# Deformable Slice-to-Volume Registration for Motion Correction in Fetal Body MRI

## TL;DR

This paper introduces a deformable slice-to-volume registration method for fetal MRI that effectively corrects non-rigid motion artifacts in fetal body and placenta imaging, improving reconstruction quality.

## Contribution

The paper presents a novel hierarchical deformable SVR approach with outlier rejection, advancing motion correction techniques for fetal body and placenta MRI beyond rigid registration methods.

## Key findings

- DSVR outperforms SVR and PVR in simulated experiments.
- Quantitative improvements demonstrated on 20 fetal MRI datasets.
- Qualitative evaluation on 100 fetal cases shows enhanced image quality.

## Abstract

In in-utero MRI, motion correction for fetal body and placenta poses a particular challenge due to the presence of local non-rigid transformations of organs caused by bending and stretching. The existing slice-to-volume registration (SVR) reconstruction methods are widely employed for motion correction of fetal brain that undergoes only rigid transformation. However, for reconstruction of fetal body and placenta, rigid registration cannot resolve the issue of misregistrations due to deformable motion, resulting in degradation of features in the reconstructed volume. We propose a Deformable SVR (DSVR), a novel approach for non-rigid motion correction of fetal MRI based on a hierarchical deformable SVR scheme to allow high resolution reconstruction of the fetal body and placenta. Additionally, a robust scheme for structure-based rejection of outliers minimises the impact of registration errors. The improved performance of DSVR in comparison to SVR and patch-to-volume registration (PVR) methods is quantitatively demonstrated in simulated experiments and 20 fetal MRI datasets from 28-31 weeks gestational age (GA) range with varying degree of motion corruption. In addition, we present qualitative evaluation of 100 fetal body cases from 20-34 weeks GA range.