title: Surgically implantable magnetic resonance angiography coils improve resolution to allow visualization of blood flow dynamics.
abstract: 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
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Surgery, Yale University School of Medicine, New Haven, CT, USA.
authors.forename: Tamara N
authors.initials: TN
authors.lastname: Fitzgerald
authors.forename: Akihito
authors.initials: A
authors.lastname: Muto
authors.forename: Tiffany T
authors.initials: TT
authors.lastname: Fancher
authors.forename: Peter B
authors.initials: PB
authors.lastname: Brown
authors.forename: Karen A
authors.initials: KA
authors.lastname: Martin
authors.forename: Bart E
authors.initials: BE
authors.lastname: Muhs
authors.forename: Douglas L
authors.initials: DL
authors.lastname: Rothman
authors.forename: R Todd
authors.initials: RT
authors.lastname: Constable
authors.forename: Smita
authors.initials: S
authors.lastname: Sampath
authors.forename: Alan
authors.initials: A
authors.lastname: Dardik
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity; D002339:Carotid Arteries / Q000000981:diagnostic imaging / Q000503:physiopathology*; D016893:Carotid Stenosis / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000503:physiopathology; D004195:Disease Models, Animal; D004867:Equipment Design; D007090:Image Interpretation, Computer-Assisted; D016018:Least-Squares Analysis; D018810:Magnetic Resonance Angiography / Q000295:instrumentation*; D008297:Male; D008955:Models, Cardiovascular; D011237:Predictive Value of Tests; D011817:Rabbits; D012039:Regional Blood Flow; D015203:Reproducibility of Results; D018608:Ultrasonography, Doppler