The inferior vena cava (IVC) and aorta are both seen in most cases, as in the ultrasound scan in the right. It is possible for a novice to confuse the two.
The aorta is situated anterior to the vertebral bodies and left of midline, whereas the IVC lies to the right of midline. The aorta tapers and tends to be tortuous and move to the left. It can be calcified anteriorly which can make the ultrasound view more difficult.