Registration MR and CT images

Operating system:registraiton
Slicer version:4.11.20200930
Expected behavior:Registration MRI and CT images without any trouble
Actual behavior:Since the CT image I have is cut from the lower part of the noise,many structures in the MR image do not correspond to the CT,so the registration process cannot be performed completely. What I should do? What do you suggest?

In general, you need to crop the two input volumes to approximately the same region before attempting to register. The computed transform can then be applied to the entire non-cropped volume.

So how can I make this clipping process the most simple and convenient?

For cropping volumes, the easiest is to use Crop volume module.