# Effects and Correction of Patient Bulk Motion in Cranial DENSE MRI

## TL;DR

This study shows that patient movement during DENSE MRI scans affects accuracy, but motion correction methods can significantly improve results.

## Contribution

The study introduces and evaluates motion correction methods to improve DENSE MRI accuracy in the presence of bulk patient motion.

## Key findings

- Induced motion significantly altered displacement measures and caused artifacts in DENSE MRI scans.
- Motion correction reduced intensity variations and phase wrap artifacts, improving scan consistency.
- Test–retest reproducibility improved significantly after applying motion correction.

## Abstract

Applications of DENSE to measure cardiac driven brain tissue pulsations are highly sensitive to bulk patient motion due to the sub-millimeter displacement encoding required, limiting its accuracy, reproducibility, and use in pediatric and aging populations. This study aims to assess the impact of induced bulk motion on DENSE scans and to what extent these motion effects can be mitigated with existing and newly proposed methods.

Participants (N = 10) underwent test–retest 2D DENSE scans at three slice locations with and without induced motion using a 3.0 T system. Brain displacement fields were calculated using pipelines without and with motion correction based on polynomial fitting to an outer ring of brain tissue. Subsequently, voxel-wise comparisons were made between scans and pipelines to evaluate scan repeatability and measure biases in displacement measures.

In comparing scans with and without induced motion, motion significantly impacted displacement measures, resulting in intensity variations and phase wrap artifacts, as well as increased the mean peak-to-peak displacements. Motion-correction removed the intensity variations and phase wrap observed in phase images, and reduced variations between scans taken with and without induced motion (Rcorr.2=0.45±0.29,Rcorr.2=0.96±0.05; RMSDuncorr. = 0.089 ± 0.005 mm, RMSDcorr. = 0.00788 ± 0.00004 mm). Test–retest reproducibility increased after motion correction with induced motion (ρuncorr. = 0.46 ± 0.38, ρcorr. = 0.98 ± 0.01), and in the absence of induced motion (ρuncorr. = 0.76 ± 0.35, ρcorr. = 0.98 ± 0.02).

Motion correction significantly improved the correspondence of DENSE measures acquired during induced motion and improved test–retest reproducibility, even in the absence of induced motion.