Anterior commissure - posterior commissure line
The anterior commissure - posterior commissure line (AC-PC line), also known as the bicommissural line, has been adopted as a convenient standard by the neuroimaging community, and in most instances is the reference plane for axial imaging in everyday scanning. The creation of a standard image plane makes it easier to perform comparisons between exams.
It is described on midline sagittal images and is similar to the orbitomeatal line traditionally used on CT, although the AC-PC line is typically ~9 degrees steeper than the orbitomeatal line 2.
An alternative and less commonly used description of the line proposed by Schaltenbrand draws the line through the midpoint of both the anterior and posterior commissures, resulting in a slightly shallower angle 1,3.
Use for CT of the brain
Prior to widespread volumetric CT brain acquisition which has allowed axial images to be reformatted along the AC-PC line, a number of techniques were developed to approximate the CT gantry tilt such that axial images generated were similar to the AC-PC line. Such methods include:
- tuberculum sellae and the external occipital protuberance line 4
- hard palate line + 12 degrees 5
- aligning with the planum sphenoidale
- 1. Talairach J, Tournoux P. Co-planar stereotaxic atlas of the human brain. Thieme Publishing Group. ISBN:3137117011. Read it at Google Books - Find it at Amazon
- 2. Weiss KL, Pan H, Storrs J et-al. Clinical brain MR imaging prescriptions in Talairach space: technologist- and computer-driven methods. AJNR Am J Neuroradiol. 2003;24 (5): 922-9. AJNR Am J Neuroradiol (full text) - Pubmed citation
- 3. Schaltenbrand G, Bailey P, eds. Introduction to Stereotaxis with an Atlas of Human Brain. Vol 1–2. Stuttgart: Thiene;1959
- 4. Y.I. Kim, K.J. Ahn, Y.A. Chung, B.S. Kim. A New Reference Line for the Brain CT: The Tuberculum Sellae-Occipital Protuberance Line is Parallel to the Anterior/Posterior Commissure Line. American Journal of Neuroradiology. 30 (9): 1704. doi:10.3174/ajnr.A1676 - Pubmed
- 5. Kenneth L. Weiss, Judd Storrs, Jane L. Weiss, William Strub. CT Brain Prescriptions in Talairach Space: A New Clinical Standard. American Journal of Neuroradiology. 25 (2): 233. Pubmed