I am completely new to the world of image registration.
Can anyone please help me define the steps that I should take to register 3D CT images of 2 different patient? for instance to what type should I change the images, resampling etc
If you are looking to implement your own (e.g. you want to write a script that processes many images), then try SimpleITK. A general overview of the toolkit’s fundamental concepts is available here with registration overview available here. Registration examples are available both on the toolkit’s read the docs pages and in the Jupyter notebook repository (6* series).