Characterisation of Children's Head Motion for Magnetic Resonance Imaging With and Without General Anaesthesia.

Hannah Eichhorn,Martin Nørgaard,Andreea-Veronica Vascan,Andreas H Ellegaard,Melanie Ganz,Sune Høgild Keller,Jakob M Slipsager,Lisbeth Marner

doi:10.3389/fradi.2021.789632

Abstract

Head motion is one of the major reasons for artefacts in Magnetic Resonance Imaging (MRI), which is especially challenging for children who are often intimidated by the dimensions of the MR scanner. In order to optimise the MRI acquisition for children in the clinical setting, insights into children's motion patterns are essential. In this work, we analyse motion data from 61 paediatric patients. We compare structural MRI data of children imaged with and without general anaesthesia (GA), all scanned using the same hybrid PET/MR scanner. We analyse several metrics of motion based on the displacement relative to a reference, decompose the transformation matrix into translation and rotation, as well as investigate whether different regions in the brain are affected differently by the children's motion. Head motion for children without GA was significantly higher, with a median of the mean displacements of 2.19 ± 0.93 mm (median ± standard deviation) during 41.7±7.5 min scans; however, even anaesthetised children showed residual head motion (mean displacement of 1.12±0.35 mm). For both patient groups translation along the z-axis (along the scanner bore) was significantly larger in absolute terms (GA / no GA: 0.87±0.29/0.92 ± 0.49 mm) compared to the other directions. Considering directionality, both patient groups were moving in negative z-direction and thus, out of the scanner. The awake children additionally showed significantly more nodding rotation (0.33±0.20°). In future studies as well as in the clinical setting, these predominant types of motion need to be taken into consideration to limit artefacts and reduce re-scans due to poor image quality.

Highlights

For Magnetic Resonance Imaging (MRI), artefacts are most frequently caused by patient head motion due to long acquisition times of typically 30–60 min [1]
As described in the Introduction, Afacan et al [1] investigated the correlation of motion metrics like mean and maximum displacement and motion-free time with image quality based on motion estimates, which were measured with two sensors placed on the patient’s forehead
We showed that even children under general anaesthesia (GA) show an amount of motion on the order of 1– 2 mm mean displacement, which can impact MR image quality

Summary

Introduction

For Magnetic Resonance Imaging (MRI), artefacts are most frequently caused by patient head motion due to long acquisition times of typically 30–60 min [1]. These artefacts manifest as ghosting, blurring or signal variations, reducing overall image quality and resulting in unsuccessful diagnoses [2]. Andre et al [3] determined the percentage of at least partly repeated MRI examinations to approximately 20%, leading to an estimated increased cost of 115,000 US dollars per scanner per year in the US due to motion. Slipsager et al [7] calculated the additional cost for using GA in MRI examinations to 319,000 US dollars per scanner per year in Denmark. There are concerns about adverse events like airway obstruction or oxygen desaturation of GA in young children [1, 4, 8, 9]

Objectives

Methods

Results

Discussion

Conclusion