title: Vessel-wall imaging and quantification of flow-mediated dilation using water-selective 3D SSFP-echo.
abstract: BACKGROUND
  To introduce a new, efficient method for vessel-wall imaging of carotid and peripheral arteries by means of a flow-sensitive 3D water-selective SSFP-echo pulse sequence.
  
  
  METHODS
  Periodic applications of RF pulses will generate two transverse steady states, immediately after and before an RF pulse; the latter being referred to as the SSFP-echo. The SSFP-echo signal for water protons in blood is spoiled as a result of moving spins losing phase coherence in the presence of a gradient pulse along the flow direction. Bloch equation simulations were performed over a wide range of velocities to evaluate the flow sensitivity of the SSFP-echo signal. Vessel walls of carotid and femoral and popliteal arteries were imaged at 3 T. In two patients with peripheral artery disease the femoral arteries were imaged bilaterally to demonstrate method's potential to visualize atherosclerotic plaques. The method was also evaluated as a means to measure femoral artery flow-mediated dilation (FMD) in response to cuff-induced ischemia in four subjects.
  
  
  RESULTS
  The SSFP-echo pulse sequence, which does not have a dedicated blood signal suppression preparation, achieved low blood signal permitting discrimination of the carotid and peripheral arterial walls with in-plane spatial resolution ranging from 0.5 to 0.69 mm and slice thickness of 2 to 3 mm, i.e. comparable to conventional 2D vessel-wall imaging techniques. The results of the simulations were in good agreement with analytical solution and observations for both vascular territories examined. Scan time ranged from 2.5 to 5 s per slice yielding a contrast-to-noise ratio between the vessel wall and lumen from 3.5 to 17. Mean femoral FMD in the four subjects was 9%, in good qualitative agreement with literature values.
  
  
  CONCLUSIONS
  Water-selective 3D SSFP-echo pulse sequence is a potential alternative to 2D vessel-wall imaging. The proposed method is fast, robust, applicable to a wide range of flow velocities, and straightforward to implement.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Langham
authors.forename: Cheng
authors.initials: C
authors.lastname: Li
authors.forename: Erin K
authors.initials: EK
authors.lastname: Englund
authors.forename: Erica N
authors.initials: EN
authors.lastname: Chirico
authors.forename: Emile R
authors.initials: ER
authors.lastname: Mohler
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Floyd
authors.affiliation: Department of Radiology, School of Medicine, University of Pennsylvania, Philadelphia, USA. wehrli@mail.med.upenn.edu.
authors.forename: Felix W
authors.initials: FW
authors.lastname: Wehrli
mesh_terms: D000328:Adult; D000368:Aged; D001783:Blood Flow Velocity; D002339:Carotid Arteries / Q000503:physiopathology*; D003198:Computer Simulation; D005263:Femoral Artery / Q000503:physiopathology*; D006801:Humans; D006940:Hyperemia / Q000503:physiopathology; D021621:Imaging, Three-Dimensional; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008875:Middle Aged; D008955:Models, Cardiovascular; D058729:Peripheral Arterial Disease / Q000175:diagnosis* / Q000503:physiopathology; D011150:Popliteal Artery / Q000503:physiopathology*; D011237:Predictive Value of Tests; D012039:Regional Blood Flow; D059629:Signal-To-Noise Ratio; D014664:Vasodilation