The Effect of Aging on Deformations of the Superficial Femoral Artery Resulting from Hip and Knee Flexion: Potential Clinical Implications

MR angiography was performed in the supine position (a) and in a position with partial hip and knee flexion (b).

Centerline paths of the SFA and its branches were constructed for geometric analysis. (a) Approximate centerline paths were identified by hand from MR angiography volumetric data. (b) Lumen boundaries were then found by two-dimensional segmentation, and last, (c) true centerline paths were constructed from these segmentations.

Branch vessel fiducial markers were identified on the centerline path of the SFA. (a) Lumen centers of branch artery ostia were identified, and then (b) these points were projected onto the SFA centerline to determine bifurcation points.

Arterial deformations were quantified using the centerline paths of the main vessel and its branches. (a) Axial strain was calculated by the percent change in centerline path length from one state to another, (b) twisting angle was defined as the change in angle of separation between two branch vectors off of the main vessel path, and (c) change in curvature of a vessel segment was computed as the difference in centerline path curvature between two states where l is the arc length between adjacent sampled points.

For axial length and axial twist deformations, average values were calculated for the top, middle, and bottom thirds of the artery. The averages were computed by weighting the deformations of the vessel segments (between branch points) by their respective arc lengths.

Maximum intensity projections of MR angiograms of a young adult (top row) and older adult (bottom row) in the supine position (left column) and in the leg-flexed position (right column). Note that, whereas the SFAs of the young subject remained straight with leg flexion, the SFAs in the older adult exhibited redundancy and vessel kinking.

Illustration for off-axis deflection. The off-axis deflection metric is defined as the ratio of the off-axis distance of the vessel centerline from the straight line between the ends of the centerline path (P–Q) and the straight line distance between the ends of the centerline path (A–B).