Virtuo CD manager disk images (.vdi) can be perhaps converted to other formats, including standard ISO disk images. This can be usually done with some dedicated disk image handling tools that have conversion option, for example MagicISO or UltraISO.
Also worth mentioning is that VirtualBox disk images share the same extension and might potentially be converted in the same manner, albeit this is a complete different vdi to iso conversion.Open VDI file Open ISO file
A powerful CD/DVD-image-file editor, CD burner, and CD/DVD-backup tool
One of the disk image handling utilities and the default program for ISZ images