Fraser, Brett wrote:
> Does anyone know what the DICOM tag is for "exposure index" that may be used
> on a CR unit.


herman oosterwijk wrote:
> Here is some more info:
>
> this is the definition of that Attribute (0018,1405)acc to the DICOM
> standard:
>
> Indication of the applied dose, in manufacturer specific units.
>
> Notes: 1. This value is intended to provide a single location where
> manufacturer specific information can be found for annotation on a display
> or film, that has meaning to a knowledgeable observer.
>
> 2. This may be a calculated or measured
> value. Examples are the detector entrance dose (KB), the CR sensitivity
> value (S), or the logarithmic median (lgM).
>
> I remember that some vendors initially put this in private tags, so be aware
> that this still might occur.
>
> Most of the time, the DICOM conformance statement will tell you where to
> find it (or if anything fails, a DICOM dump).
>
> Herman O.


Hi Herman

You are quoting the definition of Relative X-Ray Exposure (0018,1405)
from the X-Ray Acquisition Dose Module that is used in the DX family
images, not the CR image object.

The definition in the CR Image Module is less specific:

"Relative x-ray exposure on the plate. Meaning of values is implementation
specific. May be used to adjust the dynamic range of the plate digitizer
(scanner)."

Further, in practice many vendors do not populate this value, but do
send a value in Sensitivity (0018,6000), which is described as "Read out
sensitivity.". Perhaps they are using this to send S value, Exposure Index
or whatever they choose to call it.

You might want to dump these tags in your images (as well as private tags)
and look for numeric values that correspond to what is being displayed
on the console or printed on the film as exposure index.

From my experience, Agfa, Fuji, Philips, Siemens send a value in (0018,6000)
and not (0018,1405).

GE seems to send (different) values in (0018,1405) and (0018,6000).

Hologic and Kodak send a value in (0018,1405) and not (0018,6000).

Canon and Swissray do not send either. The Canon conformance statement
lists (0018,6000) as being sent, but I do not see it in their images,
and they do not describe private attributes. Swissray describes a bunch
of private attributes in their conformance statement, though it is not
obvious to me which might correspond to what you are looking for
(Latitude Reduction looked promising, but isn't present in the images
that I have encountered).

For example:

"Manufacturer" "Relative X-ray Exposure" "Sensitivity"

"AGFA" "" "400.000000"
"Canon Inc." "" ""
"FUJI PHOTO FILM Co., ltd. " "" "283 "
"GE MEDICAL SYSTEMS" "88" "0.201527"
"HOLOGIC, Inc. " "215 " ""
"KODAK " "2310" ""
"Philips Medical Systems " "" "165.000000"
"SIEMENS " "" "800 "
"Swissray" "" ""

Perhaps any vendor listening in with more information about this could
pass it on.

David