: Annual QC tests and tolerances levels for X-ray CT.

Test quantity	Acceptable	Achievable
CT alignment lights	± 5 mm	± 1 mm
SPR accuracy	± 2 mm	± 1 mm
CT number	± 5 from baseline value^a	± 4
Image Noise	± 25% from baseline value^a	±10% of the baseline
Uniformity	± 10	± 4
Artefact	No artefacts to affect diagnostic confidence	No visible artefacts
CTDIvol	< ± 20% manufacturer’s recommendations and console displayed dose values