add feature pyramid network (FPN) for detection

[Can-Zhao]

Signed-off-by: Can Zhao canz@nvidia.com

Fixes #4341 .

Description

add feature pyramid network (FPN) for detection

Status

Ready/Work in progress/Hold

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

[Nic-Ma]

Hi @Can-Zhao ,

Please import torchvision as optional import, refer to:
https://github.com/Project-MONAI/MONAI/blob/dev/monai/networks/nets/torchvision_fc.py#L17

Thanks.

[Can-Zhao]

Hi @Can-Zhao ,

Please import torchvision as optional import, refer to: https://github.com/Project-MONAI/MONAI/blob/dev/monai/networks/nets/torchvision_fc.py#L17

Thanks.

Thank you! Done

[wyli]

backbone adapted from torchvision with 2d/3d support

[wyli]

/build