BUG: Use the SOP Class UID instead of the Modality tag to check if a volume is a CT when determining the pixel units. This is needed to handle cases in which a secondary capture has the Modality tag set to the modality of the original image. #2080
At the moment there's no need to do the same for PET because getPTPixelUnits returns an empty string if no unit is found.
ENH: Some linguistic fixes to the changelog.