title: 4-D flow magnetic resonance imaging: blood flow quantification compared to 2-D phase-contrast magnetic resonance imaging and Doppler echocardiography.
abstract: BACKGROUND
  Doppler echocardiography (echo) is the reference standard for blood flow velocity analysis, and two-dimensional (2-D) phase-contrast magnetic resonance imaging (MRI) is considered the reference standard for quantitative blood flow assessment. However, both clinical standard-of-care techniques are limited by 2-D acquisitions and single-direction velocity encoding and may make them inadequate to assess the complex three-dimensional hemodynamics seen in congenital heart disease. Four-dimensional flow MRI (4-D flow) enables qualitative and quantitative analysis of complex blood flow in the heart and great arteries.
  
  
  OBJECTIVE
  The objectives of this study are to compare 4-D flow with 2-D phase-contrast MRI for quantification of aortic and pulmonary flow and to evaluate the advantage of 4-D flow-based volumetric flow analysis compared to 2-D phase-contrast MRI and echo for peak velocity assessment in children and young adults.
  
  
  METHODS
  Two-dimensional phase-contrast MRI of the aortic root, main pulmonary artery (MPA), and right and left pulmonary arteries (RPA, LPA) and 4-D flow with volumetric coverage of the aorta and pulmonary arteries were performed in 50 patients (mean age: 13.1 ± 6.4 years). Four-dimensional flow analyses included calculation of net flow and regurgitant fraction with 4-D flow analysis planes similarly positioned to 2-D planes. In addition, 4-D flow volumetric assessment of aortic root/ascending aorta and MPA peak velocities was performed and compared to 2-D phase-contrast MRI and echo.
  
  
  RESULTS
  Excellent correlation and agreement were found between 2-D phase-contrast MRI and 4-D flow for net flow (r = 0.97, P < 0.001) and excellent correlation with good agreement was found for regurgitant fraction (r = 0.88, P < 0.001) in all vessels. Two-dimensional phase-contrast MRI significantly underestimated aortic (P = 0.032) and MPA (P < 0.001) peak velocities compared to echo, while volumetric 4-D flow analysis resulted in higher (aortic: P = 0.001) or similar (MPA: P = 0.98) peak velocities relative to echo.
  
  
  CONCLUSIONS
  Excellent flow parameter agreement between 2-D phase-contrast MRI and 4-D flow and the improved volumetric 4-D flow velocity analysis relative to echo suggests that 4-D flow has the potential to become a clinical alternative to 2-D phase-contrast MRI.
authors.affiliation: Department of Medical Imaging #9, Ann & Robert H. Lurie Children's Hospital of Chicago, 225 E. Chicago Ave., Chicago, IL, 60611, USA.
authors.forename: Maya
authors.initials: M
authors.lastname: Gabbour
authors.forename: Susanne
authors.initials: S
authors.lastname: Schnell
authors.forename: Kelly
authors.initials: K
authors.lastname: Jarvis
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Robinson
authors.forename: Michael
authors.initials: M
authors.lastname: Markl
authors.forename: Cynthia K
authors.initials: CK
authors.lastname: Rigsby
mesh_terms: D000293:Adolescent; D000328:Adult; D001011:Aorta / Q000503:physiopathology*; D001783:Blood Flow Velocity / Q000502:physiology*; D002648:Child; D002675:Child, Preschool; D003287:Contrast Media; D015150:Echocardiography, Doppler; D005260:Female; D005682:Gadolinium; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D009942:Organometallic Compounds; D011651:Pulmonary Artery / Q000503:physiopathology*
chemical_list: D003287:Contrast Media; D009942:Organometallic Compounds; D005682:Gadolinium; C109932:gadofosveset trisodium