Between-scanner variability.

<p>(a) Percentage linear scaling error across the three orthogonal directions in the MRI systems with median values shown by the black dashes and (b) the percent volumetric error with values predicted by the median scaling errors shown by the dashed lines. Scaling errors are based on the internal dimensions of the whole phantom measured on scans in all imaging planes, while volumetric errors are based on the central frustum-shaped compartment segmented on axial scans. Only the standard protocol was used to evaluate scanner “A” as no stroke protocols were utilized at this center prior to our study.</p

Imaging Parameters of Standard (“a”) and Stroke (“b”-“f”) Pulse Sequences.

<p>Imaging Parameters of Standard (“a”) and Stroke (“b”-“f”) Pulse Sequences.</p

Deformation needed to recover reference CT scans from MRI data.

<p>The maps show the in-plane absolute Euclidean displacement required to recover the true shape of the phantom in axial (<i>x-y</i>) and coronal (<i>x-z</i>) MRI data from the between-scanner variability assessment. Phase encoding is in the horizontal direction (<i>x</i>) in both planes. It is evident that scanning using an identical (standard) sequence ensures better correspondence between images from scanners “B”-“F” in terms of distortion effects. Correspondence declined when stroke sequences “b”-“f” were used, particularly in the coronal plane. Furthermore, overall distortion was characterized by two differing patterns; images from system “A” were uniformly stretched in both directions, whereas minor non-linearities were present in images from systems “B”-“F”. It should be emphasized that while these deformation maps successfully demonstrate the overall distortion of the MRI data compared to reference images, they do not represent the true geometric distortion in the MRI systems; a phantom with a large number of equidistant control points (grid structure) is often required for this purpose. Corresponding MRI images are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0162545#pone.0162545.s003" target="_blank">S2 Fig</a>.</p

Within-scanner variability.

<p>(a) Percent linear scaling error across the three orthogonal directions and (b) the percent volumetric error measured in system “A” using the standard sequence “a” after calibration of the gradient coils. The colored lines in (a) follow the median values at each time point. d indicates day; w, week; m, month. “d0” is the baseline time point immediately after calibration.</p

Details of Scanners and Imaging Coils.

<p>Details of Scanners and Imaging Coils.</p