Converting signed DICOM files to unsigned DICOM files

[Kars]

Dear all,

I'm analyzing a few hundred CT scans of different types/brands. Most of the scans represents normal WW/WL values and Hounsfield units ).
However, a few CT scans are having extreme WW/WL values. If I perform a calcium scoring (using ImageJ with a threshold of 600 HU) then the output show unlikely values.

I'm not very familiar with DICOM headers, but all scans with these abnormal WW/WL values are showing a Pixel Representation of 1 instead of 0 (scans with normal WW/WL. Changing this DICOM tag (0028,0103) seems to provide normal Hounsfield values but different images of the scan series changes (smaller field of view, some completely white images).

It seems to be that ImageJ can not handle signed pixels/data correctly. I already did a search on Internet and ImageJ mailinglist, but I can not found a solution for this problem or to convert signed pixels to unsigned pixels correctly (done by hand results in inappropriate CT scans as mentioned earlier).

Is there a solution for this problem?

Thank you all in advance!

EDIT: I already tried Plugins -> Tools -> Signed 16-bit to Unsigned. However, imageJ shows a message 'signed 16-bit image required'. I'm sure that the images (scans) are 16 bits and signed pixels (pixel presentation=1).