title: Quantification of thoracic blood flow using volumetric magnetic resonance imaging with radial velocity encoding: in vivo validation.
abstract: OBJECTIVE
  The objective of this study was to validate radially undersampled 5-point velocity-encoded time-resolved flow-sensitive magnetic resonance imaging (MRI) ("PC-VIPR", phase contrast vastly undersampled imaging with isotropic resolution projection reconstruction magnetic resonance) for the quantification of ascending aortic (AAO) and main pulmonary artery (MPA) flow in vivo.
  
  
  METHODS
  Data from 18 healthy volunteers (41.6 ± 16.2 years [range, 22-73 years]; body mass index, 26.0 ± 3.5 [19.1-31.4]) scanned at 3 T with a 32-channel coil were included. The left and right ventricular stroke volumes calculated from contiguous short-axis CINE-balanced steady state free precession (CINE-bSSFP) slices were used as the primary reference for cardiac output. Flow measured from 2-dimensional phase contrast MRI (2D-PC-MRI) in the AAO and the MPA served as the secondary reference. Time-resolved 4-dimensional flow-sensitive MRI (4D flow MRI) using PC-VIPR was performed with a velocity sensitivity of Venc = 150 cm/s reconstructed to 20 time frames at 1.4-mm isotropic spatial resolution. In 11 of 20 volunteers, phantom-corrected 4D flow MRI data were also assessed. Differences between methods of calculating the left ventricular and right ventricular cardiac output were assessed with the Bland-Altman analysis (BA, mean difference ±2SD). The QP/QS-ratio was calculated for each method.
  
  
  RESULTS
  Initially, PC-VIPR compared unfavorably with CINE-bSSFP (left ventricular stroke volume: 96.5 ± 14.4 mL; right ventricular stroke volume: 93.6 ± 14.0 mL vs 81.2 ± 24.3 mL [AAO] and 85.6 ± 25.4 mL [MPA]; P = 0.027 and 0.25) with BA differences of -14.6 ± 44.0 mL (AAO) and -9.0 ± 45.9 mL (MPA). Whereas phantom correction had minor effects on 2D-PC-MRI results and comparison with CINE-bSSFP, it improved PC-VIPR results: BA differences between CINE-bSSFP and PC-VIPR after correction were -1.4 ± 15.3 mL (AAO) and -4.1 ± 16.1 mL (MPA); BA comparison with 2D-PC-MRI improved to -12.0 ± 48.1 mL (AAO) and -2.2 ± 19.5 mL (MPA). QP/QS-ratio results for all techniques were within physiologic limits.
  
  
  CONCLUSIONS
  Accurate quantification of AAO and MPA flows with radially undersampled 4D flow MRI applying 5-point velocity encoding is achievable when phantom correction is used.
authors.affiliation: From the *University Hospital Schleswig-Holstein, Campus Lübeck, Clinic for Radiology and Nuclear Medicine, Lübeck, Germany; Departments of †Radiology, ‡Medical Physics, §Biomedical Engineering, and ∥Medicine, University of Wisconsin-Madison, Madison, WI.
authors.forename: Alex
authors.initials: A
authors.lastname: Frydrychowicz
authors.forename: Oliver
authors.initials: O
authors.lastname: Wieben
authors.forename: Eric
authors.initials: E
authors.lastname: Niespodzany
authors.forename: Scott B
authors.initials: SB
authors.lastname: Reeder
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Johnson
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: François
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D001011:Aorta / Q000502:physiology*; D001783:Blood Flow Velocity / Q000502:physiology*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011651:Pulmonary Artery / Q000473:pathology / Q000502:physiology*; D011652:Pulmonary Circulation / Q000502:physiology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013909:Thorax / Q000502:physiology; D055815:Young Adult