I didn’t think of it until today but DICOM images are the equivalent of RAW file format for cameras. Both formats store additional image information than a JPEG for instance in order to allow for greater image adjustments after the image is created. Also both formats prevent you from making adjustments and saving the adjustments back to the same file format (with some exceptions). So if a radiology technician shoots an ankle image and then uses the CR software to make adjustments, those adjustments WILL NOT be saved back to the DICOM image, unless…
Saving level adjustments to the DICOM header
There are two interesting DICOM elements that store image contrast levels within the DICOM header:
Window Center (0028,1050) – WC
Window Width (0028,1051) – WW
I finally found out that these numbers represent level adjustments, however the naming of these elements is still a mystery to me. I just happened to notice some of my radiographs in Sante DICOM editor were showing different image contrast between the thumbnail view and full image view and figured something had to be causing this. I did a bit of DICOM header comparison between files and found these elements.
Anyway, Sante DICOM editor v5 (radiograph software that is well worth the purchase price if you need to view or edit x-ray images) has a tool under View/Panes and Status Bar/Level-Window Dialog Box which allows you to adjust the image levels/contrast. WW seems to be a contrast adjustment while WW seems to be brightness control (do not ask me why they are named this way). Note that when you make adjustments in the image editor you must enter the values from the Level-Window Dialog Box to the DICOM header elements if you wish to save the adjustments to the actual DICOM file (this is not automatically done for you). Below is a short video clip showing how to make adjustments:
Side note: One additional item I learned is that you can not seem to adjust the image levels if element 0028,3010 is defined (as this is probably set by the image software when the images are taken).