Today I had two DICOM knee images (right and left) that were shot separately, but I needed them together on the same image to be consistent with a project I was working on.  Here is how I pulled it off.  The process is rather convoluted but it worked.  I will try to post some pictures and more details later.

This was convoluted but seemed to work.  Follow these steps roughly:
– load both two DICOM images we want to merge (9.dcm and 10.dcm) into Photoshop
– expand the 9.dcm canvas double size (image to the left)
– copy 10.dcm image and paste into 9.dcm as another layer, position the layer and merge
– crop image to desired size
– note image pixel size of merged image to use later
– export image as lossless TIFF
– in Sante DICOM viewer, batch convert the TIFF image to DICOM
– at this point you will have a plain DICOM image that will work, but if you want the annotations and scale bars etc. that matches the 9.dcm original

image then you have to do a bit more trickery
– save the newly created DICOM file (merged 9 and 10.dcm images) as 9-10_no-anno.dcm
– open the 9.dcm file and make a copy of the header template and save that as 9.dcm.sdt
– load the 9-10_no-anno.dcm file back into Sante, got to edit the template and insert template (choosing the 9.dcm.sdt template you just created)
– modify the 0028,0010 and 0028,0011 DICOM elements to match the pixel size of your merged image (everything else can remain the same from the 9.dcm

file)
– save the new DICOM changes to 9-10_with-anno.dcm and close the file
– load the 9-10_with-anno.dcm back into Sante and choose Image/Invert intensity
– save this file as copy of 9-10_with-anno.dcm
– close the file and load it back into Sante to confirm everything looks correct