I would suggest ImageJ, which is a Java-based image processing program developed at the National Institutes of Health (NIH). It has a very low memory footprint,

I would suggest ImageJ, which is a Java-based image processing program developed at the National Institutes of Health (NIH). It has a very low memory footprint, built-in support for most DICOM file formats, a ton of extensions, and (of course) cross-platform support. As an added bonus, you can run it as a portable app.