Vector analysis of the wall shear rate at the human aortoiliac bifurcation using cine MR velocity mapping.
OBJECTIVE
Small or oscillatory wall shear stress accelerates atherosclerosis. MR velocity mapping is feasible for vector analysis of wall shear rate (a spatial gradient of blood flow velocity at the vessel wall) in humans. A relationship between anatomic variations at the aortoiliac bifurcation and characteristics of wall shear rate was evaluated.


METHODS
To obtain two components of wall shear rate vectors, an axial component along the vessel axis and a nonaxial component perpendicular to the former at the inner and outer walls of the common iliac arteries just distal to the aortoiliac bifurcation, we performed cine MR velocity mapping with three orthogonal velocity-encoded directions in seven volunteers.


RESULTS
The peak axial component at the outer wall (120.6 +/- 37.2 sec(-1)) was smaller than that at the inner wall (196.0 +/- 53.7 sec(-1)) (p < 0.01). Oscillation described by a time integral of the axial component in recessive blood flow direction over integrals in dominant and recessive directions at the outer wall was greater (0.24 +/- 0.11) than that at the inner wall (0.15 +/- 0.08) (p < 0.01). The intersecting angle between the extrapolation of the aortic axis and the direction of the axis of the common iliac artery correlated positively with the peak axial component (r = 0.577, p < 0.05) and inversely with oscillation (r = 0.603, p < 0.05).


CONCLUSIONS
Three-dimensional vector analysis with MR velocity mapping revealed that the outer wall at the aortoiliac bifurcation showed low and oscillatory shear rate, and this inclination was increased when the takeoff angle of the iliac artery was small.
Tsuji
Taeko
T
Department of Cardiovascular Medicine, Faculty of Medicine, University of Tokyo, Hongo 7-3-1, Bunkyo-ku Tokyo 1138655, Japan.
Suzuki
Jun-ichi
J
Shimamoto
Ryoichi
R
Yamazaki
Tadashi
T
Nakajima
Toshiaki
T
Nagai
Ryozo
R
Komatsu
Shuhei
S
Ohtomo
Kuni
K
Toyo-Oka
Teruhiko
T
Omata
Masao
M
D000328:Adult; D001012:Aorta, Abdominal / Q000502:physiology*; D001783:Blood Flow Velocity; D006801:Humans; D007083:Iliac Artery / Q000502:physiology*; D019028:Magnetic Resonance Imaging, Cine; D008297:Male; D012016:Reference Values; D015203:Reproducibility of Results; D013314:Stress, Mechanical