748 replace AsChannelFirst as EnsureChannelFirst

[KumoLiu]

Signed-off-by: KumoLiu [email protected]

Fixes #748 .

Description

Replace AsChannelFirst as EnsureChannelFirst which is more robust.

Status

Work in progress

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[Nic-Ma]

Hi @wyli ,

@KumoLiu is trying to update all the tutorials for EnsureChannelFirst and run them to verify locally.
As you know, many tutorials may not be easy to set up the environment and run, I think maybe we should ask the PICs to update the AsChannelFirst and AddChannel of these tutorials when they update MetaTensor?
What do you think?

Thanks.

[wyli]

sure, I think we update the basics, these should be fine. Perhaps @KumoLiu could help add a warning message in AddChannel in the core codebase https://github.com/Project-MONAI/MONAI/blob/422cc6dcf5e7ba5243d5d585d632a7d54e0622e6/monai/transforms/utility/array.py#L176 with the metatensor we can identify some false cases now.