To estimate and compare the diagnostic accuracy of DUS, TCD/TCCD, MRA and CTA for detecting relevant vertebral artery stenosis in symptomatic patients with (posterior circulation) ischaemic stroke or TIA as well as in asymptomatic patients. A patient is considered asymptomatic in this review when he or she did not have any clinical signs or symptoms related to stroke or TIA of the posterior circulation in the last six to 12 months. This includes patients that were in fact symptomatic of anterior circulation pathology and were investigated by a combination of the aforementioned image modalities (see Participants below).

As the accuracy of imaging may depend on the location of the stenosis in the vertebral artery we are planning to analyse the data according to the location of the stenosis. The vertebral artery can be divided into four anatomical parts: V1 to V3 form the extracranial vertebral artery and V4 forms the intracranial vertebral artery (Khan 2007, Figure 2).