In vivo quantification of femoral-popliteal compression during isometric thigh contraction: Assessment using MR angiography

Abstract

Purpose: To quantify femoral-popliteal vessel deformation during thigh contraction.

Materials and methods: Eleven subjects underwent a magnetic resonance (MR) examination of the femoral-popliteal vasculature on a 1.5 T system. A custom 3D balanced steady-state free precession (SSFP) sequence was implemented to image a 15-20-cm segment of the vasculature during relaxation and voluntary isometric thigh contraction. The arterial and venous lumina were outlined using a semiautomated method. For the artery, this outline was fit to an ellipse whose aspect ratio was used to describe arterial deformation, while venous deformation was characterized by its cross-sectional area.

Results: Focal compression of the femoral-popliteal artery during contraction was observed 94-143 mm superior to the condyle that corresponds to the distal adductor canal (AC) immediately superior to the adductor hiatus. This was illustrated by a significant reduction (P < or = 0.05) in aspect ratio from 0.88 +/- 0.06 during relaxation to 0.77 +/- 0.09 during contraction. A negligible change in arterial aspect ratio was observed inferior to the AC and in the proximal AC. Similarly, venous area was dramatically reduced in the distal AC region during contraction.

Conclusion: Rapid 3D SSFP MR angiography of the femoral-popliteal vasculature during thigh contraction demonstrated focal compression of the artery in the distal AC region. This may help explain the high stent failure rate and the high likelihood of atherosclerotic disease in the AC. J. Magn. Reson.

Figure 1

a) Schematic diagram shows that an axial imaging plane that is oblique with respect to the main vessel axis results in a skewed vessel cross-section. To correct for this effect, vessel edge coordinates (γ, β, α) in the imaging coordinate system were transformed into a new coordinate system given by the plane normal to the vessel. The normal vector n⃗ was based on artery center coordinates in images immediately preceding (0, 0, 0) and subsequent (δx, δy, 2t) to a given slice. c⃗ and ϕ are the axis and angle of rotation, respectively, that transforms the axial imaging plane (x, y) to the corrected plane (x’, y’).b) Transformed edge coordinates (γ′, β′) were then fit to an ellipse characterized by its semimajor and semiminor axes, a and b, respectively.

Figure 2

Images of a circular-cylindrical phantom and corresponding uncorrected and corrected best-fit ellipse contours for axial (top row) and double oblique (bottom row) phantom orientations. Aspect ratio and area measurements for the uncorrected ellipse in the double oblique plane (bottom row, middle column) do not properly represent the phantom cross-section. Contour coordinates of the uncorrected ellipse were transformed into a new coordinate system such that the uncorrected axial ellipse and corrected double oblique ellipse were well-matched.

Figure 3

Representative 3D SSFP images of the thigh during relaxation and contraction at three locations: (a, b) inferior to the AC, (c, d), distal AC, and (e, f) and proximal AC. The thigh is relaxed in the left column and contracted in the right. Note the muscle action in the distal AC (d), where the vastus medialis muscle compresses the femoral-popliteal artery and vein. Zoomed images (5 × 5 cm²) are inset to show greater detail. Solid markers indicate the femoral-popliteal artery and open markers the vein. AC = adductor canal, AM = adductor magnus muscle, BFL = long head of biceps femoris muscle, BFS = short head of biceps femoris muscle, F = femur, G = gracilis muscle, RF = rectus femoris muscle, S = sartorius muscle, SM = semimembranosus muscle, ST = semitendinosus muscle, VI = vastus intermedius muscle, VL= vastus lateralis muscle, and VM = vastus medialis muscle.

Figure 4

Mean artery aspect ratio (a) and p-values corresponding to aspect ratio change during contraction (b) (n = 11). A statistically significant change in aspect ratio was seen in the distal AC (p ≤ 0.05), while negligible compression was seen inferior to the AC or in the proximal AC. Note that d = 0 corresponds to the condyle, d = 0.22 to the adductor hiatus, and d = 1 to the femoral head. The p = 0.05 significance level is shown in (b) for reference (dashed line).

Figure 5

Mean artery and vein area (a) and p-values corresponding to area change during contraction (b) (n = 11). In general, the change in artery area was negligible. The reduction in vein area was found to be most statistically significant in the distal AC, while negligible change was observed near the mid-thigh and marginal significance was observed near the condyle. Note that d = 0 corresponds to the inferior condyle, d = 0.22 to the adductor hiatus, and d = 1 to the femoral head. The p = 0.05 significance level is shown in (b) for reference (dashed line).

Figure 6

Mean blood velocity in the femoral-popliteal artery and vein (n=11). A pulse oximeter on the index finger was used for cardiac gating.