Just to clairfy, is NHP the correct posture/alignment for taking a ceph? Or are techs adjusting patients to a specific plane, prior to the ceph being taken?
Great question and very succinctly expressed so it's clear (to me) what you are asking.
Assuming that NHP stands for Natural Head Position, here is a link to an article (although there are many articles on this) on the subject matter.
https://www.sciencedirect.com/science/article/pii/S2395921516301179#fig0005When reading the article, it's important to differentiate 'Natural Head Position' from 'Natural (head) POSTURE' because both sound so similar.
Here is an excerpt from the article regarding the Frankfurt Horizont:
[The Frankfort Horizontal Plane (FHP) is one of the most used planes in cephalometry. It was adopted with the purpose of orienting the skull in a similar way to the natural head position. In cephalometric practice this plane presents two difficulties: a) Problems in locating accurately its two reference points, especially Porion, b)
The operator assumes that the Frankfurt plane is parallel to the true horizontal plane which does not occur in many individuals, there have been observed differences of up to 10 degrees and even more.17 Arnett mentions:18 no one walks with the Frankfort plane parallel to the ground and we can have a patient in natural head position but with the Frankfurt Plane inclined upwards or downwards.]
And another concept from the study:
[ Concepts used in the study.
Natural head position (assisted) It is defined as an innate, physiological and reproducible position of the head. It is obtained when the patient is in a relaxed position, sitting or standing, looking into the horizon or into an external reference point (mirror, mark on the wall, etc.) at eye level2., 3., 4., 5., 6., 7., 8., 9., 10., 11., 12., 13. or at the same level as the olives
Natural head posture (orthoposition) It is the physiological position that a person shows when giving a step forward. This posture is different among individuals and may vary if the person has nasal obstruction or other physiological anomalies2,3,29]