Source code for monai.apps.reconstruction.networks.nets.complex_unet

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# Licensed under the Apache License, Version 2.0 (the "License");
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from typing import Optional, Sequence, Union

import torch.nn as nn
from torch import Tensor

from monai.apps.reconstruction.networks.nets.utils import (
from monai.networks.nets.basic_unet import BasicUNet

[docs]class ComplexUnet(nn.Module): """ This variant of U-Net handles complex-value input/output. It can be used as a model to learn sensitivity maps in multi-coil MRI data. It is built based on :py:class:`monai.networks.nets.BasicUNet` by default but the user can input their convolutional model as well. ComplexUnet also applies default normalization to the input which makes it more stable to train. The data being a (complex) 2-channel tensor is a requirement for using this model. Modified and adopted from: Args: spatial_dims: number of spatial dimensions. features: six integers as numbers of features. denotes number of channels in each layer. act: activation type and arguments. Defaults to LeakyReLU. norm: feature normalization type and arguments. Defaults to instance norm. bias: whether to have a bias term in convolution blocks. Defaults to True. dropout: dropout ratio. Defaults to 0.0. upsample: upsampling mode, available options are ``"deconv"``, ``"pixelshuffle"``, ``"nontrainable"``. pad_factor: an integer denoting the number which each padded dimension will be divisible to. For example, 16 means each dimension will be divisible by 16 after padding conv_net: the learning model used inside the ComplexUnet. The default is :py:class:`monai.networks.nets.basic_unet`. The only requirement on the model is to have 2 as input and output number of channels. """ def __init__( self, spatial_dims: int = 2, features: Sequence[int] = (32, 32, 64, 128, 256, 32), act: Union[str, tuple] = ("LeakyReLU", {"negative_slope": 0.1, "inplace": True}), norm: Union[str, tuple] = ("instance", {"affine": True}), bias: bool = True, dropout: Union[float, tuple] = 0.0, upsample: str = "deconv", pad_factor: int = 16, conv_net: Optional[nn.Module] = None, ): super().__init__() if conv_net is None: self.unet = BasicUNet( spatial_dims=spatial_dims, in_channels=2, out_channels=2, features=features, act=act, norm=norm, bias=bias, dropout=dropout, upsample=upsample, ) else: # assume the first layer is convolutional and # check whether in_channels == 2 params = [p.shape for p in conv_net.parameters()] if params[0][1] != 2: raise ValueError(f"in_channels should be 2 but it's {params[0][1]}.") self.unet = conv_net self.pad_factor = pad_factor
[docs] def forward(self, x: Tensor) -> Tensor: """ Args: x: input of shape (B,C,H,W,2) for 2D data or (B,C,H,W,D,2) for 3D data Returns: output of shape (B,C,H,W,2) for 2D data or (B,C,H,W,D,2) for 3D data """ # suppose the input is 2D, the comment in front of each operator below shows the shape after that operator x = reshape_complex_to_channel_dim(x) # x will be of shape (B,C*2,H,W) x, mean, std = complex_normalize(x) # x will be of shape (B,C*2,H,W) # pad input x, padding_sizes = divisible_pad_t( x, k=self.pad_factor ) # x will be of shape (B,C*2,H',W') where H' and W' are for after padding x = self.unet(x) # inverse padding x = inverse_divisible_pad_t(x, padding_sizes) # x will be of shape (B,C*2,H,W) x = x * std + mean x = reshape_channel_complex_to_last_dim(x) # x will be of shape (B,C,H,W,2) return x