How to remove the grey bounding box caused in transforms

[sherjy]

Hiii, this is a example picture after post-processing. It seems the target is surrounded by a grey bounding box. I want to remove the grey bounding box by black background. I'm troubled by this for a while since I tried with several monai transformations to remove this box, but the grey part was still left. Could you give some guidance for me. Thanks in advance!!!
Here is a demo picture which has a target CT with a surrounding box part:

[Nic-Ma]

Hi @sherjy ,

Thanks for your interest here.
I think maybe you can try the CropForeground transform of MONAI?

Thanks.

[sherjy]

Thanks for your advice!! I found there's some wrong with my preset select_fn value. After modifying it, the problem solves.

[Nic-Ma]

Glad to see your good progress!

Thanks.