Start with the annotation of the preselected origin landmarks. The midpoint on the anterior border of the anterior curvature of the foramen magnum is called basion. To annotate basion for the axial section, locate the deepest end of the curvature of the section of the foramen magnum.
For the sagittal section, look for the most posterior point of the midsection of the foramen magnum. For the coronal section, look for the inferior midpoint of the curvature of the foramen magnum. The most superior, posterior and external point located at the upper margin of each ear canal is called porion.
To annotate porion for the axial section, look for the edge of the margin of the external auditory meatus. For the sagittal section, look for the point of intersection of the eustachian tube with the bony canal. For the coronal section, look for the midpoint on the inferior border of the superior curvature.
The vertical line through the point roughly bisects the ear canal. The landmark nasion is located at the intersection of the suture between the frontal bone and the nasal bones. For the axial section, look for the midpoint at the height of curvature of the suture.
For the sagittal section, look for the anterior point of the suture where the frontal and nasal bones meet. For the coronal section, look for the center of the frontal nasal suture. The vertical line through it roughly bisects the nose.
Orbitale is the most an inferior point on the inferior orbital rim. To annotate this, set the frontal view or bony window as default and clip axially from inferior to superior until the curvature of the lower margin of the orbit is reached to locate the inferior most point of the lower curvature of the orbit. Use 2D views to confirm that the landmark is on the bone.
Adjust the sagittal and coronal sections to reflect the anterior positioning of orbitale. Ensure that the landmark is anterior in position just to the point where the orbital rim starts to curve out. The most superior and anterior point of the superior orbital rim is called supraorbitale.
To annotate it, set the frontal view as default in the 3D volume, and gradually clip axially from superior to inferior until the curvature of the upper margin of the orbit is reached to locate the most superior point of the upper border of the orbit. Adjust the sagittal and coronal sections to reflect the anterior positioning of the landmark. Ensure that the landmark is anterior in position just to the point where the orbital room starts to curve out.
For the sella midpoint, look for the center of the sella turcica or hypophyseal fossa, which is a saddle shaped depression in the body of the sphenoid bone where the pituitary gland or hypothesis is positioned. Adjust the landmark to the center of the sella turcica in all planes. For the sagittal section, place the landmark in the center of the sella turcica.
For the axial and coronal sections, adjust the views accordingly. Next, trace the right mandibular profile with a series of points. Then do the same for the left mandibular profile.
After tracing the mandibular profile, the landmarks, condilion, gonion, and antigonion are annotated automatically. Identify the condilion as the most posterior and superior point on the condyle and the gonion as the most outward point on the angle formed by the junction of the ramus and the body of the mandible. Then identify the antigonion as the highest point of the concavity of the lower border of the ramus where it joins the body of the mandible.
The frontal and three-quarter views of a full head CBCT scan of a human skull with all the annotated three D landmarks included in the current configuration are presented in this figure.
