CT angiography.

The advent of spiral (helical, volume) CT has revolutionised the performance of body CT and allowed the development of CT angiography (CTA). CT angiography is a non-invasive method of visualising the vascular system and in some instances can replace conventional angiography. In spiral CT a volume of data is obtained rapidly with no respiratory misregistration at peak vascular opacification following the peripheral injection of contrast. Appropriate timing will ensure that either the venous or arterial tree is visualised and from the volume of data multiple overlapping slices can be obtained to generate 2D and 3D images with no increase in radiation to the patient. CT angiography may be performed as a dedicated study or be undertaken retrospectively using post-processing of data from a conventional diagnostic spiral scan to provide additional information about the vascular tree. When undertaken as a dedicated study CTA is quicker, less invasive and less costly than a conventional angiogram with a decrease in the radiation dose to the patient; however, the spatial resolution is limited with vessels less than 2 mm not visualised and there is no contrast saving.