title: Magnetic resonance assessment of pulmonary (QP) to systemic (QS) flows using 4D phase-contrast imaging: pilot study comparison with standard through-plane 2D phase-contrast imaging.
abstract: OBJECTIVE
  To investigate four-dimensional (4D) phase-contrast (PC) magnetic resonance (MR) in the evaluation of intracardiac shunts by simultaneous assessment of pulmonary (QP) and systemic (QS) flows in a pilot study and to compare results to through-plane two-dimensional (2D) PC MR.
  
  
  METHODS
  Institutional review board approval and written informed consent were obtained. Nineteen patients with suspected intracardiac shunts underwent cardiac MR at 1.5T. Assessments of QP and QS were performed using free-breathing retrospectively gated 2D PC gradient recalled echo (GRE; 1.6 × 1.6 × 5 mm(3)) imaging with one-dimensional through-plane velocity encoding gradient (venc = 150 cm/s) in consecutive measurements for the main pulmonary artery (MPA) and ascending aorta (AA), respectively. A prospectively triggered 4D PC GRE technique (2.4 × 1.8 × 3 mm(3)) with three orthogonal venc directions was also used with volume coverage of both MPA and AA.
  
  
  RESULTS
  QP and QS assessed by 4D PC correlated with 2D PC acquisitions (r = 0.92 and r = 0.67 respectively; P < .0001 for both) but demonstrated significant underestimation of individual flow volumes (-21.9 ± 12.2 mL; P < .0001 and -10.7 ± 13.1 mL; P = .0023, respectively). Calculated QP:QS ratios demonstrated high correlation (r = 0.78; P < .0001) and no significant differences between 4D PC and 2D PC acquisitions (-0.09 ± 0.24, P = .14). Image acquisition times for 2D PC assessment of QP and QS were 2.98 ± 0.52 and 2.84 ± 0.50 minutes, respectively (P = .038), whereas time to acquire 4D PC images was significantly longer, 18.75 ± 4.58 minutes (P < .001).
  
  
  CONCLUSIONS
  Four-dimensional PC MR imaging allows for accurate assessment of QP:QS ratios in the evaluation of intracardiac shunts while absolute flow volumes demonstrate offsets. Further refinement of the technique with improvement in acquisition times may be required before widespread clinical implementation.
authors.affiliation: Department of Medical Imaging, Peter Munk Cardiac Centre, Toronto General Hospital, University Health Network, University of Toronto, 585 University Ave, Toronto, Ontario M5G 2N2, Canada.
authors.forename: Kate
authors.initials: K
authors.lastname: Hanneman
authors.affiliation: Department of Medical Imaging, Peter Munk Cardiac Centre, Toronto General Hospital, University Health Network, University of Toronto, 585 University Ave, Toronto, Ontario M5G 2N2, Canada.
authors.forename: Milani
authors.initials: M
authors.lastname: Sivagnanam
authors.affiliation: Department of Medical Imaging, Peter Munk Cardiac Centre, Toronto General Hospital, University Health Network, University of Toronto, 585 University Ave, Toronto, Ontario M5G 2N2, Canada.
authors.forename: Elsie T
authors.initials: ET
authors.lastname: Nguyen
authors.affiliation: Department of Medical Imaging, Peter Munk Cardiac Centre, Toronto General Hospital, University Health Network, University of Toronto, 585 University Ave, Toronto, Ontario M5G 2N2, Canada; Division of Cardiology, Peter Munk Cardiac Centre, Toronto General Hospital, University Health Network, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Rachel
authors.initials: R
authors.lastname: Wald
authors.affiliation: Siemens AG Healthcare Sector, Erlangen, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Greiser
authors.affiliation: Department of Medical Imaging, Peter Munk Cardiac Centre, Toronto General Hospital, University Health Network, University of Toronto, 585 University Ave, Toronto, Ontario M5G 2N2, Canada; Division of Cardiology, Peter Munk Cardiac Centre, Toronto General Hospital, University Health Network, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Crean
authors.affiliation: Department of Medical Imaging, Peter Munk Cardiac Centre, Toronto General Hospital, University Health Network, University of Toronto, 585 University Ave, Toronto, Ontario M5G 2N2, Canada.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Ley
authors.affiliation: Department of Medical Imaging, Peter Munk Cardiac Centre, Toronto General Hospital, University Health Network, University of Toronto, 585 University Ave, Toronto, Ontario M5G 2N2, Canada. Electronic address: Bernd.Wintersperger@uhn.ca.
authors.forename: Bernd J
authors.initials: BJ
authors.lastname: Wintersperger
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D001011:Aorta / Q000503:physiopathology*; D001783:Blood Flow Velocity; D005260:Female; D054092:Foramen Ovale, Patent / Q000503:physiopathology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008168:Lung; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D011651:Pulmonary Artery / Q000503:physiopathology*; D011652:Pulmonary Circulation; D015203:Reproducibility of Results; D055425:Respiratory-Gated Imaging Techniques / Q000379:methods; D012680:Sensitivity and Specificity; D055815:Young Adult
keywords: Magnetic resonance imaging; heart defects, congenital; heart septal defects, atrial; heart septal defects, ventricular; magnetic resonance angiography