VECTOR ANALYSIS OF THE HEMODYNAMICS OF ATHEROGENESIS IN THE HUMAN THORACIC AORTA USING MR VELOCITY MAPPING

OBJECTIVE. Our study was designed to assess the applicability of MR ve locity mapping for vector analysis of the hemodynamics of atherogenesi s. SUBJECTS AND METHODS. MR velocity mapping was used to measure axial and nonaxial elements and the length of the wall shear rate (a spatia l gradient of near-wall flow velocity parallel to the vessel wall) vec tor at 16 time points per cardiac cycle at eight anatomic locations of the thoracic aorta in six healthy subjects. An oscillatory shear inde x (a ratio of blood Bow volume in the recessive direction divided by t he sum of blood flow volume in both dominant and recessive directions) was introduced for analysis of the degree of oscillation. RESULTS. Th e time-averaged length, axial element, and nonaxial element of the wal l shear rate vector were 118 +/- 53 sec(-1), 106 +/- 55 sec(-1), and 3 3 +/- 23 sec(-1), respectively. The oscillatory shear index in the: ax ial direction was 0.06 +/- 0.10 and that in the nonaxial direction was 0.07 +/- 0.13. At the inner wall of the distal portion of the aortic arch, the length of the wall shear rate was smallest (74 +/- 32 sec(-1 )) and oscillation in the axial direction was largest (0.16 +/- 0.19). CONCLUSION. Vector analysis of the wall shear rate in the thoracic ao rta was successfully done with MR velocity mapping in humans. MR veloc ity mapping can noninvasively evaluate the hemodynamics of atherogenes is induced by the complicated blood flow.