If the images are in DICOM format, which is common, then dcm2niix should be able to convert them https://github.com/rordenlab/dcm2niix

I think it can handle a few other formats as well. Once they are .nii(.gz) files, then mricrogl (https://www.nitrc.org/projects/mricrogl) should be able to render it - of course, for a brain scan - this would be your whole head. Brain extraction is performed by more specialized software, but that would get you started.