v0.5 to v0.6 migration guide

Migrating your v0.5 code to v0.6

In MONAI v0.6, we enhanced the design of metrics and postprocessing transforms to provide more flexible and advanced features, which, in the meantime, brought some slightly breaking changes.

To help users smoothly migrate the existing code from MONAI v0.5 to v0.6, this document shows the detailed steps with example code.

Decollate batch-first Tensor to list of channel-first Tensors after model forward and loss backward