# Scanner Invariant Representations for Diffusion MRI Harmonization

## TL;DR

This paper introduces a novel deep learning method using invariant representations to correct for site and scanner biases in diffusion MRI, improving data harmonization across multiple sources.

## Contribution

The paper proposes a new approach leveraging invariant representations via variational auto-encoders to harmonize multi-site diffusion MRI data, addressing scanner and protocol biases.

## Key findings

- Improved harmonization performance on MICCAI CDMRI dataset
- Outperforms recent baseline methods in multi-site data mapping
- Effective in creating scanner-invariant MRI representations

## Abstract

Purpose: In the present work we describe the correction of diffusion-weighted MRI for site and scanner biases using a novel method based on invariant representation. Theory and Methods: Pooled imaging data from multiple sources are subject to variation between the sources. Correcting for these biases has become very important as imaging studies increase in size and multi-site cases become more common. We propose learning an intermediate representation invariant to site/protocol variables, a technique adapted from information theory-based algorithmic fairness; by leveraging the data processing inequality, such a representation can then be used to create an image reconstruction that is uninformative of its original source, yet still faithful to underlying structures. To implement this, we use a deep learning method based on variational auto-encoders (VAE) to construct scanner invariant encodings of the imaging data. Results: To evaluate our method, we use training data from the 2018 MICCAI Computational Diffusion MRI (CDMRI) Challenge Harmonization dataset. Our proposed method shows improvements on independent test data relative to a recently published baseline method on each subtask, mapping data from three different scanning contexts to and from one separate target scanning context. Conclusion: As imaging studies continue to grow, the use of pooled multi-site imaging will similarly increase. Invariant representation presents a strong candidate for the harmonization of these data.