SurrealGAN 0.0.2

A python implementation of Surreal-GAN for semisupervised representation learning

Surreal-GAN

Surreal-GAN is a semi-supervised representation learning method which is designed to identify disease-related heterogeneity among the patient group. Surreal-GAN parses complex disease-related imaging patterns into low dimensional representation indices (r-indices) with each dimension indicating the severity of one relatively homogeneous imaging pattern.

The key point of the Surreal-GAN model is modelling disease as a continuous process and learning infinite transformation directions from CN to PT, with each direction capturing a specific combination of patterns and severity. The idea is realized by learning one transformation function, f, which takes both normal data and a continuous latent variable as inputs and output synthesized-PT data whose distribution is indistinguishable from that of real PT data. (As shown in the schematic diagram) Several different regularizations were introduced to further guide the transformation function. An inverse function g, jointly trained with f, is used for deriving R-indices after training process.

License

Copyright (c) 2016 University of Pennsylvania. All rights reserved. See https://www.cbica.upenn.edu/sbia/software/license.html

Installation

We highly recommend the users to install Anaconda3 on your machine. After installing Anaconda3, Smile-GAN can be used following this procedure:

We recommend the users to use the Conda virtual environment:

$ conda create --name surrealgan python=3.8

Activate the virtual environment

$ conda activate surrealgan

Install SurrealGAN from PyPi:

$ pip install SurrealGAN

Input structure

Main functions of SurrealGAN basically takes two panda dataframes as data inputs, data and covariate (optional). Columns with name 'participant_id' and 'diagnosis' must exist in both dataframes. Some conventions for the group label/diagnosis: -1 represents healthy control (CN) and 1 represents patient (PT); categorical variables, such as sex, should be encoded to numbers: Female for 0 and Male for 1, for example.

Example for data:

participant_id    diagnosis    ROI1    ROI2 ...
subject-1	    -1         325.4   603.4
subject-2            1         260.5   580.3
subject-3           -1         326.5   623.4
subject-4            1         301.7   590.5
subject-5            1	       293.1   595.1
subject-6            1         287.8   608.9

Example for covariate

participant_id    diagnosis    age    sex ...
subject-1	    -1         57.3   0
subject-2 	     1         43.5   1
subject-3           -1         53.8   1
subject-4            1         56.0   0
subject-5            1	       60.0   1
subject-6            1         62.5   0

Example

We offer a toy dataset in the folder of SurrealGAN/dataset.

import pandas as pd
from SurrealGAN.Surreal_GAN_representation_learning import repetitive_representation_learning

train_data = pd.read_csv('train_roi.csv')
covariate = pd.read_csv('train_cov.csv')

output_dir = "PATH_OUTPUT_DIR"
npattern = 3
final_saving_epoch = 42000
max_epoch = 43000

## two important hyperparamters
lam = 0.2
gamma = 6

There are some hyper parameters need to be set by the user:

batch_size: Size of the batch for each training epoch. (Default to be 100) It is necessary to be reset to 1/8 - 1/10 of the PT sample size.

mu: coefficient controlling the relative importance of cluster_loss in training objective function. (Default to be 0.2) It is necessary to try different mu values between 0.05 and 0.6 and use results which give the highest pattern c-index as returned in the output file.

gamma: coefficient controlling the relative importance of change_loss in training objective function. (Default to be 6). The default value is robust to different cases, but users can try smaller or larger values if results with gamma=6 gives low pattern c-index as returned in the output file.

repetition_number = 20  # number of repetitions (at least 5 repetition\
	   is need to give the most reliable and reproducible result)
data_fraction = 1 # fraction of data used in each repetition
repetitive_representation_learning(train_data, npattern, repetition_number, data_fraction, final_saving_epoch, max_epoch, output_dir, \
		lr = 0.0008, batchsize=120, verbose=False, lipschitz_k=0.5, covariate= None, start_repetition=0, lam=lam, gamma = gamma)

repetitive_representation_learning is the main function for representation learning via Surreal-GAN. It performs the representation learning process repetitively with predefined number of repetitions. Each repetition will save models in a subfolder called "repetition_i", in which the model will be saved every 5000 epochs before the final_saving_epoch while saving criteria are satisfied. The function will automiatically choose the optimal saving epochs via pattern-agr-index and pattern-diff-agr-index (explained below) among results.

After determining the optimal saving epoch, the repetition which has the highest agreements (measured by pattern-agr-index) with all other repetitions will be used to derive the final R-indices. Given the randomness in training procedure, it is necessary to run at least 10 repetitions to derive a reliable and reproducible result.

Since the repetition training process may take long training time on a normal desktop computer, the function enables early stop and later resumption. Users can set stop_repetition to be early stopping point and start_repetition to be the starting repetition index. This will also enable the user to run several repetitions in parellel.

The function automatically saves an csv file with clustering results and returns the same dataframe. The dataframe also includes the path to the final selected model (the model used for deriving final R-indices), pattern c-index among all repretitively derived results, as well as selected model pattern c-index (average concordance indices between the selected repetitions and all other repetitions.

Two evaluation metrics used for measuring agreements between results and selecting the optimal model:

• pattern-agr-index: With M dimensional R-indices derived by two different models defined as r¹ and r², pattern-agr-index is defined as the average of M concordance indices for all dimensions, C(r¹_i, r²_i).

• pattern-diff-agr-index: With M dimensional R-indices derived by two different models defined as r¹ and r², pattern-diff-agr-index is defined as the average of M(M-1)/2 concordance indices for differences among all dimensions, C(r¹_i-r¹_j, r²_i-r²_j).

model_dir = 'PATH_TO_SAVED_MODEL' #the path to the final selected model (the one returned by function "repetitive_representation_learning")
r_indices = apply_saved_model(model_dir, train_data, covariate=None)

apply_saved_model is a function used for deriving representation (R-indices) for new patient data using a previously saved model. Input data and covariate (optional) should be panda dataframe with same format shown before. Only PT data, for which the user want to derive R-indices, need to be provided with diagnoses set to be 1. PT data can be any samples inside or outside of the training set. The function returns R-indices of PT data following the order of PT in the provided dataframe.

Citation

If you use this package for research, please cite the following paper:

@inproceedings{yang2022surrealgan,
title={Surreal-{GAN}:Semi-Supervised Representation Learning via {GAN} for uncovering heterogeneous disease-related imaging patterns},
author={Zhijian Yang and Junhao Wen and Christos Davatzikos},
booktitle={International Conference on Learning Representations},
year={2022},
url={https://openreview.net/forum?id=nf3A0WZsXS5}
}