Fig. 2.

Between-session head movement results from Experiment 1 (re-positioning trials where each of the four subjects came out of the scanner, removed the head-cast, put it back on and re-entered 10 times). a) Variability of absolute coil locations. Dots show the standard deviation of the absolute coil location over the course of the experiment. Repositioning is precise to within <0.6 mm standard deviation for any coil in any dimension. b) Coil-coil distance variability. The standard deviations are calculated from the distances between the fiducial coils measured in Experiment 1. The distances vary <0.5 mm which is within the range of measurement error, as illustrated by the phantom measurements (black squares). c) Reference coil-standard coil distance variability. Same format as b, but based on the distances between each of the three standard fiducial coils and a reference coil placed on the nose. There is more variability with normal subjects than the phantom. d) Scatter plot showing absolute locations of reference coil in head-centred (standard coil-defined) space. This plot illustrates dimensions along which the reference coil location varies relative to the standard coils: mostly in the Z dimension (up-down). e) Location of the reference coil in head-centred space. Bars encode standard deviation of absolute position of the reference coil in head-centred space measured across 10 repositioning trials. The location of the reference coil deviates <1.2 mm from the fiducial coils in the worst case. Note that variability along the Z dimension is also relatively high with the phantom. The standard deviation over all subjects was 0.50, 0.57, and 0.80 mm for the X, Y and Z dimensions respectively.