Training β-VAE by Aggregating a Learned Gaussian Posterior with a Decoupled Decoder

Main Take Away Message

• Unsupervised skull shape completion using a variational autoencoder (poster).

• The reconstruction (Dice) loss does not decrease given a large beta in a regular beta-VAE(e.g., beta=100). Note: the initial decrease is due to random initialization of the network before training. The loss does not decrease to a desired small value, as in the following curve in red.

• The latent variables from beta=100 can be used for reconstruction by using an independent decoder, and the reconstruction (dice) loss can decrease to a desirable small value.

• The encoder of the VAE trained using a large beta and the independently trained decoder can be aggragated to form a new VAE that satisfies the latent Gaussian assumption and can produce good reconstruction.

Code

zcr→co = zts + γDEVcr
zfa→co = zts + γDEVfa

(1) train the initial VAE using beta=100 or beta=0.0001

python monaiSkullVAE.py --phase train
#python monaiSkullVAE.py --phase test

(2) train a decoder using the latent variables from the previously trained VAE (beta=100)

python VAEDecoderRetrain.py --phase train
#python VAEDecoderRetrain.py --phase test

the decoupled decoder 'newDecoder' takes as input the latent variables 'z' from Step (1) and outputs a reconstruction, using only the reconstruction (dice) loss

# model is the trained VAE with beta=100. z is the latent variable corresponding to an 'input'.
_,_,_,z=model.forward(inputs)
z=torch.tensor(z.cpu().detach().numpy())
# 'newDecoder' is the decoupled decoder
recon_batch = newDecoder(z)

(3) make predictions using the aggregated VAE (encoder from beta=100 + decoupled decoder)

python AggreegateVAE.py

Dataset

Download the dataset here. The dataset is extended from the AutoImplant Challenge. There are 100 healthy skulls, 100 skulls with facial and craial defects:

Latent Distributions of the skull variables (Dimension of latent variables reduced from 32 to 2 for illustrative purposes)

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References:

Dataset (SkullFix)

@inproceedings{li2020dataset,
  title={Dataset descriptor for the AutoImplant cranial implant design challenge},
  author={Li, Jianning and Egger, Jan},
  booktitle={Cranial Implant Design Challenge},
  pages={10--15},
  year={2020},
  organization={Springer}
}

Methods

@article{li2022training,
  title={Training β-VAE by Aggregating a Learned Gaussian Posterior with a Decoupled Decoder},
  author={Li, Jianning and Fragemann, Jana and Ahmadi, Seyed-Ahmad and Kleesiek, Jens and Egger, Jan},
  journal={arXiv preprint arXiv:2209.14783},
  year={2022}
}

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⭐ Check out our other skull-reconstruction project with MONAI at SkullRec

📧 For questions about the codes, feel free to contact [email protected]