Ultrasound and Color Doppler imaging of vertebral artery:

The vertebral arteries course through the foramen of the transverse processes of the cervical vertebrae (from C-6 upwards). The vertebral artery is seen sonographically, between the transverse processes of the cervical vertebrae, as segments. The part within the transverse processes is hidden by the bone. The normal vertebral artery (see color Doppler images above) shows the same direction of flow (and hence the same color as the common carotid artery anterior to it).

http://www.ultrasound-images.com/vascular.htm