title: Improved measurement of pressure gradients in aortic coarctation by magnetic resonance imaging.
abstract: OBJECTIVE
  This study evaluated whether magnetic resonance imaging (MRI) and magnetic resonance (MR) phase velocity mapping could provide accurate estimates of stenosis severity and pressure gradients in aortic coarctation.
  
  
  BACKGROUND
  Clinical management of aortic coarctation requires determination of lesion location and severity and quantification of the pressure gradient across the constricted area.
  
  
  METHODS
  Using a series of anatomically accurate models of aortic coarctation, the laboratory portion of this study found that the loss coefficient (K), commonly taken to be 4.0 in the simplified Bernoulli equation delta P = KV2, was a function of stenosis severity. The values of the loss coefficient ranged from 2.8 for a 50% stenosis to 4.9 for a 90% stenosis. Magnetic resonance imaging and MR phase velocity mapping were then used to determine coarctation severity and pressure gradient in 32 patients.
  
  
  RESULTS
  Application of the new severity-dependent loss coefficients found that pressure gradients deviated from 1 to 17 mm Hg compared with calculations made with the commonly used value of 4.0. Comparison of MR estimates of pressure gradient with Doppler ultrasound estimates (in 22 of 32 patients) and with catheter pressure measurements (in 6 of 32 patients) supports the conclusion that the severity-based loss coefficient provides improved estimates of pressure gradients.
  
  
  CONCLUSIONS
  This study suggests that MRI could be used as a complete diagnostic tool for accurate evaluation of aortic coarctation, by determining stenosis location and severity and by accurately estimating pressure gradients.
authors.affiliation: Department of Radiology, Emory University School of Medicine, Atlanta, Georgia 30322, USA. oshinski@turlubuki.eushc.org
authors.forename: J N
authors.initials: JN
authors.lastname: Oshinski
authors.forename: W J
authors.initials: WJ
authors.lastname: Parks
authors.forename: C P
authors.initials: CP
authors.lastname: Markou
authors.forename: H L
authors.initials: HL
authors.lastname: Bergman
authors.forename: B E
authors.initials: BE
authors.lastname: Larson
authors.forename: D N
authors.initials: DN
authors.lastname: Ku
authors.forename: S
authors.initials: S
authors.lastname: Mukundan
authors.forename: R I
authors.initials: RI
authors.lastname: Pettigrew
mesh_terms: D000293:Adolescent; D000328:Adult; D001011:Aorta / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D001017:Aortic Coarctation / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000503:physiopathology*; D001783:Blood Flow Velocity; D002648:Child; D002675:Child, Preschool; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007223:Infant; D018810:Magnetic Resonance Angiography; D019047:Phantoms, Imaging; D011312:Pressure; D018608:Ultrasonography, Doppler