Mask scalar volume vs masking within the registration

Hi everyone,

I am now using Slicer 4.11.0 and want to register pre-surgical CT to post-surgical CT (breast). The two images were acquired using different CT table (curved vs flat), and there are some metal markers on the breast skin in post-surgical CT (shown below).

I know from FAQ manual (https://www.slicer.org/wiki/Documentation/4.10/FAQ#Masking) that masking is a powerful tool and I want to use it in my registration. But I am not sure about the difference between “mask scalar volume” and “masking within the registration”.

If I just mask the breast region in registration, can the unexpected misleading effect of markers and CT table be well handled? (I am not quite certain about “This does not mean that the rest is not registered, but rather that it moves along passively, i.e. areas outside the mask do not actively contribute to the cost function that determines the quality of the match.”) Or do I need to mask these relatively high intensity regions and set them to background value (-1024)?

Which one would be more reasonable? Hope for some advice, thanks a lot!

Crayon

This post should clarify:

I will try the methods mentioned in this post. Thank you very much!

Crayon