Hi, I'm using MRIcroGL to convert whole body PET imaging in cancer patients. I'm using another software (MIM) to contour the disease - is it possible to convert these contours from DICOM to NIfTI using MRIcroGL? When I try it nothing happens.

I do not have enough information to answer this question. MIM is a proprietary professional tool, and I have no idea how it stores its contours. I do not have access to this tool. You can always use MRIcroGL's drawing tools to mark regions. If you use a professional tool like MIM, you are entitled to professional support. I would contact them to see how the data can be exported.