Method for retrospective estimation of natural head movement during structural MRI

Abstract

Background: Head motion during brain structural MRI scans biases brain morphometry measurements but quantitative retrospective methods estimating head motion from structural MRI have not been evaluated.

Purpose: To verify the hypothesis that two metrics retrospectively computed from MR images: 1) average edge strength (AES, reduced with image blurring) and 2) entropy (ENT, increased with blurring and ringing artifacts) could be sensitive to in-scanner head motion during acquisition of T₁ -weighted MR images.

Study type: Retrospective.

Population/subjects/phantom/specimen/animal model: In all, 83 healthy control (HC) and 120 Parkinson's disease (PD) patients.

Field strength/sequence: 3D magnetization-prepared rapid gradient-echo (MPRAGE) images at 3T.

Assessment: We 1) compared AES and ENT distribution between HC and PD; 2) evaluated the correlation between tremor score (TS) and AES (or ENT) in PD; and 3) investigated cortical regions showing an association between AES (or ENT) and local and network-level covariance measures of cortical thickness (CT), gray to white matter contrast (GWC) and gray matter density maps (GMx).

Statistical tests: 1) Student's t-test. 2) Spearman's rank correlation. 3) General linear model and partial least square analysis.

Results: AES, but not ENT, differentiated HC and PD (P = 0.02, HC median AES = 39.8, interquartile range = 9.8, PD median AES = 37.6, interquartile range = 8.1). In PD, AES correlated negatively with TS (ρ = -0.21, P = 0.02) and showed a significant relationship (|Z| >3, P < 0.001) with structural covariance of CT and GWC in 54 out of 68 cortical regions.

Data conclusion: In clinical populations prone to head motion, AES can provide a reliable retrospective index of motion during structural scans, identifying brain areas whose morphometric measures covary with motion.

Level of evidence: 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;48:927-937.

Keywords: Parkinson's disease; average edge strength; brain morphometry; brain structural MRI; entropy; head motion.