The vertebral artery is divided into four segments (V1–V4; Figure 1). The V1 segment originates at the subclavian artery and extends to the transverse foramina of either the fifth or sixth ...

Stenosis or occlusion can involve both proximal and distal segments of the subclavian ... the proximal left subclavian artery. Flow reversal can occur in both the vertebral and internal mammary ...