dcm2niix VS simnibs

Keep in mind that DICOM images are always converted to the NIfTI format when dealing with neuroimaging data, so the different software are expecting this image type. You should always keep the original DICOM files in your archive, but convert them to NIfTI and use that as your raw data input. To convert DICOM to NIfTI, you can use a tool like dcm2niix dcm2niix.

When I try to execute the .exe in the link you have provided the program does not run. However, according to this site: https://github.com/rordenlab/dcm2niix! the niix is included in MRIcroGL which I have tried.

The spatial resolution of the scan is typically in the DICOM header, isn't it? Maybe try running the DICOM through something like dcm2niix (https://github.com/rordenlab/dcm2niix) which will convert to a NIFTI formatted image and generate a JSON file from the header. The header support isn't complete, so it might not get things correct from your CT image (or from an animal scanner for that matter), but it's worth a shot. I imagine there are similar tools for CT.

What I would recommend is to use either SimNIBS, so you load the imaging data that you have and then it generates the mesh for you, since this program needs the mesh to perform brain stimulation simulations (you don't care about the simulation part, but only for the mesh). A direct tutorial reference for SimNIBS can be found here.