Creating an ISO from a Hyper-V Machine
If you want to use MDT to capture your reference VM, you should create and use a 'capture image', then boot your VM on this image and follow the process.
note your VM must be syspreped and generalized in order to capture it. So first of all, run sysprep -generalize -shutdown, then boot to your capture image.
More information here : http://www.vkernel.ro/blog/sysprep-and-capture-a-windows-image-with-mdt-2012