FYI: MBR2GPT is now available in Windows 10 version 1703 (Windows 10 Creator's Update) and later versions. The tool is available in both the full OS environment and in Windows PE.
If apparently will convert an offline Windows MBR disk to a GPT disk.
Perhaps, useful if you want to transfer your OS to a larger 3 or 4TB Hard Disk. Once you have transferred the image to the new disk, you should be able to convert the new disk to GPT and then increase the size of the partitions or create a new partition to use the remainder of the drive.
I have not tested this myself yet...