title: Test-retest reliability of fMRI experiments during robot-assisted active and passive stepping.
abstract: BACKGROUND
  Brain activity has been shown to undergo cortical and sub-cortical functional reorganisation over the course of gait rehabilitation in patients suffering from a spinal cord injury or a stroke. These changes however, have not been completely elucidated by neuroimaging to date, mainly due to the scarcity of long-term, follow-up investigations. The magnetic resonance imaging (MRI) compatible stepper MARCOS was specifically developed to enable the investigation of the supraspinal adaptations in paretic patients undergoing gait-rehabilitation in a controlled and repeatable manner. In view of future clinical research, the present study aims at examining the test-retest reliability of functional MRI (fMRI) experiments using MARCOS.
  
  
  METHODS
  The effect of repeated active and passive stepping movements on brain activity was investigated in 16 healthy participants from fMRI data collected in two separate imaging sessions six weeks apart. Root mean square errors (RMSE) were calculated for the metrics of motor performance. Regional overlap of brain activation between sessions, as well as an intra-class correlation coefficient (ICC) was computed from the single-subject and group activation maps for five regions of interest (ROI).
  
  
  RESULTS
  Data from eight participants had to be excluded due to excessive head motion. Reliability of motor performance was higher during passive than active movements, as seen in 4.5- to 13-fold lower RMSE for passive movements. In contrast, ICC ranged from 0.48 to 0.72 during passive movements and from 0.77 to 0.85 during active movements. Regional overlap of activations was also higher during active than during passive movements.
  
  
  CONCLUSIONS
  These findings imply that an increased variability of motor performance during active movements of healthy participants may be associated with a stable neuronal activation pattern across repeated measurements. In contrast, a stable motor performance during passive movements may be accompanied by a confined reliability of brain activation across repeated measurements.
authors.affiliation: Department of Health Sciences and Technology, Sensory-Motor Systems (SMS) Lab, ETH Zurich, ML G 59, Sonneggstrasse 3, 8092, Zurich, Switzerland. lukas.jaeger@hest.ethz.ch.|Medical Faculty, University of Zurich, Zurich, Switzerland. lukas.jaeger@hest.ethz.ch.|Clinic of Neuroradiology, University Hospital of Zurich, Zurich, Switzerland. lukas.jaeger@hest.ethz.ch.
authors.forename: Lukas
authors.initials: L
authors.lastname: Jaeger
authors.affiliation: Department of Health Sciences and Technology, Sensory-Motor Systems (SMS) Lab, ETH Zurich, ML G 59, Sonneggstrasse 3, 8092, Zurich, Switzerland. laura.marchal@hest.ethz.ch.|Medical Faculty, University of Zurich, Zurich, Switzerland. laura.marchal@hest.ethz.ch.
authors.forename: Laura
authors.initials: L
authors.lastname: Marchal-Crespo
authors.affiliation: Department of Health Sciences and Technology, Sensory-Motor Systems (SMS) Lab, ETH Zurich, ML G 59, Sonneggstrasse 3, 8092, Zurich, Switzerland. peter.wolf@hest.ethz.ch.|Medical Faculty, University of Zurich, Zurich, Switzerland. peter.wolf@hest.ethz.ch.
authors.forename: Peter
authors.initials: P
authors.lastname: Wolf
authors.affiliation: Department of Health Sciences and Technology, Sensory-Motor Systems (SMS) Lab, ETH Zurich, ML G 59, Sonneggstrasse 3, 8092, Zurich, Switzerland. robert.riener@hest.ethz.ch.|Medical Faculty, University of Zurich, Zurich, Switzerland. robert.riener@hest.ethz.ch.
authors.forename: Robert
authors.initials: R
authors.lastname: Riener
authors.affiliation: Clinic of Neuroradiology, University Hospital of Zurich, Zurich, Switzerland. spyros.kollias@usz.ch.
authors.forename: Spyros
authors.initials: S
authors.lastname: Kollias
authors.affiliation: Clinic of Neuroradiology, University Hospital of Zurich, Zurich, Switzerland. lars.michels@usz.ch.|Center of MR-Research, University Children's Hospital, Zurich, Switzerland. lars.michels@usz.ch.
authors.forename: Lars
authors.initials: L
authors.lastname: Michels
mesh_terms: D000368:Aged; D016477:Artifacts; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D015203:Reproducibility of Results; D012371:Robotics / Q000295:instrumentation*