title: Real-time magnetic resonance imaging technique for determining left ventricle pressure-volume loops.
abstract: BACKGROUND
  Rapid determination of the left ventricular (LV) pressure-volume (PV) relationship as loading conditions are varied is the gold standard for assessment of LV function. Cine magnetic resonance imaging (MRI) does not have sufficient spatiotemporal resolution to assess beat-to-beat changes of the LV PV relationship required to measure the LV end-systolic elastance (EES) or preload-recruitable stroke work (PRSW). Our aim was to investigate real-time MRI and semiautomated LV measurement of LV volume to measure PV relations in large animals under normal and inotropically stressed physiologic conditions.
  
  
  METHODS
  We determined that PV relationships could be accurately measured using an image exposure time Tex less than 100 ms and frame rate Tfr less than 50 ms at elevated heart rates (∼140 beats per minute) using a golden angle radial MRI k-space trajectory and active contour segmentation.
  
  
  RESULTS
  With an optimized exposure time (Tex=95 ms and frame rate Tfr=2.8 ms), we found that there was no significant difference between cine and real-time MRI at rest in end-diastolic volume, end-systolic volume, ejection fraction, stroke volume, or cardiac output (n=5, p<0.05) at either normal or elevated heart rates. We found EES increased from 1.9±0.7 to 3.1±0.3 mm Hg/mL and PRSW increased from 6.2±1.2 to 9.1±0.9 mm Hg during continuous intravenous dobutamine infusion (n=5, p<0.05).
  
  
  CONCLUSIONS
  Real-time MRI can assess LV volumes, EES, and PRSW at baseline and elevated inotropic states.
authors.affiliation: Gorman Cardiovascular Research Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Walter R T
authors.initials: WR
authors.lastname: Witschey
authors.affiliation: Gorman Cardiovascular Research Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Francisco
authors.initials: F
authors.lastname: Contijoch
authors.affiliation: Gorman Cardiovascular Research Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Jeremy R
authors.initials: JR
authors.lastname: McGarvey
authors.affiliation: Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Victor A
authors.initials: VA
authors.lastname: Ferrari
authors.affiliation: National Institutes of Health, Bethesda, Maryland.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Hansen
authors.affiliation: Gorman Cardiovascular Research Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Madonna E
authors.initials: ME
authors.lastname: Lee
authors.affiliation: Gorman Cardiovascular Research Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Takebayashi
authors.affiliation: Gorman Cardiovascular Research Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Chikashi
authors.initials: C
authors.lastname: Aoki
authors.affiliation: Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Julio A
authors.initials: JA
authors.lastname: Chirinos
authors.affiliation: Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Yushkevich
authors.affiliation: Gorman Cardiovascular Research Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Joseph H
authors.initials: JH
authors.lastname: Gorman
authors.affiliation: Gorman Cardiovascular Research Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Radiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: James J
authors.initials: JJ
authors.lastname: Pilla
authors.affiliation: Gorman Cardiovascular Research Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania. Electronic address: robert.gorman@uphs.upenn.edu.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Gorman
mesh_terms: D000818:Animals; D002302:Cardiac Output / Q000502:physiology; D004195:Disease Models, Animal; D006339:Heart Rate; D006352:Heart Ventricles / Q000503:physiopathology; D007090:Image Interpretation, Computer-Assisted; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods*; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology; D011897:Random Allocation; D012680:Sensitivity and Specificity; D013318:Stroke Volume / Q000502:physiology*; D013552:Swine; D018487:Ventricular Dysfunction, Left / Q000175:diagnosis*; D016277:Ventricular Function, Left / Q000502:physiology*; D017725:Ventricular Pressure / Q000502:physiology*