No doubt you're right about involving a Health Physicist, Ian ... but I think you'll find that notions of
speed ("Speed Class", "Sensitivity" and what-have-you) - 100, 300, 400
etc. - do not directly relate to the algorithms pertinent to CD/DR ... hence the use of the "Exposure Index" in modern systems.
On the other hand (and rather confusingly) I have seen data from various manufacturers (Agfa, Fuji) - that may well be out of date by now - that do indeed mention "speed" in some of their published algorithms (for instance, "equivalent screen/film system speed" - referred to as S-value).
The EI is related to the radiation dose received by the imaging plate and should be similar for all exposures made for a specific examination (
eg, lumbar spine AP, and what-have-you). This provides a way to monitor and record the radiation dose submitted and to determine if there are changes due to specific radiographers, particular x-ray rooms, or over time
etc.. The EI is a useful metric for quality control.
The trouble is that (for instance) the Fuji S-value differs to the Philips EI, which does not relate directly with the Agfa EI ...
etc., etc. ... so yes, great care needs to be taken by "clever people" concerned (such as the Physicist)!
Back in Ye Olde days of film cassettes, we needed to be careful about "speed" ... not only in terms of intensifying screens (inside film cassettes) but also regarding he film itself ("fast" film
etc.). Needless to say, there are many interesting aspects involved in the production of x-ray images.
Meanwhile (for anyone else interested), there is a lot of this stuff available on line:-
this report (.pdf) for example.
This .pdf is also good. Looking up "Agfa MUSICA" should prove interesting as well (for those seeking current "state of the art"). I find myself wishing we had info. like this available "back in the day".
