I have solved this now. I mistakenly chose Simple mode instead of Traditional mode when using MakeDisk.
I want to create an image of my c drive but the only options are:
Backup this computer to an alternate drive
Restore a backup to this computer
Validate a previous backup to check its integrity
Copy a hard drive to another hard drive
I took a guess and opted for 'Backup this computer to an alternate drive' but when it came to the part where you chose a name and location for the .tbi there was no choice.