Fig. 3.

Axial MRI image at L3–4 demonstrating measurements in relationship to the anterior intervertebral plane: a the anterior edge of the psoas muscle (extending just anterior to the intervertebral plane in this image), b the anterior aspect of the lumbar plexus, c the location of the femoral nerve beginning the L3–4 level, d the position of the posterior edge of either the inferior vena cava or right iliac vein depending on level, e the anteroposterior diameter of the psoas muscle. The diagram also includes measurement (f), the transverse distance between the lateral aspect of the intervertebral disc and the medial aspect of the lumbar plexus