As far as I know there is no file format for an image you can burn to a clean flash drive and make it bootable.
Since to make a flash drive, you have to make it bootable and then copy the OS files to it, possibly you could use a script in Diskpart to configure the drive and then just copy the files.
If you are trying to create a portable version of the OS you could run from the flash drive, I have no experience. But since there are not formats for such a file, it would have to guess it is not possible to just be able to save or burn such a configuration.
I do see some sites that discuss cloning a flash drive. Maybe something like that might get you started. And if you can clone one, possibly you could back it up and re-image. But again, I have not tried.