Perceptual Loss with mednet 3D multiple channels

[SomeUserName1]

Describe the bug
Perceptual loss with 3D volumes and the medicalnet network types currently works with one channel only, as MedNet3D takes single channel 3D volumes as input. However the code in MedicalNetPerceptualSimilarity suggests that it is intended to work with multiple channels.

To Reproduce
Use PerceptualLoss with spatial_dims=3, is_fake_3d=False, network_type='medicalnet_resnet50_23datasets' and 3D volumes with multiple channels, e.g. with fMRI, phase-cycle bSSFP, DTI, ... as data.

Expected behavior
MedicalNetPerceptualSimilarity passes the input channelwise and averages (the latter is already implemented).

Environment

MONAI environment

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Printing MONAI config...

MONAI version: 1.3.0
Numpy version: 1.26.4
Pytorch version: 2.2.1+cu121
MONAI flags: HAS_EXT = False, USE_COMPILED = False, USE_META_DICT = False
MONAI rev id: 865972f
MONAI file: /home//workspace/UNet-bSSFP/unet-venv/lib/python3.11/site-packages/monai/init.py

Optional dependencies:
Pytorch Ignite version: NOT INSTALLED or UNKNOWN VERSION.
ITK version: NOT INSTALLED or UNKNOWN VERSION.
Nibabel version: 5.2.0
scikit-image version: NOT INSTALLED or UNKNOWN VERSION.
scipy version: 1.12.0
Pillow version: 10.2.0
Tensorboard version: 2.16.2
gdown version: 4.7.3
TorchVision version: 0.17.1+cu121
tqdm version: 4.66.2
lmdb version: NOT INSTALLED or UNKNOWN VERSION.
psutil version: 5.9.8
pandas version: 2.0.3
einops version: NOT INSTALLED or UNKNOWN VERSION.
transformers version: NOT INSTALLED or UNKNOWN VERSION.
mlflow version: NOT INSTALLED or UNKNOWN VERSION.
pynrrd version: NOT INSTALLED or UNKNOWN VERSION.
clearml version: NOT INSTALLED or UNKNOWN VERSION.

For details about installing the optional dependencies, please visit:
https://docs.monai.io/en/latest/installation.html#installing-the-recommended-dependencies

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Printing system config...

System: Linux
Linux version: Arch Linux
Platform: Linux-6.7.4-zen1-1-zen-x86_64-with-glibc2.39
Processor:
Machine: x86_64
Python version: 3.11.7
Process name: python
Command: ['python', '-c', 'import monai; monai.config.print_debug_info()']
Open files: []
Num physical CPUs: 24
Num logical CPUs: 32
Num usable CPUs: 32
CPU usage (%): [93.7, 62.3, 79.0, 40.4, 61.9, 78.7, 56.0, 98.4, 96.5, 19.7, 23.0, 97.6, 96.4, 99.2, 99.6, 30.3, 99.6, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0]
CPU freq. (MHz): 3461
Load avg. in last 1, 5, 15 mins (%): [87.6, 86.7, 82.9]
Disk usage (%): 44.8
Avg. sensor temp. (Celsius): UNKNOWN for given OS
Total physical memory (GB): 62.6
Available memory (GB): 25.2
Used memory (GB): 32.0

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Printing GPU config...

Num GPUs: 1
Has CUDA: True
CUDA version: 12.1
cuDNN enabled: True
NVIDIA_TF32_OVERRIDE: None
TORCH_ALLOW_TF32_CUBLAS_OVERRIDE: None
cuDNN version: 8902
Current device: 0
Library compiled for CUDA architectures: ['sm_50', 'sm_60', 'sm_70', 'sm_75', 'sm_80', 'sm_86', 'sm_90']
GPU 0 Name: NVIDIA GeForce RTX 4090 Laptop GPU
GPU 0 Is integrated: False
GPU 0 Is multi GPU board: False
GPU 0 Multi processor count: 76
GPU 0 Total memory (GB): 15.7
GPU 0 CUDA capability (maj.min): 8.9

Additional context
Add any other context about the problem here.