A lot of people use ImageJ's DICOM plugin to work with these files. Imagemagick can also convert DICOM images to other formats which may be easier to work with. GIMP can also do it I think but not sure how complete/stable the implementation is. Unfortunately Octave doesn't yet have anything equivalent to Matlab's dicomread() function.
I mean FDA approved. I want DICOM ( bio-medical Image) processing toolkit for purpose of basic image processing and segmentation " vessel tree segmentation" and Measurement ...