Coronal view of CTA image, V1 and V2 segments of the vertebral artery. Measured variables; V1L—the length of the VA from the origin to the point of entry into the transverse foramen; V2L—the length of the VA from the point of entry into the transverse foramen to the transverse foramen of the C2 cervical vertebra; V1D—the diameter of the V1 segment at a midpoint between origin and point of entry into the transverse foramen; V2D—the diameter of the VA V2 segment at a fixed point between C4 and C3 pedicles