Background: Magnetic resonance angiography (MRA) is clinically useful but of limited applicability to small animal models due to poor signal resolution, with typical voxel sizes of 1 mm(3) that are insufficient to analyze vessels of diameter <1 mm. We determined whether surgically implantable, extravascular MRA coils increase signal resolution adequately to examine blood flow dynamics
Methods: A custom MRA coil was surgically implanted near the carotid artery of a New Zealand White rabbit. A stenosis was created in the carotid artery to induce complicated, non-laminar flow. Phase contrast images were obtained on multiple axial planes with 3T MRA and through-plane velocity profiles were calculated under laminar and complicated flow conditions. These velocity profiles were fit to a laminar flow model using ordinary least squares in order to quantify the degree of flow complication (Matlab). Flow was also measured with a Doppler flow probe; vessel diameters and flow velocities were compared with duplex ultrasound
Results: Carotid artery blood flow was 24.7 +/- 2.6 ml/min prior to stenosis creation and reduced to 12.0 +/- 1.7 ml/min following injury (n=3). An MRA voxel size of 0.1 x 0.1 x 5 mm was achieved. The control carotid artery diameter was 1.9 +/- 0.1 mm, and cross-sectional images containing 318 +/- 22 voxels were acquired (n=26). Velocity profiles resembled laminar flow proximal to the stenosis, and then became more complicated just proximal and distal to the stenosis. Laminar flow conditions returned downstream of the stenosis
Conclusion: Implantable, extra-vascular coils enable small MRA voxel sizes to reproducibly calculate complex velocity profiles under both laminar and complicated flow in a small animal model. This technique may be applied to study blood flow dynamics of vessel remodeling and atherogenesis.
Copyright 2010. Published by Elsevier Inc.