I'm thrilled to see a CP clarifying that the Pixel Padding shouldn't
be a pixel value in the image, but I was wondering about the fact that
the CP retains the note saying that, when the relationship between
pixel value and X-Ray intensity is known, "that a value equivalent to
are be used".

I would have guessed that there cases where air could actually be
present inside the anatomy. (Mouth and nasal passages? Introduced as
part of a test? Inside of an open wound?)

What am I missing?