title: Transstenotic pressure gradients: measurement in swine--retrospectively ECG-gated 3D phase-contrast MR angiography versus endovascular pressure-sensing guidewires.
abstract: OBJECTIVE
  To prospectively evaluate the hypothesis that retrospectively electrocardiographically gated phase contrast with vastly undersampled isotropic projection reconstruction (VIPR) magnetic resonance (MR) angiography data sets can be used to measure transstenotic pressure gradients (TSPGs) in vivo.
  
  
  METHODS
  TSPGs were calculated by using phase-contrast VIPR MR angiography data sets; measurements obtained with a pair of endovascular pressure-sensing guidewires served as a reference standard. With institutional animal care and use committee approval, 12 swine underwent surgical creation of stenoses at the left common carotid, right renal, and left external iliac arteries. The percentage stenosis and reference diameter of the lesions were calculated from conventional digital subtraction angiograms. A pair of 0.014-inch pressure-sensing guidewires was placed in tandem; sensors 1 cm distal and 1 cm proximal to the lesions measured the mean TSPG. Phase-contrast VIPR phase difference images were analyzed with an iterative technique based on the Navier-Stokes equations to determine the mean TSPG. Pearson product correlation was calculated, and Bland-Altman plots were generated to determine the degree of agreement between the two methods.
  
  
  RESULTS
  Twenty-one lesions (12 carotid, nine iliac; mean percentage stenosis, 52.4%; range, 29.8%-64.9%; mean reference diameter, 3.4 mm; range, 2.4-5.6 mm) were analyzed. For carotid and iliac lesions, phase-contrast VIPR and guidewire TSPG measurements were highly correlated (r = 0.952, P < .001). Bland-Altman plots (bias, 0.86 mm Hg; limits of agreement: -6.17 to 7.88 mm Hg) showed good agreement. Measurements in renal lesions (n = 9) were poorly correlated (r = -0.081, P = .835) and were excluded because of image degradation secondary to respiratory motion.
  
  
  CONCLUSIONS
  Phase-contrast MR angiography with VIPR enables reliable measurements of TSPG in carotid and iliac lesions that are comparable to those obtained with endovascular pressure-sensing guidewires. However, further work to compensate for respiratory motion is required to extend this technique to the renal arteries.
authors.affiliation: Department of Radiology, University of Wisconsin Hospital and Clinics, 600 Highland Ave, CSC E3/311, Madison, WI 53792, USA. lum@wisc.edu
authors.forename: Darren P
authors.initials: DP
authors.lastname: Lum
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Johnson
authors.forename: Russell K
authors.initials: RK
authors.lastname: Paul
authors.forename: Aquilla S
authors.initials: AS
authors.lastname: Turk
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Consigny
authors.forename: Julie R
authors.initials: JR
authors.lastname: Grinde
authors.forename: Charles A
authors.initials: CA
authors.lastname: Mistretta
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Grist
mesh_terms: D000818:Animals; D001157:Arterial Occlusive Diseases / Q000175:diagnosis* / Q000503:physiopathology; D016893:Carotid Stenosis / Q000175:diagnosis / Q000503:physiopathology; D003251:Constriction, Pathologic; D004562:Electrocardiography; D007083:Iliac Artery / Q000473:pathology / Q000503:physiopathology; D021621:Imaging, Three-Dimensional; D018810:Magnetic Resonance Angiography / Q000379:methods*; D011312:Pressure; D011446:Prospective Studies; D013552:Swine