# Head Motion in Diffusion Magnetic Resonance Imaging: Quantification, Mitigation, and Structural Associations in Large, Cross‐Sectional Datasets Across the Lifespan

## TL;DR

This study examines head motion during MRI scans, finding that modern preprocessing reduces motion effects and that motion does not affect brain connectivity measurements.

## Contribution

The study provides a large-scale characterization of motion during diffusion MRI and evaluates the effectiveness of modern preprocessing in mitigating motion biases.

## Key findings

- Subjects typically move 1–2 mm/min during diffusion MRI scans, primarily in the anterior–posterior direction and rotation around the right–left axis.
- Modern preprocessing pipelines effectively mitigate motion to the point where biases are not detectable with current analysis techniques.
- There are no apparent differences in microstructure or macrostructural connections between participants with high and low motion.

## Abstract

Head motion during diffusion magnetic resonance imaging (MRI) scans can cause numerous artifacts and biases subsequent quantification. However, a thorough characterization of motion across multiple scans, cohorts, and consortiums has not been performed. To address this, we designed a study with three aims. First, we aimed to characterize subject motion across several large cohorts, utilizing 13 cohorts comprised of 16,995 imaging sessions (age 0.1–100 years, mean age = 63 years; 7220 females; 3175 cognitively impaired adults; 471 developmentally delayed children) to describe the magnitude and directions of subject movement. Second, we aimed to investigate whether state‐of‐the‐art diffusion preprocessing pipelines mitigate biases in quantitative measures of microstructure and connectivity by taking advantage of datasets with scan‐rescan acquisitions and ask whether there are detectable differences between the same subjects when scans and rescans have differing levels of motion. Third, we aimed to investigate whether there are structural connectivity differences between movers and non‐movers. We found that (1) subjects typically move 1–2 mm/min with most motion as translation in the anterior–posterior direction and rotation around the right–left axis; (2) Modern preprocessing pipelines can effectively mitigate motion to the point where biases are not detectable with current analysis techniques; and (3) There are no apparent differences in microstructure or macrostructural connections in participants who exhibit high motion versus those that exhibit low motion. Overall, characterizing motion magnitude and directions, as well as motion correlates, informs and improves motion mitigation strategies and image processing pipelines.

We characterized motion during diffusion MRI scans across 16,995 image sessions and find that (1) modern preprocessing pipelines effectively mitigate motion to the point where biases are not detectable, and (2) that there are no apparent differences in microstructure or connectivity in volunteers who exhibit high motion versus those that exhibit low motion.