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: