Asymmetric aortic expansion of the aneurysm neck: Analysis and visualization of shape changes with electrocardiogram-gated magnetic resonance imaging

These transverse magnetic resonance images perpendicular to the aorta show one cardiac phase of the aortic distention (A) before and (B) after automatic segmentation of the aortic lumen. C, Super-sampling the image results in smoother segmentation.

A, An example of typical aortic center of mass (COM) displacement is shown in which the COM coordinates are plotted for each cardiac phase. Radii are measured from these coordinates for each cardiac phase. B, Schematic image shows one circle expanding to a larger circle. Neglecting COM movement results in incorrect measurement of radial expansion. Radii during the maximum expansion should not be measured from point A but from point B.

Plots show (A) radius change and (B) corresponding minimum and maximum diameter. An example of a preoperative measurement is shown. A, Radius change is measured over 360 axes and plotted. An ellipsis is fitted and the magnitude and direction of the maximum (Ra) and minimum radius change (Rb) are calculated. B, Illustration shows the corresponding maximum and minimum radii in mm. A, Anterior; L, left; P, posterior; R, right.

The mean radial distention before and after endovascular aneurysm repair (EVAR) is presented with the standard deviation (error bars). At each level, the radius change over the minor and major axis differed significantly both preoperatively and postoperatively (P ≤ .002). There was no significant difference between pre-EVAR and post-EVAR radius changes (P > .05). The percentages above the bars indicate the percentages of radius change.

The asymmetry ratio before and after endovascular aneurysm repair (EVAR) is calculated as radius change over the major axis divided by radius change over the minor axis (Ra/Rb). The dashed line is a ratio of 1.0, which represents symmetric expansion. The horizontal line in the middle of each box indicates the median; the top and bottom borders of the box mark the 75th and 25th percentiles, respectively; and the whiskers mark the range. At each level, there was no significant difference (P > .1) between pre-EVAR and post-EVAR asymmetry ratios.

The major preoperative axis direction of distention is drawn for each patient (lines). The mean axis (dark green line) with −1 and +1 standard deviation (light green) is also shown. The mean axis is calculated with the orientation anteriorly (−90° to 90). Note that all orientations are also mirrored in the posterior direction. A, Anterior, L, left; P, posterior; R, right.