title: Noninvasive assessment of transstenotic pressure gradients in porcine renal artery stenoses by using vastly undersampled phase-contrast MR angiography.
abstract: OBJECTIVE
  To compare noninvasive transstenotic pressure gradient (TSPG) measurements derived from high-spatial- and temporal-resolution four-dimensional magnetic resonance (MR) flow measurements with invasive measurements obtained from endovascular pressure wires with digital subtraction angiographic guidance.
  
  
  METHODS
  After Animal Care and Use Committee approval, bilateral renal artery stenosis (RAS) was created surgically in 12 swine. Respiratory-gated phase-contrast vastly undersampled isotropic projection (VIPR) MR angiography of the renal arteries was performed with a 1.5-T clinical MR system (repetition time, 11.4 msec; echo time [first echo], 3.7 msec; 18,000 projection angles; imaging volume, 260 × 260 × 200 mm; acquired isotropic spatial resolution, 1.0 × 1.0 × 1.0 mm; velocity encoding, 150 cm/sec). Velocities measured with phase-contrast VIPR were used to calculate TSPGs by using Navier-Stokes equations. These were compared with endovascular pressure measurements (mean and peak) performed by using fluoroscopic guidance with regression analysis.
  
  
  RESULTS
  In 19 renal arteries with an average stenosis of 62% (range, 0%-87%), there was excellent correlation between the noninvasive TSPG measurement with phase-contrast VIPR and invasive TSPG measurement for mean TSPG (R² = 95.4%) and strong correlation between noninvasive TSPG and invasive TSPG for the peak TSPG measures (R² = 82.6%). The phase-contrast VIPR-derived TSPG measures were slightly lower than the endovascular measurements. In four arteries with severe stenoses and one occlusion (mean, 86%; range, 75%-100%), the residual lumen within the stenosis was too small to determine TSPG with phase-contrast VIPR.
  
  
  CONCLUSIONS
  The unenhanced MR angiographic technique with phase-contrast VIPR allows for accurate noninvasive assessment of hemodynamic significance in a porcine model of RAS with highly accurate TSPG measurements.
authors.affiliation: Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705-2275, USA.
authors.forename: Thorsten A
authors.initials: TA
authors.lastname: Bley
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Johnson
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: François
authors.forename: Scott B
authors.initials: SB
authors.lastname: Reeder
authors.forename: Mark L
authors.initials: ML
authors.lastname: Schiebler
authors.forename: Benjamin
authors.initials: B
authors.lastname: R Landgraf
authors.forename: Daniel
authors.initials: D
authors.lastname: Consigny
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Grist
authors.forename: Oliver
authors.initials: O
authors.lastname: Wieben
mesh_terms: D000818:Animals; D018810:Magnetic Resonance Angiography / Q000379:methods*; D011859:Radiography; D012078:Renal Artery Obstruction / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D013552:Swine